KR101446698B1 - Method of preparing negative active material for rechargeable lithium battery, and negative active material and rechargeable lithium battery prepared from the same - Google Patents

Abstract

Preparing a solution containing spherical natural graphite particles and a solvent, ultrasonifying the solution, and drying the ultrasound-treated solution to prepare graphite-modified particles. The negative active material for a lithium secondary battery according to claim 1, And a negative electrode active material and a lithium secondary battery fabricated therefrom.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method for producing a negative electrode active material for a lithium secondary battery, and a negative electrode active material and a lithium secondary battery produced therefrom,

A negative electrode active material for a lithium secondary battery, and a lithium secondary battery produced from the negative electrode active material.

At present, a crystalline graphite material is used as an anode active material of a lithium secondary battery. Crystalline graphite is divided into artificial graphite and natural graphite. Since the artificial graphite is generally obtained by carbonizing the carbon precursor under an inert atmosphere at a high temperature of about 2800 DEG C or higher to remove impurities and graphitizing the carbon precursor, the use of natural graphite is increasing.

When the natural graphite particles are used as the negative electrode active material, the uniformity of the slurry application during electrode production is lowered due to the anisotropic nature of the particle shape, and flaky graphite particles are oriented along the current collector by rolling and press- There is a problem that the characteristics of the semiconductor device are greatly deteriorated. Therefore, natural graphite, which is currently commercialized, is a spherical natural graphite obtained by granulating scaly graphite into a spherical shape. However, in the case of the spherical natural graphite, there is a need to improve the high rate charge / discharge characteristics and cycle life characteristics.

One embodiment of the present invention is to provide a method for producing a negative electrode active material for a lithium secondary battery, which is excellent in high rate charge / discharge characteristics and cycle life characteristics.

Another embodiment is to provide a negative electrode active material for a lithium secondary battery produced from the method for producing the negative electrode active material.

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

One embodiment includes preparing a solution comprising spheroidized natural graphite particles and a solvent; Ultrasonifying the solution; And drying the ultrasound-treated solution to prepare graphite-modified particles. The present invention also provides a method for manufacturing a negative electrode active material for a lithium secondary battery.

The spherical natural graphite particles may be prepared by granulating the natural graphite particles into spherical particles.

The spherical natural graphite particles may have an average particle diameter (D50) of 3 to 40 mu m.

The solvent is at least one selected from the group consisting of water, N-methylpyrrolidone, dimethylformamide, toluene, ethylene, dimethylacetamide, acetone, methyl ethyl ketone, hexane, tetrahydrofuran, decane, ethanol, methanol, isopropanol, One can be included.

The spherical natural graphite particles may be included 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 an intensity of 50 to 1200 W and a time of 0.1 to 30 minutes, and may have a frequency of 10 to 40 Hz.

The drying may be carried out by at least one spray drying method selected from rotary spraying, nozzle spraying and ultrasonic spraying; A drying method using a rotary evaporator; Vacuum drying method; Or by natural drying methods.

The solution may further comprise a carbon precursor. In this case, the step of preparing the graphite-modified particles may further include the step of heat-treating the graphite-modified particles to prepare a graphite-modified composite particle, Deg.] C to 2500 [deg.] C, and may be carried out under an atmosphere containing nitrogen, argon, hydrogen, or a mixed gas thereof, or under vacuum.

The carbon precursor may be selected from the group consisting of citric acid, stearic acid, sucrose, polyvinylidene fluoride, carboxymethylcellulose (CMC), hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, (EPDM), sulfonated EPDM, starch, phenolic resin, furan resin, per furyl alcohol, polyacrylic acid, polyacrylic sodium, polyacrylonitrile, polyimide, epoxy resin, cellulose, styrene, polyvinyl Alcohol, polyvinyl chloride, coal pitch, petroleum pitch, mesophase pitch, low molecular weight heavy oil, glucose, gelatin and saccharides.

The carbon precursor may be included in an amount of 0.1 to 80 parts by weight based on 100 parts by weight of the spherical natural graphite particles.

The solution may further comprise a lithium compound. In this case, the step of preparing the graphite-modified particles may further include a step of heat-treating the graphite-modified particles to prepare a graphite-modified composite particle, Deg.] C to 2500 [deg.] C, and the heat treatment may be performed in an atmosphere containing nitrogen, argon, hydrogen, air, oxygen, or a mixture gas thereof, or under vacuum.

The lithium compound is lithium hydroxide containing LiOH or LiOH (H ₂ O); Lithium nitrate (LiNO _3); Lithium acetate containing CH 3 COO Li or CH 3 COO Li 2 (H ₂ O); Lithium carbonate (Li ₂ CO ₃ ); And at least one selected from lithium fluoride (LiF).

The lithium compound may be included in an amount of 0.1 to 50 parts by weight based on 100 parts by weight of the spherical natural graphite particles.

