A silicon-carbon negative electrode material with low expansion rate and its preparation method and application

Abstract

The present application discloses a silicon-carbon negative electrode material with low expansion rate and its preparation method and application, which relates to the technical field of silicon-carbon negative electrode materials. First, amorphous silicon and acetylene black are mixed in a glycerol solution, and then tin oxide is added. After ultrasonic dispersion, a tin oxide-amorphous silicon-acetylene black mixture is obtained. Then, a polyvinyl pyrrolidone solution is added to the mixture, mechanically stirred evenly, and a hydrothermal reaction is carried out at a constant temperature in an electric constant temperature drying oven to evaporate the glycerol solvent and grind to obtain a silicon / carbon composite material; chitin is added to the silicon / carbon composite material and mixed evenly, and then cooled, and then ethylene carbonate is added to gradually solidify to obtain a silicon-carbon negative electrode precursor material, which is then carbon-coated by chemical vapor deposition to obtain a silicon-carbon negative electrode material. Therefore, the present application adopts the above-mentioned silicon-carbon negative electrode material and its preparation method and application to solve the problems of large volume expansion rate and poor cycle capacity of negative electrode materials in the prior art.

Description

Technical Field

[0001] The present application relates to the technical field of silicon-carbon negative electrode materials, and in particular to a silicon-carbon negative electrode material with a low expansion rate, a preparation method thereof, and an application thereof. Background Art

[0002] With the rapid development of electric vehicles, mobile devices, and other fields, the demand for lithium-ion batteries continues to increase. However, traditional lithium-ion battery anode materials, such as graphite, are unable to meet the energy density and cycle life requirements of modern devices due to their low specific capacity and high volume expansion rate. Therefore, there is an urgent need for a silicon-carbon anode material with a low expansion rate, as well as its preparation and application. Summary of the Invention

[0003] The purpose of this application is to provide a silicon-carbon negative electrode material with a low expansion rate and its preparation method and application, so as to solve the problems of large volume expansion rate and poor cycle capacity of negative electrode materials in the prior art.

[0004] The present application provides a method for preparing a silicon-carbon negative electrode material with a low expansion rate, comprising the following steps: S1, preparing a silicon-carbon composite material: mixing amorphous silicon and acetylene black in a glycerol solution, then adding tin oxide, and obtaining a tin oxide-amorphous silicon-acetylene black mixture after ultrasonic dispersion, adding a polyvinyl pyrrolidone solution to the obtained tin oxide-amorphous silicon-acetylene black mixture, mechanically stirring it evenly, and conducting a hydrothermal reaction at a constant temperature in an electric constant temperature drying oven, evaporating the glycerol solvent, and grinding to obtain a silicon / carbon composite material.

[0005] S2, adding chitosan to the silicon / carbon composite material obtained in step S1, mixing evenly, cooling the mixture, and then adding ethylene carbonate to gradually solidify the mixture to obtain a silicon-carbon negative electrode precursor material;

[0006] S3. The silicon-carbon negative electrode precursor material obtained in step S2 is subjected to carbon coating treatment by chemical vapor deposition to obtain a carbon-coated silicon-carbon negative electrode material.

[0007] Preferably, in step S1, the mass ratio of amorphous silicon to acetylene black is 8:2, the amount of tin oxide added is 8% of the total mass of amorphous silicon and acetylene black, the amount of polyvinyl pyrrolidone added is 5% of the mass of the tin oxide-amorphous silicon-acetylene black mixture, and the mass of the glycerol solution is 10 times the total mass of amorphous silicon and acetylene black.

[0008] Preferably, in step S2, the mass ratio of the silicon / carbon composite material to chitin is 10:3, and the amount of ethylene carbonate added is 15% of the total mass of the silicon / carbon composite material and chitin.

[0009] Preferably, in step S1, the mechanical stirring time is 2 hours, the mechanical stirring speed is 1000 rpm, the temperature of the electric heating constant temperature box is 80° C., and the hydrothermal reaction time is 3 hours.

