KR101460774B1 - Negative active material for rechargeable lithium battery, method of preparing the same, and negative electrode and rechargeable lithium battery including the same - Google Patents

Abstract

Core particles, and at least a portion of the lithium carbonate particles embedded in the surface of the core particles, wherein the core particles comprise crystalline spheroidal natural graphite particles, and crystalline spheroidal natural graphite and amorphous graphite particles on the surface of the crystalline spheroidal natural graphite And a composite layer comprising a carbon-coated coating layer, a method for producing the same, and a negative electrode and a lithium secondary battery comprising the same.

Description

TECHNICAL FIELD The present invention relates to a negative electrode active material for a lithium secondary battery, a method for producing the same, a negative electrode and a lithium secondary battery including the negative electrode active material, a method for producing the same,

A negative electrode active material for a lithium secondary battery, a production method thereof, and a negative electrode and a lithium secondary battery comprising the same.

The lithium secondary battery uses a material capable of reversibly inserting and desorbing lithium ions for the positive electrode and the negative electrode, and a carbon material is mainly used for the negative electrode active material. Generally, carbon materials are classified into crystalline graphite and amorphous carbon.

In recent years, the use of natural graphite has increased significantly in recent years. In particular, the use of graphite granulated in the form of spheres, or the surface of powders in which the graphite is spherically granulated is coated with amorphous carbon One powder is used as an anode active material.

Such an anode active material has a limited performance of the battery.

One embodiment is to provide a negative electrode active material for a lithium secondary battery excellent in cycle life characteristics and high rate charge / discharge characteristics.

Another embodiment is to provide a method for producing the negative electrode active material.

Another embodiment is to provide a negative electrode for a lithium secondary battery comprising the negative electrode active material.

Another embodiment is to provide a lithium secondary battery including the negative electrode.

One embodiment includes core particles; And at least a portion of the lithium carbonate particles embedded in the surface of the core particle, wherein the core particle is a crystalline sphincterized natural graphite particle, and a crystalline sphincterized natural graphite and a surface of the crystalline spheric natural graphite coated with an amorphous carbon Wherein the negative electrode active material is at least one selected from the group consisting of composite particles comprising a metal oxide and a coating layer formed on the negative electrode active material.

The lithium carbonate particles may be included in an amount of 0.1 to 20% by weight based on the total amount of the negative electrode active material.

The crystalline spherical natural graphite particles and the crystalline spherical natural graphite can be obtained by assembling the scaly natural graphite into a spherical shape, respectively.

When the core particle is the composite particle, the thickness of the coating layer may be 0.001 to 2 mu m.

When the core particle is the composite particle, the amorphous carbon may be at least one selected from soft carbon and hard carbon.

The soft carbon may be obtained from at least one selected from a coal-based pitch, a petroleum pitch, a polyvinyl chloride, a mesophase pitch, a tar, and a low molecular weight heavy oil. The hard carbon may be a polyvinyl alcohol resin, furfuryl alcohol ) Resin, triton, citric acid, stearic acid, sucrose, polyvinylidene fluoride, carboxymethylcellulose, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polyethylene, polypropylene, ethylene-propylene (EPDM), polyacrylic acid, polyacrylic sodium, polyacrylonitrile, glucose, gelatin, saccharides, phenolic resin, naphthalene resin, polyamide resin, furan resin, polyimide resin, cellulose resin, styrene resin, epoxy resin And a vinyl chloride resin.

Another embodiment provides a method for preparing a mixture comprising: mixing core particles and lithium acetate to obtain a mixture; Drying the mixture to obtain a dried product; And heat treating the dried material, wherein the core particles are composed of crystalline spheroidal natural graphite particles and a composite spherical natural graphite particle and a composite particle comprising a coating layer coated on the surface of the crystalline spheroidal natural graphite with amorphous carbon The negative electrode active material for a lithium secondary battery,

The lithium acetate may be mixed in an amount of 0.1 to 50 parts by weight based on 100 parts by weight of the core particles.

Another embodiment is a method of manufacturing a carbon nanotube, comprising: coating a surface of crystalline spheroidized natural graphite with an amorphous carbon precursor; Crystalline spherical natural graphite coated with the amorphous carbon precursor, and lithium acetate to obtain a mixture; Drying the mixture to obtain a dried product; And heat-treating the dried material. The present invention also provides a method for manufacturing a negative electrode active material for a lithium secondary battery.

Another embodiment provides a method for preparing a mixture comprising: mixing a crystalline spherical natural graphite, an amorphous carbon precursor, and lithium acetate to obtain a mixture; Drying the mixture to obtain a dried product; And heat-treating the dried material. The present invention also provides a method for manufacturing a negative electrode active material for a lithium secondary battery.

In another embodiment, there is provided a method for producing a carbon nanotube, comprising: preparing a solution including crystalline spheroidized natural graphite, amorphous carbon precursor, and a solvent; Ultrasonifying the solution; Drying the ultrasonic treated solution to prepare graphite-modified particles; Mixing the graphite-modified particles and lithium acetate to obtain a mixture; Drying the mixture to obtain a dried product; And heat-treating the dried material. The present invention also provides a method for manufacturing a negative electrode active material for a lithium secondary battery.

The lithium acetate may be mixed in an amount of 0.1 to 100 parts by weight based on 100 parts by weight of the crystalline spheroidal natural graphite.

Wherein the amorphous carbon precursor is at least one soft carbon feedstock selected from coal based pitches, petroleum pitches, polyvinyl chloride, mesophase pitches, tar and low molecular weight heavy oils; Polyvinyl alcohol resin, furfuryl alcohol resin, triton, citric acid, stearic acid, sucrose, polyvinylidene fluoride, carboxymethylcellulose, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone (EPDM), polyacrylic acid, polyacrylic acid, polyacrylonitrile, glucose, gelatin, saccharides, phenolic resins, naphthalene resins, polyamide resins, furan resins, poly At least one hard carbon raw material selected from a mid resin, a cellulose resin, a styrene resin, an epoxy resin and a vinyl chloride resin; Or a combination thereof.

The mixing can be performed by dry mixing, wet mixing, or a combination thereof.

