KR102277243B1 - Manufacturing method of Anode Active Material including Silicon Composite - Google Patents

Abstract

The present invention is
A) preparing a core by mixing polycrystalline silicon and single crystal silicon and then pulverizing in an organic solvent;
B) forming a shell including a first conductive carbon surrounding the core by heat-treating after inputting the precursor of the first conductive carbon to the prepared core; and
C) preparing a silicon composite in which a second conductive carbon is positioned on all or part of the shell surface by adding a second conductive carbon after forming the shell and heat-treating;
It relates to a method for producing a negative active material comprising: a high-capacity negative electrode active material having excellent conductivity, and a lithium secondary battery having excellent lifespan characteristics, output characteristics and safety including the same

Description

Manufacturing method of Anode Active Material including Silicon Composite

The present invention relates to a method for manufacturing a negative active material including a high-capacity silicon composite having excellent conductivity.

Lithium secondary batteries are widely used as power sources for mobile electronic devices, including mobile phones, and their application fields are expanding as demand for large devices such as electric vehicles increases.

Meanwhile, most of the currently commercialized lithium secondary batteries use a carbon-based material as an anode active material. In particular, graphite shows a very reversible charge/discharge behavior due to the uniaxial orientation of the graphite layer, showing excellent lifespan characteristics, and exhibiting a potential almost similar to that of lithium metal. It has the advantage of being able to obtain high energy. However, despite these advantages, the low theoretical capacity (372 mAh/g) of graphite acts as a limit at the present time when a high-capacity battery is required.

Accordingly, there is an attempt to use a metal material such as Si, Sn, Al, etc., which exhibits a relatively high capacity, as a material that can replace the carbon-based negative electrode active material. However, these metal materials cause large volume expansion and contraction during the insertion and desorption of lithium, which may cause micronization and loss of conduction paths, thereby reducing overall battery performance, such as deterioration of lifespan characteristics.

In order to solve this problem, various carbon materials are simply mixed with Si, fine powdered Si is chemically fixed on the carbon surface using a silane coupling agent, etc., or amorphous carbon is fixed on the Si surface through CVD, etc. There is this.

However, in the case of a material in which a carbon material is simply mixed with Si, carbon is liberated from Si in a process where Si undergoes large volume expansion and contraction as charging and discharging proceed, which leads to a significant decrease in lifespan characteristics due to deterioration of electrical conductivity. there is a problem.

In addition, the material in which fine powder of Si is chemically fixed to the carbon surface using a silane coupling agent or CVD does not have a long bonding duration by the silane coupling agent or CVD, so as the charge/discharge cycle progresses, the lifespan characteristics may decrease. Moreover, there is a problem in that it is difficult to obtain a negative electrode material of stable quality by uniformly performing the physicochemical adhesion.

Despite these various attempts, the problem of electrode damage due to expansion of Si during the discharge process was still raised.

Therefore, there is a high need for a high-capacity anode active material having excellent conductivity and a lithium secondary battery having excellent lifespan characteristics and output characteristics, including the same, and high safety.

An object of the present invention is to solve the problems of the prior art as described above and the technical problems that have been requested from the past.

Specifically, it is an object of the present invention to provide a method of manufacturing a negative active material including a high-capacity silicon composite having excellent conductivity capable of manufacturing a lithium secondary battery having excellent safety and lifespan characteristics and output characteristics.

The present invention is

A) preparing a core by mixing polycrystalline silicon and single crystal silicon and then pulverizing in an organic solvent;

B) by adding a precursor of the first conductive carbon to the prepared core and then heat-treating to surround the core to form a shell including one conductive carbon; and

C) preparing a silicon composite in which the second conductive carbon is positioned on all or part of the shell surface by adding a second conductive carbon after forming the shell and heat-treating;

It provides a method of manufacturing a negative active material comprising a.

The core is a primary particle and may include secondary particles formed by arranging pulverized polycrystalline silicon particles and pulverized single crystal silicon particles having different aspect ratios.

The shape of the pulverized polycrystalline silicon particles may be needle-like, and the shape of the pulverized single-crystal silicon particles may be plate-like.

The aspect ratio of the pulverized polycrystalline silicon particles may be greater than 4.0 and less than or equal to 10, and the aspect ratio of the pulverized single crystal silicon particles may be greater than or equal to 1.0 and less than or equal to 4.0.

The mixing ratio of the polycrystalline silicon and the single crystal silicon may be 30:70 to 70:30 by weight.

The precursor of the first conductive carbon may be a precursor of amorphous carbon.

The precursor of the amorphous carbon may be one or more selected from the group consisting of coal-based pitch, mesophase pitch, petroleum-based pitch, coal-based oil, petroleum-based heavy oil, organic synthetic pitch, phenolic resin, furan resin, and polyimide resin. have.

The content of the precursor of the first conductive carbon may be 5 to 30 parts by weight based on 100 parts by weight of the polycrystalline silicon and single crystal silicon blend.

The second conductive carbon may be crystalline carbon.

The content of the second conductive carbon may be 1 to 10 parts by weight based on 100 parts by weight of the polycrystalline silicon and single crystal silicon blend.

In step a), a dispersant may be additionally added to suppress agglomeration of the compounded silicone.

