KR20200103336A - An anode active material for a lithium secondary battery - Google Patents

Abstract

The present invention relates to a novel negative electrode active material for a lithium secondary battery. The negative electrode active material of the present invention can improve the initial efficiency and rapid charging performance of the battery in a balanced manner.

Description

An anode active material for a lithium secondary battery

The present invention relates to a negative active material for a lithium secondary battery, a method of preparing the negative active material, a negative electrode including the negative active material, and a lithium secondary battery including the negative electrode.

Conventional lithium secondary batteries use amorphous carbon and crystalline carbon as negative active materials, and charging and discharging are performed while repeating a process in which lithium ions of a positive electrode are inserted and desorbed into a negative electrode.

In particular, as in Patent Document 1, the use of a negative electrode active material in the form of a mixture of artificial graphite, which is a crystalline carbon, and amorphous carbon, is also confirmed.

However, in the case of a negative electrode active material containing artificial graphite, which is a crystalline carbon, a problem of lowering fairness may occur due to low adhesion to the negative electrode, and a problem of lowering the resistance characteristics of the battery may occur. Therefore, there is a problem that the overall economic feasibility is also deteriorated.

KR 10-2008-0036255 A

An object of the present invention is to provide an economical negative electrode active material with excellent charge/discharge and resistance characteristics of a battery, improved rapid charging performance, and improved processability.

The present invention,

A core that does not contain crystalline carbon and contains amorphous carbon; And

A shell surrounding the core and containing natural graphite without including amorphous carbon and artificial graphite; including,

Provide a negative active material.

In the negative active material according to an embodiment of the present invention, the amorphous carbon is soft carbon, hard carbon, coke, mesocarbon microbeads (MCMB) fired at 1500° C. or lower, And at least one selected from the group consisting of mesophase pitch-based carbon fiber (MPCF).

In the negative active material according to an embodiment of the present invention, the average diameter of the negative active material may be 50 μm to 100 μm.

In addition, the present invention provides a method for preparing a negative electrode active material of the present invention comprising the step of mixing and spheroidizing amorphous carbon and natural graphite.

In the method of manufacturing a negative active material according to an embodiment of the present invention, a mixed weight ratio of the amorphous carbon and the natural graphite may be 5:95-20:80.

In addition, the present invention provides a negative electrode comprising the negative active material of the present invention.

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

By the negative active material of the present invention, initial efficiency and rapid charging performance of a battery may be improved in a balanced manner, and resistance characteristics and processability of the battery may also be greatly improved.

1 is a schematic diagram showing a method of manufacturing an anode active material of the present invention.

Hereinafter, the present invention will be described in more detail. If there are no other definitions in the technical and scientific terms used at this time, they have the meanings commonly understood by those of ordinary skill in the technical field to which this invention belongs, and the following description will unnecessarily obscure the subject matter of the present invention. Description of possible known functions and configurations will be omitted.

The present invention,

A core that does not contain crystalline carbon and contains amorphous carbon; And

A shell surrounding the core and containing natural graphite without including amorphous carbon and artificial graphite; including,

Provide a negative active material.

First, the core of the negative electrode active material of the present invention is characterized in that it does not contain crystalline carbon but contains amorphous carbon. That is, any crystalline carbon known to a person skilled in the art is not included in the core of the negative active material of the present invention, and the crystalline carbon is exemplified by artificial graphite, natural graphite, graphitized coke, graphitized mesocarbon microbeads ( mesocarbon microbead: MCMB), and graphitized mesophase pitch-based carbon fiber (MPCF) may be at least one selected from the group consisting of.

In the negative active material according to an embodiment of the present invention, the amorphous carbon is preferably soft carbon, hard carbon, coke, mesocarbon microbeads fired at 1500°C or less (MCMB). ), and mesophase pitch-based carbon fiber (MPCF) may be at least one or more selected from the group consisting of, but is not limited thereto.

A negative electrode active material according to an embodiment of the present invention is preferably, a core made of amorphous carbon; And a shell made of natural graphite; may be a negative active material including.

