JP5671772B2 - Lithium ion secondary battery - Google Patents

Description

The present invention relates to a lithium ion secondary battery. More specifically, the present invention provides excellent cycle characteristics and high output characteristics by using a non-aqueous electrolyte containing a specific component and a specific negative electrode active material. The present invention relates to a lithium ion secondary battery.

  In the field of information-related equipment and communication equipment, along with the downsizing of personal computers, video cameras, mobile phones, etc., lithium-ion secondary batteries have been put to practical use because of their high energy density as the power source used for these equipment. It has become widespread. In recent years, in addition to the above-mentioned fields, in the field of automobiles, lithium ion has been developed mainly for use as a power source for electric vehicles that are urgently developed against the background of environmental problems and resource problems. Secondary batteries are being considered.

  Among lithium ion secondary batteries, secondary batteries using metallic lithium as a negative electrode have been actively studied since long ago as batteries capable of achieving high capacity. However, these batteries have a problem that metallic lithium grows in a dendrite shape due to repeated charge and discharge, eventually reaches the positive electrode and causes a short circuit inside the battery. This is the biggest technical problem when putting batteries into practical use.

  Therefore, a nonaqueous electrolyte secondary battery using a carbonaceous material capable of inserting and extracting lithium ions such as coke, artificial graphite, and natural graphite has been proposed for the negative electrode. In such a non-aqueous electrolyte secondary battery, since lithium does not exist in a metal state, formation of dendrites is suppressed, and battery life and safety can be improved. In particular, graphite-based carbonaceous materials such as artificial graphite and natural graphite are expected as materials capable of improving the energy density per unit volume.

  However, lithium primary batteries are generally preferred as non-aqueous electrolyte secondary batteries using various graphite-based electrode materials alone or mixed with other negative electrode materials capable of occluding and releasing lithium as negative electrodes. When an electrolytic solution containing propylene carbonate used as a main solvent is used, the decomposition reaction of the solvent proceeds vigorously on the surface of the graphite electrode, and smooth insertion and extraction of lithium into the graphite electrode becomes impossible. On the other hand, ethylene carbonate is often used as the main solvent of the electrolyte of non-aqueous electrolyte secondary batteries because of such a small amount of decomposition. However, even when ethylene carbonate is used as the main solvent, the surface of the electrode is charged and discharged. Since the electrolytic solution is decomposed, there is a problem in that charge / discharge efficiency and cycle characteristics are deteriorated.

  Further, when a lithium ion secondary battery is used as a power source for an electric vehicle, the electric vehicle requires a large amount of energy when starting and accelerating, and the large amount of energy generated when decelerating must be efficiently regenerated. Secondary batteries are required to have high output characteristics. In lithium ion secondary batteries used in ordinary notebook computers, capacity retention at a low current density with respect to charge / discharge is emphasized. However, as a power source for electric vehicles, after deterioration of the charge / discharge cycle rather than this characteristic, However, it is important to maintain the output characteristics at high power.

  Thus, as a means for improving the output characteristics of a lithium ion secondary battery, many techniques have been studied for various battery components including positive and negative electrode active materials. As a technique relating to the negative electrode active material, Patent Document 1 uses a negative electrode active material in which deterioration is suppressed and only the vicinity of the surface is a low crystalline carbonaceous carbon material and the inside thereof is crystalline graphite. Although there is a description of a lithium ion secondary battery that is less likely to have a reduced relative discharge capacity and excellent cycle characteristics even at times, even this method has not been sufficient in terms of output characteristics in the latter cycle.

Further, as a technique related to a non-aqueous electrolyte, Patent Document 2 discloses that in a non-aqueous electrolyte secondary battery, when lithium monofluorophosphate or lithium difluorophosphate is added to the non-aqueous electrolyte, a good quality is obtained at the electrode interface. It is described that the formation of a film suppresses the decomposition of the electrolytic solution and provides a battery with improved storage characteristics. However, problems still remain, such as not being able to obtain sufficient output characteristics after cycling even if this method is used.
WO2003 / 034518 Japanese Patent Laid-Open No. 11-67270

  The present invention has been made in view of the background art, and its problem is to realize high output characteristics from the initial stage to the end of the cycle while maintaining the effect of improving the cycle characteristics even when the size is increased. Another object of the present invention is to provide a lithium ion secondary battery that can maintain output characteristics at high power even after deterioration after performing a charge / discharge cycle.

Invention intensively studied in view of the above problems, a negative electrode active material for a particular configuration, by using a non-aqueous electrolyte containing a specific reduction compound, even when the large, good The present invention has been completed by finding that high output characteristics can be realized while maintaining excellent cycle characteristics.

［一般式（１）中、Ｒ^１及びＲ^２は互いに同一であっても異なっていてもよい炭素数１〜１２の有機基を表し、ｎは３〜１０の整数を表す。］

［一般式（２）中、Ｒ^３〜Ｒ^５は互いに同一であっても異なっていてもよい炭素数１〜１２の有機基を表し、ｘは１〜３の整数を表し、ｐ、ｑ及びｒはそれぞれ０〜３の整数を表し、１≦ｐ＋ｑ＋ｒ≦３である。］

［一般式（３）中、Ｒ^６〜Ｒ^８は互いに同一であっても異なっていてもよい炭素数１〜１２の有機基を表し、ＡはＨ、Ｃ、Ｎ、Ｏ、Ｆ、Ｓ、Ｓｉ及び／又はＰから構成される基を表す。］ That is, the present invention is a lithium ion secondary battery including a non-aqueous electrolyte solution containing at least a negative electrode active material, a positive electrode active material, and a lithium salt, wherein the non-aqueous electrolyte solution has the general formula (1). A cyclic siloxane compound represented by general formula (2), a fluorosilane compound represented by general formula (2), a compound represented by general formula (3), a compound having an SF bond in the molecule, nitrate, nitrite, monofluoro A non-aqueous electrolyte containing at least 10 ppm of at least one compound selected from the group consisting of phosphate, difluorophosphate, acetate and propionate in the entire non-aqueous electrolyte, and The present invention provides a lithium ion secondary battery characterized in that the negative electrode active material contains two or more carbonaceous materials having different crystallinity.

[In General Formula (1), R ¹ and R ² represent the same or different organic group having 1 to 12 carbon atoms, and n represents an integer of 3 to 10. ]

[In General Formula (2), R ^{3 to} R ⁵ represent an organic group having 1 to 12 carbon atoms which may be the same or different from each other, x represents an integer of 1 to 3, p, q and Each r represents an integer of 0 to 3, and 1 ≦ p + q + r ≦ 3. ]

[In General Formula (3), R ^{6 to} R ⁸ represent an organic group having 1 to 12 carbon atoms which may be the same as or different from each other, and A represents H, C, N, O, F, S, Represents a group composed of Si and / or P; ]

  According to the present invention, while maintaining the effect of improving the cycle characteristics, high output characteristics can be realized from the beginning to the end of the cycle, and the output characteristics at high power can be obtained even after deterioration after performing the charge / discharge cycle. A lithium ion secondary battery that is maintained and particularly suitable as a large battery can be provided.

  Hereinafter, embodiments of the present invention will be described in detail. However, the description of the constituent elements described below is an example (representative example) of an embodiment of the present invention, and is not limited to these specific contents. Various modifications can be made within the scope of the gist.

<Non-aqueous electrolyte>
The non-aqueous electrolyte used in the lithium ion secondary battery of the present invention contains a lithium salt and a non-aqueous solvent that dissolves the lithium salt.
[Lithium salt]
The lithium salt is not particularly limited as long as it is known to be used as an electrolyte of a non-aqueous electrolyte solution for a lithium ion secondary battery, and examples thereof include the following.

Inorganic lithium salt:
Inorganic fluoride salts such as LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiSbF ₆ ; perhalogenates such as LiClO ₄ , LiBrO ₄ , LiIO ₄ ; inorganic chloride salts such as LiAlCl ₄ .
Fluorine-containing organic lithium salt:
Perfluoroalkane sulfonates such as LiCF ₃ SO ₃ ; LiN (CF ₃ SO ₂ ) ₂ , LiN (CF ₃ CF ₂ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), etc. Perfluoroalkanesulfonylimide salt; Perfluoroalkanesulfonylmethide salt such as LiC (CF ₃ SO ₂ ) ₃ ; Li [PF ₅ (CF ₂ CF ₂ CF ₃ )], Li [PF ₄ (CF ₂ CF ₂ CF _{3) 2} ], Li [PF ₃ (CF ₂ CF ₂ CF ₃ ) ₃ ], Li [PF ₅ (CF ₂ CF ₂ CF ₂ CF ₃ )], Li [PF ₄ (CF ₂ CF ₂ CF ₂ CF ₃ ) ₂ ], Fluoroalkyl fluorophosphates such as Li [PF ₃ (CF ₂ CF ₂ CF ₂ CF ₃ ) ₃ ].
Oxalatoborate salt:
Lithium difluorooxalatoborate, lithium bis (oxalato) borate and the like.

These may be used individually by 1 type, or may use 2 or more types together by arbitrary combinations and ratios. Among these, LiPF ₆ , LiBF _{4 and the} like are preferable, and LiPF ₆ is particularly preferable when comprehensively judging the solubility in the non-aqueous solvent, the charge / discharge characteristics in the case of the secondary battery, the output characteristics, the cycle characteristics, and the like. .

  The concentration of the lithium salt in the nonaqueous electrolytic solution is not particularly limited, but is usually 0.3 mol / L or more, preferably 0.6 mol / L or more, more preferably 0.7 mol / L or more. Moreover, the upper limit is 2 mol / L or less normally, Preferably it is 1.8 mol / L or less, More preferably, it is 1.7 mol / L or less. If the concentration is too low, the electrical conductivity of the non-aqueous electrolyte may be insufficient. On the other hand, if the concentration is too high, the electrical conductivity may decrease due to an increase in viscosity. Performance may be degraded.

  The non-aqueous electrolyte preferably contains a fluorine-containing lithium salt as the lithium salt, and the concentration of the fluorine-containing lithium salt in the non-aqueous electrolyte is not particularly limited, but is 0.5 mol / L or more. The amount is particularly preferably 0.7 mol / L or more. Moreover, the upper limit is preferably 2 mol / L or less, particularly preferably 1.7 mol / L or less. If the concentration is too low, the electrical conductivity of the non-aqueous electrolyte solution may be insufficient. On the other hand, if the concentration is too high, the electrical conductivity decreases due to an increase in viscosity, and the performance of the lithium ion secondary battery May decrease.

Lithium salts may be used singly or in combination of two or more in any combination and ratio. Preferred examples when two or more lithium salts are used are LiPF ₆ and LiBF _4. In this case, the proportion of LiBF _{4 in} the total of both is particularly preferably 0.01% by mass or more and 20% by mass or less, more preferably 0.1% by mass or more and 5% by mass. More preferably, it is as follows. Another preferred example is the combined use of an inorganic fluoride salt and a perfluoroalkanesulfonylimide salt. In this case, the proportion of the inorganic fluoride salt in the total of both is 70% by mass or more and 99% by mass. % Or less, particularly preferably 80% by mass or more and 98% by mass or less. The combined use of both has the effect of suppressing deterioration due to high temperature storage.

[Nonaqueous solvent]
As the non-aqueous solvent, it can be appropriately selected from those conventionally proposed as solvents for non-aqueous electrolyte solutions. For example, the following are mentioned.
1) Cyclic carbonate:
As for carbon number of the alkylene group which comprises a cyclic carbonate, 2-6 are preferable, Most preferably, it is 2-4. Specific examples include ethylene carbonate, propylene carbonate, butylene carbonate, and the like. Of these, ethylene carbonate and propylene carbonate are preferable.
2) Chain carbonate:
As the chain carbonate, dialkyl carbonate is preferable, and the number of carbon atoms of the alkyl group is preferably 1 to 5, and particularly preferably 1 to 4, respectively. Specific examples include dialkyl carbonates such as dimethyl carbonate, diethyl carbonate, di-n-propyl carbonate, ethyl methyl carbonate, methyl-n-propyl carbonate, and ethyl-n-propyl carbonate. Of these, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate are preferable.
3) Cyclic ester:
Specific examples include γ-butyrolactone and γ-valerolactone.
4) Chain ester:
Specific examples include methyl acetate, ethyl acetate, propyl acetate, and methyl propionate.
5) Cyclic ether:
Specific examples include tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran and the like.
6) Chain ether:
Specific examples include dimethoxyethane and dimethoxymethane.
7) Sulfur-containing organic solvent:
Specific examples include sulfolane and diethylsulfone.

  These may be used alone or in combination of two or more, but it is preferable to use in combination of two or more. For example, it is preferable to use a high dielectric constant solvent such as cyclic carbonates and cyclic esters in combination with a low viscosity solvent such as chain carbonates and chain esters.

  One preferred combination of non-aqueous solvents is a combination mainly composed of cyclic carbonates and chain carbonates. Among them, the total of the cyclic carbonates and the chain carbonates in the nonaqueous solvent is 85% by volume or more, preferably 90% by volume or more, and more preferably 95% by volume or more. Further, the capacity of the cyclic carbonate with respect to the total of the cyclic carbonate and the chain carbonate is 5% or more, preferably 10% or more, more preferably 15% or more, usually 50% or less, preferably 35% or less, More preferably, it is 30% or less. It is particularly preferred that the above preferred volume range of the total amount of carbonates occupying the entire non-aqueous solvent is combined with the preferred above volume range of cyclic carbonates relative to cyclic and chain carbonates.

  Specific examples of preferred combinations of cyclic carbonates and chain carbonates include ethylene carbonate and dimethyl carbonate, ethylene carbonate and diethyl carbonate, ethylene carbonate and ethyl methyl carbonate, ethylene carbonate and dimethyl carbonate and diethyl carbonate, ethylene carbonate and dimethyl carbonate And ethyl methyl carbonate, ethylene carbonate, diethyl carbonate, and ethyl methyl carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. A combination in which propylene carbonate is further added to the combination of these ethylene carbonates and chain carbonates is also a preferable combination. In the case of containing propylene carbonate, the volume ratio of ethylene carbonate to propylene carbonate is preferably 99: 1 to 40:60, particularly preferably 95: 5 to 50:50.

  Among these, those containing asymmetric chain carbonates are more preferable, particularly ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate, ethylene carbonate, diethyl carbonate and ethyl methyl carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl. Those containing ethylene carbonate such as methyl carbonate, symmetric chain carbonates, and asymmetric chain carbonates are preferred because of a good balance between cycle characteristics and large current discharge characteristics. Among these, those in which the asymmetric chain carbonate is ethyl methyl carbonate are preferable, and the alkyl group constituting the dialkyl carbonate preferably has 1 to 2 carbon atoms.

  Other examples of preferred non-aqueous solvents are those containing chain esters. In particular, those containing a chain ester in the mixed solvent of cyclic carbonates and chain carbonates are preferable from the viewpoint of improving the low-temperature characteristics of the battery. Examples of the chain esters include methyl acetate and ethyl acetate. preferable. The capacity of the chain ester in the non-aqueous solvent is usually 5% or more, preferably 8% or more, more preferably 15% or more, usually 50% or less, preferably 35% or less, more preferably 30% or less, More preferably, it is 25% or less.

  Examples of other preferable non-aqueous solvents include one organic solvent selected from the group consisting of ethylene carbonate, propylene carbonate, γ-butyrolactone and γ-valerolactone, or two or more organic solvents selected from the group. The mixed solvent becomes 60% by volume or more of the whole. Such a mixed solvent preferably has a flash point of 50 ° C. or higher, and particularly preferably has a flash point of 70 ° C. or higher. A non-aqueous electrolyte using this solvent reduces evaporation of the solvent and leakage even when used at high temperatures. Among them, the amount of γ-butyrolactone in the nonaqueous solvent is 60% by volume or more, and the total of ethylene carbonate and γ-butyrolactone in the nonaqueous solvent is 80% by volume or more, preferably 90% by volume or more. And the volume ratio of ethylene carbonate to γ-butyrolactone is 5:95 to 45:55, or the total of ethylene carbonate and propylene carbonate in the non-aqueous solvent is 80% by volume or more, preferably 90% When the ratio of ethylene carbonate to propylene carbonate is 30:70 to 60:40, the balance between cycle characteristics and large current discharge characteristics is generally improved.

[Specific compounds]
The non-aqueous electrolyte solution of the present invention includes a cyclic siloxane compound represented by the general formula (1), a fluorosilane compound represented by the general formula (2), a compound represented by the general formula (3), and S in the molecule. At least one compound selected from the group consisting of a compound having —F bond, nitrate, nitrite, monofluorophosphate, difluorophosphate, acetate and propionate (hereinafter referred to as “specific compound”) Is sometimes abbreviated as “)” in an amount of 10 ppm or more.

  By combining a non-aqueous electrolyte containing such a specific compound and a negative electrode active material containing two or more types of carbonaceous materials having different crystallinity, further, a composite containing two or more types of carbonaceous materials having different crystallinity By combining with a negative electrode active material containing a carbonaceous material, there is an effect that output characteristics are maintained even after long-term use.

[[Cyclic Siloxane Compound Represented by General Formula (1)]]
R ¹ and although R ² are identical there may be different even if an organic group having 1 to 12 carbon atoms with each other, as R ¹ and R ² in the general formula (1) cyclic siloxane compound represented by, Chain alkyl groups such as methyl group, ethyl group, n-propyl group, isopropyl group, butyl group, isobutyl group, sec-butyl group and t-butyl group; cyclic alkyl groups such as cyclohexyl group and norbornyl group; vinyl group, Alkenyl groups such as 1-propenyl group, allyl group, butenyl group, 1,3-butadienyl group; alkynyl groups such as ethynyl group, propynyl group, butynyl group; halogenated alkyl groups such as trifluoromethyl group; 3-pyrrolidino An alkyl group having a saturated heterocyclic group such as a propyl group; an aryl group such as a phenyl group optionally having an alkyl substituent; a phenylmethyl group; Examples thereof include aralkyl groups such as nylethyl group; trialkylsilyl groups such as trimethylsilyl group; trialkylsiloxy groups such as trimethylsiloxy group.

Among them, those having a smaller number of carbon atoms are more likely to exhibit characteristics, and organic groups having 1 to 6 carbon atoms are preferable. Alkenyl groups act on non-aqueous electrolytes and coatings on electrode surfaces to improve input / output characteristics, and aryl groups have the effect of capturing radicals generated in the battery during charge and discharge to improve overall battery performance. Therefore, it is preferable. Accordingly, R ¹ and R ² are particularly preferably a methyl group, a vinyl group, or a phenyl group.

