KR102051072B1 - Composite anode active material, a method of preparing the composite anode material, and Lithium secondary battery comprising the composite anode active material - Google Patents

Abstract

The present invention is plate graphite; A metal alloyable with lithium disposed on the plate graphite surface; And silicon particles disposed on a surface of the plate graphite, a surface of a metal alloyable with lithium, or a combination thereof.

Description

Composite anode active material, a method of manufacturing the same, and a lithium secondary battery having a negative electrode comprising the same {Composite anode active material, a method of preparing the composite anode material, and Lithium secondary battery comprising the composite anode active material}

It relates to a composite cathode active material, and a negative electrode and a lithium battery comprising the same.

Lithium batteries have high voltage and high energy density and are used in various applications. For example, fields such as electric vehicles (HEV, PHEV) can operate at a high temperature, a large amount of electricity needs to be charged or discharged and must be used for a long time, so a high discharge capacity and excellent life characteristics are required. .

The carbonaceous material is porous and stable because of its small volume change during charge and discharge. In general, however, carbon-based materials have low battery capacity due to the porous structure of carbon. For example, the theoretical capacity of high crystalline graphite is 372 mAh / g in LiC ₆ composition. In addition, the high rate characteristic is low.

A metal capable of alloying with lithium may be used as the cathode active material having a high capacitance together with the carbonaceous material. For example, the metal alloyable with lithium is Si, Sn, Al, and the like. Among these, active research is being conducted on the negative electrode active material using the ball-milling Si particles together with the carbon-based material.

However, a silicon oxide layer is formed on the surface of the silicon particles during the fabrication and use of the ball-milling Si particles, and this silicon oxide layer has a problem of decreasing initial efficiency.

In addition, a metal capable of alloying with lithium, such as silicon, has a high discharge capacity, but the volume change rate of silicon reaches about 3.7 times during the charging and discharging process, so that a crack occurs in the negative electrode active material including silicon, resulting in deterioration of life characteristics. Can be.

In order to solve the above problems, there is still a need for a negative electrode active material having a high initial efficiency and excellent life characteristics and a method for producing the same.

One aspect is to provide a novel negative electrode active material.

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

Another aspect is to provide a lithium secondary battery including a negative electrode employing the negative electrode active material.

According to one aspect,

Plate-like graphite;

A metal alloyable with lithium disposed on the surface of the plate graphite; And

Silicon particles disposed on a surface of the plate graphite, a surface of a metal alloyable with lithium, or a combination thereof;

There is provided a composite cathode active material comprising a.

According to the other side,

(a) mixing a mixture of plate-like graphite and a metal alloyable with lithium to obtain a composite cathode active material precursor; And

(b) providing silicon particles on a surface of the composite cathode active material precursor;

Including,

Providing the silicon particles is provided by a chemical vapor deposition (CVD) of the silane gas, there is provided a method for producing a composite cathode active material.

According to another aspect,

A negative electrode including the negative electrode active material,

Anode, and

A lithium secondary battery comprising an electrolyte is provided.

According to one aspect, a lithium secondary battery including a negative electrode employing a composite cathode active material provided with silicon particles on a surface in a dot form has high initial efficiency and excellent lifespan characteristics. In particular, by providing the silicon particles in the form of dots on the surface of the composite cathode active material, it is possible to relieve the stress applied to the composite cathode active material during charging and discharging, thereby having excellent life characteristics.

1A is a SEM photograph of a composite cathode active material precursor prepared according to Preparation Example 1, and FIG. 1B is a SEM photograph of a composite cathode active material precursor prepared according to Comparative Preparation Example 1. FIG.
FIG. 2A is a SEM photograph of a composite cathode active material precursor prepared according to Preparation Example 2, and FIG. 2B is a SEM photograph of a composite cathode active material precursor prepared according to Comparative Preparation Example 2. FIG.
3 is a diagram of charge and discharge graphs of the lithium secondary batteries prepared in Example 3 and Comparative Example 2. FIG.
4 to 6 are graphs of electrochemical evaluation data measured by comparing Examples 4 and Comparative Examples 3 to 5, respectively.
7 is a SEM photograph showing the surface of the composite cathode active material according to the change of the dispersant content.
8 is a schematic diagram of a lithium battery according to an exemplary embodiment.
<Explanation of symbols for the main parts of the drawings>
1: lithium battery 2: negative electrode
3: anode 4: separator
5: battery case 6: cap assembly

The present inventive concept described below may apply various transformations and have various embodiments, and specific embodiments will be illustrated in the drawings and described in detail in the written description. However, this is not intended to limit the present invention to specific embodiments, and it should be understood to include all transformations, equivalents, or substitutes included in the technical scope of the present invention.

The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting of the inventive concepts. Singular expressions include plural expressions unless the context clearly indicates otherwise. Hereinafter, terms such as "comprise" or "have" are intended to indicate that there is a feature, number, step, action, component, part, component, material, or combination thereof described in the specification, one or the same. It is to be understood that the foregoing does not exclude in advance the possibility of the presence or addition of other features, numbers, steps, operations, components, parts, components, materials, or combinations thereof.

In the drawings, thicknesses are enlarged or reduced in order to clearly express various layers and areas. Like parts are designated by like reference numerals throughout the specification. When a part of a layer, film, region, plate, etc. in the specification is said to be "on" or "on" another part, this includes not only being directly above another part but also having another part in between. . The terms are used only to distinguish one component from another.

Hereinafter, a lithium secondary battery including a composite anode active material and an anode including the composite cathode active material according to exemplary embodiments will be described in more detail.

Composite cathode active material according to one embodiment is plate graphite; A metal alloyable with lithium disposed on the surface of the plate graphite; And a silicon coating layer disposed on the surface of the plate graphite, the surface of the metal alloyable with lithium, or a combination thereof.

According to one embodiment, the silicon coating layer may form a discontinuous coating layer on the surface of the composite cathode active material. For example, the silicon coating layer may have an island shape. As another example, the silicon coating layer may be provided on the surface of the composite cathode active material in the form of dots.

The composite cathode active material may have a silicon coating layer formed on the surface as a discontinuous coating layer or exist in a dot form, thereby securing a space capable of accommodating the expansion of the silicon coating layer. Therefore, since the stress generated in the silicon coating layer during charge and discharge can be sufficiently relaxed, the life characteristics of the composite cathode active material are improved.

