Method for manufacturing negative electrode material

Abstract

To provide a method for manufacturing a negative electrode material.SOLUTION: There is provided a method for manufacturing a negative electrode material that comprises a silicon oxide powder coated with a carbon film. The method includes: a step A of mixing many silicon oxide powders with a planed amount of pitch powder without using any liquid organic solvents, so as to obtain a mixture; a step B of heating the mixture at a heating rate ranging from 0.65°C / min to 1.25°C / min to a carbonization temperature of 600°C or above, then maintaining the mixture at the carbonization temperature for at least 5 hours, thereby melting the planed amount of pitch powder to be coated on a surface of each of the silicon oxide powders, and carbonizing melted pitch to obtain many initial silicon oxide powders, a surface of each of the initial silicon oxide powders being coated with a corresponding carbon film; and a step C of selecting, from the many initial silicon oxide powders, silicon oxide powders, which are coated with the carbon film and have a mean particle size ranging from 2 μm to 11 μm, as a negative electrode material.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to a method for producing a silicon-based negative electrode material, and more particularly to a method for producing a negative electrode material made of silicon oxide powder coated with a carbon film. [Background technology]

[0002] Among the commonly available rechargeable batteries, lithium-ion secondary batteries are the widely used and preferred rechargeable battery.

[0003] Common lithium-ion secondary batteries use lithium cobalt oxide (LiCoO2, abbreviated as LCO), lithium iron phosphate (LiFePO4, abbreviated as LFP), or lithium manganese oxide (LiMn2O4, abbreviated as LMO) as their positive electrode materials, while their negative electrode materials include early carbon materials and recently developed silicon-based materials.

[0004] Patent Document 1 discloses a method for producing a carbon-coated Si / SiC composite active material.

[0005] The manufacturing method includes steps A to G in order.

[0006] Step A is a step of ultrasonically mixing silicon, silicon carbide (SiC), and acetone to obtain a Si / SiC material; Step B is a step of stirring the ground pitch and acetone until the pitch dissolves in the acetone to obtain a pitch material; Step C is a step of stirring the Si / SiC material and the pitch material to obtain a first mixture; Step D is a step of ultrasonically oscillating the first mixture; Step E is a step of suction filtering the first mixture while stirring; Step F is a step of heating the first mixture to 600°C to 1200°C and maintaining it for 1 hour to 12 hours; and Step G is a step of slowly cooling the heated first mixture to room temperature to obtain a carbon-coated Si / SiC composite active material.

[0007] The carbon-coated Si / SiC composite active material obtained by the manufacturing method of Patent Document 1 can be used as a negative electrode material for lithium-ion secondary batteries. However, in the manufacturing method of Patent Document 1, in order to coat the Si / SiC material with carbon, it is necessary to completely dissolve pitch in acetone to obtain the pitch material, and then to stir the Si / SiC material and the pitch material.

[0008] In step E, the first mixture must be subjected to suction filtration.

[0009] In terms of material costs and time costs of the manufacturing method, the use of acetone increases material costs, and processes such as dissolving pitch, ultrasonic vibration, stirring, and suction filtration further increase time costs.

[0010] Furthermore, the manufacturing method of Patent Document 1 involves dissolving pitch in acetone, making it difficult to realize mass production. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Taiwan Patent No. 1636614 Summary of the Invention [Problem to be solved by the invention]

[0012] Therefore, improving the manufacturing method of a negative electrode material whose main component is silicon, and manufacturing the negative electrode material with lower material and time costs, has become a challenge for researchers in this field to solve.

[0013] Therefore, an object of the present invention is to provide a method for producing an anode material made of silicon oxide powder coated with a carbon film, which can save material costs and time costs. [Means for solving the problem]

[0014] The present invention relates to a method for producing an anode material comprising silicon oxide powder coated with a carbon film, and Step A: mixing a number of silicon oxide powders with a predetermined amount of pitch powder to obtain a mixture without using a liquid organic solvent; Step B: heating the mixture to a carbonization temperature of 600°C or higher at a heating rate in the range of 0.65°C / min to 1.25°C / min, and then maintaining the mixture at the carbonization temperature for at least 5 hours, thereby melting the predetermined amount of pitch powder and coating the surface of each of the silicon oxide powders with a carbon film, and simultaneously carbonizing the molten pitch to obtain a number of initial silicon oxide powders, the surface of each of the initial silicon oxide powders being coated with a corresponding carbon film; and step C of selecting, from the large number of initial silicon oxide powders, silicon oxide powder coated with a carbon film having an average particle size in the range of 2 μm to 11 μm as the negative electrode material. [Effects of the Invention]

