KR101631735B1 - Anode active material for lithium secondary battery and preparation method of thereof - Google Patents

Abstract

And an amorphous carbon coating layer is formed on the carbon composite material in which the spherical or elliptic carbon-based particles and the scaly conductive material are combined. The present invention also relates to a method for producing the negative electrode material for a lithium secondary battery. By using the negative electrode material of the present invention for a negative electrode of a lithium secondary battery, it is possible not only to improve the conductivity, but also to suppress the reactivity between the negative electrode material and the electrolyte solution, thereby improving the discharge capacity, efficiency and life characteristics.

Description

TECHNICAL FIELD The present invention relates to an anode material for a lithium secondary battery, and an anode material for a lithium secondary battery,

The present invention relates to an anode material comprising an amorphous carbon coating layer on a carbon composite material formed by combining spherical or elliptic carbon-based particles and a scaly conductive material, and a method for producing the same.

BACKGROUND ART [0002] With the recent development of the information communication industry, as electronic devices have become smaller, lighter, thinner, and portable, there is a growing demand for higher energy density of batteries used as power sources for such electronic devices. Lithium secondary batteries are the ones that can best meet these demands, and researches on them are actively under way.

The anode material of the lithium secondary battery is mainly composed of a carbon-based material, and the carbon-based materials include crystalline carbon and amorphous carbon. Crystalline carbon is represented by graphite carbon such as natural graphite and artificial graphite. Amorphous carbon is a mixture of non-graphitizable carbons (hard carbons) obtained by carbonizing a polymer resin and heat- And graphitizable carbons (soft carbons).

Generally, soft carbons are produced by applying heat of 1000 degrees Celsius to the coke, which is a byproduct of crude oil refining process. Unlike conventional graphite or cemented carbonaceous materials, the output is high and the time required for charging short.

On the other hand, hard carbons can be produced by carbonizing materials such as resins, thermosetting polymers, wood, and the like. When such cured carbon is used as a cathode material for a lithium secondary battery, the reversible capacity is as high as 400 mAh / g or more due to the microcavity, but the initial efficiency is as small as about 70%, so that it is irreversibly consumed when used as an electrode of a lithium secondary battery There is a disadvantage in that the amount of lithium is large.

This irreversible part is caused by the fact that the electrolyte is decomposed at the surface of the electrode during charging to form a solid electrolyte interphase (SEI), which is a surface coating, and a case where lithium stored in the carbon particles during charging is discharged It may be due to the fact that In the case of the former, it is known that the generation of the surface coating is a major irreversible cause.

Accordingly, various methods have been tried to suppress the generation of the surface coating.

For example, there is a method of coating cured carbon using a pitch or resin. However, in this case, there is a problem that the particles stick to each other due to the pitch or the resin, and oxidative stabilization is required to overcome this problem. However, if the oxidation stabilization process is performed, the coating process becomes complicated and the irreversible capacity increases.

Accordingly, development of a negative electrode material capable of replacing a conventional negative electrode material and capable of improving discharge capacity, efficiency and lifetime characteristics when applied to a lithium secondary battery is required.

An object of the present invention is to provide an anode material for a lithium secondary battery which not only has improved conductivity, but also has excellent output characteristics and rate characteristics, and a method for producing the same.

In order to solve the above problems, the present invention provides an anode material comprising an amorphous carbon coating layer on a carbon composite material formed by combining spherical or elliptic carbon-based particles and a scaly conductive material.

The negative electrode material of the present invention can be used for a current collector and a negative electrode including an anode material on at least one side of the current collector. The present invention can provide a lithium secondary battery including the positive electrode, the negative electrode, and the separator interposed between the positive electrode and the negative electrode using such a negative electrode.

The present invention also relates to a method for producing a carbon composite material, which comprises: mixing a spherical or elliptic carbon-based particle and a scaly conductive material to form a carbon composite; And coating the carbon composite with amorphous carbon and heat-treating the carbon composite to form an amorphous carbon coating layer on the carbon composite.