Meanwhile, a carbon-silicon composite in which a silicon coating layer is formed on the surface of spheroidal graphite is already known, but when the silicon content is increased to increase the capacity, the silicon coating layer becomes thicker, and thus the stress generated during charging and discharging increases, resulting in a life characteristic. This remarkably deteriorating problem has existed.

To solve this problem, nano silicon particles are provided on the surface of spherical graphite to increase the surface area on which silicon can be applied, and by depositing silicon thereon, a thinner silicon content equivalent to that of conventional carbon-silicon composites can be obtained. The technique of constituting the silicone coating layer was invented by the present inventors, and achieved improvement of life characteristics over a certain level.

However, the deterioration of the life characteristics due to the expansion of the silicon coating layer is still a problem to be overcome from the practical point of view, and this problem is to use a plate graphite having a relatively large BET specific surface area in place of spherical graphite, It could be solved by constructing a discontinuous coating layer.

Specifically, the present inventor in the process of carefully examining the correlation between the BET specific surface area value and the capacity increase amount according to the deposition of the silicon coating layer, when the capacity increase amount and the BET specific surface area value of the composite cathode active material satisfy the following equation 1 The present invention has been completed in view of the fact that the silicone coating layer is formed in a discontinuous dot shape and the life characteristics are remarkably improved.

Therefore, the composite cathode active material may satisfy the following Equation 1:

<Equation 1>

Capacity increase (mAh / g) / BET specific surface area (m ² / g) <10

Here, the capacity increase amount means a difference between the initial capacity of the plate graphite and the initial capacity after the silicon coating layer is disposed. The BET specific surface area refers to the specific surface area of the final composite cathode active material.

According to one embodiment, the composite cathode active material has a BET specific surface area of 20 to 40 (m ² / g), and the content of the silicon particles is 6% to 14% by weight based on the total weight of the composite cathode active material. However, the present invention is not limited thereto, and the BET specific surface area value and the content of silicon particles satisfying Equation 1 may be easily selected.

According to one embodiment, the composite cathode active material may further include a dispersant.

Since the composite cathode active material further includes a dispersant, the metal alloyable with lithium may be uniformly disposed on the surface of the carbon-based material. By uniformly dispersing a metal alloyable with lithium, the surface area on which silicon particles can be deposited is increased, and a certain amount of silicon can be made into a thinner silicon coating layer thickness. In addition, if the coating layer having the same thickness as the silicon coating layer of the conventional carbon-silicon composite, it can include a larger amount of silicon, the capacity can be significantly increased.

In addition, by uniformly distributing metal alloyable with lithium on the surface of the plate graphite, the silicon coating layer deposited thereon can also be uniformly formed, and as a result, the efficiency according to the charge / discharge cycle is improved.

The dispersant is nonconductive or conductive. According to one embodiment, the dispersant is conductive. The dispersant allows for a uniform distribution of the alloyable metal with lithium while at the same time providing an electron transfer path between the lithium and alloyable metals and carbon-based materials to improve electrical conductivity. As a result, the composite cathode active material according to the embodiment improves the efficiency per cycle.

According to one embodiment, the dispersing agent may include carbon fibers such as carbon black, acetylene black, ketjen black, carbon fibers such as vapor-grown carbon fibers, graphite fine particles or combinations thereof. However, the present invention is not limited thereto, and any material for uniformly mixing the active material and the bain can be used as a dispersant.

In the composite cathode active material according to one embodiment, the metal alloyable with lithium may be distributed on all or part of the surface of the plate graphite. For example, the metal alloyable with lithium may be present in the form of an island or a thin film superimposed on the surface of the plate graphite.

In the composite cathode active material according to one embodiment, the metal alloyable with lithium is uniformly distributed on the surface of the plate graphite. By uniformly dispersing the metal alloyable with lithium, it is possible to include more silicon particles in the composite cathode active material while maintaining a constant thickness of the silicon coating layer, it is possible to manufacture a composite cathode active material of high capacity and high initial efficiency.

In the composite cathode active material according to one embodiment, the metal alloyable with lithium is at least one metal selected from the group consisting of Si, Sn, Al, Ge, Pb, Zn, Ag and Au, alloys thereof, oxides thereof, these Nitrides thereof, nitrides thereof, carbides thereof, or composites thereof with carbon-based materials.

For example, the metal alloyable with lithium may include Si particles, Si oxide particles, or a combination thereof. The surface of the Si particles may be oxidized in air to form Si oxides.

In the composite cathode active material according to one embodiment, the metal alloyable with lithium is non-spherical silicon particles. For example, the metal alloyable with lithium is amorphous silicon particles.

Median diameter of the silicon particles of the amorphous are (D ₅₀₎ may be a 20 nm to 300 nm, may be any of a range represented by any two values selected within this range.

For example, the median particle size of the amorphous silicon particles is (D ₅₀ ) is 25 nm to 300 nm. For example, the median particle size of the amorphous silicon particles is (D ₅₀ ) is 30 nm to 300 nm. For example, the median particle size of the amorphous silicon particles is (D ₅₀ ) is 35 nm to 300 nm. For example, the median particle size of the amorphous silicon particles is (D ₅₀ ) is 40 nm to 300 nm. For example, the median particle size of the amorphous silicon particles is (D ₅₀ ) is 45 nm to 300 nm. For example, the median particle size of the amorphous silicon particles is (D ₅₀ ) is 50 nm to 300 nm. For example, the median particle size of the amorphous silicon particles is (D ₅₀ ) is 20 nm to 290 nm. For example, the median particle size of the amorphous silicon particles is (D ₅₀ ) is 20 nm to 280 nm. For example, the median particle size of the amorphous silicon particles is (D ₅₀ ) is 20 nm to 270 nm. For example, the median particle size of the amorphous silicon particles is (D ₅₀ ) is 20 nm to 260 nm. For example, the median particle size of the amorphous silicon particles is (D ₅₀ ) is 20 nm to 250 nm.

The median particle size of the silicon particles can be adjusted according to the progress time of the ball milling process, when the particle diameter falls within the above range, high capacity and excellent life characteristics are guaranteed. For example, when the median particle size of the silicon particles is less than 20 nm by the ball milling process, since the silicon oxide film is formed on the surface of the silicon particles during the ball milling process, it becomes difficult to maintain the shape of the silicon particles, As a result, it is difficult to be used as a composite cathode active material material. In the case where the median particle size of the silicon particles obtained by the ball milling process exceeds 300 nm, the life characteristics are lowered due to the large stress during charge and discharge.