The drying may be carried out by a natural drying method, a vacuum drying method, a spray drying method, or a combination thereof.

The drying may be performed by the spray drying method, and the spray drying method may be performed at a temperature of 100 to 300 ° C.

The heat treatment may be performed at a temperature of 200 to 2000 ° C.

The heat treatment may be carried out at a temperature of 200 to 2000 ° C for 1 minute to 10 hours, or to a temperature of 200 to 2000 ° C at a constant rate and then cooling without holding time.

Wherein the heat treatment is performed in an atmosphere containing nitrogen, air, oxygen, argon, or a mixed gas thereof; Or under vacuum.

The solvent may be selected from the group consisting of water, N-methylpyrrolidone, dimethylformamide, toluene, ethylene, dimethylacetamide, acetone, methyl ethyl ketone, hexane, tetrahydrofuran, decane, ethanol, methanol, isopropanol, . ≪ / RTI >

The crystalline spherical natural graphite may be contained in an amount of 0.1 to 200 parts by weight based on 100 parts by weight of the solvent.

The ultrasonic waves may be irradiated at a frequency of 10 to 40 kHz and a frequency of 50 to 1200 W for 0.1 to 30 minutes.

Another embodiment provides a negative electrode for a lithium secondary battery comprising the negative electrode active material.

Another embodiment further comprises: the cathode; anode; And a lithium secondary battery comprising the electrolyte.

The details of other embodiments are included in the detailed description below.

A lithium secondary battery having excellent initial charge / discharge efficiency, cycle life characteristics, and high rate charge / discharge characteristics can be realized.

Figure 1 is a thermogravimetric analysis (TGA) graph of the lithium acetate used in the examples.
2 is an X-ray diffraction pattern (XRD) graph of the negative electrode active material according to Example 1. Fig.
3A and 3B are scanning electron microscope (SEM) photographs of a low magnification and a high magnification of the negative electrode active material according to the fourth embodiment, respectively.
4A and 4B are scanning electron microscope (SEM) photographs of low magnification and high magnification of the negative electrode active material according to Example 5, respectively.
5A and 5B are scanning electron microscope (SEM) photographs of a low magnification and a high magnification of the negative electrode active material according to Example 6, respectively.
6A and 6B are scanning electron microscope (SEM) photographs of a low magnification and a high magnification of the negative electrode active material according to Example 8, respectively.
7A and 7B are scanning electron microscope (SEM) photographs of low magnification and high magnification of the negative electrode active material according to Comparative Example 1, respectively.
8A and 8B are scanning electron microscope (SEM) photographs of a low magnification and a high magnification of the negative electrode active material according to Comparative Example 2, respectively.
9A and 9B are scanning electron microscope (SEM) photographs of low magnification and high magnification of the negative electrode active material according to Comparative Example 5, respectively.
10A and 10B are scanning electron microscope (SEM) photographs of low magnification and high magnification of the negative electrode active material according to Comparative Example 3, respectively.
11 is a thermogravimetric analysis (TGA) graph of the negative electrode active material according to Example 2 and Comparative Example 1. Fig.
12 is a Raman spectrum analysis graph of the negative electrode active material according to Examples 6 and 7 and Comparative Example 2. FIG.
13 is a Raman spectrum analysis graph of the negative electrode active material according to Example 8 and Comparative Example 5. FIG.
14 is an X-ray diffraction pattern (XRD) graph of the negative electrode active material according to Examples 1 to 5 and Comparative Example 1. Fig.
15 is an X-ray diffraction pattern (XRD) graph of the negative electrode active material according to Examples 6 and 7 and Comparative Example 2. Fig.
16A and 16B are X-ray diffraction patterns (XRD) graphs of the negative electrode active material according to Example 8 and Comparative Example 5. Fig.

Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited thereto, and the present invention is only defined by the scope of the following claims.

The negative electrode active material for a lithium secondary battery according to an embodiment provides core particles surface-modified by lithium carbonate particles. Specifically, the negative electrode active material may include core particles and at least a part of the lithium carbonate particles embedded in the surface of the core particles. In other words, lithium carbonate particles are uniformly coated on the surface of the core particles, and at least a part of the lithium carbonate particles are embedded in the surface of the core particles. The fact that it is embedded in the surface of the core particle means that at least a part of the lithium carbonate particle is inserted into the core particle. When a negative electrode active material having a structure in which at least a portion of the lithium carbonate particles are embedded in the surface of the core particles is used, a lithium secondary battery having excellent cycle life characteristics and high rate charge / discharge characteristics can be realized.

The core particles may be at least one selected from the group consisting of crystalline spheroidal natural graphite particles and composite particles comprising crystalline spheroidal natural graphite and a coating layer coated with amorphous carbon on the surface of the crystalline spheroidal natural graphite.

The crystalline spherical natural graphite particles and the crystalline spherical natural graphite can be obtained by assembling the scaly natural graphite into a spherical shape, respectively.

Specifically, the flake natural graphite powder having an average particle size of 30 탆 or more is repeatedly processed by using a rotary machine to grind the flake by the collision between the inner surface of the rotary machine and the flake natural graphite powder, And the granulated graphite natural graphite particles and the crystalline sphincted natural graphite can be respectively produced.

The crystalline spherical natural graphite particles and the crystalline spherical natural graphite may be formed in a cabbage or a random phase, respectively, and may be formed in a circular shape as well as an elliptical shape. Specifically, three- May be a spherical shape having an index of about 0.8 or more.

The crystalline spherical natural graphite particles and the crystalline spheroidal natural graphite each may have an average particle size (D50) of 3 to 40 mu m, and more specifically, an average particle size (D50) of 5 to 30 mu m. When having an average particle diameter within the above range, the initial charge / discharge efficiency, the high rate charge / discharge characteristics, the life characteristics and the low temperature charge / discharge characteristics by the lithium acetate treatment are excellent. The average particle diameter (D50) means a particle diameter corresponding to a cumulative volume of 50 vol% in the particle size distribution.

The amorphous carbon constituting the composite particle may be amorphous carbon or quasi-crystalline carbon, and may be at least one selected from soft carbon and hard carbon.