[0015] In the above method, in step A, a large amount of silicon oxide powder is mixed with a predetermined amount of pitch powder without using a liquid organic solvent, so there is no need to perform time-consuming suction filtration, thereby saving material costs and time costs. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 10 is a diagram showing the relationship between capacity retention and charge C-rate in a specific example. [Figure 2] FIG. 10 is a diagram showing the relationship between the capacity retention rate and the discharge C-rate in a specific example. [Figure 3] FIG. 10 is a diagram showing the relationship between the capacity retention rate and the number of charge / discharge cycles in a specific example. [Figure 4] FIG. 10 is a diagram showing the relationship between the capacity retention rate and the charge C rate in a specific example. [Figure 5] FIG. 10 is a diagram showing the relationship between the capacity retention rate and the number of charge / discharge cycles in a specific example. [Figure 6] FIG. 10 is a graph showing the relationship between the capacity retention rate and the charge C rate in a specific example and a comparative example. [Figure 7] FIG. 10 is a graph showing the relationship between the capacity retention rate and the discharge C rate in specific examples and comparative examples. [Figure 8] FIG. 1 is a graph showing the relationship between the capacity retention rate and the number of charge / discharge cycles in specific examples and comparative examples. [Figure 9] 1A to 1C are X-ray diffraction (hereinafter abbreviated as "XRD") diagrams of specific examples and comparative examples. [Figure 10] FIG. 1 is a diagram showing Raman spectra of specific examples and comparative examples. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0018] An embodiment of the method of the present invention for producing a negative electrode material that is silicon oxide powder coated with a carbon film is a production method comprising the following steps A to C.

[0019] Step A is a step of mixing a large amount (i.e., one batch amount) of silicon oxide powder with a predetermined amount of pitch powder without using any liquid organic solvent to obtain a mixture.

[0020] In some embodiments of the present invention, in step A, the predetermined amount of pitch powder has a particle size distribution in which the D10 particle size is in the range of 0.5 μm to 2 μm, the D50 particle size is in the range of 2 μm to 4 μm, and the D90 particle size is in the range of 5 μm to 9 μm.

[0021] Step B is a step in which the mixture obtained in Step A is heated to a carbonization temperature of 600°C or higher at a heating rate in the range of 0.65°C / min to 1.25°C / min, and then maintained at the carbonization temperature for at least 5 hours, thereby melting a predetermined amount of pitch powder and coating the surface of each silicon oxide powder, and simultaneously carbonizing the molten pitch, thereby obtaining a large number of initial silicon oxide powders.

[0022] By step B, the surface of each initial silicon oxide powder is coated with a corresponding carbon film.

[0023] The purpose of heating the mixture obtained in step A to the carbonization temperature at the heating rate and then maintaining the temperature at the carbonization temperature for at least 5 hours is to utilize the softening point of the pitch so that a predetermined amount of pitch powder reaches the softening point by heating and begins to soften, and during further heating, the softened pitch is melted to reduce the viscosity of the pitch, and the pitch with reduced viscosity coats the surface of each silicon oxide powder, so that the carbon atoms in the melted pitch that coat the surface of the silicon oxide powder are reorganized into sp 2 This is to allow sufficient time for hybrid orbitals to form and to form carbon films that cover the surfaces of the respective initial silicon oxide powder particles.

[0024] Thus, in some embodiments, in step A, the predetermined amount of pitch powder has a softening point of 250°C or higher and a carbon / hydrogen ratio in the range of 1.43 to 1.66, and the amount of silicon oxide powder is 100 parts by weight and the amount of pitch powder is 1 part by weight to 10 parts by weight, relative to the total weight of the resulting mixture.

[0025] In some embodiments, in step B, the carbonization temperature is in the range of 600°C to 1100°C, and the carbon film coating the surface of each initial silicon oxide powder has a thickness in the range of 0.5 μm to 2 μm.