In the composite cathode active material according to one embodiment, the silicon coating layer comprises amorphous or semi-crystalline silicon particles. In this case, the silicon coating layer may maintain a stable structure with less risk of cracking the crystal due to volume expansion. Unlike crystalline silicon, amorphous or quasi-crystalline silicon has no directivity in which lithium is absorbed, thereby uniformly expanding in volume and having high lithium transfer rate. Amorphous or semi-crystalline silicon is less stress or strain than lithium absorption or desorption compared to crystalline silicon, it is possible to maintain a stable structure during the charge and discharge process.

In the composite cathode active material according to one embodiment, the silicon coating layer may have a dot shape, the thickness is 3 nm to 50 nm. When the silicon coating layer has a thickness in the above range, it becomes a very thin thin film form, the volume expansion can be sufficiently suppressed during charging and discharging, the rate rate is greatly increased. If the thickness of the silicon coating layer is less than 3 nm, it is difficult to expect a sufficient capacity increase effect, if it exceeds 50 nm, desorption of silicon particles occurs due to volume expansion during charging and discharging, so that the capacity and rate characteristics are deteriorated. Occurs.

In addition, the general negative electrode active material for a lithium secondary battery is a mixture of different materials to produce a slurry, so that the separation of the active material according to the volume change during the charge and discharge process may occur, the silicon coating layer is a metal and alloy capable of alloying with lithium in the form of a thin film and And / or bonded to a carbon-based material, it is possible to prevent layer separation during charge and discharge. As a result, rapid charge and discharge become easy.

Composite cathode active material according to one embodiment may further include a carbon coating layer on the outermost.

The carbon coating layer may include amorphous carbon. For example, the carbon included in the coating layer may be a fired product of a carbon precursor. The carbon precursor may be used in the art, and any carbon-based material may be used as long as the carbon-based material is obtained by firing. For example, the carbon precursor may be at least one selected from the group consisting of a polymer, coal tar pitch, petroleum pitch, meso-phase pitch, coke, low molecular weight heavy oil, coal-based pitch, and derivatives thereof. The carbon coating layer is formed on the outermost surface of the composite cathode active material to form SEI and prevent the metal particles from contacting with the electrolyte due to the selective passage of Li + ions. In addition, the carbon coating layer suppresses volume expansion during charging and discharging, and serves to improve the electrical conductivity by acting as an electron transfer passage in the composite cathode active material.

The carbon coating layer may have a thickness of 2 nm to 5 μm, and may be in any range represented by two arbitrary values selected within the above range. When the thickness of the carbon coating layer is within the above range, the electrical conductivity is improved, and at the same time the volume expansion can be sufficiently suppressed. If the thickness of the carbon coating layer is less than 2 nm, it is not expected to improve the sufficient electrical conductivity and the role of the buffer layer to accommodate the volume expansion of the silicon, if the thickness of the carbon coating layer exceeds 5 ㎛, the lithium absorption and At the time of release, the carbon coating acts as a resistance, causing a decrease in rate.

Hereinafter, a method of manufacturing a composite cathode active material according to another embodiment will be described.

Method for producing a composite cathode active material according to one embodiment,

(a) mixing a mixture of plate-like graphite and a metal alloyable with lithium to obtain a composite cathode active material precursor; And

(b) providing a silicon coating layer on a surface of the composite anode active material precursor;

Including,

Providing the silicon coating layer may be performed by chemical vapor deposition (CVD) of silane gas.

The method of manufacturing the composite cathode active material may further include ball milling the metal alloyable with the lithium before step (a). Accordingly, the metal alloyable with lithium may be ball-milled nanoparticles. For example, the metal alloyable with lithium may be ball-milled silicon particles.

The ball milling process includes wet or dry ball milling, and a person skilled in the art may select an appropriate ball milling process depending on the size and use of metal particles alloyable with the desired lithium.

As an example of the medium used for wet ball milling, an organic solvent may be used. For example, the medium includes, but is not limited to, isopropyl alcohol solvent, any medium that can be used for wet ball milling in the art can be used.

The ball milling process may be performed at a temperature lower than room temperature. For example, the ball milling process may be performed at a temperature of 25 ° C or less.

In the method of preparing a composite cathode active material, in the step (a), the mixture further includes a dispersant. The weight ratio of the metal capable of alloying with lithium: the dispersant: the carbonaceous material may be 1% to 15%: 1% to 15%: 70% to 98%, but is not limited thereto. For example, the weight ratio is 1: 1: 98, 1: 2: 97, 2: 2: 96, 10:10:80, 15:15:70, 1:15:84, or 15: 1: 84 The present invention may be, but is not limited to, any combination that falls within the above range.

Step (b) of the composite cathode active material manufacturing method is performed by chemical vapor deposition at a temperature of about 400 ℃ to about 600 ℃ using a silane-based gas. If the step (b) is performed below 400 ° C., the silicon coating layer may not be deposited, and when the temperature exceeds 600 ° C., the silicon coating layer may be converted into a crystalline silicon film.

The temperature for chemical vapor deposition in step (b) may be appropriately selected within the above range in consideration of the thickness of the desired silicon coating layer.

The silane-based gas can be easily selected by those skilled in the art as long as it is a silicon-based precursor capable of releasing Si atoms by gasification in the above temperature range.

For example, the silane-based gas may be silane (silane, SiH ₄ ), dichlorosilane (Dichlorosilane, SiH ₂ Cl ₂ ), silicon tetrafluoride (SiF ₄ ), silicon tetratride (Silicon) Tetrachloride, SiCl ₄ ), methylsilane (Methylsilane, CH ₃ SiH ₃ ), disilane (Disilane, Si ₂ H ₆ ), or a combination thereof may be a silicon-based precursor.

The method of manufacturing the composite cathode active material further includes, after the step (b), adding a carbon precursor and performing a heat treatment to form a carbon coating layer. The heat treatment is at a temperature of about 800 ℃ to about 1100 ℃. When heat treatment is performed in the above temperature range, a carbon coating layer may be formed from pyrolysis of the carbon precursor.