  In general formula (1), n represents an integer of 3 to 10, but an integer of 3 to 6 is preferable, and 3 or 4 is particularly preferable.

  Examples of the cyclic siloxane compound represented by the general formula (1) include, for example, hexamethylcyclotrisiloxane, hexaethylcyclotrisiloxane, hexaphenylcyclotrisiloxane, 1,3,5-trimethyl-1,3,5. -Cyclotrisiloxane such as trivinylcyclotrisiloxane, cyclotetrasiloxane such as octamethylcyclotetrasiloxane, cyclopentasiloxane such as decamethylcyclopentasiloxane, and the like. Of these, cyclotrisiloxane is particularly preferred.

[[Fluorosilane compound represented by general formula (2)]]
R ^{3 to} R ⁵ in the fluorosilane compound represented by the general formula (2) are organic groups having 1 to 12 carbon atoms which may be the same as or different from each other, but R in the general formula (1) Examples of the chain alkyl group, cyclic alkyl group, alkenyl group, alkynyl group, halogenated alkyl group, alkyl group having a saturated heterocyclic group, phenyl group optionally having an alkyl group, etc. mentioned as examples of ¹ and R ² In addition to aryl groups, aralkyl groups, trialkylsilyl groups, trialkylsiloxy groups, carbonyl groups such as ethoxycarbonylethyl groups; carboxyl groups such as acetoxy groups, acetoxymethyl groups, trifluoroacetoxy groups; methoxy groups, ethoxy groups, Oxy group such as propoxy group, butoxy group, phenoxy group, allyloxy group; amino group such as allylamino group; Mention may be made of the group, and the like.

  In general formula (2), x represents an integer of 1 to 3, p, q, and r each represents an integer of 0 to 3, and 1 ≦ p + q + r ≦ 3. Inevitably, x + p + q + r = 4.

  Examples of the fluorosilane compound represented by the general formula (2) include trimethylfluorosilane, triethylfluorosilane, tripropylfluorosilane, phenyldimethylfluorosilane, triphenylfluorosilane, vinyldimethylfluorosilane, vinyldiethylfluorosilane, In addition to monofluorosilanes such as vinyldiphenylfluorosilane, trimethoxyfluorosilane, and triethoxyfluorosilane, difluorosilanes such as dimethyldifluorosilane, diethyldifluorosilane, divinyldifluorosilane, and ethylvinyldifluorosilane; methyltrifluorosilane, Also included are trifluorosilanes such as ethyltrifluorosilane.

  If the boiling point of the fluorosilane compound represented by the general formula (2) is low, it will volatilize, and therefore it may be difficult to contain a predetermined amount in the non-aqueous electrolyte. Moreover, even if it is made to contain in a non-aqueous electrolyte solution, there exists a possibility that it may volatilize on the conditions that the heat_generation | fever of a battery by charging / discharging or external environment becomes high temperature. Accordingly, those having a boiling point of 50 ° C. or higher at 1 atm are preferable, and those having a boiling point of 60 ° C. or higher are particularly preferable.

  Further, like the compound of the general formula (1), the organic group having a smaller number of carbon atoms is more effective, and the alkenyl group having 1 to 6 carbon atoms acts on the non-aqueous electrolyte solution or the electrode surface coating. Thus, the input / output characteristics are improved, and the aryl group has the effect of capturing radicals generated in the battery during charge / discharge and improving the overall battery performance. Therefore, from this viewpoint, the organic group is preferably a methyl group, a vinyl group, or a phenyl group, and examples of the compound include trimethylfluorosilane, vinyldimethylfluorosilane, phenyldimethylfluorosilane, and vinyldiphenylfluorosilane. .

[[Compound represented by formula (3)]]
R ^{6 to} R ⁸ in the compound represented by the general formula (3) are organic groups having 1 to 12 carbon atoms which may be the same as or different from each other. A chain alkyl group, a cyclic alkyl group, an alkenyl group, an alkynyl group, a halogenated alkyl group, an alkyl group having a saturated heterocyclic group, or an alkyl group, which are mentioned as examples of R ^{3 to} R ⁵ Aryl groups such as phenyl groups, aralkyl groups, trialkylsilyl groups, trialkylsiloxy groups, carbonyl groups, carboxyl groups, oxy groups, amino groups, benzyl groups, and the like can be similarly exemplified.

  A in the compound represented by the general formula (3) is not particularly limited as long as A is a group composed of H, C, N, O, F, S, Si and / or P, but the general formula (3) C, S, Si or P is preferable as the element directly bonded to the oxygen atom therein. Examples of the existence form of these atoms include a chain alkyl group, a cyclic alkyl group, an alkenyl group, an alkynyl group, a halogenated alkyl group, a carbonyl group, a sulfonyl group, a trialkylsilyl group, a phosphoryl group, and a phosphinyl group. Those are preferred. The molecular weight of the compound represented by the general formula (3) is preferably 1000 or less, particularly preferably 800 or less, and more preferably 500 or less.

  Examples of the compound represented by the general formula (3) include siloxane compounds such as hexamethyldisiloxane, 1,3-diethyltetramethyldisiloxane, hexaethyldisiloxane, and octamethyltrisiloxane; methoxytrimethylsilane, ethoxy Alkoxysilanes such as trimethylsilane; peroxides such as bis (trimethylsilyl) peroxide; carboxylic acid esters such as trimethylsilyl acetate, triethylsilyl acetate, trimethylsilyl propionate, trimethylsilyl methacrylate, and trimethylsilyl trifluoroacetate; methanesulfonic acid Sulfonic acid esters such as trimethylsilyl, trimethylsilyl ethanesulfonate, triethylsilyl methanesulfonate, trimethylsilyl fluoromethanesulfonate; bis (trimethylsilyl) Sulfuric esters such as sulfates; tris (trimethylsiloxy) borate esters such as boron; tris (trimethylsilyl) phosphate, tris (trimethylsilyl) phosphite phosphoric acid or phosphorous acid esters such as phosphite and the like.

  Of these, siloxane compounds, sulfonic acid esters, and sulfuric acid esters are preferable, and sulfonic acid esters are particularly preferable. The siloxane compound is preferably hexamethyldisiloxane, the sulfonic acid ester is preferably trimethylsilyl methanesulfonate, and the sulfuric acid ester is preferably bis (trimethylsilyl) sulfate.

[[Compound with SF bond in molecule]]
The compound having an S—F bond in the molecule is not particularly limited, but sulfonyl fluorides and fluorosulfonic acid esters are preferable. For example, methanesulfonyl fluoride, ethanesulfonyl fluoride, methanebis (sulfonylfluoride), ethane-1,2-bis (sulfonylfluoride), propane-1,3-bis (sulfonylfluoride), butane-1,4 -Bis (sulfonyl fluoride), difluoromethane bis (sulfonyl fluoride), 1,1,2,2-tetrafluoroethane-1,2-bis (sulfonyl fluoride), 1,1,2,2,3 Examples include 3-hexafluoropropane-1,3-bis (sulfonyl fluoride), methyl fluorosulfonate, ethyl fluorosulfonate, and the like. Of these, methanesulfonyl fluoride, methanebis (sulfonyl fluoride) or methyl fluorosulfonate is preferable.

[[Nitrate, nitrite, monofluorophosphate, difluorophosphate, acetate, propionate]]
The counter cation of nitrate, nitrite, monofluorophosphate, difluorophosphate, acetate, propionate is not particularly limited, but metal elements such as Li, Na, K, Mg, Ca, Fe, Cu, etc. In addition, ammonium or quaternary ammonium represented by NR ⁹ R ¹⁰ R ¹¹ R ¹² (wherein R ^{9 to} R ¹² each independently represents a hydrogen atom or an organic group having 1 to 12 carbon atoms). Is mentioned. Here, the organic group having 1 to 12 carbon atoms of R ^{9 to} R ¹² is an alkyl group which may be substituted with a halogen atom, a cycloalkyl group which may be substituted with a halogen atom, or a halogen atom. An aryl group which may be present, a nitrogen atom-containing heterocyclic group, and the like. R ^{9 to} R ¹² are each preferably a hydrogen atom, an alkyl group, a cycloalkyl group, a nitrogen atom-containing heterocyclic group, or the like. Among these counter cations, lithium, sodium, potassium, magnesium, calcium, or NR ⁹ R ¹⁰ R ¹¹ R ¹² is preferable, and lithium is particularly preferable from the viewpoint of battery characteristics when used in a lithium ion secondary battery. Of these, nitrate or difluorophosphate is preferable in terms of the effect of improving output, battery cycle and high-temperature storage characteristics, and lithium difluorophosphate is particularly preferable. In addition, those compounds synthesized in a non-aqueous solvent may be used substantially as they are, or those synthesized separately and substantially isolated may be added to the non-aqueous solvent.

  A specific compound, that is, a cyclic siloxane compound represented by the general formula (1), a fluorosilane compound represented by the general formula (2), a compound represented by the general formula (3), and an SF bond in the molecule. Compound, nitrate, nitrite, monofluorophosphate, difluorophosphate, acetate or propionate may be used alone, or two or more compounds may be used in any combination and ratio May be. Moreover, even if it is a compound classified into said each with a specific compound, 1 type may be used independently and 2 or more types of compounds may be used together by arbitrary combinations and ratios.

  The ratio of these specific compounds in the non-aqueous electrolyte solution is essential to be 10 ppm or more (0.001 mass% or more) in total with respect to the total non-aqueous electrolyte solution, but is preferably 0.01 mass% or more. Preferably it is 0.05 mass% or more, More preferably, it is 0.1 mass% or more. The upper limit is preferably 5% by mass or less, more preferably 4% by mass or less, and still more preferably 3% by mass or less. If the concentration of the specific compound is too low, it may be difficult to obtain the effect of maintaining the output characteristics even after long-term use. On the other hand, if the concentration is too high, the charge / discharge efficiency may be reduced.

  In addition, when these specific compounds are actually used in the production of secondary batteries as non-aqueous electrolytes, the content of the specific compounds is significantly reduced even if the battery is disassembled and the non-aqueous electrolyte is taken out again. There are many. Therefore, what can detect the said specific compound at least from the non-aqueous electrolyte solution extracted from the battery is considered to be included in this invention.

[Other compounds]
The non-aqueous electrolyte solution in the lithium ion secondary battery of the present invention contains a lithium salt that is an electrolyte and a specific compound as essential components. It can be contained in any amount. As such other compounds, specifically, for example,
(1) Aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, dibenzofuran; 2-fluorobiphenyl, o-cyclohexylfluoro Partially fluorinated products of the above-mentioned aromatic compounds such as benzene and p-cyclohexylfluorobenzene; fluorinated anisole such as 2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroanisole, and 3,5-difluoroanisole Overcharge inhibitors such as compounds;
(2) vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, trifluoropropylene carbonate, succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, cyclohexanedicarboxylic anhydride, etc. Negative electrode film-forming agent;
(3) Ethylene sulfite, propylene sulfite, dimethyl sulfite, propane sultone, butane sultone, methyl methanesulfonate, busulfan, methyl toluenesulfonate, dimethyl sulfate, ethylene sulfate, sulfolane, dimethyl sulfone, diethyl sulfone, dimethyl sulfoxide, diethyl sulfoxide, tetra Positive electrode protecting agents such as methylene sulfoxide, diphenyl sulfide, thioanisole, diphenyl disulfide, dipyridinium disulfide;
Etc.

  As the overcharge inhibitor, aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, and dibenzofuran are preferable. Two or more of these may be used in combination. When using 2 or more types together, it is particularly preferable to use cyclohexylbenzene or terphenyl (or a partially hydrogenated product thereof) together with t-butylbenzene or t-amylbenzene.

  As the negative electrode film forming agent, vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, succinic anhydride, and maleic anhydride are preferable. Two or more of these may be used in combination. When using 2 or more types together, it is preferable that at least 1 type uses vinylene carbonate. As the positive electrode protective agent, ethylene sulfite, propylene sulfite, propane sultone, butane sultone, methyl methanesulfonate, and busulfan are preferable. Two or more of these may be used in combination. Moreover, the combined use of a negative electrode film forming agent and a positive electrode protective agent, or the combined use of an overcharge inhibitor, a negative electrode film forming agent, and a positive electrode protective agent is particularly preferable.

  The content ratio of these other compounds in the non-aqueous electrolyte solution is not particularly limited, but is preferably 0.01% by mass or more, particularly preferably 0.1% by mass or more, respectively, based on the whole non-aqueous electrolyte solution. The upper limit is preferably 5% by mass or less, particularly preferably 3% by mass or less, and further preferably 2% by mass or less. By adding these compounds, it is possible to suppress rupture / ignition of the battery at the time of abnormality due to overcharge, and to improve the capacity maintenance characteristic and cycle characteristic after high-temperature storage.

  The method for preparing the non-aqueous electrolyte solution for the secondary battery of the present invention is not particularly limited, and is prepared by dissolving a lithium salt, a specific compound, and, if necessary, other compounds in a non-aqueous solvent according to a conventional method. be able to.

<Negative electrode>
The negative electrode used for the lithium ion secondary battery of this invention is demonstrated below.
[Negative electrode active material]
The negative electrode active material used for the negative electrode is described below.

[[Constitution]]
As the negative electrode active material, a material capable of electrochemically inserting and extracting lithium ions is used. The negative electrode active material used for the lithium ion secondary battery of the present invention is characterized by containing two or more carbonaceous materials having different crystallinity. Here, “contains two or more types of carbonaceous materials having different crystallinity” means that carbonaceous materials having different crystallinity coexist in the negative electrode, and the coexistence form is a single unit. It does not matter whether the particles are present in a mixed state, are contained in one secondary particle, or are both mixed. The negative electrode active material preferably includes a composite carbonaceous material containing two or more types of carbonaceous materials having different crystallinity. Furthermore, the composite carbonaceous material is a carbonaceous material (carbon Those containing at least one kind of material) as a secondary material can also be preferably used.

  The term “contained in one secondary particle” as used herein means that the carbonaceous materials having different crystallinity are constrained by bonding, physically constrained, and maintained by electrostatic constraining. The state etc. which are carrying out are shown. As used herein, “physical restraint” refers to a state in which one of the carbonaceous materials having different crystallinity is caught in the other, or is caught, and “electrostatic restraint” refers to crystalline property. One of the different carbonaceous materials is attached to the other by electrostatic energy. In addition, “a state constrained by a bond” means a chemical bond such as a hydrogen bond, a covalent bond, or an ionic bond.

  Among these, at least a part of the surface of the carbonaceous material serving as the core has an interface with the coating layer having different crystallinity due to bonding, so that the resistance of lithium migration between the carbonaceous materials having different crystallinity is small. It is advantageous. It does not matter whether the coating layer is formed by bonding with externally supplied materials and / or their altered materials, or by alteration of the material on the surface of the carbonaceous material. Here, the coating has a chemical bond in at least a part of the interface with the surface of the carbonaceous material, and (1) covers the entire surface, and (2) covers the carbonaceous particles locally. A state, (3) a state of selectively covering a part of the surface, and (4) a state of being present in a very small region including a chemical bond. Further, the crystallinity may change continuously or discontinuously at the interface.

  The composite carbonaceous material has an interface formed by coating and / or bonding a carbonaceous material different in crystallinity from the particulate carbonaceous material to the particulate carbonaceous material, and the crystallinity of the interface is discontinuous and / or continuous. It is preferable that it changes. There is no limitation as to which of the “particulate carbonaceous material” and the “carbonaceous material different in crystallinity from the particulate carbonaceous material” has higher crystallinity, but that the particulate carbonaceous material is higher in the present invention. It is preferable for exhibiting the above effect.

Here, the difference in crystallinity is determined by the difference in (002) plane spacing (d ₀₀₂ ), the difference in Lc, and the difference in La according to the X-ray wide angle diffraction method. The difference in crystallinity is (d ₀₀₂ ). It is preferable that 0.0002 nm or more, La is 1 nm or more, or Lc is 1 nm or more from the viewpoint of manifesting the effects of the present invention. The difference of (d ₀₀₂ ) within the above range is preferably 0.0005 nm or more, more preferably 0.001 nm or more, still more preferably 0.003 nm or more, and the upper limit is 0.03 nm or less, preferably 0.02 nm or less. Range. Below this range, the effect due to the difference in crystallinity may be reduced. On the other hand, if it exceeds this range, the crystallinity of the low crystallinity portion tends to be low, and the irreversible capacity resulting from this may increase. Further, the difference of La or Lc in the above range is preferably 2 nm or more, more preferably 5 nm or more, and further preferably 10 nm or more. Generally, graphite cannot be specified because it cannot be defined as 100 nm or more. Below this range, the effect due to the difference in crystallinity may be reduced.

  The composite carbonaceous material is obtained by coating and / or bonding a particulate carbonaceous material with a carbonaceous material having a different crystallinity from the particulate carbonaceous material, and the “particulate carbonaceous material” and the “particulate carbonaceous material” The “carbonaceous material having different crystallinity” may be either a graphite-based carbonaceous material and the other a low-crystalline carbonaceous material, and the “particulate carbonaceous material” may be a graphite-based carbonaceous material. The “carbonaceous material having different crystallinity from the carbonaceous material” is preferably a low crystalline carbonaceous material.

[[[Particulate carbonaceous material]]]
As the particulate carbonaceous material, graphite-based carbonaceous material containing natural graphite and / or artificial graphite, or (a), (b) and / or (c) having slightly lower crystallinity than these.
(A) Thermal decomposition product of organic matter selected from the group consisting of coal-based coke, petroleum-based coke, furnace black, acetylene black, and pitch-based carbon fiber (b) Organic gas carbide (c) (a) or (b ) Containing a carbonaceous material partially or wholly graphitized.

[[[[Graphitic carbonaceous material]]]]
The particulate carbonaceous material is preferably a graphite-based carbonaceous material containing natural graphite and / or artificial graphite. The graphite-based carbonaceous material refers to various carbonaceous materials with high crystallinity such that the (002) plane spacing (d ₀₀₂ ) by X-ray wide angle diffraction method is less than 0.340 nm.