The use of the negative electrode material of the present invention including the amorphous carbon coating layer on the carbon composite material in which the spherical or elliptic carbon-based particles and the scaly conductive material are combined can be used for the lithium secondary battery to improve the conductivity, The discharge capacity, efficiency and lifetime characteristics can be further improved.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate exemplary embodiments of the invention and, together with the description of the invention, It should not be construed as limited.
1 is a view showing a process for manufacturing a pitch or needle coke and a surface-coated softened carbon according to an embodiment of the present invention.
FIG. 2 is a view illustrating a method for producing a carbon composite material including an amorphous carbon coating layer using spherical carbon-based particles according to an embodiment of the present invention.
3 is a view showing a method for producing a carbon composite material including an amorphous carbon coating layer using elliptic carbon particles (pitch coke) according to an embodiment of the present invention.
4 and 5 are SEM photographs of Comparative Example 1 and Example 2 according to Experimental Example 1 of the present invention.
6 is a graph showing charge / discharge curves of the lithium secondary batteries of Example 4 and Comparative Example 4 according to Experimental Example 2 of the present invention.
7 is a graph showing the rate characteristics of lithium secondary batteries of Examples 3 and 4 and Comparative Examples 3 and 4 according to Experimental Example 3 of the present invention.
8 is a graph showing Raman characteristics for confirming the crystallinity of amorphous carbon of Example 2 and Comparative Example 2 according to Experimental Example 4 of the present invention.

Hereinafter, the present invention will be described in detail in order to facilitate understanding of the present invention.

The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and the inventor may appropriately define the concept of the term in order to best describe its invention It should be construed as meaning and concept consistent with the technical idea of the present invention.

The anode material for a lithium secondary battery of the present invention is characterized in that it includes an amorphous carbon coating layer on a carbon composite material in which spherical or elliptic carbon-based particles and a scaly conductive material are combined.

According to one embodiment of the present invention, a carbon composite material having improved conductivity characteristics can be obtained by combining spherical or elliptic carbon-based particles and a scaly conductive material, and an amorphous carbon coating layer is formed on the carbon composite material, The initial efficiency can be ensured by minimizing the edge surface of the highly reactive scaly conductive material and the desorption of the carbon-based particles and the scaly conductive material can be prevented.

As the spherical or ellipsoidal carbon-based particles used in one embodiment of the present invention, a carbonaceous material capable of intercalating and deintercalating lithium ions can be used. For example, the spherical carbon-based particles may include spherical natural graphite, and the elliptic carbon-based particles may include soft carbons, artificial graphite, pitch cokes, and soft carbon coated carbon on the surface, artificial graphite Or pitch coke, or a mixture of two or more thereof.

In one embodiment of the present invention, the pitch coke used as an elliptical carbon material is formed by using a carbon precursor such as a coal tar, a coal tar pitch, a petroleum pitch or a heavy oil, The soft carbon and the artificial graphite can be respectively produced by heat treating the pitch coke thus prepared as a raw material. Such a preparation method can be produced by a conventional method known in the art.

For example, as shown in Fig. 1, a coal tar pitch obtained by fractional distillation from coal is coked at, for example, about 400 ° C to 600 ° C to obtain a green coke Thereafter, the obtained green coke is baked by heat treatment at about 1000 ° C to 1500 ° C to obtain pitch or needle coke, which is elliptic carbon-based particles used in the present invention. Further, the obtained pitch or needle coke may be further subjected to heat treatment at about 1000 ° C to 1500 ° C to obtain softened carbon.

According to an embodiment of the present invention, the pitch cokes are surface-coated with, for example, a pitch or a polymer such as a phenolic resin, a crosslinked acrylate or the like, and then heat-treated at about 1100 ° C. to 1400 ° C., Carbon can also be used.

The softened carbon thus produced is pulverized to form indefinite particles, and then the pulverized amorphous particles are subjected to graphitization treatment at a temperature of 1000 ° C to 3000 ° C, preferably 1400 ° C to 2500 ° C to obtain artificial graphite .

The elliptic carbon-based particles prepared as described above may be uniform or non-uniform, and they may be pulverized to a desired size by a milling method to obtain particles having a desired size. The elliptic carbon-based particles may have various shapes such as, for example, a disk shape, a sweet potato shape, a rice shape, a capsule shape, and the like. Since the elliptic carbon-based particles of the above-mentioned shape have a high yield in the process, they are advantageous in terms of the overall manufacturing process including the grinding process. In addition, soft carbon or artificial graphite may be more advantageous in an extrusion process after electrode coating.