If the heat treatment temperature is less than 800 ℃ thermal decomposition does not occur sufficiently, if it exceeds 1100 ℃ SiC is formed due to the side reaction of silicon and carbon of the carbon precursor, the capacity decrease occurs.

The heat treatment may be performed for 1 hour or more. When the heat treatment is performed for less than 1 hour, sufficient thermal decomposition of the carbon precursor is not performed, so that a uniform carbon coating layer is hardly formed.

Forming the carbon coating layer may be performed under an inert atmosphere. For example, it may be performed under argon or nitrogen atmosphere. Through this, introduction of a uniform carbon coating layer is possible.

According to another aspect, a negative electrode for a lithium secondary battery includes a negative electrode current collector; And a negative electrode active material layer disposed on at least one surface of the negative electrode current collector and including the composite negative electrode active material.

The negative electrode may include a binder between the negative electrode current collector and the negative electrode active material layer or in the negative electrode active material layer. See the following for the binder.

The negative electrode and the lithium secondary battery including the same may be manufactured by the following method.

The negative electrode includes the composite negative electrode active material described above. For example, the composite negative electrode active material, a binder, and optionally a conductive material are mixed in a solvent to prepare a composite negative electrode active material composition, and then molded into a predetermined shape or copper foil. It may be prepared by a method of applying to a current collector such as (copper foil).

The binder used in the composite negative electrode active material composition may be included in the negative electrode current collector and the negative electrode active material layer or in the negative electrode active material layer as a component that assists in bonding the composite negative electrode active material and the conductive material to the current collector. It is added in 1 to 50 parts by weight based on 100 parts by weight of the composite cathode active material. For example, the binder may be added in the range of 1 to 30 parts by weight, 1 to 20 parts by weight, or 1 to 15 parts by weight based on 100 parts by weight of the composite cathode active material.

Examples of such binders include polyvinylidene fluoride, polyvinylidene chloride, polybenzimidazole, polyimide, polyvinylacetate, polyacrylonitrile, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxide Roxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polystyrene, polymethyl methacrylate, polyaniline, acrylonitrile butadiene styrene, phenolic resin, epoxy resin, polyethylene Terephthalate, polytetrafluoroethylene, polyphenylenesulfide, polyamideimide, polyetherimide, polyethersulfone, polyamide, polyacetal, polyphenylene oxide, polybutylene terephthalate, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluorine rubber, various copolymerizations Sieves and the like.

The cathode may optionally further include a conductive material to provide a conductive passage to the composite cathode active material described above to further improve electrical conductivity. As the conductive material, any material generally used in lithium batteries may be used. Examples thereof include carbon-based materials such as carbon black, acetylene black, ketjen black, and carbon fibers (eg, vapor-grown carbon fibers); Metal materials such as metal powder or metal fibers such as copper, nickel, aluminum and silver; Conductive materials containing conductive polymers such as polyphenylene derivatives or mixtures thereof can be used.

N-methylpyrrolidone (NMP), acetone, water and the like may be used as the solvent. The solvent is used in an amount of 1 to 10 parts by weight based on 100 parts by weight of the composite anode active material. When the content of the solvent is within the above range, the operation for forming the active material layer is easy.

In addition, the current collector is generally made of a thickness of 3 to 500 ㎛. The current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery. For example, the current collector may be formed on the surface of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper, or stainless steel. Surface-treated with carbon, nickel, titanium, silver and the like, aluminum-cadmium alloy and the like can be used. In addition, it is possible to enhance the bonding strength of the composite cathode active material by forming fine unevenness on the surface, it can be used in various forms such as film, sheet, foil, net, porous body, foam, nonwoven fabric.

The composite negative electrode active material composition may be directly coated on a current collector to prepare a negative electrode plate, or the composite negative electrode active material film cast on a separate support and peeled from the support may be laminated on a copper foil current collector to obtain a negative electrode plate. The negative electrode is not limited to the above enumerated forms, and may be other forms than the foregoing forms.

The composite cathode active material composition may not only be used for manufacturing an electrode of a lithium battery, but also may be printed on a flexible electrode substrate and used for manufacturing a printable battery.

Next, the anode is prepared.

For example, a cathode active material composition in which a cathode active material, a conductive material, a binder, and a solvent are mixed is prepared. The cathode active material composition is directly coated on a metal current collector to prepare a cathode plate. Alternatively, the cathode active material composition may be cast on a separate support, and then a film peeled from the support may be laminated on a metal current collector to prepare a cathode plate. The anode is not limited to the above enumerated forms and may be in any form other than the foregoing.

The positive electrode active material is a lithium-containing metal oxide, any one of those commonly used in the art can be used without limitation. For example, one or more of a complex oxide of metal and lithium selected from cobalt, manganese, nickel, and combinations thereof may be used, and specific examples thereof include Li _a A _1-b B ¹ _b D ¹ ₂ (Wherein 0.90 ≦ a ≦ 1.8, and 0 ≦ b ≦ 0.5); Li _a E _1-b B ¹ _b O _2-c D ¹ _c (wherein 0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05); LiE _2-b B ¹ _b O _4-c D ¹ _c (wherein 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05); Li _a Ni _1-bc Co _b B ¹ _c D ¹ _α (wherein 0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05, and 0 <α ≦ 2); Li _a Ni _1-bc Co _b B ¹ _c O _2-α F ¹ _α (wherein 0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05, and 0 <α <2); Li _a Ni _1-bc Co _b B ¹ _c O _2-α F ¹ ₂ (wherein 0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05, and 0 <α <2); Li _a Ni _1-bc Mn _b B ¹ _c D ¹ _α (wherein 0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05, and 0 <α ≦ 2); Li _a Ni _1-bc Mn _b B ¹ _c O _2-α F ¹ _α (wherein 0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05, and 0 <α <2); Li _a Ni _1-bc Mn _b B ¹ _c O _2-α F ¹ ₂ (wherein 0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05, and 0 <α <2); Li _a Ni _b E _c G _d O ₂ (wherein 0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.9, 0 ≦ c ≦ 0.5, and 0.001 ≦ d ≦ 0.1); Li _a Ni _b Co _c Mn _d GeO ₂ (wherein 0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.9, 0 ≦ c ≦ 0.5, 0 ≦ d ≦ 0.5, and 0.001 ≦ e ≦ 0.1); Li _a NiG _b O ₂ (wherein 0.90 ≦ a ≦ 1.8 and 0.001 ≦ b ≦ 0.1); Li _a CoG _b O ₂ (wherein 0.90 ≦ a ≦ 1.8 and 0.001 ≦ b ≦ 0.1); Li _a MnG _b O ₂ (wherein 0.90 ≦ a ≦ 1.8 and 0.001 ≦ b ≦ 0.1); Li _a Mn ₂ G _b O ₄ (wherein 0.90 ≦ a ≦ 1.8 and 0.001 ≦ b ≦ 0.1); QO ₂ ; QS ₂ ; LiQS ₂ ; V ₂ O ₅ ; LiV ₂ O ₅ ; LiI ¹ O ₂ ; LiNiVO ₄ ; Li _(3-f) J ₂ (PO ₄ ) ₃ (0 ≦ f ≦ 2); Li _(3-f) Fe ₂ (PO ₄ ) ₃ (0 ≦ f ≦ 2); Compounds represented by any of the formulas of LiFePO ₄ can be used:

In the above formula, A is Ni, Co, Mn, or a combination thereof; B is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements or combinations thereof; D is O, F, S, P, or a combination thereof; E is Co, Mn, or a combination thereof; F is F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; Q is Ti, Mo, Mn, or a combination thereof; I is Cr, V, Fe, Sc, Y, or a combination thereof; J is V, Cr, Mn, Co, Ni, Cu, or a combination thereof.

For example, LiCoO ₂ , LiMn _x O _2x (x = 1, 2), LiNi _1-x Mn _x O _2x (0 <x <1), LiNi _1-xy Co _x Mn _y O ₂ (0 ≦ _x ≦ 0.5, 0 ≦ y ≦ 0.5), LiFePO _4, and the like.

Of course, it is also possible to use a coating layer on the surface of the compound, or may be used by mixing the compound having a compound with the coating layer. This coating layer may comprise a coating element compound of an oxide of a coating element, a hydroxide, an oxy hydroxide of a coating element, an oxycarbonate of a coating element, or a hydroxycarbonate of a coating element. The compounds constituting these coating layers may be amorphous or crystalline. As the coating element included in the coating layer, Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr or a mixture thereof may be used. The coating layer forming process may use any coating method as long as it can be coated with the above compounds by a method that does not adversely affect the physical properties of the positive electrode active material (for example, spray coating or dipping method). Detailed descriptions thereof will be omitted since they can be understood by those skilled in the art.

The conductive material, the binder and the solvent in the positive electrode active material composition may be the same as the case of the negative electrode active material composition.

The amount of the positive electrode active material, the conductive material, the binder, and the solvent is at a level commonly used in lithium secondary batteries. At least one of the conductive material, the binder, and the solvent may be omitted according to the use and configuration of the lithium battery.

Next, a separator to be inserted between the positive electrode and the negative electrode is prepared.

The separator may be used as long as it is commonly used in lithium batteries. A low resistance to the ion migration of the electrolyte and excellent in the ability to hydrate the electrolyte can be used. For example, it is selected from glass fiber, polyester, Teflon, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), or a combination thereof, and may be in a nonwoven or woven form. For example, a rollable separator such as polyethylene or polypropylene may be used for a lithium ion battery, and a separator having excellent organic electrolyte solution impregnation ability may be used for a lithium ion polymer battery. For example, the separator may be manufactured according to the following method.

A separator composition is prepared by mixing a polymer resin, a filler, and a solvent. The separator composition may be directly coated and dried on the electrode to form a separator. Alternatively, after the separator composition is cast and dried on a support, a separator film separated from the support may be laminated on the electrode to form a separator.

The polymer resin used to manufacture the separator is not particularly limited, and any materials used for the binder of the electrode plate may be used. For example, vinylidene fluoride / hexafluoropropylene copolymer, polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate or mixtures thereof and the like can be used.

Next, the electrolyte is prepared.

For example, the electrolyte may be an organic electrolyte. In addition, the electrolyte may be a solid. For example, it may be boron oxide, lithium oxynitride, and the like, but is not limited thereto, and any one that can be used as a solid electrolyte in the art may be used. The solid electrolyte may be formed on the negative electrode by sputtering or the like.

For example, the organic electrolyte may be prepared by dissolving lithium salt in an organic solvent.

The organic solvent may be used as long as it can be used as an organic solvent in the art. For example, propylene carbonate, ethylene carbonate, fluoroethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl isopropyl carbonate, dipropyl carbonate, dibutyl carbonate , Benzonitrile, acetonitrile, tetrahydrofuran, 2-methyltetrahydrofuran, γ-butyrolactone, dioxolane, 4-methyldioxolane, N, N-dimethylformamide, dimethylacetamide, dimethyl sulfoxide , Dioxane, 1,2-dimethoxyethane, sulfolane, dichloroethane, chlorobenzene, nitrobenzene, diethylene glycol, dimethyl ether or a mixture thereof.

Any lithium salt may be used as long as it can be used as a lithium salt in the art. For example, LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiAlO ₂ , LiAlCl ₄ , LiN (C _x F _{2x + 1} SO ₂ ) (C _y F _{2y + 1} SO ₂ ) (where x and y are natural numbers), LiCl, LiI or a mixture thereof.

As shown in FIG. 1, the lithium battery 1 includes a positive electrode 3, a negative electrode 2, and a separator 4. The positive electrode 3, the negative electrode 2, and the separator 4 described above are wound or folded to be accommodated in the battery case 5. Subsequently, the organic electrolyte is injected into the battery case 5 and sealed with a cap assembly 6 to complete the lithium battery 1. The battery case 5 may be cylindrical, rectangular, thin film, or the like. For example, the lithium battery 1 may be a thin film type battery. The lithium battery 1 may be a lithium ion battery.

A separator may be disposed between the positive electrode and the negative electrode to form a battery structure. The battery structure is stacked in a bi-cell structure, and then impregnated in an organic electrolyte, and the resultant is accommodated in a pouch and sealed to complete a lithium ion polymer battery.

In addition, a plurality of battery structures may be stacked to form a battery pack, and the battery pack may be used in any device requiring high capacity and high power. For example, it can be used in notebooks, smartphones, electric vehicles and the like.

