Preparation method and application of silicon-carbon negative electrode material

Abstract

The application relates to a preparation method and application of a silicon-carbon negative electrode material, and comprises the following steps: (1) dispersing silicon carbide nanoparticles, an alkaline reagent and a dispersing agent in water to obtain slurry A; dispersing a phenolic monomer, an aldehyde monomer and an initiator in water to obtain slurry B; (2) mixing and stirring slurry A and slurry B to carry out a reaction, and then heating and solidifying to obtain a phenolic aldehyde resin doped with silicon carbide nanoparticles P-SiC; (3) carrying out first carbonization treatment on P-SiC, mixing the obtained carbonization product with a strong alkali to carry out alkali activation treatment, cooling and crushing to obtain porous carbon doped with silicon carbide nanoparticles C-SiC; and (4) placing C-SiC in a reactor, and sequentially carrying out silicon deposition and carbon deposition treatment by using a chemical vapor deposition method to obtain the silicon-carbon negative electrode material. The negative electrode material prepared by the above method has high compressive strength and high gram capacity, can effectively inhibit volume expansion in a charging process, and can effectively improve the cycle performance of a high-capacity battery.

Description

Technical Field

[0001] This invention relates to the field of battery technology, specifically to a method for preparing and applying a silicon-carbon anode material. Background Technology

[0002] With the rapid development of new energy vehicles, large-scale energy storage, and portable electronic devices, the market is placing increasingly higher demands on the energy density of power batteries. The performance of power batteries largely depends on their electrode materials, especially the negative electrode material. Currently, commercial lithium-ion batteries widely use graphite as the negative electrode material, but its theoretical specific capacity is relatively low (approximately 372 mAh / g), which has become a bottleneck restricting further improvements in the energy density of lithium-ion batteries.

[0003] Silicon (Si) is considered one of the most promising anode materials for next-generation high-energy-density lithium-ion batteries due to its extremely high theoretical specific capacity (up to 4200 mAh / g at room temperature, more than 10 times that of graphite), moderate lithium intercalation potential, environmental friendliness, and abundant reserves. However, silicon faces severe challenges in its commercial application. During charging and discharging, it undergoes an alloying reaction with lithium, accompanied by a huge volume expansion effect (>300%).

[0004] To overcome the aforementioned drawbacks, those skilled in the art typically employ a "silicon-carbon composite" approach, which involves combining nano-sized silicon materials with carbonaceous materials (such as graphite and amorphous carbon) to utilize the excellent electrical conductivity and mechanical stability of carbon materials to buffer the volume expansion of silicon. However, existing silicon-carbon anode materials still suffer from the following defects: silicon and carbon are difficult to bond uniformly and tightly in the anode material, and the compressive strength is low. During the rolling process in battery fabrication, and under the enormous internal stress generated by silicon expansion during cycling, the material structure is prone to collapse, failing to provide a stable and robust constraint space for the volume expansion of silicon, leading to continuous growth of the SEI film and rapid capacity decay.

[0005] Therefore, there is an urgent need for a method to prepare silicon-carbon anode materials with both high specific capacity and high compressive strength, so as to effectively suppress the volume expansion of silicon during lithium intercalation and maintain the integrity and stability of the electrode structure. This is of great significance for realizing power batteries with high energy density and long cycle life. Summary of the Invention

[0006] To address the problems of low compressive strength and easy breakage during battery rolling and long-term cycling of existing silicon-carbon anode materials, leading to deterioration in cycle performance, this invention provides a method for preparing and applying a silicon-carbon anode material. Silicon carbide nanoparticles are introduced during the in-situ polymerization preparation of a porous carbon precursor. After carbonization and alkali activation treatment, a porous carbon C-SiC with uniformly doped silicon carbide nanoparticles is formed. Further, an in-situ doped silicon-carbon anode material is prepared through CVD vapor-phase silicon infiltration and carbon coating processes. The silicon-carbon anode material prepared by this method can significantly improve the overall compressive strength of the material without sacrificing specific capacity. During cycling, it can effectively absorb the stress caused by the expansion of silicon nanoparticles, thereby improving the cycle performance of the battery.

[0007] Specifically, the following technical solutions are provided: The first aspect of this invention provides a method for preparing a silicon-carbon anode material, comprising the following steps: (1) Silicon carbide nanoparticles, alkaline reagents and dispersants are dispersed in water to obtain slurry A; phenolic monomers, aldehyde monomers and initiators are dispersed in water to obtain slurry B; (2) Mix and stir the slurry A and the slurry B, and then heat and cure to obtain phenolic resin doped with silicon carbide nanoparticles; (3) The phenolic resin doped with silicon carbide nanoparticles is subjected to carbonization treatment, and the carbonization product is subjected to alkali activation treatment with a strong alkali. After cooling and crushing, porous carbon particles doped with silicon carbide nanoparticles are obtained. (4) The porous carbon particles doped with silicon carbide nanoparticles are placed in a reactor and silicon deposition and carbon deposition are performed sequentially by chemical vapor deposition to obtain the silicon-carbon anode material.

[0008] Further, in step (1), the particle size D50 of the silicon carbide nanoparticles is preferably 20-100 nm.

[0009] Further, in step (1), the alkaline reagent includes, but is not limited to, one or more of ammonia, sodium hydroxide, and potassium hydroxide, and the dispersant includes, but is not limited to, one or more of polyethyleneimine, methyltriethoxysilane, vinyltriethoxysilane, N-(β-aminoethyl)-γ-aminopropyltrimeth(eth)oxysilane, γ-(2,3-epoxypropoxy)propyltrimethoxysilane, 3-aminopropyltriethoxysilane, and γ-(methacryloyloxy)propyltrimethoxysilane.

