KR101281946B1 - Anode active material comprising soft carbon particle with controlled pore distribution and litium secondary battery with improved low-temperature output properties - Google Patents

Abstract

The present invention relates to soft carbon particles in which pores of a certain size are increased. More specifically, crystal change materials are introduced to increase the pore volume of 1 to 10 nm to optimize occlusion of lithium ions. The present invention relates to a digraphitizable carbon particle and a lithium secondary battery having improved low temperature output.
In the present invention, micropores may be formed in the digraphitizable carbon particles through introduction of a crystal change material and heat treatment under specific conditions, and the low temperature output of the secondary battery may be improved by the micropores.

Description

ANODE ACTIVE MATERIAL COMPRISING SOFT CARBON PARTICLE WITH CONTROLLED PORE DISTRIBUTION AND LITIUM SECONDARY BATTERY WITH IMPROVED LOW-TEMPERATURE OUTPUT PROPERTIES}

The present invention relates to soft carbon particles in which pores of a certain size are increased. More specifically, crystal change materials are introduced to increase the pore volume of 1 to 10 nm to optimize occlusion of lithium ions. The present invention relates to a digraphitizable carbon particle and a lithium secondary battery having improved low temperature output.

BACKGROUND ART Portable electronic devices such as portable telephones and notebook computers have been developed, and the demand for secondary batteries as their energy sources is rapidly increasing. In addition, in order to reduce problems caused by global warming and the use of fossil fuels, hybrid electric vehicles (EVs) and electric motor-driven electric vehicles (EVs) have been developed and the use of secondary batteries . Accordingly, a lot of research has been conducted on a secondary battery that can meet various demands, and in particular, there is a trend of increasing demand for a lithium secondary battery having a high energy density, a high discharge voltage, and an output.

The lithium secondary battery has a structure in which a non-aqueous electrolyte containing lithium salt is impregnated in an electrode assembly having a porous separator interposed between a positive electrode and a negative electrode on which an active material is coated on a current collector. The positive electrode active material is mainly composed of lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium composite oxide and the like, and the negative electrode active material is mainly composed of a carbon-based material.

Carbonaceous materials are composed of soft carbon having a layered crystal structure that is easily graphitized, hard carbon that is difficult to graphitize, and a layered crystal structure such as natural graphite. Classify as graphite.

A negative electrode made of a graphite-based material, which is a layered crystal mainly used as a negative electrode active material, has a limit in increasing the theoretical maximum capacity, and thus it is difficult to play a sufficient role as an energy source of a rapidly changing next-generation mobile device.

In addition, the amorphous carbon-based compound such as carbon dioxide is very high discharge capacity of 280 to 450 mAh / g, while the initial efficiency is very low, such as 70 to 80%, has a high irreversible capacity, low bulk density and electrical conductivity, energy density Has a bad problem. In order to compensate for each of these disadvantages, a research has been attempted to produce an electrode with a mixed negative electrode active material of a graphite-based carbon compound and an amorphous carbon-based compound.

In connection with the above research, Korean Patent Laid-Open No. 2011-0033995 discloses a negative electrode material for electrode mixture composed of a mixture containing an amorphous carbonaceous compound and a flake-like crystalline carbonaceous compound, and a high output lithium secondary battery including the same.

However, the patent controls the mixing ratio of the soft carbon and the flaky crystalline carbon compound of the amorphous carbon compound to fill the empty space between the soft carbon compound to increase the energy density, thereby obtaining excellent battery characteristics This does not seem to solve the disadvantage of the amorphous carbon-based compound itself.

Thus, no attempt has been made to optimize the activation site where lithium ions can be occluded by controlling the pore distribution of the particles in the digraphitizable carbon particles.

Accordingly, the present inventors have studied and tried to optimize the activation site where lithium ions may be occluded in the digraphitizable carbon particles that can be applied as a negative electrode active material of a lithium secondary battery. When introduced into the digraphitizable carbon particles, the present invention has been completed by discovering that the pore volume of 1 to 10 nm in size that optimizes occlusion of lithium ions is increased to improve the low temperature output of the battery.