In the negative active material according to an embodiment of the present invention, the average diameter (D ₅₀ ) of the negative active material may be preferably 50 μm to 100 μm, and more preferably 75 μm to 100 μm. When the average diameter of the negative active material is less than 50 μm, it is difficult to form a shell having an appropriate thickness, so that the initial efficiency of the battery may decrease. When the average diameter of the negative electrode active material is more than 100 μm, the shell becomes considerably thick, so that the rapid charging performance of the battery may not be improved. That is, when the average diameter (D ₅₀ ) of the negative active material is 50 μm to 100 μm, there may be an advantage in that initial efficiency and rapid charging performance of the battery are significantly improved in a balanced manner.

In addition, as shown in the schematic diagram of FIG. 1, the present invention provides a method for producing a negative active material of the present invention, including the step of mixing and spheroidizing amorphous carbon and natural graphite.

In the method of manufacturing an anode active material according to an embodiment of the present invention, the average diameter (D ₅₀ ) of the amorphous carbon applied to the spheronization step may be preferably 7 μm or less, and the natural graphite applied to the spheronization step The average length (L ₅₀ ) of may be preferably 50 μm or more. The average diameter (D ₅₀ ) of the amorphous carbon applied to the spheronization step may be more preferably 5 μm or less, and the average length (L ₅₀ ) of the natural graphite applied to the spheronization step is more preferably 70 μm or more. I can.

In the method for producing a negative active material according to an embodiment of the present invention, the spheronization may be performed through a drum mixer, but a dry tumbler, a super mixer, a Henschel mixer, a flash mixer, an air blender, a flow jet mixer, and a revocon mixer , Pug Mixer, Nauta Mixer, Ribbon Mixer, Spartan Flower, Redige Mixer, Planetary Mixer, and other devices such as screw type kneaders, defoaming kneaders, paint shakers, pressure kneaders, and kneaders such as two rolls. Although it may be used, the device for spheroidization is not limited thereto, and a device capable of mixing two or more materials may be appropriately selected and used.

In the method for producing a negative active material according to an embodiment of the present invention, the drum mixer may be rotated for 2 to 6 hours at a rotational speed of preferably 700 rpm to 2,500 rpm, more preferably 1000 rpm to 2,000 rpm. It may be to rotate for 3 to 5 hours at a rotational speed. When the rotational speed of the drum mixer is less than 700 rpm and less than 2 hours, there may be a problem in that the rotational force is insufficient, and the natural graphite of the shell of the negative electrode active material is not sufficiently spherical in the form of surrounding amorphous carbon of the core. have. When the rotational speed of the drum mixer exceeds 2,500 rpm and exceeds 6 hours, due to excessive rotational force, the natural graphite of the shell of the negative electrode active material is cut off and the area of the amorphous carbon of the core that cannot be wrapped increases. Initial efficiency and rapid charging performance may be deteriorated.

In the method of manufacturing a negative active material according to an embodiment of the present invention, the mixed weight ratio of the amorphous carbon and the natural graphite applied to the spheronization step may be preferably 5:95-20:80, more preferably 5 :95-10:90 can be. By the application of the mixing weight ratio, the natural graphite of the shell of the negative electrode active material can be spheronized in a form that sufficiently surrounds the amorphous carbon of the core.

The present invention provides a negative electrode including the negative electrode active material of the present invention, and also provides a lithium secondary battery including the negative electrode.

In addition to the negative electrode, a lithium secondary battery according to an embodiment of the present invention includes a non-aqueous electrolyte; A positive electrode including a positive electrode active material; And a separator; may include.

The non-aqueous electrolyte may be made of an electrolyte and a lithium salt, and a non-aqueous organic solvent or the like may be used as the electrolyte.

As the non-aqueous organic solvent, for example, N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyllolactone, 1,2-dime Oxyethane, tetrahydroxy franc (franc), 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolone, formamide, dimethylformamide, dioxolone, acetonitrile, nitromethane, methyl formate, Methyl acetate, phosphoric acid tryester, trimethoxymethane, dioxolone derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl propionate , Or an aprotic organic solvent such as ethyl propionate may be used.

