KR20200078397A - Composite anode active material, a method of preparing the composite anode material, and a lithium secondary battery comprising the composite anode active material - Google Patents

Abstract

The present invention relates to a composite negative pole active material including: carbon-based particles; fibrous carbon grown from the carbon-based particles; a silicon coating layer formed on the carbon-based particles and the fibrous carbon; and a carbon coating layer formed on the silicon coating layer.

Description

A composite anode active material, a method of preparing the composite anode active material, and a lithium secondary battery comprising the composite anode active material}

A lithium secondary battery containing a negative electrode active material, a method for manufacturing the same, and a negative electrode including the same are used.

Lithium batteries are used for various purposes by having high voltage and high energy density. For example, electric vehicles (HEV, PHEV) require a high-capacity lithium battery that can be driven for a long time at high temperatures and has excellent charge and discharge output characteristics.

While the carbon-based material, which is a negative electrode active material mainly used in the past, is porous, the volume change during charging and discharging is excellent in cycle characteristics, whereas in general, the battery capacity is low due to the porous structure of carbon. For example, the theoretical capacity of graphite with high crystallinity is 372 mAh/g at the LiC ₆ composition. In addition, in the case of a carbon-based negative electrode active material, a problem has been pointed out that the output characteristics are significantly lowered at high-speed charging due to the intercalation and desorption mechanisms of the carbon layer.

In order to solve this problem, a metal or metalloid capable of alloying with lithium may be used as a negative electrode active material having a higher electric capacity than a carbon-based material. For example, metals or metals capable of alloying with lithium include Si, Sn, and Al. However, the lithium-alloyable metal or metalloids have a high discharge capacity, but there is a limitation in that life characteristics are low because the volume change during charging and discharging is easily deteriorated.

Therefore, there is still a need in the industry for a negative electrode active material having a high capacity, excellent output characteristics at high speed charging and discharging, and excellent cycle characteristics, and a method for manufacturing the same.

An object of the present application is to provide a lithium secondary battery comprising a composite negative electrode active material having a high capacity, excellent high rate characteristics, and excellent cycle characteristics, a manufacturing method thereof, and a negative electrode including the composite negative electrode active material.

According to one aspect, the carbon-based particles; Fibrous carbon grown from carbon-based particles; A silicon coating layer formed on the carbon-based particles and the fibrous carbon; And a carbon coating layer formed on the silicon coating layer.

According to another aspect, providing a metal precursor on the surface of the carbon-based particle to obtain a carbon-based particle carrying the metal precursor;

Reducing the metal precursor by heat-treating the carbon-based particles carrying the metal precursor;

Growing an fibrous carbon in an atmosphere containing a carbon-containing gas;

Forming a silicon coating layer on the carbon-based particles and fibrous carbon; And

Forming a carbon coating layer on the silicon coating layer;

A method of manufacturing a composite cathode active material is provided.

According to another aspect, the negative electrode comprising the composite negative electrode active material; anode; And it is provided a lithium secondary battery comprising an electrolyte.

The lithium secondary battery containing the composite cathode active material according to one aspect has high capacity, excellent output characteristics at a high rate, and excellent cycle characteristics.

1 is a schematic diagram of a lithium secondary battery according to an embodiment.
2 is an initial charge and discharge graph of the half cells according to Example 1 and Comparative Examples 1 to 2.
3 is a graph of the life characteristics of the half cells according to Example 1 and Comparative Examples 1 to 2.
4 is an SEM photograph of before and after growing carbon nanotubes on a graphite surface.
<Explanation of reference numerals for main parts of drawings>
1: lithium battery 2: negative electrode
3: anode 4: separator
5: battery case 6: cap assembly

The present inventive concept described below can apply various transformations and can have various embodiments, and specific embodiments are illustrated in the drawings and described in detail in the detailed description. However, this is not intended to limit this creative idea to a specific embodiment, and it should be understood to include all transformations, equivalents, or substitutes included in the technical scope of the creative idea.

The terms used below are only used to describe specific embodiments, and are not intended to limit the creative ideas. Singular expressions include plural expressions unless the context clearly indicates otherwise. In the following, the terms “comprises” or “have” are intended to indicate the presence of features, numbers, steps, operations, components, parts, components, materials or combinations thereof described in the specification, one or more thereof. It should be understood that the above other features, numbers, steps, operations, components, parts, components, materials or combinations thereof are not excluded in advance. "/" used below may be interpreted as "and" or "or" depending on the situation.