[0010] Further, in step (1), the preferred mass ratio of the silicon carbide nanoparticles, dispersant and water is (1-2):(0.5-1):(10-20).

[0011] Furthermore, in step (1), the pH of the slurry A is preferably 8-11.

[0012] Further, in step (1), the phenolic monomer can be selected from one or more of phenol, resorcinol, methylphenol, and aminophenol, the aldehyde monomer can be selected from one or more of formaldehyde, acetaldehyde, furfural, and paraformaldehyde, and the initiator includes, but is not limited to, one or more of ammonia, sodium hydroxide, potassium hydroxide, and ethylenediamine.

[0013] Further, in step (1), the preferred mass ratio of the phenolic monomer, aldehyde monomer, initiator and water is (7-10):(3-5):(0.09-0.18):(10-20).

[0014] Further, in step (2), the preferred mass ratio of slurry A to slurry B is (0.8-3.3):1000.

[0015] Furthermore, in step (2), the temperature of the stirring reaction is preferably 40-60 °C, and the time is preferably 1-3 h.

[0016] Furthermore, in step (2), the heating and curing temperature is preferably 100-200 ℃, and the time is preferably 5-10 h.

[0017] Furthermore, in step (3), the carbonization process is carried out under a protective atmosphere, which includes nitrogen.

[0018] Furthermore, in step (3), the carbonization treatment temperature is preferably 700-1000 ℃, and the time is preferably 1-3h.

[0019] Further, in step (3), the mass ratio of the carbonization product to the strong base is 1:(1-4), and the strong base is preferably potassium hydroxide and / or sodium hydroxide.

[0020] Further, in step (3), the alkali activation treatment step involves first heating to 350-450 ℃ and holding for 0.5-2 h, and then heating to 700-900 ℃ and holding for 0.5-2 h.

[0021] Furthermore, in step (3), the particle size D50 of the porous carbon particles doped with silicon carbide nanoparticles is preferably 5-10 μm.

[0022] Further, in step (4), in the step of sequentially performing silicon deposition and carbon deposition using chemical vapor deposition: the temperature is increased to 400-600 ℃ at 2-5 ℃ / min, and a first mixed gas containing gaseous silicon source and nitrogen is introduced into the reactor for vapor deposition for 6-10 h; after silicon deposition is completed, a second mixed gas containing gaseous carbon source and nitrogen is introduced for vapor deposition for 1-3 h.

[0023] Further, the volume ratio of gaseous silicon source to nitrogen in the first mixed gas is preferably (2-4):1; the volume ratio of gaseous carbon source to nitrogen in the second mixed gas is preferably (2-4):1; more preferably, the gaseous silicon source is selected from one or more of silane, silane, trichlorosilane, dichlorosilane, propane, trichlorosilane, and silicon chloride; the gaseous carbon source is selected from one or more of acetylene, methane, ethane, and ethylene.

[0024] The second aspect of the present invention provides a silicon-carbon anode material, which is prepared by the preparation method described in the first aspect; the silicon-carbon anode material includes a porous carbon core, silicon nanoparticles uniformly deposited in the pores and outer surface of the porous carbon core, and a carbon coating layer, wherein the porous carbon core includes a porous carbon matrix and silicon carbide nanoparticles embedded in the carbon matrix of the porous carbon matrix.

[0025] Furthermore, the particle size D50 of the porous carbon core is preferably 5-10 μm, the particle size D50 of the silicon carbide nanoparticles is preferably 20-100 nm, and the thickness of the carbon coating layer is preferably 20-100 nm.

[0026] Furthermore, the ratio of the particle size D50 of the silicon-carbon anode material to the particle size D50 of the silicon carbide nanoparticles is preferably 60-450.

[0027] Furthermore, the mass percentage of silicon carbide nanoparticles in the silicon-carbon anode material is preferably 5%-20%, and the mass percentage of silicon nanoparticles is 45%-50%.

[0028] A third aspect of the present invention provides a secondary battery comprising the silicon-carbon anode material described in the second aspect.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention provides a method for preparing silicon-carbon anode materials. First, silicon carbide nanoparticles are introduced during the in-situ polymerization preparation of a porous carbon precursor (phenolic resin). After carbonization and alkali activation treatment, a porous carbon C-SiC uniformly doped with silicon carbide nanoparticles is formed. The uniform doping of silicon carbide nanoparticles in the porous carbon substrate significantly improves the mechanical strength of the porous carbon substrate. Further, an in-situ doped silicon-carbon anode material with nano-silicon carbide is prepared through CVD vapor-phase silicon infiltration and carbon coating processes. The above preparation method is simple to operate, the process is controllable, and the raw material cost is low, making it suitable for mass production. More importantly, the silicon-carbon anode material prepared by the above method has high compressive strength, effectively avoiding the breakage of the anode material during battery rolling and effectively suppressing the problem of silicon nanoparticle expansion leading to pulverization of the anode material during charge-discharge cycles, thereby improving the electrochemical performance and cycle life of the battery.

[0030] The silicon-carbon anode material prepared by the above method not only has high compressive strength, but also provides a certain capacity due to the large specific surface area of ​​the silicon carbide nanoparticles introduced, which allows lithium ions to be intercalated between silicon and carbon atoms. This enables the anode material to effectively improve the cycle performance of the battery without sacrificing the specific capacity. Detailed Implementation

[0031] The present invention will be further described below with reference to specific embodiments, so that those skilled in the art can better understand and implement the present invention, but the embodiments are not intended to limit the present invention.

