Preparation method of high-rate silicon-carbon anode material

Abstract

The present invention relates to a preparation method of a high-rate silicon-carbon anode material, which includes: S1. Slowly drop a silane coupling agent into an aqueous alcohol solution, then add acetic acid to make the pH in the range of 3.5 - 5.5, and rapidly stir for 30 min to obtain solution A; S2. Add a certain amount of resin powder to solution A to obtain solution B; S3. Mix natural spherical graphite, nano-silicon powder and absolute ethanol evenly, place them in a water bath at 50 °C, evaporate while stirring until a silicon-carbon composite powder C is obtained; S4. Slowly drop solution B into the silicon-carbon composite powder C, rapidly stir for 30 min and then stand for 30 - 60 min, then place it in a water bath at 100 - 120 °C, evaporate while stirring, and wait until the solvent is completely evaporated to obtain powder D; S5. Put powder D into a high-energy ball mill for ball milling treatment; S6. Carry out high-temperature carbonization on the ball-milled powder D to obtain the final silicon-carbon anode material. Through the above steps, a silicon-carbon anode material with good stability and high initial efficiency is prepared.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium - ion batteries, and particularly to a preparation method of a high - rate silicon - carbon negative electrode material. Background Art

[0002] With the continuous progress of the electric vehicle industry, the requirements for battery performance are increasing day by day, especially the pursuit of higher battery capacity and faster charging rate. Graphite materials have shown a long cycle life in batteries due to their high safety performance and stable electrode structure. However, limited by their low specific capacity and obvious voltage hysteresis, they are currently only applicable to the field of energy storage applications with medium energy density. In contrast, silicon - based negative electrode materials are regarded as an ideal choice for the next - generation high - energy - density lithium - ion battery negative electrode materials due to their advantages such as high theoretical capacity, low working potential, rich reserves, and environmental friendliness, and have great development value and application prospects. However, silicon - based materials still have problems such as significant volume expansion during lithium storage and low reversible capacity during high - rate charge and discharge. The existing technology is to compound silicon and carbon, using graphite to improve the conductivity of the material, relieve the volume expansion of silicon, improve the structural stability, and enhance the life of the silicon - carbon negative electrode battery. However, the silicon - carbon negative electrode materials still show a low reversible capacity at high rates.

[0003] Therefore, there is an urgent need to provide a preparation method of a high - rate silicon - carbon negative electrode material to solve the above problems. Summary of the Invention

[0004] The purpose of the present invention is to overcome the deficiencies and defects of the prior art and provide a preparation method of a high - rate silicon - carbon negative electrode material, preparing a silicon - carbon negative electrode material with high performance. The obtained silicon - carbon negative electrode material has a high specific capacity, good cycle stability, and high - rate charge - discharge performance, and can meet the commercial requirements of pure electric vehicles and hybrid electric vehicles in the field of battery fast charging.

[0005] The purpose of the present invention is achieved by the following technical solutions:

[0006] A preparation method of a high - rate silicon - carbon negative electrode material includes the following steps:

[0007] S1. Slowly drip a silane coupling agent into an aqueous alcohol solution, then add acetic acid to make the pH in the range of 3.5 - 5.5, and rapidly stir for 30 min to obtain solution A;

[0008] S2. Add a certain amount of resin - type powder to solution A to obtain solution B;

[0009] S3. Mix natural spherical graphite, nano - silicon powder, and absolute ethanol evenly, place them in a water bath at 50 °C, and evaporate while stirring until a silicon - carbon composite powder C is obtained;

[0010] S4. Slowly add Solution B dropwise to the silicon-carbon composite powder C, stir rapidly for 30 min, then let it stand for 30 - 60 min, and then place it in a water bath at 100 - 120 °C, evaporate while stirring. After the solvent is completely evaporated, powder D is obtained;

[0011] S5. Put powder D into a high-energy ball mill for ball milling treatment;

[0012] S6. Subject the ball-milled powder D to high-temperature carbonization to obtain the final silicon-carbon anode material.

[0013] As a preferred technical solution of the present invention, in S1, the silane coupling agent is one of vinyltrimethoxysilane, vinyltriethoxysilane, and isocyanatopropyltriethoxysilane. The mass percentage of the silane coupling agent is 0.5% - 2%, preferably 0.5% - 1%, and the mass percentage of the alcohol aqueous solution is 98% - 99.5%, preferably 99% - 99.5%.

[0014] As a preferred technical solution of the present invention, in S1, the solute of the alcohol aqueous solution is one of ethanol or isopropanol, and the solution concentration is 10% - 25%.