The soft carbon may be obtained from at least one selected from a coal-based pitch, a petroleum pitch, a polyvinyl chloride, a mesophase pitch, a tar, and a low molecular weight heavy oil. The hard carbon may be a polyvinyl alcohol resin, furfuryl alcohol ) Resin, triton, citric acid, stearic acid, sucrose, polyvinylidene fluoride, carboxymethylcellulose, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polyethylene, polypropylene, ethylene-propylene (EPDM), polyacrylic acid, polyacrylic sodium, polyacrylonitrile, glucose, gelatin, saccharides, phenolic resin, naphthalene resin, polyamide resin, furan resin, polyimide resin, cellulose resin, styrene resin, epoxy resin And a vinyl chloride resin.

The thickness of the coating layer of the composite particle may be 0.001 to 2 탆, and may be 0.01 to 1 탆. When the thickness of the coating layer is within the above range, the initial charge / discharge efficiency and the high rate charge / discharge characteristics are improved.

The lithium carbonate particles may be contained in an amount of 0.1 to 20% by weight, and particularly 0.5 to 10% by weight based on the total amount of the negative electrode active material. When the lithium carbonate particles are contained within the above range, the initial charge / discharge efficiency, high rate charge / discharge characteristics and life characteristics can be improved.

The negative electrode active material may be prepared by the following method.

As a first method, the core particles and lithium acetate are mixed to obtain a mixture; Drying the mixture to obtain a dried product; And a step of subjecting the dried material to a heat treatment, thereby preparing a negative electrode active material having a structure in which the lithium carbonate particles are embedded on the surface of the core particles.

The lithium carbonate particles coated on the surface of the core particles and embedded are obtained by an oxidative decomposition reaction of the lithium acetate.

Lithium carbonate has a solubility in water of about 1.3 g / 100 mL at 25 DEG C and lithium acetate has a solubility in water of about 45.0 g / 100 mL at 25 DEG C and a higher solubility of lithium acetate. Accordingly, when the core particles and the lithium acetate are mixed, the amount of lithium carbonate coated on the surface of the core particles can be freely controlled, and thus uniform coating can be achieved.

Lithium acetate has a melting point as low as 286 ° C, so it can be easily coated by dry method.

The lithium acetate may be mixed in an amount of 0.1 to 50 parts by weight based on 100 parts by weight of the core particles, and specifically, 2.5 to 30 parts by weight. When the lithium acetate is mixed within the above range, the reversible capacity of the core particle may increase.

The core particles and the lithium acetate may be mixed by a dry mixing method or a wet mixing method, preferably by the dry mixing method.

In the dry mixing method, the core particles and the lithium acetate may be mixed using a coating apparatus in which shear stress is dominant.

In the wet mixing method, the core particles and the lithium acetate may be mixed together with the solvent, and the solvent may be water.

The drying may be carried out by a natural drying method, a vacuum drying method, a spray drying method, or a combination thereof, and preferably the spray drying method.

The spray drying method may be carried out at a temperature of 100 to 300 ° C, specifically 130 to 250 ° C. When spray drying is performed within the temperature range, lithium acetate can be uniformly coated on the surface of the crystalline spheroidized natural graphite particles.

When the drying step is performed, a structure in which lithium acetate is coated on the surface of the core particles can be obtained.

The heat treatment may be performed at a temperature of 200 to 2000 ° C, and specifically at a temperature of 250 to 1500 ° C. Also, the heat treatment may be performed at a temperature of 200 to 2000 ° C for 1 minute to 10 hours, or may be performed at a constant speed of 200 to 2000 ° C, followed by cooling without holding time. When the heat treatment is performed within the temperature range, the decomposition reaction of the lithium acetate into lithium carbonate is sufficiently performed to obtain a sufficient surface modification effect.

The heat treatment may be performed in an atmosphere containing nitrogen, air, oxygen, argon or a mixed gas thereof, or under a vacuum.

The negative electrode active material may also be manufactured by the second method as follows.

Coating the surface of the crystalline sphered natural graphite with an amorphous carbon precursor; Crystalline spherical natural graphite coated with the amorphous carbon precursor, and lithium acetate to obtain a mixture; Drying the mixture to obtain a dried product; And a step of subjecting the dried material to heat treatment to produce a negative electrode active material having a structure in which the lithium carbonate particles are embedded on the surface of the composite particles having a structure in which the surface of the crystalline sphincted natural graphite is coated with the amorphous carbon.

The negative electrode active material may also be prepared by the third method as follows.

Crystalline spherical natural graphite, amorphous carbon precursor, and lithium acetate to obtain a mixture; Drying the mixture to obtain a dried product; And a step of subjecting the dried material to heat treatment to produce a negative electrode active material having a structure in which the lithium carbonate particles are embedded on the surface of the composite particles having a structure in which the surface of the crystalline sphincted natural graphite is coated with the amorphous carbon.

The negative electrode active material may also be manufactured by the fourth method as follows.

Preparing a solution comprising crystalline sphered natural graphite, amorphous carbon precursor and a solvent; Ultrasonifying the solution; Drying the ultrasonic treated solution to prepare graphite-modified particles; Mixing the graphite-modified particles and lithium acetate to obtain a mixture; Drying the mixture to obtain a dried product; And a step of subjecting the dried material to heat treatment to produce a negative electrode active material having a structure in which the lithium carbonate particles are embedded on the surface of the composite particles having a structure in which the surface of the crystalline sphincted natural graphite is coated with the amorphous carbon.

The lithium acetate may be mixed in an amount of 0.1 to 100 parts by weight, and more specifically, in an amount of 2.5 to 50 parts by weight based on 100 parts by weight of the crystalline spherical natural graphite. When the lithium acetate is mixed in the above range, the reversible capacity of the composite particle can be increased.

Wherein the amorphous carbon precursor is at least one soft carbon feedstock selected from coal based pitches, petroleum pitches, polyvinyl chloride, mesophase pitches, tar and low molecular weight heavy oils; Polyvinyl alcohol resin, furfuryl alcohol resin, triton, citric acid, stearic acid, sucrose, polyvinylidene fluoride, carboxymethylcellulose, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone (EPDM), polyacrylic acid, polyacrylic acid, polyacrylonitrile, glucose, gelatin, saccharides, phenolic resins, naphthalene resins, polyamide resins, furan resins, poly At least one hard carbon raw material selected from a mid resin, a cellulose resin, a styrene resin, an epoxy resin and a vinyl chloride resin; Or a combination thereof.

