JP2016181603A - Lithium ion capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium ion capacitor which is high in output, and in which the delamination of a negative electrode mixture accompanying gas generation is suppressed.SOLUTION: A lithium ion capacitor comprises: a positive electrode; a negative electrode; a separator interposed between the positive and negative electrodes; and a lithium ion-conducting electrolyte. The positive electrode includes: a positive electrode current collector; and a positive electrode active material supported by the positive electrode current collector. The negative electrode includes: a negative electrode current collector; and a negative electrode mixture supported by the negative electrode current collector. The negative electrode current collector is composed of a metal porous body having a 3D mesh-like skeleton. The negative electrode mixture includes a negative electrode active material capable of occluding and releasing lithium ions, and carbon black; the content of the carbon black is 20 pts.mass or more to 100 pts.mass of the negative electrode active material.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a lithium ion capacitor using a negative electrode containing carbon black.

  While environmental problems are being highlighted, systems for converting clean energy such as sunlight or wind power into electric power and storing it as electric energy are being actively developed. As such an electricity storage device, a lithium ion secondary battery, an electric double layer capacitor, a lithium ion capacitor, and the like are known. Recently, capacitors such as an electric double layer capacitor and a lithium ion capacitor have been attracting attention from the viewpoints of excellent instantaneous charge / discharge characteristics and excellent handleability.

  A lithium ion capacitor generally includes a positive electrode, a negative electrode, a separator interposed therebetween, and a lithium ion conductive electrolyte. A polarizable electrode is used for the positive electrode, and an electrode including a current collector formed of a metal foil or the like and an electrode mixture layer formed on the surface of the current collector is used for the negative electrode. A negative electrode mixture contains a negative electrode active material, a conductive support agent, a binder, etc. (patent document 1 etc.). As the negative electrode active material, materials that occlude and release lithium ions such as graphite and hard carbon are used.

JP 2012-134236 A

  A negative electrode active material that occludes and releases (or inserts and desorbs) lithium ions is used for the negative electrode of the lithium ion capacitor. Unlike the double-layer capacitor that uses a polarizable electrode for the negative electrode, the negative electrode resistance tends to increase and the output increases because the resistance (reaction resistance) associated with the insertion and extraction of lithium ions is added to the internal resistance of the lithium ion capacitor. It is difficult to raise.

  If the conductivity of the negative electrode can be improved, the output can be easily increased. However, when the proportion of the conductive aid such as carbon black is increased in order to improve the conductivity of the negative electrode, the side reaction between the electrolyte and the conductive aid becomes remarkable. As a result, a large amount of gas is generated, and the negative electrode mixture is peeled off from the metal foil or metal sheet that is the negative electrode current collector.

  An object of the present invention is to provide a lithium ion capacitor that has high output and suppresses peeling of the negative electrode mixture accompanying gas generation.

One aspect of the present invention includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a lithium ion conductive electrolyte,
The positive electrode includes a positive electrode current collector and a positive electrode active material supported on the positive electrode current collector,
The negative electrode includes a negative electrode current collector and a negative electrode mixture supported on the negative electrode current collector,
The negative electrode current collector is a porous metal body having a three-dimensional network skeleton,
The negative electrode mixture includes a negative electrode active material that occludes and releases lithium ions, and carbon black,
The amount of the carbon black relates to a lithium ion capacitor, which is 20 parts by mass or more with respect to 100 parts by mass of the negative electrode active material.

  ADVANTAGE OF THE INVENTION According to this invention, in a lithium ion capacitor, while being able to suppress peeling of the negative mix accompanying gas generation, an output can be raised.

It is a perspective view showing roughly the appearance of a lithium ion capacitor concerning one embodiment of the present invention. FIG. 2 is a partial cross-sectional view schematically showing an internal structure when the lithium ion capacitor of FIG. 1 is viewed from the front. It is arrow sectional drawing by the III-III line of FIG.

[Description of Embodiment of the Invention]
First, the contents of the embodiment of the present invention will be listed and described.
A lithium ion capacitor according to an embodiment of the present invention includes (1) a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a lithium ion conductive electrolyte. The positive electrode includes a positive electrode current collector and a positive electrode active material supported on the positive electrode current collector, and the negative electrode includes a negative electrode current collector and a negative electrode mixture supported on the negative electrode current collector. The negative electrode current collector is a metal porous body having a three-dimensional network skeleton, the negative electrode mixture includes a negative electrode active material that absorbs and releases lithium ions, and carbon black, and the amount of carbon black is It is 20 mass parts or more with respect to 100 mass parts of active materials.

  Addition of a large amount of carbon black to the negative electrode is expected to improve conductivity and reduce DC resistance. However, when the amount of carbon black increases, gas generation due to a side reaction between the carbon black and the electrolyte becomes remarkable. When a metal foil is used for the negative electrode current collector, if a large amount of gas is generated in the negative electrode mixture layer, the negative electrode mixture is peeled off and charging / discharging cannot be repeated.

  In this embodiment, since the metal porous body having a three-dimensional network skeleton is used as the negative electrode current collector, even if gas is generated by adding a large amount of carbon black to the negative electrode mixture, the gas movement path is In many cases, gas is easily extracted from the negative electrode. Therefore, peeling of the negative electrode mixture can be suppressed. Moreover, electroconductivity increases because a negative electrode contains many carbon blacks, Thereby, DC resistance can be reduced. Surprisingly, since the proportion of carbon black in the negative electrode mixture is large, it is possible to reduce even the reaction resistance related to insertion and extraction of lithium ions by the negative electrode active material. Of the internal resistance that reduces the output of the lithium ion capacitor, the contribution of the reaction resistance is greater than the contribution of the direct current resistance. Therefore, the lithium ion capacitor can be effectively increased in output by reducing the reaction resistance. Although details are not clear, it is considered that the reaction resistance is reduced because the current collector has a three-dimensional network-like skeleton, so that a large amount of electrolyte can be held inside the negative electrode.