Accordingly, an object of the present invention is to provide a digraphitizable carbon particles having an increased pore volume of a specific size, a negative electrode mixture and an electrochemical cell comprising the same.

Digraphitized carbon particles of the present invention for achieving the above object is a crystal change material is introduced, the ratio of the pore volume (A) of 1 to 10 nm size to the pore volume (B) of 10 to 35 nm size (A / B) is in the range of 0.5 to 15.

In another aspect, the present invention is characterized by a negative electrode mixture using the digraphitizable carbon particles as a negative electrode active material and an electrochemical cell comprising the same.

The digraphitizable carbon particles of the present invention selectively increase pores of a suitable size capable of occluding lithium ions, thereby greatly improving the battery capacity when applied as a negative electrode active material of a lithium secondary battery. In particular, micropores may be formed in the graphitized carbon particles through introduction of a crystal change material and heat treatment under specific conditions, and the micropores may improve the low temperature output of the secondary battery.

1 is a pore distribution graph showing the volume according to the pore size in the digraphitizable carbon particles of the present invention.

Advantages and features of the present invention and methods of achieving them will become apparent with reference to the embodiments described in detail below. It should be understood, however, that the invention is not limited to the disclosed embodiments, but is capable of many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, To fully disclose the scope of the invention to those skilled in the art, and the invention is only defined by the scope of the claims.

Hereinafter, the digraphitizable carbon particles of the present invention and an electrochemical cell (lithium secondary battery) including the same will be described in detail.

Graphite  Carbon particles

In the digraphitizable carbon particles of the present invention, a crystal change material is introduced, so that the ratio (A / B) of pore volume (A) of 1 to 10 nm to pore volume (B) of 10 to 35 nm is 0.5 to It is characterized by being in the range of 15, preferably in the range of 2 to 12.

Specifically, looking at each pore volume, the pore volume of 1 ~ 10 nm size is 1.0 × 10 ^-3 ~ 5.0 × 10 ^-2 cc / g per particle weight, pore volume of 10 ~ 35 nm size is 0.5 per particle weight It exists in the range of x 10 ^-3 to 1.0 x 10 ^-2 cc / g. More preferably, the pore volume in the range of 1 to 10 nm is 2.0 × 10 ^-3 to 2.0 × 10 ^-2 cc / g per particle weight, and the pore volume in the range of 10 to 35 nm is 1.0 × 10 ^-3 to particle weight. It is present at 7.0 × 10 ^-3 cc / g, the volume value of the pore is measured by nitrogen adsorption and desorption method. The capacity increases as the pore volume of the size of 1 to 10 nm is increased, but if the volume exceeds the limited volume, there is a fear that the cycle characteristics are lowered.

Generally, the graphitized carbon particles have a pore volume of 10 to 35 nm in size of 1.0 × 10 ^-3 to 1.0 × 10 ^-2 cc / g per particle weight, and no micropores of size of 10 nm or less exist. .

In addition, the crystalline carbon-based compound has a path in which lithium ions are occluded and desorbed in a layered structure of carbon in approximately two dimensions, whereas in the amorphous carbon-based compound, the path for insertion of lithium ions is not so limited. Since it is relatively large, it exhibits an excellent rate characteristic. Therefore, the graphitizable carbon particles corresponding to the amorphous carbon-based compound have excellent rate characteristics, but have a disadvantage in that the irreversible capacity is as high as 20 to 30%.

However, in the digraphitizable carbon particles of the present invention, a crystal change material containing heterogeneous elements other than carbon is introduced to cause a change in crystallinity of the particles, thereby forming pores having a size of 10 nm or less, which has not previously appeared. In addition, by adjusting the initial temperature of the heat treatment process, the crystal change material is bonded with carbon to optimize the volume of the pores having a size of 10 nm or less by maximizing the pore formation due to gas desorption as a by-product. In the pores, since lithium ions can be easily occluded and desorbed, the capacity of a conventional battery can be improved.