The lithium salt is a material soluble in the non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiSbF ₆ , LiAlCl ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, lithium chloroborane, lithium lower aliphatic carboxylic acid, lithium 4 phenyl borate, imide, etc. may be used .

The positive electrode active material is preferably a composite metal oxide of at least one selected from cobalt, manganese, and nickel, and lithium. The solid solubility between metals can be made variously. In addition to these metals, Mg, Al, Co, K, Na, Ca, Si, Ti, Sn, V, Ge, Ga, B, As, Zr, Mn, Cr, Fe, An element selected from the group consisting of Sr, V, and rare earth elements may be further included. Examples of the positive electrode active material is Li _{a A 1 -} (in the above formula, 0.90 ≤ a ≤ 1.8, and _{0 ≤ b ≤ 0.5) b B} b D 2; _{Li a E 1 - b B b} O 2 - ( in the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05) c D c; _{LiE 2 - b B b O 4} - ( in the above formula, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05) c D c; Li _a Ni _{1 -b- c} Co _b B _c D _α (in the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α ≤ 2); _{Li a Ni 1 -b- c Co b} B c O 2 - α F α ( wherein, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α <2 a); Li _a Ni _{1 -bc} Co _b B _c O _2-α F ₂ (in the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α <2); Li _a Ni _{1 -b- c} Mn _b B _c D _α (in the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α ≤ 2); _{Li a Ni 1 -b- c Mn b} B c O 2 - α F α ( wherein, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α <2 a); _{Li a Ni 1 -b- c Mn b} B c O 2 - α F 2 ( wherein, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α <2 a); 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 (wherein, 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 (in the above formula, 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 (in the above formula, 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 ; LiIO 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); And LiFePO _{4 It} is possible to use a compound represented by any one of the formula.

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 may be 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 -x- y} Co _x Mn _y O ₂ (0≤ x≤0.5, 0≤y≤0.5), may be FePO ₄ or the like.

The positive or negative electrode may be prepared by dispersing an electrode active material, a binder, a conductive material, and, if necessary, a thickener in a solvent to prepare an electrode slurry composition, and then applying the slurry composition to an electrode current collector. Aluminum or aluminum alloy may be used as the positive electrode current collector, and copper or copper alloy may be commonly used as the negative electrode current collector. The positive electrode current collector and the negative electrode current collector may be in the form of foil or mesh.

The binder is a material that plays a role of a buffering effect on the expansion and contraction of the active material, such as forming a paste of the active material, mutual adhesion of the active material, adhesion to the current collector, and, for example, polyvinylidene fluoride (PVdF), polyhexafluoro Copolymer of propylene-polyvinylidene fluoride (PVdF/HFP)), poly(vinyl acetate), polyvinyl alcohol, polyethylene oxide, polyvinylpyrrolidone, alkylated polyethylene oxide, polyvinyl ether, poly(methylmetha) Acrylate), poly(ethylacrylate), polytetrafluoroethylene, polyvinyl chloride, polyacrylonitrile, polyvinylpyridine, styrene-butadiene rubber (SBR), carboxymethylcellulose (CMC), acrylonitrile -Butadiene rubber, etc. The content of the binder may be 0.1 to 30% by weight, preferably 1 to 10% by weight, based on the electrode active material. If the content of the binder is too small, the adhesion between the electrode active material and the current collector may be insufficient, and if the content of the binder is too high, the adhesion is improved, but the content of the electrode active material decreases that much, which may be disadvantageous in increasing the battery capacity.

The conductive material is used to impart conductivity to the electrode, and in the battery constituted, any material can be used as long as it does not cause chemical changes and is an electronic conductive material. At least one selected from the group consisting of conductive materials may be used. Examples of the graphite-based conductive material include artificial graphite and natural graphite, and examples of the carbon black-based conductive material include acetylene black, ketjen black, denka black, thermal black, and channel black. channel black), and examples of metal-based or metallic compound-based conductive materials include perovskite materials such as tin, tin oxide, tin phosphate (SnPO ₄ ), titanium oxide, potassium titanate, LaSrCoO ₃ , and LaSrMnO _3. have. However, it is not limited to the conductive materials listed above.