The mixing, drying, and heat treatment may be performed in the same manner as described above.

As in the fourth method, when the negative active material is prepared by ultrasonication of the solution containing the crystalline spherical natural graphite and the amorphous carbon precursor, microgap pores are formed in the surface and the grain of the crystalline sphering natural graphite . As a result, the negative electrode active material is improved in reactivity with the electrolyte solution, thereby realizing a lithium secondary battery having excellent high rate charge / discharge characteristics and cycle life characteristics.

The ultrasonic treatment may be carried out in an aqueous solution containing the crystalline spherical natural graphite and the amorphous carbon precursor or in an organic solvent. Specifically, the solvent is selected from the group consisting of water, N-methylpyrrolidone, dimethylformamide, toluene, ethylene, dimethylacetamide, acetone, methyl ethyl ketone, hexane, tetrahydrofuran, decane, ethanol, methanol, isopropanol, And combinations of these.

The crystalline spherical natural graphite may be included in an amount of 0.1 to 200 parts by weight based on 100 parts by weight of the solvent, and specifically 0.1 to 100 parts by weight. When the crystalline spherical natural graphite is contained within the above range, the effect of ultrasonic treatment in a solution state is maximized, and microvoids and gaps can be formed well on the surface and inside of the particles.

The ultrasonic waves may be irradiated for an intensity of 50 to 1200 W and a time of 0.1 to 30 minutes, specifically, an intensity of 100 to 1000 W and a time of 1 to 10 minutes. Further, the ultrasonic wave may have a frequency of 10 to 40 kHz, and more specifically, a frequency of 15 to 25 kHz. When ultrasonic waves are irradiated in the above-mentioned range, a sufficient force is transmitted to induce sufficient impact and dispersion in the crystalline spheric natural graphite, and micro-pores can be formed on the surface and inside of the crystalline spheric natural graphite .

Another embodiment provides a negative electrode for a lithium secondary battery including the negative active material, and another embodiment provides a lithium secondary battery including the negative electrode.

The lithium secondary battery may be classified into a lithium ion battery, a lithium ion polymer battery, and a lithium polymer battery according to the type of the separator and electrolyte used. The lithium secondary battery may be classified into a cylindrical shape, a square shape, a coin shape, Depending on the size, it can be divided into bulk type and thin type. The structure and the manufacturing method of these cells are well known in the art, and detailed description thereof will be omitted.

A lithium secondary battery according to an embodiment includes an electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode. The electrode assembly includes a sealing member that is housed in a battery container, impregnates the electrolyte, and seals the battery container.

The negative electrode may be prepared by mixing the above-described negative electrode active material, a binder and optionally a conductive material to prepare a composition for forming the negative electrode active material layer, and then applying the composition to an anode current collector such as copper.

Examples of the binder include polyvinyl alcohol, carboxymethylcellulose / styrene-butadiene rubber, hydroxypropylene cellulose, diacetylene cellulose, polyvinyl chloride, polyvinylpyrrolidone, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, Polypropylene and the like can be used, but the present invention is not limited thereto.

The binder may be mixed in an amount of 1 to 30% by weight based on the total amount of the composition for forming the negative electrode active material layer.

The conductive material is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, and specifically includes graphite such as natural graphite and artificial graphite; Carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskey 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 conductive material may be mixed in an amount of 0.1 to 30% by weight based on the total amount of the composition for forming the anode active material layer.

The anode current collector may have a thickness of 3 to 500 mu m. Examples of the negative electrode current collector may include stainless steel, aluminum, nickel, titanium, sintered carbon, or a surface treated with carbon, nickel, titanium, silver or the like on the surface of aluminum or stainless steel. The negative electrode current collector may have fine irregularities on its surface to increase the adhesive force of the negative electrode 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 positive electrode may be prepared by mixing the positive electrode active material, the binder and optionally a conductive material to prepare a composition for forming a positive electrode active material layer, and then applying the composition to a positive electrode current collector such as aluminum.

As the cathode active material, a compound capable of reversibly intercalating and deintercalating lithium (a lithiated intercalation compound) can be used. Concretely, at least one of complex oxides of lithium and at least one kind selected from cobalt, manganese and nickel can be used.

The electrolyte solution may be a lithium salt, a non-aqueous organic solvent, an organic solid electrolyte, or an inorganic solid electrolyte.

The lithium salt is _{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 ) ₂ NLi, chloroborane lithium, lower aliphatic carboxylate lithium, lithium 4-phenylborate, and imide.

Examples of the non-aqueous organic solvent include N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, But are not limited to, furan, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, 1,3-dimethyl-2-imidazolidone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl pyrophosphate, ethyl propionate and the like can be used. have.

Examples of the organic solid electrolytic solution include 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 and an ionic dissociation group And the like can be used.

As the inorganic solid electrolytic solution, 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 ₄ SiO ₄ - Nitrides, halides and sulfates of Li such as LiI-LiOH and Li ₃ PO ₄ -Li ₂ S-SiS ₂ can be used.

For the purpose of improving the charge-discharge characteristics and the flame retardancy, the electrolyte solution is preferably used in the form of a solution containing at least one member selected from the group consisting of pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, hexaphosphoric triamide, N, N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, aluminum trichloride, and the like can be added. Further, a halogen-containing solvent such as carbon tetrachloride, ethylene trifluoride or the like may be further added to impart nonflammability, or a carbon dioxide gas may be further added to improve high-temperature storage characteristics.

Depending on the type of the lithium secondary battery, a separator may exist between the positive electrode and the negative electrode. As such a separator, an insulating thin film having high ion permeability and mechanical strength can be used. The pore diameter of the separator may be 0.01 to 10 mu m and the thickness may be 5 to 300 mu m.