In the drawings, diameters, lengths, and thicknesses are enlarged or reduced to clearly represent various components, layers, and regions. The same reference numerals are used for similar parts throughout the specification. When parts of a layer, film, region, plate, etc. are said to be "on" or "above" another part of the specification, this includes not only the case directly above the other part but also another part in the middle. . Throughout the specification, terms such as first and second may be used to describe various components, but the components should not be limited by terms. The terms are used only to distinguish one component from another component. Some of the elements may be omitted from the drawings, but this is for the purpose of understanding the features of the invention and is not intended to exclude the omitted elements.

In this specification, "composite" is not a state in which a plurality of components having different properties are simply mixed and physically contacted, but components through mechanical, electrochemical and/or chemical reactions, etc. that cannot be reached by simple mixing. It means a state that has a certain bonding relationship with each other. For example, "composite negative electrode active material" means a negative electrode active material that is a result obtained through the above mechanical, electrochemical and/or chemical reaction.

Hereinafter, a composite cathode active material according to exemplary embodiments, a negative electrode and a lithium battery including the same, and a method of manufacturing the composite cathode active material will be described in more detail.

The composite cathode active material according to the embodiment includes carbon-based particles; Fibrous carbon grown on carbon-based particles; A silicon coating layer formed on the carbon-based particles and the fibrous carbon; And a carbon coating layer formed on the silicon coating layer.

The fibrous carbon grown from carbon-based particles provides additional specific surface area to the carbon-based particles, and functions as a conductive passage with adjacent carbon-based particles, thereby improving electrical conductivity and allowing charging and discharging at high rates. .

The introduction of the fibrous carbon increases the specific surface area, and as a result, when depositing the same amount of silicon particles, a thinner coating layer can be formed. Therefore, compared to a composite cathode active material in which a silicon nanowire or a silicon coating layer is introduced on a spherical carbon having the same capacity, volume change during charging and discharging can be reduced, and as a result, cycle characteristics are improved.

In addition, the edge site exposed to the outside of the fibrous carbon has a high reactivity with silicon particles, thereby forming a chemical Si-C bond, and as a result, a silicon layer firmly bound on the fibrous carbon Is placed. Such a solid Si-C bond can prevent separation and desorption of the silicon coating layer and the fibrous carbon due to the volume change.

In another aspect, due to the introduction of the fibrous carbon, it is possible to deposit a silicon coating layer containing a larger amount of silicon particles without lowering the cycle characteristics of the composite cathode active material, and as a result, the cycle characteristics are not deteriorated. It is possible to increase the capacity of the composite cathode active material.

In addition, the silicon coating layer containing the silicon particles repeats expansion and contraction by charging and discharging of the composite cathode active material, and in order to prevent cracks between the silicon coating layer and the fibrous carbon, carbon on the silicon coating layer is used. A coating layer is provided. In the carbon coating layer, the silicon coating layer is separated from the fibrous carbon to prevent direct contact with the electrolyte, thereby preventing the capacity degradation of the composite cathode active material. In addition, by providing a carbon coating layer on the silicon coating layer containing the silicon particles, the bonding force between the silicon coating layer and the surface of the fibrous carbon can be further increased, thereby preventing desorption of the silicon particles, which may be caused by volume expansion of the silicon particles. In addition, by introducing the carbon coating layer, it is possible to prevent the silicon particles from contacting the electrolyte or the like due to the selective passage of Li+ ions. In addition, the carbon coating layer suppresses the volume expansion during charge and discharge, and serves as an electron transfer passage in the composite cathode active material, thereby contributing to the improvement of electrical conductivity.

The carbon-based particles may include natural graphite, artificial graphite, hard carbon, soft carbon, or a combination thereof. For example, the carbon-based particles may be artificial graphite. The artificial graphite is generally prepared by uniformly mixing a petroleum-based or coal-based coke powder with a binder such as pitch or resin, followed by carbonization. In the carbonization process, the binder is volatilized to form pores in artificial graphite, and these pores can be controlled by impregnating pitch or resin or performing chemical vapor deposition in a carbon-containing gas atmosphere.

The carbon-based particles may be spherical, tubular, or plate-shaped. For example, the carbon-based particles may be spherical.

The average particle diameter (D ₅₀ ) of the carbon-based particles may be 5 to 50 μm. Here, the average particle diameter (D ₅₀ ) means the diameter of particles through which 50% of the cumulative weight passes in the particle size distribution curve. In addition, when the carbon-based particles were tubular or plate-shaped, the average particle diameter of spherical particles having the same mass was used as the average particle diameter of the tubular particles or plate-shaped particles.

The fibrous carbon may include carbon nanofibers, carbon nanotubes, or a combination thereof, but is not limited thereto, and includes any carbon material having an aspect ratio of 1 to 1000. Here, the aspect ratio means a ratio of diameter to length. The fibrous carbon may include linear or, for example, both curved or curved over its entire length or a portion thereof.