The raw material precursor used for the production of the digraphitizable carbon particles is at least one selected from the group consisting of petroleum coke, coal coke, coal-based pitch, petroleum-based pitch, mesophase pitch, mesocarbon microbeads and vinyl chloride-based resin. Although not limited thereto, the carbon atoms are not particularly limited as long as the carbon atoms have an amorphous crystal structure and exhibit excellent rate characteristics. More specifically, the carbon precursor may be prepared by partially graphitizing and pulverizing the pitch by heat treatment of the pitch and the like under an air or inert gas atmosphere.

The grinding may be performed using a mill such as a ball mill, an attention mill, a vibration mill, a disk mill, a jet mill, a rotor mill, or the like. By milling the raw materials. The milling can be a dry process, a wet process, or a combined dry and wet process. The average particle diameter and particle size distribution of the particles can be controlled by the pulverization speed, pressure, time, and the like in the pulverization process.

The digraphitizable carbon particles of the present invention are characterized in that a crystal change material is introduced. In the present invention, the crystal change material refers to a compound capable of causing a change in physical crystallinity in the carbon particles without causing a chemical reaction with the carbon component. The crystal change material is not particularly limited as long as it is a compound capable of causing a change in crystallinity, and preferably includes manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), and zinc (Zn). Group 3, 4, including a transition metal compound, boron (B), aluminum (Al), gallium (Ga), indium (In), nitrogen (N), silicon (Si), phosphorus (P), arsenic (As) Compounds containing at least one element selected from the group consisting of group and group 5 element compounds, alkali metal compounds including sodium (Na) potassium (Ka) magnesium (Mg) calcium (Ca) or alkaline earth metal compounds can be used. .

In particular, the compound containing boron (B) may be used one or more selected from the group consisting of borate, boric acid, boron oxide, boron oxide, boron nitride, boron chloride, etc., the compound containing the phosphorus (P) As the furnace, one or more selected from the group consisting of hydrogen phosphide, phosphorus pentoxide, phosphoric acid, superphosphate, oxo acid, and the like may be used, and the compound containing nitrogen (N) may be ammonia, acetonitrile, acrylonitrile, pyridine, or the like. One or more selected from the group consisting of can be used.

The heterogeneous element in the crystal change material does not undergo chemical reaction with carbon, but is positioned between carbon atoms to modify the structure and thus form pores on the surface.

The crystal change material is preferably introduced in an amount of 0.1 to 20% by weight, more preferably 1 to 10% by weight, based on the total weight of the particles. If it is used in less than the above-mentioned range, the effect of crystal change is insignificant so that the pores do not increase. If it is used in the above-mentioned range, deterioration of battery characteristics due to heterogeneous elements may appear, which is not preferable.

 The digraphitizable carbon particles of the present invention may be obtained by mixing a carbon precursor and a crystal change material and heating the same. More preferably, the carbon precursor and the crystal change material may be prepared by uniformly dispersing the solvent under a solvent and then drying and heating the same.

At this time, the heat treatment is preferably carried out by increasing the temperature at a rate of 5 ~ 20 ℃ / min at an initial temperature of 300 ~ 700 ℃, it is preferable to heat for about 1 to 5 hours at a final temperature of 1,000 ℃ or less. If the introduction temperature is less than 300 ℃, the introduction of the crystal change material is not sufficient, there is a problem that the fine pores due to the desorption of the gas generated by the introduction of the crystal change material is not formed, the final temperature is 1,000 ℃ If it is made in excess of the fine pores of 10 nm or less is collapsed there is a problem that the effect of pore enlargement due to the introduction of the crystal change material does not appear.

Further, it may be carried out under a vacuum or an inert atmosphere so as to prevent oxidation of the carbon component, and may be carried out, for example, under a nitrogen or argon atmosphere.