The present invention is

A') preparing a core by mixing polycrystalline silicon and single crystal silicon and pulverizing them in an organic solvent;

B ') after inputting the precursor of the first conductive carbon to the prepared core, heat treatment to surround the core to form a shell containing one conductive carbon;

C') preparing a first silicon composite in which a second conductive carbon is positioned on all or part of the shell surface by adding a second conductive carbon after forming the shell and heat-treating; and

D') preparing a secondary silicon composite including amorphous carbon surrounding the primary silicon composite by adding a precursor of amorphous carbon to the first silicon composite, high-temperature compression, and high-temperature firing;

may include.

The precursor of the amorphous carbon may be one or more selected from the group consisting of coal-based pitch, mesophase pitch, petroleum-based pitch, coal-based oil, petroleum-based heavy oil, organic synthetic pitch, phenolic resin, furan resin, and polyimide resin. have.

In step d'), 10 to 30 parts by weight of a precursor of amorphous carbon may be mixed based on 100 parts by weight of the primary silicon composite.

The precursor of the amorphous carbon may be one or more selected from the group consisting of coal-based pitch, mesophase pitch, petroleum-based pitch, coal-based oil, petroleum-based heavy oil, organic synthetic pitch, phenolic resin, furan resin, and polyimide resin. have.

The high-temperature compression in step d') may be performed at 120 to 250° C. for 20 to 50 minutes.

In step d'), the high-temperature sintering may be performed at 700 to 2000° C. for 1 to 2 hours.

The anode active material prepared according to the present invention is a primary particle, and since the anode active material including secondary particles formed by arranging polycrystalline silicon pulverized particles and single crystalline silicon pulverized particles having different aspect ratios, the voids in the secondary particles are minimized. Since the capacity per unit volume is maximized, the lifespan characteristics of the lithium secondary battery may be improved accordingly.

In addition, in the negative active material prepared according to the present invention, the pores remaining fine inside the secondary particles increase the passage of lithium ions during the charging and discharging process of the battery, thereby improving the output characteristics of the lithium secondary battery. .

In addition, the anode active material prepared according to the present invention has a core-shell structure, wherein the shell is made of a first conductive carbon, and it is possible to prepare an anode active material in which the second conductive carbon is located on all or part of the surface of the shell, Even if the shrinkage and expansion of silicon particles are repeated due to the insertion and desorption of lithium ions in the charging and discharging process of the battery, the first conductive carbon and the second conductive carbon act as a buffer to suppress volume expansion and damage of the core. Because it has durability, damage to the electrode can be minimized

In addition, since the anode active material prepared according to the present invention includes a secondary silicon composite formed by gathering a primary silicon composite on an amorphous carbon matrix, it is possible to minimize particle disintegration during repeated charge/discharge processes, and at the same time, silicon particles and an electrolyte solution It is possible to suppress the contact of the lithium secondary battery according to the safety can be secured.

1 is a schematic diagram schematically showing a cross-section of an anode active material manufactured according to an embodiment of the present invention; and
2 is a schematic diagram schematically illustrating a cross-section of a negative active material manufactured according to an embodiment of the present invention;
3 is an SEM photograph of the silicon composite in Experimental Example 1;
4 is data showing the average particle diameter of the silicon composite in Experimental Example 2;
5 is a photograph of the surface shape of a lithium-charged negative electrode in Experimental Example 3;
6 is a graph showing the capacity retention rate according to the cycle progress in Experimental Example 3; and
7 is a graph showing the capacity retention rate according to the cycle progress in Experimental Example 4;

Anode active material (silicon composite 100) manufacturing method

the present invention

A) preparing a core by mixing polycrystalline silicon and single crystal silicon and then pulverizing in an organic solvent;

B) by adding a precursor of the first conductive carbon to the prepared core and then heat-treating to surround the core to form a shell including one conductive carbon; and

C) preparing a silicon composite in which the second conductive carbon is positioned on all or part of the shell surface by adding a second conductive carbon after forming the shell and heat-treating;

It provides a method of manufacturing a negative active material comprising a.

Silicon has a theoretical capacity of about 3,600 mA/g, indicating a relatively high capacity compared to conventional carbon-based anode materials, but it causes large volume expansion and contraction during insertion and desorption of lithium ions, resulting in micronization and conduction. There is a problem in that life characteristics are deteriorated due to loss of path, etc.

Hereinafter, the present invention will be described with reference to FIGS. 1(a) to (c).

Referring to FIG. 1( a ), in step a), a core including secondary particles formed by arranging polycrystalline silicon pulverized particles 111 and single crystal silicon pulverized particles 112 that are primary particles and have different aspect ratios to prepare a core Since the voids in the secondary particles are minimized and the capacity per unit volume is maximized, the lifespan characteristics of the lithium secondary battery can be improved accordingly.

At the same time, due to the structural characteristics of the pores remaining inside the secondary particles, the passage of lithium ions is increased in the charging/discharging process of the battery, thereby improving the output characteristics of the lithium secondary battery.

Specifically, in step A), the polycrystalline silicon and single crystal silicon are mixed and mixed with an organic solvent to prepare a silicon slurry, which is then circulated and pulverized in a milling system.