The fibrous carbon may be grown from inside the carbon-based particles. Some of the length of the fibrous carbon may be combined by penetrating into the carbon-based particles from the surface of the carbon-based particles. By forming a structure in which a part of the fibrous carbon penetrates into the carbon-based particles, the fibrous carbon and the carbon-based particles are firmly combined to improve workability in physical mixing such as slurrying. In addition, since the area of contact between the fibrous carbon and the carbon-based particles is larger, conductivity can be improved.

The diameter of the fibrous carbon is 1 nm to 200 nm, and the length may be 100 nm to 100 μm. For example, the diameter of the fibrous carbon is 1 nm to 190 nm, 1 nm to 180 nm, 1 nm to 170 nm, 1 nm to 160 nm, 1 nm to 150 nm, 1 nm to 140 nm, 1 nm to 130 nm, 1 nm to 120 nm, 1 nm to 110 nm, 1 nm to 100 nm, 1 nm to 90 nm, 1 nm to 80 nm, 1 nm to 70 nm, 1 nm to 60 nm, 1 nm to 50 nm , 1 nm to 40 nm, 1 nm to 30 nm, 1 nm to 20 nm, 1 nm to 10 nm, or 1 nm to 5 nm. For example, the length of the fibrous carbon is 100 nm to 100 μm, 100 nm to 95 μm, 100 nm to 90 μm, 100 nm to 85 μm, 100 nm to 80 μm, 100 nm to 75 μm, 100 nm to 70 μm, 100 nm to 65 μm, 100 nm to 60 μm, 100 nm to 55 μm, 100 nm to 50 μm, 100 nm to 45 μm, 100 nm to 40 μm, 100 nm to 35 μm, 100 nm to 30 μm , 100 nm to 25 μm, 100 nm to 20 μm, 100 nm to 15 μm, 100 nm to 10 μm, 100 nm to 5 μm, 100 nm to 1 μm, 100 nm to 950 nm, 100 nm to 900 nm, 100 nm to 850 nm, 100 nm to 800 nm, 100 nm to 750 nm, 100 nm to 700 nm, 100 nm to 650 nm, 100 nm to 600 nm, 100 nm to 550 nm, 100 nm to 500 nm, 100 nm to 450 nm, 100 nm to 400 nm, 100 nm to 350 nm, 100 nm to 300 nm, 100 nm to 250 nm, 100 nm to 200 nm, or 100 nm to 150 nm.

The fibrous carbon may be included in 0.1 to 20 parts by weight based on 100 parts by weight of the carbon-based particles. For example, the fibrous carbon is 0.5 to 20 parts by weight, 1 to 20 parts by weight, 2 to 20 parts by weight, 1 to 19 parts by weight, 1 to 18 parts by weight, 1 to 1 part by weight based on 100 parts by weight of the carbon-based particles 17 parts by weight, 1 to 16 parts by weight, may be included as 1 to 15 parts by weight, but is not limited thereto. When the fibrous carbon is contained in an amount of less than 0.1 parts by weight based on 100 parts by weight of the carbon-based particles, an increase in specific surface area and an increase in conductivity may be insignificant. When the fibrous carbon exceeds 20 parts by weight with respect to 100 parts by weight of the carbon-based particles, the movement of lithium ions becomes an obstacle and the resistance increases, and the specific surface area may decrease due to the overlapping of the fibrous carbon.

The silicon coating layer may cover the carbon-based particles and/or the fibrous carbon surface. According to one embodiment, the silicon coating layer may cover both the carbon-based particles and the fibrous carbon surface. According to another embodiment, the silicon coating layer may cover a portion of the carbon-based particles and the fibrous carbon surface. For example, the silicon coating layer may be present in the form of islands on the carbon-based particles and the fibrous carbon surface.

The carbon coating layer may include an amorphous carbon material. For example, 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 obtained by firing may be used. For example, the carbon precursor may be at least one selected from the group consisting of polymer, coal tar pitch, petroleum pitch, meso-phase pitch, coke, low molecular weight heavy oil, coal-based pitch and derivatives thereof. By forming a carbon coating layer on the outermost portion of the composite cathode active material, SEI is formed and metal particles may be prevented from coming into contact with an electrolyte or the like due to selective passage of Li+ ions. In addition, the carbon coating layer suppresses the volume expansion during charge and discharge, and serves as an electron transfer passage in the composite cathode active material, thereby contributing to the improvement of electrical conductivity.