Electrochemical cell (lithium secondary battery)

Meanwhile, the present invention can provide an electrochemical cell using the above-mentioned negative electrode active material, for example, a lithium secondary battery, which will be described in detail below.

A negative electrode mixture according to an embodiment of the present invention is composed of a negative active material, a binder and a conductive material of the graphitizable carbon particles.

The binder is a component that assists the bonding between the negative electrode active material and the conductive material and the current collector, and is generally added in an amount of 1 to 50 wt% based on the total weight of the mixture including the negative electrode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, Polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene butadiene rubber, fluorine rubber, various copolymers, and the like.

The conductive material is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery. Examples of the conductive material include carbon black, acetylene black, thermal black, conductive fibers such as carbon black or metal fibers such as channel black, furnace black and graphite; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskeys such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

The negative electrode material mixture may optionally include a filler, an adhesion promoter, and the like.

The filler is an auxiliary component for suppressing the expansion of the electrode. The filler is not particularly limited as long as it is a fibrous material without causing any chemical change in the battery, and examples thereof include fibrous olefinic polymers such as fibrous polyethylene and fibrous polypropylene; Fibrous materials such as glass fibers and carbon fibers are used.

The adhesion promoter may be added in an amount of 10% by weight or less based on the binder, for example, oxalic acid, adipic acid, Formic acid, acrylic acid derivatives, itaconic acid derivatives, and the like.

The negative electrode to which the negative electrode mixture is applied on the current collector can be produced, for example, by coating the current collector with the negative electrode mixture. Specifically, a predetermined sheet-like electrode can be produced by applying a negative electrode mixture to a predetermined solvent to prepare a slurry, applying the slurry to a current collector such as a metal foil, and drying and rolling the slurry.

The electrochemical cell according to an embodiment of the present invention is configured such that the negative electrode mixture includes a negative electrode coated on a current collector.

Generally, the negative electrode is prepared by adding a negative electrode mixture to a solvent such as N-methylpyrrolidone (NMP) to prepare a slurry, and then applying the same to a current collector to dry and roll it.

Preferred examples of the solvent used in the preparation of the slurry include dimethyl sulfoxide (DMSO), alcohol, N-methylpyrrolidone (NMP), sodium carboxymethylcellulose (CMC, sodium carbonxymethylcellulose), acetone, and the like. The solvent may be used in an amount of up to 400 wt% based on the total weight of the negative electrode mixture and is removed during the drying process.

The negative electrode current collector is generally made to have a thickness of 3 to 500 mu m. Such an anode current collector is not particularly limited as long as it has conductivity without causing a chemical change in the battery, and the anode current collector may be made of a material such as copper, stainless steel, aluminum, nickel, titanium, sintered carbon, A surface treated with carbon, nickel, titanium, silver or the like, an aluminum-cadmium alloy, or the like can be used. In addition, like the positive electrode current collector, fine concavities and convexities may be formed on the surface to enhance the bonding strength of the negative electrode active material, and may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

The method of uniformly applying the negative electrode material mixture paste on the negative electrode collector may be selected from known methods in consideration of the characteristics of materials and the like or may be carried out by a new appropriate method. For example, it is preferable to distribute the paste on the current collector and uniformly disperse the paste using a doctor blade or the like. In some cases, a method of performing the distribution and dispersion processes in one process may be used. In addition, a method such as die casting, comma coating, screen printing, or the like may be employed, or may be molded on a separate substrate and then bonded to the current collector by pressing or lamination. Drying of the paste applied on the current collector is preferably dried for 12 to 72 hours in a vacuum oven at 50 ℃ to 200 ℃.

The electrochemical cell is a device for providing electricity through an electrochemical reaction, and may be a lithium secondary battery including a nonaqueous electrolyte containing a lithium salt.