In addition, the lithium secondary battery may be used in an electric vehicle (EV) because of its excellent life characteristics and high rate characteristics. For example, it may be used in a hybrid vehicle such as a plug-in hybrid electric vehicle (PHEV). It can also be used in applications where a large amount of power storage is required. For example, it can be used for electric bicycles, power tools and the like.

The present invention is described in more detail through the following Preparation Examples, Examples and Comparative Examples. However, the examples are provided to illustrate the present invention, and the scope of the present invention is not limited only to these examples.

(Production of Silicon Nanoparticles)

Preparation Example 1

Bulk silicon available on the market was introduced into a ball mill with isopropyl alcohol (IPA) medium and ground for 2 hours at low temperature (up to 25 ° C.) and at a ball mill rotation speed of 3000 to 4000 rpm to obtain ball milled silicon nanoparticles. . The median particle size (D ₅₀ ) of the ball milled silicon nanoparticles was 130 nm.

(Production of Composite Cathode Active Material Precursor)

Preparation Example 1

The silicon nanoparticles: carbon black (Super P ^™ ): plate graphite were added to a mixer at a weight ratio of 5: 2: 93, and mixed at a low temperature (25 ° C or less) for 3 hours to obtain a composite cathode active material precursor. .

SEM pictures of the composite anode active material precursor can be seen in Figure 1a.

Comparative Production Example 1

The silicon nanoparticles: carbon black (Super P ^™ ): spherical graphite were added to a mixer at a weight ratio of 5: 2: 93, and then mixed at a low temperature (below 25 ° C) for 3 hours to obtain a composite cathode active material precursor. .

SEM pictures of the composite anode active material precursor can be seen in Figure 1b.

Comparative Production Example 1-1

The silicon nanoparticles: graphite were added to a mixer in a weight ratio of 12:88 and then mixed at a low temperature (25 ° C. or less) for 2 hours to obtain a composite cathode active material precursor.

(Production of Composite Cathode Active Material Precursor Deposited with Silicon Coating Layer)

Preparation Example 2

The composite cathode active material precursor obtained in Preparation Example 1 was subjected to vapor phase chemical vapor deposition of SiH ₄ (g) for 20 minutes at a rate of 50 sccm under 475 ° C. to form a silicon coating layer on the surface of the composite anode active material precursor.

SEM images of the composite cathode active material precursor on which the silicon coating layer is deposited can be seen in FIG. 2A.

Comparative Production Example 2

The composite cathode active material precursor obtained in Comparative Example 1 was subjected to vapor chemical vapor deposition of SiH ₄ (g) for 20 minutes at a rate of 50 sccm under 475 ° C. to form a silicon coating layer on the surface of the composite anode active material precursor.

SEM images of the composite cathode active material precursor on which the silicon coating layer is deposited can be seen in FIG. 2B.

Comparative Production Example 2-1

The composite cathode active material precursor obtained in Comparative Example 1-1 was subjected to vapor chemical vapor deposition of SiH ₄ (g) at a rate of 50 sccm for 20 minutes under conditions of 475 ° C. to form a silicon coating layer on the surface of the composite anode active material precursor.

Comparative Production Example 2-2

SiH ₄ (g) was chemically vapor deposited for 30 minutes at a rate of 50 sccm under conditions of 475 ° C. to obtain a composite cathode active material precursor having a silicon coating layer deposited on the surface thereof.

(Production of Composite Cathode Active Materials)

Preparation Example 3

10 g of the composite cathode active material precursor obtained in Preparation Example 2 and 1.5 g of the pitch were added to a mixer, mixed at 25 ° C. for 120 minutes, and then heat treated at 900 ° C. for 120 minutes to produce a composite anode active material precursor.

 A composite cathode active material having a carbon coating layer was obtained.

Comparative Production Example 3

10 g of the composite cathode active material precursor obtained in Comparative Preparation Example 2 and 1.5 g of the pitch were added to a mixer and mixed at 25 ° C. for 120 minutes, followed by heat treatment at 900 ° C. for 120 minutes to form carbon at the outermost portion of the composite cathode active material precursor. A composite cathode active material having a coating layer was obtained.

Comparative Production Example 3-1

10 g of the composite cathode active material precursor obtained in Comparative Preparation Example 2-1 and 1.5 g of the pitch were added to a mixer, mixed at 25 ° C. for 120 minutes, and then heat treated at 900 ° C. for 120 minutes to form an outermost composite anode active material precursor. The composite cathode active material in which the carbon coating layer was formed was obtained.

Comparative Production Example 3-2

The silicon nanoparticles: carbon black (Super P ^TM ): spherical graphite was added to the mixer at a weight ratio of 15: 6: 79, mixed for 120 minutes at 25 ° C., and then heat treated at 900 ° C. for 120 minutes. The composite negative electrode active material in which the carbon coating layer was formed in the outermost layer of the composite negative electrode active material precursor was obtained.

Comparative Production Example 3-3

10 g of the composite cathode active material precursor obtained in Comparative Example 2-2 and 1.5 g of the pitch were added to a mixer, mixed at 25 ° C. for 120 minutes, and then heat-treated at 900 ° C. for 120 minutes to provide an outermost composite anode active material precursor. A composite cathode active material having a carbon coating layer was obtained.

(Production of a cathode)

Example 1

The composite cathode active material obtained in Preparation Example 3 and spherical graphite (having a capacity of 360mAh / g) were mixed at a weight ratio of 50:50 to be used as a cathode active material, super.P as a conductive agent, CMC as a thickener, and SBR as a binder. To prepare a slurry using a weight ratio of 96: 1: 1.5: 1.5 to the negative electrode active material / conductive agent / thickener / binder. The slurry was applied on a 18 μm thick copper current collector using conventional methods. The slurry coated with the current collector was dried at room temperature, followed by secondary drying at 120 ° C., and rolling and punching to prepare a negative electrode to be applied to a cell.

Comparative Example 1

A negative electrode was prepared in the same manner as in Example 1, except that the composite negative electrode active material obtained in Comparative Preparation Example 3 was used instead of the composite negative electrode active material obtained in Preparation Example 3.

(Manufacture of Anode)

Example 2

A mixture of lithium cobalt oxide (LCO) cathode active material, carbon conductor (super.P), and polyvinylidene fluoride (PVdF) in a weight ratio of 94: 3: 3 was mixed with N-methylpyrrolidone (NMP). A positive electrode active material slurry was prepared by mixing together through a homogenizer. A slurry of the positive electrode active material was applied to a thickness of about 120 μm on a 15 μm thick aluminum current collector using a doctor blade, dried at room temperature, dried again under vacuum and 120 ° C., and then rolled to form a current collector. An anode having a cathode active material layer disposed thereon was prepared.