The pulverized polysilicon particles 111 and the pulverized single crystal silicon particles 112 that are primary particles and have different aspect ratios may be manufactured by pulverizing polycrystalline silicon and single crystal silicon through the milling process. At the same time, the pulverized primary particles are arranged through a cycle in the milling system to produce secondary particles with minimized voids, which form a core.

That is, in the present invention, "primary particle" means each of the pulverized polycrystalline silicon particles 111 and the pulverized single crystal silicon particles 112 having different aspect ratios, and "secondary particle" refers to the primary particles, that is, the aspect ratio It is a particle formed by gathering different pulverized polycrystalline silicon particles 111 and pulverized single crystal silicon particles 112 .

In addition, in the present invention, "arrangement" means that primary particles having different aspect ratios are gathered to form secondary particles so that the voids formed inside the secondary particles are minimized.

The milling process may be performed using a beads mill, a high energy ball mill, a planetary mill, a stirred ball mill, a vibration mill, and the like. Specifically, a bead mill or a ball mill may be used, which may be made of a chemically inert material that does not react with silicon and organic matter, and more specifically, made of a zirconia material.

Polycrystalline silicon and single-crystal silicon exhibit a certain shape when pulverized using physical and chemical methods as a characteristic according to the crystal structure, for example,

The shapes of the pulverized polycrystalline silicon particles 111 and the pulverized single crystal silicon particles 112 may be plate-like, needle-like, rectangular parallelepiped, prismatic, ellipsoidal, columnar, or the like.

Preferably, the shape of the pulverized polycrystalline silicon particles 111 may be a needle shape, and the shape of the pulverized single crystal silicon particles 112 may be a plate shape. Here, "acicular" or "plate-shaped" has an approximate shape even if it is not a complete needle or plate, and irregularities may be formed on the surface.

The shapes of the pulverized polycrystalline silicon particles 111 and the pulverized single crystal silicon particles 112 may be expressed by an aspect ratio.

In the present invention, the aspect ratio of the pulverized polycrystalline silicon particles 111 may be greater than 4.0 and less than or equal to 10, and the aspect ratio of the pulverized single crystal silicon particles 112 may be greater than or equal to 1.0 and less than or equal to 4.0. If it is out of the above range, the intended effect of the present invention according to the minimization of voids through the arrangement of the particles cannot be obtained, and the bond between the primary particles is weakened and cycle characteristics may be deteriorated, which is not preferable. In detail, the aspect ratio of the pulverized polycrystalline silicon particles 111 may be 5.0 or more and 9.0 or less, and the aspect ratio of the pulverized single crystal silicon particles 112 may be 1.5 or more and 3.5 or less.

The size of the pulverized polycrystalline silicon particles 111 and the pulverized single crystal silicon particles 112 as the primary particles is nano-sized, for example, by pulverizing polycrystalline silicon and single-crystal silicon having a crystal size of 1 nm to 30 nm, respectively. can be formed. It is possible to implement a high capacity within the above range and minimize the voids of the secondary particles while improving the initial efficiency.

The mixing ratio of the polycrystalline silicon as the primary particles and the single crystal silicon may be 30:70 to 70:30 by weight. When the amount of monocrystalline silicon is too large, economical efficiency is lowered in terms of cost, and when the amount of polycrystalline silicon is excessively large, there is a risk of severe micronization in the charging/discharging process of the battery. In addition, when it is out of the above range, it is not preferable because the intended effect of the present invention according to the minimization of voids cannot be obtained through the arrangement of silicon particles having different aspect ratios. Specifically, the mixing ratio of the polycrystalline silicon and the single crystal silicon may be 40:60 to 60:40 by weight.

As mentioned above, due to the structural characteristics of the micropores remaining inside the secondary particles, the lithium ion movement path increases during the charging/discharging process of the battery, thereby improving the output characteristics of the lithium secondary battery.

The organic solvent is not particularly limited as long as the blended polycrystalline silicon and single crystal silicon can be uniformly dispersed, but for example, aromatic hydrocarbons such as benzene, toluene, xylene, and mesitylene, methyl ethyl ketone, acetone, and methyl amyl ketone. , methyl isobutyl ketone, ketones such as cyclohexanone, ethanol, propanol, butanol, hexanol, cyclohexanol, ethylene glycol, may be one or two or more selected from the group consisting of alcohols such as glycerin.

The content of the organic solvent may be 100 parts by weight to 300 parts by weight based on 100 parts by weight of the blended polycrystalline silicon and single crystal silicon. If it is out of the above range, silicon may not be sufficiently dispersed or economic feasibility may be lowered in the manufacturing process, which is not preferable.

Referring to FIG. 1(b), step b) is a process of heat-treating after inputting the precursor of the first conductive carbon to the manufactured core, surrounding the core, which is a secondary particle, and including the first conductive carbon 120 a shell is formed.

The method of forming the shell including the first conductive carbon 120 in step b) is not limited, and either a dry coating method such as vapor deposition, CVD (chemical vapor deposition) method, or a liquid coating method such as impregnation and spraying can be used. have.