[0026] In some embodiments, in step A, the predetermined amount of pitch powder is 3 parts by weight to 5 parts by weight based on the total weight of the resulting mixture, and in some embodiments, in step B, the carbonization temperature is in the range of 600°C to 900°C.

[0027] In step C, from the large number of initial silicon oxide powders obtained in step B, silicon oxide powder coated with a carbon film and having an average particle size in the range of 2 μm to 11 μm is selected as the negative electrode material to be used in lithium-ion secondary batteries.

[0028] The negative electrode material used in the lithium ion secondary battery of the present invention, the method for producing the negative electrode, and the combination of the battery will be described in detail below.

[0029] <Initial materials for negative electrode and equipment used> The silicon oxide powder was purchased from Hengshui Chaofan New Energy Materials Co., Ltd., China (model number: SX-3).

[0030] The pitch powder was purchased from LONG TIME TECH. CO., LTD., Taiwan (model number: ZL250M).

[0031] The mixing in step A is carried out using a solar (or drum) mixer (internal and external rotation) (model number: BT-50) purchased from Pulian International Enterprise Co., Ltd., Taiwan.

[0032] <Method of manufacturing negative electrode material> <Example 1 (E1)> In Example 1 (E1) of the method for producing a negative electrode material of the present invention, 1 part by weight of pitch powder and 100 parts by weight of silicon oxide powder were mixed using the solar mixer without using a liquid organic solvent to obtain a mixture of Example 1 (E1).The mixture of Example 1 (E1) was then divided into six equal parts.

[0033] In Example 1 (E1), the total weight of each mixture portion is 20 kg.

[0034] Six equal portions of the mixture of Example 1 (E1) were then heated within 15 hours from 0°C to carbonization temperatures of 600°C (heating rate: 0.67°C / min), 700°C (heating rate: 0.78°C / min), 800°C (heating rate: 0.87°C / min), 900°C (heating rate: 1°C / min), 1000°C (heating rate: 1.11°C / min), and 1100°C (heating rate: 1.22°C / min), and maintained at these carbonization temperatures for at least 5 hours to obtain six batches of initial silicon oxide powder of Example 1 (E1). The surface of each initial silicon oxide powder was coated with a corresponding carbon film.

[0035] Finally, from each batch of initial silicon oxide powder, a silicon oxide powder coated with a carbon film is selected using a 400 mesh sieve as the negative electrode material of Example 1 (E1).

[0036] At the carbonization temperature of Specific Example 1 (E1), the negative electrode material heated to a carbonization temperature of 600°C was designated Specific Example 1a (E1a), the negative electrode material heated to a carbonization temperature of 700°C was designated Specific Example 1b (E1b), the negative electrode material heated to a carbonization temperature of 800°C was designated Specific Example 1c (E1c), the negative electrode material heated to a carbonization temperature of 900°C was designated Specific Example 1d (E1d), the negative electrode material heated to a carbonization temperature of 1000°C was designated Specific Example 1e (E1e), and the negative electrode material heated to a carbonization temperature of 1100°C was designated Specific Example 1f (E1f).

[0037] <Example 2 (E2)> The method for producing Example 2 (E2) of the negative electrode material of the present invention is the same as Example 1 (E1) except that 100 parts by weight of silicon oxide powder and 2 parts by weight of pitch powder are mixed.

[0038] At the carbonization temperature of Specific Example 2 (E2), the negative electrode material heated to a carbonization temperature of 600°C was designated Specific Example 2a (E2a), the negative electrode material heated to a carbonization temperature of 700°C was designated Specific Example 2b (E2b), the negative electrode material heated to a carbonization temperature of 800°C was designated Specific Example 2c (E2c), the negative electrode material heated to a carbonization temperature of 900°C was designated Specific Example 2d (E2d), the negative electrode material heated to a carbonization temperature of 1000°C was designated Specific Example 2e (E2e), and the negative electrode material heated to a carbonization temperature of 1100°C was designated Specific Example 2f (E2f).

[0039] <Example 3 (E3)> The method for producing Example 3 (E3) of the negative electrode material of the present invention is the same as Example 1 (E1) except that 100 parts by weight of silicon oxide powder and 3 parts by weight of pitch powder are mixed.