[0032] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The terms “comprising” or “including” used in this invention may also be replaced with the closed form “is” or “consisting of”.

[0033] As described in the background section, current silicon-carbon anode materials suffer from problems such as difficulty in achieving uniform and tight bonding between silicon and carbon, and low compressive strength. During the rolling process in battery fabrication, and under the enormous internal stress generated by silicon expansion during cycling, the material structure is prone to collapse, failing to provide a stable and robust binding space for the volume expansion of silicon, resulting in continuous growth of the SEI film and rapid capacity decay.

[0034] To address the above problems, this invention provides a method for preparing a silicon-carbon anode material, comprising the following steps: (1) Silicon carbide nanoparticles, alkaline reagents and dispersants are dispersed in water to obtain slurry A; phenolic monomers, aldehyde monomers and initiators are dispersed in water to obtain slurry B; (2) Mix and stir the slurry A and the slurry B, and then heat and cure to obtain phenolic resin doped with silicon carbide nanoparticles; (3) The phenolic resin doped with silicon carbide nanoparticles is subjected to carbonization treatment, and the carbonization product is subjected to alkali activation treatment with a strong alkali. After cooling and crushing, porous carbon particles doped with silicon carbide nanoparticles are obtained. (4) The porous carbon particles doped with silicon carbide nanoparticles are placed in a reactor and silicon deposition and carbon deposition are performed sequentially by chemical vapor deposition to obtain the silicon-carbon anode material.

[0035] Since the ability of vapor-deposited silicon-carbon anodes to suppress expansion depends on the porous carbon substrate itself, and while the abundant pores formed during the preparation of the porous carbon substrate are beneficial for the deposition of nano-silicon, they also weaken the overall mechanical strength of the carbon material. This makes it difficult for such silicon-carbon anode materials to maintain structural stability during the rolling process and charge-discharge cycling of batteries. Therefore, this invention aims to improve the mechanical strength of the porous carbon substrate in silicon-carbon anode materials by introducing silicon carbide nanoparticles during the in-situ polymerization of phenolic resin. After carbonization and alkali activation treatment, a porous carbon C-SiC with uniformly doped silicon carbide nanoparticles is formed. The uniform doping of silicon carbide nanoparticles in the porous carbon substrate greatly improves the mechanical strength of the porous carbon substrate. Simultaneously, the nanoscale silicon carbide has a large specific surface area and a large number of exposed silicon atoms, allowing lithium ions to intercalate between silicon and carbon atoms, thus providing a certain capacity. Based on the aforementioned porous carbon C-SiC with uniformly doped silicon carbide nanoparticles, a silicon-carbon anode material is further prepared through CVD vapor-phase silicon infiltration and carbon coating processes. The silicon-carbon anode material prepared by the above method has high compressive strength and high specific capacity, which can effectively reduce the full-charge expansion of the anode sheet, thereby improving the cycle performance of the battery.

[0036] In step (1) of the present invention, the particle size D50 of silicon carbide nanoparticles is preferably 20-100 nm, such as 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, etc., including but not limited to the values ​​listed above.

[0037] In some preferred embodiments of the present invention, silicon carbide nanoparticles are obtained by ball milling silicon powder and graphite powder under a protective atmosphere, including but not limited to nitrogen, to prevent silicon powder from oxidizing and forming silicon dioxide. Preferably, the molar ratio of silicon powder to graphite powder is 1:(1-2), the ball milling media used is 5-15 mm steel balls, the ball-to-material ratio is (15-30):1, the ball milling speed is 600-1000 r / min, and the ball milling time is 20-120 h, such as 20 h, 30 h, 40 h, 50 h, 60 h, 70 h, 80 h, 90 h, 100 h, 110 h, 120 h, etc., to obtain silicon carbide nanoparticles of different particle sizes.

[0038] In step (1) of this invention, the alkaline reagent includes, but is not limited to, one or more of ammonia, sodium hydroxide, and potassium hydroxide; the dispersant includes, but is not limited to, one or more of polyethyleneimine, methyltriethoxysilane, vinyltriethoxysilane, N-(β-aminoethyl)-γ-aminopropyltrimeth(eth)oxysilane, γ-(2,3-epoxypropoxy)propyltrimethoxysilane, 3-aminopropyltriethoxysilane, and γ-(methacryloyloxy)propyltrimethoxysilane. Adding an appropriate amount of alkaline reagent makes the solution alkaline to adjust the solution potential, thereby obtaining slurry A with better dispersibility; preferably, the pH of slurry A is preferably 8-11, for example, pH 8, 9, 10, or 11.

[0039] In step (1) of the present invention, the preferred mass ratio of silicon carbide nanoparticles, dispersant and water is (1-2):(0.5-1):(10-20); in some preferred embodiments, the dispersant is polyethyleneimine and the mass ratio of silicon carbide nanoparticles, dispersant and water is 1.5:1:10.

[0040] In step (1) of this invention, the phenolic monomer can be selected from one or more of phenol, resorcinol, methylphenol, and aminophenol, the aldehyde monomer can be selected from one or more of formaldehyde, acetaldehyde, furfural, and paraformaldehyde, and the initiator includes, but is not limited to, one or more of ammonia, sodium hydroxide, potassium hydroxide, and ethylenediamine.

[0041] In step (1) of the present invention, the preferred mass ratio of phenolic monomer, aldehyde monomer, initiator and water is (7-10):(3-5):(0.09-0.18):(10-20), more preferably, the molar ratio of phenolic monomer to aldehyde monomer is 1:(0.5-1); in some preferred embodiments, the phenolic monomer is phenol, the aldehyde monomer is formaldehyde, the initiator is ammonia, and the mass ratio of phenolic monomer, aldehyde monomer, initiator and water is 7:3:0.1:10.