The solution may further comprise a carbon precursor and a lithium compound. In this case, the step of preparing the graphite-modified particles may further include heat-treating the graphite-modified particles to prepare a graphite-modified composite particle, The heat treatment may be performed at a temperature of 150 to 2500 占 폚 and may be performed in an atmosphere containing nitrogen, argon, hydrogen, or a mixed gas thereof, or under a vacuum.

Another embodiment provides a negative electrode active material for a lithium secondary battery produced by the above method.

Another embodiment includes a negative electrode comprising the negative electrode active material; anode; And a lithium secondary battery comprising the electrolyte.

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

By using the negative electrode active material prepared according to the above production method, a lithium secondary battery having excellent high rate charge / discharge characteristics and cycle life characteristics can be realized.

1 to 6 are scanning electron microscope (SEM) photographs of the negative electrode active materials according to Examples 1 to 6, respectively.
7A and 7B are scanning electron microscope (SEM) photographs of the negative electrode active material according to Example 7 at a magnification of 5,000 and a magnification of 20,000, respectively.
8 and 9 are scanning electron microscope (SEM) photographs of the negative electrode active material according to Comparative Examples 1 and 2, respectively.
Fig. 10 shows an X-ray diffraction pattern (XRD) of the negative electrode active material according to Examples 1 and 2 and Comparative Example 1. Fig.
Fig. 11 shows an X-ray diffraction pattern (XRD) of the negative electrode active material according to Examples 3 and 7 and Comparative Example 1. Fig.
12 shows the X-ray diffraction patterns (XRD) of the negative electrode active material according to Examples 4 to 6 and Comparative Example 2. Fig.
13 to 16 are scanning electron microscope (SEM) photographs of the cathode surface prepared according to Examples 1, 4, 6 and 7, respectively.
17 and 18 are scanning electron microscope (SEM) photographs of the cathode surface prepared according to Comparative Examples 1 and 2, respectively.
19 is a graph showing the cycle life characteristics of the negative electrode prepared according to Examples 1, 3, 4 and 7 and Comparative Example 1, respectively.

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 according to one embodiment can be manufactured as follows.

A step of preparing a solution containing spherical natural graphite particles and a solvent, ultrasonic treatment of the solution, and drying the ultrasonic treated solution to prepare graphite-modified particles.

The spherical natural graphite particles can be formed by the methods disclosed in Korean Patent Publication Nos. 2003-0087986 and 2005-0009245, but are not limited thereto. For example, a step of repeatedly processing the scaly natural graphite having an average particle diameter of 30 탆 or more by using a rotary machine is performed, whereby the friction between the powder and the crushing due to the collision between the inner side of the rotary machine and the scaly natural graphite powder Processing and shearing of the powder by shearing stress, and the like, the scratched natural graphite is assembled and finally spherical natural graphite particles can be manufactured.

Natural graphite particles such as scratched graphite particles are less anisotropic and the uniformity of slurry application during electrode production is lowered and the natural graphite particles are oriented along the current collector by the rolling and pressing pressure, . According to one embodiment, highly natural isotropy can be obtained by using spherical natural graphite particles.

The spherical natural graphite particles may be formed into a cabbage or a random phase. In addition, the spheroidized natural graphite particles may be spherical as well as circular, or may be spherical having an index of about 0.8 or more, which is calculated by projecting three-dimensional natural graphite particles on a two-dimensional plane.

The spherical natural graphite particles may have an average particle diameter (D50) of 3 to 40 mu m, and more specifically, 5 to 30 mu m. When the spherical natural graphite particles having an average particle size within the above range are used as the negative electrode active material, the effect of high-rate charge-discharge characteristics by the ultrasonic treatment is enhanced.

The spherical natural graphite particles may be included in an amount of 0.1 to 200 parts by weight, and more specifically 0.1 to 100 parts by weight, based on 100 parts by weight of the solvent. When the spherical natural graphite particles are contained within the above range, the effect of ultrasonic treatment in a solution state is maximized, and micropores and gaps can be formed well on the surface and inside of the powder, and in the case of a solution containing a carbon precursor, impregnation is easy.

The solvent is at least one selected from the group consisting of water, N-methylpyrrolidone, dimethylformamide, toluene, ethylene, dimethylacetamide, acetone, methyl ethyl ketone, hexane, tetrahydrofuran, decane, ethanol, methanol, isopropanol, You can use one.

When the solution containing the spheroidized natural graphite particles is subjected to ultrasonic treatment to form the negative electrode active material, fine pores are formed on the surface and the particles of the spheroidized natural graphite particles. 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 spherical natural graphite particles or in an organic solvent.

The ultrasonic treatment causes three representative physical phenomena of fluid cavitation, localized heating, and free radical formation. The fluid cavitation is a phenomenon in which a force due to the generation and explosion of bubbles is transmitted to the ultrasonic wave treated particles. Generally, ultrasonic treatment can be performed in the form of a bath and a horn. Ultrasonic processing in the form of a bath has a frequency higher than that of the horn type so that precisely defined fluid cavitation does not occur but can be delivered uniformly through the liquid medium. In the case of ultrasonic treatment using a horn, the frequency is relatively short, and large bubbles are formed. Such bubbles can break and transfer large energy. In this way, bubbles can induce impact and dispersion on particles while repeatedly generating and destroying on the surface of the particles, and micropores can be formed on the surface and inside of the spherical natural graphite particles when the ultrasonic treatment is performed. Thus, the surface and interior of the spherical natural graphite particles can be modified through the ultrasonic treatment. As a result, the negative electrode active material having micropores formed on the surface and inside of the spherical natural graphite particles has improved reactivity with the electrolyte, thereby realizing a lithium secondary battery having high rate charge / discharge characteristics.