[0040] At the carbonization temperature of Specific Example 3 (E3), the negative electrode material heated to a carbonization temperature of 600°C was designated Specific Example 3a (E3a), the negative electrode material heated to a carbonization temperature of 700°C was designated Specific Example 3b (E3b), the negative electrode material heated to a carbonization temperature of 800°C was designated Specific Example 3c (E3c), the negative electrode material heated to a carbonization temperature of 900°C was designated Specific Example 3d (E3d), the negative electrode material heated to a carbonization temperature of 1000°C was designated Specific Example 3e (E3e), and the negative electrode material heated to a carbonization temperature of 1100°C was designated Specific Example 3f (E3f).

[0041] <Example 4 (E4)> The method for producing Example 4 (E4) of the negative electrode material of the present invention is the same as Example 1 (E1) except that 100 parts by weight of silicon oxide powder and 4 parts by weight of pitch powder are mixed.

[0042] At the carbonization temperature of Specific Example 4 (E4), the negative electrode material heated to a carbonization temperature of 600°C was designated Specific Example 4a (E4a), the negative electrode material heated to a carbonization temperature of 700°C was designated Specific Example 4b (E4b), the negative electrode material heated to a carbonization temperature of 800°C was designated Specific Example 4c (E4c), the negative electrode material heated to a carbonization temperature of 900°C was designated Specific Example 4d (E4d), the negative electrode material heated to a carbonization temperature of 1000°C was designated Specific Example 4e (E4e), and the negative electrode material heated to a carbonization temperature of 1100°C was designated Specific Example 4f (E4f).

[0043] In the manufacturing method of Example 4d (E4d), before mixing, the particle size distribution of the silicon oxide powder (SX-3) used for mixing was measured using a laser diffraction / scattering particle size distribution analyzer (model number: LS13320) purchased from Beckman Coulter Inc., USA. After selection by heating and sieving, the particle size distribution of the negative electrode material obtained in Example 4d (E4d) was also measured using the same laser diffraction / scattering particle size distribution analyzer.

[0044] The results of particle size distribution measurements are shown in Table 1.

[0045] [Table 1]

[0046] According to the results shown in Table 1, the silicon oxide powder before mixing had a particle size distribution in which the D10 particle size was 2.240 μm, the D50 particle size was 4.839 μm, and the D90 particle size was 7.876 μm, while the negative electrode material after heating and sieving had a particle size distribution in which the D10 particle size was 3.157 μm, the D50 particle size was 5.581 μm, and the D90 particle size was 9.801 μm.

[0047] When the result is calculated (ie, the particle size of the negative electrode material minus the particle size of the silicon oxide powder before mixing), the negative electrode material of Specific Example 4d (E4d) has a carbon film thickness of 0.742 μm to 1.925 μm.

[0048] <Example 5 (E5)> The manufacturing method for Example 5 (E5) of the negative electrode material of the present invention is the same as Example 4 (E4), except that the mixture is heated to a carbonization temperature of 900°C (heating rate is 0.71°C / min) within 21 hours and then maintained at the carbonization temperature for at least 5 hours.

[0049] <Initial materials for the negative electrode> Negative electrode material: Silicon oxide powder (model number: SX-3) purchased from Hengshui Chaofan New Energy Materials Co., Ltd., China, which served as Comparative Example 1 (CE1), silicon oxide powders coated with carbon films obtained in Specific Example 1d (E1d), Specific Example 2d (E2d), Specific Example 3d (E3d), Specific Example 4a (E4a), Specific Example 4b (E4b), Specific Example 4c (E4c), Specific Example 4d (E4d), Specific Example 4e (E4e), Specific Example 4f (E4f) and Specific Example 5 (E5), or a carbon silicon composite material (model number: KSC-1265) purchased from Shin-Etsu Chemical Co., Ltd., which served as Comparative Example 2 (CE2), was used.

[0050] Other materials used are as follows:

[0051] Carboxymethyl cellulose (model number: JSR-104A, hereinafter abbreviated as "CMC") was purchased from JSR Corporation.

[0052] Carbon nanotubes (model number: TUBALL BATT H2O SWCNT, hereinafter abbreviated as "CNTs") were purchased from Hefei Nano Semiconductor Co., Ltd., China, and Shenyang East Chemical Science-Tech Co., Ltd., China.