  The amount of carbon black is preferably (2) 20 parts by mass to 500 parts by mass, and (3) 20 parts by mass to 200 parts by mass with respect to 100 parts by mass of the negative electrode active material. When the amount of carbon black is within such a range, a high output can be obtained while securing a high capacity.

  (4) The skeleton of the negative electrode current collector preferably has a cavity inside (that is, is hollow). In this case, the gas movement path increases, and the negative electrode is easily compressed in the thickness direction, which is advantageous from the viewpoint of increasing the capacity.

  (5) The thickness of the negative electrode is preferably 100 μm to 2000 μm. Generally, when the thickness of the negative electrode is large as described above, it is difficult to ensure a high output. However, since the negative electrode contains a lot of carbon black, the resistance (particularly, reaction resistance) of the negative electrode can be reduced although the thickness of the negative electrode is large, so that high output can be secured.

  (6) The positive electrode current collector is preferably a porous metal body having a three-dimensional network skeleton. This is advantageous from the viewpoint of increasing the capacity of the lithium ion capacitor because the number of gas movement paths increases and the capacity of the positive electrode is easily increased.

[Details of the embodiment of the invention]
Specific examples of the lithium ion capacitor according to the embodiment of the present invention will be described below with reference to the drawings as appropriate. In addition, this invention is not limited to these illustrations, is shown by the attached claim, and is intended that all the changes within the meaning and range equivalent to the claim are included. .

The lithium ion capacitor includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a lithium conductive electrolyte. Each element will be described in detail below.
(Negative electrode)
The negative electrode includes a negative electrode current collector and a negative electrode mixture supported on the negative electrode current collector.
As the negative electrode current collector, a porous metal body having a three-dimensional network skeleton is used. The three-dimensional network-like skeleton means a skeleton having a fiber part (or a rod-like part) formed of metal, and the fiber parts are three-dimensionally connected to form a network network or a structure thereof. That is, the negative electrode current collector can include a plurality of fiber portions (or rod-shaped portions), and the plurality of fiber portions are three-dimensionally connected to form a three-dimensional network skeleton.
The material of the negative electrode current collector (metal constituting the metal porous body) is preferably copper, copper alloy, nickel, nickel alloy, stainless steel, or the like.

  The negative electrode current collector covers a resin porous body (resin foam, resin nonwoven fabric, etc.) having continuous voids with a metal constituting the current collector, for example, by plating, and removes the resin. Can be formed. Each of the obtained negative electrode current collectors has a large number of cell-like pores corresponding to the shape of the resin porous body, and the continuous pores in which these cell-like pores communicate (that is, Communication hole). It is preferable that an opening (or window) is formed between the adjacent cellular holes, and the holes communicate with each other. By using a negative electrode current collector having a three-dimensional network-like skeleton, it is easy to move even if gas is generated, so that peeling of the negative electrode mixture is suppressed.

  The porosity of the negative electrode current collector is, for example, 30% by volume to 99% by volume, preferably 50% by volume to 98% by volume, more preferably before the negative electrode is produced (or before the negative electrode mixture is supported). Is 80% to 98% by volume or 90% to 98% by volume. When the porosity is in such a range, it is easy to increase the filling rate of the negative electrode mixture, which is advantageous in terms of increasing the capacity.

In the produced negative electrode, the porosity of the negative electrode current collector is, for example, 10 volume% to 50 volume%, and preferably 15 volume% to 40 volume% or 20 volume% to 40 volume%. When the porosity of the negative electrode current collector in the negative electrode is in such a range, it is easy to further suppress the peeling of the negative electrode mixture and to further reduce the reaction resistance. The porosity of the negative electrode current collector in the negative electrode is, for example, ½ or less, preferably 2/5, of the porosity of the negative electrode current collector before the negative electrode is manufactured (or before the negative electrode mixture is supported). Or 1/3 or less. When the porosity ratio is in such a range, it is easy to increase the capacity while suppressing gas generation.
Note that the porosity of the current collector is obtained by calculating the volume of the metal in the current collector from the mass of the current collector and the density of the metal constituting the current collector, and the ratio of the volume to the apparent volume of the current collector. It can be obtained by calculating (volume%).

  The average pore diameter in the three-dimensional network skeleton of the current collector (average diameter of communicating cell-like pores) is, for example, 50 μm to 1000 μm, preferably 100 μm to 900 μm, before the negative electrode mixture is supported. More preferably, it is 350 micrometers-900 micrometers. When the average pore diameter is in such a range, it is easy to fill the negative electrode mixture, which is advantageous in terms of increasing the capacity.

  In the produced negative electrode, the average pore diameter of the current collector is, for example, 40 μm to 800 μm, and preferably 80 μm to 700 μm or 250 μm to 600 μm. When the average pore diameter of the current collector in the negative electrode is in such a range, peeling of the negative electrode mixture can be further suppressed and reaction resistance can be further reduced.

  The average pore diameter of the current collector is parallel to the thickness direction of a three-dimensional mesh-like skeleton portion of a scanning electron microscope (SEM) photograph having a cross section parallel to the thickness direction of the current collector (or negative electrode). The average value is calculated by measuring the number of cells per inch (number of vacancies) in each direction (vertical) and the direction perpendicular to the thickness direction (horizontal), and the reciprocal of the average value is the average pore diameter. Can be obtained as

The specific surface area of the negative electrode current collector (BET specific surface area) is, in a state before (or prior to carrying a negative electrode mixture) to produce a negative electrode, for example, a 100cm ² / g~700cm ² / g, preferably 100cm ² / g to 600 cm ² / g. When the specific surface area is in such a range, it is easy to fill the negative electrode mixture, which is advantageous in terms of increasing the capacity.