The lithium secondary battery may have a structure in which a lithium salt-containing nonaqueous electrolyte solution is impregnated in an electrode assembly having a separator interposed between the negative electrode and the positive electrode.

Other components of the lithium secondary battery according to the present invention are as follows

The positive electrode is prepared, for example, by coating a mixture of a positive electrode active material, a conductive material and a binder on a positive electrode current collector, and then drying the mixture. Optionally, a filler may be further added to the mixture.

The cathode current collector generally has a thickness of 3 to 500 mu m. The positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, sintered carbon or a surface of aluminum or stainless steel Treated with carbon, nickel, titanium, silver or the like may be used. The current collector may have fine irregularities on the surface thereof to increase the adhesive force of the cathode active material, and various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric are possible. The cathode active material may be a layered compound such as lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), or a compound substituted with a transition metal or higher; Lithium manganese oxides such as Li _{1 + y} Mn _{2 -y} O ₄ (where y is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ and LiMnO ₂ ; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ and Cu ₂ VO ₇ ; A Ni-site type lithium nickel oxide represented by the formula LiNi _{1 -y} MO ₂ (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga and y = 0.01 to 0.3); Formula LiMn _{2 -y} MO ₂ (wherein M = Co, Ni, Fe, Cr, Zn or Ta and y = 0.01 to 0.1) or Li ₂ Mn ₃ MO ₈ (wherein M = Fe, Co, Ni, Lithium manganese composite oxide represented by Cu or Zn); A LiMn ₂ O ₄ disulfide compound in which a part of Li in the formula is substituted with an alkaline earth metal ion; Fe ₂ (MoO ₄ ) ₃ and the like can be used, but are not limited thereto.

The separation membrane is interposed between the anode and the cathode, and an insulating thin film having high ion permeability and mechanical strength is used. As such a separation membrane, for example, a sheet or a nonwoven fabric made of an olefin-based polymer such as polypropylene which is chemically resistant and hydrophobic, glass fiber, polyethylene or the like is used. When a solid electrolyte such as a polymer is used as an electrolyte, the solid electrolyte may also serve as a separation membrane.

The lithium salt-containing nonaqueous electrolyte solution is composed of an electrolyte solution and a lithium salt. As the electrolyte solution, a nonaqueous organic solvent, an organic solid electrolyte, and an inorganic solid electrolyte may be used.

Examples of the non-aqueous organic solvent include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, and gamma Butyl lactone, 1,2-dimethoxy ethane, tetrahydroxy franc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxorone, formamide, dimethylformamide, dioxolon , Acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxy methane, dioxorone derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbo Aprotic organic solvents such as nate derivatives, tetrahydrofuran derivatives, ethers, methyl pyroionate and ethyl propionate can be used.

Examples of the organic solid electrolyte include a polymer electrolyte such as a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, an agitation lysine, a polyester sulfide, a polyvinyl alcohol, a polyvinylidene fluoride A polymer including an acid dissociation group, and the like can be used.

As the inorganic solid electrolyte, for example, Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO _4- LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Li Nitrides, halides, sulfates, and the like of ₄ SiO ₄ -LiI-LiOH, Li ₃ PO _4- Li ₂ S-SiS _2, and the like can be used.

The lithium salt is a material that is readily soluble in the non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO 4, LiBF 4, LiB 10 Cl 10, LiPF 6, LiCF 3 SO 3, LiCF 3 CO 2, LiAsF _{6, LiSbF 6, LiAlCl 4,} CH 3 SO 3 Li, CF 3 SO 3 Li, (CF 3 SO 2) NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, lithium tetraphenyl borate and imide .

For the purpose of improving the charge / discharge characteristics and the flame retardancy, the electrolytic solution is preferably mixed with an organic solvent such as pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, Benzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, . In some cases, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride may be further added to impart nonflammability, or a carbon dioxide gas may be further added to improve high-temperature storage characteristics.

Hereinafter, the digraphitizable carbon particles of the present invention will be described in detail through preferred examples and comparative examples of the present invention.