The thickness of the carbon coating layer may be 2 nm to 5 μm, and may be any range represented by two arbitrary values selected within the range. When the thickness of the carbon coating layer is within the above range, electrical conductivity is improved, and at the same time, volume expansion can be sufficiently suppressed. When the thickness of the carbon coating layer is less than 2 nm, it is not possible to expect a sufficient improvement in electrical conductivity and the role of a buffer layer capable of accommodating the volume expansion of silicon, and when the thickness of the carbon coating layer exceeds 5 μm, lithium is absorbed into the rechargeable battery and Upon release, the carbon coating layer acts as a resistance, causing rate drop.

The specific surface area of the composite cathode active material may be 0.3 m ² g ^-1 to 100 m ² g ^-1 . For example, the specific surface area of the composite cathode active material is 0.3 m ² g ^-1 to 100 m ² g ^-1 , 0.3 m ² g ^-1 to 90 m ² g ^-1 , 0.3 m ² g ^-1 to 80 m ² g ^-1 , 0.3 m ² g ^-1 to 70 m ² g ^-1 , 0.3 m ² g ^-1 to 60 m ² g ^-1 , 0.3 m ² g ^-1 to 50 m ² g ^-1 , 0.3 m ² g ^-1 to 40 m ² g ^-1 , 0.3 m ² g ^-1 to 30 m ² g ^-1 , 0.5 m ² g ^-1 to 29 m ² g ^-1 _, 0.5 m ² g ^-1 to 28 m ² g ^-1 _, 0.5 m ² g ^-1 to 27 m ² g ^-1 _, or 0.5 m ² g ^-1 to 26 m ² g ^-1 , but is not limited thereto. Since the composite cathode active material has the specific surface area, it is possible to realize a lithium secondary battery having excellent initial efficiency and excellent output characteristics.

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

A method of manufacturing a composite cathode active material according to an embodiment includes providing a metal precursor on a surface of a carbon-based particle to obtain a carbon-based particle carrying a metal precursor; Reducing the metal precursor by heat-treating the carbon-based particles carrying the metal precursor; Growing an fibrous carbon in an atmosphere containing a carbon-containing gas; Forming a silicon coating layer on the carbon-based particles and fibrous carbon; And forming a carbon coating layer on the silicon coating layer.

The step of obtaining the carbon-based particles carrying the metal precursor may be obtained by supporting the metal precursor on the surface of the carbon-based particles by a sol-gel method, a precipitation method, a hydrothermal reaction method, a spray pyrolysis method, a powder drying method, or a ball mill method. .

The metal precursor may be one or more selected from carbonates, nitrides, hydroxides, oxides, chlorides, and acetates of metals, transition metals, or combinations thereof.

According to one embodiment, the metal is at least one metal selected from Group 2 elements, and the transition metal is at least one transition metal selected from Groups 3 to 12.

The average particle diameter (D ₅₀ ) of the metal precursor may be 10 to 500 nm, but is not limited thereto, and may have a particle size that can be carried in the carbon-based particles.

The step of reducing the metal precursor includes the step of heat-treating the carbon-based particles carrying the metal precursor at 500 to 700° C. under a hydrogen atmosphere, and the metal reduced by the heat-treating step penetrates into the carbon-based particles. . The metal precursor is supported in the carbon-based particles by etching the carbon-based particles while reacting with the carbon-based particles in the process of being reduced to produce a carbon-containing gas (eg, methane gas).

Subsequently, by growing fibrous carbon in an atmosphere containing a carbon-containing gas, the fibrous carbon can be grown from the inside of the carbon-based particles. As the fibrous carbon is grown from the inside of the carbon-based particles, the contact area and the bonding area of the carbon-based particles and the fibrous carbon are increased, thereby improving the bonding strength and conductivity.

The step of growing the fibrous carbon may include a step of heat treatment at 400 to 800°C.

The step of growing the fibrous carbon may be grown by chemical vapor deposition in a gas atmosphere containing carbon, such as carbon monoxide, methane, acetylene, and ethylene, at 400 to 800°C.

After the step of growing the fibrous carbon, it may further include a step of washing with acid. By the washing step, the metal that has acted as a catalyst in the growth of the fibrous carbon can be removed.

An example in which fibrous carbon is grown on the surface of carbon-based particles is shown in FIG. 4. Referring to FIG. 4, carbon-based particles (right) on which carbon nanotubes are grown on the surface of the carbon-based particles (left) can be confirmed. In addition, although the carbon-based particles themselves had a BET (specific surface area) value of 4.75 m ² /g, it was confirmed that when carbon nanotubes were grown on the surface of the carbon-based particles, they had a specific surface area of 25.2 m ² /g. That is, it was confirmed that as the carbon nanotubes were grown on the surface of the carbon-based particles, the specific surface area increased about 6 times.