[0042] In step (2) of this invention, the preferred mass ratio of slurry A to slurry B is (0.8-3.3):1000, for example, 0.8:1000, 1.5:1000, 3.2:1000, etc. Preferably, slurry A and slurry B are stirred at 40-60 ℃ (for example, 50 ℃) for 1-3 h (for example, 2 h) to make them uniformly mixed, and then heated and cured at 100-200 ℃ for 5-10 h to obtain phenolic resin doped with silicon carbide nanoparticles.

[0043] In step (3) of this invention, the carbonization process is carried out under a protective atmosphere, which includes, but is not limited to, nitrogen. The preferred temperature for the carbonization process is 700-1000 ℃, and the preferred time is 1-3 h. In some preferred embodiments, phenolic resin doped with silicon carbide nanoparticles is placed in a tube furnace, and nitrogen flow rate is set to 0.5-2 L / min for 1-2 h. Then, the nitrogen flow rate is reduced to 0.1-0.5 L / min, and the temperature is increased to 700-1000 ℃ (e.g., 700 ℃, 800 ℃, 900 ℃, 1000 ℃, etc.) at a heating rate of 2-5 ℃ / min. The carbonization process is carried out for 1-3 h (e.g., 1 h, 2 h, 3 h, etc.), and the carbonized product is obtained after natural cooling.

[0044] In step (3) of this invention, the carbonization product is mixed with a strong alkali at a mass ratio of 1:(1-4), such as 1:1, 1:2, 1:3, 1:4, etc., and the strong alkali can be selected from potassium hydroxide and / or sodium hydroxide. In the alkali activation treatment step: the temperature is first raised to 350-450 ℃ (e.g., 350 ℃, 400 ℃, 450 ℃, etc.) and held for 0.5-2 h (e.g., 0.5 h, 1 h, 1.5 h, 2 h, etc.), and then the temperature is raised to 700-900 ℃ (e.g., 700 ℃, 800 ℃, 900 ℃, etc.) and held for 0.5-2 h (e.g., 0.5 h, 1 h, 1.5 h, 2 h, etc.). By mixing the carbonization product with a strong alkali for alkali activation treatment, porous carbon particles with porous structures of doped silicon carbide nanoparticles are formed to buffer the deformation of the negative electrode material during charging and discharging. It is important to note that the amount of strong alkali used should not be too much or too little. If the amount is too little, it will not be able to form a sufficient pore structure to accommodate silicon nanoparticles and effectively buffer deformation. If the amount is too much, the porosity will be too high, the compressive strength of the porous carbon substrate will be reduced, and the cycling performance of the material will be affected.

[0045] In some preferred embodiments, the carbonization product is uniformly mixed with strong alkali powder and placed in a crucible, which is then placed in a tube furnace. Nitrogen gas flow rate is set at 0.5-2 L / min for 1-3 h, then the nitrogen gas flow rate is reduced to 0.1-0.5 L / min, and the temperature is increased to 350-450 °C at a heating rate of 2-5 °C / min and held for 0.5-2 h. Then the temperature is increased to 700-900 °C at a heating rate of 5-10 °C / min and activated for 0.5-2 h.

[0046] In step (3) of the present invention, the particle size D50 of the porous carbon particles doped with silicon carbide nanoparticles is preferably 5-10 μm, such as 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, etc., including but not limited to the values ​​listed above.

[0047] In step (4) of this invention, in the step of sequentially performing silicon deposition and carbon deposition using chemical vapor deposition: the temperature is increased to 400-600 ℃ at 2-5 ℃ / min (for example, increased to 500 ℃ at 2 ℃ / min), and a first mixed gas containing gaseous silicon source and nitrogen is introduced into the reactor for vapor deposition for 6-10 h; after silicon deposition is completed, a second mixed gas containing gaseous carbon source and nitrogen is introduced for vapor deposition for 1-3 h.

[0048] Preferably, the volume ratio of gaseous silicon source to nitrogen in the first mixed gas is (2-4):1, for example, 2:1, 3:1, 4:1, etc.; the volume ratio of gaseous carbon source to nitrogen in the second mixed gas is preferably (2-4):1, for example, 2:1, 3:1, 4:1, etc.; more preferably, the gaseous silicon source is selected from one or more of silane, silane, trichlorosilane, dichlorosilane, propane, trichlorosilane, and silicon chloride; the gaseous carbon source is selected from one or more of acetylene, methane, ethane, and ethylene.

[0049] The present invention also provides a silicon-carbon anode material prepared by the above-described preparation method. This silicon-carbon anode material includes a porous carbon core, silicon nanoparticles uniformly deposited within and on the outer surface of the porous carbon core pores, and a carbon coating layer. The porous carbon core comprises a porous carbon matrix and silicon carbide nanoparticles embedded in the carbon matrix of the porous carbon matrix.

[0050] In this invention, the particle size D50 of the porous carbon core is preferably 5-10 μm, such as 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, etc.; the particle size D50 of the silicon carbide nanoparticles is preferably 20-100 nm, such as 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, etc.; the thickness of the carbon coating layer is preferably 20-100 nm, such as 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, etc.