[0053] Conductive carbon black (model number: Super P) purchased from Timcal, Switzerland.

[0054] Styrene-butadiene rubber (model number: MAC350HC, hereinafter abbreviated as "SBR") purchased from Nippon Paper Industries Co., Ltd.

[0055] <Production of negative electrodes> First, CMC, CNTs, and deionized water were mixed uniformly to obtain a mixed solution, which was then divided into several equal parts.

[0056] Then, conductive carbon black, each negative electrode material, SBR, and deionized water were added to each equal portion of the mixed solution in order to form a plurality of conductive slurries, each containing one type of negative electrode material.

[0057] Finally, each conductive slurry was applied to a copper foil having a thickness of 14 μm, and then dried at 150° C. for 12 hours to remove the deionized water in each conductive slurry, thereby obtaining each negative electrode.

[0058] Each negative electrode includes a corresponding copper foil and a conductive film having a thickness of 25 μm to 35 μm formed on the copper foil.

[0059] Each conductive film contains, based on its total weight, 5.6 wt% CMC, 0.3 wt% CNTs, 12 wt% conductive carbon black, 77.6 wt% anode material, and 4.5 wt% SBR.

[0060] <Manufacture of CR2032 Half-Cell (Coin Cell)> The CR2032 half-cell was obtained by assembling each negative electrode, a lithium foil as the positive electrode, an electrolytic solution, and a separator film (purchased from Celgard, USA; materials: polyethylene (abbreviation: PE) and polypropylene (abbreviation: PP)).

[0061] The electrolytic solution contains a lithium hexafluorophosphate (hereinafter abbreviated as LiPF6) solution with a concentration of 1.2 M at 97 wt% based on its total weight, 1 wt% of vinylene carbonate, and 2 wt% of propane sultone.

[0062] The LiPF6 solution contains LiPF6, ethylene carbonate (hereinafter abbreviated as EC), ethylene methyl carbonate (hereinafter abbreviated as EMC), and dimethyl carbonate (hereinafter abbreviated as DMC), and the volume ratio of EC:EMC:DMC is 1:2:3.

[0063] The CR2032 half-cells assembled with the negative electrode materials of Specific Example 1d (E1d), Specific Example 2d (E2d), Specific Example 3d (E3d), Specific Example 4a (E4a), Specific Example 4b (E4b), Specific Example 4c (E4c), Specific Example 4d (E4d), Specific Example 4e (E4e), Specific Example 4f (EAF), Specific Example 5 (E5), Comparative Example 1 (CE1), and Comparative Example 2 (CE2) are represented as Specific Example 1D (E1D), Specific Example 2D (E2D), Specific Example 3D (E3D), Specific Example 4A (E4A), Specific Example 4B (E4B), Specific Example 4C (E4C), Specific Example 4D (E4D), Specific Example 4E (E4E), Specific Example 4F (E4F), Specific Example 5 (E5), Comparative Example 1 (CE1), and Comparative Example 2 (CE2), respectively.

[0064] And to verify the reproducibility of the performance of the CR2032 half-cells of each specific example (E1D, E2D, E3D, E4A, E4B, E4C, E4D, E4E, E4F, E5), before assembling the CR2032 half-cells, each negative electrode was cut into a plurality of negative electrode sheets, and after assembly, the corresponding number of CR2032 half-cells were obtained.

[0065] The pitch content and carbonization temperature of the negative electrode materials of each specific example (E1D, E2D, E3D, E4A, E4B, E4C, E4D, E4E, E4F, E5) and each comparative example (CE1, CE2) are shown in Table 2.

[0066]

Table 2

[0067] <Performance Test of CR2032 Half-Cell> Using a battery test device (manufactured by Maccor, USA, model number: Series 4000), the charge capacity and discharge capacity of the CR2032 half-cells were measured under general measurement conditions and high load measurement conditions. When measuring at different charge C-rates or discharge C-rates, new CR2032 half-cells of specific examples or comparative examples were used for measurement.

[0068] The general measurement conditions are a temperature of 25°C, a charge cut-off voltage of 0.01 V, and a discharge cut-off voltage of 1.8 V.

[0069] The high load measurement conditions are a temperature of 25°C, a charge end voltage of 0 V, and a discharge end voltage of 1.2 V.