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 waves may have a frequency of 10 to 40 Hz, and more specifically, a frequency of 15 to 25 Hz. When ultrasonic waves are irradiated in the above-mentioned range, sufficient force is transmitted to induce sufficient impact and dispersion in the spheroidized natural graphite particles, and micropores can be formed on the surface and inside of the spherical natural graphite particles .

The drying may be carried out by at least one spray drying method selected from rotary spraying, nozzle spraying and ultrasonic spraying; A drying method using a rotary evaporator; Vacuum drying method; Or by natural drying methods.

The solution may further include a carbon precursor in addition to the spherical natural graphite particles. In this case, the solution containing the spherical natural graphite particles, the carbon precursor and the solvent may be dried after the ultrasonic treatment to produce the graphite-modified particles as in the above-described method of producing the graphite-modified particles, A step of heat-treating the particles to produce a graphite-modified composite particle in which the carbon precursor is carbonized.

When the anode active material of the spherical natural graphite particles is used, compression of the spherical natural graphite particles may occur due to the pressing process. When the carbon precursor and the solvent include the ultrasonic wave, Is impregnated with the surface of the spherical natural graphite particle and the gap in the particle, and in the case of the graphite-modified composite particle in which the carbon precursor is carbonized according to the subsequent heat treatment step, the particle pressing phenomenon is prevented, Charge and discharge characteristics can be improved.

The carbon precursor may be selected from the group consisting of citric acid, stearic acid, sucrose, polyvinylidene fluoride, carboxymethylcellulose (CMC), hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, (EPDM), sulfonated EPDM, starch, phenolic resin, furan resin, per furyl alcohol, polyacrylic acid, polyacrylic sodium, polyacrylonitrile, polyimide, epoxy resin, cellulose, styrene, polyvinyl At least one selected from the group consisting of alcohol, polyvinyl chloride, coal pitch, petroleum pitch, mesophase pitch, low molecular weight heavy oil, glucose, gelatin and saccharides may be used.

The ultrasonic treatment may be carried out in an aqueous solution in which the carbon precursor is dissolved or in an organic solvent.

When the graphite-modified particles obtained by the ultrasonic treatment are subjected to the heat treatment, the carbon precursor is carbonized to form low-crystalline carbon and amorphous carbon, and the surface of the spheroidized natural graphite particles is carbon-coated and formed by ultrasonic treatment It is possible to obtain a graphite-modified composite particle having a low-crystalline carbon and an amorphous carbon in the gap in the spheroidized graphite particle.

The heat treatment may be performed at a temperature of 500 to 2500 ° C, specifically, at a temperature of 500 to 2000 ° C, more specifically, at a temperature of 900 to 1500 ° C. When the heat treatment is performed within the above temperature range, the hetero-element corresponding to the impurity can be sufficiently removed in the carbonization process of the carbon precursor, thereby reducing the irreversible capacity and improving the charge-discharge characteristics.

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

The carbon precursor may be contained in an amount of 0.1 to 80 parts by weight, specifically 0.5 to 50 parts by weight, based on 100 parts by weight of the spherical natural graphite particles. When the carbon precursor is contained within the above range, the distribution of microvoids formed on the surface and inside of the spherical natural graphite particles can be appropriately maintained.

The solution may further include a lithium compound in addition to the spherical natural graphite particles. In this case, the solution containing the spherical natural graphite particles, the lithium compound, and the solvent may be dried after the ultrasonic treatment to produce the graphite-modified particles as in the method of producing the graphite-modified particles described above, A step of heat treating the particles to produce a graphite-modified composite particle can be further roughened.

When the lithium compound is added, the irreversible reaction of the spherical natural graphite particles is reduced, and at the same time, the high rate charging / discharging characteristics of the lithium secondary battery can be improved.

The lithium compound is lithium hydroxide containing LiOH or LiOH (H ₂ O); Lithium nitrate (LiNO _3); Lithium acetate containing CH 3 COO Li or CH 3 COO Li 2 (H ₂ O); Lithium carbonate (Li ₂ CO ₃ ); And lithium fluoride (LiF) may be used, but the present invention is not limited thereto.

The ultrasonic treatment may be carried out in an aqueous solution in which the lithium compound is dissolved or in an organic solvent.

When the graphite-modified particles obtained by the ultrasonic treatment are subjected to the heat treatment, decomposition reaction of the lithium compound occurs to form lithium oxide (Li ₂ O), lithium fluoride (LiF) and lithium carbonate (Li ₂ CO ₃ ) It is possible to obtain a graphite-modified composite particle in which the surface of the natural graphite particles and the surface inside the spheroidized natural graphite particles are further modified.