The content of the conductive material is preferably 0.1 to 10% by weight based on the electrode active material. When the content of the conductive material is less than 0.1% by weight, the electrochemical properties decrease, and when it exceeds 10% by weight, the energy density per weight decreases.

The thickener is not particularly limited as long as it can control the viscosity of the active material slurry, but for example, carboxymethyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, and the like may be used.

As a solvent in which an electrode active material, a binder, a conductive material, and the like are dispersed, a non-aqueous organic solvent or an aqueous solvent is used. Examples of the non-aqueous organic solvent include N-methyl-2-pyrrolididone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, and tetrahydrofuran.

A lithium secondary battery according to an embodiment of the present invention may include a separator that prevents a short circuit between a positive electrode and a negative electrode and provides a passage for lithium ions. Such separators include polypropylene, polyethylene, polyethylene/polypropylene, Polyolefin-based polymer films such as polyethylene/polypropylene/polyethylene, polypropylene/polyethylene/polypropylene, or a multilayer thereof, microporous films, woven fabrics, and nonwoven fabrics may be used. In addition, a film coated with a resin having excellent stability on a porous polyolefin film may be used.

The lithium secondary battery according to an embodiment of the present invention may be formed in other shapes such as a cylindrical shape or a pouch type in addition to a square shape. The secondary battery is suitable for applications requiring high voltage, high output, and high temperature driving, such as an electric vehicle, in addition to applications such as conventional mobile phones and portable computers. In addition, the secondary battery can be used in hybrid vehicles, etc. in combination with existing internal combustion engines, fuel cells, supercapacitors, etc., and can be used for electric bicycles, power tools, and all other uses requiring high output, high voltage and high temperature driving. Can be used.

Hereinafter, examples and experimental examples of the present invention will be described. However, the following examples and experimental examples are only preferred examples of the present invention, and the present invention is not limited to the following examples and experimental examples.

[Analysis of negative electrode active material]

After dispersing the negative active material by adding an antacid to a solution in which the negative active material prepared in each Example and Comparative Example was mixed in a ratio of 95% water and 5% negative active material, a micro particle size analyzer (device name: mastersizer3000, manufacturer: Malvern Instruments Ltd) to determine the form and average diameter of the active material. Observed.

Example

[Example 1]: Preparation of the negative active material of the present invention

Hard carbon having an average diameter (D ₅₀ ) of 3 µm and natural graphite having an average length (L ₅₀ ) of 75 µm were added to a drum mixer at a weight ratio of 10:90, and mixed while rotating at a speed of 1,500 rpm for 4 hours. Through a sieving process, a negative electrode active material having an average diameter (D ₅₀ ) of 25 μm was prepared in a spherical shape in which natural graphite was wrapped around hard carbon.

[Example 2]: Preparation of the negative active material of the present invention

Hard carbon having an average diameter (D ₅₀ ) of 3 μm and natural graphite having an average length (L ₅₀ ) of 120 μm were added to a drum mixer at a weight ratio of 10:90, and mixed while rotating at a speed of 1,500 rpm for 4 hours. Through a sieving process, a negative electrode active material having an average diameter (D ₅₀ ) of 40 μm was prepared in a spherical shape in which natural graphite was wrapped around hard carbon.

[Example 3]: Preparation of the negative active material of the present invention

Hard carbon having an average diameter (D ₅₀ ) of 3 µm and natural graphite having an average length (L ₅₀ ) of 150 µm were added to a drum mixer at a weight ratio of 10:90, and mixed while rotating at a speed of 1,500 rpm for 4 hours. Through a sieving process, a negative active material having an average diameter (D ₅₀ ) of 50 μm was prepared in a spherical shape in which natural graphite was wrapped around hard carbon.

[Example 4]: Preparation of the negative active material of the present invention

Hard carbon having an average diameter (D ₅₀ ) of 3 µm and natural graphite having an average length (L ₅₀ ) of 220 µm were added to a drum mixer at a weight ratio of 10:90, and mixed while rotating at a speed of 1,500 rpm for 4 hours. Through a sieving process, a negative electrode active material having an average diameter (D ₅₀ ) of 75 μm was prepared in a spherical shape in which natural graphite was wrapped around the hard carbon.

