阅读说明：本技术 制备负极活性材料的方法 (Method for preparing negative active material ) 是由 李昌周 禹相昱 郑东燮 金贤撤 于 2020-01-14 设计创作，主要内容包括：本发明涉及一种制备负极活性材料的方法,所述方法包括以下步骤：通过在石墨上设置沥青,然后进行第一热处理来形成第一碳涂层；以及通过在所述第一碳涂层上设置液态树脂,然后进行第二热处理来形成第二碳涂层。(The present invention relates to a method of preparing an anode active material, the method comprising the steps of: forming a first carbon coating by disposing pitch on graphite and then performing a first heat treatment; and forming a second carbon coating layer by disposing a liquid resin on the first carbon coating layer and then performing a second heat treatment.)

1. A method of preparing an anode active material, the method comprising:

disposing pitch on graphite and performing a first heat treatment to form a first carbon coating; and

disposing a liquid resin on the first carbon coating and performing a second heat treatment to form a second carbon coating.

2. The method of claim 1, wherein the graphite comprises at least one selected from the group consisting of natural graphite, artificial graphite, and MCMB.

3. The method of claim 1, wherein the graphite has an average particle size (D)₅₀) Is 5 μm to 30 μm.

4. The method of claim 1, wherein the asphalt comprises at least one of coal-based asphalt and petroleum-based asphalt.

5. The method of claim 1, wherein the weight ratio of the graphite to the first carbon coating is 1.0000:0.0052 to 1.0000: 0.0474.

6. The method of claim 1, wherein the temperature for the first heat treatment is 500 ℃ to 2000 ℃.

7. The method of claim 1, wherein the resin comprises at least one selected from the group consisting of epoxy, polyurethane, and phenolic resins.

8. The method of claim 1, wherein the temperature of the second heat treatment is 500 ℃ to 2000 ℃.

9. The method of claim 1, wherein the weight ratio of the graphite to the second carbon coating is 1.0000:0.0052 to 1.0000: 0.0474.

10. The method of claim 1, wherein the weight ratio of the first carbon coating to the second carbon coating is from 10:90 to 90: 10.

11. The method of claim 1, wherein the second carbon coating is in contact with the first carbon coating.

Technical Field

Cross Reference to Related Applications

This application claims the benefit of korean patent application No. 10-2019-0004797, filed on 14.1.2019 to the korean intellectual property office, the disclosure of which is incorporated herein by reference in its entirety.

Technical Field

The present invention relates to a method of preparing an anode active material, the method including disposing pitch on graphite and performing a first heat treatment to form a first carbon coating, and disposing a liquid resin on the first carbon coating and performing a second heat treatment to form a second carbon coating.

Background

As the use of fossil fuels is rapidly increasing, the use demand for alternative energy or clean energy is increasing, and as a part of this trend, the most active research field is the field of power generation and storage using electrochemical reactions.

Currently, a typical example of an electrochemical device using such electrochemical energy is a secondary battery, and the field of use thereof is increasing. In recent years, as technical development and demand of portable devices such as portable computers, mobile phones, and cameras have increased, demand for secondary batteries as energy sources has increased significantly. In general, a secondary battery is composed of a positive electrode, a negative electrode, an electrolyte, and a separator. The anode contains an anode active material for intercalating and deintercalating lithium ions from the cathode, and as the anode active material, a graphite-based active material such as natural graphite or artificial graphite can be used.

On the other hand, due to the development of electric vehicles and the like, improvement of the quick charging performance of the secondary battery is an important issue. In order to improve the rapid charging performance of the secondary battery, a technique of coating the graphite surface with hard carbon is generally used. However, when the surface of graphite is coated with hard carbon, the specific surface area of the active material is excessively increased when the electrode is roll-pressed, which hinders the inhibition of the deintercalation of lithium ions, so that there is a problem that the high-temperature storage performance of the battery is deteriorated.

Therefore, there is a need for a novel method capable of simultaneously satisfying the fast charge performance and the high-temperature storage performance of a secondary battery when using a graphite-based anode active material.

Disclosure of Invention

Technical problem

An aspect of the present invention is to provide a method of preparing an anode active material capable of satisfying both a fast charge property and a high-temperature storage property of a secondary battery during charge/discharge of the battery when using a graphite-based anode active material.