The length of the major axis of the elliptic carbon-based particles is not particularly limited, but may be, for example, from 5 탆 to 30 탆, preferably from 15 탆 to 25 탆.

 If the major axis length of the elliptic carbon-based particles is less than 5 탆, the initial efficiency of the battery may decrease due to the increase of the specific surface area, and the battery performance may deteriorate. If the length exceeds 30 탆, And the capacity retention rate may be low because the filling density is low.

In addition, the elliptic carbon-based particles according to an embodiment of the present invention have a specific surface area of 6 to 10 m 2 / g and have a compression density of 1.3 g / cc to 1.6 g / cc under a pressure of 4 kN to 8 kN But it is not limited thereto.

In general, it is preferable to remove various impurities in the carbon precursor to uniformly grow crystals of the carbon-based particles obtained as described above. The amount of the quinoline insoluble component in the pitch may be controlled by dissolving the carbon precursor in an organic solvent such as tetrahydrofuran, quinoline, benzene, toluene, or the like, and removing the insoluble component in the organic solvent. To remove impurities of macromolecular mass from the tar.

If impurities are contained in the pitch, the soft carbon and the graphitization process may not be smoothly performed.

Also, according to one embodiment of the present invention, spherical carbon-based particles may be included.

According to an embodiment of the present invention, the spherical carbon-based particles may be in a uniform or non-uniform shape, and may include a full spherical shape to a roughly irregular shape.

The spherical carbon-based particles may be spherical natural graphite, and the spherical carbon-based particles may have an average particle diameter (D ₅₀ ) of 5 탆 to 30 탆. When the average particle diameter (D ₅₀ ) of the spherical carbon-based particles is less than 5 μm, the initial efficiency of the battery may decrease due to the increase of the specific surface area, and the battery performance may be deteriorated. When the average particle diameter (D ₅₀ ) They may penetrate through the separator to cause a short circuit, and the capacity retention rate may be low because the filling density is low.

The average particle size of the spherical carbon-based particles according to one embodiment of the present invention can be measured using, for example, a laser diffraction method. The laser diffraction method generally enables measurement of a particle diameter of several millimeters from a submicron region, resulting in high reproducibility and high degradability. The average particle diameter (D ₅₀ ) of the spherical carbon-based particles can be defined as the particle diameter based on 50% of the particle diameter distribution.

The method for measuring the average particle diameter (D ₅₀ ) of the spherical carbon-based particles according to an embodiment of the present invention may be, for example, a method of dispersing spherical natural graphite, spherical carbon-based particles, in a solution of ethanol / water, The sample was introduced into a particle size measuring apparatus (for example, Microtrac MT 3000), and an ultrasonic wave of about 28 kHz was irradiated at an output of 60 W, and then an average particle diameter (D ₅₀ ) of 50% of the particle diameter distribution in the measuring apparatus was calculated have.

The spherical carbon-based particles satisfying the range of the present invention can be obtained by sphering natural graphite for about 30 to 100 m / sec for 10 to 30 minutes, for example, but are not limited thereto.

According to an embodiment of the present invention, the spherical carbon-based particles preferably have a specific surface area (BET-SSA) of 2 m 2 / g to 8 m 2 / g. If the specific surface area of the spherical carbon-based particles is less than 2 m < 2 > / g, the adhesion between electrodes may deteriorate. If the specific surface area exceeds 8 m2 / g, the initial irreversible capacity not.

According to an embodiment of the present invention, the specific surface area may be measured by a BET (Brunauer-Emmett-Teller; BET) method. For example, it can be measured by a BET 6-point method by a nitrogen gas adsorption / distribution method using a porosimetry analyzer (Bell Japan Inc, Belsorp-II mini).

The scaly graphite material used in the present invention is preferably scaly natural graphite or artificial graphite, and the fine particles remaining in the carbon-based particle process are collected and classified into, for example, flake type Or may be obtained by pulverizing it in a mechanized manner, but the present invention is not limited thereto.