[Example 5]: Preparation of the negative active material of the present invention

Hard carbon having an average diameter (D ₅₀ ) of 3 µm and natural graphite having an average length (L ₅₀ ) of 310 µm were introduced into a drum mixer at a weight ratio of 10:90, and mixed while rotating at a speed of 1,500 rpm for 4 hours. Through a sieving process, a negative active material having an average diameter (D ₅₀ ) of 100 μm was prepared in a spherical shape in which the hard carbon was wrapped with natural graphite.

[Example 6]: Preparation of the negative active material of the present invention

Hard carbon having an average diameter (D ₅₀ ) of 3 µm and natural graphite having an average length (L ₅₀ ) of 400 µm were introduced into a drum mixer at a weight ratio of 10:90, and mixed while rotating at a speed of 1,500 rpm for 4 hours. Through a sieving process, a negative active material having an average diameter (D ₅₀ ) of 125 μm and a spherical shape in which natural graphite is wrapped around hard carbon was prepared.

[Example 7]: Preparation of the negative active material of the present invention

Hard carbon having an average diameter (D ₅₀ ) of 3 μm and natural graphite having an average length (L ₅₀ ) of 450 μm were added to a drum mixer at a weight ratio of 10:90, and mixed while rotating at a speed of 1,500 rpm for 4 hours. Through a sieving process, a negative electrode active material having an average diameter (D ₅₀ ) of 150 μm and a spherical shape in which natural graphite is wrapped around hard carbon was prepared.

[Comparative Example 1]: Preparation of a control negative active material

Hard carbon having an average diameter (D ₅₀ ) of 7 µm and artificial graphite having an average length (L ₅₀ ) of 120 µm were added to a drum mixer at a weight ratio of 10:90, and mixed while rotating at a speed of 1,500 rpm for 4 hours. Through a sieving process, a negative electrode active material having an average diameter (D ₅₀ ) of 45 μm was prepared in a spherical shape in which the hard carbon was wrapped with artificial graphite.

Experimental example

[Experimental Example 1]: Measurement of initial efficiency of a battery

A negative active material was prepared in a weight ratio of negative active material: SBR: CMC = 97.0: 1.5: 1.5 to prepare a negative electrode mixture, and then the negative electrode mixture was coated on a copper foil, dried and rolled to form a coin-shaped half-cell (half cell). coin cell) was prepared. In the cell, lithium metal was used as a counter electrode, and an electrolyte in which 1M LiPF ₆ was dissolved in a carbonate solvent was used.

The initial efficiency (1 ^st efficiency) of the manufactured coin-type half cell was measured, and the results are shown in Table 1. The initial efficiency, specifically, was charged in CC mode to 5 mV at a current density of 0.1 C during charging, and then maintained at a constant rate of 5 mV in CV mode to complete charging when the current density reached 0.005 C. Initial efficiency was obtained by completing the discharge in CC mode up to 1.5 V with a current density of 0.1 C during discharge.

Negative active material Initial efficiency of battery (%) Example 1 85.4 Example 2 86.1 Example 3 91.8 Example 4 92.1 Example 5 92.2 Example 6 92.2 Example 7 92.1 Hard carbon (average diameter (D ₅₀ ): 7㎛) 79

According to [Table 1], when using the negative active material of the present invention according to the embodiment, the initial efficiency of the battery can be greatly improved compared to the case of using a negative active material consisting of only amorphous carbon (hard carbon). In particular, the negative active material of the present invention according to Example 3-7 has an average diameter of 50 μm or more, and may induce a more remarkably improved initial efficiency of the battery.

[Experimental Example 2]: Measurement of battery fast charging performance (2 C)

The coin-type half-cell prepared in Experimental Example 1 was charged and discharged using an electrochemical charger and discharger. The charge/discharge rate was set to 0.1 C-rate, 3 cycles were charged/discharged, and the current value of the C-rate was calculated based on the absolute discharge capacity of the 3rd cycle, and 24 minutes 　 rapid charging was performed at 2 C. After the rapid charging 　 progress, the SOC time point at which Li-plating was performed, and a rest for 1 hour thereafter was given to confirm the voltage relaxation profile. After rapid charging 　 progress, the SOC time point at which Li-plating is performed is shown in Table 2 below.