[0015] As a preferred technical solution of the present invention, in S2, the resin powder is one of epoxy resin, phenolic resin, polystyrene, polypropylene, and polytetrafluoroethylene. The mass ratio of the resin powder to Solution A is 1:20 - 50.

[0016] As a preferred technical solution of the present invention, in S3, the mass ratio of natural spherical graphite, nano-silicon powder, and absolute ethanol is 8 - 9:1 - 2:20 - 50.

[0017] As a preferred technical solution of the present invention, in S4, the mass ratio of the silicon-carbon composite powder C to Solution B is 1:2 - 5.

[0018] As a preferred technical solution of the present invention, in S5, the ball milling time is 5 - 12 h, and the rotation speed is 200 - 500 r / min.

[0019] As a preferred technical solution of the present invention, the high-temperature carbonization in S6 is specifically as follows: in an inert gas atmosphere, heat up to 800 - 900 °C at a heating rate of 2 - 5 °C / min, and carbonize for 60 - 120 min.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] In the present invention, by slowly dropping a silane coupling agent into an aqueous alcohol solution and adding acetic acid to adjust the pH to 3.5 - 5.5, the silane coupling agent can be rapidly hydrolyzed. Then, resin - like powder is added to allow the C - Y functional group of the silane coupling agent to react with the resin - like powder, forming a strong molecular bond. By fully mixing natural spherical graphite and nano - silicon powder in absolute ethanol, the nano - silicon powder can be evenly adsorbed on the spherical graphite. After stirring and evaporation in a water bath, a silicon - carbon composite material is obtained. Then, by slowly dropping solution B into the obtained silicon - carbon composite material, the Si - X functional group of the silane coupling agent combines with the silicon - carbon. Through high - energy ball milling, granulation and shaping are achieved, improving the battery rate performance. Finally, through high - temperature carbonization, the resin - like powder forms a uniform coating layer. The coating layer has a porous structure, which can provide more lithium - ion transmission channels, enabling a relatively high reversible capacity at high rates and meeting the commercial requirements of pure electric vehicles and hybrid electric vehicles in the field of fast battery charging. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a process flow chart of the present invention.

[0023] Figure 2 It is a test chart of the electrochemical performance of Example 1 of the present invention.

[0024] Figure 3 It is a test chart of the electrochemical performance of Example 2 of the present invention.

[0025] Figure 4 It is a test chart of the electrochemical performance of Example 3 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0026] The present invention will be further described in detail below in conjunction with examples and the accompanying drawings, but the implementation manners of the present invention are not limited thereto.

[0027] The specific implementation process of the present invention is as follows:

[0028] As Figure 1 shown, a preparation method of a high - rate silicon - carbon anode material includes the following steps:

[0029] S1. Slowly drop a silane coupling agent into an aqueous alcohol solution, then add acetic acid to make the pH in the range of 3.5 - 5.5, and rapidly stir for 30 min to obtain solution A;

[0030] S2. Add a certain amount of resin - like powder to solution A to obtain solution B;

[0031] S3. Mix natural spherical graphite, nano - silicon powder and absolute ethanol evenly, place them in a water bath at 50 °C, stir and evaporate simultaneously until a silicon - carbon composite powder C is obtained;

[0032] S4. Slowly drop solution B into silicon-carbon composite powder C, quickly stir for 30 min, then let it stand for 30 - 60 min, and then place it in a water bath at 100 - 120 °C, stirring and evaporating at the same time. After the solvent is completely evaporated, powder D is obtained;

[0033] S5. Put powder D into a high-energy ball mill for ball milling treatment;

[0034] S6. Perform high-temperature carbonization on the ball-milled powder D to obtain the final silicon-carbon anode material.