The scaly graphical material has a major axis length of 5 to 7 탆, preferably 5 to 6 탆, a specific surface area of 7 m 2 / g to 10 m 2 / g, a compression density of 1.5 g / cc to 1.8 g / cc.

A method for coating a carbon composite material obtained by complexing spherical carbon particles and a scaly conductive material according to an embodiment of the present invention with amorphous carbon is shown in FIG. 2, A method of coating the composite with amorphous carbon is shown in Fig.

Specifically, the method for manufacturing an anode material according to an embodiment of the present invention includes: forming a carbon composite material by mixing spherical or elliptic carbon-based particles and a scaly conductive material; And coating the carbon composite with amorphous carbon and heat-treating the carbon composite to form an amorphous carbon coating layer on the carbon composite.

In one embodiment of the present invention, the mixing ratio of the spherical or elliptic carbon-based particles to the scaly conductive material is 75 to 95 parts by weight: 5 to 25 parts by weight, preferably 80 to 90 parts by weight: 10 to 20 parts by weight . If the weight of the scaly conductive material exceeds the above range, the spherical or elliptic carbon-based particles may be excessively covered to increase the specific surface area, thereby increasing the decomposition reaction of the electrolytic solution. If the weight is less than the above range, The composite is not entirely composed of the carbon-based particles, and the conductivity may be lowered.

The mixing method for preparing the carbon composite material may be simple mixing or mechanical mixing using a conventional method known in the art. For example, a carbon composite can be formed by simply mixing with a motor or by rotating a ball or a ball mill at a rotation speed of 100 to 1000 rpm to mechanically apply compressive stress.

As described above, by compositing spherical or elliptic carbon-based particles with a scaly conductive material, a carbon composite having improved conductivity characteristics can be obtained.

The mixture ratio of the carbon composite material and the amorphous carbon is 90 to 99 parts by weight, 1 to 10 parts by weight, preferably 90 to 95 parts by weight, and 5 to 10 parts by weight. When the weight of the amorphous carbon is less than 1 part by weight, the total coating amount is insufficient, so that the bonding between the carbon-based particles and the scaly conductive material is not good or the entire coating is insufficient, If the amount is more than 10 parts by weight, there may be a problem that the powder obtained in the process of carbonization after the carbonization is aggregated due to entanglement between the particles.

The amorphous carbon is preferably a coal-based pitch or a petroleum pitch.

In the present invention, the coating step comprises mixing the carbon-based complex and the amorphous carbon in an organic solvent selected from the group consisting of ethanol, acetone, tetrahydrofuran, pyridine, quinoline and benzoquinone, for example, using a motar Or by mixing them using a ball milling, inducing, mixer or motar and coating them under an inert atmosphere at a temperature of 1000 ° C. to 2000 ° C., preferably 1000 ° C. to 1500 ° C. The amorphous carbon coating layer can be formed on the carbon composite as shown in Fig. 2 by heat treatment for 5 to 10 hours. In the heat treatment process, when the temperature is lower than 1000 캜, residual organic matter or inorganic matters may remain, which may increase the resistance of the coating layer and can not form a desirable SEI layer, have. If the temperature exceeds 2000 ° C, there may be a problem such as an increase in the process ratio.

The amorphous carbon coating layer formed as described above may be uniformly or non-uniformly coated on the composite body in which the spherical or elliptic carbon-based particles and the scaly conductive material are combined.

The thickness of the amorphous carbon coating layer is not particularly limited, but may be, for example, 10 nm to 50 nm, preferably 10 nm to 20 nm.

As described above, the amorphous carbon is coated on the spherical or ellipsoidal carbon-based composite containing the scaly conductive material to minimize the edge surface of the scaly conductive material highly reactive with the electrolytic solution, thereby securing the initial efficiency , It is possible to prevent desorption of the spherical or elliptic carbon-based particles and the flaky graphite conductive material.

The negative electrode material of the present invention thus manufactured can be manufactured into a negative electrode according to a manufacturing method commonly used in the art. Also, the anode according to the present invention can be produced by a conventional method in the art, like the cathode.