Technical scheme

According to an aspect of the present invention, there is provided a method of preparing an anode active material, the method including disposing pitch on graphite and performing a first heat treatment to form a first carbon coating, and disposing a liquid resin on the first carbon coating and performing a second heat treatment to form a second carbon coating.

Advantageous effects

According to the present invention, by providing a first carbon coating derived from pitch on the surface of graphite and then providing a second carbon coating derived from resin on the first carbon coating, the specific surface area of the anode active material can be maintained at an appropriate level, so that the rapid charging performance of the battery can be improved. In addition, the interface between the first carbon coating layer and the second carbon coating layer is significantly present, which suppresses the deintercalation of lithium ions, so that the high-temperature storage performance of the battery can be improved.

Detailed Description

Hereinafter, the present invention will be described in more detail to facilitate understanding of the present invention.

It should be understood that the words or terms used in the specification and claims should not be construed as having meanings defined in commonly used dictionaries. It should be further understood that the words or terms should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the technical idea of the present invention, based on the principle that the inventor can appropriately define the meaning of the words or terms to best explain the invention.

The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting of the invention. Terms in the singular may include the plural unless the context clearly dictates otherwise.

In this specification, it will be understood that the terms "comprises," "comprising," or "having" are intended to specify the presence of stated features, integers, steps, elements, or groups thereof, but do not preclude the presence or addition of one or more other features, integers, steps, elements, or groups thereof.

In the present specification, D₅₀Can be defined as the particle size corresponding to 50% of the cumulative volume in the particle size distribution curve of the particles. D₅₀Can be measured by, for example, laser diffraction. Laser diffraction methods are generally capable of measuring particle sizes from the submicron range to several millimeters, so that highly reproducible and high resolution results can be obtained.

< method for producing negative electrode active Material >

A method of preparing an anode active material according to an embodiment of the present invention may include disposing pitch on graphite and performing a first heat treatment to form a first carbon coating, and disposing a liquid resin on the first carbon coating and performing a second heat treatment to form a second carbon coating.

(1) A step of disposing pitch on graphite and performing a first heat treatment to form a first carbon coating layer

The graphite is in the form of particles, and may correspond to a core of the negative active material. The graphite may include at least one selected from the group consisting of natural graphite, artificial graphite, and mesocarbon microbeads (MCMB), and particularly, may be artificial graphite. When the graphite is artificial graphite, the volume expansion of the artificial graphite during the charge/discharge of the battery is relatively small, and the electrolyte side reaction is reduced, so that the life characteristics of the battery can be improved. However, the graphite is not limited to artificial graphite.

The graphite may have an average particle diameter (D50) of 5 to 30 μm, specifically 8 to 25 μm, more specifically 9 to 22 μm. When the above range is satisfied, the specific surface area is not too large, so that the high-temperature storage performance of the battery can be improved. In addition, since a proper size is maintained, a surface area in contact with the electrolyte is secured, thereby facilitating intercalation and deintercalation of lithium ions, whereby the rapid charging performance of the battery can be improved.

The graphite may have at least one of a secondary particle shape formed by assembling a flake coke, a fibrous coke, a mosaic coke, a shot coke, a needle coke, or a mosaic coke. In particular, in order to improve the quick charging performance of the battery and the durability and life characteristics of the battery, the graphite is preferably in the form of secondary particles formed by assembling needle coke or mosaic coke, and among the above, artificial graphite is preferable.

The needle coke or the shot coke is a raw material of the primary particles, and may have an average particle diameter (D50) of 3 to 15 μm, specifically 5 to 12 μm. When the above dimensions are satisfied, the specific surface area can be at an appropriate level, so that the quick-charging performance and the high-temperature storage performance can be improved.

The pitch may be a black carbonaceous solid residue obtained when tar obtained from dry matter of coal, wood or organic matter is distilled. Specifically, the asphalt may include at least one of coal-based asphalt and petroleum-based asphalt.

If the first carbon coating is formed on the graphite with a resin instead of pitch, both the first carbon coating and the second carbon coating are formed with the resin, so that the interface between the first carbon coating and the second carbon coating may not be significantly formed. Therefore, it may be difficult to improve the high-temperature storage performance of the battery since the deintercalation of lithium ions that have been intercalated into graphite cannot be effectively suppressed. On the other hand, when the first carbon coating layer is formed by pitch, an interface is significantly formed between the first carbon coating layer and the second carbon coating layer, so that deintercalation of lithium ions can be effectively suppressed, whereby the high-temperature storage performance of the battery can be improved.