  In a preferred embodiment, the three-dimensional network skeleton of the negative electrode current collector has a cavity inside (that is, is hollow). The cavity in the skeleton is formed by removing the porous resin body. The cavity in the skeleton of the negative electrode current collector may have a communication hole shape, and such a skeleton has a tunnel shape or a tube shape. A negative electrode current collector having a hollow skeleton is extremely lightweight while having a bulky three-dimensional structure. The width of the cavity inside the skeleton before compression is an average value, for example, 0.5 μm to 5.0 μm, preferably 1.0 μm to 4.0 μm or 2.0 μm to 3.0 μm. The average value of the width of the cavity is obtained by measuring and averaging the width of the cavity at a plurality of arbitrarily selected locations (for example, 10 locations) in the SEM photograph of the cross section parallel to the thickness direction of the current collector. be able to.

The negative electrode mixture includes a negative electrode active material and carbon black. The negative electrode mixture may further contain a binder as necessary.
As the negative electrode active material, a material that occludes and releases (or inserts and desorbs) lithium ions is used. Such materials cause a Faraday reaction during charging and discharging.

  Examples of the material include a carbon material (also referred to as a first carbon material) that occludes and releases (or inserts and desorbs) lithium ions, lithium titanium oxide (such as spinel type lithium titanium oxide), silicon oxide, and the like. Products, silicon alloys, tin oxides, and tin alloys. Examples of the first carbon material include graphitizable carbon (soft carbon), non-graphitizable carbon (hard carbon), graphite (natural graphite, artificial graphite, etc.) and the like. A negative electrode active material may be used individually by 1 type, and may be used in combination of 2 or more type. The negative electrode active material preferably has a theoretical capacity of 300 mAh / g or more.

Of the negative electrode active materials, the first carbon material is preferable, and graphite and / or hard carbon is particularly preferable. The average particle size of the first carbon material is preferably 1 μm to 20 μm, and more preferably 2 μm to 15 μm, from the viewpoint that the negative electrode active material in the negative electrode is highly filled and side reactions with the electrolyte are easy to suppress. preferable.
In the present specification, the average particle diameter means a volume-based median diameter (D ₅₀ ) in the particle size distribution obtained by laser diffraction particle size distribution measurement.

  Carbon black functions as a conductive aid. As carbon black, any carbon black can be used without particular limitation as long as it is used as a conductive aid for a lithium ion capacitor. Specific examples of carbon black include acetylene black, ketjen black, thermal black, furnace black, channel black, and disk black. Carbon black can be used individually by 1 type or in combination of 2 or more types. Among carbon blacks, acetylene black and / or ketjen black are preferable from the viewpoint of obtaining higher conductivity. If necessary, a conductive aid other than carbon black, such as carbon fiber and / or metal fiber, may be used in combination.

  In the present embodiment, by using a large amount of carbon black for the negative electrode active material, not only the direct current resistance of the negative electrode but also the reaction resistance can be greatly reduced. The amount of carbon black is 20 parts by mass or more with respect to 100 parts by mass of the negative electrode active material, preferably 25 parts by mass or more, more preferably 30 parts by mass or more or 40 parts by mass or more. The amount of carbon black can be, for example, 500 parts by mass or less, preferably 300 parts by mass or less or 200 parts by mass or less, with respect to 100 parts by mass of the negative electrode active material. These lower limit values and upper limit values can be arbitrarily combined. The amount of carbon black with respect to 100 parts by mass of the negative electrode active material is, for example, 20 parts by mass to 500 parts by mass, 25 parts by mass to 500 parts by mass, 20 parts by mass to 300 parts by mass, or 20 parts by mass to 200 parts by mass. Also good.

  The type of the binder is not particularly limited. For example, a polyvinylidene fluoride (PVDF) and a fluorine resin such as polytetrafluoroethylene; a chlorine-containing vinyl resin such as polyvinyl chloride; a polyolefin resin; a rubber-like material such as styrene butadiene rubber Polymers; polyvinyl pyrrolidone; polyvinyl alcohol; and cellulose derivatives such as carboxymethyl cellulose can be used. A binder can be used individually by 1 type or in combination of 2 or more types.

  The amount of the binder is, for example, 1 part by mass to 20 parts by mass, preferably 2 parts by mass to 15 parts by mass, and more preferably 3 parts by mass to 12 parts by mass with respect to 100 parts by mass of the negative electrode active material. When the amount of the binder is in such a range, the effect of suppressing the peeling of the negative electrode mixture can be further enhanced.

  The negative electrode is obtained by preparing a negative electrode mixture, supporting the negative electrode mixture on a negative electrode current collector, and compressing (or rolling) the support in the thickness direction. You may dry-process in the stage of the support and / or the stage which compressed the support.

  The negative electrode mixture supported on the negative electrode current collector is usually used in the form of a slurry containing the constituent components of the negative electrode mixture (negative electrode active material, carbon black, binder, etc.). The negative electrode mixture slurry is obtained by dispersing the components of the negative electrode mixture in a dispersion medium. As the dispersion medium, for example, water, an organic solvent such as N-methyl-2-pyrrolidone (NMP), a mixed solvent of water and an organic solvent, or the like is used.

  The thickness of a negative electrode can be selected from the range of 100 micrometers-2000 micrometers, for example, Preferably it is 150 micrometers-2000 micrometers. When the thickness of the negative electrode is in such a range, a high capacity is easily obtained. When the thickness of the negative electrode is large (for example, when it is 100 μm or more or 150 μm or more), it is generally difficult to increase the output. However, according to the present embodiment, not only the direct current resistance but also the reaction resistance that greatly contributes to the output can be reduced, so that a high output can be ensured even if the thickness of the negative electrode is large as described above. .