For example, it is possible to prepare a slurry by mixing and stirring a binder and a solvent, a conductive material and a dispersant, if necessary, to the cathode material and the anode material of the present invention, applying the mixture to a current collector, and compressing the electrode material.

The binder used in the present invention is a binder used for binding a positive electrode material and an anode material particle to form a molded body, and is preferably made of polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), styrene-butadiene rubber -butadiene rubber (SBR) or the like is used. The binder may be any one selected from the group consisting of a solvent-based binder represented by polyvinylidene (PVdF) (that is, a binder containing an organic solvent as a solvent), acrylonitrile-butadiene rubber, styrene-butadiene rubber, Or an aqueous binder (that is, a binder comprising water as a solvent), which is a mixture of two or more of these. Unlike solvent binders, water based binders are economical, environmentally friendly, harmless to the health of workers, and have a greater binding effect than solvent based binders, thereby increasing the proportion of active materials of the same type, thereby enabling high capacity. The aqueous binder is preferably a styrene-butadiene rubber.

As the cathode active material, a lithium-containing transition metal oxide may be preferably used. For example, Li _x CoO ₂ (0.5 <x <1.3), Li _x NiO ₂ (0.5 <x <1.3), Li _x MnO _{2 x <1.3), Li x Mn} 2 O 4 (0.5 <x <1.3), Li x (Ni a Co b Mn c) O 2 (0.5 <x <1.3, 0 <a <1, 0 <b <1, Li _x Co _{1- y} Mn _y O ₂ (where 0 <c <1, a + b + c = 1), Li _x Ni _1-y Co _y O ₂ 0.5 <x <1.3, 0≤y < 1), Li x Ni 1 -y Mn y O 2 (0.5 <x <1.3, O≤y <1), Li x (Ni a Co b Mn c) O 4 ( (0.5 <x <1.3, 0 <a <2, 0 <b <2, 0 <c <2, a + b + c = 2), Li _x Mn _{2 -z} Ni _z O ₄ (0.5 <x <1.3, 0 <z <2), Li _x CoPO ₄ (0.5 <x <1.3) and Li _x FePO ₄ (0.5 <z <2), Li _x Mn _{2 -z} Co _z O ₄ x < 1.3), or a mixture of two or more thereof. The lithium-containing transition metal oxide may be coated with a metal such as aluminum (Al) or a metal oxide. In addition to the lithium-containing transition metal oxide, sulfide, selenide and halide may also be used.

When the electrode is manufactured, a lithium secondary battery having a separator and an electrolyte interposed between the positive electrode and the negative electrode, which is conventionally used in the art, can be manufactured using the electrode.

In the electrolyte used in the present invention, the lithium salt that may be included as the electrolyte may be any of those conventionally used in an electrolyte for a lithium secondary battery. For example, examples of the anion of the lithium salt include F ^- , Cl ^- , Br ^{- _{, I -, NO 3 -,}} N (CN) 2 -, BF 4 -, ClO 4 -, PF 6 -, (CF 3) 2 PF 4 -, (CF 3) 3 PF 3 -, (CF 3) 4 _{^{PF 2 -, (CF 3)}} 5 PF -, (CF 3) 6 P -, CF 3 SO 3 -, CF 3 CF 2 SO 3 -, (CF 3 SO 2) 2 N -, (FSO 2) 2 N _{^{-, CF 3 CF 2 (CF}} 3) 2 CO -, (CF 3 SO 2) 2 CH -, (SF 5) 3 C -, (CF 3 SO 2) 3 C -, CF 3 (CF 2) 7 SO ₃ ^- , CF ₃ CO ₂ ^- , CH ₃ CO ₂ ^- , SCN ^- and (CF ₃ CF ₂ SO ₂ ) ₂ N ^- .