(Manufacture of Lithium Secondary Battery)

Example 3

A negative electrode prepared in Example 1 and Comparative Example 1 was wound in a circular shape of 16 mm, a positive electrode was wound in a circular shape of 15 mm, and a separator was disposed between the positive electrode and the negative electrode to prepare a 2032 type coin full cell.

As the separator, a 14 µm thick polyethylene-polypropylene copolymer separator was used.

As an electrolyte, 1.3 M LiPF ₆ dissolved in an EC (ethylene carbonate): DEC (diethylene carbonate): FEC (fluoroethylene carbonate) (2: 6: 2 volume ratio) mixed solvent was used as an electrolyte.

Comparative Example 2

A coin full cell of type 2032 was manufactured in the same manner as in Example 1, except that the cathode obtained in Comparative Example 1 was used instead of the anode obtained in Example 1.

Evaluation Example 1 Evaluation of Particle Size of Composite Cathode Active Material

The particle size distribution of the composite cathode active material obtained in Preparation Example 3 and Comparative Preparation Example 3 was analyzed using Microtrac S3500 manufactured by Microtrac, and the results are shown in Table 1 below.

Particle size distribution Preparation Example 3
(Μm) Comparative Production Example 3
(Μm) D10 3.22 14.57 D50 6.13 20.4. D90 12.06 30.11

As shown in Table 1, it can be seen that the composite cathode active material obtained in Preparation Example 3 using plate graphite has a smaller particle size than the composite cathode active material of Comparative Preparation Example 3 using spherical graphite. In particular, in the case of D50 it can be seen that the use of plate-like graphite has a particle size of 1/3 compared to the case of using a spherical graphite.

Evaluation Example 2: Evaluation of Charge and Discharge Characteristics

The lithium secondary batteries prepared in Example 3 and Comparative Example 2 start charging at a charge rate of 0.1 C-rate at 25 ° C., and the voltage is charged up to 0.005V, wherein the battery is charged to have a constant voltage at a constant current. Thereafter, the battery was discharged at a constant current until it reached 2.0V at a discharge rate of 0.1 C-rate. After one charge and discharge cycle as described above, the charge and discharge cycle of 0.5 C-rate is repeated in the charge and discharge cycle 200 times continuously with a voltage section of 0.005V to 2.0V. Some of the charge and discharge test results are shown in Table 2 below, and a cycle life graph of the charge and discharge test results is shown in FIG. 3.

Initial efficiency and capacity maintenance rate were respectively calculated from the following formulas (1) to (2).

 <Equation 1>

The initial efficiency (%) = [discharge capacity / charge capacity at 1 ^st cycle at 1 ^st cycle] ㅧ 100

 <Equation 2>

Capacity retention rate [%] = [discharge capacity of 150 ^rd cycles / discharge capacity of 3 ^rd cycles] ㅧ 100

Initial efficiency
[%] Capacity maintenance rate
(150 cycles)
[%] Example 3 80.3 81.2 Comparative Example 2 83.4 74.3

As shown in Table 2, in the case of Example 3, it can be seen that the initial efficiency is lower than in Comparative Example 2, which is a composite cathode having a significantly smaller particle size compared to the composite cathode active material used in Comparative Example 2 This is because an active material is used. However, it can be seen that the secondary battery manufactured according to Example 3 showed an excellent capacity retention rate compared to the secondary battery of Comparative Example 2 in a repeated charge / discharge cycle.

(Production of half cell)

Example 4

In the composite negative electrode active material obtained in Preparation Example 3, a slurry was prepared in the ratio of negative electrode active material: conductive material: binder in the ratio of 95.5: 1: 3.5. Here, Super P was used as the conductive material, and carboxymethyl cellulose (CMC) and styrene-butadiene-rubber (SBR) were used as the binder.

The slurry was uniformly coated on a copper foil, dried in an 80 ° C. oven for about 2 hours, and then roll-pressed to further dry in a 110 ° C. vacuum oven for about 12 hours to prepare a negative electrode.

The prepared negative electrode is used as a working electrode, a lithium foil is used as a counter electrode, a polyethylene membrane is inserted into a separator between the negative electrode and the counter electrode, and EC / EMC / DEC is mixed in a volume ratio of 3/5/2. CR2016 half-cells were prepared according to a commonly known process using a liquid electrolyte solution in which 10.0% by weight of FEC was added to a solvent and LiPF ₆ was added at a concentration of 1.3 M as a lithium salt.

Comparative Examples 3 to 5

CR2016 half-cells were prepared in the same manner as in Example 4, except that the composite cathode active materials obtained in Comparative Preparation Examples 3-1 to 3-3 were used instead of the composite cathode active materials obtained in Preparation Example 3.

Evaluation Example 3 Evaluation of Electrochemical Properties

After charging the half-cells prepared according to Example 4 and Comparative Examples 3 to 5 at a charge rate of 0.1 C-rate at 25 ° C., the voltage was charged to 0.005V, and then charged to have a constant voltage at a constant current. Charge at a constant voltage until it reaches below the constant current (0.01C). Thereafter, the battery was discharged at a constant current until it reached 1.5V at a discharge rate of 0.1 C-rate. After the two charge and discharge cycles as described above, the charge and discharge cycle of 0.5C-rate is repeated in the charge and discharge cycle 30 times continuously with a voltage section of 0.005V to 1.5V. Some of the charge and discharge test results are shown in Tables 3 to 5 below, and the charge and discharge test results graphs are shown in FIGS. 4 to 6.

Initial efficiency was calculated from Equation 1 below.

 <Equation 1>

The initial efficiency (%) = [discharge capacity / charge capacity at 1 ^st cycle at 1 ^st cycle] ㅧ 100

Initial capacity
[mAh / g] Initial efficiency
[%] Example 4 710 84.5 Comparative Example 3 703 84.1

As shown in Table 3, Comparative Example 3 using a composite cathode active material containing no dispersant compared to Example 4 can be seen that the initial capacity and the initial efficiency was low. In addition, according to FIG. 4, the coulombic efficiency is maintained at about 99.5 at 50 cycles in Example 4, but the coulombic efficiency is lowered at about 99.0 at 50 cycles in Comparative Example 3.