The temperature of the first heat treatment may be 500 ℃ to 2000 ℃, specifically 900 ℃ to 1500 ℃, more specifically 1000 ℃ to 1300 ℃. When the above range is satisfied, the amount of hydrogen in the first carbon coating layer is suppressed, so that the reaction between lithium ions and hydrogen can be reduced, and the crystallinity of graphite does not excessively increase, so that the rapid charging performance can be improved.

The weight ratio of the graphite to the first carbon coating can be 1.0000:0.0052 to 1.0000:0.0474, specifically 1.0000:0.0103 to 1.0000:0.0421, more specifically 1.0000:0.0155 to 1.0000: 0.0211. When the above range is satisfied, the transfer resistance of charge is reduced while the capacity per unit weight of the negative electrode active material is maintained at an appropriate level, so that the quick charging performance of the battery can be improved.

The first carbon coating may be in contact with a surface of the graphite. The first carbon coating may cover at least a part of the surface of the graphite, in particular the entire surface thereof.

(2) A step of providing a liquid resin on the first carbon coating layer and performing a second heat treatment to form a second carbon coating layer

The liquid resin may be an amorphous liquid substance composed of an organic compound and a derivative thereof. Specifically, the resin may include at least one selected from the group consisting of an epoxy resin, a polyurethane resin, and a phenolic resin. If the second carbon coating is formed on the first carbon coating using pitch instead of resin, the specific surface area of the anode active material is insufficient, and thus the quick charge performance of the battery may be deteriorated. In addition, since both the first carbon coating layer and the second carbon coating layer are formed using pitch, the interface between the first carbon coating layer and the second carbon coating layer is not significantly formed. Therefore, the deintercalation of lithium ions cannot be suppressed, and thus the high-temperature storage performance of the battery is deteriorated.

On the other hand, when the second carbon coating layer is formed by the resin, the second carbon coating layer is located on the surface of the anode active material, so that the specific surface area of the anode active material is increased to a desired level, thereby improving the quick charge performance of the battery. In addition, an interface is significantly formed between the first carbon coating layer formed by pitch and the second carbon coating layer formed with a liquid resin to suppress the deintercalation of lithium ions, so that the high-temperature storage performance of the battery can be improved.

The temperature of the second heat treatment may be 500 ℃ to 2000 ℃, specifically 900 ℃ to 1500 ℃, more specifically 1000 ℃ to 1300 ℃. When the above range is satisfied, the amount of hydrogen in the second carbon coating layer is suppressed, so that the reaction between lithium ions and hydrogen can be reduced.

The weight ratio of the graphite to the second carbon coating can be 1.0000:0.0052 to 1.0000:0.0474, specifically 1.0000:0.0103 to 1.0000:0.0421, more specifically 1.0000:0.0155 to 1.0000: 0.0200. When the above range is satisfied, the transfer resistance of charge is reduced while the capacity per unit weight of the negative electrode active material is maintained at an appropriate level, so that the quick charging performance of the battery can be improved.

The second carbon coating may be in contact with the first carbon coating. The second carbon coating may cover at least a part of the surface of the first carbon coating, in particular the entire surface thereof.

Since the second carbon coating layer is formed with a resin, the graphite and the first carbon coating layer can be uniformly coated. Therefore, the quick charging performance of the battery can be improved. In addition, due to the interface between the first carbon coating layer and the second carbon coating layer, unnecessary deintercalation of lithium ions is prevented, so that high-temperature storage performance of the battery can be improved.

The weight ratio of the first carbon coating to the second carbon coating can be 10:90 to 90:10, specifically 15:85 to 85:15, more specifically 40:60 to 60: 40. When the above range is satisfied, the quick-charging performance and the high-temperature storage performance of the battery can be further improved.

< negative electrode active Material >

The anode active material may be the anode active material prepared by the method of preparing the anode active material of the above embodiment. Specifically, the negative active material includes graphite, a first carbon coating layer disposed on the graphite, and a second carbon coating layer disposed on the first carbon coating layer, wherein the first carbon coating layer is formed by performing a first heat treatment on pitch, and the second carbon coating layer is formed by performing a second heat treatment on a liquid resin. The graphite, the first carbon coating, the second carbon coating, the pitch, the liquid resin are the same as those described in the above embodiments, and thus the description thereof is omitted.