  In the negative electrode, the negative electrode active material is preferably supported (pre-doped) with lithium ions. By pre-doping lithium ions into the negative electrode active material, the potential of the negative electrode can be sufficiently lowered, and the capacity of the negative electrode can be increased. The pre-doping of lithium ions can be performed by a known method. The lithium ion pre-doping may be performed before the lithium ion capacitor is assembled, or may be performed in the lithium ion capacitor.

DC resistance of the anode is preferably at 3.0Ω · cm ² or less, and more preferably 1.5 [Omega · cm ² or less.
In this embodiment, the reaction resistance of the negative electrode can be reduced to 4.5 Ω · cm ² or less, preferably 3.0 Ω · cm ² or less, more preferably 1.5 Ω · cm ² or less.
The direct current resistance and reaction resistance of the negative electrode can be determined, for example, by the alternating current impedance method.

(Positive electrode)
The positive electrode includes a positive electrode current collector and a positive electrode active material (or a positive electrode mixture) supported on the positive electrode current collector. The positive electrode mixture may contain a conductive additive and / or a binder in addition to the positive electrode active material.
The material for the positive electrode current collector is preferably aluminum or an aluminum alloy.

  The positive electrode current collector may be a metal foil, but is preferably a metal porous body from the viewpoint of balance with the negative electrode, increase in capacity, and ease of gas distribution. Those having the three-dimensional network skeleton as described (particularly, a hollow skeleton) are preferable. The porosity, average pore diameter, specific surface area, width of the cavity inside the skeleton, and the like of the metal porous body can be appropriately selected from the ranges exemplified for the negative electrode current collector. The positive electrode current collector can be produced according to the case of the negative electrode current collector using aluminum or an aluminum alloy as the metal when the resin porous body is coated with the metal.

  The positive electrode active material preferably includes a material that reversibly carries at least an anion (an anion contained in the electrolyte). Such a material may be a material that reversibly carries anions and cations contained in the electrolyte. The material that reversibly carries at least an anion includes a material that adsorbs and desorbs at least an anion, a material that absorbs and desorbs at least an anion (or insertion and desorption), and the like. The former is a material that causes a non-Faraday reaction during charging and discharging, and the latter is a material that causes a Faraday reaction during charging and discharging.

As a material that adsorbs and desorbs at least anions, a porous carbon material (also referred to as a second carbon material) can be preferably used. As the second carbon material, activated carbon is preferable.
As the activated carbon, known ones used for capacitors can be used. Examples of the raw material of activated carbon include wood; coconut shells; pulp waste liquid; coal or coal-based pitch obtained by thermal decomposition thereof; heavy oil or petroleum-based pitch obtained by thermal decomposition thereof; phenol resin and the like. The activated carbon is preferably activated.
The average particle size of the activated carbon is not particularly limited, but is preferably 20 μm or less, and more preferably 3 μm to 15 μm.

The specific surface area of the activated carbon (BET specific surface area) is not particularly limited, but is preferably 800m ² / g~3000m ² / g, more preferably 1500m ² / g~3000m ² / g. When the specific surface area is in such a range, it is advantageous for increasing the capacitance of the lithium ion capacitor, and the internal resistance can be easily reduced. Moreover, it is easy to obtain a higher output. Activated carbon may be used alone or in combination of two or more (for example, two or more having different raw materials, average particle diameter and / or specific surface area).

  As a material that absorbs and releases at least anions, for example, a porous carbon material (also referred to as a third carbon material) having fine pores such as nanoporous carbon, mesoporous carbon, and microporous carbon can be preferably used. As the third carbon material, nanoporous carbon having a fine pore size of, for example, 0.1 nm to 100 nm is preferable.

Of these materials, materials that adsorb and desorb at least anions, particularly activated carbon, are preferred.
The content of activated carbon in the positive electrode active material is preferably 80% by mass to 100% by mass, and may be 90% by mass to 100% by mass. It is also preferred that the positive electrode active material contains only activated carbon.

  The conductive auxiliary agent is not particularly limited, and can be appropriately selected from carbon black exemplified for the negative electrode mixture, conductive auxiliary agents other than carbon black, and the like. A conductive support agent can be used individually by 1 type or in combination of 2 or more types. The quantity of a conductive support agent is 1 mass part-15 mass parts with respect to 100 mass parts of positive electrode active materials, for example.

As a binder, it can select suitably from what was illustrated about the negative mix. The amount of the binder with respect to 100 parts by mass of the positive electrode active material can be appropriately selected from the range of the amount of the binder with respect to 100 parts by mass of the negative electrode active material described for the negative electrode mixture.
The thickness of a positive electrode can be suitably selected from the range of 50 micrometers-2000 micrometers, for example. When a three-dimensional network metal porous body is used as the positive electrode current collector, the thickness of the positive electrode is, for example, 100 μm to 2000 μm, preferably 400 μm to 2000 μm.

  The positive electrode can be formed, for example, by supporting a positive electrode active material (or a positive electrode mixture) on a positive electrode current collector. More specifically, the positive electrode can be formed by applying or filling a positive electrode mixture on the positive electrode current collector and compressing (or rolling) it in the thickness direction. As in the case of the negative electrode mixture, the positive electrode mixture is usually used in the form of a slurry containing the components of the positive electrode mixture.

(Separator)
The separator has ion permeability, is interposed between the positive electrode and the negative electrode, and physically separates them to prevent a short circuit. The separator has a porous structure and allows ions to pass through by holding an electrolyte in the pores. As a material of the separator, for example, polyolefin such as polyethylene and polypropylene; polyester such as polyethylene terephthalate; polyamide; polyimide; cellulose; glass fiber and the like can be used.
The average pore diameter of the separator is not particularly limited, and is, for example, about 0.01 μm to 5 μm. The thickness of the separator is not particularly limited, and is, for example, about 10 μm to 100 μm.