  Specific examples of the graphite-based carbonaceous material include natural graphite, artificial graphite, or a mechanically pulverized product thereof, a reheated product, a reheated product of expanded graphite, or a powder selected from high-purity purified products of these graphites. preferable. Specific examples of the artificial graphite include coal tar pitch, coal heavy oil, atmospheric residue, petroleum heavy oil, aromatic hydrocarbon, nitrogen-containing cyclic compound, sulfur-containing cyclic compound, polyphenylene, polyvinyl chloride. One or more organic substances selected from polyvinyl alcohol, polyacrylonitrile, polyvinyl butyral, natural polymer, polyphenylene sulfide, polyphenylene oxide, furfuryl alcohol resin, phenol-formaldehyde resin, imide resin, and the like, What was graphitized at a firing temperature of about 3200 ° C. or lower and pulverized by an appropriate pulverizing means is preferable.

(Physical properties of graphite carbonaceous materials)
As for the properties of the graphite-based carbonaceous material, it is desirable that one or more of the following (1) to (11) are simultaneously satisfied.

(1) X-ray parameters The graphite-based carbonaceous material preferably has a d-value (interlayer distance) of the lattice plane (002 plane) determined by X-ray diffraction by the Gakushin method of 0.335 nm or more. Moreover, although a minimum is less than 0.340 nm from a definition, Preferably it is 0.337 nm or less. If the d value is too large, the crystallinity may decrease and the initial irreversible capacity may increase. On the other hand, 0.335 is the theoretical value of graphite. The crystallite size (Lc) of the carbon material determined by X-ray diffraction by the Gakushin method is usually in the range of 30 nm or more, preferably 50 nm or more, more preferably 100 nm or more. Below this range, the crystallinity may decrease and the initial irreversible capacity may increase.

(2) Ash content The ash content in the graphite-based carbonaceous material is 1% by mass or less, particularly 0.5% by mass or less, in particular 0.1% by mass or less, with respect to the total mass of the graphite-based carbonaceous material. It is preferably 1 ppm or more. When the above range is exceeded, deterioration of the battery performance due to the reaction with the electrolyte during charging / discharging may not be negligible. Below this range, the manufacturing process requires a lot of time, energy and equipment for preventing contamination, which may increase costs.

(3) Volume-based average particle diameter The volume-based average particle diameter of the graphite-based carbonaceous material is such that the volume-based average particle diameter (median diameter) determined by the laser diffraction / scattering method is usually 1 μm or more, preferably 3 μm or more. Preferably it is 5 micrometers or more, More preferably, it is 7 micrometers or more. Moreover, an upper limit is 100 micrometers or less normally, Preferably it is 50 micrometers or less, More preferably, it is 40 micrometers or less, More preferably, it is 30 micrometers or less, Most preferably, it is 25 micrometers or less. If it falls below the above range, the irreversible capacity may increase, leading to loss of the initial battery capacity. On the other hand, if the ratio exceeds the above range, a non-uniform coating surface tends to be formed at the time of forming an electrode plate, which may be undesirable in the battery manufacturing process.

  In the present invention, the volume-based average particle size is determined by dispersing carbon powder in a 0.2% by mass aqueous solution (about 1 mL) of polyoxyethylene (20) sorbitan monolaurate, which is a surfactant, and a laser diffraction particle size distribution analyzer. It is defined by the median diameter measured using (for example, LA-700 manufactured by Horiba, Ltd.).

(4) Raman R value, Raman half-value width The Raman R value of the graphite-based carbonaceous material measured by using an argon ion laser Raman spectrum method is usually 0.01 or more, preferably 0.03 or more, more preferably 0.10. As described above, the upper limit is 0.60 or less, preferably 0.40 or less. When the Raman R value is below this range, the crystallinity of the particle surface becomes too high, and there are cases where the number of sites where Li enters between layers decreases with charge / discharge. That is, charge acceptance may be reduced. On the other hand, if it exceeds this range, the crystallinity of the particle surface will decrease, the reactivity with the electrolyte will increase, and the efficiency may decrease and the generation of gas may increase.

Further, the Raman half-width in the vicinity of 1580 cm ⁻¹ of the graphite-based carbonaceous material is not particularly limited, but is usually 10 cm ⁻¹ or more, preferably 15 cm ⁻¹ or more, and the upper limit is usually 60 cm ⁻¹ or less, preferably 45 cm ⁻¹ or less. More preferably, it is in the range of 40 cm ⁻¹ or less. When the Raman half width is less than this range, the crystallinity of the particle surface becomes too high, and there are cases where the number of sites where Li enters between layers decreases with charge and discharge. That is, charge acceptance may be reduced. On the other hand, if it exceeds this range, the crystallinity of the particle surface will decrease, the reactivity with the electrolyte will increase, and the efficiency may decrease and the generation of gas may increase.

The Raman spectrum is measured by using Raman spectroscopy (for example, a Raman spectrometer manufactured by JASCO Corporation), and the sample is naturally dropped into the measurement cell, and the sample is filled, and the measurement is performed by applying an argon ion laser beam to the sample surface in the cell. While irradiating, the cell is rotated in a plane perpendicular to the laser beam. The obtained Raman spectrum, the intensity I _A of the peak P _A in the vicinity of 1580 cm ^-1, and measuring the intensity I _B of a peak P _B in the vicinity of 1360 cm ^-1, the intensity ratio R (R = I _B / I _A ) Is calculated and defined as the Raman R value of the carbon material. Further, the half width of the peak P _A near 1580 cm ^{−1 of} the obtained Raman spectrum is measured, and this is defined as the Raman half width of the carbon material.

The Raman measurement conditions here are as follows.
Argon ion laser wavelength: 514.5nm
・ Laser power on the sample: 15-25mW
・ Resolution: 10-20cm ^-1
Measurement range: 1100-1730 cm ^-1
・ Raman R value, half width analysis: Background processing ・ Smoothing processing: Simple average, 5 points of convolution

(5) BET specific surface area The specific surface area of the graphite-based carbonaceous material measured using the BET method is usually 0.1 m ² / g or more, preferably 0.7 m ² / g or more, more preferably 1 m ² / g or more, More preferably, it is 1.5 m ² / g or more. The upper limit is usually 100 m ² / g or less, preferably 25 m ² / g or less, more preferably 15 m ² / g or less, and still more preferably 10 m ² / g or less. When the value of the specific surface area is less than this range, the acceptability of lithium is likely to deteriorate during charging when used as a negative electrode material, and lithium may easily precipitate on the electrode surface. On the other hand, when it exceeds this range, when used as a negative electrode material, the reactivity with the electrolyte increases, gas generation tends to increase, and a preferable battery may not be obtained.

  The BET specific surface area was measured by using a surface area meter (for example, a fully automatic surface area measuring device manufactured by Okura Riken), preliminarily drying the sample for 15 minutes at 350 ° C. under a nitrogen flow, and then measuring the relative pressure of nitrogen with respect to atmospheric pressure. This is defined by a value measured by a nitrogen adsorption BET one-point method using a gas flow method, using a nitrogen-helium mixed gas that is accurately adjusted to have a value of 0.3.

(6) Pore distribution As the graphite-based carbonaceous material, the amount of voids in the particle corresponding to a diameter of 0.01 μm or more and 1 μm or less, and the amount of irregularities due to the step of the particle surface, obtained by mercury porosimetry (mercury intrusion method). 0.01 mL / g or more, preferably 0.05 mL / g or more, more preferably 0.1 mL / g or more, and the upper limit is 0.6 mL / g or less, preferably 0.4 mL / g or less, more preferably 0. The range is 3 mL / g or less. If it exceeds this range, a large amount of binder may be required when forming an electrode plate. On the other hand, if it falls below this range, the high current density charge / discharge characteristics may deteriorate, and the effect of relaxing the expansion and contraction of the electrode during charge / discharge may not be obtained.

  Further, the total pore volume is preferably 0.1 mL / g or more, more preferably 0.25 mL / g or more, and the upper limit is 10 mL / g or less, preferably 5 mL / g or less, more preferably 2 mL / g or less. It is. If this range is exceeded, a large amount of binder may be required during electrode plate formation. If it is less than that, it may not be possible to obtain the effect of dispersing the thickener or the binder during the electrode plate formation.

  The average pore diameter is preferably 0.05 μm or more, more preferably 0.1 μm or more, further preferably 0.5 μm or more, and the upper limit is 50 μm or less, preferably 20 μm or less, more preferably 10 μm or less. Beyond this range, a large amount of binder may be required. On the other hand, if it falls below this range, the high current density charge / discharge characteristics may deteriorate.

  As an apparatus for mercury porosimetry, a mercury porosimeter (Autopore 9520: manufactured by Micromeritex Corporation) was used. A sample (negative electrode material) was weighed so as to have a value of about 0.2 g, sealed in a powder cell, and pretreated by degassing at room temperature under vacuum (50 μmHg or less) for 10 minutes. Subsequently, the pressure was reduced to 4 psia (about 28 kPa), mercury was introduced, the pressure was increased stepwise from 4 psia (about 28 kPa) to 40000 psia (about 280 MPa), and then the pressure was reduced to 25 psia (about 170 kPa). The number of steps at the time of pressure increase was 80 points or more, and the mercury intrusion amount was measured after an equilibration time of 10 seconds in each step. The pore distribution was calculated from the mercury intrusion curve thus obtained using the Washburn equation. The mercury surface tension (γ) was calculated as 485 dyne / cm, and the contact angle (ψ) was calculated as 140 °. As the average pore diameter, the pore diameter when the cumulative pore volume was 50% was used.

(7) Circularity As the degree of sphericity of the graphite-based carbonaceous material, the circularity of particles having a particle size in the range of 3 to 40 μm is preferably 0.1 or more, particularly preferably 0.5 or more, more preferably 0.8 or more, more preferably 0.85 or more, and most preferably 0.9 or more. High circularity is preferable because high current density charge / discharge characteristics are improved. The circularity is defined by the following formula. When the circularity is 1, a theoretical sphere is obtained.
Circularity = (perimeter of equivalent circle having the same area as the particle projection shape) / (actual circumference of particle projection shape)

  As the value of the circularity, for example, a flow type particle image analyzer (for example, FPIA manufactured by Sysmex Industrial Co., Ltd.) is used, and about 0.2 g of a sample is mixed with polyoxyethylene (20) sorbitan monolaurate as a surfactant. Particles having a detection range of 0.6 to 400 μm and a particle size in the range of 3 to 40 μm after being dispersed in a 0.2 mass% aqueous solution (about 50 mL) and irradiated with an ultrasonic wave of 28 kHz for 1 minute at an output of 60 W Use the value measured for.

  The method for improving the degree of circularity is not particularly limited, but a spheroidized sphere is preferable because the shape of the interparticle void when the electrode body is formed is preferable. Examples of spheroidizing treatment include a method of mechanically approaching a sphere by applying a shearing force and a compressive force, a mechanical / physical processing method of granulating a plurality of fine particles by the binder or the adhesive force of the particles themselves, etc. Is mentioned.

(8) True density The true density of the graphite-based carbonaceous material is usually 2 g / cm ³ or more, preferably 2.1 g / cm ³ or more, more preferably 2.2 g / cm ³ or more, and further preferably 2.22 g / cm. ^The upper limit is 2.26 g / cm ³ or less. The upper limit is the theoretical value of graphite. Below this range, the crystallinity of the carbon is too low and the initial irreversible capacity may increase. In the present invention, the true density is defined by a value measured by a liquid phase substitution method (pycnometer method) using butanol.

(9) Tap density The tap density of the graphite-based carbonaceous material is usually 0.1 g / cm ³ or more, preferably 0.5 g / cm ³ or more, more preferably 0.7 g / cm ³ or more, particularly preferably 0.9 g. / Cm ³ or more is desired. The upper limit is preferably 2 g / cm ³ or less, more preferably 1.8 g / cm ³ or less, and particularly preferably 1.6 g / cm ³ or less. When the tap density is below this range, the packing density is difficult to increase when used as a negative electrode, and a high-capacity battery may not be obtained. On the other hand, if it exceeds this range, there are too few voids between the particles in the electrode, it becomes difficult to ensure conductivity between the particles, and it may be difficult to obtain preferable battery characteristics.

In the present invention, the tap density is measured by passing a sieve having a mesh size of 300 μm, dropping the sample onto a 20 cm ³ tapping cell and filling the sample up to the upper end surface of the cell, Tapping with a stroke length of 10 mm is performed 1000 times using a tap denser), and the bulk density obtained from the volume at that time and the weight of the sample is defined as the tap density.

(10) Orientation ratio (powder)
The orientation ratio of the graphite-based carbonaceous material is usually 0.005 or more, preferably 0.01 or more, more preferably 0.015 or more, and the upper limit is theoretically 0.67 or less. Below this range, the high-density charge / discharge characteristics may deteriorate.

  The orientation ratio is measured by X-ray diffraction. The peaks of (110) and (004) diffraction are integrated by fitting the peaks of (110) and (004) diffraction of carbon by X-ray diffraction using asymmetric Pearson VII as a profile function. Each intensity is calculated. From the obtained integrated intensity, a ratio represented by (110) diffraction integrated intensity / (004) diffraction integrated intensity is calculated and defined as an active material orientation ratio.

The X-ray diffraction measurement conditions here are as follows. “2θ” indicates a diffraction angle.
-Target: Cu (Kα ray) graphite monochromator-Slit: Divergence slit = 1 degree, Receiving slit = 0.1 mm, Scattering slit = 1 degree-Measurement range and step angle / measurement time:
(110) plane: 76.5 degrees ≦ 2θ ≦ 78.5 degrees 0.01 degrees / 3 seconds (004) plane: 53.5 degrees ≦ 2θ ≦ 56.0 degrees 0.01 degrees / 3 seconds

(11) Aspect ratio (powder)
The aspect ratio of the graphite-based carbonaceous material is theoretically 1 or more, and the upper limit is 10 or less, preferably 8 or less, more preferably 5 or less. If the upper limit is exceeded, streaking or a uniform coated surface may not be obtained during electrode plate formation, and the high current density charge / discharge characteristics may deteriorate.

  The aspect ratio is expressed as A / B when the longest diameter A of the carbon material particles when observed three-dimensionally and the shortest diameter B perpendicular to the carbon material particles. The carbon particles are observed with a scanning electron microscope capable of magnifying observation. Arbitrary 50 graphite particles fixed to an end face of a metal having a thickness of 50 μm or less are selected, and the stage on which the sample is fixed is rotated and tilted to measure A and B, and the average of A / B Find the value.

[[[[Low crystalline carbonaceous material]]]]
The low crystalline carbonaceous material refers to a carbonaceous material with low crystallinity such that the (002) plane spacing (d ₀₀₂ ) by the X-ray wide angle diffraction method is 0.340 nm or more.

(Composition of low crystalline carbonaceous material)
The “carbonaceous material having different crystallinity from the particulate carbonaceous material” is preferably a low crystalline carbonaceous material rather than the particulate carbonaceous material. Further, the following (d) or (e) carbide is particularly preferable.
(D) Coal heavy oil, DC heavy oil, cracked heavy oil, aromatic hydrocarbon, N ring compound, S ring compound, polyphenylene, organic synthetic polymer, natural polymer, thermoplastic resin and Carbonizable organic substances selected from the group consisting of thermosetting resins (e) These carbonizable organic substances dissolved in low molecular organic solvents

  As coal-based heavy oil, coal tar pitch from dry pitch to hard pitch, dry distillation liquefied oil, etc. are preferable, and as DC heavy oil, normal pressure residual oil, reduced pressure residual oil, etc. are preferable, cracked petroleum heavy oil, etc. The crude oil is preferably ethylene tar or the like by-produced during thermal decomposition of crude oil, naphtha, etc., and the aromatic hydrocarbon is preferably acenaphthylene, decacyclene, anthracene, phenanthrene, etc., and the N-ring compound is phenazine, acridine, etc. Preferably, the S ring compound is preferably thiophene, bithiophene, etc., the polyphenylene is preferably biphenyl, terphenyl, etc., and the organic synthetic polymer is polyvinyl chloride, polyvinyl alcohol, polyvinyl butyral, insolubilization treatment thereof. Products, polyacrylonitrile, polypyrrole, polythiophene Polystyrene, etc. are preferred, natural polymers are preferably polysaccharides such as cellulose, lignin, mannan, polygalacturonic acid, chitosan, saccharose, etc., and thermoplastic resins are preferably polyphenylene sulfide, polyphenylene oxide, etc. As the curable resin, a furfuryl alcohol resin, a phenol-formaldehyde resin, an imide resin or the like is preferable.

  The “carbonaceous material having different crystallinity from the particulate carbonaceous material” is preferably a carbide of the above-mentioned “carbonizable organic material”, and the “carbonizable organic material” is preferably benzene, toluene, xylene, quinoline. It is also preferable to be a carbide such as a solution dissolved in a low molecular organic solvent such as n-hexane. In addition, the “carbonaceous material having different crystallinity from the particulate carbonaceous material” is preferably a carbonized carbon of coal-based coke or petroleum-based coke.

  The above (d) or (e) is particularly preferably liquid. That is, it is preferable to advance carbonization in the liquid phase from the viewpoint of interface formation with the graphite-based carbonaceous material part.

(Physical properties of low crystalline carbonaceous materials)
As the physical properties of the low crystalline carbonaceous material, it is desirable that one or more of the following (1) to (5) are simultaneously satisfied. In addition, one kind of low crystalline carbonaceous material exhibiting such physical properties may be used alone, or two or more kinds may be used in any combination and ratio.

(1) X-ray parameter For the low crystalline carbonaceous material part, the d value (interlayer distance) of the lattice plane (002 plane) obtained by X-ray diffraction by the Gakushin method is 0.340 nm or more from the definition. It is preferably 0.340 nm or more, particularly preferably 0.341 nm or more. The upper limit is preferably 0.380 nm or less, particularly preferably 0.355 nm or less, and further preferably 0.350 nm or less. If the d value is too large, the surface may be extremely low in crystallinity, and the irreversible capacity may increase. If it is too small, the effect of improving the charge acceptance obtained by placing the low crystalline carbonaceous material on the surface is small. The effect of the present invention may be reduced. The crystallite size (Lc) of the carbon material determined by X-ray diffraction by the Gakushin method is usually in the range of 1 nm or more, preferably 1.5 nm or more. Below this range, the crystallinity may decrease and the increase in initial irreversible capacity may increase.