[0070] The initial coulombic efficiency (ICE) of each CR2032 half-cell was calculated from the first cycle charge capacity and first cycle discharge capacity at a charge / discharge rate of 0.1 C.

[0071] The cycle life of each CR2032 half cell was measured by measuring the number of cycles at room temperature and high load with a charge / discharge C rate of 0.5C.

[0072] Each of the above types of measurements is performed using a new CR2032 half cell of each specific example or comparative example.

[0073] According to Table 3 below, the ICEs measured under standard measurement conditions for the CR2032 half-cells No. 1, No. 2, and No. 3 of Example 4D (E4D) were 78.40%, 78.30%, and 78.44%, respectively. This demonstrates that the ICE reproducibility of each CR2032 half-cell of Example 4D (E4D) of the present invention is nearly consistent.

[0074] [Table 3]

[0075] According to Table 4 below, the ICEs measured under high-load conditions for the CR2032 half-cells of Example 4 (E4A, E4B, E4C, E4D, E4E, and E4F) were 65.80%, 63.90%, 66.81%, 72.74%, 71.28%, and 73.02%, respectively. That is, the ICEs for the CR2032 half-cells of Example 4 (E4A, E4B, E4C, E4D, E4E, and E4F) of the present invention increased with the carbonization temperature of the negative electrode material used.

[0076] [Table 4]

[0077] According to the relationship between capacity retention and charge C rate shown in Figure 1, the capacity retention of each of Specific Examples 4 (E4A, E4B, E4C, E4D, E4E, and E4F) decreased as the charge C rate increased under high-load measurement conditions. However, according to the relationship between capacity retention and discharge C rate (high-load measurement conditions) shown in Figure 2, Specific Example 4A (E4A) maintained a capacity retention of approximately 70% when the discharge C rate was 3C, Specific Example 4B (E4B), Specific Example 4C (E4C), Specific Example 4E (E4E), and Specific Example 4F (E4F) all maintained a capacity retention of approximately 80% when the discharge C rate was 3C, and Specific Example 4D (E4D) maintained a capacity retention of 90% or more when the discharge C rate was 3C.

[0078] This indicates that when the carbonization temperature was set to 900°C in the method for producing the negative electrode material of the present invention, the performance of the CR2032 half cell assembled with the obtained negative electrode material was the best.

[0079] Furthermore, according to the relationship between capacity retention and the number of charge-discharge cycles (high load measurement conditions) shown in Figure 3, in Specific Example 4B (E4B), Specific Example 4C (E4C), Specific Example 4D (E4D), and Specific Example 4F (E4F), the number of charge-discharge cycles when the capacity retention was 80% was between 17 and 19, and in Specific Example 4B (E4B), Specific Example 4C (E4C), and Specific Example 4D (E4D), the capacity retention was maintained at 45% or more when the number of charge-discharge cycles reached 50.

[0080] In contrast, in Specific Example 4A (E4A), Specific Example 4E (E4E), and Specific Example 4F (E4F), the capacity retention rate fell to 35% or less when the number of charge / discharge cycles reached 50. This indicates that the cycle life of a CR2032 half-cell assembled with the obtained negative electrode material was better when the carbonization temperature was set to 700°C to 900°C in the manufacturing method of the negative electrode material of the present invention.

[0081] According to the relationship between the capacity retention rate and the charge C rate (high load measurement conditions) shown in FIG. 4, the capacity retention rates of Specific Example 4D (E4D) and Specific Example 5 (E5) decreased with increasing charge C rate, and the capacity retention rate of Specific Example 5 (E5) was superior to that of Specific Example 4D (E4D).

[0082] Furthermore, according to the relationship between the capacity retention rate and the number of charge-discharge cycles (high load measurement conditions) shown in FIG. 5, in Specific Example 4D (E4D) and Specific Example 5 (E5), the number of charge-discharge cycles when the capacity retention rate was 80% was 19 and 33, respectively, and the capacity retention rates when the number of charge-discharge cycles reached 50 were more than 45% and more than 60%, respectively.

[0083] According to the analysis results of FIG. 5, the CR2032 half-cell of Example 5 (E5) (heating rate 0.71° C. / min) exhibited a better cycle life than Example 4D (E4D).

