KR101772402B1 - Method for preparing anode active material and anode active material for lithium secondary battery prepared thereby - Google Patents

Abstract

The present invention provides a method of preparing a negative electrode active material capable of improving orientation and a method of manufacturing a negative electrode active material for a lithium secondary battery produced by the method.
The lithium secondary battery including the negative electrode active material of the present invention has a small percentage change in the thickness of the electrode and can improve the life characteristics.

Description

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

The present invention relates to a method for manufacturing a negative electrode active material for a lithium secondary battery and a negative electrode active material produced therefrom, which improves the orientation properties of the negative electrode active material and can significantly reduce the rate of expansion of the electrode while exhibiting stable cycle characteristics in application of the secondary battery .

2. Description of the Related Art In recent years, a secondary battery with a high capacity has been required due to miniaturization of electronic devices. In particular, lithium secondary batteries having higher energy density than nickel-cadmium batteries and nickel-hydrogen batteries have attracted attention. Although lithium metal is used as the anode material of such a lithium secondary battery at first, a carbon-based material capable of preventing the occurrence of lithium dendrite is used.

Carbon materials used as electrode active materials are mainly classified into crystalline graphite and amorphous graphite raw materials. Examples of the crystalline graphite material include artificial graphite, natural graphite, and kish graphite. Amorphous carbon materials include soft carbon (soft carbon) obtained by calcining a coal-based pitch or a petroleum pitch at a high temperature ), Hard carbon obtained by firing a polymer resin such as phenol resin, and the like.

In the case of the graphite material described above, spherical graphite has low anisotropy of the material and is advantageous for maintaining uniformity of voltage and current distribution. On the other hand, graphite of flake (scaly graphite) is used as an anode material for lithium secondary battery It is difficult to form a coating layer having a predetermined thickness because of the anisotropy of the material itself and the subsequent inferiority of flowability due to mixing and slurrying with a solvent or a binder, And the like. In addition, due to the disadvantages of the particle shape, the voltage and current distribution inside the battery may be unevenly distributed due to the low density and the increase of the specific surface area. Therefore, spherical particles are still the most prevalent in terms of share of materials used.

Conventionally, spherical particles are mainly used as an anode material by spheroidizing a flaky high crystalline graphite material by a mechanical grinding method. The mechanically pulverized, round-shaped graphite particles have an improved orientation property and can be expected to reduce the expansion coefficient of the electrode, rather than the flaky particles arranged in one axis. However, in recent years, as the thickness of a mobile IT device becomes thinner, the thickness expansion rate of a battery inserted therein is expected to be lower. Therefore, an anode active material having an expansion coefficient lower than that of spherical particles is required.

SUMMARY OF THE INVENTION The present invention has been conceived to solve the problems as described above, and it is an object of the present invention to provide a method of manufacturing a battery, And a low expansion anode active material which can be produced by the above method. The present invention also provides a method for producing a negative active material for a lithium secondary battery,

(I) applying a mechanical external force to the graphite material in the form of a flake, wherein a part or all of the edge of the graphite material has primary particles with a curved or wrinkled shape ; (ii) coating the primary particles with an amorphous carbon precursor; And (iii) annealing the coated amorphous carbon precursor at a temperature higher than the carbonization temperature to assemble the anode active material.

(I) applying a mechanical external force to the spheroidized graphite particles, wherein a part or all of the flake graphite flakes in the particles are randomly exfoliated or broken into primary particles having a broken shape ; (ii) coating the primary particles with an amorphous carbon precursor; And (iii) annealing the coated amorphous carbon precursor at a temperature higher than the carbonization temperature to assemble the anode active material.

The present invention also provides a negative active material for a lithium secondary battery produced by the above-described method.

More specifically, the negative electrode active material comprises (a) at least one amorphous graphite primary particle; And (b) an amorphous carbon layer formed on at least a portion of the primary particle surface, the amorphous carbon layer having a secondary particle structure in which primary particles are assembled by the amorphous carbon layer, .

According to a preferred embodiment of the present invention, the negative electrode active material has an orientation index [I (002)] represented by the ratio of the X-ray diffraction intensity [I (002)] of the (002) crystal face to the X- I (002) / I (110)] may range from 50 to 110.

Here, the negative electrode active material may have a tap density of 0.5 to 0.8 g / cc and an average particle diameter of 10 to 30 탆.