(2) Ash content The ash content in the low crystalline carbonaceous material part is 1% by mass or less, particularly 0.5% by mass or less, especially 0.1% by mass or less, and the lower limit relative to the total mass of the composite carbonaceous material It is preferably 1 ppm or more. When the above range is exceeded, deterioration of the battery performance due to the reaction with the electrolyte during charging / discharging may not be negligible. Below this range, the manufacturing process requires a lot of time, energy and equipment for preventing contamination, which may increase costs.

(4) Raman R value, Raman half-value width The R value of the low crystalline carbonaceous material portion measured using the argon ion laser Raman spectrum method is usually 0.5 or more, preferably 0.7 or more, more preferably 0.8. 9 or more and the upper limit is 1.5 or less, preferably 1.2 or less. When the Raman R value is below this range, the crystallinity of the particle surface becomes too high, and there are cases where the number of sites where Li enters between layers decreases with charge / discharge. That is, charge acceptance may be reduced. In addition, when the negative electrode is densified by applying it to the current collector and then pressing it, the crystals are likely to be oriented in a direction parallel to the electrode plate, which may lead to a decrease in load characteristics. On the other hand, if it exceeds this range, the crystallinity of the particle surface will decrease, the reactivity with the electrolyte will increase, and the efficiency may decrease and the generation of gas may increase.

Although the Raman half-value width of the near 1580 cm ^-1 of the low crystalline carbonaceous material portion is not particularly limited, usually 40 cm ^-1 or more, preferably 50 cm ^-1 or more, and as the upper limit, usually 100 cm ^-1 or less, preferably 90cm ^- The range is ¹ or less, more preferably 80 cm ⁻¹ or less. When the Raman half width is less than this range, the crystallinity of the particle surface becomes too high, and there are cases where the number of sites where Li enters between layers decreases with charge and discharge. That is, charge acceptance may be reduced. In addition, when the negative electrode is densified by applying it to the current collector and then pressing it, the crystals are likely to be oriented in a direction parallel to the electrode plate, which may lead to a decrease in load characteristics. On the other hand, if it exceeds this range, the crystallinity of the particle surface will decrease, the reactivity with the electrolyte will increase, and the efficiency may decrease and the generation of gas may increase.

(4) True density The true density of the low crystalline carbonaceous material portion is usually 1.4 g / cm ³ or more, preferably 1.5 g / cm ³ or more, more preferably 1.6 g / cm ³ or more, and still more preferably 1. 0.7 g / cm ³ or more, and the upper limit is 2.1 g / cm ³ or less, preferably 2 g / cm ³ or less. If this range is exceeded, charge acceptance may be impaired. Below this range, the crystallinity of the carbon is too low and the initial irreversible capacity may increase.

(5) Orientation ratio The orientation ratio of the low crystalline carbonaceous material portion is usually 0.005 or more, preferably 0.01 or more, more preferably 0.015 or more, and the upper limit is theoretically 0.67 or less. Below this range, the high-density charge / discharge characteristics are undesirably lowered. The orientation ratio is measured by X-ray diffraction. The peaks of (110) and (004) diffraction are integrated by fitting the peaks of (110) and (004) diffraction of carbon by X-ray diffraction using asymmetric Pearson VII as a profile function. Each intensity is calculated. From the obtained integrated intensity, a ratio represented by (110) diffraction integrated intensity / (004) diffraction integrated intensity is calculated and defined as the active material orientation ratio of the electrode.

[[[Composite carbonaceous material]]]
The composite carbonaceous material used in the lithium ion secondary battery of the present invention preferably contains “particulate carbonaceous material” and “carbonaceous material having different crystallinity from the particulate carbonaceous material”. Either is a graphite-based carbonaceous material and the other is only required to be a low crystalline carbonaceous material. Preferably, the “particulate carbonaceous material” is a graphite-based carbonaceous material, and the “carbonaceous material having crystallinity different from the particulate carbonaceous material” is a low crystalline carbonaceous material.

  In the composite carbonaceous material, the mass ratio of the graphite-based carbonaceous material and the low crystalline carbonaceous material is preferably 50/50 or more, more preferably 80/20 or more, particularly preferably 90/10 or more, preferably 99 A range of 0.9 / 0.1 or less, more preferably 99/1 or less, particularly preferably 98/2 or less is desirable. If the above range is exceeded, the effect of having two types of crystalline carbonaceous materials may not be obtained. If the range is below the above range, the initial irreversible capacity tends to increase, which is a problem in battery design. There is. The graphite-based carbonaceous material is preferably 50% by mass or more based on the entire composite carbonaceous material.

(Physical properties of composite carbonaceous materials)
As the composite carbonaceous material, it is desirable that any one or more of the following (1) to (11) are simultaneously satisfied. Moreover, 1 type of composite carbonaceous materials which show this physical property may be used independently, or 2 or more types may be used together by arbitrary combinations and ratios.

(1) X-ray parameters The composite carbonaceous material preferably has a d-value (interlayer distance) of the lattice plane (002 plane) determined by X-ray diffraction by the Gakushin method of 0.335 nm or more, usually 0.350 nm. In the following, it is desired that the thickness is preferably 0.345 nm or less, more preferably 0.340 nm or less. Further, the crystallite size (Lc) of the carbon material determined by X-ray diffraction by the Gakushin method is usually 1.5 nm or more, preferably 3.0 nm or more. Below this range, the crystallinity may decrease and the increase in initial irreversible capacity may increase.

(2) Ash content The ash content in the composite carbonaceous material is 1% by mass or less, particularly 0.5% by mass or less, particularly 0.1% by mass or less, and the lower limit is 1 ppm or more with respect to the total mass of the composite carbonaceous material. It is preferable that When the above range is exceeded, deterioration of the battery performance due to the reaction with the electrolyte during charging / discharging may not be negligible. Below this range, the manufacturing process requires a lot of time, energy and equipment for preventing contamination, which may increase costs.

(3) Volume-based average particle diameter The volume-based average particle diameter of the composite carbonaceous material is usually 1 μm or more, preferably 3 μm or more, more preferably a volume-based average particle diameter (median diameter) determined by a laser diffraction / scattering method. Is 5 μm or more, more preferably 7 μm or more. Moreover, an upper limit is 100 micrometers or less normally, Preferably it is 50 micrometers or less, More preferably, it is 40 micrometers or less, More preferably, it is 30 micrometers or less, Most preferably, it is 25 micrometers or less. If it falls below the above range, the irreversible capacity may increase, leading to loss of the initial battery capacity. On the other hand, if the ratio exceeds the above range, a non-uniform coating surface tends to be formed at the time of forming an electrode plate, which may be undesirable in the battery manufacturing process.

(4) Raman R value, Raman half-value width The Raman R value of the composite carbonaceous material measured using an argon ion laser Raman spectrum method is usually 0.03 or more, preferably 0.10 or more, more preferably 0.15 or more. The upper limit is 0.60 or less, preferably 0.50 or less. When the Raman R value is below this range, the crystallinity of the particle surface becomes too high, and there are cases where the number of sites where Li enters between layers decreases with charge / discharge. That is, charge acceptance may be reduced. In addition, when the negative electrode is densified by applying it to the current collector and then pressing it, the crystals are likely to be oriented in a direction parallel to the electrode plate, which may lead to a decrease in load characteristics. On the other hand, if it exceeds this range, the crystallinity of the particle surface will decrease, the reactivity with the electrolyte will increase, and the efficiency may decrease and the generation of gas may increase.

Further, the Raman half-width in the vicinity of 1580 cm ^{−1 of the} composite carbonaceous material is not particularly limited, but is usually 15 cm ⁻¹ or more, preferably 20 cm ⁻¹ or more, and the upper limit is usually 70 cm ⁻¹ or less, preferably 60 cm ⁻¹ or less, More preferably, it is the range of 50 cm <^-1> or less. When the Raman half width is less than this range, the crystallinity of the particle surface becomes too high, and there are cases where the number of sites where Li enters between layers decreases with charge and discharge. That is, charge acceptance may be reduced. In addition, when the negative electrode is densified by applying it to the current collector and then pressing it, the crystals are likely to be oriented in a direction parallel to the electrode plate, which may lead to a decrease in load characteristics. On the other hand, if it exceeds this range, the crystallinity of the particle surface will decrease, the reactivity with the electrolyte will increase, and the efficiency may decrease and the generation of gas may increase.

(5) BET specific surface area The specific surface area of the composite carbonaceous material measured using the BET method is usually 0.1 m ² / g or more, preferably 0.7 m ² / g or more, more preferably 1 m ² / g or more, and more Preferably it is 1.5 m ² / g or more. The upper limit is usually 100 m ² / g or less, preferably 25 m ² / g or less, more preferably 15 m ² / g or less, and still more preferably 10 m ² / g or less. When the value of the specific surface area is less than this range, the acceptability of lithium is likely to deteriorate during charging when used as a negative electrode material, and lithium may easily precipitate on the electrode surface. On the other hand, when it exceeds this range, when used as a negative electrode material, the reactivity with the electrolyte increases, gas generation tends to increase, and a preferable battery may not be obtained.

(6) Pore distribution As the composite carbonaceous material, the amount of voids in the particle corresponding to a diameter of 0.01 μm or more and 1 μm or less, the amount of irregularities due to the step of the particle surface, determined by mercury porosimetry (mercury intrusion method), 0.01 mL / g or more, preferably 0.05 mL / g or more, more preferably 0.1 mL / g or more, and the upper limit is 0.6 mL / g or less, preferably 0.4 mL / g or less, more preferably 0.3 mL / G or less. If it exceeds this range, a large amount of binder may be required when forming an electrode plate. If it is less than the range, the high current density charge / discharge characteristics may be deteriorated, and the effect of relaxing the expansion / contraction of the electrode during charge / discharge may not be obtained.

  Further, the total pore volume is preferably 0.1 mL / g or more, more preferably 0.25 mL / g or more, and the upper limit is 10 mL / g or less, preferably 5 mL / g or less, more preferably 2 mL / g or less. It is. If this range is exceeded, a large amount of binder may be required during electrode plate formation. If it is less than that, it may not be possible to obtain the effect of dispersing the thickener or the binder during the electrode plate formation.

  The average pore diameter is preferably 0.05 μm or more, more preferably 0.1 μm or more, further preferably 0.5 μm or more, and the upper limit is 80 μm or less, preferably 50 μm or less, more preferably 20 μm or less. Beyond this range, a large amount of binder may be required. If it is less, the high current density charge / discharge characteristics may deteriorate.

(7) Circularity As the degree of sphericity of the composite carbonaceous material, the circularity of particles having a particle size in the range of 3 to 40 μm is preferably 0.85 or more, more preferably 0.87 or more, and still more preferably 0. It is preferable that the circularity is .9 or more because high current density charge / discharge characteristics are improved.

(8) True density The true density of the composite carbonaceous material is usually 1.9 g / cm ³ or more, preferably 2 g / cm ³ or more, more preferably 2.1 g / cm ³ or more, and even more preferably 2.2 g / cm ^3. The upper limit is 2.26 g / cm ³ or less. The upper limit is the theoretical value of graphite. Below this range, the crystallinity of the carbon is too low and the initial irreversible capacity may increase.

(9) Tap density The tap density of the composite carbonaceous material is usually 0.1 g / cm ³ or more, preferably 0.5 g / cm ³ or more, more preferably 0.7 g / cm ³ or more, and particularly preferably 1 g / cm. It is desired to be cm ³ or more. Further, it is preferably 2 g / cm ³ or less, more preferably 1.8 g / cm ³ or less, and particularly preferably 1.6 g / cm ³ or less. When the tap density is below this range, the packing density is difficult to increase when used as a negative electrode, and a high-capacity battery may not be obtained. On the other hand, if it exceeds this range, there are too few voids between the particles in the electrode, it becomes difficult to ensure conductivity between the particles, and it may be difficult to obtain preferable battery characteristics. The tap density is measured and defined by the same method as described above.

(10) Orientation ratio (powder)
The orientation ratio of the composite carbonaceous material is usually 0.005 or more, preferably 0.01 or more, more preferably 0.015 or more, and the upper limit is theoretically 0.67 or less. Below this range, the high-density charge / discharge characteristics may deteriorate.

(11) Aspect ratio (powder)
The aspect ratio of the composite carbonaceous material is theoretically 1 or more, and the upper limit is 10 or less, preferably 8 or less, and more preferably 5 or less. If the upper limit is exceeded, streaking or a uniform coated surface may not be obtained during electrode plate formation, and the high current density charge / discharge characteristics may deteriorate.

(Production method of composite carbonaceous material)
Although the manufacturing method of these composite carbonaceous materials is not particularly limited, the following methods are exemplified. A composite of a graphite-based carbonaceous material and a low-crystalline carbonaceous material is obtained by heat-treating a mixture of a carbon precursor and a graphite-based carbonaceous material powder using the carbon precursor to obtain a low-crystalline carbonaceous material as it is. A method for obtaining a composite powder, a method in which a low-crystalline carbonaceous material powder obtained by partially carbonizing the carbon precursor described above is prepared in advance, mixed with a graphite-based carbonaceous material powder, and heat-treated to form a composite. , A method of preparing the above-mentioned low crystalline carbonaceous material powder in advance, mixing the graphite-based carbonaceous material powder, the low crystalline carbonaceous material powder, and the carbon precursor, and heat-treating the composite. It can be adopted. In the latter two methods of preparing the low crystalline carbonaceous material powder in advance, low crystalline carbonaceous material particles having an average particle diameter of 1/10 or less of the average particle diameter of the graphite-based carbonaceous material particles are used. It is preferable. In addition, by applying mechanical energy such as pulverization of low crystalline carbonaceous material and graphite-based carbonaceous material prepared in advance, it is also possible to adopt a method in which the other is engulfed or an electrostatically attached structure. Is possible.

  Heat a mixture of graphite-based carbonaceous material particles and carbon precursor to obtain an intermediate material, or heat a mixture of graphite-based carbonaceous material particles and low crystalline carbonaceous material particles and a carbon precursor. Thus, it is preferable to obtain a composite carbonaceous material in which a low crystalline carbonaceous material is finally combined with graphite-based carbonaceous material particles by carbonization firing and pulverization.

The manufacturing process for obtaining such a composite carbonaceous material is divided into the following four processes.
First step: (graphite-based carbonaceous material particles or (mixed particles of graphite-based carbonaceous material particles and low-crystalline carbonaceous material particles)) and a carbon precursor of the low-crystalline carbonaceous material particles, and, if necessary, a solvent. These are mixed using various commercially available mixers and kneaders to obtain a mixture.

  Second step: The mixture is heated to obtain an intermediate material from which volatile components generated from the solvent and the carbon precursor are removed. At this time, if necessary, the mixture may be stirred. Further, even if the volatile matter remains, it is not a problem because it is removed in a later third step.

  Third step: The mixture or the intermediate substance is heated to 400 ° C. or more and 3200 ° C. or less in an inert gas atmosphere such as nitrogen gas, carbon dioxide gas, argon gas, etc. to obtain graphite / low crystalline carbonaceous material / composite material. .

  Fourth step: The composite material is subjected to powder processing such as pulverization, pulverization, and classification as required.

  Among these steps, the second step and the fourth step may be omitted depending on circumstances, and the fourth step may be performed before the third step. However, when the fourth step is performed before the third step, powder processing such as pulverization, pulverization, and classification is performed again as necessary to obtain a composite carbonaceous material.

  In addition, the heat history temperature condition is important as the heat treatment condition in the third step. The lower limit of the temperature is usually 400 ° C. or higher, preferably 900 ° C. or higher, although it varies slightly depending on the type of carbon precursor and its thermal history. On the other hand, the upper limit temperature can be raised to a temperature that basically does not have a structural order exceeding the crystal structure of the graphite-based carbonaceous material particle nucleus. Therefore, the upper limit temperature of the heat treatment is usually 3200 ° C. or lower, preferably 2000 ° C. or lower, more preferably 1500 ° C. or lower. Under such heat treatment conditions, the heating rate, cooling rate, heat treatment time, etc. can be arbitrarily set according to the purpose. Further, after heat treatment in a relatively low temperature region, the temperature can be raised to a predetermined temperature. In addition, the reactor used for this process may be a batch type or a continuous type, and may be one or more.

[[Sub-material mix]]
In addition to the composite carbonaceous material, the negative electrode active material in the lithium ion secondary battery of the present invention contains one or more carbonaceous materials (carbonaceous materials) having different carbonaceous properties, thereby further improving battery performance. It is possible to improve. The “physical properties of carbonaceous material” described here are X-ray diffraction parameters, median diameter, aspect ratio, BET specific surface area, orientation ratio, Raman R value, tap density, true density, pore distribution, circularity, ash content Exhibit one or more characteristics. Further, as a preferred embodiment, when the volume-based particle size distribution is not symmetrical with respect to the median diameter, it contains two or more carbon materials having different Raman R values, and the X-ray parameters are different. And so on. As an example of the effect, electrical resistance is reduced by containing carbon materials such as graphite such as natural graphite and artificial graphite, carbon black such as acetylene black, and amorphous carbon such as needle coke as secondary materials. For example. These may be used individually by 1 type, or may use 2 or more types together by arbitrary combinations and a ratio. When added as a secondary material, it is 0.1% by mass or more, preferably 0.5% by mass or more, more preferably 0.6% by mass or more, and the upper limit is 80% by mass or less, preferably 50% by mass or less. More preferably, it is 40 mass% or less, More preferably, it is the range of 30 mass% or less. Below this range, it is difficult to obtain the effect of improving conductivity, which is not preferable. If it exceeds, an increase in the initial irreversible capacity is caused, which is not preferable.

[Electrode production]
The negative electrode may be manufactured by a conventional method. For example, it is formed by adding a binder, a solvent, and, if necessary, a thickener, a conductive material, a filler, etc. to a negative electrode active material to form a slurry, which is applied to a current collector, dried and then pressed. Can do. The thickness of the negative electrode active material layer per side in the stage immediately before the electrolytic solution pouring step of the battery is usually 15 μm or more, preferably 20 μm or more, more preferably 30 μm or more, and the upper limit is 150 μm or less, preferably 120 μm or less, More preferably, it is 100 μm or less. If it exceeds this range, the electrolyte solution hardly penetrates to the vicinity of the current collector interface, which is not preferable in that the high current density charge / discharge characteristics are deteriorated. On the other hand, if it falls below this range, the volume ratio of the current collector to the negative electrode active material increases, and the battery capacity decreases, which is not preferable. Further, the negative electrode active material may be roll-formed to form a sheet electrode, or may be formed into a pellet electrode by compression molding.

