KR101349066B1 - Anode active material comprising graphite particle with modified surface and litium secondary battery employed with the same - Google Patents

Abstract

The present invention relates to a surface-modified graphite particles, more specifically, the rough portion of the surface is removed by the continuous stress, the side reaction is reduced while maintaining a high degree of crystallinity, and the occlusion of lithium ions due to the formation of fine pores is easy It can be made, when used as a negative electrode active material of a lithium secondary battery relates to graphite particles that can greatly improve the output characteristics.
The graphite particles of the present invention can lower the surface roughness by continuous stress, can increase the specific surface area in a state where the crystallinity of the surface is kept high, and the output of the lithium secondary battery can be improved.

Description

Anode active material consisting of surface-modified graphite particles, and a lithium secondary battery comprising the same {ANODE ACTIVE MATERIAL COMPRISING GRAPHITE PARTICLE WITH MODIFIED SURFACE AND LITIUM SECONDARY BATTERY EMPLOYED WITH THE SAME}

The present invention relates to a surface-modified graphite particles, and more particularly, to remove coarse portions of the surface by continuous stress, thereby reducing side reactions, maintaining a high degree of crystallinity, reducing the resistance of the particles, and lithium ions due to the formation of fine pores. It can be easily occluded, when used as a negative electrode active material of a lithium secondary battery relates to graphite particles that can greatly improve the output characteristics.

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.

Among them, graphite has an excellent voltage flatness and is advantageously applied to a battery active material because it can provide a battery having excellent coulombic efficiency in the first cycle. Of the crystalline carbon, natural graphite, which has the most crystallinity, has the advantage of showing a discharge capacity almost equal to the theoretical capacity. However, graphite has a limit in increasing 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 the case of using graphite as the negative electrode active material, when the high crystallinity graphite is used, when the lithium insertion / desorption reaction on the side of the negative electrode active material becomes slow during rapid charging and discharging, the battery voltage rapidly reaches an upper limit or a lower limit. There is a problem of stopping further progression. In addition, when graphite having a high crystallinity is used, heat treatment must be performed at a high temperature or for a long time. Accordingly, an impurity phase that causes the structure of carbon to collapse or an irreversible reaction appears, and the crystallinity is lowered to improve the output characteristics. Efforts have also been made to increase the efficiency by increasing the surface area of the particles.

On the other hand, Japanese Laid-Open Patent Publication No. 2002-0029720 discloses a novel modified graphite particle that can be used as a negative electrode active material having excellent charge and discharge characteristics, in particular, the ratio between the average particle diameter and the BET specific surface area through surface modification using an air flow classifier. Graphite particles in a specific range are disclosed.

However, there is no mention of controlling the crystallinity of the graphite particles in the patent, and research on the negative electrode active material that can derive excellent output characteristics while maintaining the crystallinity of the particles is still insignificant.

^{1 -} The present inventors have found that the crystallinity of the graphite particles while still maintaining excellent output characteristics naegoja led to research, efforts result, the Raman peak intensity (I _d) and 1580 ~ 1620 cm in the range of 1300 ~ 1400 cm ^-1 in the spectrum When the graphite particles exhibiting a low intensity ratio I _d / I _g between the peak intensity (I _g ) in the range are applied as the negative electrode active material by the reduction of the surface roughness and the formation of fine pores, the output of the battery can be greatly improved. The present invention was completed by discovering.

Accordingly, an object of the present invention is to provide a graphite particle, a negative electrode mixture, and an electrochemical cell having high crystallinity and constant specific surface area and fine pores formed by surface modification.

In order to achieve the above object, the graphite particles of the present invention have a surface whose surface is modified with continuous stress, so that the peak intensity (I _d ) in the range of 1300 to 1400 cm ^{−1 and} the range of 1580 to 1620 cm ^{−1 in} the Raman spectral spectrum peak intensity (I _g) and in the intensity ratio I _d / I _g 0.01 to 0.2 range between, characterized in that the BET specific surface area of particles is represented by 3.0 ~ 10.0 m ² / g range.

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

The graphite particles of the present invention can lower the surface roughness by continuous stress, can increase the specific surface area in a state where the crystallinity of the surface is kept high, and the output of the lithium secondary battery can be improved. Therefore, the coating of the particles may be minimized and applied to the negative active material, and the charge and discharge efficiency may be excellent due to the reduction of side reactions, and thus may be widely used in the industry.

1 shows an SEM image of the surface modified graphite particles of the present invention.
Figure 2 is a graph showing the area distribution according to the pore size of the surface-modified graphite 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 surface-modified graphite particles of the present invention and an electrochemical cell (lithium secondary battery) including the same will be described in detail.