In the present invention, by performing the process of forming the flaky graphite material to have a predetermined shape or peeling or splitting the flaky flakes in the particle by using the spheroidized graphite particles, the negative electrode active material Can be improved. Accordingly, when the negative electrode active material is applied to a battery, low expansion rate and long life characteristics of the battery can be ensured, which can be usefully applied to electrode materials of ultra-thin mobile IT devices.

1 is a scanning electron microscope (SEM) photograph showing the shapes of a conventional plate graphite material and a negative electrode active material prepared in Example 1 of the present invention.
2 is a photograph showing the shape change of the negative electrode active material according to one embodiment of the present invention.
3 is a photograph showing a shape change of the negative electrode active material according to another embodiment of the present invention.
FIG. 4 is a graph showing a change in orientation index obtained by XRD analysis of the anode active materials prepared in Examples 1 and 2 and Comparative Examples 1 and 2. FIG.
5 is a graph showing the rate of change of thickness of a battery according to a normal temperature lifetime by using the batteries of Examples 1 and 2 and Comparative Examples 1 and 2.

Hereinafter, the present invention will be described in detail.

The expansion ratio of the battery has various causes, but the expansion ratio of the negative electrode is a main cause. In order to reduce the rate of expansion of the negative electrode described above, the present invention intends to introduce a new manufacturing process capable of producing negative electrode active material particles with improved orientation.

More specifically, the present invention relates to a process for producing a graphite-based graphite material by applying an external force to a flake-shaped graphite material or spheroidized graphite particles as raw materials and adjusting them to a range where they are not pulverized or (similarly) a small crack is generated between the grains having the orientation of the grains, thereby changing the orientation of the grains as a whole.

Since the negative electrode active material having improved orientation properties through such a process has a lower crystal orientation ratio than conventional spheroidized particles, it can completely absorb the volume expansion caused by bonding with lithium ions during charging and discharging in the negative electrode active material have. Therefore, the overall electrode plate volume is not increased, the expansion rate of the battery can be drastically reduced, and the lifetime characteristics of the lithium secondary battery including the lithium secondary battery can be stably maintained.

≪ Production method of negative electrode active material >

Hereinafter, a method of manufacturing the negative electrode active material according to the present invention will be described. However, the present invention is not limited to the following production methods, and the steps of each process may be modified or selectively mixed if necessary.

In one preferred embodiment of the above production method, a primary particle having a specific shape is formed by applying a mechanical external force to a flaky graphite material or spheroidized graphite particles, and the surface of the primary particle is coated with an amorphous carbon precursor And then heat-treating and assembling the post-coated carbon precursor at a temperature higher than carbonization. At this time, if necessary, a secondary heat treatment step or a classification step may be further carried out.

More specifically, the negative electrode active material of the present invention can be largely manufactured in accordance with two embodiments. However, it is not particularly limited.

A first preferred embodiment for producing the negative electrode active material of the present invention comprises the steps of (i) applying a mechanical external force to a flake graphite material, wherein a part or all of the edge portion of the graphite material has primary particles (Step S10); (ii) coating the primary particles with an amorphous carbon precursor ('S20 step'); And (iii) annealing and annealing the coated amorphous carbon precursor at a temperature above the carbonization temperature (step S30).

Hereinafter, the manufacturing method will be described separately for each process step as follows.

(1) a primary particle production step (hereinafter referred to as 'S10 step');

In the step S10, a mechanical external force is applied to the flake graphite material, and the external force is adjusted to the extent that the flake graphite material is not pulverized or spheroidized or pseudo spheroidized to form primary particles.

As the raw material of the crystalline carbon material for use in the production of the negative electrode active material in the present invention, a graphite material having a purity of 90% or more on a flake basis can be used.

In general, graphite having a high crystallinity grows regularly in a regular manner and exhibits a flake (scaly, scaly) appearance. In addition, since the shape of the finally obtained negative electrode active material reflects the shape of the graphite as the raw material, the shape of the graphite is preferably close to the spherical shape, and the graphite having the aspect ratio (ratio of the major axis length to the minor axis length of the particles) It is good. Further, d002, which is a measurement value of X-ray diffraction, may be less than 0.337 nm.

Non-limiting examples of usable graphite materials include commercially available flake natural graphite, Kish Graphite or mixtures thereof.