[0010] Preferably, in step S1, evaporating the glycerol solvent is performed in an oven at a temperature of 90° C. for 4 hours.

[0011] Preferably, in step S2, before adding chitosan to the silicon / carbon composite material obtained in step S1 and mixing them evenly, the chitosan is dried in an oven and then ground to a particle size of 50 mesh.

[0012] Preferably, in step S2, the cooling rate is 5°C / min, and the temperature is lowered to 10°C.

[0013] Preferably, in step S3, the temperature of the carbon coating is 850-900°C, the gas source used is acetylene, methane, liquefied gas or gaseous carbon source, and the duration is 1 hour.

[0014] The present application provides a silicon-carbon negative electrode material obtained according to the preparation method of the above-mentioned silicon-carbon negative electrode material with low expansion rate.

[0015] The present application provides an application of a silicon-carbon negative electrode material obtained according to the above-mentioned method for preparing a silicon-carbon negative electrode material with a low expansion rate in a lithium battery.

[0016] Therefore, the present application adopts the above-mentioned low expansion rate silicon-carbon negative electrode material and its preparation method and application, which has the following beneficial effects:

[0017] (1) Amorphous silicon, doped heteroatom materials and acetylene black can be effectively dispersed in propylene glycol solution by ultrasonic dispersion and mechanical stirring, which improves the uniformity of the mixture and is beneficial to the bulk doping of silicon-carbon negative electrode materials, thereby improving the overall performance of the material.

[0018] (2) The addition of chitin may form a certain pore structure in the silicon-carbon composite material, which helps to increase the specific surface area of ​​the material and thus improve its electrochemical performance.

[0019] (3) This application significantly improves the performance of the battery by adjusting the ratio between the various raw materials. DETAILED DESCRIPTION

[0020] Example 1

[0021] First, amorphous silicon powder and acetylene black are mixed in a ratio of 8:2 and then added to a glycerol solution (the mass of the glycerol solution is about 10 times the total mass of the amorphous silicon and acetylene black). Then, tin oxide is added in an amount of 8% of the total mass of the amorphous silicon and acetylene black. Ultrasonic dispersion is performed using an ultrasonic disperser for 10 minutes. After ultrasonic dispersion, a tin oxide-amorphous silicon-acetylene black mixture is obtained. The tin oxide-amorphous silicon-acetylene black mixture is transferred to a magnetic stirrer, polyvinyl pyrrolidone is added, and mechanical stirring is performed at a stirring speed of 1000 rpm for about 2 hours until the mixture becomes viscous. The mixture is then transferred to an electric constant temperature drying oven, set to 80°C, and subjected to a hydrothermal reaction for 3 hours. After the hydrothermal reaction is completed, the mixture is removed and placed in an oven set to 90°C for 4 hours to evaporate the glycerol solvent. After evaporation is complete, the resulting solid material is removed and ground to the desired particle size to obtain a silicon / carbon composite material.

[0022] S2. Pre-treat the chitosan. Add the pre-treated chitosan to the silicon / carbon composite obtained in step S1, mix thoroughly, and then cool the mixture at a rate of 5°C / min. Then, add ethylene carbonate to gradually solidify the mixture, thereby obtaining the silicon-carbon anode material. The chitosan is pre-treated by first removing moisture from the chitosan and drying it in an oven at 80°C for 2 hours. The dried chitosan is then ground to an average particle size of 50 mesh. 100g of the dried silicon / carbon composite is placed in a stirring vessel, and 30g of the pre-treated chitosan is added. A stirrer is started and the chitosan and silicon / carbon composite are mixed at a low speed until they are thoroughly mixed. After thorough mixing, the stirring vessel is placed in a cooling device and the temperature is gradually lowered. Stirring is continued during the cooling process to ensure that the chitosan and silicon / carbon composite are fully integrated. The mixture temperature is lowered to 10°C at a rate of 5°C / min. After cooling, ethylene carbonate is added. The amount of ethylene carbonate added is 15% of the total mass of the silicon / carbon composite and chitosan. During the addition of ethylene carbonate, stirring is maintained to ensure that the mixture is evenly contacted with the ethylene carbonate. As the mixture gradually solidifies, stirring is stopped to obtain a silicon-carbon negative electrode precursor material.