The following examples and comparative examples are for illustrative purposes only and are not intended to limit the scope of the present invention.

Example  One

Phosphorous pentoxide was dispersed in solvent distilled water so as to be 5.0 wt% in the total composition as a crystal change material in the amorphous carbon precursor obtained by grinding in the form of petroleum coke powder, and then mixed and dried to obtain a dried product. Next, the dried material was heated at an initial temperature of 300 ° C. at a heating rate of 10 ° C./min, and then heated up to 900 ° C., and then heat-treated at 900 ° C. for 1 hour to prepare digraphitizable carbon particles.

Example  2

Phosphorous pentoxide as a crystal change material was dispersed in an amorphous carbon precursor obtained by pulverizing into a petroleum coke powder in a solvent distilled water so as to be 5.0% by weight in the total composition, mixed and dried to obtain a dried product. Next, the dried material was heated at an initial temperature of 500 ° C. at a heating rate of 10 ° C./min, and then heated up to 900 ° C., and then heat-treated at 900 ° C. for 1 hour to prepare digraphitizable carbon particles.

Example  3

Phosphorous pentoxide as a crystal change material was dispersed in an amorphous carbon precursor obtained by pulverizing into a petroleum coke powder in a solvent distilled water so as to be 5.0% by weight in the total composition, mixed and dried to obtain a dried product. Next, the dried material was heated at an initial temperature of 700 ° C. at a temperature increase rate of 10 ° C./min, and then heated up to 900 ° C., and then heat-treated at 900 ° C. for 1 hour to prepare digraphitizable carbon particles.

Comparative example  One

Phosphorous pentoxide as a crystal change material was dispersed in an amorphous carbon precursor obtained by pulverizing into a petroleum coke powder in a solvent distilled water so as to be 5.0% by weight in the total composition, mixed and dried to obtain a dried product. Next, the dried material was heated at an introduction temperature of 25 ° C. at a temperature rising rate of 10 ° C./min, and then heated up to 900 ° C., and then heat-treated at 900 ° C. for 1 hour to prepare digraphitizable carbon particles.

Experimental Example  One : Graphite  Pore distribution of carbon particles

The pore distribution of the digraphitizable carbon particles was confirmed by adsorption of nitrogen gas. The carbon particles of Examples and Comparative Examples were heat treated at a pressure of 10 mmHg at a temperature of 250 ° C. for 3 hours to desorb all the gases adsorbed on the surface. Then, pore distribution of 35 nm or less was analyzed by using a QSDFT (Quenched Solid Density Functional Therory) method for analyzing micro mesopores of amorphous carbon at 77 K with nitrogen, and the results are shown in Table 1 and FIG. 1. In this case, the fine pore ratio means a value obtained by dividing the pore volume A of 10 nm or less by the pore volume B value of 10 to 35 nm.

1 to 10 nm pore volume (cc / g) (A) 10 to 35 nm pore volume (cc / g) (B) Micropore Ratio (A / B) Example 1 2.01 × 10 ^-3 2.18 × 10 ^-3 0.92 Example 2 15.3 × 10 ^-3 1.33 × 10 ^-3 11.5 Example 3 3.47 × 10 ^-3 1.4 × 10 ^-3 2.47 Comparative example 0 6.2 × 10 ^-3 0

As shown in Table 1, unlike the comparative example, it can be seen that the digraphitizable carbon particles of Examples are formed with pores having a size of 1 to 10 nm.

Experimental Example  2: Lithium secondary battery Charging and discharging  Measure efficiency

Experiments were carried out in order to measure the charge / discharge efficiency of a lithium secondary battery to which the negative electrode active materials of the examples and comparative examples were applied.