< negative electrode >

The anode according to still another embodiment of the present invention may include an anode active material layer containing an anode active material. Specifically, the anode may include a current collector and an anode active material layer disposed on the current collector.

The current collector is not particularly limited as long as it has conductivity without causing chemical changes in the battery. For example, as the current collector, copper, stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel surface-treated with one of carbon, nickel, titanium, silver, or the like may be used. In particular, transition metals such as copper and nickel, which well adsorb carbon, may be used as the current collector. The thickness of the current collector may be 6 to 20 μm, but the thickness of the current collector is not limited thereto.

The anode active material layer may be disposed on the current collector. The anode active material layer may be disposed on at least one surface of the current collector, specifically, on one surface or both surfaces thereof.

The negative active material layer may include a negative active material. The anode active material may be the anode active material prepared by the method of preparing an anode active material of the above embodiment.

The negative electrode may further include at least one of a binder and a conductive material.

The binder may include at least any one selected from the group consisting of: polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, a material in which hydrogen is substituted with Li, Na, or Ca, and the like, and combinations thereof. In addition, the adhesive may comprise various copolymers thereof.

The conductive material is not particularly limited as long as it has conductivity without causing chemical changes in the battery. For example, graphite, such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black (Ketjen black), channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; conductive tubes, such as carbon nanotubes; a fluorocarbon powder; metal powders such as aluminum powder and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives and the like.

< Secondary Battery >

The secondary battery according to still another embodiment of the present invention may include an anode, and the anode may be the same as the anode of the above-described embodiment.

Specifically, the secondary battery may include an anode, a cathode, a separator interposed between the cathode and the anode, and an electrolyte. The negative electrode is the same as the above negative electrode. Since the anode has already been described above, a detailed description thereof will be omitted.

The positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and including a positive electrode active material.

In the positive electrode, the positive electrode current collector is not particularly limited as long as it has conductivity without causing chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel surface-treated with one of carbon, nickel, titanium, silver, and the like may be used. In addition, the cathode current collector may generally have a thickness of 3 to 500 μm, and fine irregularities may be formed on the surface of the cathode current collector to improve adhesion of the cathode active material. For example, the cathode current collector may be used in various forms such as a film, a sheet, a foil, a mesh, a porous body, a foam, and a non-woven fabric.

The positive electrode active material may be a positive electrode active material commonly used in the art. Specifically, the positive active material may be a layered compound such as lithium cobalt oxide (LiCoO)₂) And lithium nickel oxide (LiNiO)₂) Or a compound substituted with one or more transition metals; lithium iron oxides, e.g. LiFe₃O₄(ii) a Lithium manganese oxides, e.g. Li_1+c1Mn_2-c1O₄(0≤c1≤0.33)、LiMnO₃、LiMn₂O₃And LiMnO₂(ii) a Lithium copper oxide (Li)₂CuO₂) (ii) a Vanadium oxides, e.g. LiV₃O₈、V₂O₅And Cu₂V₂O₇(ii) a From the formula LiNi_1-c2M_c2O₂(wherein M is any one of Co, Mn, Al, Cu, Fe, Mg, B or Ga, and 0.01. ltoreq. c 2. ltoreq.0.3); of the formula LiMn_2-c3M_c3O₂(wherein M is any one of Co, Ni, Fe, Cr, Zn or Ta, and 0.01. ltoreq. c 3. ltoreq.0.1) or a compound represented by the formula Li₂Mn₃MO₈(wherein M is any one of Fe, Co, Ni, Cu, or Zn); LiMn in which a part of Li in the formula is replaced with an alkaline earth metal ion₂O₄And the like, but are not limited thereto. The positive electrode may be Li metal.

The positive electrode active material layer may include a positive electrode conductive material and a positive electrode binder, and the above-described positive electrode active material.

At this time, the cathode conductive material is used to impart conductivity to the electrode, and any cathode conductive material may be used without particular limitation so long as it has electron conductivity without causing chemical changes in the constructed battery. Specific examples of the positive electrode conductive material may include graphite, such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fibers; metal powders or metal fibers of, for example, copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides such as titanium oxide; or a conductive polymer such as a polyphenylene derivative, and either one thereof or a mixture of two or more thereof may be used.

In addition, the cathode binder serves to improve the adhesion between the cathode active material particles and the adhesion between the cathode active material and the cathode current collector. Specific examples of the cathode binder may include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and any one thereof or a mixture of two or more thereof may be used.