The first conductive carbon precursor may be a precursor of amorphous carbon. The amorphous carbon can suppress the expansion of the core by properly imparting strength to maintain the shape of the core shell. Specifically, it may be one or more selected from the group consisting of coal-based pitch, mesophase pitch, petroleum-based pitch, coal-based oil, petroleum-based heavy oil, organic synthetic pitch, phenol resin, furan resin, and polyimide resin. Since petroleum-based pitch is obtained by refining impurity components from the high boiling point residue remaining after rectifying crude oil, it can be preferably used.

The content of the first conductive carbon precursor may be 5 to 30 parts by weight based on 100 parts by weight of the polycrystalline silicon and single crystal silicon blend. If the content is less than the above range, the core may not be sufficiently wrapped and the reactivity with the electrolyte may be increased, which may decrease cycle characteristics. If the content is too large, dispersion stability may be reduced when forming the negative electrode mixture, which is not preferable. In detail, the content of the first conductive carbon precursor may be 5 to 20 parts by weight based on 100 parts by weight of the polycrystalline silicon and single crystal silicon blend.

In step b), the first conductive carbon precursor is added and impurities such as hydrocarbons and sulfur having a relatively low boiling point are removed through heat treatment in an inert atmosphere in a temperature range of 100° C. to 700° C. to surround the core and conduct the first conductivity. A shell including carbon 120 may be formed. For example, when petroleum-based pitch is used as the first conductive carbon precursor, carbides of pitch may be formed as amorphous carbon through heat treatment.

Referring to Figure 1 (c), after forming the core-shell structure, the second conductive carbon 130 is added and then heat-treated to prepare a silicon composite in which the second conductive carbon is located on all or part of the surface of the core-shell. have.

The second conductive carbon 130 may further improve electrical conductivity while forming a conductive passage. The second conductive carbon 130 may be crystalline carbon, for example, one selected from the group consisting of natural graphite, artificial graphite, expanded graphite, graphene, carbon black, fullerene soot, or It may be a combination of two or more types, but is not limited thereto. Specifically, it may be graphene, which is a single layer of graphite.

The second conductive carbon 130 may form a film on all or part of the shell including the first conductive carbon 120 . In detail, a film of 60 to 100% based on the total surface volume of the first conductive carbon 120 may be formed, and the thickness may be 10 to 50 nm. If the film formation range is too small out of the above range, there is a risk that electrical conductivity may be lowered, which is not preferable.

The content of the second conductive carbon 130 may be 1 to 10 parts by weight based on 100 parts by weight of the polycrystalline silicon and single crystal silicon blend. If the content is less than the above range, the core may not be sufficiently wrapped and the reactivity with the electrolyte may be increased, which may decrease cycle characteristics. If the content is too large, dispersion stability may be reduced when forming the negative electrode mixture, which is not preferable. In detail, the content of the second conductive carbon may be 3 to 8 parts by weight based on 100 parts by weight of the polycrystalline silicon and single crystal silicon blend.

The heat treatment may be performed in an oven drying method, for example, may be performed at 100 °C to 250 °C.

In some cases, it is possible to prepare a dispersed silicone slurry by adding a dispersant in the blending process or grinding process of step a), or to suppress agglomeration of the blended silicone slurry during the grinding process.

The dispersant may be used without limitation as long as it is known in the art, for example, N-methyl-2-pyrrolidone, diacetone alcohol, dimethylformaldehyde, propylene glycol monomethyl ether, methyl cellosolve, ethyl cellosolve, butyl Cellosolve, isopropyl cellosolve, acetylacetone, methyl isobutyl ketone, n-butyl acetate, cellosolve acetate, toluene, xylene, etc. may be used alone or in combination.

The dispersant may be 1 to 5 parts by weight based on 100 parts by weight of polycrystalline silicon and single crystal silicon, and if it is less than this, it is difficult to exert the intended effect of the present invention, and if it is more than this, it is not preferable because it may interfere with the formation of secondary particles. .

Anode active material (secondary silicon composite 300) manufacturing method

The present invention is

A') preparing a core by mixing polycrystalline silicon and single crystal silicon and pulverizing them in an organic solvent;

B') forming a shell including a first conductive carbon 220 surrounding the core by heat-treating after inputting the precursor of the first conductive carbon to the prepared core;

C') preparing the first silicon composite 200 in which the second conductive carbon 230 is located on all or part of the shell surface by adding a second conductive carbon 230 after forming the shell and heat-treating; and

D') by adding a precursor of amorphous carbon to the first silicon composite 200, high temperature compression, and high temperature firing to produce a secondary silicon composite 300 comprising amorphous carbon 310 surrounding the first silicon composite step;

It provides a method of manufacturing a negative active material comprising a.

The secondary silicon composite 300 according to the present invention is formed as if one or more primary silicon composites 200 are gathered on the first amorphous carbon matrix 310 to form one particle, so that the primary silicon composite By supporting (200), more appropriate strength can be given, so that particle shape collapse can be minimized during repeated charging and discharging, and conductivity can be improved.

The primary silicon composite 200 may be manufactured by the method described above.

Hereinafter, the present invention will be described with reference to FIGS. 2(a) to (c).

Referring to FIG. 2(a), in step A'), a core including secondary particles formed by arranging polycrystalline silicon pulverized particles 211 and single crystal silicon pulverized particles 212 that are primary particles and have different aspect ratios. Since the capacity per unit volume is maximized by minimizing the voids in the secondary particles, the lifespan characteristics of the lithium secondary battery can be improved accordingly.

