A method for preparing carbon-silicon negative electrode material

Abstract

The present invention relates to the field of electrode material technology, and specifically to a method for preparing a carbon-silicon negative electrode material. The method includes the steps of carbon precursor pre-carbonization, activation and impurity removal, modification, secondary carbonization, silicon deposition, carbon coating, etc. The carbon precursor can be selected from resin or biomass. The prepared silicon-carbon negative electrode material has a unique porous structure and a reasonable silicon-carbon composite system, which provides rich storage sites for lithium ions, effectively inhibits side reactions, reduces capacity attenuation, and reduces volume expansion. The specific process optimizes the material performance, improves the lithium ion transmission efficiency and conductivity, comprehensively improves the comprehensive performance of the battery, and solves many problems of negative electrode materials in the prior art.

Description

Technical Field

[0001] The present invention relates to the technical field of electrode materials, and in particular to a method for preparing a carbon-silicon negative electrode material. Background Art

[0002] With the rapid development of electronic devices, electric vehicles, and other fields, the performance requirements for lithium-ion batteries are also increasing. As a highly efficient energy storage device, the performance of lithium-ion batteries directly affects the user experience and development prospects of related equipment. Among them, the anode material, as a key component of lithium-ion batteries, plays a vital role in the overall performance of the battery.

[0003] While traditional graphite anode materials offer excellent conductivity and a low lithium insertion potential, their theoretical specific capacity is low, making them inadequate for the high-energy-density lithium-ion batteries they demand. Therefore, developing anode materials with higher specific capacities has become a research hotspot. Silicon, a highly promising anode material, boasts a theoretical specific capacity of up to 4200 mAh / g, more than ten times that of graphite anode materials. However, silicon undergoes significant volume changes (up to 300%) during charge and discharge, which can lead to pulverization and shedding of silicon particles, further damaging the electrode structure and rapidly decreasing battery capacity. Furthermore, an unstable solid electrolyte interphase (SEI) film readily forms on the silicon surface, consuming significant amounts of lithium ions and reducing the battery's initial coulombic efficiency. This increases the battery's internal resistance, impacting its charge and discharge performance.

[0004] To address the issues facing silicon anode materials, researchers have explored various approaches, such as preparing silicon-based composite materials and nanostructured silicon materials. Silicon-carbon composites are a widely studied system. By combining silicon with carbon materials, the buffering effect of the carbon material can be exploited to mitigate silicon's volume expansion while simultaneously improving the material's conductivity. However, existing silicon-carbon anode materials still suffer from several deficiencies during their preparation. These include inadequate porous structure design, which limits lithium-ion storage sites; low graphitization, which affects lithium-ion transport efficiency; and a lack of an effective surface coating, which prevents side reactions between silicon and the electrolyte. These issues hinder existing silicon-carbon anode materials from meeting practical application requirements in terms of discharge capacity, initial coulombic efficiency, cycling stability, and volume expansion control. Therefore, developing a silicon-carbon anode material with high discharge capacity, high initial coulombic efficiency, good cycling stability, and low volume expansion is of great practical significance. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to propose a method for preparing a carbon-silicon negative electrode material, so as to develop a silicon-carbon negative electrode material with high discharge capacity, high first coulombic efficiency, good cycle stability and low volume expansion rate.

[0006] Based on the above objectives, the present invention provides a method for preparing a silicon-carbon negative electrode material, comprising the following steps:

[0007] (1) The carbon precursor is placed in a semi-continuous rotary kiln, nitrogen is introduced as an inert gas, and after the air in the kiln is exhausted, the temperature is increased to 550-650°C at a heating rate of 5°C / min, maintained for 2.5-3.5 hours, and then naturally cooled to room temperature to obtain a pre-carbonized precursor;

[0008] (2) The pre-carbonized precursor is placed in an activation furnace, and nitrogen is introduced as an inert gas. After the air in the kiln is exhausted, the temperature is increased to 750-850°C at a heating rate of 5°C / min, and then carbon dioxide gas is introduced and maintained for 3.5-4.5 hours. After natural cooling to room temperature, the precursor is placed in dilute hydrochloric acid and stirred for 1.5-2.5 hours. After centrifugation, the precursor is washed with hydrofluoric acid solution and then washed with deionized water until neutral. The precursor is dried to obtain a pre-carbonized precursor having been removed from the impurities.