The flake graphite material may have an average particle size in the range of 10 to 100 mu m, preferably 20 to 50 mu m. If the average particle size of the graphite material falls within the above range, the impurity content in the raw material is not excessively high, and the effect of primary particle formation can be exhibited as it is.

On the other hand, in the present invention, the use of a flaky graphite material is described, but it is also within the scope of the present invention to use a graphite material such as artificial graphite other than flakes. In the case of a non-flake-like graphite material, it may be used as a flake by pulverization using a known pulverizer.

The mixing and grinding apparatuses known in the art can be used as a device for imparting a mechanical external force in the step S10. Such a device will process the surface of the graphite material using the forces of compression, impact, shear, and friction. Non-limiting examples of usable mixing / grinding apparatuses include, but are not limited to, mechanofusion, roll milling, ball milling, attrition milling, planetary milling, Such as shaker milling, disk milling, shape milling, vertical shape milling, rotor blade milling, nauta milling, nobilta milling, Milling, V Mixing, and Jet Milling may be used.

The mixing / pulverizing time is adjusted within a suitable range so that the graphite raw material is repeatedly supplied or the graphitized raw material is allowed to stay in the pulverizer for a predetermined time, depending on the kind or amount of the graphite. In one example, the linear velocity may range from 10 to 40 m / s, and preferably from 30 to 40 m / s.

When the mechanical process is performed using the mechanical device as described above, primary particles in which graphite flakes on the flake in the graphite material (see FIG. 1 (a)) are folded or wrinkled in a polygonal shape are obtained 1 (b)). At this time, the crumpled angle? Of the edge portion may be in a range of 0 <? <180, preferably 0 <? <90.

At this time, a small crack exists between crystal grains having an orientation in a certain direction inside the primary grains, thereby changing the orientation of the grains as a whole. At the same time, fluidity between the crystal grains can be ensured through the cracks caused by the fine particulate impurities existing in the inside, and these fine particles can be assembled while forming micropores in a non-uniform direction.

(2) coating with an amorphous carbon precursor (hereinafter referred to as 'S20 step'),

In step S20, the amorphous carbon precursor is coated for the electrical characteristics of the primary particles obtained in the previous step S10 as the anode active material.

As a preferable example thereof, an amorphous carbon precursor is added to the bent or crushed primary particles, and homogeneously mixed, followed by stirring using a mechanical stirrer, whereby the amorphous carbon precursor is dispersed on the surface of the primary particles Is coated.

The amorphous carbon precursor is not particularly limited as long as it is a graphitizable material by firing, and conventional materials known in the art can be used without limitation. For example, there are a petroleum pitch, a coal pitch, a mesophase pitch, a coal tar pitch, a heat treated pitch, a vinyl chloride resin, a vinyl polymer, an aromatic hydrocarbon, a nitrogen compound, a sulfur compound, a coal liquefied oil, Based heavy oil, a cracked heavy oil or a mixture of at least one of these. The amount thereof may be in the range of 2 to 30 parts by weight, preferably in the range of 5 to 15 parts by weight, based on 100 parts by weight of the flake graphite material.

If the amorphous carbon material is used in an excessively large amount, a too thick film layer is formed to deteriorate electrical characteristics. If the amorphous carbon material is used in an excessively small amount, a too thin film layer is formed, resulting in peeling of the film during charge and discharge, . In general, it is preferable to use a material having a small average diameter of the flaky graphite material, for example, a powder having a particle diameter of 10 mu m or less, as the amorphous carbon material.

In step S20, the coating method may be performed by any conventional mixing method known in the art. For uniform mixing, general mixing may be performed or a dry or wet mechanical milling method may be used have. For example, it may be carried out by mixing and stirring the primary particles and the amorphous carbon precursor using a coater such as Convective, Tumbler, Impaction, High Shear, . The coating may be conducted in a dry process, a wet process, or a combined process of dry and wet combination. In this case, the conditions can be appropriately adjusted according to the content of the primary particles, the content of the primary particles, and the content and the content of the amorphous carbon precursor. For example, stirring may be performed at 100 to 2000 rpm for 10 minutes to 100 minutes.

When the amorphous carbon precursor and the primary particles are stirred under the above conditions, heat is generated due to friction and shear force, and the amorphous carbon precursor is melted due to the generated heat, thereby helping uniform coating of the primary particles .