Surface modified graphite particles

Graphite particles of the present invention the surface is modified by a continuous stress, as measured by the Raman spectroscopic spectrum peak intensity in the range of 1300-1400 cm ^-1 (I _d) and 1580 ~ 1620 cm ^- peak intensity in the range from ¹ (I The strength ratio I _d / I _g between _g ) is in the range of 0.01 to 0.2.

In the Raman spectral spectrum, carbon having low crystallinity shows crystallinity close to amorphous carbon, so that the I _d / I _g value is large, whereas the graphite particles of the present invention exhibit higher crystallinity than general graphite particles. 1300-1400 peak (D band) in the range of ~ 1620 cm ^-1 and 1580 cm ^- the distinction between the peak (G band) in the range of ¹ is displayed clearly. The peak of the D band is due to the amorphous portion of the particle surface, and the peak of the G band is due to the crystalline portion. The 1300-1400 peak intensity (I _d) in the range of ~ 1620 cm ^-1 and 1580 cm ^- I intensity ratio between the peak intensity range (I _g) of _d ¹ / I _g may be less than or equal to 0.18 and more preferably .

In addition, the graphite particles of the present invention can remove the coarse portion of the surface by the continuous stress to reduce side reactions occurring on the surface, thereby improving the coulombic efficiency. The surface modification causes the graphite particles to have a BET specific surface area in the range of 3.0 to 10.0 m ² / g, preferably 4.0 to 7.0 m ² / g. The said BET specific surface area shall mean the specific surface area obtained by interpreting a nitrogen adsorption isotherm by the BET multipoint method in the Brunauer-Emmett-Teller (BET) method. When the BET specific surface area is less than the above range, it is difficult to improve the output characteristics. When the above BET specific surface area is exceeded, the influence of side reaction between the electrolyte and the graphite particles is increased, the irreversible capacity in the first cycle is large, the energy density is low, and the cathode There is a problem that a large amount of binder is required in the preparation of the.

On the other hand, the graphite particles of the present invention is a pore size of 2 nm or less appear in the range of 0.5 ~ 1.5 m ² / g. On the other hand, the pores of about 2 to 10 nm size are all clogged and do not exist, only micropores of 2 nm or less are formed in the pores of 10 nm or less. The fine pores can facilitate the entry and exit of lithium ions, thereby improving the input and output characteristics. As described above, the graphite particles of the present invention can improve the input / output characteristics by increasing the number of entrances and exits that are open toward the electrolyte of the negative electrode material when the lithium ions are doped or undoped.

In addition, the graphite particles of the present invention have a meso pore area having a pore size of 10 to 100 nm in the range of 1.0 to 4.0 m ² / g. The mesopores are pores of a size that is easy to occlude lithium, and when the high current is applied, they can move without resistance. When the ratio (A / B) of the mesopore area (A) of 10 to 100 nm in size to the micropore area (B) of 2 nm or less is present within the range of 1.0 to 4.5, the output characteristic is best, and preferably Is preferably in the range 1.5 to 3.0.

On the other hand, the average particle size D ₅₀ of the surface-modified graphite particles is preferably present in the range 10 ~ 50 ㎛. When the average particle size is less than the above range, the specific surface area of the graphite particles becomes too large, which causes problems such as clogging of the filter due to agglomeration of the negative electrode active material and decrease in stability due to an increase in slurry viscosity. And the charge / discharge capacity of the battery is lowered.

Method for producing surface modified graphite particles

The graphite particles of the present invention are prepared through surface modification of graphite, and in particular, the graphite particles whose surface is modified by continuous stress may be prepared by coating a carbon precursor on graphite.

Natural graphite, artificial graphite, and the like may be used as the graphite, but may be used by mixing them. As the raw material of the artificial graphite, carbides of resins and the like may be used, but the present invention is not limited thereto. Any material capable of graphitizing may be used without particular limitation.

The graphite may be used regardless of the shape of ordinary plate graphite, spherical graphite, fibrous graphite, and the like, and it is preferable to use spherical graphite. The spherical graphite may be prepared by mechanical grinding or chemical methods of the conventional plate-like graphite. In particular, the mechanical grinding is 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. It can be carried out by milling using. 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.

Although it is suggested that spherical graphite can be used as a preferable example of the graphite, ordinary plate-like graphite or fibrous graphite may be used without spherical formation.

In addition, although the coating described later may be performed after the spheroidization, it may be spherical after the coating process described later regardless of the shape of the graphite.

Carbon precursors coated on the graphite include petroleum pitch, coal pitch, mesophase pitch, coal tar pitch, heat treatment pitch, vinyl chloride resin, vinyl polymer, aromatic hydrocarbon, nitrogen ring compound, sulfur ring compound, coal liquefied oil Coal-based heavy oil, DC-based heavy oil such as asphaltene, petroleum-based heavy oil such as naphtha tar produced by thermal decomposition of crude oil, naphtha and the like, cracked heavy oil and the like can be used.