[[Current collector]]
As the current collector for holding the negative electrode active material, a known material can be arbitrarily used. Examples of the current collector for the negative electrode include metal materials such as copper, nickel, stainless steel, and nickel-plated steel. Of these, copper is particularly preferable from the viewpoint of ease of processing and cost. When the current collector is a metal material, examples of the shape of the current collector include metal foil, metal cylinder, metal coil, metal plate, metal thin film, expanded metal, punch metal, and foam metal. Among them, a metal thin film is preferable, a copper foil is more preferable, and a rolled copper foil by a rolling method and an electrolytic copper foil by an electrolytic method are more preferable, and both can be used as a current collector. When the thickness of the copper foil is less than 25 μm, a copper alloy (phosphor bronze, titanium copper, Corson alloy, Cu—Cr—Zr alloy, etc.) having higher strength than pure copper can be used.

  A current collector made of a copper foil produced by a rolling method is suitable for use in a small cylindrical battery because the copper crystals are arranged in the rolling direction so that the negative electrode is hard to crack even if it is rounded sharply or rounded at an acute angle. be able to. For example, an electrolytic copper foil is prepared by immersing a metal drum in an electrolytic solution in which copper ions are dissolved, and flowing current while rotating the copper drum, thereby depositing copper on the surface of the drum and peeling it off. It is obtained. Copper may be deposited on the surface of the rolled copper foil by an electrolytic method. One side or both sides of the copper foil may be subjected to a roughening treatment or a surface treatment (for example, a chromate treatment having a thickness of about several nm to 1 μm, a base treatment such as Ti).

Further, the following physical properties are desired for the current collector substrate.
(1) Average surface roughness (Ra)
The average surface roughness (Ra) of the active material thin film forming surface of the current collector substrate defined by the method described in JIS B0601-1994 is not particularly limited, but is usually 0.01 μm or more, preferably 0.03 μm or more, usually It is 1.5 μm or less, preferably 1.3 μm or less, particularly preferably 1.0 μm or less. By setting the average surface roughness (Ra) of the current collector substrate within the range between the lower limit and the upper limit described above, good charge / discharge cycle characteristics can be expected. By setting it to the above lower limit or more, the area of the interface with the active material thin film is increased, and the adhesion with the active material thin film is improved. The upper limit of the average surface roughness (Ra) is not particularly limited, but those having an average surface roughness (Ra) exceeding 1.5 μm are generally difficult to obtain as foils having a practical thickness as a battery. 1.5 μm or less is preferable.

(2) Tensile strength The tensile strength of the current collector substrate is not particularly limited, but is usually 50 N / mm ² or more, preferably 100 N / mm ² or more, and more preferably 150 N / mm ² or more. The tensile strength is obtained by dividing the maximum tensile force required until the test piece breaks by the cross-sectional area of the test piece. The tensile strength in the present invention is measured by the same apparatus and method as the elongation rate. If the current collector substrate has a high tensile strength, cracking of the current collector substrate due to expansion / contraction of the active material thin film accompanying charging / discharging can be suppressed, and good cycle characteristics can be obtained.

(3) 0.2% proof stress of 0.2% proof stress current collector substrate is not particularly limited, normally 30 N / mm ² or more, preferably 100 N / mm ² or more, particularly preferably 150 N / mm ² or more . The 0.2% proof stress is the magnitude of the load necessary to give a plastic (permanent) strain of 0.2%. It means that The 0.2% proof stress in the present invention is measured by the same apparatus and method as the elongation rate. If the current collector substrate has a high 0.2% proof stress, plastic deformation of the current collector substrate due to expansion / contraction of the active material thin film accompanying charging / discharging can be suppressed, and good cycle characteristics can be obtained. it can. Although the thickness of a metal thin film is arbitrary, it is 1 micrometer or more normally, Preferably it is 3 micrometers or more, More preferably, it is 5 micrometers or more. Moreover, an upper limit is 1 mm or less normally, Preferably it is 100 micrometers or less, More preferably, it is 30 micrometers or less. If the thickness is less than 1 μm, the strength is lowered, so that coating becomes difficult, which is not preferable in the process. If the thickness is larger than 100 μm, it is difficult to change the shape of the desired electrode by winding or the like, which is not preferable. The metal thin film may be mesh.

[[Ratio of current collector to active material layer thickness]]
The ratio of the thickness of the current collector to the active material layer is not particularly limited, but the value of (thickness of active material layer on one side immediately before electrolyte injection) / (thickness of current collector) is 150 or less, Preferably it is 20 or less, More preferably, it is 10 or less, and a minimum is 0.1 or more, Preferably it is 0.4 or more, More preferably, it is the range of 1 or more. Above this range, the current collector generates heat due to Joule heat during high current density charge / discharge, which is not preferable. Below this range, the volume ratio of the current collector to the negative electrode active material increases and the battery capacity decreases, which is not preferable.

[[Electrode density]]
The electrode structure when the negative electrode active material is converted into an electrode is not particularly limited, but the density of the active material present on the current collector is preferably 1 g / cm ³ or more, more preferably 1.2 g / cm ^3. above, still more preferably 1.3 g / cm ³ or more, 2 g / cm ^3, preferably up 1.9 g / cm ³ or less, more preferably 1.8 g / cm ³ or less, more preferably 1.7g / Cm ³ or less. Exceeding this range is preferable because the active material particles are destroyed, the initial irreversible capacity increases, the permeability of the electrolyte solution near the current collector / active material interface decreases, and the high current density charge / discharge characteristics decrease. Absent. On the other hand, if it is lower, the conductivity between the active materials is lowered, the battery resistance is increased, and the capacity per unit volume is lowered.

[[binder]]
The binder for binding the active material is not particularly limited as long as it is a material that is stable with respect to the electrolyte and the solvent used when manufacturing the electrode. Specifically, resin-based polymers such as polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, nitrocellulose; SBR (styrene-butadiene rubber), isoprene rubber, butadiene rubber, fluorine rubber, Rubber polymers such as NBR (acrylonitrile-butadiene rubber) and ethylene-propylene rubber; styrene / butadiene / styrene block copolymers and hydrogenated products thereof; EPDM (ethylene / propylene / diene terpolymer), styrene / Thermoplastic elastomeric polymers such as ethylene / butadiene / styrene copolymers, styrene / isoprene / styrene block copolymers and hydrogenated products thereof; syndiotactic-1,2-polybutadiene, polyvinyl acetate, Soft resinous polymers such as tylene / vinyl acetate copolymer, propylene / α-olefin copolymer; polyvinylidene fluoride, polytetrafluoroethylene, fluorinated polyvinylidene fluoride, polytetrafluoroethylene / ethylene copolymer, etc. Fluoropolymers; polymer compositions having ionic conductivity of alkali metal ions (especially lithium ions). These may be used individually by 1 type, or may use 2 or more types together by arbitrary combinations and a ratio.

  The solvent for forming the slurry is not particularly limited as long as it is a solvent that can dissolve or disperse the active material, binder, thickener and conductive material used as necessary. Either an aqueous solvent or an organic solvent may be used. Examples of the aqueous solvent include water, a mixed solvent of alcohol and water, and examples of the organic solvent include N-methylpyrrolidone (NMP), dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, acrylic acid. Methyl, diethyltriamine, N, N-dimethylaminopropylamine, tetrahydrofuran (THF), toluene, acetone, diethyl ether, dimethylacetamide, hexamerylphosphalamide, dimethyl sulfoxide, benzene, xylene, quinoline, pyridine, methylnaphthalene And hexane. In particular, when an aqueous solvent is used, a dispersant or the like is added to the above-described thickener, and a slurry such as SBR is formed. In addition, these may be used individually by 1 type, or may use 2 or more types together by arbitrary combinations and a ratio.

  The ratio of the binder to the active material is 0.1% by mass or more, preferably 0.5% by mass or more, more preferably 0.6% by mass or more, and the upper limit is 20% by mass or less, preferably 15% by mass or less. More preferably, it is 10 mass% or less, More preferably, it is the range of 8 mass% or less. If it exceeds this range, the binder ratio in which the binder amount does not contribute to the battery capacity may increase, and the battery capacity may decrease. On the other hand, if it is lower, the strength of the negative electrode is lowered, which may be undesirable in the battery production process. In particular, when the main component contains a rubbery polymer typified by SBR, the ratio of the binder to the active material is 0.1% by mass or more, preferably 0.5% by mass or more, and more preferably 0.8%. The upper limit is 5% by mass or less, preferably 3% by mass or less, and more preferably 2% by mass or less. Further, when the main component contains a fluorine-based polymer typified by polyvinylidene fluoride, the ratio to the active material is 1% by mass or more, preferably 2% by mass or more, more preferably 3% by mass or more. As an upper limit, it is 15 mass% or less, Preferably it is 10 mass% or less, More preferably, it is the range of 8 mass% or less.

  A thickener is usually used to adjust the viscosity of the slurry. The thickener is not particularly limited, and specific examples include carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, and salts thereof. These may be used individually by 1 type, or may use 2 or more types together by arbitrary combinations and a ratio. When a thickener is further added, the ratio of the thickener to the active material is 0.1% by mass or more, preferably 0.5% or more, more preferably 0.6% or more. It is 5 mass% or less, Preferably it is 3 mass% or less, More preferably, it is the range of 2 mass% or less. Below this range, applicability may be significantly reduced. If it exceeds the upper limit, the ratio of the active material in the negative electrode active material layer may be reduced, resulting in a problem that the capacity of the battery is reduced and a problem that the resistance between the negative electrode active materials is increased.

[[Plate orientation ratio]]
The electrode plate orientation ratio is 0.001 or more, preferably 0.005 or more, more preferably 0.01 or more, and the upper limit is 0.67 or less, which is a theoretical value. Below this range, the high-density charge / discharge characteristics are undesirably lowered.

  The measurement of the electrode plate orientation ratio is as follows. About the negative electrode after pressing to the target density, the active material orientation ratio of the electrode is measured by X-ray diffraction. The specific method is not particularly limited, but as a standard method, peak separation is performed by fitting the peaks of (110) and (004) diffraction of carbon by X-ray diffraction using asymmetric Pearson VII as a profile function. The integrated intensities of the peaks of (110) diffraction and (004) diffraction are calculated. From the obtained integrated intensity, a ratio represented by (110) diffraction integrated intensity / (004) diffraction integrated intensity is calculated. The electrode active material orientation ratio calculated by this measurement is defined as the electrode plate orientation ratio.

The X-ray diffraction measurement conditions here are as follows. “2θ” indicates a diffraction angle.
Target: Cu (Kα ray) graphite monochromator
(110) plane: 76.5 degrees ≦ 2θ ≦ 78.5 degrees 0.01 degrees / 3 seconds (004) plane: 53.5 degrees ≦ 2θ ≦ 56.0 degrees 0.01 degrees / 3 seconds Sample preparation: Fix the electrode to the glass plate with double-sided tape with a thickness of 0.1 mm

[[Impedance]]
The resistance of the negative electrode when charged to 60% of the nominal capacity from the discharged state is preferably 100Ω or less, particularly preferably 50Ω or less, more preferably 20Ω or less, and / or the double layer capacity is preferably 1 × 10 ⁻⁶ F or more. Particularly preferably, it is 1 × 10 ⁻⁵ F or more, more preferably 1 × 10 ⁻⁴ F or more. Within this range, the output characteristics are good and preferable.

The resistance and double layer capacity of the negative electrode are measured by the following procedure. The lithium-ion secondary battery to be measured is charged at a current value that can be charged for 5 hours in a nominal capacity, then maintained in a state where it is not charged / discharged for 20 minutes, and then discharged at a current value that can be discharged in 1 hour for a nominal capacity. The capacity when the capacity is 80% or more of the nominal capacity is used. About the lithium ion secondary battery of the above-mentioned discharge state, it charges to 60% of a nominal capacity with the electric current value which can charge a nominal capacity in 5 hours, Immediately transfers a lithium ion secondary battery in the glove box under argon gas atmosphere. Here, the lithium ion secondary battery is quickly disassembled and taken out in a state where the negative electrode does not discharge or short-circuit, and if it is a double-sided coated electrode, the electrode active material on one side is peeled off without damaging the electrode active material on the other side, Two electrodes are punched to 12.5 mmφ, and are opposed to each other so that the active material surface does not shift through a separator. 60 μL of the electrolytic solution used in the battery is dropped and adhered between the separator and both negative electrodes, and kept in a state where it is not in contact with the outside air, the current collectors of both negative electrodes are made conductive, and the AC impedance method is performed. The measurement was performed at a temperature of 25 ° C. and a complex impedance measurement was performed in a frequency band of 10 ⁻² to 10 ⁵ Hz, and the surface resistance (R) was obtained by approximating the arc of the negative resistance component of the obtained Cole-Cole plot with a semicircle. And double layer capacity | capacitance (Cdl) is calculated | required.

[Positive electrode]
The positive electrode used for the non-aqueous electrolyte secondary battery of the present invention will be described below.
[[Positive electrode active material]]
The positive electrode active material used for the positive electrode is described below.

[[[composition]]]
The positive electrode active material is not particularly limited as long as it can electrochemically occlude and release lithium ions. A substance containing lithium and at least one transition metal is preferable, and examples thereof include a lithium transition metal composite oxide and a lithium-containing transition metal phosphate compound.

The transition metal of the lithium transition metal composite oxide is preferably V, Ti, Cr, Mn, Fe, Co, Ni, Cu or the like, and specific examples include lithium / cobalt composite oxide such as LiCoO ₂ or LiNiO ₂ . Lithium / nickel composite oxide, LiMnO ₂ , LiMn ₂ O ₄ , Li ₂ MnO _{3 and} other lithium / manganese composite oxides, Al, Ti , V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, and those substituted with other metals such as Si. Specific examples of the substituted ones include, for example, LiNi _0.5 Mn _0.5 O ₂ , LiNi _0.85 Co _0.10 Al _0.05 O ₂ , LiNi _0.33 Co _0.33 Mn _0.33 O ₂ , LiMn _1.8 Al _0.2 O ₄ , LiMn _1.5 Ni _0.5 O _4, etc. Is mentioned.

As the transition metal of the lithium-containing transition metal phosphate compound, V, Ti, Cr, Mn, Fe, Co, Ni, Cu and the like are preferable, and specific examples include, for example, LiFePO ₄ , Li ₃ Fe ₂ (PO ₄ ). ₃ , iron phosphates such as LiFeP ₂ O ₇ , cobalt phosphates such as LiCoPO ₄ , and some of the transition metal atoms that are the main components of these lithium transition metal phosphate compounds are Al, Ti, V, Cr, Mn , Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, Nb, Si and the like substituted with other metals.

[[[Surface coating]]]
In addition, a material in which a material having a composition different from that of the material constituting the positive electrode active material is attached to the surface of the positive electrode active material can be used. Surface adhering substances include aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, bismuth oxide, lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate And sulfates such as aluminum sulfate, carbonates such as lithium carbonate, calcium carbonate, and magnesium carbonate, and carbon.

  These surface adhering substances are, for example, a method of dissolving or suspending in a solvent and impregnating and drying the positive electrode active material, and a method of dissolving or suspending a surface adhering substance precursor in a solvent and impregnating and adding to the positive electrode active material, followed by heating. It can be made to adhere to the positive electrode active material surface by the method of making it react by the method etc., the method of adding to a positive electrode active material precursor, and baking simultaneously. In addition, when making carbon adhere, the method of making carbonaceous adhere mechanically later in the form of activated carbon etc. can also be used, for example.

  The amount of the surface adhering substance is by mass with respect to the positive electrode active material, preferably 0.1 ppm or more, more preferably 1 ppm or more, still more preferably 10 ppm or more, and the upper limit is preferably 20% by mass or less, more preferably, as the lower limit. It is used at 10 mass% or less, more preferably 5 mass% or less. The surface adhering substance can suppress the oxidation reaction of the non-aqueous electrolyte solution on the surface of the positive electrode active material, and can improve the battery life. However, when the amount of the adhering quantity is too small, the effect is not sufficiently exhibited. If the amount is too large, the resistance may increase in order to inhibit the entry and exit of lithium ions.

[[[shape]]]
As the shape of the positive electrode active material particles in the present invention, a lump shape, a polyhedron shape, a sphere shape, an oval sphere shape, a plate shape, a needle shape, a column shape, etc., which are conventionally used, are used. It is preferably formed by forming particles, and the shape of the secondary particles is spherical or elliptical. In general, an electrochemical element expands and contracts as the active material in the electrode expands and contracts as it is charged and discharged. Therefore, the active material is easily damaged due to the stress or the conductive path is broken. Therefore, it is preferable that the primary particles are aggregated to form secondary particles, rather than a single particle active material having only primary particles, in order to relieve expansion and contraction stress and prevent deterioration. In addition, spherical or oval spherical particles are less oriented during molding of the electrode than plate-like equiaxed particles, so that the expansion and contraction of the electrode during charging and discharging is small, and the electrode is produced. The mixing with the conductive material is also preferable because it is easy to mix uniformly.

[[[Tap density]]]
The tap density (bulk density) of the positive electrode active material is usually 1.3 g / cm ³ or more, preferably 1.5 g / cm ³ or more, more preferably 1.6 g / cm ³ or more, and most preferably 1.7 g / cm. ³ or more. If the tap density of the positive electrode active material is lower than the lower limit, the amount of the required dispersion medium increases when the positive electrode active material layer is formed, and the necessary amount of the conductive material and the binder increases. In some cases, the filling rate of the substance is limited, and the battery capacity is limited. By using a metal composite oxide powder having a high tap density, a high-density positive electrode active material layer can be formed. In general, the tap density is preferably as large as possible, but there is no particular upper limit. However, if the tap density is too large, diffusion of lithium ions using the non-aqueous electrolyte solution as a medium in the positive electrode active material layer becomes rate-determining, and load characteristics may be likely to deteriorate. Usually, it is 2.5 g / cm ³ or less, preferably 2.4 g / cm ³ or less. The tap density is measured and defined by the same method as described above.