(3) Heat treatment step (hereinafter referred to as 'S30 step')

In step S30, when the amorphous carbon precursor is fixed on the surface of the primary particles and stabilized, a heat treatment is performed to improve carbonation, impurity removal, and surface property.

The heat treatment may be carried out at a temperature of 600 to 1500 DEG C for 30 minutes to 72 hours. At this time, if the heat treatment is performed under the above-described conditions, the amorphous carbon precursor is stabilized, carbonization can proceed sufficiently, and the impurities in the carbon material can be completely removed.

As the amorphous carbon precursor coated on the surface of the primary graphite particles is subjected to the heat treatment step as described above, the carbonized material removes impurities therein and becomes hard carbon, thereby stabilizing the entire coating layer and improving the coating property.

In order to improve the crystallinity / homogeneity of the crystalline graphite material after the heat treatment and to improve the surface property of the amorphous carbon layer, it is preferable to heat the mixture at a temperature of 1000 ° C to 3,000 ° C, preferably 1000 ° C to 1500 ° C for 30 minutes to 72 hours for 2 The step of heat treatment with the car can be further carried out.

The thickness of the coating layer formed by the amorphous carbon is preferably in the range of 0.001 to 1 mu m in view of the capacity and the voltage flatness of the battery, but is not particularly limited to this.

FIG. 2 is a photograph showing the shape change of the negative electrode active material according to the first embodiment of the present invention.

More specifically, an external force is applied to the raw flake-like graphite material (Fig. 2 (a)) to form warped primary or secondary crushed particles (Fig. 2 (b)), The carbon precursor is applied (Fig. 2 (c)), followed by heat treatment and granulation (Fig. 2 (d)) to form a negative electrode active material.

A second preferred embodiment for producing the negative electrode active material of the present invention is to use spherical carbon particles instead of the flake graphite material used as the starting material in the first embodiment.

In a second preferred embodiment of producing the negative electrode active material, (i) a mechanical external force is applied to the spheroidized graphite particles, wherein a part or all of the graphite slices on the flake in the particle are randomly exfoliated ) Or forming primary particles having a broken shape ('S11 step'); (ii) coating the primary particles with an amorphous carbon precursor ('S20 step'); And (iii) annealing and annealing the coated amorphous carbon precursor at a temperature above the carbonization temperature (step S30).

(1-1) Primary particle production step (hereinafter referred to as 'S11 step')

In step S11, a mechanical external force is applied to the spheroidized graphite particles, and the spherical graphite particles are processed by controlling the external force to the extent that the spherical graphite particles are not pulverized. When such an external force adjusted to a specific range is applied, a part or all of the flaky graphite flakes in the spheroidized graphite particles are randomly exfoliated or the primary particles of the squared shape .

In the present invention, the carbon particles can be used without limitation in carbon particles spherulated in accordance with a conventional method known in the art. For example, a material formed by assembling and solidifying a carbon material with a mechanical external force may be used.

The spheroidized graphite particles may be spherical in shape by forming a plurality of flake graphite pieces into a spherical shape. More specifically, any one of a single flaked carbon material may be rolled or a plurality of flaky carbon materials (e.g., graphite flakes) may be assembled by assembling. In particular, it is preferable that a plurality of flake-shaped carbon materials exhibit a shape assembled into a concentric circle.

The spheroidized graphite particles may be natural graphite, artificial graphite, kish graphite, or pyrolytic graphite, and soft carbon, hard carbon, petroleum cokes, coal cokes, or a mixture of at least one thereof may be used . The shape of the graphite is preferably spherical, and graphite having an aspect ratio (ratio of the major axis length to the minor axis length of the particles) of 3 or less is preferably used. Further, d002, which is a measurement value of X-ray diffraction, may be less than 0.337 nm.

The spheroidized graphite particles are controlled to spherical particles having an average particle size that can be used as an anode material of a secondary battery, for example, in the range of 10 to 40 mu m, preferably 10 to 30 mu m. At this time, the average grain size in the machining process can be adjusted through appropriate selection of machining conditions.

In the step S11, spherical graphite particles are processed using a mechanical external force applying device. The mixing and grinding apparatuses known in the art can be used without limitation. For example, the mixing / grinding apparatus used in the above step S10 may be used in the same manner. Also, the mixing / pulverizing conditions are not particularly limited, and for example, the linear velocity may range from 10 to 40 m / s, and preferably from 15 to 30 m / s.