The separator specifically includes an olefin-based polymer such as polypropylene having chemical resistance and hydrophobicity; A sheet or a nonwoven fabric made of glass fiber, polyethylene or the like can be used. When a solid electrolyte such as a polymer is used as the electrolytic solution, the solid electrolytic solution may also serve as a separation membrane.

Hereinafter, preferred embodiments and comparative examples of the present invention will be described. However, the following embodiments are merely preferred embodiments of the present invention, and the present invention is not limited to the following embodiments.

(Preparation of negative electrode active material)

Example  One

1 part by weight (based on 100 parts by weight of distilled water) and 0.025 part by weight of lithium acetate (CH ₃ COO.Li.H ₂ O ₂ ) (average particle diameter D50) of 12 μm were added to 1 part by weight of crystalline spherical natural graphite particles (POSCO- 100 parts by weight of distilled water) was added to 100 parts by weight of distilled water, followed by mixing with a magnetic stirrer for 1 hour to obtain a mixture. The mixture was naturally dried at 100 ° C to obtain a dried product coated with lithium acetate. The obtained dried product was heated at a rate of 5 ° C / min. After reaching 450 ° C, it was heat treated in an air atmosphere without holding time, and was then cooled to produce an anode active material.

Example  2

An anode active material was prepared in the same manner as in Example 1, except that 0.05 parts by weight of lithium acetate (based on 100 parts by weight of distilled water) was used instead of 0.025 parts by weight of lithium acetate (100 parts by weight of distilled water) in Example 1.

Example  3

An anode active material was prepared in the same manner as in Example 1, except that 0.1 parts by weight of lithium acetate (based on 100 parts by weight of distilled water) was used instead of 0.025 parts by weight of lithium acetate (100 parts by weight of distilled water) in Example 1.

Example  4

An anode active material was prepared in the same manner as in Example 1, except that 0.15 parts by weight of lithium acetate (based on 100 parts by weight of distilled water) was used instead of 0.025 parts by weight of lithium acetate (100 parts by weight of distilled water) in Example 1.

Example  5

1 part by weight (based on 100 parts by weight of distilled water) and 0.15 parts by weight of lithium acetate (CH ₃ COO.Li.H ₂ O ₂ ) (average particle size D50) of 12 μm were added to 1 part by weight of crystalline spherical natural graphite particles (POSCO- 100 parts by weight of distilled water) was added to 100 parts by weight of distilled water, followed by mixing with a magnetic stirrer for 1 hour to obtain a mixture. The mixture was naturally dried at 100 DEG C to obtain a dried product coated with lithium acetate. The obtained dried product was heated at a rate of 5 ° C per minute, and after reaching 350 ° C, it was heat treated in an air atmosphere for 1 hour and then cooled to prepare an anode active material.

Example  6

The average particle diameter (D50) of the crystalline spheroidizing natural graphite composite particles coated with carbon 13㎛ (POSCO Chem teksa, S12C) 1 part by weight (based on 100 parts by weight of distilled water) and lithium acetate (CH ₃ COO and Li-2H ₂ 0 ) (100 parts by weight of distilled water) was added to 100 parts by weight of distilled water, followed by mixing with a magnetic stirrer for 1 hour to obtain a mixture. The mixture was naturally dried at 100 ° C to obtain a dried product coated with lithium acetate. The obtained dried product was heated at a rate of 5 ° C / min. After reaching 450 ° C, it was heat treated in an air atmosphere without holding time, and was then cooled to produce an anode active material.

Example  7

The average particle diameter (D50) of the crystalline spheroidizing natural graphite composite particles coated with carbon 13㎛ (POSCO Chem teksa, S12C) 1 part by weight (based on 100 parts by weight of distilled water) and lithium acetate (CH ₃ COO and Li-2H ₂ 0 ) (100 parts by weight of distilled water) was added to 100 parts by weight of distilled water, followed by mixing with a magnetic stirrer for 1 hour to obtain a mixture. The mixture was naturally dried at 100 ° C to obtain a dried product coated with lithium acetate. The obtained dried product was heated at a rate of 5 ° C / min. After reaching 400 ° C, the product was heat treated in an air atmosphere without holding time and then cooled to produce an anode active material.

Example  8

1 part by weight (based on 100 parts by weight of distilled water) and 0.05 part by weight of petroleum pitch (based on 100 parts by weight of distilled water) of crystalline spherical natural graphite particles having an average particle diameter (D50) of 16 占 퐉 (POSCO Chemtex, S16) rotor mill (rotating at a rate of 5000 to 20000 rpm in a few seconds to several minutes) to obtain a crystalline spherical natural graphite powder coated with a petroleum pitch.

A solution in distilled water containing 100 parts by weight of the lithium acetate (CH ₃ COO and Li-2H ₂ 0) 0.1 parts by weight (100 parts by weight of distilled water basis) were prepared. 1 part by weight (based on 100 parts by weight of distilled water) of crystalline spherical natural graphite powder coated with the petroleum pitch was added to the prepared solution, stirred for 1 hour using a magnetic stirrer, spray dry) to obtain crystalline spheroidal natural graphite modified powder.

The crystalline spherical natural graphite modified powder was heat-treated at 1,200 ° C for 1 hour in an argon (Ar) atmosphere, followed by furnace cooling to prepare an anode active material.

Comparative Example  One

Crystalline spherical natural graphite particles (POSCO Chemtech, S12) having an average particle diameter (D50) of 12 mu m were used as an anode active material.

Comparative Example  2

Crystalline spherical natural graphite composite particles (POSCO Chemtech, S12C) coated with carbon having an average particle diameter (D50) of 13 mu m were used as an anode active material.

Comparative Example  3

1 part by weight (based on 100 parts by weight of distilled water) and 0.06 part by weight of lithium carbonate (Li ₂ CO ₃ ) (based on 100 parts by weight of distilled water) of crystalline spheroidal natural graphite particles having an average particle diameter (D50) ) Were added to 100 parts by weight of distilled water and mixed for 1 hour using a magnetic stirrer to obtain a mixture. The mixture was naturally dried at 100 ° C. to prepare an anode active material.