The heat treatment may be performed at a temperature of 150 to 2500 占 폚, specifically 200 to 1500 占 폚. When the heat treatment is performed within the above-mentioned temperature range, the decomposition reaction of the lithium compound occurs sufficiently and the surface of the spheroidized natural graphite particles is further modified, thereby reducing the irreversible capacity and improving the charge-discharge characteristics.

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

The lithium compound may be included in an amount of 0.1 to 50 parts by weight, and more specifically 0.3 to 30 parts by weight, based on 100 parts by weight of the spherical natural graphite particles. When the lithium compound is contained within the above range, the lithium compound is impregnated and distributed between the microvoids of the spherical natural graphite particles, so that the charge-discharge characteristics such as the initial charge-discharge efficiency can be improved.

The solution may further contain both the carbon precursor and the lithium compound in addition to the spherical natural graphite particles. In this case, the solution containing the spherical natural graphite particles, the carbon precursor, the lithium compound, and the solvent may be dried after the ultrasonic treatment to produce the graphite-modified particles as in the method of producing the graphite-modified particles described above , And heat-treating the graphite-modified particles to produce a graphite-modified composite particle.

The kind and content of the carbon precursor and the lithium compound are as described above.

The heat treatment may be performed at a temperature of 150 to 2500 DEG C and may be performed in an atmosphere containing nitrogen, argon, hydrogen, or a mixed gas thereof, or under vacuum.

According to another embodiment, there is provided a negative electrode active material produced according to the above-described production method.

The negative electrode active material may include spherical natural graphite particles whose surface has been modified. Also, the negative electrode active material may include graphite-modified composite particles in which the surface of the spheroidized natural graphite particles and the inner surface of the spheroidized natural graphite particles are coated with low-crystalline carbon and amorphous carbon. Also, the negative electrode active material may include graphite-modified composite particles in which the surface of the spherical natural graphite particles and the inner surface of the spherical natural graphite particles are coated with low-crystalline carbon and amorphous carbon containing a lithium compound.

According to another embodiment, there is provided a lithium secondary battery including the negative electrode, the positive electrode and the electrolyte solution including the negative active material.

The lithium secondary battery can 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 can 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.

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 the negative electrode current collector.

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

The positive electrode may also be prepared by mixing the positive electrode active material, the binder and optionally a conductive material to form a composition for forming a positive electrode active material layer, and then applying the composition to a positive electrode current collector such as aluminum.

The electrolytic solution is a lithium salt; And non-aqueous organic solvents, organic solid electrolytes, inorganic solid electrolytes, and the like.

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, ricifrcr, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, An ether, a methyl ethyl pyrophonate, an ethyl propionate, a methyl ethyl ketone derivative, a methyl ethyl ketone derivative, a methyl ethyl ketone derivative, Etc. may be used.

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 of spherical natural graphite particles (Carbonics, SGB10L) having an average particle size (D50) of 11 μm was added to 100 parts by weight of a solvent mixed with distilled water and acetone at a weight ratio of 6: 4, and then stirred using a magnetic stirrer At the same time, ultrasonically treated at a frequency of 20 Hz for 375W and for 5 minutes, and then dried naturally at 80 DEG C to prepare graphite-modified particles.

Example  2

1 part by weight of spherical natural graphite particles (Carbonics, SGB10L) having an average particle size (D50) of 11 μm was added to 100 parts by weight of a solvent mixed with distilled water and acetone at a weight ratio of 6: 4, and then stirred using a magnetic stirrer At the same time, subjected to ultrasonic treatment for 10 minutes at an intensity of 375 W at a frequency of 20 Hz, and then dried naturally at 80 캜 to prepare graphite-modified particles.

Example  3

A solution containing 0.025 part by weight of lithium acetate in 100 parts by weight of distilled water was prepared. 1 part by weight of spherical natural graphite particles (Carbonics, SGB10L) having an average particle diameter (D50) of 11 mu m was added to the solution and ultrasonicated for 10 minutes at a frequency of 20 Hz and at an intensity of 375 W, Lt; 0 > C to prepare graphite-modified particles. The graphite-modified particles were heat-treated at 450 캜 in an air atmosphere without holding time and then subjected to a furnace cooling to prepare graphite-modified composite particles having an average particle size (D50) of 13 탆.

Example  4

A solution containing 0.08 part by weight of petroleum pitch (yield after carbonization: 0.05% by weight) in 100 parts by weight of tetrahydrofuran was prepared. 1 part by weight of spherical natural graphite particles (Carbonics, SGB10L) having an average particle diameter (D50) of 11 mu m was added to the prepared solution, and the mixture was stirred and ultrasonicated for 5 minutes at a frequency of 20 Hz and at an intensity of 375 W, Lt; 0 > C to prepare graphite-modified particles. The graphite-modified particles were heat-treated at 1200 ° C for 1 hour in an argon atmosphere and then subjected to furnace cooling to prepare graphite-modified composite particles having an average particle size (D50) of 12.8 탆.