When a mechanical process is performed using a mechanical device as described above, some or all of the flake-shaped graphite flakes in the spheroidized graphite particles as raw materials are randomly exfoliated or broken into primary particles having a broken shape Is obtained.

The primary particles may be amorphous particles having a shape of a cabbage or an onion which is partly or entirely peeled off or peeled off.

As in the step S10, small cracks exist between crystal grains having an orientation in a certain direction within the primary particles, thereby effecting the effect of deforming the orientation of the crystal grains as a whole. Therefore, the orientation property for reducing the rate of expansion of the negative electrode is further improved.

After step S11 described above, steps S20 to S30 are sequentially performed in the same manner as in the first embodiment, whereby the negative electrode active material can be produced. The negative electrode active material of the present invention thus produced may have a structure as shown in FIG. 3 (d).

FIG. 3 is a photograph showing a change in shape of a negative electrode active material according to a second embodiment of the present invention.

More specifically, primary particles (Fig. 3 (b) to Fig. 3 (c)) are formed by applying an external force to spheroidized graphite particles (Fig. 3 The carbon precursor is applied, followed by heat treatment and granulation (FIG. 3 (d)) to form a negative electrode active material.

&Lt; Negative electrode active material &

The present invention provides a negative electrode active material for a lithium secondary battery, which is produced by the above-described method.

More specifically, the negative electrode active material comprises (a) at least one amorphous graphite primary particle; And (b) an amorphous carbon layer formed on part or all of the surface of the primary particle, wherein the amorphous carbon layer has a secondary particle structure in which primary particles are partially assembled and adhered and assembled, And a structure including voids in the structure.

Here, the amorphous primary particles may have a structure according to the above-described two embodiments. For example, the graphite flakes on the flakes include polygonal folded or wrinkled edges, and the crumpled angle? Of the edges may range from 0 <? <180 degrees, or some or all of the plurality of envelope layers may be peeled off or peeled off Cabbage or onion shaped amorphous particles.

The negative electrode active material of the present invention has a crystal orientation ratio in a specific range and is characterized in that the negative electrode active material absorbs the volumetric expansion of the metal during charging and discharging of the lithium secondary battery. Accordingly, the degree of thickness expansion of the battery including the battery can be reduced, thereby improving the volume expansion and life characteristics of the battery.

This orientation index indicates that the crystal structures inside the cathode are arranged in a certain direction and can be measured by X-ray diffraction (XRD).

More specifically, the negative electrode active material has an orientation index I (002) / I (110) which is represented by the ratio of the X-ray diffraction intensity of the (002) crystal face to the X-ray diffraction intensity of the (110) )] May range from 50 to 110, preferably from 70 to 100.

At this time, the XRD measurement can be performed under the conventional methods and conditions known in the art, whereby the orientation index of the cathode can be measured.

According to a preferred embodiment of the present invention, the negative electrode active material may have a tap density in the range of 0.5 to 0.8 g / cc and an average particle diameter of 10 to 30 탆.

1 is a scanning electron microscope (SEM) photograph showing the shapes of the natural graphite and the negative electrode active material (natural graphite) prepared in Example 1, which is a preferred embodiment of the present invention.

2 and 3 are photographs showing the shape changes of the negative electrode active material prepared in Examples 1 and 2, respectively. FIG. 4 is a graph showing the orientation indices of the negative active materials prepared in Examples 1 and 2, and it can be confirmed that the negative active material has a crystal orientation ratio adjusted to a specific range. Therefore, when the battery is manufactured using the above-mentioned negative electrode active material, the orientation property is improved compared to conventional spheroidized carbon particles, and thus it is possible to provide a battery having a reduction in thickness expansion rate, a high capacity and a long life.

<Cathode>

The negative electrode active material prepared in the present invention can be used as an anode material for a secondary battery, and can also be applied to, for example, a conductive material for fuel cell separator, graphite for refractory, or an electrode material for a positive electrode for a secondary battery.

The present invention provides an anode material for a secondary battery and a lithium secondary battery including the same.

At this time, the negative electrode material of the present invention is required to include at least the negative electrode active material having the above-described improved orientation. For example, the negative electrode active material itself may be used as a negative electrode active material, or a negative electrode material mixture obtained by mixing the negative electrode active material and a binder, a negative electrode material mixture paste obtained by further adding a solvent, Falls within the scope of the negative electrode material of the invention.