[0051] More preferably, the ratio of the particle size D50 of the silicon-carbon anode material to the particle size D50 of the silicon carbide nanoparticles is preferably 60-450, such as 60, 100, 200, 300, 400, 450, etc., including but not limited to the ratios listed above. By controlling the ratio of the two particle sizes within a suitable range, such as 60-450, a silicon-carbon anode material with both high capacity and high compressive strength can be obtained. If the particle size of the silicon carbide nanoparticles is too small, the ratio of the two will be too large, which will not effectively improve its strength. If the particle size of the silicon carbide nanoparticles is too large, the ratio of the two will be too small, which will cause a loss of the bulk material (carbon, silicon) proportion, resulting in poor specific capacity performance.

[0052] In this invention, the preferred mass percentage of silicon carbide nanoparticles in the silicon-carbon anode material is 5%-20%, such as 5%, 10%, 15%, 20%, etc., including but not limited to the mass percentages listed above. The silicon-carbon anode material prepared by this invention should not contain too many or too few silicon carbide nanoparticles. If there are too few silicon carbide nanoparticles, the compressive strength of the silicon-carbon anode material cannot be effectively improved; if there are too many silicon carbide nanoparticles, the compressive strength will decrease. During the in-situ doping process, excessive addition of nano-silicon carbide leads to uneven dispersion and significant agglomeration, which in turn affects the overall compressive strength of the material and the specific capacity of the anode material.

[0053] In this invention, the mass ratio of silicon nanoparticles in the silicon-carbon anode material is preferably 45%-50%, which enables the prepared silicon-carbon anode material to have high capacity while maintaining structural stability during charging and discharging.

[0054] The present invention also provides a secondary battery comprising the aforementioned silicon-carbon anode material. This secondary battery not only has high capacity but also exhibits minimal electrode rebound when fully charged and excellent cycle stability.

[0055] In the following examples and comparative examples, the particle size of silicon carbide nanoparticles and silicon-carbon anode materials was tested using a Malvern laser particle size analyzer. Example 1

[0056] This embodiment relates to the preparation of a silicon-carbon anode material, as detailed below: Preparation of silicon carbide nanoparticles: Silicon powder and graphite powder were mixed in a molar ratio of 1:1.5 to form a powder mixture, which was then added to a ball mill jar along with steel balls with a diameter of 10 mm. The ball-to-particle mass ratio was 20:1. Nitrogen gas was introduced into the ball mill jar as a protective gas to prevent the silicon powder from oxidizing and forming silicon dioxide. The ball mill jar was rotated at 800 r / min for 40 h to prepare silicon carbide nanoparticles with a D50 of 40 nm.

[0057] Preparation of phenolic resin doped with silicon carbide nanoparticles: 1.5 kg of silicon carbide nanoparticles, 10 L of water, 150 mL of ammonia, and 1 kg of polyethyleneimine (PEI) were added to a reactor. Stirring was started at 800 r / min for 3 h to obtain silicon carbide nanoparticle slurry A. 7 kg of phenol, 3 kg of formaldehyde solution, 0.1 L of ammonia, and 10 L of water were added to the reactor. Stirring was started at 200 rpm / min for 2 h to obtain phenolic solution B. Slurry A (0.02 kg) and solution B (25 kg) were mixed at a mass ratio of 0.8:1000. The mixture was stirred at 50 ℃ for 2 h, then quickly dispensed into suitable containers and placed in a box furnace. The furnace was heated to 170 ℃ and cured for 10 h to obtain solid resin. The solid resin was mechanically pulverized into small particles to obtain resin doped with silicon carbide nanoparticles.

[0058] Preparation of porous carbon particles doped with silicon carbide nanoparticles: The resin sample doped with silicon carbide nanoparticles prepared in step (2) was placed in a tube furnace, and nitrogen flow was set at 2 L / min for 2 h. Then, the nitrogen flow rate was reduced to 0.5 L / min, and the temperature was increased to 900 °C at a heating rate of 5 °C / min for 2 h. After natural cooling, the carbonized material was obtained. The above carbonized material was mixed with KOH powder at an alkali-to-carbon ratio of 1:2 and placed in a nickel crucible. Then, it was placed in a tube furnace, and nitrogen flow was set at 0.5 L / min for 1 h. Then, the nitrogen flow rate was reduced to 0.5 L / min, and the temperature was increased to 450 °C at a heating rate of 5 °C / min for 0.5 h. Then, the temperature was increased to 900 °C at a heating rate of 5 °C / min for 12 h. After natural cooling, porous carbon particles doped with silicon carbide nanoparticles were obtained.

[0059] Preparation of silicon-carbon anode material: The porous carbon particles doped with silicon carbide nanoparticles prepared in step (3) are placed in a rotary furnace, and the nitrogen flow rate is set to 13 L / min for 1 h. The nitrogen flow rate is then reduced to 1 L / min, and the temperature is increased to 500 ℃ at 2 ℃ / min. A gaseous silicon source is introduced, and silicon is deposited using chemical vapor deposition. The ratio of gaseous silicon source to nitrogen flow rate is 2:1, and the vapor deposition lasts for 10 h. After the silicon deposition is completed, the valve of the gaseous silicon source is closed, the nitrogen flow rate remains unchanged, and gaseous carbon source methane is introduced. The gaseous carbon source flow rate is 1 L / min, and the vapor deposition lasts for 2 h. The material is then cooled and discharged to obtain the silicon-carbon anode material. Example 2

[0060] This embodiment relates to the preparation of a silicon-carbon anode material. The only difference from Example 1 is that in step (2), slurry A (0.038 kg) and solution B (25 kg) are mixed at a mass ratio of 1.5:1000. All other operations are the same, and the corresponding silicon-carbon anode material is prepared. Example 3