[0009] (3) The impurity-removed pre-carbonized precursor is put into a mixed solution of ethanol and deionized water, and then the silane coupling agent KH-550 is added, the temperature is raised to 50-60 ° C, and stirred for 3-5 hours. Then, cobalt nitrate hexahydrate in an amount equimolar to the silane coupling agent KH-550 is added, and the stirring is continued for 1-3 hours. The mixture is centrifuged and dried to obtain a modified precursor;

[0010] (4) The modified precursor was placed in a carbonization furnace, and an argon-hydrogen mixture was introduced. The air in the furnace was exhausted and the temperature was raised to 380-420°C at a heating rate of 5°C / min, maintained for 1.5-2.5h. Then, argon was introduced and the temperature was raised to 1150-1250°C at a heating rate of 3°C / min, maintained for 2.5-3.5h. After naturally cooling to room temperature, a porous carbon material was obtained.

[0011] (5) The porous carbon material was placed in a CVD furnace, argon gas was introduced, the air in the furnace was exhausted, the temperature was raised to 450-550°C at a heating rate of 5°C / min, monosilane gas was introduced at a flow rate of 40-60 mL / min for 1.5-2.5 h, and the material was naturally cooled to room temperature to obtain a silicon-deposited porous carbon material;

[0012] (6) The silicon-silicon deposited porous carbon material was placed in a CVD furnace, argon gas was introduced, the air in the furnace was exhausted, the temperature was raised to 750-850°C at a heating rate of 8°C / min, methane gas was introduced at a flow rate of 80-120 mL / min for 2.5-3.5 hours, and the material was naturally cooled to room temperature to obtain a silicon-carbon negative electrode material.

[0013] Preferably, the carbon precursor in step (1) is resin or biomass.

[0014] Preferably, the resin is one of polyacrylonitrile, phenolic resin, epoxy resin and polyimide.

[0015] Preferably, the biomass is one of walnut shells, coconut shells, peanut shells, bamboo powder, and wood matrix.

[0016] Preferably, the flow rate of carbon dioxide gas in step (2) is 5-20 L / min.

[0017] Preferably, the concentration of the dilute hydrochloric acid in step (2) is 0.08M-0.15M, and the concentration of the hydrofluoric acid solution is 0.3wt%-0.8wt%.

[0018] Preferably, the volume ratio of ethanol to deionized water in the mixed solution in step (3) is 1:5.

[0019] Preferably, the amount of silane coupling agent KH-550 added in step (3) is 0.5%-1.5% of the weight of the impurity-removed pre-carbonized precursor.

[0020] Compared with traditional negative electrode materials, the silicon-carbon negative electrode material prepared by the present invention shows significant beneficial effects in many aspects and effectively solves many problems existing in the prior art.

[0021] In terms of lithium-ion storage capacity, the silicon-carbon anode material has a unique porous structure and a rational silicon-carbon composite system, providing abundant and efficient storage sites for lithium ions. This enables the material to accommodate more lithium ions during the charge and discharge process, greatly improving the battery's discharge capacity and meeting the battery capacity requirements of high-energy-density devices.

[0022] First coulombic efficiency (FCE) is a key indicator of battery performance. The silicon-carbon anode material of the present invention effectively suppresses side reactions between the electrode and the electrolyte during the initial charge and discharge process. This is due to the material's excellent structural stability, which reduces irreversible capacity loss and ensures a high FCE. This means that during the battery's initial use, the battery's energy can be more fully utilized, improving its efficiency.

[0023] Cyclic stability is key to long-term battery performance. The materials of this invention maintain stable structure and performance after multiple charge-discharge cycles. The rational design of the material allows it to withstand volume changes during lithium ion insertion and extraction, minimizing capacity decay. Over extended charge-discharge cycles, the battery maintains a high capacity, extending its service life and reducing its cost.