At the same time, due to the structural characteristics of the pores remaining inside the secondary particles, the passage of lithium ions is increased in the charging/discharging process of the battery, thereby improving the output characteristics of the lithium secondary battery.

Specifically, in step A'), the polycrystalline silicon and single crystal silicon are mixed and mixed with an organic solvent to prepare a silicon slurry, which is then circulated in a milling system and pulverized.

The pulverized polycrystalline silicon particles 211 and the pulverized single crystal silicon particles 212 that are primary particles and have different aspect ratios may be manufactured by pulverizing polycrystalline silicon and single crystal silicon through the milling process. At the same time, the pulverized primary particles are arranged through a cycle in the milling system to produce secondary particles with minimized voids, which form a core.

That is, in the present invention, "primary particle" means each of the pulverized polycrystalline silicon particles 211 and the pulverized single crystal silicon particle 212 having different aspect ratios, and the "secondary particle" refers to the primary particles, that is, the aspect ratio It is a particle formed by gathering different pulverized polycrystalline silicon particles 211 and pulverized single crystal silicon particles 212 .

In addition, in the present invention, "arrangement" means that primary particles having different aspect ratios are gathered to form secondary particles so that the voids formed inside the secondary particles are minimized.

The milling process may be performed using a beads mill, a high energy ball mill, a planetary mill, a stirred ball mill, a vibration mill, and the like. Specifically, a bead mill or a ball mill may be used, which may be made of a chemically inert material that does not react with silicon and organic matter, and more specifically, made of a zirconia material.

Polycrystalline silicon and single-crystal silicon exhibit a certain shape when pulverized using physical and chemical methods as a characteristic according to the crystal structure, for example,

The shapes of the pulverized polycrystalline silicon particles 211 and the pulverized single crystal silicon particles 212 may be plate-like, needle-like, rectangular parallelepiped, prismatic, ellipsoidal, columnar, or the like.

Preferably, the shape of the pulverized polycrystalline silicon particles 211 may be a needle shape, and the shape of the pulverized single crystal silicon particles 212 may be a plate shape. Here, "acicular" or "plate-shaped" has an approximate shape even if it is not a complete needle or plate, and irregularities may be formed on the surface.

The shapes of the pulverized polycrystalline silicon particles 211 and the pulverized single crystal silicon particles 212 may be expressed by an aspect ratio.

In the present invention, the aspect ratio of the pulverized polycrystalline silicon particles 211 may be greater than 4.0 and less than or equal to 10, and the aspect ratio of the pulverized single crystal silicon particles 212 may be greater than or equal to 1.0 and less than or equal to 4.0. If it is out of the above range, the intended effect of the present invention according to the minimization of voids through the arrangement of the particles cannot be obtained, and the bond between the primary particles is weakened and cycle characteristics may be deteriorated, which is not preferable. In detail, the aspect ratio of the pulverized polycrystalline silicon particles 211 may be 5.0 or more and 9.0 or less, and the aspect ratio of the pulverized single crystal silicon particles 212 may be 1.5 or more and 3.5 or less.

The size of the pulverized polycrystalline silicon particles 211 and the pulverized single-crystal silicon particles 212 as the primary particles is nano-sized, for example, by pulverizing polycrystalline silicon and single-crystal silicon having a crystal size of 1 nm to 30 nm, respectively. can be formed. It is possible to implement a high capacity within the above range and minimize the voids of the secondary particles while improving the initial efficiency.

The mixing ratio of the polycrystalline silicon as the primary particles and the single crystal silicon may be 30:70 to 70:30 by weight. When the amount of the monocrystalline silicon is too large, economical efficiency is lowered in terms of cost, and when the amount of the polycrystalline silicon is excessively large, there is a risk of severe micronization in the charging/discharging process of the battery. In addition, when it is out of the above range, it is not preferable because the intended effect of the present invention according to the minimization of voids cannot be obtained through the arrangement of silicon particles having different aspect ratios. Specifically, the mixing ratio of the polycrystalline silicon and the single crystal silicon may be 40:60 to 60:40 by weight.

As mentioned above, due to the structural characteristics of the micropores remaining inside the secondary particles, the lithium ion movement path increases during the charging/discharging process of the battery, thereby improving the output characteristics of the lithium secondary battery.

The organic solvent is not particularly limited as long as the blended polycrystalline silicon and single crystal silicon can be uniformly dispersed, but for example, aromatic hydrocarbons such as benzene, toluene, xylene, and mesitylene, methyl ethyl ketone, acetone, and methyl amyl ketone. , methyl isobutyl ketone, ketones such as cyclohexanone, ethanol, propanol, butanol, hexanol, cyclohexanol, ethylene glycol, may be one or two or more selected from the group consisting of alcohols such as glycerin.

The content of the organic solvent may be 100 parts by weight to 300 parts by weight based on 100 parts by weight of the blended polycrystalline silicon and single crystal silicon. If it is out of the above range, silicon may not be sufficiently dispersed or economic feasibility may be lowered in the manufacturing process, which is not preferable.