[0023] S3. Carbon coating the silicon-carbon anode precursor material obtained in step S2 using a mixture of acetylene and methane at 850°C for 1 hour using chemical vapor deposition to obtain a negative electrode material. This negative electrode material is directly used as a silicon-carbon anode material and fabricated into a negative electrode sheet, which is then used in a lithium-ion battery.

[0024] Comparative Example 1

[0025] First, amorphous silicon powder and acetylene black are mixed in a ratio of 9:2 and then added to a glycerol solution (the mass of the glycerol solution is about 10 times the total mass of the amorphous silicon and acetylene black). Then, tin oxide is added in an amount of 8% of the total mass of the amorphous silicon and acetylene black. Ultrasonic dispersion is performed using an ultrasonic disperser for 10 minutes. After ultrasonic dispersion, a tin oxide-amorphous silicon-acetylene black mixture is obtained. The tin oxide-amorphous silicon-acetylene black mixture is transferred to a magnetic stirrer, polyvinyl pyrrolidone is added, and mechanical stirring is performed at a stirring speed of 1000 rpm for about 2 hours until the mixture becomes viscous. The mixture is then transferred to an electric constant temperature drying oven, set to 80°C, and subjected to a hydrothermal reaction for 3 hours. After the hydrothermal reaction is completed, the mixture is removed and placed in an oven set to 90°C for 4 hours to evaporate the glycerol solvent. After the evaporation is complete, the resulting solid material is removed and ground to the desired particle size to obtain a silicon / carbon composite material.

[0026] S2. Pre-treat the chitosan. Add the pre-treated chitosan to the silicon / carbon composite obtained in step S1, mix thoroughly, and then cool the mixture at a rate of 5°C / min. Then, add ethylene carbonate to gradually solidify the mixture, thereby obtaining the silicon-carbon anode material. The chitosan is pre-treated by first removing moisture from the chitosan and drying it in an oven at 80°C for 2 hours. The dried chitosan is then ground to an average particle size of 50 mesh. 100g of the dried silicon / carbon composite is placed in a stirring vessel, and 30g of the pre-treated chitosan is added. A stirrer is started and the chitosan and silicon / carbon composite are mixed at a low speed until they are thoroughly mixed. After thorough mixing, the stirring vessel is placed in a cooling device and the temperature is gradually lowered. Stirring is continued during the cooling process to ensure that the chitosan and silicon / carbon composite are fully integrated. The mixture temperature is lowered to 10°C at a rate of 5°C / min. After cooling, ethylene carbonate is added. The amount of ethylene carbonate added is 15% of the total mass of the silicon / carbon composite and chitosan. During the addition of ethylene carbonate, stirring is maintained to ensure that the mixture is evenly contacted with the ethylene carbonate. As the mixture gradually solidifies, stirring is stopped to obtain a silicon-carbon negative electrode precursor material.

[0027] S3. Carbon coating the silicon-carbon anode precursor material obtained in step S2 using a mixture of acetylene and methane at 850°C for 1 hour using chemical vapor deposition to obtain a negative electrode material. This negative electrode material is directly used as a silicon-carbon anode material and fabricated into a negative electrode sheet, which is then used in a lithium-ion battery.