As the organic solvent contained in the electrolytic solution used in the present invention, the organic solvent commonly used in the electrolyte for a lithium secondary battery can be used without limitation, and examples thereof include propylene carbonate (PC), ethylene carbonate (ethylene carbonate) EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl propyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxy Ethane, vinylene carbonate, sulfolane, gamma-butyrolactone, propylene sulfite, and tetrahydrofuran, or a mixture of two or more thereof. In particular, ethylene carbonate and propylene carbonate, which are cyclic carbonates in the carbonate-based organic solvent, can be preferably used because they have high permittivity as a high-viscosity organic solvent and dissociate the lithium salt in the electrolyte well. To such a cyclic carbonate, dimethyl carbonate and diethyl When a low viscosity, low dielectric constant linear carbonate such as carbonate is mixed in an appropriate ratio, an electrolyte having a high electric conductivity can be prepared, and thus it can be more preferably used.

Alternatively, the electrolytic solution stored in accordance with the present invention may further include an additive such as an overcharge inhibitor or the like contained in an ordinary electrolytic solution.

As the separator, a conventional porous polymer film conventionally used as a separator, for example, a polyolefin such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer and an ethylene / methacrylate copolymer A porous polymer film made of a high molecular weight polymer may be used alone or in a laminated manner, or a nonwoven fabric made of a conventional porous nonwoven fabric such as a glass fiber having a high melting point, a polyethylene terephthalate fiber or the like may be used. It is not.

The external shape of the lithium secondary battery of the present invention is not particularly limited, but may be a cylindrical shape, a square shape, a pouch shape, a coin shape, or the like using a can.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to examples. However, the embodiments according to the present invention may be modified into various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments of the present invention are provided to enable those skilled in the art to more fully understand the present invention.

Example

EXAMPLES The present invention will be further illustrated by the following examples and experimental examples, but the present invention is not limited by these examples and experimental examples.

&Lt; Preparation of negative electrode material &

Example  One

A coal tar pitch obtained by fractional distillation from coal was coked and then heat-treated at 550 ° C and then fired at 1400 ° C to have a major axis length of 10 μm to 12 μm and a specific surface area An elliptical pitch coke having a compression density of 1.3 g / cc was obtained under a pressure of 4 Kn / m 2 / g to 8 m 2 / g.

The elliptical pitch coke and the scaly graphite conductive material having a major axis length of 6 탆 were mixed at a ratio of 90 parts by weight and 10 parts by weight, respectively, and assembled by a mechanical method to obtain a carbon composite material.

The carbon composite thus obtained and the coal pitch were mixed at a ratio of 95 parts by weight: 5 parts by weight and coated by ball milling, followed by heat treatment at 1000 占 폚 in an Ar atmosphere to prepare an anode material having an average major axis length of 18 占 퐉 to 25 占 퐉 Respectively.

Example  2

By introducing the average particle diameter of 100 ㎛ a spherical natural graphite particle formation device (Nara Hybridization System, NHS-2 ), the rotor speed (rotor Speed) 65 m / sec 10 minutes sphering treatment, the average particle diameter (D ₅₀₎ 20 ㎛ , FWHM of 7.0 mu m, and BET specific surface area of 2.60 m &lt; 2 &gt; / g.

The prepared spherical natural graphite particles and a flaky graphite conductive material having an average major axis length of 6 탆 were mixed in a ratio of 90 parts by weight to 10 parts by weight and assembled by a mechanical method to obtain a carbon composite material.

The carbon composite thus obtained and the coal pitch were mixed at a ratio of 95 parts by weight: 5 parts by weight and coated by ball milling, followed by heat treatment at 1000 占 폚 in an Ar atmosphere to prepare an anode material having an average particle diameter of 18 占 퐉 to 25 占 퐉 .

Comparative Example  One

An anode material was prepared in the same manner as in Example 1, except that a coal-based pitch was coated on a pitch coke not mixed with a scaly conductive material.

Comparative Example  2

An anode material was prepared in the same manner as in Example 2, except that the carbon-based composite and the coal-based pitch were simply mixed at a ratio of 95 parts by weight and 5 parts by weight, respectively.

&Lt; Production of lithium secondary battery >

Example  3 and 4

SBR (styrene-butadiene rubber) as a binder, carboxy methyl cellulose (CMC) as a thickening agent, and acetylene black as a conductive material were mixed in a weight ratio of 95: 2: 2: 1 in the anode material obtained in Examples 1 and 2, And then mixed with water (H ₂ O) as a solvent to prepare a uniform negative electrode slurry. The prepared negative electrode slurry was coated on one side of the copper current collector to a thickness of 65 μm, dried and rolled, and then punched to a required size to prepare a negative electrode.

Ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 30:70, and LiPF ₆ was added to the non-aqueous electrolyte solvent to prepare a 1 M LiPF ₆ non-aqueous electrolyte.

Also, a lithium metal foil was used as a counter electrode, that is, an anode, a polyolefin separator was interposed between both electrodes, and the electrolyte solution was injected to prepare a coin-type lithium secondary battery.

Comparative Example  3 and 4

A coin-type lithium secondary battery was prepared in the same manner as in Examples 3 and 4 except that the negative electrode material prepared in Comparative Examples 1 and 2 was used.

Experimental Example  One

<SEM micrograph>

SEM micrographs of the negative electrode materials prepared in Comparative Examples 1 and 2 were confirmed, and the results are shown in FIGS. 4 and 5. FIG.

FIG. 4 is a SEM image of an anode material in which the scaly conductive material prepared in Comparative Example 1 is not combined, and FIG. 5 is an SEM image of an anode material in which scintillation conductive material is mixed with the spherical carbon- will be.

As can be seen from FIG. 5, in contrast to the SEM photograph of the negative electrode material of Comparative Example 1, it can be confirmed that the negative electrode material of Example 2 is composed of the scaly graphite composite in the carbon-based particles.

Experimental Example  2

<Charge-discharge characteristics>

Charge-discharge characteristics of the lithium secondary batteries obtained in Example 4 and Comparative Example 4 were measured. 6.

In the initial third cycle of the coin-type lithium secondary battery manufactured in Example 4 and Comparative Example 4, after charging at 0.1 constant current / constant voltage (CC / CV) up to 5 mV, the current reached 0.005 C at 5 mV Charging was carried out until this time. In the case of discharge, 1.0 V vs. Li / Li ^{&lt; + &} gt ;. The results are shown in Fig.

As can be seen from FIG. 6, compared with the lithium secondary battery of Comparative Example 4, in which the amorphous carbon coating layer was not coated on the carbon composite material and the anode material was simply mixed, the anode material containing the amorphous carbon coating layer on the carbon composite material It is confirmed that the rate characteristics of the lithium secondary battery of Example 4 including the lithium secondary battery are improved.

Experimental Example  3

<Evaluation of rate characteristics>

The rate characteristics of the lithium secondary batteries obtained in Examples 3 and 4 and Comparative Examples 3 and 4 were measured. The battery was charged to 5 mV at 0.1 C constant current / constant voltage (CC / CV), then discharged at constant current mode until the current reached 0.005 C at 5 mV and then terminated. The discharge of the battery was discharged at 0.1 C, 0.5 C, 1 C, 2 C, 5 C, and 10 C to 1.0 V. The results are shown in Fig.

As shown in FIG. 7, the lithium secondary batteries of Examples 3 and 4 of the present invention had similar standard capacities (%) up to 2C as compared with the lithium secondary batteries of Comparative Examples 1 and 2. However, As shown in Fig.

Experimental Example  4

Raman analysis was performed to confirm the crystallinity of the amorphous carbon coating layer coated on the carbon composite having the spherical carbon particles and the scaly conductive material as in Example 2 and Comparative Example 2. [ Raman analysis was carried out using a HN200 Nano Raman analyzer at a raman shift range of 1000 to 1800 cm ^-1 under a laser radiation condition of 532 nm. The results are shown in Fig.

As shown in Fig. 8, the carbon-based composite material of carbon-based particles and scaly conductive material, as in Example 2, exhibited a structural disorder-related D in the region of 1200 to 1500 cm ^-1 due to the amorphous carbon coated on the surface thereof It can be seen that the peak due to the vibration mode by 'D' and 'D' is broadly observed. [0097] As described above, unlike Comparative Example 2, the amorphous carbon It can be confirmed that a coating layer is formed.