The step of forming the silicon coating layer may be to deposit silicon nanoparticles by a chemical vapor deposition method of silane gas. By chemical vapor deposition, silicon nanoparticles can be uniformly deposited on the surfaces of fibrous carbon and carbon-based particles.

The silane gas is silane (SiH ₄ ), dichlorosilane (SiH ₂ Cl ₂ ), silicon tetrafluoride (Silicon Tetrafluoride, SiF ₄ ), silicon tetratloride (Silicon Tetrachloride, SiCl ₄ ) , Methylsilane (CH ₃ SiH ₃ ), Disilane (Si ₂ H ₆ ), or a combination thereof may be a silicon-based precursor.

According to one embodiment, the step of providing the silicon coating layer may be performed at a temperature of 400 ℃ to 900 ℃. For example, the step of providing the silicon coating layer may be performed at a temperature of 500°C to 900°C, 600°C to 900°C, or 700°C to 900°C, but is not limited thereto, and the composition and thickness of the desired coating layer It can be selected according to.

The step of forming the carbon coating layer is formed by adding a carbon precursor and heat treatment.

The carbon precursor may be, for example, one or more selected from the group consisting of polymers, coal tar pitch, petroleum pitch, meso-phase pitch, coke, low molecular heavy oil, coal-based pitch, and derivatives thereof.

The heat treatment may be performed at a temperature of 800°C to 1100°C. When the heat treatment temperature is less than 800°C, thermal decomposition does not sufficiently occur, and when it exceeds 1100°C, SiC is formed due to side reaction of silicon nanoparticles of the silicon coating layer and carbon of the carbon precursor, resulting in capacity reduction. On the other hand, a solid Si-C bond is formed between the silicon nanoparticles of the silicon coating layer and the carbon atoms of the fibrous carbon through heat treatment within the above range, thereby desorbing the silicon particles despite volume changes due to charging and discharging of the silicon coating layer. Can be prevented.

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 achieved, making it difficult to form a uniform carbon coating layer.

The step of 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, it is possible to introduce a uniform carbon coating layer.

The negative electrode according to another embodiment includes the composite negative electrode active material. The negative electrode is 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 above-described composite negative electrode active material.

The negative electrode may include a binder between the negative electrode current collector and the composite negative electrode active material layer or in the composite negative electrode active material layer. The binder will be described later.

The negative electrode and the lithium secondary battery including the same may be manufactured as follows.

The negative electrode includes the above-described composite negative electrode active material, for example, by mixing the above-described composite negative electrode active material, a binder, and optionally a conductive material in a solvent to prepare a composite negative electrode active material composition, and then molding it into a certain shape, or copper foil (copper foil) can be prepared by applying to the current collector.

The binder used in the composite negative electrode active material composition is a component that assists in bonding the composite negative electrode active material and the conductive material to the current collector, and may be included between the negative electrode current collector and the composite negative electrode active material layer or in the composite negative electrode active material layer. In addition, 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 a 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 a binder include polyvinylidene fluoride, polyvinylidene chloride, polybenzimidazole, polyimide, polyvinyl acetate, polyacrylonitrile, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxy Oxypropylcellulose, recycled cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polystyrene, polymethylmethacrylate, polyaniline, acrylonitrilebutadienestyrene, phenol resin, epoxy resin, polyethylene Terephthalate, polytetrafluoroethylene, polyphenylene sulfide, polyamideimide, polyetherimide, polyethersulfone, polyamide, polyacetal, polyphenylene oxide, polybutylene terephthalate, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluorine rubber, various copolymers, and the like.

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

As the solvent, N-methylpyrrolidone (NMP), acetone, water, or the like can be used. The content of the solvent is 1 to 10 parts by weight based on 100 parts by weight of the composite cathode 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 to a thickness of 3 to 500 μm. The current collector is not particularly limited as long as it has conductivity without causing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surfaces Carbon, nickel, titanium, silver, or the like, aluminum-cadmium alloy, or the like may be used. In addition, it is possible to form fine irregularities on the surface to enhance the bonding force of the negative electrode active material, and can be used in various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics.

A negative electrode plate can be obtained by directly coating the prepared composite negative electrode active material composition on a current collector, or by laminating a composite negative electrode active material film cast on a separate support and peeled from the support to a copper foil current collector. The cathode is not limited to the above-listed forms, and may be in a form other than the above-mentioned forms.

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

Next, the anode is prepared.