The separator serves to separate the negative electrode and the positive electrode and provide a moving path of lithium ions. Any separator may be used without particular limitation so long as it is a separator generally used in a secondary battery. In particular, a separator having excellent electrolyte moisture content and low resistance to ion movement in the electrolyte is preferable. Specifically, a porous polymer film, for example, a porous polymer film made using a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene/butene copolymer, an ethylene/hexene copolymer, and an ethylene/methacrylate copolymer, or having a laminated structure of two or more layers thereof may be used. In addition, a typical porous nonwoven fabric, such as a nonwoven fabric formed of glass fibers having a high melting point or polyethylene terephthalate fibers, etc., may be used as the separator. In addition, a coated separator including a ceramic component or a polymer material may be used to ensure heat resistance or mechanical strength, and a separator having a single-layer or multi-layer structure may be selectively used.

The electrolyte may be an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, a melt-type inorganic electrolyte, etc., which may be used to manufacture a lithium secondary battery, but is not limited thereto.

Specifically, the electrolyte may include a nonaqueous organic solvent and a lithium salt.

As the non-aqueous organic solvent, for example, aprotic organic solvents such as N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ -butyrolactone, 1, 2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1, 3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphotriester, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1, 3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ether, methyl propionate and ethyl propionate can be used.

In particular, among carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, have a high dielectric constant as a high-viscosity organic solvent to cause good dissociation of lithium salts, and thus may be preferably used. Further, when such cyclic carbonate is mixed with a low viscosity and low dielectric constant linear carbonate (e.g., dimethyl carbonate and diethyl carbonate) in an appropriate ratio, an electrolyte having high conductivity may be prepared, and thus the electrolyte may be more preferably used.

As the metal salt, a lithium salt may be used. The lithium salt is a material that is easily soluble in the non-aqueous electrolyte. For example, as the anion of the lithium salt, one or more selected from the group consisting of: f^-、Cl^-、I^-、NO₃ ^-、N(CN)₂ ^-、BF₄ ^-、ClO₄ ^-、PF₆ ^-、(CF₃)₂PF₄ ^-、(CF₃)₃PF₃ ^-、(CF₃)₄PF₂ ^-、(CF₃)₅PF^-、(CF₃)₆P^-、CF₃SO₃ ^-、CF₃CF₂SO₃ ^-、(CF₃SO₂)₂N^-、(FSO₂)₂N^-、CF₃CF₂(CF₃)₂CO^-、(CF₃SO₂)₂CH^-、(SF₅)₃C^-、(CF₃SO₂)₃C^-、CF₃(CF₂)₇SO₃ ^-、CF₃CO₂ ^-、CH₃CO₂ ^-、SCN^-And (CF)₃CF₂SO₂)₂N^-。

In the electrolyte, in order to improve the life characteristics of the battery, suppress the decrease in the capacity of the battery, and improve the discharge capacity of the battery, one or more additives may be included in addition to the above-mentioned electrolyte components, for example, halogenated alkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, N-glyme, hexamethylphosphoric triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted compoundsOxazolidinone, N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, aluminum trichloride, or the like.

According to still another embodiment of the present invention, there are provided a battery module including the secondary battery as a unit cell, and a battery pack including the battery module. The battery module and the battery pack include the secondary battery having high capacity, high rate performance, and cycle performance, and thus may be used as a power source for medium-and large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

Hereinafter, preferred embodiments of the present invention will be described in detail to facilitate understanding of the present invention. However, the embodiments are merely examples of the present invention, and thus, it is apparent to those skilled in the art that various modifications and variations can be made without departing from the scope and spirit of the present invention as disclosed in the appended claims. It is apparent that such changes and modifications fall within the scope of the appended claims.

Examples and comparative examples

Example 1: preparation of negative active material

(1) Forming a first carbon coating

Average particle diameter (D)₅₀) Needle coke of 8 μm was mixed with pitch, and then the mixture was assembled, followed by heat treatment to prepare an average particle diameter (D)₅₀) Artificial graphite in the form of secondary particles of 17 μm, which was used as the core. The core and petroleum-based solid pitch are mixed, and then the mixture is put into a carbonization furnace to be heat-treated at 1300 ℃ to form a first carbon coating layer on the core. The weight ratio of the core to the first carbon coating was 1: 0.0155.