Referring to FIG. 2(b), the step b') is a process of heat-treating after inputting the precursor of the first conductive carbon to the prepared core, and surrounding the core, which is the secondary particle, of the first conductive carbon 220 . A shell containing it is formed.

The method of forming the shell including the first conductive carbon 220 in step b ') is not limited, and either a dry coating method such as vapor deposition, chemical vapor deposition (CVD) method, or a liquid coating method such as impregnation and spraying can be used. can

The first conductive carbon precursor may be a precursor of amorphous carbon. The amorphous carbon can suppress the expansion of the core by properly imparting strength to maintain the shape of the core shell. Specifically, it may be one or more selected from the group consisting of coal-based pitch, mesophase pitch, petroleum-based pitch, coal-based oil, petroleum-based heavy oil, organic synthetic pitch, phenol resin, furan resin, and polyimide resin. Since petroleum-based pitch is obtained by refining impurity components from the high boiling point residue remaining after rectifying crude oil, it can be preferably used.

The content of the first conductive carbon precursor may be 5 to 30 parts by weight based on 100 parts by weight of the polycrystalline silicon and single crystal silicon blend. If the content is less than the above range, the core may not be sufficiently wrapped and the reactivity with the electrolyte may be increased, which may decrease cycle characteristics. If the content is too large, dispersion stability may be reduced when forming the negative electrode mixture, which is not preferable. In detail, the content of the first conductive carbon precursor may be 5 to 20 parts by weight based on 100 parts by weight of the polycrystalline silicon and single crystal silicon blend.

In the step b'), the first conductive carbon precursor is added and impurities such as hydrocarbons and sulfur having a relatively low boiling point are removed through heat treatment in an inert atmosphere in a temperature range of 100° C. to 700° C. to surround the core. A shell including conductive carbon 220 may be formed. For example, when petroleum-based pitch is used as the first conductive carbon precursor, carbides of pitch may be formed as amorphous carbon through heat treatment.

After forming the core-shell structure, a silicon composite in which the second conductive carbon is located on all or a part of the surface of the core-shell may be manufactured by heat-treating after the second conductive carbon 230 is added.

The second conductive carbon 230 may further improve electrical conductivity while forming a conductive passage. The second conductive carbon 230 may be crystalline carbon, for example, one selected from the group consisting of natural graphite, artificial graphite, expanded graphite, graphene, carbon black, fullerene soot, or It may be a combination of two or more types, but is not limited thereto. Specifically, it may be graphene, which is a single layer of graphite.

The second conductive carbon 230 may form a film on all or part of the shell including the first conductive carbon 220 . Specifically, a film of 60 to 100% based on the total volume of the first conductive carbon 220 surface may be formed, and the thickness may be 10 to 50 nm. If the film formation range is too small out of the above range, there is a risk that electrical conductivity may be lowered, which is not preferable.

The content of the second conductive carbon 230 may be 1 to 10 parts by weight based on 100 parts by weight of the polycrystalline silicon and single crystal silicon blend. If the content is less than the above range, the core may not be sufficiently wrapped and the reactivity with the electrolyte may be increased, which may decrease cycle characteristics. If the content is too large, dispersion stability may be reduced when forming the negative electrode mixture, which is not preferable. In detail, the content of the second conductive carbon may be 3 to 8 parts by weight based on 100 parts by weight of the polycrystalline silicon and single crystal silicon blend.

The heat treatment may be performed in an oven drying method, for example, may be performed at 100 °C to 250 °C.

In some cases, it is possible to prepare a dispersed silicone slurry by adding a dispersant in the blending process or grinding process of step a'), or to suppress aggregation of the blended silicone slurry during the grinding process.

The dispersant may be used without limitation as long as it is known in the art, for example, N-methyl-2-pyrrolidone, diacetone alcohol, dimethylformaldehyde, propylene glycol monomethyl ether, methyl cellosolve, ethyl cellosolve, butyl Cellosolve, isopropyl cellosolve, acetylacetone, methyl isobutyl ketone, n-butyl acetate, cellosolve acetate, toluene, xylene, etc. may be used alone or in combination.

The dispersant may be 1 to 5 parts by weight based on 100 parts by weight of polycrystalline silicon and single crystal silicon, and if it is less than this, it is difficult to exert the intended effect of the present invention, and if it is more than this, it is not preferable because it may interfere with the formation of secondary particles. .

Referring to FIG. 2(d), in step D'), a precursor of amorphous carbon is added to the primary silicon composite, high-temperature compression and high-temperature firing, and amorphous carbon 310 surrounding the primary silicon composite 200 is included. manufacturing a secondary silicon composite 300;

The amorphous carbon precursor is, for example, selected from the group consisting of coal-based pitch, mesophase pitch, petroleum-based pitch, coal-based oil, petroleum-based heavy oil, organic synthetic pitch, phenolic resin, furan resin, and polyimide resin There may be more than one. The amorphous carbon precursor may use the same material as the first conductive carbon precursor, and in some cases, a different material may be used. Specifically, it may be a coal-based pitch.

In step d'), 10 to 30 parts by weight of a precursor of amorphous carbon may be mixed based on 100 parts by weight of the primary silicon composite. When the content of the amorphous carbon precursor is large or small outside the above range, it is difficult to form an amorphous matrix, and it is difficult to exert the intended effect of the present invention.