[0028] Comparative Example 2

[0029] First, amorphous silicon powder and acetylene black are mixed in a ratio of 7:2 and then added to a glycerol solution (the mass of the glycerol solution is about 10 times the total mass of the amorphous silicon and acetylene black). Then, tin oxide is added in an amount of 8% of the total mass of the amorphous silicon and acetylene black. Ultrasonic dispersion is performed using an ultrasonic disperser for 10 minutes. After ultrasonic dispersion, a tin oxide-amorphous silicon-acetylene black mixture is obtained. The tin oxide-amorphous silicon-acetylene black mixture is transferred to a magnetic stirrer, polyvinyl pyrrolidone is added, and mechanical stirring is performed at a stirring speed of 1000 rpm for about 2 hours until the mixture becomes viscous. The mixture is then transferred to an electric constant temperature drying oven, set to 80°C, and subjected to a hydrothermal reaction for 3 hours. After the hydrothermal reaction is completed, the mixture is removed and placed in an oven set to 90°C for 4 hours to evaporate the glycerol solvent. After evaporation is complete, the resulting solid material is removed and ground to the desired particle size to obtain a silicon / carbon composite material.

[0030] S2. Pre-treat the chitosan. Add the pre-treated chitosan to the silicon / carbon composite obtained in step S1, mix thoroughly, and then cool the mixture at a rate of 5°C / min. Then, add ethylene carbonate to gradually solidify the mixture, thereby obtaining the silicon-carbon anode material. The chitosan is pre-treated by first removing moisture from the chitosan and drying it in an oven at 80°C for 2 hours. The dried chitosan is then ground to an average particle size of 50 mesh. 100g of the dried silicon / carbon composite is placed in a stirring vessel, and 30g of the pre-treated chitosan is added. A stirrer is started and the chitosan and silicon / carbon composite are mixed at a low speed until they are thoroughly mixed. After thorough mixing, the stirring vessel is placed in a cooling device and the temperature is gradually lowered. Stirring is continued during the cooling process to ensure that the chitosan and silicon / carbon composite are fully integrated. The mixture temperature is lowered to 10°C at a rate of 5°C / min. After cooling, ethylene carbonate is added. The amount of ethylene carbonate added is 15% of the total mass of the silicon / carbon composite and chitosan. During the addition of ethylene carbonate, stirring is maintained to ensure that the mixture is evenly contacted with the ethylene carbonate. As the mixture gradually solidifies, stirring is stopped to obtain a silicon-carbon negative electrode precursor material.

[0031] S3. Carbon coating the silicon-carbon anode precursor material obtained in step S2 using a mixture of acetylene and methane at 850°C for 1 hour using chemical vapor deposition to obtain a negative electrode material. This negative electrode material is directly used as a silicon-carbon anode material and fabricated into a negative electrode sheet, which is then used in a lithium-ion battery.

[0032] Comparative Example 3

[0033] First, amorphous silicon powder and acetylene black are mixed in a ratio of 8:2 and then added to a glycerol solution (the mass of the glycerol solution is about 10 times the total mass of the amorphous silicon and acetylene black). Then, tin oxide is added in an amount of 8% of the total mass of the amorphous silicon and acetylene black. Ultrasonic dispersion is performed using an ultrasonic disperser for 10 minutes. After ultrasonic dispersion, a tin oxide-amorphous silicon-acetylene black mixture is obtained. The tin oxide-amorphous silicon-acetylene black mixture is transferred to a magnetic stirrer, polyvinyl pyrrolidone is added, and mechanical stirring is performed at a stirring speed of 1000 rpm for about 2 hours until the mixture becomes viscous. The mixture is then transferred to an electric constant temperature drying oven, set to 80°C, and subjected to a hydrothermal reaction for 3 hours. After the hydrothermal reaction is completed, the mixture is removed and placed in an oven set to 90°C for 4 hours to evaporate the glycerol solvent. After evaporation is complete, the resulting solid material is removed and ground to the desired particle size to obtain a silicon / carbon composite material.