Negative active material Li-plating SOC (%)
(2C quick charge) Example 3 88.2 Example 4 87.9 Example 5 87.8 Example 6 80.1 Natural graphite (average length (L ₅₀ ): 120 ㎛) 75

According to [Table 2], when using the negative active material of the present invention according to the embodiment, it is possible to significantly improve the rapid charging performance of the battery compared to the case of using the negative active material consisting of only natural graphite. In particular, the negative active material of the present invention according to Example 3-5 has an average diameter of 50 µm to 100 µm, and may induce a more remarkably improved battery fast charging performance.

[Experimental Example 3]: Measurement of adhesion of negative active material

The adhesion between the 　cathode 　electrode plate and the 　cathode active material of the coin-shaped half-cell prepared in Experimental Example 1 was measured, and the results are shown in Table 3. The adhesive strength between the negative electrode plate and the negative electrode active material is determined by attaching a 3M tape with a certain length and width to the surface of the negative electrode active material, and then performing a 180 degree peel-off test using an Instron's tensile strength tester. gf/20mm) was measured. The results are shown in Table 3 below.

Negative active material Adhesion to cathode (gf/20mm) Example 3 40 Comparative Example 1 15

According to [Table 3], it is confirmed that the negative electrode active material of the present invention according to the embodiment has remarkably improved adhesion to the negative electrode as compared to the case of the negative electrode active material including the artificial graphite shell (Comparative Example 1). That is, it is confirmed that the negative electrode active material of the present invention exhibits high adhesion to the negative electrode, thereby improving processability.

[Experimental Example 4]: DC-IR (Direct Current-Internal Resistance) measurement of a battery

Initial DC-IR of the battery was measured at room temperature, and DC-IR was calculated as follows and shown in Table 4 below. A battery in a 50% charged state (hereinafter, SOC50) (coin-type half cell manufactured according to Experimental Example 1) was charged at 0.5C-rate for 10 seconds. The battery was made into SOC50 again, paused for 10 minutes, and then charged at 1.0C-rate for 10 seconds. The battery was made into SOC50 again, rested for 10 minutes, and then charged at 2.0C-rate for 10 seconds. DC-IR was calculated during charging by using the voltage and current obtained at each C-rate. And the battery in a 50% charged state was discharged for 10 seconds at 0.5C-rate. The battery was made into SOC50 again, paused for 10 minutes, and then discharged for 10 seconds at 1.0C-rate. The battery was made into SOC50 again, rested for 10 minutes, and then discharged at 2.0C-rate for 10 seconds. DC-IR was calculated during discharge using the voltage and current obtained at each C-rate.

Negative active material Initial DC-IR (mOhm) of the battery Example 3 1.34 Comparative Example 1 1.45

According to [Table 4], it is confirmed that the negative active material of the present invention according to the embodiment significantly reduces the DC-IR of the battery as compared to the case of the negative active material including the artificial graphite shell (Comparative Example 1). That is, it is confirmed that the negative active material of the present invention can also improve the resistance characteristics of the battery.

Claims (7)

A core that does not contain crystalline carbon and contains amorphous carbon; And
A shell surrounding the core and containing natural graphite without including amorphous carbon and artificial graphite; including,
Negative active material. The method of claim 1,
The amorphous carbon is soft carbon, hard carbon, coke, mesocarbon microbeads (MCMB) calcined at 1500°C or less, and mesophase pitch-based carbon fibers. carbon fiber: MPCF) at least one negative active material selected from the group consisting of. The method of claim 1,
The negative active material has an average diameter of 50 μm to 100 μm. A method for producing a negative active material according to claim 1, comprising the step of mixing amorphous carbon and natural graphite to form a sphere. The method of claim 4,
A method for producing a negative active material in which the amorphous carbon and the natural graphite are mixed in a weight ratio of 5:95 to 20:80. A negative electrode comprising the negative active material according to any one of claims 1 to 3. A lithium secondary battery comprising the negative electrode according to claim 6.

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