First, the negative electrode plate was dissolved in 10% by weight of polyvinylidene fluoride as a binder in an N-methyl pyrrolidone solvent, and then mixed with 90% by weight of the negative electrode active material powders of Examples and Comparative Examples to make a slurry, and a Cu foil current collector. It was applied by casting on (coating), which was rolled by a roll press to prepare a negative electrode. The negative electrode plate thus prepared was dried in an oven at 120 ° C.

A coin-type lithium secondary battery was manufactured using lithium metal foil as a counter electrode and a prepared negative electrode active material electrode plate and using 1M LiPF 6 / ethylene carbonate / dimethyl carbonate as an electrolyte.

Then, after constant-current constant voltage charging at a rate of 5 hours (0.2C) under a room temperature (25 ° C) atmosphere, it was discharged at a rate of 5 hours (0.2C) until the end voltage of discharge reached 1.5V, and again charged under the same conditions. After 5 hours (0.2C) constant current constant voltage charging, and discharged until the end voltage reached 1.5V at a high rate (5.0C), the room temperature high rate output was measured. Then, after charging the constant current constant voltage at a rate of 5 hours (0.2C) under a low temperature (-20 ° C) atmosphere, the battery was discharged at a high rate (5.0C) until the end voltage of discharge reached 1.5V, and the low temperature high rate output was measured. It is shown in Table 2 below. The low temperature output is represented by Equation 1 below.

[Equation 1]

Low temperature discharge (%) Example 1 42 Example 2 59 Example 3 47 Comparative example 29

As shown in Table 2, it was confirmed that the digraphitizable carbon particles of Example showed a lower temperature output than the particles of the comparative example does not have fine pores of 1 ~ 10 nm size.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. . Accordingly, the true scope of the present invention should be determined by the following claims.

Claims (9)

Crystal change material is introduced, characterized in that the ratio (A / B) of the pore volume (A) of 1 to 10 nm size to the pore volume (B) of 10 to 35 nm size is present in the range of 0.5 to 15 Soft carbon particles.
The method of claim 1,
The pore volume of 1 to 10 nm size is 1.0 × 10 ^-3 to 5.0 × 10 ^-2 cc / g per particle weight, and the pore volume of 10 to 35 nm size is 0.5 × 10 ^-3 to 1.0 × 10 ⁻ per particle weight. Digraphitizable carbon particles, characterized in that in the range of ² cc / g.
The method of claim 1,
The crystal change material is a transition metal compound including manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), boron (B), aluminum (Al), gallium (Ga) Group 3, 4 and 5 elemental compounds, including indium (In), nitrogen (N), silicon (Si), phosphorus (P), arsenic (As), sodium (Na) potassium (Ka) magnesium (Mg A digraphitizable carbon particle comprising at least one element selected from the group consisting of alkali metal compounds or alkaline earth metal compounds comprising calcium (Ca).
The method of claim 3, wherein
The crystal change material is boron (B), phosphorus (P) or nitrogen (N) characterized in that the graphitizable carbon particles.
The method of claim 1,
The precursor precursor of the digraphitizable carbon particles is produced by at least one selected from the group consisting of petroleum coke, coal coke, coal pitch, petroleum pitch, mesophase pitch, mesocarbon microbeads and vinyl chloride resin Digraphitizable carbon particles.
The method of claim 1,
The crystal change material is a graphitizable carbon particles, characterized in that the introduction of 0.1 to 20% by weight based on the total weight of the particles.
A negative electrode mixture comprising a negative electrode active material consisting of the digraphitizable carbon particles of any one of claims 1 to 6.
The lithium secondary battery according to claim 7, wherein the negative electrode mixture comprises a negative electrode coated on a current collector.
Mixing a carbon precursor prepared from at least one selected from the group consisting of petroleum coke, coal coke, coal-based pitch, petroleum-based pitch, mesophase pitch, mesocarbon microbeads and vinyl chloride-based resin with a crystal change material to obtain a mixture ; And
Carbonizing the mixture at an initial temperature of 300 to 700 ° C .;
Method for producing a negative electrode active material for a lithium secondary battery comprising a.

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