Comparative Example  4

1 part by weight (based on 100 parts by weight of distilled water) and 0.06 part by weight of lithium carbonate (Li ₂ CO ₃ ) (based on 100 parts by weight of distilled water) of crystalline spheroidal natural graphite particles having an average particle diameter (D50) ) Were added to 100 parts by weight of distilled water and mixed for 1 hour using a magnetic stirrer to obtain a mixture. The mixture was naturally dried at 100 占 폚 to obtain a dried product coated with lithium carbonate. The obtained dried product was heated at a rate of 5 ° C / min. After reaching 450 ° C, it was heat treated in an air atmosphere without holding time, and was then cooled to produce an anode active material.

Comparative Example  5

(Spherical natural graphite particles having an average particle diameter of 16 占 퐉 (POSCO Chemtexa, S16) and petroleum pitch were charged into a rotor mill (rotated at a speed of 5000 to 20000 rpm in a few seconds to several minutes) at a weight ratio of 1: To obtain a crystalline spheroidal natural graphite powder coated with a petroleum pitch.

The crystalline spherical natural graphite powder coated with the petroleum pitch was heat treated at 1,200 ° C for 1 hour in an argon (Ar) atmosphere, and then cooled to produce an anode active material.

Evaluation 1: Lithium acetate Thermal weight ( TGA ) analysis

FIG. 1 is a thermogravimetric analysis (TGA) graph of lithium acetate used in Examples, and FIG. 2 is an X-ray diffraction pattern (XRD) graph of a negative electrode active material according to Example 1. FIG.

Referring to FIGS. 1 and 2, lithium acetate has a primary weight loss due to dehydration reaction at about 200 ° C or lower, secondary weight reduction occurs from about 350 ° C to about 400 ° C, and a crystalline phase of lithium carbonate is produced .

Evaluation 2: Scanning electron microscope of the anode active material SEM ) analysis

FIGS. 3A and 3B are scanning electron microscope (SEM) photographs of a negative electrode active material according to Example 4 at a low magnification and a high magnification, respectively. FIGS. 4A and 4B are SEM photographs of a negative electrode active material according to Example 5, (SEM), and FIGS. 5A and 5B are scanning electron micrographs (SEM) photographs of a negative electrode active material according to Example 6 at a low magnification and a high magnification, respectively. FIG. 6A and FIG. And high magnification scanning electron microscope (SEM) photographs.

3A to 6B, it can be seen that lithium carbonate particles are uniformly coated on the surface of the core particles in the case of the negative electrode active material produced according to Examples 4 to 6 and 8, and in particular, It can be confirmed that it is embedded on the surface of the particle.

7A and 7B are SEM micrographs of a negative electrode active material according to Comparative Example 1 at a low magnification and a high magnification, respectively. FIGS. 8A and 8B are SEM images of a negative electrode active material according to Comparative Example 2, (SEM), and FIGS. 9A and 9B are scanning electron microscope (SEM) photographs of a low magnification and a high magnification of the negative electrode active material according to Comparative Example 5, respectively.

Referring to FIGS. 7A and 9B, it can be seen that the negative active material used in Comparative Examples 1, 2, and 5 has a smooth and flat surface.

10A and 10B are scanning electron microscope (SEM) photographs of low magnification and high magnification of the negative electrode active material according to Comparative Example 3, respectively.

10A and 10B, it can be seen that the amount of lithium carbonate particles existing on the surface of the core particles of the negative electrode active material prepared in Comparative Example 3 is very small and the lithium carbonate particles are partially aggregated.

Evaluation 3: Thermal weight ( TGA ) analysis

The negative electrode active material according to Example 2 and Comparative Example 1 was subjected to thermogravimetric analysis (TGA) in an air atmosphere, and the results are shown in FIG.

11 is a thermogravimetric analysis (TGA) graph of the negative electrode active material according to Example 2 and Comparative Example 1. Fig.

Referring to FIG. 11, it can be seen that the mass reduction of the negative electrode active material prepared in Example 2 was significantly lowered at a lower temperature than that of Comparative Example 1. This is seen as a result of lithium acetate and lithium carbonate on the surface of the core particles in Example 2 promoting the oxidation of core particles, specifically crystalline spherical natural graphite particles.

Evaluation 4: Raman spectrum analysis of negative electrode active material

FIG. 12 is a graph of Raman spectrum analysis of negative electrode active materials according to Examples 6 and 7 and Comparative Example 2, and FIG. 13 is a graph of Raman spectrum analysis of negative active material according to Example 8 and Comparative Example 5.

12, the ratio R (I _D / I _G) between the peak of 1580 cm ^-1 corresponding to the crystalline spheroidized natural graphite particles and the intensity of the peak of 1360 cm ^-1 corresponding to the amorphous carbon ) Decreased with increasing the heat treatment temperature. This means that the amorphous phase gradually changes to a crystalline state at the surface of the core particle. This indicates that the phase transition of lithium acetate to lithium carbonate during the heat treatment and the etching reaction due to the oxidation of the coating layer of the amorphous carbon are simultaneously progressed. As a result, it can be seen that the coating layer of the amorphous carbon coated on the crystalline spheroidized natural graphite particles gradually disappears as the heat treatment temperature is increased.

Referring to FIG. 13, in the case of Example 8 coated with lithium acetate, the peak of 1580 cm ^-1 corresponding to crystalline spheroidized natural graphite particles and the peak of 1360 cm ^-1 corresponding to amorphous carbon It can be confirmed that the ratio R value (I _D / I _G ) of the strength is small. This means that the amorphous phase gradually changes to a crystalline state at the surface of the core particle. This indicates that the phase transition of lithium acetate to lithium carbonate during the heat treatment and the etching reaction due to the oxidation of the coating layer of the amorphous carbon are simultaneously progressed.

Evaluation 5: X-ray of anode active material Diffraction pattern ( XRD ) analysis

FIG. 14 is an X-ray diffraction pattern (XRD) graph of the negative electrode active material according to Examples 1 to 5 and Comparative Example 1, and FIG. 15 is a graph showing the XRD pattern of the negative electrode active material according to Examples 6 and 7 and Comparative Example 2 (XRD) graph, and FIGS. 16A and 16B are XRD graphs of the negative electrode active material according to Example 8 and Comparative Example 5. FIG.