The negative electrode may be manufactured according to a conventional method known in the art. For example, a slurry is prepared by mixing and stirring a binder, a conductive agent, and a dispersant, if necessary, to an electrode active material, Followed by compression and drying.

The electrode material such as a dispersion medium, a binder, a conductive agent, and a current collector may be a conventional one known in the art, and the binder may be suitably used in an amount of 1 to 10 parts by weight based on the weight of the electrode active material and 1 to 30 parts by weight of the conductive material .

Examples of usable conductive agents include carbon black, acetylene black series or Gulf Oil Company, ketjen black, Vulcan XC-72, Super P, and the like.

Typical examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF) or a copolymer thereof, styrene butadiene rubber (SBR), cellulose and the like. Representative examples of the dispersing agent include isopropyl alcohol, N Methylpyrrolidone (NMP), acetone, and the like.

The current collector of the metal material may be any metal that has high conductivity and is a metal that can easily adhere the paste of the material and does not have reactivity in the voltage range of the battery. For example, a mesh, a foil, or the like of aluminum, copper, or stainless steel may be used.

<Lithium secondary battery>

In addition, the present invention provides a secondary battery, preferably a lithium secondary battery, including the electrode.

The lithium secondary battery of the present invention is not particularly limited except for using the above-described negative electrode active material with improved orientation, and can be manufactured according to a conventional method known in the art. For example, a separation membrane may be inserted between an anode and a cathode, and a nonaqueous electrolyte may be charged.

The lithium secondary battery of the present invention includes a cathode, a cathode, a separator, and an electrolyte as battery components. Components of the anode, the separator, the electrolyte, and other additives, if necessary, other than the cathode described above, Which is the same as that of the lithium secondary battery.

For example, the cathode may be a conventional cathode active material for lithium secondary batteries known in the art, and examples thereof include LiM _x O _y (M = Co, Ni, Mn, Co _a Ni _b Mn _c ) Lithium manganese composite oxides such as LiMn ₂ O ₄ , lithium nickel oxides such as LiNiO ₂ , lithium cobalt oxides such as LiCoO ₂ , and manganese, nickel, and cobalt of these oxides, (E.g., vanadium oxide containing lithium) or chalcogen compounds (e.g., manganese dioxide, titanium disulfide, molybdenum disulfide, etc.), and the like.

Also, the non-aqueous electrolyte includes electrolytic components commonly known in the art, such as an electrolyte salt and an electrolyte solvent.

(I) a cation selected from the group consisting of Li ⁺ , Na ⁺ , K ⁺ and (ii) a cation selected from the group consisting of PF ₆ ^- , BF ₄ ^- , Cl ^- , Br ^- , I ^- , ClO ₄ ^- , AsF ₆ ^- A combination of anions selected from the group consisting of CH ₃ CO ₂ ^- , CF ₃ SO ₃ ^- , N (CF ₃ SO ₂ ) ₂ ^- and C (CF ₂ SO ₂ ) ₃ ^- . Specific examples of the lithium salt include LiClO ₄ , LiCF ₃ SO ₃ , LiPF ₆ , LiBF ₄ , LiAsF ₆ , and LiN (CF ₃ SO ₂ ) ₂ . These electrolyte salts may be used alone or in combination of two or more.

The electrolyte solvent may be selected from cyclic carbonates, linear carbonates, lactones, ethers, esters, acetonitriles, lactams, and ketones.

Examples of the cyclic carbonate include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC) and fluoroethylene carbonate (FEC). Examples of the linear carbonate include diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), and methyl propyl carbonate (MPC). Examples of the lactone include gamma butyrolactone (GBL), and examples of the ether include dibutyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1,2-diethoxyethane, and the like. Examples of the ester include methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, butyl propionate, methyl pivalate and the like. Examples of the lactam include N-methyl-2-pyrrolidone (NMP), and the ketone is polymethyl vinyl ketone. The halogen derivative of the organic solvent may be used, but is not limited thereto. In addition, the organic solvent may be glyme, diglyme, triglyme, or tetraglyme. These organic solvents may be used alone or in combination of two or more.