[0024] Volume expansion is a major challenge faced by silicon anode materials. However, the silicon-carbon anode material of the present invention exhibits minimal volume change during the initial charge and discharge process. This further demonstrates the stability and expansion resistance of the material structure, effectively preventing electrode structural damage and battery performance degradation caused by volume expansion. This lower volume expansion rate helps improve battery safety and reduce potential safety hazards caused by battery expansion.

[0025] Furthermore, the present invention utilizes a series of processes during material preparation, such as specialized catalytic treatment and coating, to further optimize the material's performance. These processes result in a more regular graphite structure and a stable surface coating, enhancing lithium ion transport efficiency and the material's electrical conductivity, thereby comprehensively improving the battery's overall performance. DETAILED DESCRIPTION

[0026] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to specific embodiments.

[0027] The model of the phenolic resin powder in the specific embodiment of the present invention is PF131.

[0028] Example 1:

[0029] (1) Phenolic resin powder was placed in a semi-continuous rotary kiln, nitrogen was introduced as an inert gas, and after exhausting the air in the kiln, the temperature was increased to 550°C at a heating rate of 5°C / min, maintained for 2.5 h, and naturally cooled to room temperature to obtain a pre-carbonized precursor;

[0030] (2) The pre-carbonized precursor was placed in an activation furnace, nitrogen was introduced as an inert gas, and after the air in the kiln was exhausted, the temperature was raised to 750°C at a heating rate of 5°C / min, and then carbon dioxide gas was introduced at a flow rate of 10L / min and maintained for 3.5h. After natural cooling to room temperature, the precursor was placed in 0.08M dilute hydrochloric acid with a bath ratio of 1:10 and stirred for 1.5h. After centrifugation, the precursor was washed three times with a 0.3wt% hydrofluoric acid solution, and then washed with deionized water until neutral, and dried to obtain a pre-carbonized precursor with impurities removed;

[0031] (3) The impurity-removed pre-carbonized precursor was added into a mixed solution of ethanol and deionized water (volume ratio of 1:5) with a bath ratio of 1:5, and then 0.5% of the weight of the impurity-removed pre-carbonized precursor was added with a silane coupling agent KH-550. The temperature was raised to 50°C and stirred for 3 hours. Then, cobalt nitrate hexahydrate in an amount equimolar to the silane coupling agent KH-550 was added, and the mixture was stirred for 1 hour. The mixture was centrifuged and dried to obtain a modified precursor.

[0032] (4) The modified precursor was placed in a carbonization furnace, and an argon-hydrogen mixture (containing 5 vol% hydrogen) was introduced. The air in the furnace was exhausted, and the temperature was raised to 380 °C at a heating rate of 5 °C / min and maintained for 1.5 h. Then, argon was introduced at a flow rate of 10 L / min, and the temperature was raised to 1150 °C at a heating rate of 3 °C / min and maintained for 2.5 h. After naturally cooling to room temperature, a porous carbon material was obtained;

[0033] (5) The porous carbon material was placed in a CVD furnace, argon gas was introduced, the air in the furnace was exhausted, the temperature was raised to 450°C at a heating rate of 5°C / min, and monosilane gas was introduced at a flow rate of 40 mL / min for 1.5 h to deposit silicon on the carbon substrate. After naturally cooling to room temperature, a silicon-deposited porous carbon material was obtained;

[0034] (6) The silicon-silicon deposited porous carbon material was placed in a CVD furnace, argon gas was introduced, the air in the furnace was exhausted, and the temperature was raised to 750°C at a heating rate of 8°C / min. Methane gas was introduced at a flow rate of 80 mL / min for 2.5 hours to uniformly coat the carbon on the silicon-carbon matrix. After naturally cooling to room temperature, a silicon-carbon negative electrode material was obtained.