[0061] This embodiment relates to the preparation of a silicon-carbon anode material. The only difference from Example 1 is that in step (2), slurry A (0.08 kg) and solution B (25 kg) are mixed at a mass ratio of 3.2:1000. All other operations are the same, and the corresponding silicon-carbon anode material is prepared. Example 4

[0062] This embodiment relates to the preparation of a silicon-carbon anode material. The only difference from Example 1 is that in step (2), slurry A (0.093 kg) and solution B (25 kg) are mixed at a mass ratio of 3.7:1000. All other operations are the same, and the corresponding silicon-carbon anode material is prepared. Example 5

[0063] This embodiment relates to the preparation of a silicon-carbon anode material. The only difference from Example 1 is that the ball milling time in step (1) is 60 h, and the particle size D50 of the prepared silicon carbide nanoparticles is 30 nm. All other operations are the same, and the corresponding silicon-carbon anode material is prepared. Example 6

[0064] This embodiment relates to the preparation of a silicon-carbon anode material. The only difference from Example 1 is that the ball milling time in step (1) is 100 h, and the particle size D50 of the prepared silicon carbide nanoparticles is 16 nm. The other operations are the same, and the corresponding silicon-carbon anode material with a particle size D50 of 8 μm is prepared. Example 7

[0065] This embodiment relates to the preparation of a silicon-carbon anode material. The only difference from Example 1 is that the ball milling time in step (1) is 10 h, and the particle size D50 of the prepared silicon carbide nanoparticles is 160 nm. All other operations are the same, and the corresponding silicon-carbon anode material is prepared. Comparative Example 1

[0066] This comparative example relates to the preparation of a silicon-carbon anode material. The only difference from Example 1 is that silicon carbide nanoparticles were not introduced, and solid resin was directly prepared from phenolic solution B. All other operations were the same, and the corresponding silicon-carbon anode material was obtained. Comparative Example 2

[0067] This comparative example relates to the preparation of a silicon-carbon anode material. The only difference from Example 1 is that in step (2), silicon carbide nanoparticles are directly mixed with phenolic resin, as follows: 7 kg of phenol, 3 kg of formaldehyde solution, 0.1 L of ammonia, and 1 L of water were added to a reaction vessel. Stirring was started at 200 rpm / min for 2 h to obtain a phenolic solution. The solution was then stirred at 50 °C for 2 h. The solution was quickly dispensed into suitable containers and placed in a box furnace. The furnace was heated to 170 °C and cured for 10 h. The solid resin was mechanically pulverized into resin B with a particle size of approximately 8 μm. Resin B powder and silicon carbide nanoparticles were added to a mixer at a mass ratio of 100:6. Stirring was started for physical blending to obtain a resin mixture containing silicon carbide nanoparticles.

[0068] The remaining operations were the same, and the corresponding silicon-carbon anode material was prepared. Performance Testing and Applications

[0069] The silicon carbide content and compressive strength of the silicon-carbon anode materials prepared in the above embodiments and comparative examples were tested, as follows: Silicon carbide content test: All silicon-carbon anodes of the above examples and comparative examples were digested with aqua regia. After digestion, the insoluble matter was filtered out. Finally, the silicon content was tested by ICP. Since silicon carbide hardly reacts with aqua regia at room temperature, it can be filtered out.

[0070] Compressive Strength Test: The compressive strength of the spherical silicon-carbon anode material is characterized using a single-particle strength tester. The specific method is as follows: A micro-compression testing machine is used. The sample to be tested is placed in the fixture and clamped. The required compressive strength test is selected, and appropriate test parameters are set. The compressive strength of the material is determined by characterizing the strength of particle breakage. Test Principle: A flat indenter with a diameter of 50 μm is selected. The sample is clamped in the middle using two indicators, and the sample is measured in increments of 0.1 μm (when using a ×50 objective lens) until it reaches 200 μm. A test force with a constant rate of increase is applied to the sample, which is then fixed between the upper pressure bar and the lower pressure plate. The deformation of the sample is then automatically measured. The test force can be set to 9.8 mN. The pressure and deformation during the sample deformation process are measured and recorded. The obtained data are plotted on the x-axis as compressive displacement and on the y-axis as test force. The compressive strength of the material is calculated by taking the test force at the inflection point of the curve.

[0071] The test results are shown in Table 1 below: Table 1

[0072] In the table, M1 represents the mass of silicon carbide, M2 represents the mass of silicon-carbon anode material, D2 represents the particle size D50 of silicon-carbon anode material, and D1 represents the particle size D50 of silicon carbide nanoparticles.

[0073] Lithium-ion batteries were prepared using the silicon-carbon anode materials prepared in the above embodiments and comparative examples as anode active materials. The specific capacity, full-charge electrode rebound, and cycle performance of each lithium-ion battery were tested, as detailed below: Specific capacity test: The silicon-carbon anode materials prepared in the above examples and comparative examples were mixed in a mass ratio of silicon-carbon composite material (anode active material): polyacrylic acid resin (PAA): carbon nanotubes (CNT): conductive carbon black (SP) of 82:7:1:10. The mixture was prepared into a slurry with deionized water and uniformly coated on copper foil. The mixture was then vacuum dried at 80 °C for 24 h to obtain the battery electrode for the experiment. A lithium sheet was used as the counter electrode, and a 1.1 mol / L LiPF6 electrolyte was used. The solvent was a four-component mixed solvent with ethylene carbonate (EC): vinylene carbonate (VC): dimethyl carbonate (DMC): fluoroethylene carbonate (FEC) = 1:1:1:1. A polypropylene microporous membrane was used as the separator, and the cells were assembled into CR2025 coin cells in a vacuum glove box. Constant current charge-discharge test was performed on the Blue Electricity Tester. The charge-discharge steps were as follows: constant current 0.1 C discharge to 5 mV, then constant current 0.02 C discharge to 5 mV, and constant current 0.1 C charge to 2 V. The capacity of the coin cell was measured. The specific capacity of the silicon-carbon anode material was calculated according to the formula: specific capacity = capacity / mass of anode active material.