[0084] According to Table 5 below, the CR2032 half-cells of the specific examples (E1D, E2D, E3D, E4D) and Comparative Example 2 (CE2) had ICEs of 70.50%, 71.20%, 71.00%, 72.74%, and 71.80%, respectively, measured under high-load measurement conditions, all of which had an ICE of 70% or more.

[0085] This indicates that the higher the content of pitch powder in the negative electrode material of the CR2032 half-cells of the specific examples (E1D, E2D, E3D, E4D), the higher the ICE of the CR2032 half-cells of the specific examples (E1D, E2D, E3D, E4D).

[0086] Also, the ICE of the CR2032 half-cell of Example 4D (E4D) is higher than the ICE of a CR2032 half-cell assembled with commercially available KSC-1625 anode material.

[0087] [Table 5]

[0088] According to the relationship between capacity retention and charge C rate (high load measurement conditions) shown in Figure 6, Specific Example 4D (E4D) showed that the fast charge capacity when the charge C rate was 2C or less was about 5% lower than that of Comparative Example 2 (CE2). However, Figure 6 also shows that Specific Example 4D (E4D) showed that the fast charge capacity when the charge C rate was 3C was about 20% higher than that of Comparative Example 2 (CE2).

[0089] Furthermore, according to the relationship between capacity retention and discharge C rate (high-load measurement conditions) shown in Figure 7, Specific Example 4D (E4D) exhibited rapid discharge capability similar to that of Comparative Example 2 (CE2) when the discharge C rate was 0.5C or less. However, Figure 7 also shows that Specific Example 4D (E4D) exhibited higher rapid discharge capability than Comparative Example 2 (CE2) when the discharge C rate was 1C or more, and in particular, the rapid discharge capability at a discharge C rate of 3C was approximately 10% higher than that of Comparative Example 2 (CE2). Furthermore, Specific Example 4D (E4D) maintained a capacity retention of 93% when the discharge C rate was 3C.

[0090] According to the relationship between capacity retention and the number of charge-discharge cycles (high-load measurement conditions) shown in Figure 8, Specific Example 4D (E4D) exhibited a lower capacity retention than Comparative Example 2 (CE2) when the number of charge-discharge cycles was 35 or less. However, the capacity retention of Specific Example 4D (E4D) after the number of charge-discharge cycles exceeded 35 was higher than that of Comparative Example 2 (CE2). Furthermore, the capacity retention of Specific Example 4D (E4D) after the number of charge-discharge cycles reached 50 was about 10% higher than that of Comparative Example 2 (CE2).

[0091] 9, the XRD patterns of Example 4D (E4D) and Comparative Example 2 (CE2) show three peaks indicative of Si(111), Si(220), and Si(311) near angles of 28 degrees, 47 degrees, and 56 degrees in Example 4D (E4D). The intensities of the peaks at these three locations in Comparative Example 2 (CE2) are clearly higher than those in Example 4D (E4D).

[0092] The volume expansion after forming an alloy between silicon crystal and lithium metal is about 2 to 2.5 times that of silicon oxide, so silicon's ability to withstand volume expansion is lower than that of silicon oxide.

[0093] According to the results of FIG. 9 in conjunction with the results of FIG. 8, the negative electrode material of Comparative Example 2 (CE2) (commercially available KSC-1265) contains silicon crystals, and therefore, after 50 charge-discharge cycle measurements, the capacity retention rate was approximately 10% lower than that of Specific Example 4D (E4D).

[0094] According to the Raman spectra of the negative electrode materials of Specific Example 4 (E4a, E4b, E4c, E4d, E4e, and E4f) and Comparative Example 2 (CE2) shown in FIG. 10, the I of the negative electrode materials of Specific Example 4 (E4a, E4b, E4c, E4d, E4e, and E4f) of the present invention is D / I G are all below 1.0, and the I of the negative electrode material of Comparative Example 2 (CE2) D / I G The σ is as high as 1.5. This indicates that the carbon film defects in the negative electrode material of Example 4d (E4d) of the present invention are fewer than those in the negative electrode material of Comparative Example 2 (CE2). Furthermore, as shown in Figures 6 and 7, after the negative electrode material of Example 4d (E4d) was assembled into a CR2032 half cell (E4D), the rapid charge / discharge capability of the CR2032 half cell (E4D) was superior to that of the CR2032 half cell of Comparative Example 2 (CE2).