[0035] Example 2:

[0036] (1) Phenolic resin powder was placed in a semi-continuous rotary kiln, nitrogen was introduced as an inert gas, and after exhausting the air in the kiln, the temperature was increased to 600°C at a heating rate of 5°C / min, maintained for 3 h, and naturally cooled to room temperature to obtain a pre-carbonized precursor;

[0037] (2) The pre-carbonized precursor was placed in an activation furnace, nitrogen was introduced as an inert gas, and after the air in the kiln was exhausted, the temperature was raised to 800°C at a heating rate of 5°C / min, and then carbon dioxide gas was introduced at a flow rate of 10L / min and maintained for 4 hours. After natural cooling to room temperature, the precursor was placed in 0.1M dilute hydrochloric acid with a bath ratio of 1:10 and stirred for 2 hours. After centrifugation, the precursor was washed three times with a 0.5wt% hydrofluoric acid solution, and then washed with deionized water until neutral, and dried to obtain a pre-carbonized precursor with impurities removed;

[0038] (3) The impurity-removed pre-carbonized precursor was added into a mixed solution of ethanol and deionized water (volume ratio of 1:5) with a bath ratio of 1:5, and then 1% of the weight of the impurity-removed pre-carbonized precursor was added into the solution. The temperature was raised to 55°C and stirred for 4 hours. Then, cobalt nitrate hexahydrate in an amount equimolar to that of the silane coupling agent KH-550 was added into the solution. The solution was stirred for 2 hours, centrifuged, and dried to obtain a modified precursor.

[0039] (4) The modified precursor was placed in a carbonization furnace, and an argon-hydrogen mixture (containing 5 vol% hydrogen) was introduced. The air in the furnace was exhausted, and the temperature was raised to 400 °C at a heating rate of 5 °C / min and maintained for 2 h. Then, argon was introduced at a flow rate of 10 L / min, and the temperature was raised to 1200 °C at a heating rate of 3 °C / min and maintained for 3 h. After naturally cooling to room temperature, a porous carbon material was obtained;

[0040] (5) The porous carbon material was placed in a CVD furnace, argon gas was introduced, the air in the furnace was exhausted, the temperature was raised to 500°C at a heating rate of 5°C / min, and monosilane gas was introduced at a flow rate of 50 mL / min for 2 h to deposit silicon on the carbon substrate. After naturally cooling to room temperature, a silicon-deposited porous carbon material was obtained;

[0041] (6) The silicon-silicon deposited porous carbon material was placed in a CVD furnace, argon gas was introduced, the air in the furnace was exhausted, the temperature was raised to 800°C at a heating rate of 8°C / min, and methane gas was introduced at a flow rate of 100 mL / min for 3 hours to uniformly coat the carbon on the silicon-carbon matrix. After naturally cooling to room temperature, the silicon-carbon negative electrode material was obtained.

[0042] Example 3:

[0043] (1) Phenolic resin powder was placed in a semi-continuous rotary kiln, nitrogen was introduced as an inert gas, and after exhausting the air in the kiln, the temperature was increased to 650°C at a heating rate of 5°C / min, maintained for 3.5 hours, and naturally cooled to room temperature to obtain a pre-carbonized precursor;

[0044] (2) The pre-carbonized precursor was placed in an activation furnace, nitrogen was introduced as an inert gas, and after the air in the kiln was exhausted, the temperature was raised to 850°C at a heating rate of 5°C / min, and then carbon dioxide gas was introduced at a flow rate of 10L / min and maintained for 4.5 hours. After natural cooling to room temperature, the precursor was placed in 0.15M dilute hydrochloric acid with a bath ratio of 1:10 and stirred for 2.5 hours. After centrifugation, the precursor was washed three times with a 0.8wt% hydrofluoric acid solution, and then washed with deionized water until neutral, and dried to obtain a pre-carbonized precursor with impurities removed;

[0045] (3) The impurity-removed pre-carbonized precursor was added into a mixed solution of ethanol and deionized water (volume ratio of 1:5) with a bath ratio of 1:5, and then 1.5% of the weight of the impurity-removed pre-carbonized precursor was added with a silane coupling agent KH-550. The mixture was heated to 50-60°C and stirred for 5 hours. Then, cobalt nitrate hexahydrate in an amount equimolar to that of the silane coupling agent KH-550 was added, and the mixture was stirred for 3 hours. The mixture was centrifuged and dried to obtain a modified precursor.