[0074] Preparation of lithium-ion batteries: The negative electrode consists of 94% silicon-carbon negative electrode material and graphite mixed active material (the silicon-carbon negative electrode material is mixed at a ratio of 25%), 1.5% carbon black conductive agent, 0.05% carbon nanotubes, and 5% sodium carboxymethyl cellulose. The preparation process involves adding deionized water to the active material, conductive agent, and binder, stirring, adjusting the viscosity to obtain a negative electrode slurry, coating it on at least one side of the negative electrode copper foil current collector, drying, and pressing to obtain a silicon negative electrode sheet with a thickness of 100 μm. The positive electrode consists of 97% high-nickel ternary positive electrode material (NMC622, chemical formula LiNi). 0.6 Mn 0.2 Co 0.2 The battery consists of 0.08% carbon black conductive agent, 2% carbon black conductive agent, 0.08% CNT, and 1% PVDF binder. The preparation process involves adding active material, conductive agent, binder, and solvent NMP, stirring, adjusting viscosity to obtain a positive electrode slurry, coating it on at least one side of the positive electrode aluminum foil current collector, drying, and pressing it into a sheet to obtain the positive electrode sheet. The silicon negative electrode sheet, separator (polypropylene microporous film), and positive electrode sheet are wound to obtain the battery cell. The battery cell is then assembled into a battery case, dried, and injected with electrolyte (1 mol / L LiPF6 electrolyte, the solvent is a four-component mixed solvent, ethylene carbonate (EC): vinylene carbonate (VC): dimethyl carbonate (DMC): fluoroethylene carbonate (FEC) = 1:1:1:1), encapsulated, formed, and capacity tested to obtain a lithium-ion battery.

[0075] Full charge electrode rebound test: Using the Blue Battery testing system, the above lithium-ion battery was placed at 25 ℃ for 5 minutes, discharged at 1C constant current to 2.5 V, placed for 15 minutes, charged at 1C constant current to 3.65 V, and then charged at 3.65 V constant voltage to ≤0.05 C. After being placed for 5 minutes, the electrode was disassembled to test the thickness d1 of the negative electrode. Full charge electrode rebound = (d1-d0) / d0×100%, where d0 is the initial thickness of the negative electrode.

[0076] 25℃ Cycle Test: The above lithium-ion battery was charged to 3.65 V at 25℃ using a constant current and constant voltage of 1C, and left to stand for 30 minutes. Then it was discharged to 2.5 V using a constant current of 1C, and left to stand for 30 minutes. The capacity was recorded as the initial discharge capacity. The above steps were repeated until the capacity decayed to 80% of the initial discharge capacity. The number of cycles was recorded.

[0077] The test results are shown in Table 2 below: Table 2

[0078] As shown in Tables 1 and 2, compared with the silicon-carbon anode material prepared without silicon carbide nanoparticles in Comparative Example 1, the compressive strength of the silicon-carbon anode materials prepared in Examples 1-7 is significantly improved, and the cycle performance of the prepared lithium-ion batteries is better. Among them, the silicon-carbon anode materials prepared by introducing appropriate amounts and sizes of silicon carbide nanoparticles (Examples 1, 2 and 5) have higher specific capacity and the full-charge electrode rebound is greatly improved.

[0079] Furthermore, as shown in Examples 1-4, the compressive strength of the prepared silicon-carbon anode material initially increases and then decreases with the increase of silicon carbide nanoparticle addition. This is because excessive addition of silicon carbide nanoparticles during the in-situ doping process leads to uneven dispersion and agglomeration, which in turn affects the compressive strength of the material. Table 2 shows that, compared to Comparative Example 1, adding a small amount of silicon carbide nanoparticles is beneficial to improving the specific capacity of the silicon-carbon anode material. However, with the increase of the addition amount, the specific capacity gradually decreases, even falling below that of Comparative Example 1. Correspondingly, the full-charge electrode rebound rate of the lithium-ion battery initially decreases and then increases with the increase of silicon carbide nanoparticle addition. The overall cycle performance of the prepared battery also shows an initial increase followed by a decrease. Preferably, the content of silicon carbide nanoparticles in the silicon-carbon anode material is less than 20%.

[0080] As can be seen from Examples 1 and 5-7, the particle size of the introduced silicon carbide nanoparticles affects the compressive strength of the silicon-carbon anode material and the cycle performance of the lithium-ion battery constructed from the silicon-carbon anode material. If the particle size of the silicon carbide nanoparticles is too small (Example 6), it cannot effectively improve the problem of full-charge electrode rebound. If the particle size is too large (Example 7), although it can effectively alleviate the problem of full-charge electrode rebound, the specific capacity is significantly reduced.

[0081] Furthermore, as can be seen from Example 1 and Comparative Example 2, compared to Example 1 which added silicon carbide nanoparticles during the in-situ polymerization of resin, the silicon-carbon anode material prepared by directly physical blending silicon carbide nanoparticles with resin in Comparative Example 2 not only showed no improvement in compressive strength compared to the silicon-carbon anode material prepared without the introduction of silicon carbide nanoparticles (Comparative Example 1), but also exhibited a significant decrease in specific capacity. In fact, the cycle performance of the prepared lithium-ion battery decreased. This is because the physically blended silicon carbide nanoparticles degrade the conductivity between the electrode layer particles, resulting in severe polarization, significant loss of specific capacity, and deterioration of cycle performance.