For example, a positive electrode active material composition in which a positive electrode active material, a conductive material, a binder, and a solvent are mixed is prepared. The positive electrode active material composition is directly coated on a metal current collector to prepare a positive electrode plate. Alternatively, after the positive electrode active material composition is cast on a separate support, a film peeled from the support can be laminated on a metal current collector to produce a positive electrode plate. The positive electrode is not limited to the types listed above, and may be in a form other than the above-described types.

The positive electrode active material is a lithium-containing metal oxide, and can be used without limitation as long as it is commonly used in the art. For example, one or more of a complex oxide of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof can be used. As another example, Li _a A _1-b B ¹ _b D ¹ ₂ (where 0.90 ≤ a ≤ 1.8, and 0 ≤ b ≤ 0.5); Li _a E _1-b B ¹ _b O _2-c D ¹ _c (where 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 (where 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); Li _a Ni _1-bc Co _b B ¹ _c D ¹ _α (where 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α ≤ 2); Li _a Ni _1-bc Co _b B ¹ _c O _2-α F ¹ _α (where 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α <2); Li _a Ni _1-bc Mn _b B ¹ _c D ¹ _α (where 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 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, 0 <α <2); Li _a Ni _1-bc Mn _b B ¹ _c O _2-α F ¹ ₂ (where 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α <2); Li _a Ni _b E _c G _d O ₂ (In the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0.001 ≤ d ≤ 0.1.); Li _a Ni _b Co _c Mn _d GeO ₂ (where 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5, 0.001 ≤ e ≤ 0.1); Li _a NiG _b O ₂ (in the above formula, 0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1.); Li _a CoG _b O ₂ (where 0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li _a MnG _b O ₂ (in the above formula, 0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li _a Mn ₂ G _b O ₄ (where 0.90 ≤ a ≤ 1.8, 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 one of the formulas of LiFePO ₄ can be used:

In the above formula, A is Ni, Co, Mn, or a combination thereof; B ¹ is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements or combinations thereof; D ¹ is O, F, S, P, or a combination thereof; E is Co, Mn, or a combination thereof; F ¹ is F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or combinations thereof; Q is Ti, Mo, Mn, or a combination thereof; I is Cr, V, Fe, Sc, Y, or combinations 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, a compound having a coating layer on the surface of the compound may also be used, or a compound having a coating layer and the compound may be mixed and used. The coating layer may include an oxide of a coating element, a hydroxide, an oxyhydroxide of a coating element, an oxycarbonate of a coating element, or a coating element compound of a hydroxycarbonate of a coating element. The compounds constituting these coating layers may be amorphous or crystalline. As a 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 can be used. In the coating layer forming process, any coating method may be used as long as the compound can be coated by a method that does not adversely affect the physical properties of the positive electrode active material by using these elements (for example, spray coating, immersion method, etc.). Since it can be well understood by people in the field, detailed description will be omitted.

In the positive electrode active material composition, a conductive material, a binder, and a solvent may be the same as the negative electrode active material composition.

The content of the positive electrode active material, conductive material, binder, and solvent is a level commonly used in lithium secondary batteries. Depending on the use and configuration of the lithium battery, one or more of the conductive material, binder, and solvent may be omitted.

Next, a separator to be inserted between the anode and the cathode is prepared.

The separator can be used as long as it is commonly used in lithium batteries. A low resistance to electrolyte ion migration and an excellent electrolyte-moisturizing ability may be used. For example, selected from glass fiber, polyester, Teflon, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), or a combination thereof, non-woven or woven form may be used. For example, a rollable separator such as polyethylene or polypropylene is used for the lithium ion battery, and a separator having excellent organic electrolyte impregnation ability may be used for the lithium ion polymer battery. For example, the separator can 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 peeled from the support may be laminated on the electrode to form a separator.

The polymer resin used in the production of the separator is not particularly limited, and all materials used for the bonding material of the electrode plate can be used. For example, vinylidene fluoride/hexafluoropropylene copolymer, polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethylmethacrylate, or a mixture thereof may be used.

Next, an electrolyte is prepared.

For example, the electrolyte may be an organic electrolyte solution. Further, the electrolyte may be solid. For example, it may be boron oxide, lithium oxynitride, and the like, but is not limited thereto, and any material that can be used as a solid electrolyte in the art may be used. The solid electrolyte may be formed on the cathode by a method such as sputtering.

For example, the organic electrolyte may be prepared by dissolving a 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, dimethylsulfoxide , Dioxane, 1,2-dimethoxyethane, sulfolane, dichloroethane, chlorobenzene, nitrobenzene, diethylene glycol, dimethyl ether or mixtures thereof.