Example  5

A solution containing 0.16 part by weight of petroleum pitch (yield after carbonization: 0.1% by weight) in 100 parts by weight of tetrahydrofuran was prepared. 1 part by weight of spherical natural graphite particles (Carbonics, SGB10L) having an average particle diameter (D50) of 11 mu m was added to the prepared solution, and the mixture was stirred and ultrasonicated for 5 minutes at a frequency of 20 Hz and at an intensity of 375 W, Lt; 0 > C to prepare graphite-modified particles. The graphite-modified particles were heat-treated at 1200 ° C for 1 hour in an argon atmosphere, and then subjected to furnace cooling to prepare graphite-modified composite particles having an average particle size (D50) of 13.4 탆.

Example  6

A solution containing 0.5 part by weight of polyacrylic acid in 100 parts by weight of distilled water was prepared. 1 part by weight of spherical natural graphite particles (Carbonics, SGB10L) having an average particle size (D50) of 11 mu m was added to the prepared solution, and the mixture was stirred and sonicated for 5 minutes at a frequency of 20 Hz and at an intensity of 375 W, And spray dried to prepare graphite-modified particles. The graphite-modified particles were heat-treated at 900 ° C for 1 hour in an argon (Ar) atmosphere and then furnace-cooled to prepare graphite-modified composite particles having an average particle size (D50) of 13 탆.

Example  7

A solution containing 0.5 part by weight of polyacrylic acid and 0.1 part by weight of lithium acetate was prepared in 100 parts by weight of distilled water. 1 part by weight of spherical natural graphite particles (Carbonics Inc., SGB10L) having an average particle diameter (D50) of 11 占 퐉 was added to the prepared solution, stirred at a frequency of 20 Hz and ultrasonicated for 5 minutes at a frequency of 20 Hz And then spray-dried at 160 DEG C to prepare graphite-modified particles. The graphite-modified particles were heat-treated at 900 ° C for 1 hour in an argon (Ar) atmosphere, and then subjected to furnace cooling to prepare graphite-modified composite particles having an average particle size (D50) of 16μm.

Comparative Example  One

Spherical natural graphite particles (Carbonics, SGB10L) having an average particle diameter (D50) of 11 mu m were used as an anode active material.

Comparative Example  2

A solution containing 0.08 part by weight of petroleum pitch (yield after carbonization: 0.05% by weight) in 100 parts by weight of tetrahydrofuran was prepared. 1 part by weight of spherical natural graphite particles (Carbonics, SGB10L) having an average particle diameter (D50) of 11 mu m was added to the solution, stirred for 1 hour, naturally dried at 80 DEG C and argon And then carbonized to obtain spherical natural graphite particles.

Evaluation 1: Scanning electron microscope of negative electrode active material SEM ) Photo analysis

SEM photographs of each of the negative electrode active materials prepared in Examples 1 to 7 and Comparative Examples 1 and 2 are shown in Figs. 1 to 9.

FIGS. 1 to 6 are scanning electron microscope (SEM) photographs of the negative electrode active materials according to Examples 1 to 6, FIGS. 7A and 7B are SEM photographs of the negative electrode active material according to Example 7, And a 20,000 magnification. 8 and 9 are scanning electron microscope (SEM) photographs of the negative electrode active material according to Comparative Examples 1 and 2, respectively.

Referring to FIGS. 1 to 7B, it can be confirmed that microvoids are formed on the surface of spherical natural graphite particles in the negative electrode active materials of Examples 1 to 3. The negative electrode active materials of Examples 4 to 7 were obtained by coating carbon on the surface of the spherical natural graphite particles and the surface of the spherical natural graphite particles so that the size of the micropores became finer on the surface of the spherical natural graphite particles, In the case of the heat treatment after the ultrasonic treatment in the solution containing the carbon precursor and the lithium acetate together, it can be confirmed that the lithium carbonate particles are present on the particle surface in the case of Example 7.

The negative electrode active material of Comparative Example 1 was obtained by not subjecting the spherical natural graphite particles to the ultrasonic treatment and showed the surface of the spherical natural graphite particles and the negative electrode active material of Comparative Example 2 was a graphite particle not yet ultrasonicated Which indicates that carbon particles are coated on the surface of the spheroidized natural graphite particles.

Evaluation 2: Analysis of particle size distribution of anode active material

The average particle size (D50) of the negative electrode active material is shown in Table 1 below by measuring the particle size distribution of the negative electrode active material prepared in Examples 1 to 7 and Comparative Examples 1 and 2 by the laser diffraction scattering particle size distribution measurement method.