[[[Median diameter d ₅₀ ]]]
The median diameter d _{50 of the} particles (when the primary particles are aggregated to form secondary particles) is usually 0.1 μm or more, preferably 0.5 μm or more, more preferably 1 μm or more, most The upper limit is usually 20 μm or less, preferably 18 μm or less, more preferably 16 μm or less, and most preferably 15 μm or less. If the lower limit is not reached, a high tap density product may not be obtained, and if the upper limit is exceeded, it takes time to diffuse lithium in the particles. When a conductive material, a binder, or the like is slurried with a solvent and applied as a thin film, problems such as streaking may occur. Here, by mixing two or more types of positive electrode active materials having different median diameters d ₅₀ , the filling property at the time of forming the positive electrode can be further improved.

The median diameter d ₅₀ in the present invention is measured by a known laser diffraction / scattering particle size distribution measuring device. When LA-920 manufactured by HORIBA is used as a particle size distribution meter, a 0.1% by mass sodium hexametaphosphate aqueous solution is used as a dispersion medium for measurement, and a measurement refractive index of 1.24 is set after ultrasonic dispersion for 5 minutes. Measured.

[[[Average primary particle size]]]
When primary particles are aggregated to form secondary particles, the average primary particle diameter of the positive electrode active material is usually 0.01 μm or more, preferably 0.05 μm or more, more preferably 0.08 μm or more, Most preferably, it is 0.1 μm or more, and the upper limit is usually 3 μm or less, preferably 2 μm or less, more preferably 1 μm or less, and most preferably 0.6 μm or less. If the above upper limit is exceeded, it is difficult to form spherical secondary particles, which adversely affects the powder filling property, or the specific surface area is greatly reduced, so that there is a high possibility that battery performance such as output characteristics will deteriorate. is there. On the other hand, when the value falls below the lower limit, there is a case where problems such as inferior reversibility of charge / discharge are usually caused because crystals are not developed.

  The primary particle diameter is measured by observation using a scanning electron microscope (SEM). Specifically, in a photograph at a magnification of 10000 times, the longest value of the intercept by the left and right boundary lines of the primary particles with respect to the horizontal straight line is obtained for any 50 primary particles and obtained by taking the average value. It is done.

[[[BET specific surface area]]]
The BET specific surface area of the positive electrode active material used for the secondary battery of the present invention is 0.2 m ² / g or more, preferably 0.3 m ² / g or more, more preferably 0.4 m ² / g or more, and the upper limit is 4 m. ² / g or less, preferably 2.5 m ² / g or less, more preferably 1.5 m ² / g or less. If the BET specific surface area is smaller than this range, the battery performance tends to be lowered, and if the BET specific surface area is larger, the tap density is difficult to increase, and there may be a problem in applicability when forming the positive electrode active material.

  The BET specific surface area is determined by using a surface area meter (for example, a fully automated surface area measuring device manufactured by Okura Riken), preliminarily drying the sample for 30 minutes at 150 ° C. under nitrogen flow, and then measuring the relative pressure of nitrogen relative to atmospheric pressure. It is defined by a value measured by a nitrogen adsorption BET one-point method using a gas flow method using a nitrogen-helium mixed gas that is accurately adjusted to have a value of 0.3.

[[[Production method]]]
As a manufacturing method of the positive electrode active material, a general method is used as a manufacturing method of the inorganic compound. In particular, various methods are conceivable for producing a spherical or elliptical spherical active material. For example, transition metal raw materials such as transition metal nitrates and transition metal sulfates and, if necessary, raw materials of other elements are mixed with water. It is dissolved or pulverized and dispersed in a solvent such as, and the pH is adjusted while stirring to produce and recover a spherical precursor, which is dried as necessary, and then LiOH, Li ₂ CO ₃ , LiNO _3, etc. A method of obtaining an active material by adding a Li source of the above, a transition metal source material such as transition metal nitrate, transition metal sulfate, transition metal hydroxide, transition metal oxide, and other elements as required The raw material is dissolved or pulverized and dispersed in a solvent such as water, and is then dried and molded with a spray dryer or the like to obtain a spherical or elliptical precursor, and LiOH, Li ₂ CO ₃ , LiNO _{3 and} other Li Add the source at high temperature A method of obtaining an active material by firing, a transition metal source material such as transition metal nitrate, transition metal sulfate, transition metal hydroxide, transition metal oxide, and LiOH such as LiOH, Li ₂ CO ₃ , and LiNO ₃ Dissolve or pulverize the source and other elemental raw materials as necessary in a solvent such as water, and dry-mold them with a spray drier or the like to obtain a spherical or elliptical precursor, which is heated at a high temperature. Examples thereof include a method for obtaining an active material by firing.

[[Composition of positive electrode]]
Below, the structure of the positive electrode used for this invention is described.
[[[Electrode structure and fabrication method]]]
The positive electrode for a lithium ion secondary battery of the present invention is produced by forming a positive electrode active material layer containing a positive electrode active material and a binder on a current collector. Manufacture of the positive electrode using a positive electrode active material can be performed by a conventional method. That is, a positive electrode active material and a binder, and if necessary, a conductive material and a thickener mixed in a dry form are pressure-bonded to a positive electrode current collector, or these materials are liquid media A positive electrode can be obtained by forming a positive electrode active material layer on the current collector by applying it to a positive electrode current collector and drying it as a slurry by dissolving or dispersing in a slurry.

  Two or more types of positive electrode active materials may be mixed in advance and used, or may be mixed by adding them simultaneously when forming the positive electrode.

[[[Positive electrode active material]]]
The content of the positive electrode active material used in the positive electrode of the lithium ion secondary battery of the present invention in the positive electrode active material layer is preferably 80% by mass or more, more preferably 82% by mass or more, and particularly preferably 84% by mass or more. It is. Moreover, an upper limit becomes like this. Preferably it is 95 mass% or less, More preferably, it is 93 mass% or less. If the content of the positive electrode active material in the positive electrode active material layer is low, the electric capacity may be insufficient. Conversely, if the content is too high, the strength of the positive electrode may be insufficient.

[[[Conductive material]]]
A known conductive material can be arbitrarily used as the conductive material. Specific examples include metal materials such as copper and nickel; graphite such as natural graphite and artificial graphite (graphite); carbon black such as acetylene black; and carbon materials such as amorphous carbon such as needle coke. In addition, these may be used individually by 1 type and may use 2 or more types together by arbitrary combinations and a ratio.

  The conductive material is usually 0.01% by mass or more, preferably 0.1% by mass or more, more preferably 1% by mass or more in the positive electrode active material layer, and the upper limit is usually 50% by mass or less, preferably It is used so as to contain 30% by mass or less, more preferably 15% by mass or less. If the content is lower than this range, the conductivity may be insufficient. Conversely, if the content is higher than this range, the battery capacity may decrease.

[[[Binder]]]
The binder used in the production of the positive electrode active material layer is not particularly limited, and in the case of a coating method, any material that can be dissolved or dispersed in the liquid medium used in electrode production may be used. , Polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, aromatic polyamide, cellulose, nitrocellulose, and other resin polymers; SBR (styrene-butadiene rubber), NBR (acrylonitrile-butadiene rubber), fluorine rubber, isoprene rubber, butadiene Rubber-like polymers such as rubber and ethylene-propylene rubber; styrene / butadiene / styrene block copolymer or hydrogenated product thereof, EPDM (ethylene / propylene / diene terpolymer), styrene / ethylene / butadiene / ethylene copolymer Polymer, styrene / isoprene Thermoplastic elastomeric polymers such as styrene block copolymers or hydrogenated products thereof; syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene / vinyl acetate copolymers, propylene / α-olefin copolymers, etc. Soft polymer such as polyvinylidene fluoride (PVdF), polytetrafluoroethylene, fluorinated polyvinylidene fluoride, polytetrafluoroethylene / ethylene copolymer, etc .; alkali metal ions (especially lithium ions) Examples thereof include a polymer composition having ion conductivity. In addition, these substances may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and ratios.

  The ratio of the binder in the positive electrode active material layer is usually 0.1% by mass or more, preferably 1% by mass or more, more preferably 3% by mass or more, and the upper limit is usually 80% by mass or less, preferably 60% by mass. % Or less, more preferably 40% by mass or less, and most preferably 10% by mass or less. When the ratio of the binder is too low, the positive electrode active material cannot be sufficiently retained and the positive electrode has insufficient mechanical strength, which may deteriorate battery performance such as cycle characteristics. On the other hand, if it is too high, battery capacity and conductivity may be reduced.

[[[Liquid medium]]]
The liquid medium for forming the slurry may be any type of solvent that can dissolve or disperse the positive electrode active material, the conductive material, the binder, and the thickener used as necessary. There is no particular limitation, and either an aqueous solvent or an organic solvent may be used.

  Examples of the aqueous medium include water, a mixed medium of alcohol and water, and the like. Examples of the organic medium include aliphatic hydrocarbons such as hexane; aromatic hydrocarbons such as benzene, toluene, xylene, and methylnaphthalene; heterocyclic compounds such as quinoline and pyridine; ketones such as acetone, methyl ethyl ketone, and cyclohexanone. Esters such as methyl acetate and methyl acrylate; amines such as diethylenetriamine and N, N-dimethylaminopropylamine; ethers such as diethyl ether, propylene oxide and tetrahydrofuran (THF); N-methylpyrrolidone (NMP) Amides such as dimethylformamide and dimethylacetamide; aprotic polar solvents such as hexamethylphosphalamide and dimethylsulfoxide.

[[[Thickener]]]
In particular, when an aqueous medium is used, it is preferable to make a slurry using a thickener and a latex such as styrene-butadiene rubber (SBR). A thickener is usually used to adjust the viscosity of the slurry. The thickener is not particularly limited, and specific examples include carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, and salts thereof. These may be used individually by 1 type, or may use 2 or more types together by arbitrary combinations and a ratio. When a thickener is further added, the ratio of the thickener to the active material is 0.1% by mass or more, preferably 0.5% by mass or more, more preferably 0.6% by mass or more. The upper limit is 5% by mass or less, preferably 3% by mass or less, more preferably 2% by mass or less. Below this range, applicability may be significantly reduced. If it exceeds, the ratio of the active material in the positive electrode active material layer may decrease, and there may be a problem that the capacity of the battery decreases and a problem that the resistance between the positive electrode active materials increases.

[[[Consolidation]]]
The positive electrode active material layer obtained by coating and drying is preferably consolidated by a hand press, a roller press or the like in order to increase the packing density of the positive electrode active material. Density of the positive electrode active material layer is preferably 1.5 g / cm ³ or more as a lower limit, more preferably 2 g / cm ^3, and even more preferably at 2.2 g / cm ³ or more, the upper limit, preferably 3.5g / Cm ³ or less, more preferably 3 g / cm ³ or less, and even more preferably 2.8 g / cm ³ or less. If this range is exceeded, the permeability of the non-aqueous electrolyte solution to the vicinity of the current collector / active material interface may decrease, and the charge / discharge characteristics at a high current density may decrease. On the other hand, if it is lower, the conductivity between the active materials may be reduced, and the battery resistance may be increased.

[[[Current collector]]]
There is no restriction | limiting in particular as a material of a positive electrode electrical power collector, A well-known thing can be used arbitrarily. Specific examples include metal materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum; and carbon materials such as carbon cloth and carbon paper. Of these, metal materials, particularly aluminum, are preferred.

  Examples of the shape of the current collector include metal foil, metal cylinder, metal coil, metal plate, metal thin film, expanded metal, punch metal, and foam metal in the case of a metal material. A thin film, a carbon cylinder, etc. are mentioned. Of these, metal thin films are preferred. In addition, you may form a thin film suitably in mesh shape. Although the thickness of the thin film is arbitrary, it is usually 1 μm or more, preferably 3 μm or more, more preferably 5 μm or more, and the upper limit is usually 1 mm or less, preferably 100 μm or less, more preferably 50 μm or less. If the thin film is thinner than this range, the strength required for the current collector may be insufficient. Conversely, if the thin film is thicker than this range, the handleability may be impaired.

  The thickness ratio between the current collector and the positive electrode active material layer is not particularly limited, but (thickness of active material layer on one side immediately before non-aqueous electrolyte injection) / (thickness of current collector) is 20 or less. More preferably, it is 15 or less, most preferably 10 or less, and the lower limit is preferably 0.5 or more, more preferably 0.8 or more, and most preferably 1 or more. Above this range, the current collector may generate heat due to Joule heat during high current density charge / discharge. Below this range, the volume ratio of the current collector to the positive electrode active material increases and the battery capacity may decrease.

[[[Electrode area]]]
When using the non-aqueous electrolyte of the present invention, it is preferable that the area of the positive electrode active material layer is larger than the outer surface area of the battery outer case from the viewpoint of increasing the stability at high output and high temperature. Specifically, the total electrode area of the positive electrode with respect to the surface area of the exterior of the secondary battery is preferably 20 times or more, and more preferably 40 times or more. The outer surface area of the outer case, in the case of a bottomed square shape, means the total area obtained by calculation from the vertical, horizontal, and thickness dimensions of the case part filled with the power generation element excluding the protruding part of the terminal. . In the case of a bottomed cylindrical shape, the geometric surface area approximates the case portion filled with the power generation element excluding the protruding portion of the terminal as a cylinder. The total electrode area of the positive electrode is the geometric surface area of the positive electrode mixture layer facing the mixture layer containing the negative electrode active material, and in the structure in which the positive electrode mixture layer is formed on both sides via the current collector foil. , The sum of the areas where each surface is calculated separately.

[[[Discharge capacity]]]
When the non-aqueous electrolyte for secondary battery of the present invention is used, the electric capacity of the battery element housed in one battery case of the secondary battery (electric capacity when the battery is discharged from the fully charged state to the discharged state) ) Is 3 ampere hours (Ah) or more, since the effect of improving the low temperature discharge characteristics is increased. Therefore, the positive electrode plate is preferably designed so that the discharge capacity is fully charged and is 3 ampere hours (Ah) or more and 20 Ah or less, and more preferably 4 Ah or more and 10 Ah or less. If it is less than 3 Ah, the voltage drop due to the electrode reaction resistance becomes large when taking out a large current, and the power efficiency may deteriorate. Above 20 Ah, the electrode reaction resistance decreases and the power efficiency improves, but the temperature distribution due to the internal heat generation of the battery during pulse charge / discharge is large, the durability of repeated charge / discharge is inferior, and abnormalities such as overcharge and internal short circuit When the heat release efficiency deteriorates due to sudden heat generation at the time, the probability that the internal pressure rises and the gas release valve operates (valve operation), or the battery contents erupt violently (explosion) increases. There is.

[[[Positive electrode plate thickness]]]
The thickness of the positive electrode plate is not particularly limited, but from the viewpoint of high capacity and high output, the thickness of the composite layer obtained by subtracting the metal foil thickness of the core material is relative to one side of the current collector. The lower limit is preferably 10 μm or more, more preferably 20 μm or more, and the upper limit is preferably 200 μm or less, more preferably 100 μm or less.

<Lithium ion secondary battery>
Hereinafter, the non-aqueous electrolyte secondary battery of the present invention will be described in detail.

[Battery shape]
The battery shape is not particularly limited, and examples thereof include a bottomed cylindrical shape, a bottomed square shape, a thin shape, a sheet shape, and a paper shape. When incorporating into a system or device, in order to increase the volumetric efficiency and increase the storage capacity, it may be of a different shape such as a horseshoe shape, a comb shape, etc. considering the fit to the peripheral system arranged around the battery . From the viewpoint of efficiently releasing the heat inside the battery to the outside, a rectangular shape having at least one surface that is relatively flat and has a large area is preferable.

  In a battery having a bottomed cylindrical shape, since the outer surface area with respect to the power generating element to be filled becomes small, it is preferable to design so that Joule heat generated by the internal resistance at the time of charging and discharging efficiently escapes to the outside. Moreover, it is preferable to design so that the filling ratio of the substance having high thermal conductivity is increased and the temperature distribution inside is reduced.

In the bottomed square shape, the ratio between the area S of the largest surface (the product of the width and height of the outer dimensions excluding the terminal portion, unit cm ² ) and the thickness T (unit cm) of the battery outer shape The 2S / T value is preferably 100 or more, and more preferably 200 or more. By increasing the maximum surface, it is possible to improve characteristics such as cycle performance and high-temperature storage even for high-power and large-capacity batteries, and increase the heat dissipation efficiency during abnormal heat generation. Can be prevented from becoming a dangerous state.

[Battery configuration]
The lithium ion secondary battery of the present invention includes at least a positive electrode and a negative electrode capable of occluding and releasing lithium ions, a non-aqueous electrolyte, a separator disposed between the positive electrode and the negative electrode, a current collecting terminal, and an outer case. The If necessary, a protective element may be mounted inside the battery and / or outside the battery.

[Separator]
The separator used in the present invention has a predetermined mechanical strength that electrically insulates both electrodes, has a high ion permeability, and has resistance to oxidation on the side in contact with the positive electrode and reduction on the negative electrode side. There is no particular limitation as long as it has both. As a material for the separator having such required characteristics, a resin, an inorganic material, glass fiber, or the like is used. As the resin, olefin polymer, fluorine polymer, cellulose polymer, polyimide, nylon and the like are used. Specifically, it is preferable to select from materials that are stable with respect to the electrolytic solution and have excellent liquid retention properties, and it is preferable to use a porous sheet or nonwoven fabric made of a polyolefin such as polyethylene or polypropylene.

  As the inorganic substance, oxides such as alumina and silicon dioxide, nitrides such as aluminum nitride and silicon nitride, and sulfates such as barium sulfate and calcium sulfate are used, and those having a particle shape or fiber shape are used. As the form, a thin film shape such as a non-woven fabric, a woven fabric, or a microporous film is used. In the thin film shape, those having a pore diameter of 0.01 to 1 μm and a thickness of 5 to 50 μm are preferably used. In addition to the independent thin film shape, a separator formed by forming a composite porous layer containing the inorganic particles on the surface layer of the positive electrode and / or the negative electrode using a resin binder can be used. For example, a porous layer may be formed on both surfaces of the positive electrode using alumina particles having a 90% particle size of less than 1 μm as a binder.

[Electrode group]
The electrode group has a laminated structure in which the positive electrode plate and the negative electrode plate are interposed via the separator, and a structure in which the positive electrode plate and the negative electrode plate are wound in a spiral shape via the separator. Either may be used.

  The ratio of the volume of the electrode group to the battery internal volume (hereinafter referred to as electrode group occupancy) is preferably 40% to 90%, and more preferably 50% to 80%. If the electrode group occupancy is less than 40%, the battery capacity is small, and if it is 90% or more, the void space is small, the member expands when the battery becomes high temperature, and the vapor pressure of the liquid component of the electrolyte is high. As a result, the internal pressure rises, and various characteristics such as charge / discharge repetition performance and high-temperature storage as a battery are deteriorated. Further, a gas release valve that releases the internal pressure to the outside may operate.