(Electrolytes)
The electrolyte contains lithium ions and anions and exhibits lithium ion conductivity. As the electrolyte, for example, an ionic liquid containing lithium ions and anions is used in addition to an organic electrolyte in which a salt (lithium salt) of lithium ions and anions is dissolved in a nonaqueous solvent (or an organic solvent). The electrolyte may further contain a cation (second cation described later) other than lithium ions (first cation).

  The organic electrolyte can contain an ionic liquid and / or an additive in addition to the non-aqueous solvent and the lithium salt. However, the total content of the nonaqueous solvent and the lithium salt in the electrolyte is, for example, 60% by mass to 100% by mass, and preferably 80% by mass to 100% by mass.

In this specification, an ionic liquid is synonymous with a salt (molten salt) in a molten state, and is a liquid ionic substance composed of an anion and a cation (such as lithium ion).
When an ionic liquid is used for the electrolyte, the electrolyte can contain a nonaqueous solvent and / or an additive in addition to the ionic liquid. However, the content of the ionic liquid in the electrolyte is preferably 60% by mass to 100% by mass, and may be 80% by mass to 100% by mass or 90% by mass to 100% by mass.

From the viewpoint of low temperature characteristics and the like, it is preferable to use an electrolyte containing an organic solvent. From the viewpoint of suppressing the decomposition of the electrolyte as much as possible, an electrolyte containing an ionic liquid is preferably used, and an electrolyte containing an ionic liquid and an organic solvent may be used.
The concentration of the lithium salt or lithium ion in the electrolyte can be appropriately selected from the range of 0.3 mol / L to 5.0 mol / L, for example.

The kind of the first anion (anion constituting the lithium salt) contained in the organic electrolyte is not particularly limited. For example, anion of a fluorine-containing acid (hexafluorophosphate ion, tetrafluoroborate ion, etc.), perchlorate ion , Anions of oxyacids having an oxalate group [bis (oxalato) borate ion (B (C ₂ O ₄ ) ₂ ⁻ ), tris (oxalato) phosphate ion (P (C ₂ O ₄ ) ₃ ⁻ ) and the like], fluoroalkanes Examples include sulfonic acid anions [trifluoromethanesulfonic acid ion (CF ₃ SO ₃ ⁻ ) and the like], bissulfonylamide anions, and the like. The organic electrolyte may contain a kind of first anion, or may contain two or more kinds of first anions.

Examples of the bissulfonylamide anion include bis (fluorosulfonyl) amide anion (FSA ⁻ : bis (fluorosulfonyl) amide anion), bis (trifluoromethylsulfonyl) amide anion (TFSA ⁻ : bis (trifluoromethylsulfamide) amide anion. ), (Fluorosulfonyl) (perfluoroalkylsulfonyl) amide anion [(FSO ₂ ) (CF ₃ SO ₂ ) N ⁻ etc.] and the like. Of these, FSA ^- is preferred.

  The non-aqueous solvent is not particularly limited, and a known non-aqueous solvent used for a lithium ion capacitor can be used. Non-aqueous solvents include, for example, cyclic carbonates such as ethylene carbonate, propylene carbonate, and butylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate; cyclic carbonates such as γ-butyrolactone. Etc. can be preferably used. A non-aqueous solvent may be used individually by 1 type, and may be used in combination of 2 or more type.

The ionic liquid contains a salt of lithium ions and anions (second anions). The ionic liquid may further contain a second cation other than lithium ions (or a molten salt of the second cation and the second anion).
As the second anion, a bissulfonylamide anion is preferably used. The bissulfonylamide anion can be selected from those similar to those exemplified for the first anion. The ionic liquid may contain a kind of second anion, or may contain two or more kinds of second anions.

  Examples of the second cation include inorganic cations other than lithium ions and organic cations. Examples of inorganic cations include alkali metal ions (sodium ions, potassium ions, etc.) other than lithium ions, alkaline earth metal ions, ammonium ions, and the like. The ionic liquid may contain one kind of second cation, and may contain two or more kinds of second cation. The second cation may be an inorganic cation, but is preferably an organic cation.

Organic cations include cations derived from aliphatic amines, alicyclic amines or aromatic amines (for example, quaternary ammonium cations), as well as cations having nitrogen-containing heterocycles (that is, derived from cyclic amines). Examples thereof include nitrogen-containing onium cations such as cations), sulfur-containing onium cations, and phosphorus-containing onium cations.
Among organic cations, in particular, a cation having a pyrrolidine, pyridine, or imidazole skeleton as a nitrogen-containing heterocyclic skeleton in addition to a quaternary ammonium cation is preferable.

Specific examples of the organic cation include tetraalkylammonium cation (TEA ⁺ : tetraethylammonium cation), methyltriethylammonium cation (TEMA ⁺ : methyltriethylammonium cation) and the like; 1-methyl-1-propylpyrrolidinium cation (MPPY) ⁺ : 1-methyl-1-propylpyrrolidinium cation, 1-butyl-1-methylpyrrolidinium cation (MBPY ⁺ : 1-butyl-1-methylpyrrolidinium cation); 1-ethyl-3-methylimidazolium cation (EMI ⁺ : 1-ethyl-3-methylimidazolium cati n), 1-butyl-3-methylimidazolium cation ^{(BMI +: 1-buthyl-} 3-methylimidazolium cation) and the like.