In the coating process, the carbon precursor is preferably used in an amount of 1 to 25 parts by weight relative to graphite, in consideration of a modification effect on the graphite surface.

In addition, the coating may be performed using a coater for convective coating, tumbler, adhesive coating, or shear coating. The coating may be performed in a dry process or a wet process, or a combination of dry and wet processes. In the coating process, the degree of surface modification of particles, mesopores and fine particles may be changed by changing the coating speed, pressure, time, temperature, and dosage. The area of the pores can be adjusted.

Through the coating process, the graphite particles whose surface is modified with continuous stress are smoothed by removing rough parts on the graphite surface by friction and shear stress, lowering the total specific surface area and removing the empty space inside each of the granulated particles. As a result, the filling density can be improved to improve the initial charging and discharging efficiency, and the binder can be present between the graphite particles during the production of the electrode plate, thereby increasing the adhesive force, thereby improving the life characteristics.

The graphite particles of the present invention may be manufactured as a negative electrode active material through heat treatment, and the heat treatment process is preferably performed at 1,000 ° C. or higher, preferably 1,200 to 1,500 ° C. If the heat treatment temperature is less than 1,000 ° C., the removal of impurities is insufficient. It may also be carried out under vacuum or inert atmosphere so as to prevent oxidation of the carbon component, for example under nitrogen or argon atmosphere.

Although the heat treatment is performed after the coating process, the heat treatment may be performed at a lower temperature than the heat treatment temperature before the coating process, and then further heat treatment at the heat treatment temperature after the coating process.

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, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, 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 NMP to prepare a slurry, coating the same on a current collector, and drying and rolling.

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 collector, fine unevenness can be formed on the surface to enhance the bonding force of the negative electrode active material, and it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams and nonwoven fabrics.

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 a single process may be used. Other methods such as die casting, comma coating, and screen printing may be employed, or they may be formed on a separate substrate and then joined to the current collector by a pressing or lamination method. Drying of the paste applied on the current collector is preferably performed in a vacuum oven at 50 to 200 DEG C for 12 to 72 hours.

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 , Cu ₂ VO ₇ and the like; 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 the present invention is 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.

Examples of the inorganic solid electrolyte include 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 , Nitrides, halides and sulfates of Li such as Li ₄ SiO ₄ -LiI-LiOH and Li ₃ PO ₄ -Li ₂ S-SiS ₂ 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 graphite particles of the present invention will be described in detail with reference to preferred embodiments of the present invention.

The following examples are only for illustrating the present invention, but the scope of the present invention is not limited to the following examples.

Example  One

The spheroidized graphite particles were subjected to surface modification using 10 parts by weight of petroleum pitch relative to 100 parts by weight of graphite. The coating was performed for 1 minute at a linear speed of 30 rpm using a convective coater. The coating was heated at 25 ° C. at a temperature increase rate of 10 ° C./min, heated to 1500 ° C., and then heat-treated at 1500 ° C. for 1 hour to obtain surface-modified graphite particles.

Example  2

The spheroidized graphite particles were surface modified using 10 parts by weight of petroleum-based pitch with respect to 100 parts by weight of graphite. The coating was performed for 5 minutes at a linear speed of 30 rpm using a convective coater. The coating was heated at 25 ° C. at a temperature increase rate of 10 ° C./min, heated to 1500 ° C., and then heat-treated at 1500 ° C. for 1 hour to obtain surface-modified graphite particles.

Example  3

The spheroidized graphite particles were surface modified using 10 parts by weight of petroleum-based pitch with respect to 100 parts by weight of graphite. The coating was performed for 10 minutes at a linear speed of 30 rpm using a convective coater. The coating was heated at 25 ° C. at a temperature increase rate of 10 ° C./min, heated to 1500 ° C., and then heat-treated at 1500 ° C. for 1 hour to obtain surface-modified graphite particles.

Example  4

The spheroidized graphite particles were surface modified using 10 parts by weight of petroleum-based pitch with respect to 100 parts by weight of graphite. The coating was done for 20 minutes at a linear speed of 30 rpm using a convective coater. The coating was heated at 25 ° C. at a temperature increase rate of 10 ° C./min, heated to 1500 ° C., and then heat-treated at 1500 ° C. for 1 hour to obtain surface-modified graphite particles.

Comparative Example  One

The spheroidized graphite particles were heated at a temperature increase rate of 10 ° C./min at 25 ° C. without a coating process, and heated to 1500 ° C., and then heat-treated at 1500 ° C. for 1 hour to obtain surface modified graphite particles.