[Current collection structure]
The current collecting structure is not particularly limited, but in order to more effectively realize the low temperature discharge characteristics by the non-aqueous electrolyte solution of the present invention, it is necessary to have a structure that reduces the resistance of the wiring part and the joint part. There is. When such an internal resistance is small, the effect of using the nonaqueous electrolytic solution of the present invention is exhibited particularly well.

  In the case where the electrode group has the laminated structure described above, a structure formed by bundling the metal core portions of the electrode layers and welding them to the terminals is preferably used. When the area of one electrode increases, the internal resistance increases. Therefore, it is also preferable to provide a plurality of terminals in the electrode to reduce the resistance. When the electrode group has the winding structure described above, the internal resistance can be lowered by providing a plurality of lead structures for the positive electrode and the negative electrode, respectively, and bundling the terminals.

  By optimizing the above structure, the internal resistance can be made as small as possible. In a battery used at a large current, the impedance measured by the 10 kHz AC method (hereinafter abbreviated as “DC resistance component”) is preferably 10 milliohms (mΩ) or less, and the DC resistance component is 5 milliohms (mΩ). It is more preferable to make it below. When the direct current resistance component is less than 0.1 milliohm (mΩ), the high output characteristics are improved, but the ratio of the current collecting structure used increases and the battery capacity may decrease.

  The non-aqueous electrolyte of the present invention is effective in reducing reaction resistance related to lithium insertion / extraction with respect to the electrode active material, which is considered to be a factor that can realize good low-temperature discharge characteristics. However, it has been found that a battery having a large direct current resistance is inhibited by the direct current resistance and the effect of reducing the reaction resistance cannot be reflected 100% on the low temperature discharge characteristics. This can be improved by using a battery having a small DC resistance component, and the effect of the non-aqueous electrolyte solution of the present invention can be sufficiently exhibited.

  Further, from the viewpoint of drawing out the effect of the non-aqueous electrolyte and producing a battery having high low-temperature discharge characteristics, this requirement and the electric capacity of the battery element housed in one battery exterior of the secondary battery described above. It is particularly preferable to satisfy the requirement that (the electric capacity when the battery is discharged from the fully charged state to the discharged state) is 3 ampere hours (Ah) or more at the same time.

[Exterior case]
The material of the outer case is not particularly limited as long as it is a substance that is stable with respect to the non-aqueous electrolyte used. Specifically, a nickel-plated steel plate, stainless steel, aluminum, an aluminum alloy, a metal such as a magnesium alloy, or a laminated film (laminate film) of a resin and an aluminum foil is used. From the viewpoint of weight reduction, an aluminum or aluminum alloy metal or a laminate film is preferably used.

  In the exterior case using the above metals, a laser-sealed, resistance-welded, ultrasonic welding is used to weld the metals together to form a sealed sealed structure, or a caulking structure using the above-mentioned metals via a resin gasket To do.

  Examples of the outer case using the laminate film include those having a sealed and sealed structure by heat-sealing resin layers. In order to improve the sealing performance, a resin different from the resin used for the laminate film may be interposed between the resin layers. In particular, when a resin layer is heat-sealed through a current collecting terminal to form a sealed structure, a metal and a resin are joined, so that a resin having a polar group or a modified group having a polar group introduced as an intervening resin is used. Resins are preferably used.

[Protective element]
As the above-mentioned protective element, PTC (Positive Temperature Coefficient), thermal fuse, thermistor, whose resistance increases when abnormal heat generation or excessive current flows, current that flows in the circuit due to sudden rise in battery internal pressure or internal temperature during abnormal heat generation For example, a valve (current cutoff valve) that shuts off the current is mentioned. It is preferable to select a protective element that does not operate under normal use at a high current. From the viewpoint of high output, it is more preferable that the protective element is designed so as not to cause abnormal heat generation or thermal runaway without a protective element.

<Action>
When combined with a non-aqueous electrolyte containing a specific substance and a negative electrode active material containing a composite carbonaceous material, it is high from the beginning to the end of the cycle while maintaining the effect of improving cycle characteristics even when the size is increased. The principle of operation that can provide a lithium ion secondary battery that can realize output characteristics and can maintain output characteristics at high power even after deterioration after charging and discharging cycles is not clear, but the principle of action Although the present invention is not limited by this, it is generated by the reaction between the particle surface in which the portion having high crystallinity and the portion having low crystallinity are combined with the specific compound at the first charging after the battery is formed. , SEI (Solid Electrolyte Interface) film is a film that does not become an output resistance, and this contributes to cycle characteristics and initial output characteristics. Furthermore, since this SEI is special compared to the case where it does not contain a specific compound, SEI dissolution due to repeated charge and discharge can be suppressed, and the influence of increased resistance of the positive electrode can be reduced. The output is considered to be maintained.

EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated further more concretely, this invention is not limited to these Examples, unless the summary is exceeded.
In addition, Examples 18-51 shall be read as Reference Examples 18-51, and Examples 53-54 shall be read as Reference Examples 53-54.

(Preparation of negative electrode active material 1)
In order to prevent mixing of coarse particles of commercially available natural graphite powder as a particulate carbonaceous material, a sieve of ASTM 400 mesh was repeated 5 times. The negative electrode material obtained here was a carbonaceous material (A).

(Preparation of negative electrode active material 2)
The petroleum heavy oil obtained at the time of naphtha pyrolysis was carbonized at 1300 ° C. in an inert gas, and then the sintered product was classified to obtain a carbonaceous material (B). In order to prevent coarse particles from being mixed, the classification process was repeated five times using ASTM 400 mesh sieving.

(Preparation of negative electrode active material 3)
A mixture of 95% by mass of the carbonaceous material (A) and 5% by mass of the carbonaceous material (B) was designated as a two-crystalline carbonaceous mixture (C).

(Preparation of negative electrode active material 4)
The carbonaceous material (A) is mixed with petroleum heavy oil obtained at the time of naphtha pyrolysis, subjected to carbonization treatment at 1300 ° C. in an inert gas, and then the sintered product is classified, whereby the carbonaceous material (A ) A composite carbonaceous material (D) was obtained in which carbonaceous materials having different crystallinity were deposited on the particle surface. During classification, ASTM 400 mesh sieving was repeated 5 times in order to prevent the inclusion of coarse particles. From the residual carbon ratio, it was confirmed that the obtained negative electrode active material powder was coated with 5 parts by weight of a low crystalline carbonaceous material with respect to 95 parts by weight of graphite.

(Preparation of negative electrode active material 5)
In the production 4 of the negative electrode active material, the same procedure as in the production 4 of the negative electrode active material was carried out except that the heavy petroleum oil obtained during naphtha pyrolysis was reduced and mixed, and 1 part by weight with respect to 99 parts by weight of graphite. A composite carbonaceous material (E) coated with a low crystalline carbonaceous material was obtained.

(Preparation of negative electrode active material 6)
In the production 4 of the negative electrode active material, the same procedure as in Production 4 of the negative electrode active material was carried out except that the heavy petroleum oil obtained during naphtha pyrolysis was increased and mixed, and 10 parts by weight with respect to 90 parts by weight of graphite. A composite carbonaceous material (F) coated with a low crystalline carbonaceous material was obtained.

(Preparation of negative electrode active material 7)
In the production 4 of the negative electrode active material, 30 parts by weight with respect to 70 parts by weight of graphite was performed in the same manner as in the production 4 of the negative electrode active material except that the heavy petroleum oil obtained during naphtha pyrolysis was increased and mixed. A composite carbonaceous material (G) coated with a low crystalline carbonaceous material was obtained.

(Preparation of negative electrode active material 8)
In the production 4 of the negative electrode active material, the same procedure as in the production 4 of the negative electrode active material was performed except that the graphitization treatment was performed at 3000 ° C. in an inert gas. A composite carbonaceous material (I) coated with a carbonaceous material was obtained.

(Preparation of negative electrode active material 9)
The carbonaceous material (A) is mixed with a phenol-formaldehyde solution, carbonized at 1300 ° C. in an inert gas, and then the sintered product is classified, whereby the carbonaceous material having different crystallinity on the surface of the graphite particles. A composite carbonaceous powder coated with is obtained. In classifying treatment, in order to prevent mixing of coarse particles, a sieve of ASTM 400 mesh was repeated 5 times to obtain a composite carbonaceous material (J). From the residual carbon ratio, it was confirmed that the obtained negative electrode active material powder was coated with 5 parts by weight of a low crystalline carbonaceous material with respect to 95 parts by weight of graphite.

(Preparation of negative electrode active material 10)
Coal tar pitch having a quinoline insoluble content of 0.05% by mass or less was heat-treated in a reaction furnace at 460 ° C. for 10 hours, and the resulting bulk carbonaceous matter was pulverized using a pulverizer (Orient Mill manufactured by Seishin Enterprise Co., Ltd.). Further, the mixture was finely pulverized using a fine pulverizer (Tsubo Mill manufactured by Matsubo Co., Ltd.) and refined to a median diameter of 17 μm. The particles were packed in a metal container and heat-treated at 540 ° C. for 2 hours under a nitrogen gas flow in a box-shaped electric furnace. The obtained lump is pulverized with a coarse crusher (Roll jaw crusher manufactured by Yoshida Seisakusho), and further pulverized with a fine pulverizer (turbo mill manufactured by Matsubo). The resulting powder is put into a container and a nitrogen atmosphere is obtained in an electric furnace. Below, it baked at 1300 degreeC for 1 hour. Thereafter, the sintered product was classified to obtain a carbonaceous material (K). During classification, ASTM 400 mesh sieving was repeated 5 times in order to prevent the inclusion of coarse particles.

(Preparation of negative electrode active material 11)
The carbonaceous material (K) is mixed with a phenol-formaldehyde solution, carbonized at 1300 ° C. in an inert gas, and then the sintered product is classified, whereby the carbonaceous material having different crystallinity on the graphite particle surface. A composite carbonaceous powder coated with is obtained. In classifying, in order to prevent mixing of coarse particles, ASTM 400 mesh sieving was repeated 5 times to obtain a composite carbonaceous material (L). From the residual carbon ratio, it was confirmed that the obtained negative electrode active material powder was coated with 40 parts by weight of a low crystalline carbonaceous material with respect to 60 parts by weight of graphite.

(Preparation of negative electrode active material 12)
The carbonaceous material (K) is mixed with petroleum heavy oil obtained at the time of naphtha pyrolysis, subjected to carbonization treatment at 1300 ° C. in an inert gas, and then the sintered product is classified to obtain a graphite particle surface. A composite carbonaceous powder coated with carbonaceous materials having different crystallinity was obtained. In classifying treatment, in order to prevent the inclusion of coarse particles, ASTM 400 mesh sieving was repeated 5 times to obtain a composite carbonaceous material (M). From the residual carbon ratio, it was confirmed that the obtained negative electrode active material powder was coated with 5 parts by weight of a low crystalline carbonaceous material with respect to 95 parts by weight of graphite.

(Preparation of negative electrode active material 13)
Coal tar pitch having a quinoline insoluble content of 0.05% by mass or less was heat-treated in a reaction furnace at 460 ° C. for 10 hours, and the resulting bulk carbonaceous matter was pulverized using a pulverizer (Orient Mill manufactured by Seishin Enterprise Co., Ltd.). Further, the mixture was finely pulverized using a fine pulverizer (Tsubo Mill manufactured by Matsubo Co., Ltd.) and refined to a median diameter of 17 μm. The particles were packed in a metal container and heat-treated at 540 ° C. for 2 hours under a nitrogen gas flow in a box-shaped electric furnace. The obtained lump is pulverized with a coarse crusher (Roll jaw crusher manufactured by Yoshida Seisakusho), and further pulverized with a fine pulverizer (turbo mill manufactured by Matsubo). Then, it was baked at 1000 ° C. for 1 hour. Furthermore, the calcined powder was transferred to a graphite crucible and graphitized at 3000 ° C. for 5 hours under an inert atmosphere using a direct current furnace to obtain a carbonaceous material (N). The carbonaceous material (N) is mixed with petroleum heavy oil obtained at the time of naphtha pyrolysis, carbonized at 900 ° C. in an inert gas, and then the sintered product is classified, whereby the surface of the graphite particles A composite carbonaceous material (O) having a carbonaceous material having different crystallinity was obtained. During classification, ASTM 400 mesh sieving was repeated 5 times in order to prevent the inclusion of coarse particles. From the residual carbon ratio, it was confirmed that the obtained negative electrode active material powder was coated with 5 parts by weight of a low crystalline carbonaceous material with respect to 95 parts by weight of graphite.

(Preparation of negative electrode active material 14)
In the production 4 of the negative electrode active material, the same procedure as in the production 4 of the negative electrode active material was performed except that flake-like natural graphite was used instead of the carbonaceous material (A), and 5 parts by weight with respect to 95 parts by weight of graphite. A composite carbonaceous material (P) coated with a low crystalline carbonaceous material was obtained.

(Preparation of negative electrode active material 15)
In the production 14 of the negative electrode active material, the same procedure as in Production 4 of the negative electrode active material was carried out except that the heavy petroleum oil obtained during naphtha pyrolysis was reduced and mixed, and the obtained powder was transferred to a graphite crucible. Instead, it was graphitized at 3000 ° C. for 5 hours in an inert atmosphere using a direct electric furnace. Thereafter, the sintered product was classified to obtain a composite carbonaceous material (Q) in which carbonaceous materials having different crystallinity were deposited on the particle surfaces. During classification, ASTM 400 mesh sieving was repeated 5 times in order to prevent the inclusion of coarse particles. It was found that the obtained composite carbonaceous material (Q) was coated with 1 part by weight of low crystalline carbonaceous material with respect to 99 parts by weight of graphite from the residual carbon ratio.

(Preparation of negative electrode active material 16)
In the production 4 of the negative electrode active material, the same procedure as in the production 4 of the negative electrode active material was performed except that natural graphite having a volume average particle size of 48 μm was used instead of the carbonaceous material (A). A composite carbonaceous material (R) coated with 5 parts by weight of a low crystalline carbonaceous material was obtained.

(Preparation of negative electrode active material 17)
In the production 4 of the negative electrode active material, the same procedure as in Production 4 of the negative electrode active material was used, except that natural graphite in which 1% of the ash content of the carbonaceous material (A) was low was left. 95 parts by weight of graphite A composite carbonaceous material (S) coated with 5 parts by weight of a low crystalline carbonaceous material was obtained.

Table 1 shows the physical properties of the obtained negative electrode active material. The method for measuring physical properties is as described above.

[Production of battery]
<< Preparation of positive electrode 1 >>
90% by mass of lithium cobaltate (LiCoO ₂ ) as a positive electrode active material, 5% by mass of acetylene black as a conductive material, and 5% by mass of polyvinylidene fluoride (PVdF) as a binder, an N-methylpyrrolidone solvent Mixed in to a slurry. The obtained slurry was applied to both sides of an aluminum foil having a thickness of 15 μm, dried, and rolled to a thickness of 80 μm with a pressing machine, and the active material layer was uncoated with a width of 100 mm, a length of 100 mm and a width of 30 mm. It cut out into the shape which has a process part, and was set as the positive electrode. At this time, the density of the active material of the positive electrode was 2.35 g / cm ³ .

<< Preparation of positive electrode 2 >>
In the production of the positive electrode 1, the positive electrode was produced in the same manner except that the mass of the active material applied on one side was double.

<< Preparation of positive electrode 3 >>
90% by mass of LiNi _0.80 Co _0.15 Al _0.05 O ₂ as a positive electrode active material, 5% by mass of acetylene black as a conductive material, and 5% by mass of polyvinylidene fluoride (PVdF) as a binder, Were slurried by mixing in N-methylpyrrolidone solvent. The obtained slurry was applied to both sides of an aluminum foil having a thickness of 15 μm, dried, and rolled to a thickness of 65 μm with a press machine, and the active material layer was uncoated with a width of 100 mm, a length of 100 mm and a width of 30 mm. It cut out into the shape which has a process part, and was set as the positive electrode. At this time, the density of the active material of the positive electrode was 2.35 g / cm ³ .

<< Preparation of negative electrode 1 >>
98 parts by weight of the negative electrode active material, 100 parts by weight of an aqueous dispersion of sodium carboxymethylcellulose (concentration of 1% by weight of carboxymethylcellulose sodium) as a thickener and a binder, and an aqueous dispersion of styrene-butadiene rubber (styrene) -Butadiene rubber concentration 50 mass%) 2 parts by weight was added and mixed with a disperser to form a slurry. The obtained slurry was applied to both sides of a rolled copper foil having a thickness of 10 μm, dried, and rolled to a thickness of 75 μm with a press machine, and the active material layer size was 104 mm wide, 104 mm long and 30 mm wide. It cut out in the shape which has a coating part, and was set as the negative electrode. At this time, the density of the active material of the negative electrode was 1.35 g / cm ³ .

<< Preparation of negative electrode 2 >>
A negative electrode was prepared in the same manner except that the weight of the active material applied on one side was doubled in preparation of the negative electrode 1.

<< Preparation of negative electrode 3 >>
A negative electrode was prepared in the same manner except that the density of the active material on one side was 1.70 g / cm ³ in Preparation of negative electrode 1.

<< Fabrication of negative electrode 4 >>
95 parts by weight of composite carbonaceous material A, 100 parts by weight of aqueous dispersion of sodium carboxymethyl cellulose (concentration of 1% by weight of sodium carboxymethyl cellulose) as a thickener and binder, respectively, and aqueous dispersion of styrene-butadiene rubber ( 8 parts by weight of styrene-butadiene rubber (concentration: 50% by mass) was added and mixed with a disperser to form a slurry. The obtained slurry was applied on both sides of a copper foil having a thickness of 10 μm, dried, and rolled to a thickness of 75 μm with a press machine, and the active material layer size was 104 mm in width, 104 mm in length, and 30 mm in width. It cut out in the shape which has a process part, and was set as the negative electrode. At this time, the density of the active material of the negative electrode was 1.35 g / cm ³ .

<< Preparation of Electrolytic Solution 1 >>
Under a dry argon atmosphere, a well-dried hexafluorophosphorus at a concentration of 1 mol / L in a mixture of ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) (volume ratio 3: 3: 4) Lithium acid (LiPF ₆ ) was dissolved. Furthermore, lithium difluorophosphate (LiPO ₂ F ₂ ) was contained so as to be 0.3% by mass.