Referring to FIGS. 14 and 15, it can be seen that the negative active material prepared in Examples 1 to 5 and Examples 6 and 7 has a phase transition of lithium acetate to lithium carbonate. As the amount of lithium acetate increases, lithium carbonate The diffraction peaks of the first-order diffraction peaks are increased.

Also, referring to FIG. 16A, it can be seen that lithium acetate is phase-transformed to lithium carbonate in Example 8 coated with lithium acetate. Referring to FIG. 16B, it can be seen that 43 degrees 2 (corresponding to the rhombohedral structure) theta) and 46 degrees (2 theta) diffraction peaks disappear after treatment with lithium acetate, which means that the degree of graphitization is increased.

(Production of lithium secondary battery)

Each of the negative electrode active materials prepared in Examples 1 to 8 and Comparative Examples 1 to 5 and CMC / SBR (carboxymethylcellulose / styrene-butadiene rubber) were mixed in distilled water at a weight ratio of 96: 4 to prepare an anode slurry. The negative electrode slurry was coated on a copper foil, followed by drying and pressing to prepare respective negative electrodes.

Each of the negative electrodes and the lithium metal were used as positive electrodes, and a separator made of a porous polypropylene film was interposed between the negative electrode and the positive electrode to form an electrode assembly. Then, an electrolytic solution prepared by dissolving 1 M of LiPF ₆ in a mixed solvent of diethyl carbonate (DEC) and ethylene carbonate (EC) (DEC: EC = 1: 1) was added to prepare a lithium secondary battery.

Evaluation 6: Initial of lithium secondary battery Charging and discharging  Character analysis

The lithium secondary batteries manufactured in Examples 1 to 7 and Comparative Examples 1 to 4 were charged and discharged under the following conditions to evaluate initial charge-discharge characteristics, and the results are shown in Table 1 below.

Charging was performed in a CC / CV mode with a current density of 70 mA / g, the termination voltage was maintained at 0.01 V, and charging was terminated when the current was 7 mA / g. The discharge was performed in CC mode with a current density of 70 mA / g and the termination voltage was maintained at 1.5V.

In Table 1, the initial efficiency (%) is obtained as a percentage of the initial discharge capacity to the initial charge capacity.

It can be seen from the following Table 1 that the initial charge-discharge efficiency is superior to Comparative Examples 1 to 4 when the negative electrode active materials prepared in Examples 1 to 7 are used.

Evaluation 7: High rate of lithium secondary battery Charging and discharging  Character analysis

The lithium secondary batteries produced in Examples 1 to 7 and Comparative Examples 1 to 4 were charged and discharged under the following conditions to evaluate high-rate charging characteristics and high-rate discharging characteristics, and the results are shown in Table 1 below.

For high rate charging (lithium insertion) characteristics, charging was done in CC mode with a current density in the range of 70 to 700 mA / g, with the termination voltage maintained at 0.01 V and discharge at CC mode at a current density of 70 mA / And the end voltage was maintained at 1.5V.

In the case of high-rate discharge (lithium-tallis) characteristics, charging was performed in CC / CV mode at a current density of 70 mA / g, the end voltage was maintained at 0.01 V and charging was terminated when the current was 7 mA / g. The discharge was performed in CC mode at a current density of 70 to 3500 mA / g and the termination voltage was maintained at 1.5V.

It can be seen from the following Table 1 that the high rate characteristics of charging and discharging are superior to those of Comparative Examples 1 to 4 when the negative electrode active material prepared in Examples 1 to 7 is used.

Evaluation 8: Analysis of cycle life characteristics of lithium secondary battery

The lithium secondary batteries manufactured in Examples 1 to 7 and Comparative Examples 1 to 4 were charged and discharged under the following conditions to evaluate cycle life characteristics. The results are shown in Table 1 below.

Charging was performed in CC / CV mode with a current density of 175 mA / g (0.5 C), the end voltage was maintained at 0.01 V, and charging was terminated when the current was 17.5 mA / g. The discharge was performed in a CC mode with a current density of 175 mA / g (0.5 C), the end voltage was maintained at 1.5 V, and a total of 50 cycles were performed.

In the following Table 1, the capacity retention rate (%) is the percentage value of the reversible capacity at the third cycle with respect to the reversible capacity at the 50th cycle.

It can be seen from the following Table 1 that when the negative electrode active materials prepared in Examples 1 to 7 were used, the capacity retention ratio after 50 cycles was superior to those of Comparative Examples 1 to 4.

Initial efficiency (%) High rate charging characteristic High rate discharge characteristic Capacity retention rate
(%) Charging capacity (mAh / g) Discharge capacity (mAh / g) 70mA / g 350mA / g 700mA / g 70mA / g 350mA / g 700mA / g 1750mA / g 3500 mA / g Example 1 91.1 334 215 86 357 357 355 326 218 89 Example 2 92.1 338 212 72 350 350 348 326 210 94 Example 3 92.3 330 237 118 345 344 343 339 311 96 Example 4 92.9 330 248 127 338 337 335 324 280 96 Example 5 91.8 320 216 97 335 335 334 324 280 98 Example 6 92.4 323 227 112 343 341 339 337 319 92 Example 7 92.4 326 243 128 343 342 341 335 318 98 Comparative Example 1 90.2 338 162 51 359 359 355 304 179 81 Comparative Example 2 91.3 316 224 106 356 347 339 328 308 70 Comparative Example 3 90.6 326 188 68 349 348 344 276 154 86 Comparative Example 4 91 339 200 88 345 340 335 306 191 89

In Table 1, when the anode active material prepared by treating lithium acetate with lithium carbonate according to one embodiment has a structure embedded in the surface of the core particles, it has high initial efficiency and high rate charge / discharge characteristics and cycle life characteristics It can be understood that this excellent lithium secondary battery can be realized.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims. As will be understood by those skilled in the art. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive.