Example Comparative Example One 2 3 4 5 6 7 One 2 Average particle size (D50) (占 퐉) of the negative electrode active material 11.4 11.5 13 12.8 13.4 13 16 11 12.5

As shown in Table 1, in the case of Examples 1 and 2 in which ultrasonic treatment was performed and in Example 3 in which ultrasonic treatment was performed in a solution containing a lithium compound, as compared with the case of Comparative Example 1 in which ultrasonic treatment was not performed, The average particle size (D50) of the active material is increased. Compared with the case of Examples 4 to 6 in which the solution containing the carbon precursor was ultrasonicated and the case of Example 7 in which the ultrasonic treatment was performed in the solution containing the carbon precursor and the lithium compound, The average particle size (D50) of the negative electrode active material is increased. This is due to the formation of microvoids on the surface and inside of the spheroidized natural graphite particles by opening a gap between spherical natural graphite particles through ultrasonic treatment.

Evaluation 3: Specific surface area  analysis

The specific surface area (BET surface area) of the negative electrode active materials prepared in Examples 1 to 7 and Comparative Examples 1 and 2 was measured by gas adsorption / desorption, and the results are shown in Table 2 below.

Example Comparative Example One 2 3 4 5 6 7 One 2 Specific surface area (m ² / g) of the negative electrode active material 6.7 6.8 7 9.2 9.6 10 11 6.6 1.6

It can be seen from the above Table 2 that the specific surface area of the negative electrode active material is increased as compared with the case of Comparative Example 1 in which the ultrasonic treatment is not performed in Examples 1 and 2 in which the ultrasonic treatment is performed. In addition, it can be confirmed that the specific surface area is increased compared to the case of Comparative Example 1 in the case of the ultrasonic treatment in the solution containing the lithium compound. Compared with the case of Examples 4 to 6 in which ultrasonic treatment was carried out in a solution containing a carbon precursor and in the case of Example 7 in which a carbon precursor and a solution containing a lithium compound were subjected to ultrasonic treatment, It can be confirmed that the specific surface area of the active material is greatly increased. This is due to the formation of microvoids on the surface and inside of the spheroidized natural graphite particles by opening a gap between spherical natural graphite particles through ultrasonic treatment.

Evaluation 4: X-ray of anode active material diffraction  Pattern analysis

Crystallinity of the negative active material prepared in Examples 1 to 7 and Comparative Examples 1 and 2 was measured using an X-ray diffraction pattern analyzer, and the results are shown in FIGS. 10 to 12.

Fig. 10 shows the X-ray diffraction pattern (XRD) of the negative electrode active material according to Examples 1 and 2 and Comparative Example 1, Fig. 11 shows the X-ray diffraction pattern (XRD) of the negative electrode active material according to Examples 3 and 7 and Comparative Example 1, (XRD), and FIG. 12 shows an X-ray diffraction pattern (XRD) of the negative electrode active material according to Examples 4 to 6 and Comparative Example 2.

10 and 12, it can be seen that the crystallinity of the spherical natural graphite particles is maintained as it is even when the spherical natural graphite particles are subjected to ultrasonic treatment. Also, referring to FIG. 11, it can be confirmed that lithium carbonate is formed in Examples 3 and 7 in which a solution containing a lithium compound is subjected to heat treatment after ultrasonic treatment.

(Preparation of Test Cell)

Each of the negative electrode active materials prepared in Examples 1 to 7 and Comparative Examples 1 and 2 and CMC / SBR (carboxymethylcellulose / styrene-butadiene rubber) were mixed in distilled water at a weight ratio of 95: 5 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.

Using the respective cathodes and lithium metal as positive electrodes, a separator made of a porous polypropylene film was laminated between the negative electrode and the positive electrode to produce an electrode assembly. Thereafter, an electrolytic solution in which 1 M of LiPF ₆ was dissolved in a mixed solvent of diethyl carbonate (DEC) and ethylene carbonate (EC) (DEC: EC = 1: 1) was added to prepare a test cell.

Evaluation 5: Scanning electron microscope of cathode ( SEM ) Photo analysis

Scanning electron microscope (SEM) photographs of the respective cathode surfaces prepared according to Examples 1, 4, 6 and 7 and Comparative Examples 1 and 2 are shown in Figs.

13 to 16 are scanning electron microscope (SEM) photographs of the surface of the negative electrode prepared according to Examples 1, 4, 6 and 7, respectively, and Figs. 17 and 18 are photographs of the negative electrode surface prepared according to Comparative Examples 1 and 2 It is an electron microscope (SEM) photograph.

Spheroidal natural graphite particles not coated with carbon are squeezed during sintering process to produce spherical natural graphite particles. Referring to FIGS. 13 and 17, it can be seen that the degree of the pressing phenomenon due to the pressing process in manufacturing the negative electrode according to Example 1 and Comparative Example 1 is similar. 14 to 16 and 18, compared to the case of Comparative Example 2 in Examples 4, 6 and 7 ultrasonically treated with a solution containing a carbon precursor, the compression of the particles due to the pressing process during the manufacturing of the negative electrode was similar , And that in Examples 4, 6 and 7 and Comparative Example 2, the pressing phenomenon of particles was improved as compared with the case of Example 1 and Comparative Example 1.

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

The initial charge-discharge characteristics of Examples 1 to 7 and Comparative Examples 1 and 2 were evaluated by the following method using the prepared test cell, and the results are shown in Table 3 below.