  The lithium ion capacitor according to this embodiment includes, for example, (a) a step of forming an electrode group with a separator interposed between the positive electrode and the negative electrode, and (b) a step of housing the electrode group and the electrolyte in a cell case. It can manufacture by going through. After step (b), if necessary, the gas generated in the lithium ion capacitor may be discharged out of the lithium ion capacitor from a valve (such as a safety valve described later) provided in the cell case.

  FIG. 1 is a perspective view showing the appearance of a lithium ion capacitor according to an embodiment of the present invention. FIG. 2 is a partial cross-sectional view showing an internal structure when the lithium ion capacitor of FIG. 1 is viewed from the front. 3 is a cross-sectional view taken along line III-III in FIG. 2 showing a part of the internal structure of the lithium ion capacitor in FIG.

  The lithium ion capacitor 10 includes an electrode group 12, a non-aqueous electrolyte (not shown), and a cell case that accommodates them. The cell case includes a case body 14 and a sealing plate 16 that seals the open end of the case body 14. In the illustrated example, the cell case has a square shape.

  The electrode group 12 includes a plurality of sheet-like positive electrodes 18 and a plurality of sheet-like negative electrodes 20. The positive electrode 18 and the negative electrode 20 are alternately stacked with the separator 21 interposed therebetween. The separator 21 is formed in a bag shape so as to accommodate the positive electrode 18 therein, but the shape of the separator is not particularly limited. The positive electrode 18 includes a positive electrode current collector 22 and a positive electrode active material (specifically, a positive electrode mixture). The negative electrode 20 includes a negative electrode current collector 24 and a negative electrode mixture. In FIG. 3, it is difficult to distinguish between the electrode and the current collector, and therefore, the electrode and the current collector are indicated by the same element.

  The sealing plate 16 includes a positive external terminal 40 electrically connected to the plurality of positive electrodes 18 and a negative external terminal 42 electrically connected to the plurality of negative electrodes 20. A safety valve 44 is provided at the center of the sealing plate 16. Further, a liquid stopper 48 that closes the liquid injection hole is attached to the sealing plate 16 at a position near the positive electrode external terminal 40 with the safety valve 44 as the center.

  In the electrode group 12, the positive electrode current collector 22 has a tab-shaped positive electrode connection portion 26, and the negative electrode current collector 24 has a tab-shaped negative electrode connection portion 28. As shown in FIG. 1, the positive electrode connection portion 26 is formed at a position near the positive electrode external terminal 40, and the negative electrode connection portion 28 is formed at a position near the negative electrode external terminal 42. Each connecting portion is preferably made of the same material as the current collector and formed integrally with the current collector.

  A first conductive spacer 30 is disposed between the adjacent positive electrode connection portions 26. Similarly, a second conductive spacer is disposed between adjacent negative electrode connection portions 28. The first conductive spacer 30 and the second conductive spacer can each be formed of a plate-like member including a conductor. However, the first conductive spacer 30 is preferably formed of a metal porous body in order to improve the adhesion with the positive electrode connection portion 26, and in particular, the same material as the positive electrode current collector 22 (for example, a metal porous body). It is preferable to form by. The second conductive spacer is also preferably formed of a porous metal material as in the case of the first conductive spacer 30, and in particular, the same material as the negative electrode current collector 24 (for example, a three-dimensional network skeleton) It is preferable to form a porous metal body.

  In the illustrated example, a through hole 36 for inserting a first fastening member (rivet) 34 is provided in the positive electrode connecting portion 26 of the positive electrode 18. The first conductive spacer 30 is also provided with a through hole 37 for inserting the first fastening member 34 at a position overlapping the through hole 36 of the positive electrode connecting portion 26. Similarly to the case of the positive electrode 18, the negative electrode connecting portion 28 of the negative electrode 20 is provided with a through hole for inserting the second fastening member (rivet). The second conductive spacer is also provided with a through hole for inserting the second fastening member at a position overlapping the through hole of the negative electrode connecting portion 28.

  The positive electrode 18 and the positive electrode external terminal 40 are electrically connected via a positive electrode lead 62. Similarly, the negative electrode 20 and the negative external terminal 42 are electrically connected via a negative electrode lead. The positive electrode lead 62 in the illustrated example is a member having an L-shaped cross section, and has a plate-like first portion 62a and a second portion 62b that are perpendicular to each other. The second portion 62 b has one or more through holes for inserting the first fastening member 34. By the first fastening member 34 inserted through the through hole, the second portion 62b is fixed in a state of being in contact with the positive electrode connecting portion 26. The negative electrode lead also has the same shape as the positive electrode lead 62 and is solidified in the negative electrode connection portion 28 in the same manner as the positive electrode lead 62.

  The cell case may be made of a polymer film or the like, but is preferably made of a metal such as aluminum, aluminum alloy, iron or stainless steel. The metal cell case may be plated as necessary.

  EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example and a comparative example, this invention is not limited to a following example.

Example 1
A lithium ion capacitor was produced according to the following procedure.
(1) Production of positive electrode (a) Production of positive electrode current collector Thermosetting polyurethane foam (porosity: 95 vol%, surface 1 inch (= 2.54 cm) Number of pores (cells) per length: About 50, 100 mm long × 30 mm wide × 1.1 mm thick) were prepared.
The foam is immersed in a conductive suspension containing graphite, carbon black (average particle size D ₅₀ : 0.5 μm), a resin binder, a penetrating agent, and an antifoaming agent, and then dried to foam. A conductive layer was formed on the surface of the body. The total content of graphite and carbon black in the suspension was 25% by mass.

The foam having the conductive layer formed on the surface was immersed in a molten salt aluminum plating bath, and a direct current having a current density of 3.6 A / dm ² was applied for 90 minutes to form an aluminum layer. The mass of the aluminum layer per apparent area of the foam was 150 g / m ² . The molten salt aluminum plating bath contained 33 mol% 1-ethyl-3-methylimidazolium chloride and 67 mol% aluminum chloride, and the temperature was 40 ° C.