Experimental Example  1: Raman spectrum of graphite particles

The Raman spectra of the graphite particles prepared in Examples and Comparative Examples were measured using an argon ion laser (wavelength λ = 514 nm). In addition, the area of mesopores and micropores was confirmed using a nitrogen gas adsorption method. The graphite 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. Afterwards, the area of mesopores and micropores was measured using NLDFT (Non-Local Density Functional Therory) method, which was assumed to be carbon slit pores at 77K. The results are shown in Table 1 below.

Raman (I _d / I _g ) BET (m ² / g) Mesopore area (m ² / g) (A) Micropore Area (m ² / g) (B) A / B ratio Example 1 0.10 5.1 2.2 1.0 2.2 Example 2 0.12 4.8 2.2 0.9 2.4 Example 3 0.17 4.7 2.0 0.8 2.5 Example 4 0.19 4.5 1.6 0.8 2.0 Comparative Example 1 0.35 3.5 0.6 0.5 1.2

For example particles embodiment, as shown in Table 1, the strength of between 1300 ~ 1400cm peak intensity in the range of ^-1 (I _d) and 1580 ~ (I _g) peak intensity in the range of 1620 cm ^-1 I ratio _d / When I _g was confirmed to be 0.10 to 0.19, it was confirmed that the surface crystallinity of the surface-modified graphite particles was kept high.

In addition, it was confirmed that the ratio (A / B) of mesopores to the micropore area exists in the range of 2.0 to 2.5.

And the SEM photograph of the graphite particles (example) prepared in Example 1 is shown in FIG. As shown in the photograph, it was confirmed that the rough portion existing on the surface of the graphite particles was removed by the above process and exhibited the shape of smooth particles.

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

An experiment was conducted as follows to measure the charge and discharge efficiency of the lithium secondary battery to which the graphite particles of the examples and the comparative example were applied.

First, the negative electrode plate is dissolved in 10% by weight of polyvinylidene fluoride as a binder in a solvent of N-methyl pyrrolidone, and then mixed with 90% by weight of graphite particles of Examples and Comparative Examples to make a slurry, and copper (Cu) foil The current collector was cast (coated) and applied, and 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 lithium metal foil was used as a negative electrode active material electrode and a counter electrode, and 1M LiPF ₆ / ethylene carbonate / dimethyl carbonate as an electrolyte was used to produce a coin type lithium secondary battery.

The battery was charged at a constant current and a constant voltage at a rate of 5 hours (0.2 C) at room temperature (25 캜), discharged at a rate of 5 hours (0.2 C) until the discharge end voltage reached 1.5 V, and charged again under the same conditions. In addition, after measuring constant current constant voltage at a rate of 5 hours (0.2C) at 25 ° C. in a 25 ° C. atmosphere to measure high output characteristics, the battery was discharged at a high rate (5.0C) until the discharge end voltage reached 1.5V, and high temperature output was measured at room temperature.

The initial capacity and output characteristics of the lithium secondary battery prepared with the negative electrode active materials of the Examples and Comparative Examples are shown in Table 2 below.

Initial capacity (mAh / ml) Output characteristic (5C / 0.2C) (%) Example 1 360 75 Example 2 362 72 Example 3 363 69 Example 4 360 66 Comparative Example 1 350 58

As shown in Table 2, the initial capacity of the Example was higher than that of the Comparative Example, and the output characteristics of the Example were also greater than the output characteristics of the Comparative Example. Therefore, it can be expected that the difference in output per volume will be greater in large cells than in small cells.

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 (8)

The surface of the graphite particle is modified by a continuous stress, the Raman intensity ratio between the spectrum 1300 ~ 1400cm ^-1 peak intensity (I _d) in the range of 1580-1620 and the peak intensity range (I _g) of the cm ^-1 I _d / I _g is in the range of 0.01 to 0.2, BET specific surface area of the particles is in the range of 3.0 to 10.0 m ² / g,
Graphite particles, characterized in that the ratio (A / B) of the meso pore area (A) of 10 to 100 nm to the micropore area (B) of the size of 2 nm or less is present in the range of 1.0 to 4.5.
delete The method of claim 1,
Graphite particles, characterized in that the fine pore area of 2 nm or less appear in the range of 0.5 ~ 1.5 m ² / g.
The method of claim 1,
Graphite particles, characterized in that the meso pore area of 10 ~ 100 nm in the range of 1.0 ~ 4.0 m ² / g.
The method of claim 1,
Graphite particles, characterized in that the surface of the graphite particles are modified through the coating process of the carbon precursor.
The method of claim 5, wherein
The coating is graphite particles, characterized in that consisting of a coater for convective coating (Convective), rotary coating (Tumbler), adhesion coating (Impaction) or shear coating (High Shear).
A negative electrode mixture comprising a negative electrode active material made of the graphite particles of any one of claims 1 and 3 to 6.
The lithium secondary battery according to claim 7, wherein the negative electrode mixture comprises a negative electrode coated on a current collector.

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