For the cells prepared according to Examples 1 to 7 and Comparative Examples 1 and 2, charging was performed in CC / CV mode at a current density of 70 mA / g (0.2 C rate), the termination voltage was maintained at 0.005 V, Charging was terminated when the current was 7 mA / g (10% current density). The discharge was performed in CC mode with a current density of 70 mA / g and the termination voltage was maintained at 2V.

In Table 3 below, the initial efficiency (%) is obtained as a percentage of the initial discharge capacity versus the initial charge capacity.

Initial efficiency (%) Example 1 90 Example 2 90 Example 3 92.5 Example 4 91.5 Example 5 91.2 Example 6 90 Example 7 91 Comparative Example 1 90 Comparative Example 2 91.5

It can be seen from Table 3 that the initial efficiency is the same as that of Comparative Example 1 in which the negative electrode active material prepared by ultrasonic treatment is not used in the case of Example 1, In the case of Example 3, the initial efficiency is greatly increased as compared with Comparative Example 1. In the case of Examples 4 to 6 using the anode active material prepared by ultrasonic treatment in the solution containing the carbon precursor and in the case of Example 7 in which the carbon precursor and the solution containing the lithium compound were ultrasonicated, And the initial efficiency is similar.

Evaluation 7: Analysis of high rate charging characteristics of lithium secondary battery

Using the prepared test cell, high-rate charging characteristics according to Examples 1 to 7 and Comparative Examples 1 and 2 were evaluated in the following manner. The results are shown in Table 4 below.

In the case of the cells prepared according to Examples 1 to 7 and Comparative Examples 1 and 2, charging was performed in CC mode at a current density of 70 to 700 mA / g, the end voltage was maintained at 0.005 V, the discharge was 70 mA / g current density, and the termination voltage was maintained at 2V.

Charging capacity (mAh / g) 70mA / g 350mA / g 700mA / g Example 1 337 225 103 Example 2 321 205 75 Example 3 327 210 72 Example 4 339 252 122 Example 5 334 209 82 Example 6 335 230 108 Example 7 331 231 100 Comparative Example 1 308 150 50 Comparative Example 2 322 200 70

It can be seen from the above Table 4 that Examples 1 to 7 using the negative electrode active material produced by ultrasonic treatment have excellent high rate charging characteristics as compared with Comparative Examples 1 and 2 using the negative active material prepared without the ultrasonic treatment Can be confirmed.

Evaluation 8: Analysis of high rate discharge characteristics of lithium secondary battery

The high-rate discharge characteristics according to Examples 1 to 7 and Comparative Examples 1 and 2 were evaluated by the following method using the prepared test cell, and the results are shown in Table 5 below.

In the case of the cells prepared according to Examples 1 to 7 and Comparative Examples 1 and 2, charging was performed in CC / CV mode at a current density of 70 mA / g, the end voltage was maintained at 0.005 V and the current was 7 mA / g (10% current density). The discharge was performed in the CC mode in the range of 70 to 3,500 mA / g, and the termination voltage was maintained at 2V.

Discharge capacity (mAh / g) 70mA / g 350mA / g 700mA / g 1750mA / g 3500 mA / g Example 1 358 357 356 349 286 Example 2 359 358 357 348 284 Example 3 354 353 350 323 282 Example 4 355 355 354 352 348 Example 5 354 351 348 346 337 Example 6 355 354 353 343 330 Example 7 349 349 347 333 330 Comparative Example 1 358 347 331 280 196 Comparative Example 2 346 332 320 305 280

It can be seen from Table 5 that Examples 1 to 7 using the negative electrode active material produced by the ultrasonic treatment have superior high rate discharge characteristics as compared with Comparative Examples 1 and 2 using the negative active material prepared without the ultrasonic treatment Can be confirmed.

Evaluation 9: Analysis of cycle life characteristics of lithium secondary battery

The cycle life according to Examples 1, 3, 4 and 7 and Comparative Example 1 was evaluated using the test cell prepared above, and the results are shown in FIG.

Charging was done in CC mode with a current density of 70 mA / g (0.2C) and the termination voltage was maintained at 0.005V. The discharge was performed in a CC mode with a current density of 70 mA / g (0.2C) and the end voltage was maintained at 2V, and a total of 50 cycles were performed.

19 is a graph showing the cycle life characteristics of the negative electrode prepared according to Examples 1, 3, 4 and 7 and Comparative Example 1, respectively.

Referring to FIG. 19, it can be seen that Examples 1, 3, 4 and 7, in which spherical natural graphite particles were subjected to ultrasonic treatment, were superior in cycle life characteristics to those of Comparative Example 1 in which ultrasonic treatment was not performed.