The foam with the aluminum layer formed on the surface was immersed in a lithium chloride-potassium chloride eutectic molten salt at 500 ° C., and a negative potential of −1 V was applied for 30 minutes to decompose the foam. The obtained aluminum porous body was taken out from the molten salt, cooled, washed with water, and dried to obtain a positive electrode current collector. The obtained positive electrode current collector has a three-dimensional network-like porous structure in which pores communicate, reflecting the pore shape of the foam, has a porosity of 94% by volume, and an average pore diameter of 550 μm. Yes, the BET specific surface area was 350 cm ² / g, and the thickness was 1000 μm. In addition, the three-dimensional mesh-like aluminum skeleton had a communication hole-like cavity formed by removing the foam. In this way, a positive electrode current collector was obtained.

(B) Preparation of positive electrode Activated carbon powder (specific surface area: 2300 m ² / g, average particle diameter D ₅₀ : about 5 μm) as a positive electrode active material, acetylene black as a conductive additive, and PVDF (containing 12% by mass concentration of PVDF) as a binder NMP solution) and NMP as a dispersion medium were mixed and stirred in a mixer to prepare a positive electrode mixture slurry. The mass ratio of each component in the slurry was activated carbon: acetylene black: PVDF = 87: 3: 10, and the solid content concentration was 30% by mass.

  The obtained positive electrode mixture slurry was filled into the current collector obtained in the step (a) using a die coater, and the filling was dried at 100 ° C. for 30 minutes. Next, the dried product was compressed in the thickness direction using a pair of rolls, to produce a positive electrode having a thickness of 900 μm.

(2) Production of negative electrode (a) Production of negative electrode current collector The amount of Cu per cm ² is 20 mg on the surface of the same thermosetting polyurethane foam used in the production of the positive electrode current collector. Then, a Cu film (conductive layer) was formed by sputtering.
A foam having a conductive layer formed on the surface was immersed in a copper sulfate plating bath, and a direct current having a cathode current density of 2 A / dm ² was applied to form a Cu layer on the surface. The copper sulfate plating bath contained 250 g / L copper sulfate, 50 g / L sulfuric acid, and 30 g / L copper chloride, and the temperature was 30 ° C.

The foam with the Cu layer formed on the surface is heat-treated at 700 ° C. in an air atmosphere to decompose the foam, and then fired in a hydrogen atmosphere to reduce the oxide film formed on the surface. Thus, a copper porous body (negative electrode current collector) was obtained. The obtained negative electrode current collector has a three-dimensional network-like porous structure in which pores communicate, reflecting the pore shape of the foam, has a porosity of 92% by volume, and an average pore diameter is It was 550 μm, the BET specific surface area was 200 cm ² / g, and the thickness was 800 μm. In addition, the three-dimensional network copper skeleton had a communication hole-like cavity formed by removing the foam.

(B) Production of negative electrode Artificial graphite powder (average particle diameter D ₅₀ : 5 μm) as a negative electrode active material, acetylene black as a conductive additive, PVDF as a binder, and NMP as a dispersion medium are mixed. Thus, a negative electrode mixture slurry was prepared. The mass ratio of the graphite powder, acetylene black, and PVDF was 100: 26.3: 5.3. The mass ratio of the graphite powder and acetylene black to PVDF was 96: 4.

The obtained negative electrode mixture slurry was filled into the current collector obtained in the step (a) using a die coater, and the filling was dried at 100 ° C. for 60 minutes. The dried product was compressed in the thickness direction using a pair of rolls to produce a negative electrode having a thickness of 200 μm. The porosity of the negative electrode current collector in the negative electrode was 30% by volume, and the average pore diameter was 400 μm.
In the steps (1) and (2), the filling amounts of the positive electrode mixture and the negative electrode mixture were adjusted so that the chargeable capacity of the negative electrode after pre-doping was about 1.2 times the capacity of the positive electrode. .

(3) Production of lithium electrode A lithium foil (thickness: 50 μm) is pressure-bonded to one surface of a punching copper foil (thickness: 20 μm, opening diameter: 50 μm, opening ratio 50%, 2 cm × 2 cm) as a current collector. Thus, a lithium electrode was produced. A nickel lead was welded to the other surface of the current collector of the lithium electrode.

(4) Production of Lithium Ion Capacitor The positive electrode and the negative electrode obtained in the above (1) and (2) were each cut into a size of 1.5 cm × 1.5 cm, and a portion having a width of 0.5 cm along one side The mixture was removed to form a current collector exposed portion. An aluminum lead was welded to the positive electrode current collector exposed portion, and a nickel lead was welded to the negative electrode current collector exposed portion. In each positive electrode and negative electrode, the area of the portion where the mixture was present was 1.5 cm ² .

  By laminating a separator made of cellulose (thickness: 30 μm) between the positive electrode and the negative electrode, a single cell electrode group was formed. A lithium electrode was further laminated on the negative electrode side of the electrode group with a glass fiber separator interposed therebetween. The obtained laminate was accommodated in a cell case made of an aluminum laminate sheet.

Next, a nonaqueous electrolyte was injected into the cell case, and impregnated into the positive electrode, the negative electrode, and the separator. Finally, the cell case was sealed while reducing the pressure with a vacuum sealer. As the non-aqueous electrolyte, a solution in which LiPF ₆ as a lithium salt was dissolved to a concentration of 1.0 mol / L in a mixed solvent containing ethylene carbonate and diethyl carbonate at a volume ratio of 1: 1 was used.