[0034] S2. Pre-treat the chitosan. Add the pre-treated chitosan to the silicon / carbon composite obtained in step S1, mix thoroughly, and then cool the mixture at a rate of 5°C / min. Then, add ethylene carbonate to gradually solidify the mixture, thereby obtaining the silicon-carbon anode material. The chitosan is pre-treated by first removing moisture from the chitosan and drying it in an oven at 80°C for 2 hours. The dried chitosan is then ground to an average particle size of 50 mesh. 100g of the dried silicon / carbon composite is placed in a stirring vessel, and 30g of the pre-treated chitosan is added. A stirrer is started and the chitosan and silicon / carbon composite are mixed at a low speed until they are thoroughly mixed. After thorough mixing, the stirring vessel is placed in a cooling device and the temperature is gradually lowered. Stirring is continued during the cooling process to ensure that the chitosan and silicon / carbon composite are fully integrated. The mixture temperature is lowered to 10°C at a rate of 5°C / min. After cooling, ethylene carbonate is added. The amount of ethylene carbonate added is 15% of the total mass of the silicon / carbon composite and chitosan. During the addition of ethylene carbonate, stirring is maintained to ensure uniform contact between the mixture and the ethylene carbonate. As the mixture solidifies, stirring is stopped. At this point, the silicon-carbon negative electrode material has been initially formed. The solidified silicon-carbon negative electrode material is removed and dried to remove excess solvent and moisture. This silicon-carbon negative electrode material is then directly used as a silicon-carbon negative electrode material and fabricated into a negative electrode sheet, which is then used in a lithium-ion battery.

[0035] Comparative Example 4

[0036] First, amorphous silicon powder and acetylene black are mixed in a ratio of 8:2 and then added to a glycerol solution (the mass of the glycerol solution is about 10 times the total mass of the amorphous silicon and acetylene black). Then, tin oxide is added in an amount of 8% of the total mass of the amorphous silicon and acetylene black. Ultrasonic dispersion is performed using an ultrasonic disperser for 10 minutes. After ultrasonic dispersion, a tin oxide-amorphous silicon-acetylene black mixture is obtained. The tin oxide-amorphous silicon-acetylene black mixture is transferred to a magnetic stirrer, polyvinyl pyrrolidone is added, and mechanical stirring is performed at a stirring speed of 1000 rpm for about 2 hours until the mixture becomes viscous. The mixture is then transferred to an electric constant temperature drying oven, set to 80°C, and subjected to a hydrothermal reaction for 3 hours. After the hydrothermal reaction is completed, the mixture is removed and placed in an oven set to 90°C for 4 hours to evaporate the glycerol solvent. After evaporation is complete, the resulting solid material is removed and ground to the desired particle size to obtain a silicon / carbon composite material.

[0037] S2. Add ethylene carbonate to the silicon / carbon composite material obtained in step S1 until it gradually solidifies. During the addition of ethylene carbonate, stir the mixture to ensure uniform contact between the silicon / carbon composite material and the ethylene carbonate. As the mixture gradually solidifies, stop stirring to obtain a silicon-carbon negative electrode precursor material.

[0038] S3. Carbon coating the silicon-carbon anode precursor material obtained in step S2 using a mixture of acetylene and methane at 850°C for 1 hour using chemical vapor deposition to obtain a negative electrode material. This negative electrode material is directly used as a silicon-carbon anode material and fabricated into a negative electrode sheet, which is then used in a lithium-ion battery.

[0039] Comparative Example 5

[0040] First, amorphous silicon powder and acetylene black are mixed in a ratio of 8:2, and then added to a glycerol solution (the mass of the glycerol solution is about 10 times the total mass of amorphous silicon and acetylene black). Ultrasonic dispersion is performed for 10 minutes using an ultrasonic disperser to obtain an amorphous silicon-acetylene black mixture. The amorphous silicon-acetylene black mixture is transferred to a magnetic stirrer, polyvinyl pyrrolidone is added, and mechanical stirring is performed at a stirring speed of 1000 rpm for about 2 hours until the mixture becomes viscous. It is then transferred to an electric constant temperature drying oven, set to 80°C, and subjected to a hydrothermal reaction for 3 hours. After the hydrothermal reaction is completed, the mixture after the hydrothermal reaction is removed and placed in an oven at 90°C for 4 hours to evaporate the glycerol solvent. After the evaporation is complete, the resulting solid material is removed and ground to the desired particle size to obtain a silicon / carbon composite material.