In the step d'), the secondary silicon composite 300 formed by gathering the primary silicon composite 200 in the high-temperature compression process may be formed, and overall mechanical strength may also be improved. The high-temperature sintering may be performed at 700 to 2000° C. for 1 to 2 hours in an inert atmosphere or a non-oxygen atmosphere. The high temperature compression and high temperature sintering temperature is not preferable because the intended effect of the present invention cannot be obtained when it is out of the optimum temperature range for forming the amorphous carbon 310 matrix.

Although described with reference to the following examples, the following examples are for the purpose of illustrating the present invention, and the scope of the present invention is not limited thereto.

<Example 1>

After mixing polycrystalline silicon and single crystal silicon in a ratio of 50:50 based on weight, 200 parts by weight of ethanol and 50 parts by weight of N-methyl-2-pyrrolidone were added based on 100 parts by weight of the mixture. After the blending, a silicon slurry containing nano silicon was prepared by pulverizing using a zirconia ball mill, and ethanol was evaporated through a spray drying process using this to prepare a core. The pulverized polycrystalline silicon particles formed through the above process were needle-shaped with an aspect ratio of 5.0 or more and 9.0 or less, and the pulverized single-crystal silicon particles had a plate shape with an aspect ratio of 1.5 or more and 3.5 or less.

10 parts by weight of petroleum pitch and 90 parts by weight of N-methyl-2-pyrrolidone were added to the core and heat-treated in an inert atmosphere at 200° C. to surround the core to prepare a shell containing carbides of pitch. The average thickness of the shell was 50 nm.

Thereafter, 5 parts by weight of graphene was added and then oven dried at 200° C. to prepare a silicon composite in which a graphene film was formed on the entire surface of the core-shell structure. The average thickness of the graphene film was 30 nm. The average particle diameter of the silicon composite is 7.5 to 8.5 μm.

<Example 2>

Using the silicon composite according to Example 1 as a primary silicone composite, 20 parts by weight of a coal-based pitch was mixed based on 100 parts by weight of the first silicon composite, followed by high temperature compression at 200° C., and calcination at 900° C. in a non-oxygen atmosphere. A secondary silicon composite including carbides of pitch surrounding the secondary silicon composite was prepared. The average particle diameter of the secondary silicon composite is 11.6 μm.

<Comparative Example 1>

A silicon-carbon composite (Si/C) having a D50 of 12.2 μm was prepared as an anode active material.

<Experimental Example 1>

The SEM photograph of the silicon composite prepared in Example 1 is shown in FIG. 3 below.

<Experimental Example 2>

The average particle size data of the silicon composite prepared in Example 1 is shown in FIG. 4 below.

According to FIG. 4, the D50 of the silicon composite was confirmed to be 8.173 μm.

<Experimental Example 3>

A negative electrode plate prepared by using each of the negative active materials according to Example 1 and Comparative Example 1 was cut in a circular shape of ^{1.4875 cm 2 as} a negative electrode, and a lithium (Li) metal thin film cut in a circular shape of ^{1.4875 cm 2 was used as a positive electrode.} did. Here, in the design of the negative electrode plate, the rolling density was 1.55 g/cc, the current density was 2.95 mA/cm ² , and the electrode plate capacity was 510 mAh/g. A separator of porous polyethylene is interposed between the positive electrode and the negative electrode, and 0.5 wt% of vinylene carbonate is dissolved in a mixed solution having a mixing volume ratio of methyl ethyl carbonate (EMC) and ethylene carbonate (EC) of 7: 3, A lithium coin half-cell was prepared by injecting an electrolyte in which 1M concentration of LiPF _{6 was dissolved.}

The thickness change rate, discharge capacity, initial efficiency, capacity retention rate, and discharge capacity and initial efficiency of Comparative Example 1 were measured using the lithium coin half cell and are shown in Table 1 below. In addition, the capacity retention ratio (CRR) of Example 1 is shown in FIG. 5, and the surface shape of the negative electrode charged with lithium after one cycle is shown in FIG. 6 below.

The first cycle (Hwaseong cycle) and the second cycle were charged and discharged at 0.1C (standard cycle), and from the 3rd cycle to the 49th cycle, charge and discharge were performed at 0.5C/discharge 1.0C. After 50 cycles, the battery is disassembled and the thickness is measured, and the thickness of the electrode after 50 cycles is compared to the average charge thickness (average value of 5 samples) in the initial charge. The rate of change was calculated.

The basic charging and discharging conditions are as follows.

- Charging condition: CC (constant current)/CV (constant voltage) (0.01V/0.01C, current cut-off)

- Discharge condition: CC (constant current) condition 1.5Vcut off

Discharge capacity (mAh/g) and initial efficiency (%) were derived from the results of one charge and discharge. Specifically, the initial efficiency (%) was derived by the following calculation.

- Initial efficiency (%) = (discharge capacity after one discharge / one charge capacity) × 100

The capacity retention rate and the electrode thickness change rate were respectively derived by the following calculations.