The lead wire of the negative electrode and the lead wire of the lithium electrode are connected to a power source outside the cell case, and charged with a current of 0.2 mA / cm ² until the negative electrode potential becomes 0 V with respect to metallic lithium. Lithium ions were pre-doped from the electrode to the negative electrode included in the electrode group. In this way, a lithium ion capacitor A1 was produced.

(5) Evaluation The following evaluation was performed on the lithium ion capacitor or the negative electrode.
(A) DC resistance and reaction resistance The DC resistance and reaction resistance of the negative electrode were measured by the AC impedance method under conditions of a voltage amplitude of 5 mV and a frequency range of 0.1 Hz to 1 MHz. Specifically, in the Nyquist diagram obtained by alternating current impedance measurement, the resistance to the intersection with the real axis is defined as direct current resistance, and the semicircular component is defined as reaction resistance.

(B) Fixed resistance (fixed resistance according to JEITA standards)
With lithium ion capacitor, in the current 2.7mA / cm ^2, and charged to the upper limit voltage 3.8 V at a current 2.7mA / cm ^2, and then discharged until the voltage becomes 2.2V. The fixed resistance (Ω) was determined from the charge / discharge curve at this time.

(C) Energy density Using a lithium ion capacitor, the battery is charged at a current of 0.50 mA / cm ² to an upper limit voltage of 3.8 V, and discharged at a current of 0.25 mA / cm ² until the voltage reaches 2.2 V. did. The energy density (Wh / L) was determined from the discharge capacity at this time.

Using a peeling lithium ion capacitor of (d) negative electrode mixture, in the current 1.0 mA / cm ^2, and charged to the upper limit voltage 3.8 V at a current 1.0 mA / cm ^2, the voltage to 2.2V Discharged until This charge / discharge cycle was repeated 30 times. Next, the lithium ion capacitor was disassembled, and peeling of the negative electrode mixture was visually observed.

Comparative Example 1
The positive electrode mixture slurry used in (1) of Example 1 was applied to one side of an aluminum foil (thickness 20 μm) as a positive electrode current collector and dried at 220 ° C. for 12 hours. The dried product was compressed in the thickness direction using a pair of rolls to produce a positive electrode having a thickness of 100 μm.

The negative electrode mixture slurry used in (2) of Example 1 was applied to one side of a copper foil (thickness 20 μm) as a negative electrode current collector and dried at 120 ° C. for 12 hours. The dried product was compressed in the thickness direction using a pair of rolls to produce a negative electrode having a thickness of 80 μm.
A lithium ion capacitor was produced and evaluated in the same manner as in Example 1 except that the positive electrode and the negative electrode thus produced were used.

Examples 2 to 4 and Comparative Example 2
A lithium ion capacitor was produced and evaluated in the same manner as in Example 1 except that the amount of carbon black relative to 100 parts by mass of the negative electrode active material (graphite) was changed as shown in Table 1. The mass ratio of the total graphite and carbon black to PVDF was 96: 4.
The results of Examples and Comparative Examples are shown in Table 1. The lithium ion capacitors of Examples 1 to 4 are A1 to A4, and the lithium ion capacitors of Comparative Examples 1 to 2 are B1 to B2. In Table 1, the CB column represents parts by mass with respect to 100 parts by mass of carbon black graphite.

As shown in Table 1, in the example, not only the direct current resistance but also the reaction resistance was greatly reduced, and the fixed resistance was also reduced. Therefore, high output was obtained. On the other hand, in Comparative Example 1 using the metal foil current collector, although the negative electrode contains the same proportion of carbon black as in Example 1, the reaction resistance of the negative electrode is larger than that of the example and the fixed resistance is also increased. It was. Even in Comparative Example 2 in which the amount of carbon black was small, the reaction resistance increased.
In the examples, no peeling of the negative electrode mixture was observed even after repeated charge and discharge, whereas in Comparative Example 1, the peeling of the negative electrode mixture was remarkable.

  In the lithium ion capacitor according to one embodiment of the present invention, an increase in the reaction resistance of the negative electrode is suppressed, high output is possible, and peeling of the negative electrode mixture can be suppressed. Therefore, it can be applied to various uses that require high output.

10: Lithium ion capacitor 12: Electrode group 14: Case body 16: Sealing plate 18: Positive electrode 20: Negative electrode 21: Separator 22: Positive electrode current collector 24: Negative electrode current collector 26: Positive electrode connection part 28: Negative electrode connection part 30: First conductive spacer 34: First fastening member 36, 37: Through hole 40: Positive external terminal 42: Negative external terminal 44: Safety valve 48: Liquid stopper 62: Positive lead 62a: First part 62b: Second part

Claims (6)

A positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a lithium ion conductive electrolyte;
The positive electrode includes a positive electrode current collector and a positive electrode active material supported on the positive electrode current collector,
The negative electrode includes a negative electrode current collector and a negative electrode mixture supported on the negative electrode current collector,
The negative electrode current collector is a porous metal body having a three-dimensional network skeleton,
The negative electrode mixture includes a negative electrode active material that occludes and releases lithium ions, and carbon black,
The amount of the carbon black is 20 parts by mass or more with respect to 100 parts by mass of the negative electrode active material.   2. The lithium ion capacitor according to claim 1, wherein an amount of the carbon black is 20 parts by mass to 500 parts by mass with respect to 100 parts by mass of the negative electrode active material.   3. The lithium ion capacitor according to claim 1, wherein an amount of the carbon black is 20 parts by mass to 200 parts by mass with respect to 100 parts by mass of the negative electrode active material.   The lithium ion capacitor according to claim 1, wherein the skeleton has a cavity inside.   5. The lithium ion capacitor according to claim 1, wherein a thickness of the negative electrode is 100 μm to 2000 μm.   The lithium ion capacitor according to any one of claims 1 to 5, wherein the positive electrode current collector is a porous metal body having a three-dimensional network skeleton.

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