[0046] (4) The modified precursor was placed in a carbonization furnace, and an argon-hydrogen mixture (containing 5 vol% hydrogen) was introduced. The air in the furnace was exhausted, and the temperature was raised to 420 °C at a heating rate of 5 °C / min and maintained for 2.5 h. Then, argon was introduced at a flow rate of 10 L / min, and the temperature was raised to 1250 °C at a heating rate of 3 °C / min and maintained for 3.5 h. After naturally cooling to room temperature, a porous carbon material was obtained;

[0047] (5) The porous carbon material was placed in a CVD furnace, argon gas was introduced, the air in the furnace was exhausted, the temperature was raised to 550°C at a heating rate of 5°C / min, and monosilane gas was introduced at a flow rate of 60 mL / min for 2.5 h to deposit silicon on the carbon substrate. After naturally cooling to room temperature, a silicon-deposited porous carbon material was obtained;

[0048] (6) The silicon-silicon deposited porous carbon material was placed in a CVD furnace, argon gas was introduced, the air in the furnace was exhausted, and the temperature was raised to 850°C at a heating rate of 8°C / min. Methane gas was introduced at a flow rate of 120 mL / min for 3.5 hours to uniformly coat the carbon on the silicon-carbon matrix. After naturally cooling to room temperature, a silicon-carbon negative electrode material was obtained.

[0049] Comparative Example 1:

[0050] The difference between Comparative Example 1 and Example 2 is that: cobalt nitrate hexahydrate is not added in step (3);

[0051] Comparative Example 2:

[0052] The difference between Comparative Example 2 and Example 2 is that the modified precursor in step (4) is replaced by a de-doped pre-carbonized precursor;

[0053] Comparative Example 3:

[0054] The difference between Comparative Example 3 and Example 2 is that: in step (4), after the modified precursor is put into the carbonization furnace, argon gas is directly introduced at a flow rate of 10 L / min, and the temperature is increased to 1200°C at a heating rate of 3°C / min and maintained for 3 hours;

[0055] Comparative Example 4:

[0056] The difference between Comparative Example 4 and Example 2 is that step (6) is deleted.

[0057] Preparation of negative electrode sheet: Take the negative electrode materials prepared in the embodiment and the comparative example respectively, and mix them in the ratio of active material: conductive agent (Super P): binder (sodium carboxymethyl cellulose) = 90:5:5 (weight ratio) to form a slurry. The slurry is evenly coated on the copper foil with a coating thickness of 120μm, and then dried in a vacuum drying oven at 80℃ for 12h to obtain an electrode sheet. Then, a sheet punching machine is used to punch out circular electrode sheets with a diameter of 12mm, and then vacuum dried at 120℃ for 24h to obtain a negative electrode sheet.

[0058] Battery assembly: The battery was assembled in an argon-filled glove box, using a lithium sheet as the counter electrode, a polypropylene microporous membrane (Celgard 2400) as the separator, and a mixed solution of 1M LiPF6 in ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) (volume ratio EC:DMC:EMC = 1:1:1). CR2032 button cells were assembled in the order of negative electrode shell, lithium sheet, separator, negative electrode sheet, gasket, spring sheet, and positive electrode shell, and sealed with a sealing machine.

[0059] Performance testing:

[0060] Capacity and initial coulombic efficiency test: The assembled button cell was left to rest for 12 hours and then tested using a battery charge and discharge tester. At room temperature, the battery was subjected to constant current charge and discharge tests at a current density of 0.1C and a charge and discharge voltage range of 0.01-2.0V. The results are shown in Table 1.

[0061] Cyclic capacity test: After completing the first charge and discharge test, the battery was subjected to a cyclic charge and discharge test at a current density of 0.5C. The charge and discharge voltage range was still 0.01-2.0V. After 800 cycles, the cycle capacity retention rate (%) was calculated as follows: discharge capacity at the 800th cycle / discharge capacity at the second cycle × 100%. The results are shown in Table 1.

[0062] Initial expansion rate test: Before battery assembly, use a micrometer to measure the initial thickness of the electrode sheet (accurate to 0.001mm), recorded as d0. After the first charge and discharge test, disassemble the battery, remove the electrode sheet, and absorb the surface electrolyte with filter paper. Measure the electrode sheet thickness again using a micrometer, recorded as d1. , the results are shown in Table 1.