[0095] According to the above, in the method for producing an anode material of the present invention, no liquid organic solvent is used when performing step A, so there is no need to perform time-consuming suction filtration to remove the liquid organic solvent, thereby saving material costs and time costs.

[0096] Furthermore, even though the method for producing the negative electrode material of the present invention does not require the use of a liquid organic solvent, the rapid charge / discharge capacity of a CR2032 half-cell assembled using a negative electrode produced with the resulting negative electrode material is sometimes superior to the rapid charge / discharge capacity of a CR2032 half-cell assembled using a negative electrode produced with the commercially available negative electrode material KSC-1265 (as shown in Figures 6 to 8). This demonstrates that the negative electrode material produced by this specific manufacturing method of the present invention has excellent performance even without the use of a liquid organic solvent. Furthermore, because there is no need for suction filtration equipment, the manufacturing method of the present invention is even more advantageous for mass production.

[0097] In summary, the method for producing an anode material made of silicon oxide powder coated with a carbon film of the present invention does not use a liquid organic solvent, thereby saving material costs and time costs, making it more advantageous for mass production, and the resulting anode material has excellent performance, thereby achieving the object of the present invention.

[0098] The above-described embodiments are illustrative for explaining the principles and effects of the present invention, and are not intended to limit the present invention. Those skilled in the art may make slight changes or modifications to the above-described embodiments without departing from the spirit and scope of the present invention. Therefore, all changes and modifications made by those skilled in the art without departing from the gist of the present invention should be considered to fall within the scope of protection of the present invention. [Industrial Applicability]

[0099] The present invention is suitable for producing a negative electrode material, and is particularly suitable for producing a negative electrode material for a lithium ion secondary battery.

Claims

1. A method for producing an anode material comprising silicon oxide powder coated with a carbon film, Step A: mixing a large number of silicon oxide powders with a predetermined amount of pitch powder without using a liquid organic solvent to obtain a mixture; Step B: heating the mixture to a carbonization temperature of 600°C or higher at a heating rate in the range of 0.65°C / min to 1.25°C / min, and then maintaining the mixture at the carbonization temperature for at least 5 hours, thereby melting the predetermined amount of pitch powder and coating the surface of each of the silicon oxide powders with a carbon film, and simultaneously carbonizing the molten pitch to obtain a plurality of initial silicon oxide powders, the surface of each of the initial silicon oxide powders being coated with a corresponding carbon film; and step C of selecting, from the large number of initial silicon oxide powders, silicon oxide powder having a specific particle size in the range of 2 μm to 11 μm as a negative electrode material; In the step A, the predetermined amount of pitch powder is 3 to 5 parts by weight based on the total weight of the mixture.

2. 2. The method for producing a negative electrode material according to claim 1, wherein in step A, the predetermined amount of pitch powder has a particle size distribution in which the D10 particle size is in the range of 0.5 μm to 2 μm, the D50 particle size is in the range of 2 μm to 4 μm, and the D90 particle size is in the range of 5 μm to 9 μm.

3. 2. The method for producing a negative electrode material according to claim 1, wherein in step A, the predetermined amount of pitch powder has a softening point of 250° C. or higher.

4. 2. The method for producing an anode material according to claim 1, wherein in step A, the predetermined amount of pitch powder has a carbon / hydrogen ratio in the range of 1.43 to 1.

66.

5. 2. The method for producing a negative electrode material according to claim 1, wherein in step A, the amount of the plurality of silicon oxide powders is 100 parts by weight and the predetermined amount of pitch powder is 1 part by weight to 10 parts by weight, based on the total weight of the mixture.

6. 2. The method for producing a negative electrode material according to claim 1, wherein in step B, the carbonization temperature is in the range of 600°C to 1100°C.

7. 7. The method for producing a negative electrode material according to claim 6, wherein in step B, the carbonization temperature is in the range of 600°C to 900°C.

8. 2. The method for producing a negative electrode material according to claim 1, wherein in step B, the carbon film coated on the surface of each of the initial silicon oxide powders has a thickness in the range of 0.5 μm to 2 μm.

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