[0041] S2. Pre-treat the chitosan. Add the pre-treated chitosan to the silicon / carbon composite obtained in step S1, mix thoroughly, and then cool the mixture at a rate of 5°C / min. Then, add ethylene carbonate to gradually solidify the mixture, thereby obtaining the silicon-carbon anode material. The chitosan is pre-treated by first removing moisture from the chitosan and drying it in an oven at 80°C for 2 hours. The dried chitosan is then ground to an average particle size of 50 mesh. 100g of the dried silicon / carbon composite is placed in a stirring vessel, and 30g of the pre-treated chitosan is added. A stirrer is started and the chitosan and silicon / carbon composite are mixed at a low speed until they are thoroughly mixed. After thorough mixing, the stirring vessel is placed in a cooling device and the temperature is gradually lowered. Stirring is continued during the cooling process to ensure that the chitosan and silicon / carbon composite are fully integrated. The mixture temperature is lowered to 10°C at a rate of 5°C / min. After cooling, ethylene carbonate is added. The amount of ethylene carbonate added is 15% of the total mass of the silicon / carbon composite and chitosan. During the addition of ethylene carbonate, stirring is maintained to ensure that the mixture is evenly contacted with the ethylene carbonate. As the mixture gradually solidifies, stirring is stopped to obtain a silicon-carbon negative electrode precursor material.

[0042] S3. Carbon coating the silicon-carbon anode precursor material obtained in step S2 using a mixture of acetylene and methane at 850°C for 1 hour using chemical vapor deposition to obtain a negative electrode material. This negative electrode material is directly used as a silicon-carbon anode material and fabricated into a negative electrode sheet, which is then used in a lithium-ion battery.

[0043] The performance test was performed on the lithium-ion battery of Example 1 and Comparative Examples 1-5. The specific test method is as follows:

[0044] Constant current charge and discharge test

[0045] The button cells packaged in the examples and comparative examples were subjected to constant current charge and discharge tests using a LANDCT2001A battery testing system. The charge and discharge mode was as follows: the battery was first discharged to 0.02 V at a constant current (0.15 mA), allowed to stand for 1 min, and then charged to 1.5 V at a constant current (0.15 mA).

[0046] Capacity fade rate test

[0047] Using a LANDCT2001A battery testing system, charge and discharge tests were performed on the packaged batteries of the embodiments and comparative examples at a constant temperature. The initial capacity of each sample was recorded. 50 charge and discharge cycles were then performed, and the final current capacity was recorded. Capacity decay rate = (initial capacity - current capacity) / initial capacity × 100%.

[0048] Table 1 Constant current charge and discharge test results

[0049] project <![CDATA[Initial charging specific capacity (mAh g -1 )]]> Example 1 589.5 Comparative Example 1 440.1 Comparative Example 2 429.6 Comparative Example 3 350.4 Comparative Example 4 340.5 Comparative Example 5 333.9

[0050] Table 2 Capacity decay rate test results

[0051]

[0052]

[0053] As can be seen from Tables 1-2, the first-cycle charge specific capacity of the low-expansion silicon-carbon negative electrode material prepared in Example 1 is higher than that of the low-expansion silicon-carbon negative electrode material prepared in Comparative Examples 1-5. As can be seen from Table 2, the capacity decay rate of the low-expansion silicon-carbon negative electrode material prepared in Example 1 is lower than that of the low-expansion silicon-carbon negative electrode material prepared in Comparative Examples 1-5. This is because the amount of amorphous silicon and acetylene black used in the preparation process of the embodiment is controlled. At the same time, the addition of chitin forms a certain pore structure in the silicon-carbon composite material, which helps to increase the specific surface area of ​​the material, thereby improving its electrochemical performance.

[0054] Therefore, the present application provides a silicon-carbon negative electrode material with a low expansion rate and its preparation method and application, which solves the problems of large volume expansion rate and poor cycle capacity in the prior art.