Any of the lithium salts can be used as long as they can be used as lithium salts 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,y is a natural number), LiCl, LiI, or mixtures thereof.

As shown in FIG. 1, the lithium battery 1 includes an anode 3, a cathode 2, and a separator 4. The above-described positive electrode 3, negative electrode 2, and separator 4 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, prismatic, thin film, or the like. For example, the lithium battery 1 may be a thin film 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. After the battery structure is stacked in a bi-cell structure, impregnated with an organic electrolytic solution, and the obtained result is accommodated in a pouch and sealed, a lithium ion polymer battery is completed.

In addition, a plurality of the battery structures are stacked to form a battery pack, and such a battery pack can be used in all devices requiring high capacity and high output. For example, it can be used for laptops, smartphones, electric vehicles, and the like.

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

The present invention will be described in more detail through the following production examples, examples and comparative examples. However, the examples are only for illustrating the present invention, and the scope of the present invention is not limited thereto.

(Production of composite cathode active material)

Manufacturing example One

Using a mechanical stirrer, 50 g of graphite and a metal precursor (2 wt% transition metal compared to graphite) are added to uniformly attach the metal precursor to the graphite surface. Under the temperature condition of 700° C., the surface of the graphite was etched by reducing the metal precursor by providing H ₂ (g) at a rate of 1.5 L/min. The etched graphite was thermally decomposed to C ₂ H ₄ (g) at a rate of 1.5 L/min under a temperature condition of 900° C. to grow CNT/CNF from the surface of the catalyst metal particles. The CNT/CNF-grown graphite was subjected to chemical vapor deposition of SiH ₄ (g) at a rate of 50 sccm/60min under a temperature condition of 550° C., thereby forming a silicon coating layer on the graphite. Under a temperature condition of 900 ℃ graphite including the silicon coating layer, the C ₂ H ₂ (g) to prepare a negative electrode active material to thermal decomposition at a rate the carbon layer coated on the silicon coating layer of 1.5L / min.

Preparation Example 2

By placing 50 g of graphite in the reactor and gold (Au) on its surface, and flowing SiH ₄ as a reaction gas under an argon (Ar) atmosphere at a temperature condition of about 400° C., graphite with silicon nanowires grown on the surface was obtained. . Thereafter, under the temperature condition of 900° C., C ₂ H ₂ (g) was thermally decomposed at a rate of 1.5 L/min to prepare a composite cathode active material coated with a carbon layer on the outermost side.

Preparation Example 3

50 g of graphite was chemically deposited at a rate of 50 sccm/60 min, SiH ₄ (g) under a temperature condition of 550° C., to prepare a negative electrode active material having a silicon coating layer formed on the graphite. Under the temperature conditions of the negative electrode active material 900 ℃, by thermal decomposition of C ₂ H ₂ (g) at a rate of 1.5L / min, to prepare a coated composite negative electrode active material layer on a silicon carbon coating layer.

At this time, with respect to the total amount of the negative electrode active material, graphite is 95% by weight, silicon is 4% by weight, and the outermost carbon is 1% by weight.

(Production of half cell)

Example 1

The composite cathode active material obtained in Preparation Example 1: a conductive material: a binder was mixed at a ratio of 95.8:1:3.2 to prepare a slurry. Here, Super P was used as the conductive material, and carboxymethylcellulose (CMC) and styrene-butadiene-rubber (SBR) were used as the binder.

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

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

Comparative Examples 1 and 2

A CR2016 half cell was manufactured in the same manner as in Example 1, except that the composite cathode active materials prepared in Preparation Examples 2 and 3 were used instead of the composite cathode active material prepared in Preparation Example 1.

Evaluation Example 1: Evaluation of electrochemical properties

The half cells prepared in Example 1 and Comparative Examples 1 to 2 start charging at a charging rate of 0.1 C-rate at 25° C., and the voltage is charged to 0.005 V, and then charged to have a constant voltage with a constant current and then constant. Charge until the voltage reaches 0.01C or less with a constant current. Then, it was discharged with a constant current until it reached 1.5V at a discharge rate of 0.1C-rate.

The initial charge/discharge curve is shown in FIG. 2, and discharge capacity and initial charge/discharge efficiency are shown in Table 1 below.

Subsequently, after an additional two charge/discharge cycles, the voltage section is set to 0.005V to 1.5V at a charge/discharge rate of 0.5C-rate, and the charge/discharge cycle is repeated 50 times continuously. The capacity retention rate due to repeated charge and discharge can be seen from FIG. 3.