The separator may use any porous material that interrupts the internal short circuit of both electrodes and impregnates the electrolyte. Examples thereof include polypropylene-based, polyethylene-based, polyolefin-based porous separation membranes, or composite porous separation membranes in which an inorganic material is added to the above-mentioned porous separation membranes.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the following Examples and Experimental Examples are merely illustrative of the present invention, and the scope of the present invention is not limited by the following Examples and Experimental Examples.

[Example 1]

1-1. Anode active material manufacturing

100 g of the graphite graphite was put into a rotating mill and operated at a linear velocity of 40 m / s for 6 minutes, and then crushed particles were mixed in a henschel mixer for 5 minutes in a henschel mixer. Thereafter, the substrate was heat-treated at 1300 ° C for 1 hour in a heat treatment furnace in a nitrogen atmosphere. Thereafter, large particles were removed, and an anode material having a center particle size of 17 mu m was obtained.

1-2. Cathode manufacture

96 parts by weight of the negative electrode active material prepared in Example 1 was added with 1 part by weight of a solution of cellulose as a binder resin, 2 parts by weight of styrene butadiene rubber (SBR) and 1 part by weight of carbon black as a conductive material to prepare a negative electrode slurry Was applied to the entire copper collector. Then, the negative electrode was prepared by rolling with a roll press.

1-3. Lithium secondary battery manufacturing

A coin type half cell was fabricated using the negative electrode and lithium metal as counter electrodes. At this time, a mixed solution (EC: EMC: DMC = 2/3/1 by volume) of ethylene carbonate (EC) / ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) in which 1.0 M LiPF ₆ was dissolved was used.

[Example 2]

100 g of the spherical graphite particles were charged into a mill and collided with air at a linear velocity of 15 m / s to decompose the particles. The particles were then mixed in a henschel mixer for 20 minutes in an amount of 5 wt% Treated at 1300 ° C for 1 hour. Thereafter, large particles were removed, and the anode material of Example 2 having a center particle size of 17 mu m was obtained.

Using the negative electrode material, a negative electrode and a lithium secondary battery were prepared in the same manner as in Example 1, respectively.

[Comparative Example 1]

100 g of graphite graphite was put into a rotating mill and operated at a linear velocity of 45 m / s for 12 minutes. Then, spheroidized particles were mixed for 5 minutes in a Henschel mixer for 20 minutes. Thereafter, the substrate was heat-treated at 1300 ° C for 1 hour in a heat treatment furnace in a nitrogen atmosphere. Thereafter, large particles were removed, and the negative electrode material of Comparative Example 1 having a center particle size of 17 mu m was obtained.

Using the negative electrode material, a negative electrode and a lithium secondary battery were prepared in the same manner as in Example 1, respectively.

[Comparative Example 2]

100 g of graphite graphite was put into a rotating mill and operated at a linear velocity of 45 m / s for 12 minutes. Then, spheroidized particles were mixed for 5 minutes in a Henschel mixer for 20 minutes. Then, it was heat-treated at 3000 ° C for 24 hours in a heat treatment furnace in a nitrogen atmosphere. Thereafter, large particles were removed to obtain an anode material of Comparative Example 2 having a center particle size of 17 mu m.

Using the negative electrode material, a negative electrode and a lithium secondary battery were prepared in the same manner as in Example 1, respectively.

[Comparative Example 3]

100 g of spheroidal graphite was charged into a rotating mill and operated at a linear velocity of 5 m / s for 6 minutes, and then spheroidized particles were mixed for 5 minutes in a Henschel mixer for 20 minutes. Thereafter, the substrate was heat-treated at 1300 ° C for 1 hour in a heat treatment furnace in a nitrogen atmosphere. Thereafter, large particles were removed to obtain an anode material of Comparative Example 3 having a center particle size of 17 mu m.

Using the negative electrode material, a negative electrode and a lithium secondary battery were prepared in the same manner as in Example 1, respectively.

 [Experimental Example 1: Measurement of orientation index]

X-ray diffractometry was performed on the negative electrode active material prepared in Examples 1 to 2 and Comparative Examples 1 to 3 using Cu Kα line. The intensity I (002) of the (002) plane of the negative electrode active material from the X- (I (002) / I (110)) which is the ratio of the intensity I (110) of the (110) plane to the intensity I The X-ray diffraction measurement was carried out according to the Japan Society for the Promotion of Science (JSPS) standard, and the results are summarized in Table 1 below.

Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Orientation index 102 96 140 160 190

[Experimental Example 2: Rate of Change in Cell Thickness and Performance Evaluation]

The batteries of the lithium secondary batteries manufactured in Examples 1 to 2 and Comparative Examples 1 to 3 were charged and discharged at 1 C to measure the thickness expansion rate of the battery for 200 cycles. The results are shown in Fig.

As a result of the tests, it was observed that the thickness expansion rate of the battery significantly increased before 50 cycles elapsed in the batteries of Comparative Examples 1 to 3 (see FIG. 5).

On the other hand, it was confirmed that the lithium secondary batteries of Examples 1 and 2 were significantly lower in the thickness expansion rate of the battery even after repeating 200 cycles. From these results, it can be seen that the lithium secondary battery including the negative electrode active material of the present invention exhibits stable cycle characteristics and significantly reduces the rate of expansion of the electrode.

Claims (15)

(i) injecting a graphite material on a flake into a device for imparting a mechanical external force, and adjusting an external force at a linear velocity of the device to 10 to 40 m / s so that part or all of the edges of the graphite material are bent Forming primary particles having a crumpled shape;
(ii) coating the primary particles with an amorphous carbon precursor; And
(iii) annealing the coated amorphous carbon precursor by heat treatment at a temperature higher than that of carbonization
Wherein the negative electrode active material for lithium secondary batteries is a lithium secondary battery. The method according to claim 1,
Wherein the primary particles formed in step (i) include edge portions formed by flaking graphite pieces in a polygonal shape or wrinkled, and a crumpled angle [theta] of the edge portion is in a range of 0 < A method for producing an anode active material. (i) injecting spheroidized graphite particles into a device for imparting a mechanical external force, and adjusting the external force at a linear velocity of 10 to 40 m / s to obtain a spherical flake graphite slice Forming primary particles partially or wholly randomly exfoliated or having a broken shape;
(ii) coating the primary particles with an amorphous carbon precursor; And
(iii) annealing the coated amorphous carbon precursor by heat treatment at a temperature higher than that of carbonization
Wherein the negative electrode active material for lithium secondary batteries is a lithium secondary battery. The method of claim 3,
Wherein the primary particles formed in step (i) are amorphous particles in the form of cabbage or onion having a part or all of a plurality of skin layers peeled or peeled off. The method according to claim 1 or 3,
The step (i) may be performed by any of a variety of methods including mechanofusion, roll milling, ball milling, attrition milling, planetary milling, shaker milling, disk milling, shape milling, vertical shape milling, rotor blade milling, nauta milling, nobilta milling, V Mixing, ) And jet milling (Zet Milling). The method for manufacturing a negative electrode active material for a lithium secondary battery according to claim 1, delete The method according to claim 1 or 3,
In the step (ii), the amorphous carbon precursor may be at least one selected from the group consisting of petroleum pitch, coal pitch, mesophase pitch, coal tar pitch, heat treated pitch, vinyl chloride resin, vinyl polymer, aromatic hydrocarbon, And at least one selected from the group consisting of asphaltene, crude oil, naphtha, petroleum heavy oil, and cracked heavy oil. The method according to claim 1 or 3,
Wherein the amount of the amorphous carbon precursor in the step (ii) ranges from 2 to 30 parts by weight based on 100 parts by weight of the flake graphite material or spheroidized graphite particles. The method according to claim 1 or 3,
Wherein the heat treatment temperature in the step (iii) is in the range of 600 to 1500 ° C. The method according to claim 1 or 3,
Further comprising the step of subjecting the material assembled by heat treatment in the step (iii) to a secondary heat treatment at a temperature of 1000 to 3000 ° C. A negative electrode active material for a lithium secondary battery produced by the method according to claim 1 or 3,
The negative electrode active material
One or more amorphous primary borers; And
And an amorphous carbon layer formed on part or all of the surface of the primary particle, the amorphous carbon layer having a secondary particle structure in which primary particles are assembled by the amorphous carbon layer,
(002) / I (110), which is the ratio of the X-ray diffraction intensity of the (002) crystal face to the X-ray diffraction intensity of the (110) crystal face measured using the Cu K? And a negative electrode active material for a lithium secondary battery. delete delete 12. The method of claim 11,
A tap density in the range of 0.6 to 0.8 g / cc, and an average particle diameter in the range of 10 to 30 占 퐉. A lithium secondary battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the negative electrode comprises the negative active material of claim 11.

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