(2) Forming a second carbon coating

The core having the first carbon coating layer formed thereon is mixed with a liquid phenolic resin, and then the mixture is put into a carbonization furnace to be heat-treated at 1300 c, thereby forming a second carbon coating layer on the core. The weight ratio of the core to the second carbon coating was 1:0.0155 (core: first carbon coating: second carbon coating: 97:1.5:1.5 weight ratio). By the above, the anode active material is finally obtained.

Example 2: preparation of negative active material

(1) Forming a first carbon coating

A first carbon coating layer was formed in the same manner as in example 1, except that the weight ratio of the core to the first carbon coating layer was 1: 0.0316.

(2) Forming a second carbon coating

A second carbon coating layer was formed in the same manner as in example 1, except that the weight ratio of the core to the second carbon coating layer was 1: 0.0211. Through the above, the anode active material was finally obtained (core: first carbon coat: second carbon coat: 95:3:2 weight ratio).

Comparative example 1: negative electrode active materialPreparation of

Average diameter (D)₅₀) Needle coke of 8 μm was mixed with pitch, and then the mixture was assembled, followed by heat treatment to prepare an average diameter (D)₅₀) Artificial graphite in the form of secondary particles of 17 μm, which was used as the core. The core and petroleum-based solid pitch are mixed, and then the mixture is put into a carbonization furnace to be heat-treated at 1300 c, thereby forming a carbon coating on the core. The weight ratio of core to carbon coating was 1: 0.0309.

Comparative example 2: preparation of negative active material

Average diameter (D)₅₀) Needle coke of 8 μm was mixed with pitch, and then the mixture was assembled, followed by heat treatment to prepare an average diameter (D)₅₀) Artificial graphite in the form of secondary particles of 17 μm, which was used as the core. The core and the liquid phenolic resin are mixed and then the mixture is put into a carbonization furnace to be heat-treated at 1300 c, thereby forming a carbon coating on the core. The weight ratio of core to carbon coating was 1: 0.0309.

Comparative example 3: preparation of negative active material

Average particle diameter (D)₅₀) Needle coke of 8 μm was mixed with pitch, and then the mixture was assembled, followed by heat treatment to prepare an average particle diameter (D)₅₀) Artificial graphite in the form of secondary particles of 17 μm, which was used as the core. The core, the petroleum-based solid asphalt, and the liquid phenolic resin are mixed, and then the mixture is put into a carbonization furnace to be heat-treated at 1300 c, thereby forming a carbon coating on the core. The weight ratio of core to carbon coating was 1: 0.0309. The weight ratio of the petroleum asphalt to the phenolic resin used was 2: 1.

Comparative example 4: preparation of negative active material

(1) Forming a first carbon coating

Average particle diameter (D)₅₀) Needle coke of 8 μm was mixed with pitch, and then the mixture was assembled, followed by heat treatment to prepare an average particle diameter (D)₅₀) Artificial graphite in the form of secondary particles of 17 μm, which was used as the core. The core and the liquid phenolic resin are mixed, and then the mixture is put into a carbonization furnace to be heat-treated at 1300 ℃ to form a first carbon coating layer on the core. The weight ratio of the core to the first carbon coating was 1: 0.0103.

(2) Forming a second carbon coating

The core having the first carbon coating layer formed thereon is mixed with petroleum-based pitch, and then the mixture is put into a carbonization furnace to be heat-treated at 1300 c, thereby forming a second carbon coating layer on the core. The weight ratio of the core to the second carbon coating was 1:0.0206 (core: first carbon coating: second carbon coating: 97:1:2 weight ratio). By the above, the anode active material is finally obtained.

Examples of the experiments

Using the negative electrode active materials of each of examples 1 and 2 and comparative examples 1 to 4, each electrode was manufactured in the following manner, and the discharge capacity, initial efficiency, quick charge performance, and high temperature storage performance of each electrode were evaluated.

Negative electrode active materials (negative electrode active materials of examples 1 and 2 and comparative examples 1 to 4, respectively), Super C65 as a conductive material, Styrene Butadiene Rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener were mixed in a weight ratio of 95.3:1:2.5:1.2, and then water was added to prepare a negative electrode slurry. The negative electrode slurry is added at a rate of 3.6mAh/cm²The supported amount of (b) was applied on a copper foil (current collector), and then rolled so that the density of the negative electrode active material layer became 1.6g/cc, followed by vacuum drying at about 130 c for 8 hours to manufacture a negative electrode of example 1.