The 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] x 100

Volume
[mAh/g] Initial efficiency
[%] Example 1 668 91.2 Comparative Example 1 642.5 89.1 Comparative Example 2 616.6 89.9

As shown in Table 1, Example 1 and Comparative Examples 1 to 2 had similar initial efficiencies. However, in the repeated charging and discharging process, a sharp decrease in capacity retention rate was observed in the half cell of Comparative Example 1 compared to the half cell of Example 1. After 50 charge and discharge cycles, the capacity retention rate was reduced by more than about 10%. In addition, the half cell of Comparative Example 2 showed a capacity retention rate of about 5% or more after 50 charge and discharge cycles compared to the half cell of Example 1. This difference in capacity retention is thought to be attributable to the structure in which the carbon fiber grown on the surface of the negative electrode active material of Example 1 and the silicon coating layer of the thin film were deposited thereon. The thin film silicon coating layer not only does not cause cracking due to volume change due to the space existing between the carbon fibers, but also, because the carbon fiber and the silicon coating layer are firmly combined, detachment due to cracking of the negative electrode active material is suppressed even after repeated charge and discharge. I think that.

In the above, preferred embodiments according to the present invention have been described with reference to the drawings and examples, but these are merely exemplary, and various modifications and other equivalent embodiments are possible from those skilled in the art. Will be able to understand. Therefore, the protection scope of the present invention should be defined by the appended claims.

Claims (20)

Carbon-based particles; Fibrous carbon grown on carbon-based particles; A silicon coating layer formed on the carbon-based particles and the fibrous carbon; And a carbon coating layer formed on the silicon coating layer. According to claim 1,
The carbon-based particle is a composite cathode active material including natural graphite, artificial graphite, hard carbon, soft carbon, or a combination thereof. According to claim 1,
A composite cathode active material having an average particle diameter (D ₅₀ ) of the carbon-based particles of 5 to 50 μm. According to claim 1,
The fibrous carbon is a composite cathode active material comprising carbon nanofibers, carbon nanotubes, or a combination thereof. According to claim 1,
The fibrous carbon is a composite cathode active material grown from inside the carbon-based particles. According to claim 1,
The diameter of the fibrous carbon is 1 nm to 200 nm, the composite cathode active material having a length of 100 nm to 100 ㎛. According to claim 1,
The fibrous carbon is a cathode active material containing 0.1 to 20 parts by weight based on 100 parts by weight of the carbon-based particles. According to claim 1,
A composite cathode active material in which the silicon coating layer covers the carbon-based particles and/or the fibrous carbon surface. According to claim 1,
The carbon coating layer is a composite cathode active material comprising an amorphous carbon material. According to claim 1,
The thickness of the carbon coating layer is 2 nm to 5 ㎛ composite cathode active material. According to claim 1,
The composite cathode active material has a specific surface area of 0.3 m ² g ^-1 to 100 m ² g ^-1 . Providing a metal precursor on the surface of the carbon-based particles to obtain carbon-based particles carrying the metal precursor;
Reducing the metal precursor by heat-treating the carbon-based particles carrying the metal precursor;
Growing an fibrous carbon in an atmosphere containing a carbon-containing gas;
Forming a silicon coating layer on the carbon-based particles and fibrous carbon; And
Forming a carbon coating layer on the silicon coating layer;
The method of manufacturing a composite cathode active material comprising a. The method of claim 12,
The metal precursor is a metal, a transition metal, or a combination of carbonate, nitride, hydroxide, oxide, chloride, and at least one selected from acetate, a method for producing a composite cathode active material. The method of claim 12,
The average particle diameter (D ₅₀ ) of the metal precursor is 10 to 500 nm, a method for producing a composite cathode active material. The method of claim 12,
The step of reducing the metal precursor includes the step of heat-treating the carbon-based particles carrying the metal precursor at 500 to 700° C. under a hydrogen atmosphere,
Method for producing a composite cathode active material, the metal reduced by the heat treatment step penetrates into the carbon-based particles. The method of claim 12,
After the step of growing the fibrous carbon, further comprising the step of washing with acid, a method for producing a composite cathode active material. The method of claim 12,
The step of growing the fibrous carbon includes a step of heat treatment at 400 to 800°C, a method of manufacturing a composite cathode active material. The method of claim 12,
The forming of the silicon coating layer is a method of manufacturing a composite cathode active material by depositing silicon nanoparticles by a chemical vapor deposition method of silane gas. The method of claim 12,
The step of forming the carbon coating layer is a method of manufacturing a composite cathode active material formed by adding a carbon precursor and heat treatment. A negative electrode comprising the composite negative electrode active material according to any one of claims 1 to 11; anode; And lithium secondary battery comprising an electrolyte.

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