[0082] The above-described embodiments are merely preferred embodiments provided to fully illustrate the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the claims.

Claims

1. A method for preparing a silicon-carbon anode material, characterized in that, Includes the following steps: (1) Silicon carbide nanoparticles, an alkaline reagent and a dispersant are dispersed in water to obtain slurry A; phenolic monomers, aldehyde monomers and an initiator are dispersed in water to obtain slurry B; the dispersant includes one or more of polyethyleneimine, methyltriethoxysilane, vinyltriethoxysilane, N-(β-aminoethyl)-γ-aminopropyltrimeth(eth)oxysilane, γ-(2,3-epoxypropoxy)propyltrimethoxysilane, 3-aminopropyltriethoxysilane and γ-(methacryloyloxy)propyltrimethoxysilane; the mass ratio of silicon carbide nanoparticles, dispersant and water is (1-2):(0.5-1):(10-20); (2) The slurry A and the slurry B are mixed and stirred to react, and then heated and cured to obtain phenolic resin doped with silicon carbide nanoparticles; the mass ratio of the slurry A to the slurry B is (0.8-3.3):1000; (3) The phenolic resin doped with silicon carbide nanoparticles is subjected to carbonization treatment, and the resulting carbonization product is subjected to alkali activation treatment with a strong alkali. After cooling and pulverization, porous carbon particles doped with silicon carbide nanoparticles are obtained. The carbonization treatment temperature is 700-1000 ℃ and the time is 1-3 h. In the alkali activation treatment step: the temperature is first raised to 350-450 ℃ and kept at that temperature for 0.5-2 h, and then the temperature is raised to 700-900 ℃ and kept at that temperature for 0.5-2 h. (4) The porous carbon particles doped with silicon carbide nanoparticles are placed in a reactor and silicon deposition and carbon deposition are performed sequentially by chemical vapor deposition to obtain the silicon-carbon anode material.

2. The preparation method according to claim 1, characterized in that, Step (1) must include at least one of the following features: (1) The particle size D50 of the silicon carbide nanoparticles is 20-100 nm; (2) The alkaline reagent includes one or more of ammonia, sodium hydroxide, and potassium hydroxide; (3) The pH of the slurry A is 8-11: (4) The phenolic monomers are selected from one or more of phenol, resorcinol, methylphenol, and aminophenol; the aldehyde monomers are selected from one or more of formaldehyde, acetaldehyde, furfural, and paraformaldehyde; and the initiator includes one or more of ammonia, sodium hydroxide, potassium hydroxide, and ethylenediamine. (5) The mass ratio of the phenolic monomer, aldehyde monomer, initiator and water is (7-10): (3-5): (0.09-0.18): (10-20).

3. The preparation method according to claim 1, characterized in that, In step (2), the temperature of the stirring reaction is 40-60 ℃ and the time is 1-3 h; The heating and curing temperature is 100-200 ℃, and the time is 5-10 h.

4. The preparation method according to claim 1, characterized in that, Step (3) must include at least one of the following features: (1) The carbonization process is carried out under a protective atmosphere, which includes nitrogen; (2) The mass ratio of the carbonization product to the strong base is 1:(1-4), and the strong base is potassium hydroxide and / or sodium hydroxide; (3) The particle size D50 of the porous carbon particles doped with silicon carbide nanoparticles is 5-10 μm.

5. The preparation method according to claim 1, characterized in that, In step (4), the step of sequentially performing silicon deposition and carbon deposition using chemical vapor deposition is as follows: the temperature is increased to 400-600 ℃ at 2-5 ℃ / min, and a first mixed gas containing gaseous silicon source and nitrogen is introduced into the reactor for vapor deposition for 6-10 h; after silicon deposition is completed, a second mixed gas containing gaseous carbon source and nitrogen is introduced for vapor deposition for 1-3 h.

6. The preparation method according to claim 5, characterized in that, The volume ratio of gaseous silicon source to nitrogen in the first mixed gas is (2-4):1; The volume ratio of gaseous carbon source to nitrogen in the second mixed gas is (2-4):1; The gaseous silicon source is selected from one or more of silane, silane, trichlorosilane, dichlorosilane, propane, trichlorosilane, and silicon chloride; The gaseous carbon source is selected from one or more of acetylene, methane, ethane, and ethylene.

7. A silicon-carbon anode material, characterized in that, The silicon-carbon anode material is prepared by the preparation method according to any one of claims 1-6; the silicon-carbon anode material includes a porous carbon core, silicon nanoparticles uniformly deposited in the pores and outer surface of the porous carbon core, and a carbon coating layer, wherein the porous carbon core includes a porous carbon matrix and silicon carbide nanoparticles embedded in the carbon matrix of the porous carbon matrix.

8. The silicon-carbon anode material according to claim 7, characterized in that, The porous carbon core has a particle size D50 of 5-10 μm, and the carbon coating layer has a thickness of 20-100 nm. The ratio of the particle size D50 of the silicon-carbon anode material to the particle size D50 of the silicon carbide nanoparticles is 60-450. The silicon carbide nanoparticles in the silicon-carbon anode material account for 5%-20% of the mass, and the silicon nanoparticles account for 45%-50% of the mass.

9. A secondary battery, characterized in that, It includes the silicon-carbon anode material as described in claim 7 or 8.

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