Claims (26)

An amorphous carbon coating layer is formed on a carbon composite material in which spherical or elliptic carbon-based particles and scaly conductive material are entirely composed,
The mixing ratio of the spherical or elliptic carbon-based particles to the scaly conductive material is 75 to 95 parts by weight: 5 to 25 parts by weight,
Wherein the amorphous carbon coating layer has a thickness of 10 nm to 50 nm.
The method according to claim 1,
The elliptic carbon-based particles may be any one selected from the group consisting of soft carbon, artificial graphite, pitch cokes and soft carbon coated on the surface thereof, artificial graphite or pitch cokes, or a mixture of two or more thereof And the negative electrode material.
The method according to claim 1,
Wherein the spherical carbon-based particles are spherical natural graphite.
The method according to claim 1,
Wherein the elliptic carbon-based particles have a major axis length of 5 占 퐉 to 30 占 퐉.
The method according to claim 1,
Wherein the spherical carbon-based particles have an average particle diameter (D ₅₀ ) of 5 탆 to 30 탆.
The method according to claim 1,
Wherein the elliptic carbon-based particles have a specific surface area of 6 m 2 / g to 10 m 2 / g and a compression density of 1.3 g / cc to 1.6 g / cc under a pressure of 4 kN to 8 kN.
The method according to claim 1,
Wherein the spherical carbon-based particles have a specific surface area of 2 m 2 / g to 8 m 2 / g.
The method according to claim 1,
Wherein the elliptic carbon-based particles are disc-shaped, sweet potato-shaped, rice-shaped or capsule-shaped, and the spherical carbon-based particles are completely spherical or potato-shaped.
The method according to claim 1,
Wherein the scaly electrical conductor is scaly natural graphite or artificial graphite.
The method according to claim 1,
And the major axis length of the scaly conductive member is 5 占 퐉 to 7 占 퐉.
The method according to claim 1,
Wherein the scaly graphical material has a specific surface area of 7 m 2 / g to 10 m 2 / g and a compression density of 1.5 g / cc to 1.8 g / cc under a pressure of 4 kN to 8 kN.
delete The method according to claim 1,
Wherein the amorphous carbon is a coal-based pitch or a petroleum-based pitch.
And a negative electrode material according to any one of claims 1 to 11 and 13, formed on at least one surface of the current collector.
A lithium secondary battery comprising a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, wherein the negative electrode is the negative electrode according to claim 14.
Forming spherical or elliptic carbon-based particles and a scaly conductive material to form a carbon composite; And
Coating the carbon composite material with amorphous carbon and heat-treating the carbon composite material to form an amorphous carbon coating layer on the carbon composite material
Wherein the negative electrode material has an average particle diameter of not more than 100 nm.
17. The method of claim 16,
The elliptic carbon-based particles may be any one selected from the group consisting of soft carbons, artificial graphite, pitch cokes, and carbon-coated soft carbon, synthetic graphite or pitch cokes, or a mixture of two or more thereof And the negative electrode material is a negative electrode material.
18. The method of claim 17,
The pitch cokes are obtained by a heat treatment at 1000 ° C to 1500 ° C using a carbon precursor and the soft carbon and artificial graphite are obtained by heat treatment at 1000 ° C to 1500 ° C and 1000 ° C to 3000 ° C respectively using pitch coke Wherein the negative electrode material has an average particle diameter of not more than 100 nm.
17. The method of claim 16,
Wherein said spherical carbon-based particles are obtained by spheroidizing natural graphite in a sphering apparatus at a rotor speed of 30 m / sec to 100 m / sec for 10 min to 30 min.
17. The method of claim 16,
Wherein the scratched conductive material is scratched natural graphite or artificial graphite.
17. The method of claim 16,
Wherein the amorphous carbon is a coal-based pitch or a petroleum pitch.
delete 17. The method of claim 16,
Wherein the mixing ratio of the carbon composite material and the amorphous carbon is 90 to 99 parts by weight: 1 to 10 parts by weight.
17. The method of claim 16,
Wherein the coating is performed by ball milling, inducing, mixing with a mixer, or using a motar.
17. The method of claim 16,
Wherein the heat treatment is performed in a temperature range of 1000 ° C to 2000 ° C.
26. The method of claim 25,
Wherein the heat treatment is performed in a temperature range of 1000 ° C to 1500 ° C.

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