[0035] Optionally, first, slowly drop the silane coupling agent into the pre-prepared aqueous alcohol solution. Slowly dropping can avoid too high local concentration and ensure the uniform dispersion of the silane coupling agent; then add acetic acid to adjust the pH to the range of 3.5 - 5.5, and quickly stir for 30 min to obtain solution A. Acetic acid as a catalyst can accelerate hydrolysis, and at the same time, when the pH of the silane coupling agent is in the range of 3.5 - 5.5, its chemical form is more stable. Then add resin powder to solution A, and fully stir to make the C-Y functional group of the silane coupling agent react with the resin powder to form a strong molecular bond, obtaining solution B; Mix natural spherical graphite with good isotropy, nano-silicon powder and absolute ethanol evenly, so that the nano-silicon powder is evenly adsorbed on the surface of the natural spherical graphite, place it in a water bath at 50 °C, stir and evaporate at the same time. After the absolute ethanol is completely volatilized, silicon-carbon composite powder C, that is, silicon-carbon composite material, is obtained; Slowly drop solution B into silicon-carbon composite powder C, quickly stir for 30 min, then let it stand for 30 - 60 min to allow the amphiphilic groups of the silane coupling agent to fully combine with silicon-carbon and resin powder, and then place it in a water bath at 100 - 120 °C, stirring and evaporating at the same time to make the Si-X functional group of the silane coupling agent combine with silicon-carbon. After the solvent is completely evaporated, powder D is obtained. Place powder D in a high-energy ball mill for ball milling, with the rotation speed of 200 - 500 r / min and the ball milling time of 5 - 12 h. Through high-energy ball milling, granulation and shaping can be achieved, and the battery rate performance can be improved. Finally, through high-temperature carbonization, the resin powder forms an amorphous porous carbon coating layer, which evenly covers the silicon-carbon anode material, improving its structural stability and rate performance. All the above mixing processes are completed in the liquid phase, so the mixing effect is good and the isotropy is high. At the same time, the porous structure of the coating layer formed by resin carbonization can provide more lithium-ion transmission channels, and a higher reversible capacity can be achieved at high rates, which can meet the commercial requirements of pure electric vehicles and hybrid electric vehicles in the field of fast battery charging.

[0036] The following further illustrates the present invention with specific embodiments. Example 1

[0037] Vinyltrimethoxysilane was slowly dropped into an aqueous isopropanol solution with a concentration of 10%. The mass percentage of vinyltrimethoxysilane was 1%, and the mass percentage of the aqueous isopropanol solution was 99%. Then acetic acid was added to adjust the pH of the solution to 3.9, and it was rapidly stirred for 30 min to obtain solution A. Polystyrene powder was added to solution A and mixed evenly to obtain solution B. The mass ratio of the above-mentioned polystyrene to solution A was 1:30. Natural spherical graphite, nano-silicon powder, and absolute ethanol were mixed evenly in a mass ratio of 9:1:20, placed in a water bath at 50 °C, and evaporated while stirring until silicon-carbon composite powder C was obtained. Solution B was slowly dropped into silicon-carbon composite powder C, rapidly stirred for 30 min and then left to stand for 30 min, and then placed in a water bath at 120 °C and evaporated while stirring. After the solvent was completely evaporated, powder D was obtained. The mass ratio of the above-mentioned solution B to silicon-carbon composite powder C was 1:2. Powder D was put into a high-energy ball mill for ball milling treatment. The ball milling time was 8 h and the rotation speed was 400 r / min. After ball milling was completed, the powder was placed in a tubular furnace. After introducing nitrogen for a period of time, it was heated to 900 °C at a heating rate of 2 °C / min and carbonized for 60 min to obtain the final silicon-carbon anode material. Electrochemical performance tests were carried out, such as Figure 2 shown. At a current of 2 A / g, the first efficiency was 83%, the first discharge specific capacity was 830 mAh / g, and the capacity was still 226 mAh / g after 100 charge-discharge cycles. Example 2

[0038] Vinyltriethoxysilane was slowly dropped into an aqueous ethanol solution with a concentration of 15%. The mass percentage of vinyltriethoxysilane was 0.5%, and the mass percentage of the aqueous isopropanol solution was 99.5%. Then acetic acid was added to adjust the pH of the solution to 3.9, and it was rapidly stirred for 30 min to obtain solution A. Polypropylene powder was added to solution A and mixed evenly to obtain solution B. The mass ratio of the above-mentioned polypropylene to solution A was 1:20. Natural spherical graphite, nano-silicon powder, and absolute ethanol were mixed evenly in a mass ratio of 8:2:40, placed in a water bath at 50 °C, and evaporated while stirring until silicon-carbon composite powder C was obtained. Solution B was slowly dropped into silicon-carbon composite powder C, rapidly stirred for 30 min and then left to stand for 30 min, and then placed in a water bath at 100 °C and evaporated while stirring. After the solvent was completely evaporated, powder D was obtained. The mass ratio of the above-mentioned solution B to silicon-carbon composite powder C was 1:3. Powder D was put into a high-energy ball mill for ball milling treatment. The ball milling time was 12 h and the rotation speed was 400 r / min. After ball milling was completed, powder D was placed in a tubular furnace. After introducing nitrogen for a period of time, it was heated to 900 °C at a heating rate of 5 °C / min and carbonized for 120 min to obtain the final silicon-carbon anode material. Electrochemical performance tests were carried out, such as Figure 3As shown, at a current of 2 A / g, the initial efficiency is 78%, the initial discharge specific capacity is 1233 mAh / g, and the capacity remains 335 mAh / g after 100 charge-discharge cycles. Example 3