Claims (24)

Core particles; And
The lithium carbonate particles present on the surface of the core particles
Lt; / RTI >
At least a portion of the lithium carbonate particles being embedded in the surface of the core particle,
Wherein the core particles are at least one selected from the group consisting of crystalline spheroidal natural graphite particles and composite particles comprising crystalline spheroidal natural graphite and a coating layer coated with amorphous carbon on the surface of the crystalline spheroidal natural graphite,
The crystalline sphincterized natural graphite particles and the crystalline sphincterized natural graphite are obtained by assembling scintillating natural graphite into a spherical shape, respectively, to obtain a negative electrode active material for a lithium secondary battery.
The method according to claim 1,
Wherein the lithium carbonate particles are contained in an amount of 0.1 to 20% by weight based on the total weight of the negative electrode active material.
delete The method according to claim 1,
When the core particle is the composite particle,
And the thickness of the coating layer is 0.001 to 2 占 퐉.
The method according to claim 1,
When the core particle is the composite particle,
Wherein the amorphous carbon is at least one selected from soft carbon and hard carbon.
6. The method of claim 5,
Wherein the soft carbon is obtained from at least one selected from coal-based pitch, petroleum pitch, polyvinyl chloride, mesophase pitch, tar and low molecular weight heavy oil,
The hard carbon may be selected from the group consisting of polyvinyl alcohol resin, furfuryl alcohol resin, triton, citric acid, stearic acid, sucrose, polyvinylidene fluoride, carboxymethylcellulose, hydroxypropylcellulose, regenerated cellulose , Polyvinylpyrrolidone, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), polyacrylic acid, polyacrylic sodium, polyacrylonitrile, glucose, gelatin, saccharides, phenolic resins, naphthalene resins, Furan resin, polyimide resin, cellulose resin, styrene resin, epoxy resin and vinyl chloride resin.
Negative electrode active material for lithium secondary battery.
Mixing the core particles and lithium acetate to obtain a mixture;
Drying the mixture to obtain a dried product; And
And heat treating the dried material,
Wherein the core particles comprise at least one selected from the group consisting of crystalline spheroidal natural graphite particles and composite particles comprising crystalline spheroidal natural graphite and a coating layer coated with amorphous carbon on the surface of the crystalline spheroidal natural graphite
A method for producing a negative electrode active material for lithium secondary batteries.
Coating the surface of the crystalline sphered natural graphite with an amorphous carbon precursor;
Crystalline spherical natural graphite coated with the amorphous carbon precursor, and lithium acetate to obtain a mixture;
Drying the mixture to obtain a dried product; And
Heat-treating the dried material
And a negative electrode active material for lithium secondary batteries.
Crystalline spherical natural graphite, amorphous carbon precursor, and lithium acetate to obtain a mixture;
Drying the mixture to obtain a dried product; And
Heat-treating the dried material
And a negative electrode active material for lithium secondary batteries.
Preparing a solution comprising crystalline sphered natural graphite, amorphous carbon precursor and a solvent;
Ultrasonifying the solution;
Drying the ultrasonic treated solution to prepare graphite-modified particles;
Mixing the graphite-modified particles and lithium acetate to obtain a mixture;
Drying the mixture to obtain a dried product; And
Heat-treating the dried material
And a negative electrode active material for lithium secondary batteries.
8. The method of claim 7,
Wherein the lithium acetate is mixed in an amount of 0.1 to 50 parts by weight based on 100 parts by weight of the core particles.
11. The method according to any one of claims 8 to 10,
Wherein the lithium acetate is mixed in an amount of 0.1 to 100 parts by weight based on 100 parts by weight of the crystalline sphered natural graphite.
11. The method according to any one of claims 8 to 10,
Wherein the amorphous carbon precursor is at least one soft carbon feedstock selected from coal based pitches, petroleum pitches, polyvinyl chloride, mesophase pitches, tar and low molecular weight heavy oils; Polyvinyl alcohol resin, furfuryl alcohol resin, triton, citric acid, stearic acid, sucrose, polyvinylidene fluoride, carboxymethylcellulose, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone (EPDM), polyacrylic acid, polyacrylic acid, polyacrylonitrile, glucose, gelatin, saccharides, phenolic resins, naphthalene resins, polyamide resins, furan resins, poly At least one hard carbon raw material selected from a mid resin, a cellulose resin, a styrene resin, an epoxy resin and a vinyl chloride resin; Or a combination thereof. ≪ RTI ID = 0.0 > 11. < / RTI >
11. The method according to any one of claims 7 to 10,
Wherein the mixing is performed by a method of dry mixing, wet mixing, or a combination thereof.
11. The method according to any one of claims 7 to 10,
Wherein the drying is performed by a natural drying method, a vacuum drying method, a spray drying method, or a combination thereof.
16. The method of claim 15,
The drying is performed by the spray drying method,
Wherein the spray drying method is performed at a temperature of 100 to 300 캜.
11. The method according to any one of claims 7 to 10,
Wherein the heat treatment is performed at a temperature of 200 to 2000 ° C.
18. The method of claim 17,
Wherein the heat treatment is performed at a temperature of 200 to 2000 ° C for 1 minute to 10 hours, or to a temperature of 200 to 2000 ° C at a constant rate, followed by cooling without holding time.
11. The method according to any one of claims 7 to 10,
Wherein the heat treatment is performed in an atmosphere containing nitrogen, air, oxygen, argon, or a mixed gas thereof; Or a negative electrode active material for a lithium secondary battery.
11. The method of claim 10,
The solvent may be selected from the group consisting of water, N-methylpyrrolidone, dimethylformamide, toluene, ethylene, dimethylacetamide, acetone, methyl ethyl ketone, hexane, tetrahydrofuran, decane, ethanol, methanol, isopropanol, And a negative electrode active material for lithium secondary batteries.
11. The method of claim 10,
Wherein the crystalline spherical natural graphite is contained in an amount of 0.1 to 200 parts by weight based on 100 parts by weight of the solvent.
11. The method of claim 10,
Wherein the ultrasonic waves are irradiated at an intensity of 50 to 1200 W and a frequency of 10 to 40 kHz for 0.1 to 30 minutes.
The negative electrode active material according to any one of claims 1, 2, and 4 to 6
And a negative electrode for a lithium secondary battery.
A cathode according to claim 23;
anode; And
Electrolyte
≪ / RTI >

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