[0063]

[0064] Data Analysis:

[0065] It can be seen from the data of Examples 1-3 in Table 1 that the silicon-carbon negative electrode material prepared by the present invention exhibits excellent comprehensive performance. It performs well in terms of discharge capacity, indicating that the material has a high lithium ion storage capacity. This is due to the unique porous structure and silicon-carbon composite system of the material, which provides abundant storage sites for lithium ions. The high initial coulombic efficiency means that during the first charge and discharge process, there are fewer side reactions between the electrode and the electrolyte, the structural stability of the material is good, and the irreversible capacity loss can be effectively reduced. The high cycle capacity retention rate indicates that the material can still maintain a stable structure and performance after multiple charge and discharge cycles, which is attributed to the reasonable design of the material, which enables it to withstand volume changes during the insertion and extraction of lithium ions. The lower initial expansion rate indicates that the volume change of the material during the first charge and discharge process is small, which further reflects the stability and anti-expansion ability of the material structure, which helps to extend the service life of the battery and improve safety.

[0066] From the data of Example 2 and Comparative Examples 1-2 in Table 1, it can be seen that Example 2 is superior to Comparative Examples 1-2 in all aspects. Overall, the discharge capacity, first coulomb efficiency and cycle capacity retention rate of Example 2 are higher, and the first expansion rate is lower. Cobalt nitrate hexahydrate plays a key role in the material preparation process. It is cobalt nitrate hexahydrate that generates cobalt in subsequent treatment, and cobalt catalyzes the graphitization process of the material, so that the material has a more regular graphite structure, thereby increasing the transmission channel of lithium ions, and improving the discharge capacity and the first coulomb efficiency. At the same time, a more regular structure also helps to improve the structural stability of the material, reduce capacity decay during the cycle, and reduce the first expansion rate.

[0067] From the data of Example 2 and Comparative Example 3 in Table 1, it can be seen that Example 2 performs better in all performance indicators. Example 2 has a large discharge capacity, high first coulomb efficiency, high cycle capacity retention rate and low first expansion rate. In step (4), after the modified precursor is put into the carbonization furnace, argon gas is directly introduced at a certain flow rate and the temperature is increased, while Example 2 is first heated to a certain temperature under an argon-hydrogen mixed gas atmosphere and maintained for a period of time. It is speculated that the cobalt reduced in the hydrogen atmosphere has a catalytic effect on graphitization. The presence of hydrogen enables the cobalt element to better exert its catalytic performance, promote the graphitization process of the material, and form a structure that is more conducive to lithium ion transmission. This structure not only improves the storage and transmission efficiency of lithium ions, increases the discharge capacity and first coulomb efficiency, but also enhances the structural stability of the material, so that the material has a higher capacity retention rate during the cycle and smaller volume expansion during the first charge and discharge.

[0068] From the data of Example 2 and Comparative Example 4 in Table 1, it can be seen that Example 2 has a higher discharge capacity, first coulomb efficiency and cycle capacity retention rate, as well as a lower first expansion rate. Comparative Example 4 does not carry out the process of introducing methane gas to coat carbon on the silicon-carbon matrix. It can be inferred that the carbon coating process is of great significance to improving material performance. The carbon produced by the decomposition of methane is evenly coated on the silicon-carbon matrix, forming a stable protective layer. This carbon coating layer can effectively inhibit the volume expansion of silicon during the charge and discharge process, reduce the direct contact between silicon and the electrolyte, thereby reducing the occurrence of side reactions and improving the first coulomb efficiency. At the same time, the carbon coating layer can also improve the conductivity of the material, promote the transmission of lithium ions, and increase the discharge capacity. In addition, the stable structure helps to improve the cycle stability of the material, so that the battery can still maintain a high capacity after multiple charge and discharge cycles.