(1) Experimental example 1: the discharge capacity, initial efficiency and quick charge performance were evaluated.

Cutting into 1.7671cm²The round lithium (Li) metal thin film of (a) is made into a positive electrode. A porous polyethylene separator was interposed between the positive electrode and the negative electrode. Then, an electrolyte in which vinylene carbonate (vinylene carbonate) was dissolved at 0.5 wt% in a mixed solution in which Ethyl Methyl Carbonate (EMC) and Ethylene Carbonate (EC) were mixed at a mixing volume ratio of 7:3 was injected thereto, andin which 1.0M concentration of LiPF was dissolved₆And then preparing. The electrolyte was injected and allowed to stand for 24 hours to manufacture a lithium coin half cell.

The manufactured half cell was charged at 0.1C current, 0.005V at 0.005C cutoff in CC/CV mode, and discharged at 0.1C current at 1.5V cutoff in CC mode. This was done three times, then the initial efficiency was evaluated in the 1 st cycle, and the discharge capacity was evaluated in the 3 rd cycle.

After the 3 rd cycle, an output voltage map according to SOC was derived while charging the half-cell to SOC 75% at a current of 3.0C. In the figure, the X-axis shows the SOC and the Y-axis shows the measured output voltage, and the rapid charging performance was evaluated using a method of determining the Li plating SOC by finding the slope change point (the point at which lithium starts to precipitate) via the dV/dQ derivative.

(2) Experimental example 3: evaluation of high temperature storage Properties

As the positive electrode active material, Li [ Ni ] was used_0.6Mn_0.2Co_0.2]O₂. A positive electrode active material, carbon black as a conductive material, and polyvinylidene fluoride (PVDF) as a binder were mixed into N-methyl-2-pyrrolidone (NMP) as a solvent at a weight ratio of 94:4:2 to prepare a positive electrode slurry.

The prepared positive electrode slurry was applied on an aluminum metal thin film having a thickness of 15 μm as a positive electrode current collector, and then dried. At this time, the temperature of the circulating air was 110 ℃. Thereafter, the aluminum metal thin film dried after the application of the positive electrode paste was rolled and then dried in a vacuum oven at 130 ℃ for 2 hours to manufacture a positive electrode including a positive electrode active material layer.

The anode (anode of each of example 1 and comparative examples 1 to 4), the fabricated cathode, and the porous polyethylene separator were assembled by a stacking method, and an electrolyte (ethylene carbonate (EC)/Ethyl Methyl Carbonate (EMC) ═ 1/2 (volume ratio) and lithium hexafluorophosphate (1M LiPF) were injected into the assembled battery₆) To manufacture a lithium secondary battery.

After the cells were activated by charging the cells to SOC 30% at a current of 0.2C, the operation of charging in the CC/CV mode (4.2V, 0.05C off) and discharging in the CC mode (0.2C current, 3.0V off) was performed 3 times. Thereafter, the secondary battery was fully charged at a current of 0.2C, and then the remaining capacity after 1 week, 2 weeks, and 4 weeks was evaluated while the battery was stored at 60 ℃. Table 1 lists the remaining capacity after 4 weeks of storage.

[ Table 1]

Referring to table 1, it can be seen that when the anode active materials of each of examples 1 and 2 in which the first carbon coating layer is formed by pitch and the second carbon coating layer is formed by resin are used, lithium is delayed to be precipitated, so that the rapid charging property is excellent and the high-temperature storage property is also excellent.

On the other hand, since comparative example 1 was coated with only asphalt, the specific surface area was reduced, and thus the quick charging performance was poor (the content of the carbon coating layer was higher than that of example 2, and thus the high-temperature storage performance was excellent). Since comparative example 2 was coated with only a resin, the quick charging property was excellent; however, the deintercalation of lithium ions cannot be prevented, so that the high-temperature storage performance is low. Since comparative example 3 was coated with the mixture of asphalt and resin, there was no interface, so that the high-temperature storage property was low, and the specific surface area was decreased as a whole, so that the quick-charging property was poor. In the case of comparative example 4, an interface was present, and thus high-temperature storage performance was excellent; however, no resin is present on the surface of the anode active material, thereby reducing the specific surface area, and thus the quick charge performance is poor.