<< Preparation of electrolyte 2 >>
Under a dry argon atmosphere, a well-dried hexafluorophosphorus at a concentration of 1 mol / L in a mixture of ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) (volume ratio 3: 3: 4) Lithium acid (LiPF ₆ ) was dissolved. Furthermore, 0.3% by mass of trimethylsilyl methanesulfonate was contained.

<< Production of Electrolytic Solution 3 >>
Under a dry argon atmosphere, a well-dried hexafluorophosphorus at a concentration of 1 mol / L in a mixture of ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) (volume ratio 3: 3: 4) Lithium acid (LiPF ₆ ) was dissolved. Furthermore, hexamethylcyclotrisiloxane was contained so that it might become 0.3 mass%.

<< Preparation of Electrolytic Solution 4 >>
Under a dry argon atmosphere, a well-dried hexafluorophosphorus at a concentration of 1 mol / L in a mixture of ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) (volume ratio 3: 3: 4) Lithium acid (LiPF ₆ ) was dissolved.

<< Production of Battery 1 >>
The 32 positive electrodes and 33 negative electrodes were alternately arranged, and the porous polyethylene sheet separator (thickness 25 μm) was laminated between each electrode. At this time, the positive electrode active material surface was faced so as not to deviate from the negative electrode active material surface. The uncoated portions of each of the positive electrode and the negative electrode were welded together to produce a current collecting tab, and an electrode group was enclosed in a battery can (outside dimension: 120 × 110 × 10 mm). Thereafter, 20 mL of a non-aqueous electrolyte solution was injected into a battery can loaded with the electrode group, sufficiently infiltrated into the electrode, and sealed to produce a prismatic battery. The rated discharge capacity of this battery is about 6 ampere hours (Ah), and the DC resistance measured by the 10 kHz AC method is about 5 milliohms (mΩ).

<Production of battery 2>
The 16 positive electrodes and the 17 negative electrodes were alternately arranged, and the porous polyethylene sheet separator (thickness 25 μm) was laminated between the electrodes. At this time, the positive electrode active material surface was faced so as not to deviate from the negative electrode active material surface. The uncoated portions of each of the positive electrode and the negative electrode were welded together to produce a current collecting tab, and an electrode group was enclosed in a battery can (outside dimension: 120 × 110 × 10 mm). Thereafter, 20 mL of a non-aqueous electrolyte solution was injected into a battery can loaded with the electrode group, sufficiently infiltrated into the electrode, and sealed to produce a prismatic battery. The rated discharge capacity of this battery is about 6 ampere hours (Ah), and the DC resistance measured by the 10 kHz AC method is about 7 milliohms (mΩ).

Example 1
A negative electrode produced as a two-crystalline carbonaceous mixture (C) using the negative electrode active material described in the section << Preparation of Negative Electrode 1 >>, a positive electrode prepared in the section << Preparation of Positive Electrode 1 >>, and produced in the section << Preparation of Electrolytic Solution 1 >> Using the electrolyte solution, a battery was prepared by the method described in “Preparation of battery 1”. This battery was measured by the method described in the section “Battery evaluation” below and the measurement method described above.

Example 2
A battery was prepared in the same manner as in Example 1 except that the composite carbonaceous material (D) was used as the negative electrode active material in the section “Preparation of negative electrode 1”, and battery evaluation described in the section “Battery evaluation” was performed.

Example 3
A battery was prepared in the same manner as in Example 1 except that the composite carbonaceous material (E) was used as the negative electrode active material in the section “Preparation of negative electrode 1”, and battery evaluation described in the section “Battery evaluation” was performed.

Example 4
A battery was prepared in the same manner as in Example 1 except that the composite carbonaceous material (F) was used as the negative electrode active material in the section “Preparation of negative electrode 1”, and battery evaluation described in the section “Battery evaluation” was performed.

Example 5
A battery was prepared in the same manner as in Example 1 except that the composite carbonaceous material (G) was used as the negative electrode active material in the section “Preparation of negative electrode 1”, and battery evaluation described in the section “Battery evaluation” was performed.
Example 6
A battery was prepared in the same manner as in Example 1 except that the composite carbonaceous material (J) was used as the negative electrode active material in the section <Preparation of negative electrode 1>, and the battery evaluation described in the section <Battery evaluation> was performed.

Example 7
A battery was prepared in the same manner as in Example 1 except that the composite carbonaceous material (I) was used as the negative electrode active material in the section <Preparation of negative electrode 1>, and the battery evaluation described in the section <Battery evaluation> was performed.

Example 8
A battery was prepared in the same manner as in Example 1 except that the composite carbonaceous material (M) was used as the negative electrode active material in the section “Preparation of negative electrode 1”, and battery evaluation described in the section “Battery evaluation” was performed.

Example 9
A battery was prepared in the same manner as in Example 1 except that the composite carbonaceous material (R) was used as the negative electrode active material in the section “Preparation of negative electrode 1”, and battery evaluation described in the section “Battery evaluation” was performed.

Example 10
A battery was prepared in the same manner as in Example 1 except that the composite carbonaceous material (L) was used as the negative electrode active material in the section “Preparation of negative electrode 1”, and battery evaluation described in the section “Battery evaluation” was performed.

Example 11
A battery was prepared in the same manner as in Example 1 except that the composite carbonaceous material (S) was used as the negative electrode active material in the section “Preparation of negative electrode 1”, and battery evaluation described in the section “Battery evaluation” was performed.

Example 12
A battery was prepared in the same manner as in Example 1 except that the composite carbonaceous material (O) was used as the negative electrode active material in the section “Preparation of negative electrode 1”, and battery evaluation described in the section “Battery evaluation” was performed.

Example 13
A battery was prepared in the same manner as in Example 1 except that the composite carbonaceous material (P) was used as the negative electrode active material in the section “Preparation of negative electrode 1”, and battery evaluation described in the section “Battery evaluation” was performed.

Example 14
A battery was prepared in the same manner as in Example 1 except that the composite carbonaceous material (Q) was used as the negative electrode active material in the section “Preparation of negative electrode 1”, and battery evaluation described in the section “Battery evaluation” was performed.

Example 15
The negative electrode produced as the composite carbonaceous material (D) as the negative electrode active material in the section << Negative Electrode Preparation 2 >>, the positive electrode produced in the section <Preparation of Positive Electrode 2 >>, and the electrolytic solution produced in the section <Preparation 1 of Electrolytic Solution> In this manner, a battery was prepared by the method described in the section << Battery preparation 2 >>. Otherwise, the battery was evaluated in the same manner as in Example 1.

Example 16
The negative electrode prepared as the composite carbonaceous material (D) as the negative electrode active material in Section << Preparation of Negative Electrode 3 >>, the positive electrode prepared in Section << Preparation of Positive Electrode 1 >>, and the electrolyte prepared in Section << Preparation of Electrolytic Solution >> In this manner, a battery was manufactured by the method described in the section << Battery preparation 1 >>. Otherwise, the battery was evaluated in the same manner as in Example 1.

Example 17
The negative electrode produced as the composite carbonaceous material (D) as the negative electrode active material of << Negative Electrode Production 4 >>, the positive electrode produced in the <Preparation of Positive Electrode 1 >>, and the electrolytic solution produced in the <Preparation of Electrolytic Solution 1 >> In this manner, a battery was manufactured by the method described in the section << Battery preparation 1 >>. Otherwise, the battery was evaluated in the same manner as in Example 1.

  The evaluation results of Examples 1 to 17 are shown in Table 2.

Examples 18-34
The batteries were evaluated in the same manner except that the electrolytic solutions of Examples 1 to 17 were replaced with the electrolytic solution prepared in the section << Preparation of Electrolytic Solution 2 >>. The evaluation results of Examples 18 to 34 are shown in Table 3.

Examples 35-51
The batteries were evaluated in the same manner except that the electrolytic solutions of Examples 1 to 17 were replaced with the electrolytic solution prepared in the section << Preparation of Electrolytic Solution 3 >>. The evaluation results of Example 35 to Example 51 are shown in Table 4.

Comparative Example 1
A battery was prepared in the same manner as in Example 1 except that the carbonaceous material (A) was used as the negative electrode active material in the section “Preparation of negative electrode 1”, and battery evaluation described in the section “Battery evaluation” was performed.

Comparative Example 2
Batteries were prepared in the same manner except that the electrolytic solution prepared in the section << Preparation of Electrolytic Solution 4 >> was used as the electrolytic solution of Comparative Example 1, and the battery evaluation described in the section << Battery Evaluation >> was performed.

Comparative Example 3
A battery was prepared in the same manner as in Example 1 except that the carbonaceous material (B) was used as the negative electrode active material in the section “Preparation of negative electrode 1”, and battery evaluation described in the section “Battery evaluation” was performed.

Comparative Example 4
A battery was prepared in the same manner as Comparative Example 3 except that the electrolytic solution prepared in the section <Preparation of Electrolytic Solution 4> was used as the electrolytic solution of Comparative Example 3, and the battery evaluation described in the section <Evaluation of the Battery> was performed. did.

Comparative Example 5
A battery was prepared in the same manner as in Example 1 except that the electrolytic solution prepared in the section <Preparation of Electrolytic Solution 4> was used as the electrolytic solution of Example 1, and the battery evaluation described in the section <Evaluation of Battery> was performed. did.

Comparative Example 6
A battery was prepared in the same manner as in Example 2 except that the electrolytic solution prepared in the section “Preparation of Electrolytic Solution 4” was used, and the battery evaluation described in the section “Battery Evaluation” was performed.

Comparative Example 7
A battery was prepared in the same manner as in Example 1 except that the carbonaceous material (K) was used as the negative electrode active material in the section “Preparation of negative electrode 1”, and battery evaluation described in the section “Battery evaluation” was performed.

Comparative Example 8
A battery was prepared in the same manner except that the electrolytic solution prepared in Section << Electrolytic Solution Preparation 4 >> was used as the electrolytic solution of Comparative Example 7, and battery evaluation described in the section << Battery Evaluation >> was performed.

Comparative Examples 9-11
The batteries were evaluated in the same manner except that the electrolytic solutions of Comparative Examples 1, 3, and 7 were replaced with the electrolytic solution prepared in the section << Preparation of Electrolytic Solution 2 >>.

Comparative Examples 12-14
The batteries were evaluated in the same manner except that the electrolytic solutions of Comparative Examples 1, 3, and 7 were replaced with the electrolytic solution prepared in the section << Preparation of Electrolytic Solution 3 >>.

  Table 5 shows the evaluation results of Comparative Examples 1 to 14.

Example 52
A negative electrode prepared as a composite carbonaceous material (D) using the negative electrode active material described in the section <Preparation of Negative Electrode 1>, a positive electrode prepared in the section <Preparation of Positive Electrode 3>, and an electrolyte prepared in the section <Preparation 1 of Electrolytic Solution>. Using the battery, a battery was prepared by the method described in Section << Battery Preparation 1 >>, and battery evaluation described in section << Battery Evaluation >> was performed.

Example 53
A battery was prepared in the same manner as in Example 52 except that the electrolytic solution prepared in Section << Electrolytic Solution Preparation 2 >> was used, and the battery evaluation described in the section << Battery Evaluation >> was performed.

Example 54
A battery was prepared in the same manner as in Example 52 except that the electrolytic solution prepared in Section << Electrolytic Solution Preparation 3 >> was used, and the battery evaluation described in the section << Battery Evaluation >> was performed.

Comparative Example 15
A battery was prepared in the same manner as in Example 52 except that the electrolytic solution prepared in Section << Electrolytic Solution Preparation 4 >> was used, and the battery evaluation described in the section << Battery Evaluation >> was performed.

  Table 6 shows the evaluation results of Examples 52 to 54 and Comparative Example 15.

<Battery evaluation>
(Capacity measurement)
For a battery that has not undergone a charge / discharge cycle, a voltage range of 4.2 V to 3.0 V at 25 ° C. and a current value of 0.2 C (the current value for discharging the rated capacity with a discharge capacity of 1 hour rate in 1 hour is 1 C. In the same manner, the following initial charge / discharge was performed for 5 cycles. The discharge capacity at the 5th cycle at this time was defined as the initial capacity. Next, the following output measurement was performed.

(Output measurement)
In a 25 ° C. environment, the battery is charged with a constant current of 0.2 C for 150 minutes, discharged at 0.1 C, 0.3 C, 1.0 C, 3.0 C, and 10.0 C, respectively, for 10 seconds. The voltage was measured. The area of the triangle surrounded by the current-voltage line and the lower limit voltage (3 V) was defined as output (W).

(Cycle test)
The cycle test was performed in a high temperature environment of 60 ° C., which is regarded as the actual use upper limit temperature of the lithium ion secondary battery. After charging with a constant current constant voltage method of 2C to a charge upper limit voltage of 4.2V, a charge / discharge cycle for discharging with a constant current of 2C to a discharge end voltage of 3.0V was defined as one cycle, and this cycle was repeated up to 500 cycles. The battery after the end of the cycle test was charged and discharged for 3 cycles under an environment of 25 ° C., and the 0.2 C discharge capacity of the third cycle was defined as the capacity after cycle. From the initial capacity measured prior to the cycle and the post-cycle capacity measured after the end of the cycle test, the cycle maintenance ratio was determined by the following formula.
Cycle maintenance ratio (%) = 100 × capacity after cycle / initial capacity

The output measurement described in the section (Output measurement) was performed on the battery after the cycle test was completed. At this time, the output maintenance rate represented by the following formula was calculated from the output before the cycle test and the output carried out after the cycle test.
Output retention rate (%) = 100 x Output after cycle test / Output before cycle

表２中、電解液は、《電解液の作製１》で作製した、ジフルオロリン酸リチウム塩（ＬｉＰＯ₂Ｆ₂）を０．３質量％含有するものである。

In Table 2, the electrolytic solution contains 0.3% by mass of lithium difluorophosphate (LiPO ₂ F ₂ ) prepared in << Preparation of Electrolytic Solution 1 >>.

表３中、電解液は、《電解液の作製２》で作製した、メタンスルホン酸トリメチルシリルを０．３質量％含有するものである。

In Table 3, the electrolytic solution contains 0.3% by mass of trimethylsilyl methanesulfonate prepared in << Preparation of Electrolytic Solution 2 >>.

表４中、電解液は、《電解液の作製３》で作製した、ヘキサメチルシクロトリシロキサンを０．３質量％含有するものである。

In Table 4, the electrolytic solution contains 0.3% by mass of hexamethylcyclotrisiloxane prepared in << Preparation of Electrolytic Solution 3 >>.

  As can be seen from the results of Tables 2 to 6, it contains lithium difluorophosphate, trimethylsilyl methanesulfonate, hexamethylcyclotrisiloxane, and the negative electrode active material contains two or more carbonaceous materials having different crystallinity. By combining this, it was found that the output maintenance rate after the cycle was dramatically improved.

  The use of the lithium ion secondary battery of the present invention is not particularly limited, and can be used for various known uses. Specific examples include notebook computers, pen input computers, mobile computers, electronic book players, mobile phones, mobile faxes, mobile copy, mobile printers, headphone stereos, video movies, LCD TVs, handy cleaners, portable CDs, minidiscs, and transceivers. Widely used in electronic notebooks, calculators, memory cards, portable tape recorders, radios, backup power supplies, motors, automobiles, motorbikes, motorbikes, bicycles, lighting equipment, toys, game equipment, watches, power tools, strobes, cameras, etc. It is what is done.

Claims (12)

A lithium ion secondary battery comprising a non-aqueous electrolyte solution containing at least a negative electrode active material, a positive electrode active material, and a lithium salt,
The non-aqueous electrolyte solution is a non-aqueous electrolyte solution containing 10 ppm or more of lithium difluorophosphate in the whole non-aqueous electrolyte solution,
And the negative electrode active material is
A graphite-based carbonaceous material containing natural graphite and / or artificial graphite;
Low crystalline carbonaceous material having lower crystallinity than the graphite-based carbonaceous material
Lithium-ion secondary battery, characterized by containing two or more crystallinity different carbonaceous material with. The anode active material, a lithium ion secondary battery according to claim 1 containing composite carbonaceous material containing the crystalline different carbonaceous material of two or more. The composite carbonaceous material has an interface formed by coating and / or bonding the low crystalline carbonaceous material to the graphite-based carbonaceous material , and the crystallinity of the interface changes discontinuously and / or continuously. The lithium ion secondary battery according to claim 2, which is a battery. The low crystalline carbonaceous material is (d) or (e)
(D) Coal heavy oil, DC heavy oil, cracked heavy oil, aromatic hydrocarbon, N ring compound, S ring compound, polyphenylene, organic synthetic polymer, natural polymer, thermoplastic resin and any one of the preceding of claims 1 to 3 is a carbide of those dissolved carbonizable organic material of the carbonizable organic material selected from the group consisting of thermosetting resin (e) (d) a low molecular organic solvent The lithium ion secondary battery according to item. Any of the lithium ion secondary battery according to claim of claims 2 to 4 wherein the graphite carbonaceous material is 50 wt% or more based on the entire composite carbonaceous material. The lithium ion secondary battery according to any one of claims 2 to 5 , wherein the composite carbonaceous material has a circularity of 0.85 or more. The composite carbonaceous material is obtained by a method comprising a step of mixing the graphite-based carbonaceous material and a carbonizable organic material and heat-treating the mixture at 400 ° C to 3200 ° C at least once. The lithium ion secondary battery according to claim 6 . The lithium ion secondary battery according to claim 7 , wherein the carbonizable organic substance is heat-treated through a liquid phase. The non-aqueous electrolyte solution, the lithium difluorophosphate in the entire nonaqueous electrolyte 0.01 mass% or more, according to any of claims 1 to claim 8 are those containing more than 5 wt% Lithium ion secondary battery. The lithium ion secondary battery according to any one of claims 1 to 9 , wherein the total area of the positive electrode area with respect to the surface area of the exterior of the secondary battery is 20 times or more in area ratio. DC resistance component of the secondary battery, a lithium ion secondary battery according to any one of claims 1 to claim 10 is 10 milliohms (milliohms) below. The lithium ion secondary according to any one of claims 1 to 11, wherein an electric capacity of a battery element housed in one battery case of the secondary battery is 3 ampere hours (Ah) or more. battery.