[0039] Isocyanatopropyltriethoxysilane was slowly dropped into an aqueous ethanol solution with a concentration of 25%. The mass percentage of isocyanatopropyltriethoxysilane was 0.5%, and the mass percentage of the isopropanol aqueous solution was 99.5%. Then acetic acid was added to adjust the pH of the solution to 4.5, and it was rapidly stirred for 30 min to obtain Solution A. Polypropylene powder was added to Solution A and mixed evenly to obtain Solution B. The mass ratio of the above polypropylene to Solution A was 1:50. Natural spherical graphite, nano-silicon powder, and absolute ethanol were mixed evenly in a mass ratio of 9:1:50, placed in a water bath at 50 °C, and evaporated while stirring until silicon-carbon composite powder C was obtained. Solution B was slowly dropped into silicon-carbon composite powder C, rapidly stirred for 30 min, then left to stand for 30 min, and then placed in a water bath at 100 °C and evaporated while stirring. After the solvent was completely evaporated, powder D was obtained. The mass ratio of the above Solution B to silicon-carbon composite powder C was 1:3. Powder D was put into a high-energy ball mill for ball milling. The ball milling time was 4 h, and the rotation speed was 500 r / min. After ball milling was completed, powder D was placed in a tubular furnace. After introducing nitrogen for a period of time, it was heated to 800 °C at a heating rate of 3 °C / min and carbonized for 60 min to obtain the final silicon-carbon negative electrode material. Electrochemical performance tests were carried out. As Figure 4 shown, at a current of 2 A / g, the initial efficiency is 80%, the initial discharge specific capacity is 693 mAh / g, and the capacity remains 291 mAh / g after 100 charge-discharge cycles.

[0040] The above embodiments only represent the implementation modes of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the patent of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention should be subject to the appended claims.

Claims

1. A method for preparing a high-rate silicon-carbon negative electrode material, characterized in that: The following steps are involved: S1. Slowly drip the silane coupling agent into the alcohol aqueous solution, then add acetic acid to make the pH range of 3.5-5.5, and stir rapidly for 30 minutes to obtain solution A; S2. Add a certain amount of resin powder to solution A to obtain solution B; S3, mixing natural spherical graphite, nano silicon powder and anhydrous ethanol evenly, placing in a 50°C water bath, stirring and evaporating, until silicon-carbon composite powder C is obtained; S4, slowly drop solution B into the silicon-carbon composite powder C, stir rapidly for 30 minutes, let stand for 30-60 minutes, then place in a water bath at 100-120°C, stir while evaporating, and wait until the solvent evaporates completely to obtain powder D; S5, placing powder D into a high-energy ball mill for ball milling; S6, high temperature carbonization of the ball-milled powder D to obtain the final silicon-carbon negative electrode material, In the S1, the silane coupling agent is one of vinyl trimethoxy silane, vinyl triethoxy silane, and isocyanate propyl triethoxy silane, and the resin powder in the S2 is one of epoxy resin and phenolic resin.

2. The method for preparing a high-rate silicon-carbon negative electrode material according to claim 1, characterized in that: In the step of slowly dripping the silane coupling agent into the alcohol aqueous solution in S1, the mass ratio of the silane coupling agent to the alcohol aqueous solution is 0.5-2:98-99.

5.

3. The method for preparing a high-rate silicon-carbon negative electrode material according to claim 1, characterized in that: The solute of the alcohol aqueous solution in S1 is ethanol or isopropanol, and the solution concentration is 10% to 25%.

4. The method for preparing a high-rate silicon-carbon negative electrode material according to claim 1, characterized in that: In S2, the mass ratio of the resin powder to the solution A is 1:20-50.

5. The method for preparing a high-rate silicon-carbon negative electrode material according to claim 1, characterized in that: The mass ratio of natural spherical graphite, nano silicon powder and anhydrous ethanol in S3 is 8-9:1-2:20-50.

6. The method for preparing a high-rate silicon-carbon negative electrode material according to claim 1, characterized in that: The mass ratio of the silicon-carbon composite powder C to the solution B in the S4 is 1:2-5.

7. The method for preparing a high-rate silicon-carbon negative electrode material according to claim 1, characterized in that: The ball milling time in S5 is 5-12 hours, and the rotation speed is 200-500 r / min.

8. The method for preparing a high-rate silicon-carbon negative electrode material according to claim 1, characterized in that: The high temperature carbonization in S6 is specifically as follows: in an inert gas atmosphere, the temperature is raised to 800-900° C. at a heating rate of 2-5° C. / min, and the carbonization is performed for 60-120 minutes.

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