Initial capacity
[mAh / g] Initial efficiency
[%] Example 4 710 84.5 Comparative Example 4 685 82.5

As shown in Table 4, Comparative Example 4 using a composite cathode active material that does not include a silicon coating layer compared to Example 4 can be seen that the initial capacity and the initial efficiency was low. In addition, according to FIG. 5, the coulombic efficiency is maintained at about 99.5 at 50 cycles in Example 4, but the coulombic efficiency is lowered at about 99.3 at 50 cycles in Comparative Example 4.

Initial capacity
[mAh / g] Initial efficiency
[%] Example 4 710 84.5 Comparative Example 5 703 86.8

As shown in Table 5, Comparative Example 5 using a composite cathode active material containing no ball-milling silicon and dispersant compared to Example 4, it can be seen that the initial capacity is lower. In addition, according to FIG. 6, the coulombic efficiency is maintained at about 99.5 at 50 cycles in Example 4, but the variation in the coulombic efficiency is large according to the number of cycles in Comparative Example 4, which is lower than that in Example 4 on average. Coulomb efficiency was shown.

Evaluation Example 4: Evaluation of Equation 1

The present inventors examined the correlation between the capacity increase and the BET specific surface area in order to form a silicon coating layer in a discontinuous dot shape on the composite cathode active material. In general, the capacity is proportional to the amount of silicon deposited, and if the BET specific surface area is increased, the silicon can be positioned independently without being connected to each other.

First, it was confirmed that silicon was deposited in the form of a continuous layer in the case of increasing the capacity of 369 mAh / g by depositing 14.76 wt% of the silicon coating layer on spherical graphite. (See Figure 2b)

On the other hand, it was confirmed that silicon was deposited in a dot shape when the silicon coating layer was deposited by 12% by weight on plate graphite to increase the capacity by 303 mAh / g. (See Figure 2A)

At this time, the BET specific surface area of the silicon deposited spheroidal graphite and platelet graphite was measured. As a result, the spherical graphite was 18.54 m ² / g, and the plated graphite was 32.62 m ² / g, which is about 1.75 times higher than the spheroidal graphite. There was a difference.

Due to the significant difference in the BET specific surface area value, it is possible to construct a dot-shaped silicon coating layer in plate graphite despite a similar increase in capacity.

Furthermore, repeated experiments were carried out by varying the capacity increase and the BET specific surface area. As a result, when the following Equation 1 is satisfied, it was confirmed that the silicon coating layer may be deposited on the surface of the composite cathode active material in the form of dots.

<Equation 1>

Evaluation Example 5: Evaluation of Dispersant Content

As another factor that could affect the BET specific surface area, the content of dispersant was investigated.

Referring to FIG. 7, as the content of the dispersant is increased from 0 wt% to 8 wt%, it can be seen that the silicon coating layer is changed from a layered form to a dot form.

It is believed that this is because the dispersant allows the ball-mill silicon particles to be uniformly dispersed, thereby maximizing the BET specific surface area.

In the above described a preferred embodiment according to the present invention with reference to the drawings and embodiments, but this is only exemplary, those skilled in the art that various modifications and equivalent other embodiments are possible from this. You will understand. Therefore, the protection scope of the present invention should be defined by the appended claims.

Claims (20)

Plate-like graphite;
Dispersants;
A metal alloyable with lithium disposed on the plate graphite surface; And
A silicon coating layer disposed on the plate graphite surface, the surface of the metal alloyable with lithium, or a combination thereof;
Including,
The metal alloyable with lithium is silicon nanoparticles with silicon oxide disposed on the surface,
The silicon coating layer includes amorphous or semicrystalline silicon particles,
The composite cathode active material in which the metal alloyable with the lithium is uniformly distributed on the surface of the plate graphite. The method of claim 1,
The silicon coating layer is a discontinuous coating layer on the surface of the composite cathode active material, composite cathode active material. The method of claim 1,
The silicon coating layer has a dot shape, composite cathode active material. delete The method of claim 1,
The dispersant comprises a carbon black, acetylene black, ketjen black, carbon fibers such as vapor-grown carbon fibers, graphite fine particles or combinations thereof. The method of claim 1,
The composite cathode active material satisfies Equation 1 below.
<Equation 1>
(Capacity increase (mAh / g) / BET specific surface area (m ² / g)) <10 The method of claim 1,
The composite cathode active material has a BET specific surface area of 20 to 40 (m ² / g),
The content of the silicon particles is 6% by weight to 14% by weight based on the total weight of the composite cathode active material, composite cathode active material. The method of claim 1,
The composite cathode active material in which the metal alloyable with the lithium is distributed on all or part of the plate graphite surface. delete delete The method of claim 1,
The metal capable of alloying with lithium is a composite cathode active material is amorphous silicon particles. The method of claim 11,
The median particle size (D ₅₀ ) of the amorphous silicon particles is 20 nm to 300 nm composite cathode active material. The method of claim 1,
A composite cathode active material further comprising a carbon coating layer on the outermost portion of the composite cathode active material. The method of claim 13,
The composite cathode active material having a thickness of the carbon coating layer is 2 nm to 5 ㎛. (a) mixing a mixture of plate graphite, a dispersant and a metal alloyable with lithium to obtain a composite cathode active material precursor; And
(b) providing a silicon coating layer on a surface of the composite anode active material precursor;
Including,
Before the step (a), further comprising the step of ball milling the metal alloyable with the lithium,
The metal alloyable with lithium is silicon nanoparticles with silicon oxide disposed on the surface,
The step of providing the silicon coating layer is performed by chemical vapor deposition (CVD) of silane gas,
The silicon coating layer comprises amorphous or semi-crystalline silicon particles, a method for producing a composite cathode active material. delete The method of claim 15,
After the step (b), further comprising the step of adding a carbon precursor, and heat treatment to form a carbon coating layer, a method for producing a composite cathode active material. The method of claim 15,
The step (b) is carried out at a temperature of 400 ℃ to 600 ℃, the composite cathode active material manufacturing method. delete A negative electrode comprising the negative electrode active material according to any one of claims 1 to 3, 5 to 8 and 11 to 14,
Anode, and
Lithium secondary battery comprising an electrolyte.

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