From this, it is possible to produce a negative electrode active material having micropores formed on the surface and inside of the spheroidized graphite particles through ultrasonic treatment, and the negative electrode active material has improved reactivity with the electrolyte solution and is excellent in high rate charge / discharge characteristics and cycle life characteristics A 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 (26)

Preparing a solution including spheroidized natural graphite particles, a carbon precursor, and a solvent, the particles being agglomerated and assembled;
Ultrasonically treating the solution to open the gap between the spheroidized natural graphite particles and the spherical natural graphite particles while maintaining the crystallinity of the spheroidized natural graphite particles;
Drying the ultrasonic treated solution to prepare graphite-modified particles; And
And heat-treating the graphite-modified particles to produce a graphite-modified composite particle having a gap formed between the surface of the spherical natural graphite particle and the surface and inside of the spherical natural graphite particle coated with low crystalline and amorphous carbon Lt; / RTI >
Wherein the ultrasonic waves are irradiated at an intensity of 100 to 1000 W and for a time of 1 to 10 minutes.
The method according to claim 1,
Wherein the spherical natural graphite particles are prepared by assembling scaly natural graphite particles into a spherical shape.
The method according to claim 1,
Wherein the spheroidized natural graphite particles have an average particle diameter (D50) of 3 to 40 占 퐉.
The method according to claim 1,
The solvent is at least one selected from the group consisting of water, N-methylpyrrolidone, dimethylformamide, toluene, ethylene, dimethylacetamide, acetone, methyl ethyl ketone, hexane, tetrahydrofuran, decane, ethanol, methanol, isopropanol, Wherein the negative electrode active material for lithium secondary battery is a lithium secondary battery.
The method according to claim 1,
Wherein the spherical natural graphite particles are contained in an amount of 0.1 to 200 parts by weight based on 100 parts by weight of the solvent.
delete The method according to claim 1,
Wherein the ultrasonic wave has a frequency of 10 to 40 Hz.
The method according to claim 1,
The drying may be carried out by at least one spray drying method selected from rotary spraying, nozzle spraying and ultrasonic spraying; A drying method using a rotary evaporator; Vacuum drying method; Or a natural drying method, for producing a negative electrode active material for a lithium secondary battery.
delete The method according to claim 1,
The carbon precursor may be selected from the group consisting of citric acid, stearic acid, sucrose, polyvinylidene fluoride, carboxymethylcellulose (CMC), hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, (EPDM), sulfonated EPDM, starch, phenolic resin, furan resin, per furyl alcohol, polyacrylic acid, polyacrylic sodium, polyacrylonitrile, polyimide, epoxy resin, cellulose, styrene, polyvinyl Wherein the negative electrode active material comprises at least one selected from the group consisting of alcohol, polyvinyl chloride, coal pitch, petroleum pitch, mesophase pitch, low molecular weight heavy oil, glucose, gelatin and saccharides.
The method according to claim 1,
Wherein the heat treatment is performed at a temperature of 500 to 2500 ° C.
The method according to claim 1,
Wherein the heat treatment is performed in an atmosphere containing nitrogen, argon, hydrogen, or a mixed gas thereof, or under vacuum.
The method according to claim 1,
Wherein the carbon precursor is contained in an amount of 0.1 to 80 parts by weight based on 100 parts by weight of the spherical natural graphite particles.
delete delete delete delete delete The method according to claim 1,
Wherein the solution further comprises a lithium compound
A method for producing a negative electrode active material for lithium secondary batteries.
20. The method of claim 19,
The lithium compound is lithium hydroxide containing LiOH or LiOH (H ₂ O); Lithium nitrate (LiNO _3); Lithium acetate containing CH 3 COO Li or CH 3 COO Li 2 (H ₂ O); Lithium carbonate (Li ₂ CO ₃ ); And lithium fluoride (LiF). 2. A method for producing a negative active material for a lithium secondary battery, comprising:
20. The method of claim 19,
Wherein the heat treatment is performed at a temperature of 150 to 2500 캜.
20. The method of claim 19,
Wherein the heat treatment is performed in an atmosphere containing nitrogen, argon, hydrogen, or a mixed gas thereof, or under vacuum.
20. The method of claim 19,
Wherein the carbon precursor is contained in an amount of 0.1 to 80 parts by weight based on 100 parts by weight of the spherical natural graphite particles,
Wherein the lithium compound is contained in an amount of 0.1 to 50 parts by weight based on 100 parts by weight of the spherical natural graphite particles.
A process for producing a polyurethane foam, which is produced by the process according to any one of claims 1 to 5, 7, 8, 10 to 13 and 19 to 23,
Spherical natural graphite particles assembled with particles grained; And
Low crystalline and amorphous carbon
And a graphite-modified composite particle comprising a graphite-
Wherein the spherical natural graphite particles have a gap formed therebetween while maintaining the crystallinity of the spherical natural graphite particles through the ultrasonic treatment,
Wherein the low crystalline and amorphous carbons are present on the surface of the spheroidized natural graphite particles and are present on the surface of the spherical natural graphite particles
Negative electrode active material for lithium secondary battery.
An anode comprising the anode active material of claim 24;
anode; And
Electrolyte
≪ / RTI > 25. The method of claim 24,
Wherein the graphite-modified composite particle further contains a lithium compound in the gap between the surface of the spherical natural graphite particle and the spherical natural graphite particles and the open spaces of the internally-
Negative electrode active material for lithium secondary battery.

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