[0055] In this specification, references to terms such as "an experimental example," "example," or "specific example" indicate that the specific features, structures, materials, or characteristics described in conjunction with that experimental example or example are included in at least one experimental example or example of the present invention. In this specification, schematic representations of the above terms do not necessarily refer to the same experimental example or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more experimental examples or examples.

[0056] Finally, it should be noted that the above experimental examples are only used to illustrate the technical solutions of the present invention rather than to limit them. Although the present invention has been described in detail with reference to the preferred experimental examples, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a silicon-carbon negative electrode material with a low expansion coefficient, characterized in that: The method comprises the following preparation steps: S1. Amorphous silicon and acetylene black are mixed in a glycerol solution, and then tin oxide is added. After ultrasonic dispersion, a tin oxide-amorphous silicon-acetylene black mixture is obtained. A polyvinyl pyrrolidone solution is added to the obtained tin oxide-amorphous silicon-acetylene black mixture, and the mixture is mechanically stirred to be uniform. A hydrothermal reaction is carried out at a constant temperature in an electric constant temperature drying oven, and the glycerol solvent is evaporated. The silicon / carbon composite material is ground to obtain a mass ratio of the amorphous silicon to the acetylene black of 8:2; S2, adding chitosan to the silicon / carbon composite material obtained in step S1, mixing evenly, cooling the mixture, and then adding ethylene carbonate to gradually solidify the mixture to obtain a silicon-carbon negative electrode precursor material; S3. The silicon-carbon negative electrode precursor material obtained in step S2 is subjected to carbon coating treatment by chemical vapor deposition to obtain a carbon-coated silicon-carbon negative electrode material.

2. The method for preparing a silicon-carbon negative electrode material with a low expansion coefficient according to claim 1, characterized in that: The amount of tin oxide added is 8% of the total mass of amorphous silicon and acetylene black, the amount of polyvinyl pyrrolidone added is 5% of the mass of the tin oxide-amorphous silicon-acetylene black mixture, and the mass of the glycerol solution is 10 times the total mass of amorphous silicon and acetylene black.

3. The method for preparing a silicon-carbon negative electrode material with a low expansion coefficient according to claim 1, characterized in that: In step S2, the mass ratio of the silicon / carbon composite material to chitin is 10:3, and the amount of ethylene carbonate added is 15% of the total mass of the silicon / carbon composite material and chitin.

4. The method for preparing a silicon-carbon negative electrode material with a low expansion coefficient according to claim 1, characterized in that: In step S1, the mechanical stirring time is 2 hours, the mechanical stirring speed is 1000 rpm, the temperature of the electric heating constant temperature box is 80° C., and the hydrothermal reaction time is 3 hours.

5. The method for preparing a silicon-carbon negative electrode material with a low expansion coefficient according to claim 1, characterized in that: In step S1, evaporation of the glycerol solvent is performed in an oven at a temperature of 90° C. for 4 hours.

6. The method for preparing a silicon-carbon negative electrode material with a low expansion coefficient according to claim 4, characterized in that: In the step S2, before chitosan is added to the silicon / carbon composite material obtained in the step S1 and mixed evenly, the chitosan is dried in an oven and then ground to a particle size of 50 mesh.

7. The method for preparing a silicon-carbon negative electrode material with a low expansion coefficient according to claim 4, characterized in that: In step S2, the temperature is lowered to 10°C at a rate of 5°C / min.

8. The method for preparing a silicon-carbon negative electrode material with a low expansion coefficient according to claim 7, characterized in that: In step S3, the temperature of the carbon coating is 850-900°C, the gas source used is acetylene, methane, liquefied gas or gaseous carbon source, and the duration is 1 hour.

9. The silicon-carbon negative electrode material obtained by the method for preparing a silicon-carbon negative electrode material with a low expansion coefficient according to any one of claims 1 to 8.

10. Use of the silicon-carbon negative electrode material obtained by the method for preparing a silicon-carbon negative electrode material with a low expansion coefficient according to claim 9 in a lithium battery.

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