- Capacity retention rate (%) = (49 discharge capacity / 1 discharge capacity) × 100

- Electrode thickness change (%) = (electrode thickness change after 50 cycles/2 electrode thickness after charging cycle) × 100

Electrode thickness change rate (%, 1 cycle) Electrode thickness change rate (%) discharge capacity
(mAh/g) Initial efficiency
(%) Capacity retention rate
(%, 50 cycles) Example 1 23.5% 0.8% 1350 87.2% 92.3% Comparative Example 1 - - 1210 86.4 -

According to Table 1, it can be seen that the negative active material according to Example 1 is a silicon carbon composite according to Comparative Example 1, and has excellent discharge capacity and initial efficiency compared to the negative active material that does not include the configuration of the present invention.

<Experimental Example 4>

A negative electrode using each of the negative active material including the secondary silicon composite prepared in Example 2 and the negative active material according to Comparative Example 1 was prepared, and NCM 111 was used as a positive active material to prepare a positive electrode. Here, the negative electrode has a rolling density of 1.53 g/cc, a current density of 2.95 mA/Cm ² , and a plate capacity of 510 mAh/g. The current density of the anode is 2.65 mA/Cm ² and N/P is 1.11. A binder containing 1.5 wt% of SBR and CMC was used, and a porous polyethylene separator was interposed between the positive electrode and the negative electrode, and the mixing volume ratio of methylethyl carbonate (EMC) and ethylene carbonate (EC) was 7: 3 A lithium secondary battery having a capacity of 0.45Ah was prepared by dissolving vinylene carbonate dissolved in 0.5% by weight in the mixed solution, _{and injecting an electrolyte in which LiPF 6 of 1M concentration was dissolved.}

The charging conditions of the lithium secondary battery were CC/CV, 0.5C charging, 4.2V/0.05C cutoff, and the discharging conditions were CC, 1.0C discharge, and 2.85V cutoff to measure capacity retention, and are shown in Tables 2 and 4 below. .

1st. Efficiency
(%) Retention
(%, @100cycles) Example 2 89.9 89.6 Comparative Example 1 87.7 86.3

Referring to Table 2 and FIG. 6 , it can be seen that the difference in initial efficiency values is very large as the cycle progresses. The higher the initial efficiency, the greater the amount of cathode material used when manufacturing a secondary battery of the same capacity, which greatly affects the cost increase, so it is essential to use an anode material with high efficiency. Accordingly, it can be confirmed that the negative active material made of the secondary silicon composite according to the present invention has high efficiency and excellent lifespan characteristics.

(100) silicon composite
(111) single crystal silicon pulverized particles
(112) polycrystalline silicon pulverized particles (112)
(120) first conductive carbon (120)
(130) second conductive carbon
(200) first silicon composite
(211) single crystal silicon pulverized particles (111)
(212) polycrystalline silicon pulverized particles (112)
(220) first conductive carbon (120)
(230) second conductive carbon
(300) second silicon composite
(310) amorphous carbon matrix
Those of ordinary skill in the art to which the present invention pertains can make various applications and modifications within the scope of the present invention based on the above contents.

Claims (16)

A) After mixing polycrystalline silicon and single crystal silicon in a ratio of 40: 60 to 60: 40 by weight, pulverized in an organic solvent to grind needle-shaped polycrystalline silicon particles having an aspect ratio of 5.0 or more and 9.0 or less and plate-shaped single crystal silicon having an aspect ratio of 1.5 or more and 3.5 or less preparing a core comprising particles;
B) After adding 5 to 20 parts by weight of a precursor of amorphous carbon to the prepared core based on 100 parts by weight of a polycrystalline silicon and single crystal silicon blend, heat treatment at 100° C. to 200° C., a shell surrounding the core and containing amorphous carbon forming a; and
C) After forming the shell, 3 to 8 parts by weight of crystalline carbon is added based on 100 parts by weight of a polycrystalline silicon and single crystal silicon blend and heat treatment to prepare a silicon composite in which crystalline carbon is located on all or part of the shell surface step;
A method of manufacturing an anode active material comprising a. delete delete delete delete delete According to claim 1, wherein the precursor of the amorphous carbon is a coal-based pitch, mesophase pitch (mesophase pitch), petroleum-based pitch, coal-based oil, petroleum-based heavy oil, organic synthetic pitch, phenol resin, furan resin and a group consisting of a polyimide resin A method of producing a negative active material, characterized in that at least one selected from. delete delete delete The method of claim 1, wherein a dispersant is additionally added to suppress aggregation of the compounded silicone in step (a). The method of claim 1,
D') A secondary silicon composite comprising amorphous carbon surrounding the first silicon composite by adding 10 to 30 parts by weight of a precursor of amorphous carbon based on 100 parts by weight of the first silicon composite, which is the silicon composite, followed by high temperature compression and high temperature firing. manufacturing;
Method for producing a negative active material, characterized in that it further comprises. 13. The group of claim 12, wherein the precursor of the amorphous carbon is coal-based pitch, mesophase pitch, petroleum-based pitch, coal-based oil, petroleum-based heavy oil, organic synthetic pitch, phenolic resin, furan resin, and polyimide resin. A method of producing a negative active material, characterized in that at least one selected from. delete delete The method according to claim 12, wherein in step D'), the high-temperature compression is performed at 120 to 250° C. for 20 to 50 minutes, and the high-temperature sintering is performed at 700 to 2000° C. for 1 to 2 hours. manufacturing method.

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