[0069] Those skilled in the art should understand that the discussion of any of the above embodiments is merely illustrative and is not intended to imply that the scope of the present invention is limited to these examples. Within the scope of the present invention, the technical features in the above embodiments or different embodiments may be combined, the steps may be implemented in any order, and there are many other variations of the different aspects of the present invention as described above, which are not provided in detail for the sake of simplicity.

Claims

1. A method for preparing a carbon-silicon negative electrode material, characterized in that: The following steps are involved: (1) The carbon precursor is placed in a semi-continuous rotary kiln, nitrogen is introduced as an inert gas, and after the air in the kiln is exhausted, the temperature is increased to 550-650°C at a heating rate of 5°C / min, maintained for 2.5-3.5 hours, and then naturally cooled to room temperature to obtain a pre-carbonized precursor; (2) The pre-carbonized precursor is placed in an activation furnace, and nitrogen is introduced as an inert gas. After the air in the kiln is exhausted, the temperature is increased to 750-850°C at a heating rate of 5°C / min, and then carbon dioxide gas is introduced and maintained for 3.5-4.5 hours. After natural cooling to room temperature, the precursor is placed in dilute hydrochloric acid and stirred for 1.5-2.5 hours. After centrifugation, the precursor is washed with hydrofluoric acid solution and then washed with deionized water until neutral. The precursor is dried to obtain a pre-carbonized precursor having been removed from the impurities. (3) The impurity-removed pre-carbonized precursor is put into a mixed solution of ethanol and deionized water, and then the silane coupling agent KH-550 is added, the temperature is raised to 50-60 ° C, and stirred for 3-5 hours. Then, cobalt nitrate hexahydrate in an amount equimolar to the silane coupling agent KH-550 is added, and the stirring is continued for 1-3 hours. The mixture is centrifuged and dried to obtain a modified precursor; (4) The modified precursor was placed in a carbonization furnace, and an argon-hydrogen mixture was introduced. The air in the furnace was exhausted and the temperature was raised to 380-420°C at a heating rate of 5°C / min, maintained for 1.5-2.5h. Then, argon was introduced and the temperature was raised to 1150-1250°C at a heating rate of 3°C / min, maintained for 2.5-3.5h. After naturally cooling to room temperature, a porous carbon material was obtained. (5) The porous carbon material was placed in a CVD furnace, argon gas was introduced, the air in the furnace was exhausted, the temperature was raised to 450-550°C at a heating rate of 5°C / min, monosilane gas was introduced at a flow rate of 40-60 mL / min for 1.5-2.5 h, and the material was naturally cooled to room temperature to obtain a silicon-deposited porous carbon material; (6) The silicon-deposited porous carbon material was placed in a CVD furnace, argon gas was introduced, the air in the furnace was exhausted, the temperature was raised to 750-850°C at a heating rate of 8°C / min, methane gas was introduced at a flow rate of 80-120 mL / min for 2.5-3.5 hours, and the material was naturally cooled to room temperature to obtain a silicon-carbon negative electrode material.

2. The method for preparing the carbon-silicon negative electrode material according to claim 1, wherein: In the step (1), the carbon precursor is a resin or a biomass.

3. The method for preparing the carbon-silicon negative electrode material according to claim 2, wherein: The resin is one of polyacrylonitrile, phenolic resin, epoxy resin and polyimide; the biomass is one of walnut shell, coconut shell, peanut shell, bamboo powder and wood matrix.

4. The method for preparing the carbon-silicon negative electrode material according to claim 1, wherein: The flow rate of carbon dioxide gas in step (2) is 5-20 L / min.

5. The method for preparing the carbon-silicon negative electrode material according to claim 1, wherein: In step (2), the concentration of the dilute hydrochloric acid is 0.08M-0.15M, and the concentration of the hydrofluoric acid solution is 0.3wt%-0.8wt%.

6. The method for preparing the carbon-silicon negative electrode material according to claim 1, wherein: The volume ratio of ethanol to deionized water in the mixed solution in step (3) is 1:

5.

7. The method for preparing the carbon-silicon negative electrode material according to claim 1, characterized in that: The amount of silane coupling agent KH-550 added in step (3) is 0.5%-1.5% of the weight of the pre-carbonized precursor after impurities removal.

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