Porous carbon material, preparation method thereof and silicon-carbon composite material

Abstract

The invention discloses a porous carbon material, a preparation method thereof and a silicon-carbon composite material, and relates to the technical field of battery materials. The method disclosed by the invention is simple in process and suitable for large-scale industrial production, the prepared porous carbon material has optimized pore size distribution and pore structure, more silane adsorption sites and stronger adsorption capacity, can accommodate more silicon and has excellent conductivity, and when the porous carbon material is used for preparing a silicon-carbon composite material, the silicon-carbon composite material can be used for preparing the silicon-carbon composite material. And the capacity, the charge-discharge efficiency, the rate capability and the cycle performance of the battery can be effectively improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of battery materials, and particularly relates to a porous carbon material, a preparation method thereof and a silicon-carbon composite material. BACKGROUND

[0002] With the continuous progress of science and technology, the demand for high-performance battery materials is increasing. As a highly potential battery anode material, silicon-carbon composite material has attracted much attention due to its high theoretical specific capacity. However, silicon has a huge volume change during charging and discharging, which easily leads to the pulverization and peeling of the electrode material, thereby reducing the cycle performance of the battery. Porous carbon material is considered as an effective carrier for improving the performance of silicon-carbon composite material due to its unique pore structure and good electrical conductivity.

[0003] At present, there are many methods for preparing porous carbon for silicon-carbon composite material, but there are still some deficiencies. For example, the specific surface area of the porous carbon prepared by some methods is small, and the pore structure is not ideal, which cannot provide enough accommodation space for silicon, thereby limiting the capacity improvement of the silicon-carbon composite material. In addition, the porous carbon prepared by conventional methods often has the problem of limited adsorption capacity for silane, which leads to poor electrical conductivity, low capacity, reduced initial efficiency and cycle performance, thereby affecting the comprehensive performance of the silicon-carbon composite material. Therefore, it is of great practical significance to develop a porous carbon material and a preparation method thereof which can further improve the performance of the silicon-carbon composite material. SUMMARY

[0004] Based on the technical problems existing in the background art, the present application provides a porous carbon material, a preparation method thereof and a silicon-carbon composite material.

[0005] The preparation method of the porous carbon material provided by the present application comprises the following steps:

[0006] S1, dissolving a carbon source in an organic solvent, then adding a metal boride and a boric acid solution, and heating and stirring to react to obtain a precursor composite A, wherein the mass ratio of the metal boride, the boric acid and the carbon source is 1:1-20:1-20; the carbon source is at least one of organic compounds containing multiple hydroxyl groups and / or multiple carboxyl groups;

[0007] S2, heating and pyrolyzing the precursor composite A in a protective gas atmosphere to obtain a product B;

[0008] S3, mixing the product B with a sulfur-containing organic compound and elemental phosphorus, and then heating at 400-800 DEG C under vacuum for 8-16 h to obtain a product C; the mass ratio of the product B, the sulfur-containing organic compound and the elemental phosphorus is 100:1-10:1-10;

[0009] S4. In a protective atmosphere, water vapor is introduced into the product C for heating and activation, and then the product is pulverized to obtain the porous carbon material.

[0010] The preparation method of this invention first involves heating and stirring a carbon source with a metal boride and boric acid in a solvent. Boric acid reacts with the hydroxyl or carboxyl groups in the carbon source via esterification or condensation to form a precursor complex with a three-dimensional network structure. This complex is then subjected to pyrolysis, sulfur and phosphorus doping, steam activation, and pulverization to obtain a porous carbon material. The metal boride undergoes a phase transition, transforming from a two-dimensional layered structure to a three-dimensional framework structure, thus creating mesopores. Furthermore, the metal boride introduces metal elements, providing more catalytic sites for subsequent steam activation and pore formation, altering the pore structure and surface chemistry of the porous carbon, and increasing the adsorption sites and adsorption energy for silanes. This allows for the inclusion of more silicon during subsequent silane deposition, thereby increasing the capacity of the silicon-carbon material. At high temperatures, it can also form partial transition metal carbides and boron carbide with the carbon source, improving the material's toughness, mitigating silicon volume expansion, reducing electrode pulverization, improving cycle performance, and constructing a conductive network to promote electron transport. The doping of metal elements also enhances the conductivity of the porous carbon material, facilitating electron transport during battery charging and discharging and reducing battery internal resistance. This improves the charge / discharge efficiency and rate performance of the battery. Boric acid forms a network structure through cross-linking with the carbon source, guiding material growth and thus adjusting the pore structure. Boric acid also decomposes at high temperatures to form boron trioxide and water. Boron trioxide is dissolved and removed during subsequent water vapor activation, forming pores. Water can act as a physical activator at high temperatures, etching carbon materials through high-temperature vaporization to form micropores and mesopores, which is more conducive to silicon deposition and buffering of volume changes. At the same time, it increases the specific surface area of ​​porous carbon, increases the contact area with the electrolyte, and improves the electrochemical performance of the battery. The introduction of sulfur and phosphorus elements not only improves performance by changing electron distribution, forming surface functional groups, and inducing defects, but also promotes the subsequent water vapor activation pore-forming process, helping to form more micropores and mesopores. Through the synergistic effect of the above processes, the pore structure of porous carbon materials can be effectively optimized, forming more micropores and mesopores, increasing the specific surface area and pore volume. The resulting porous carbon materials have a suitable pore size distribution and excellent pore structure. This structure not only increases the contact area between the carbon material and the electrolyte, which is conducive to ion diffusion, but also shortens the solid-state diffusion distance of ions, providing a fast channel for electron transfer. Thus, when this porous carbon material is used to prepare silicon-carbon composite materials, it can effectively improve the battery capacity, charge-discharge efficiency, rate performance, and cycle performance.

[0011] Preferably, in step S1, the heating and stirring reaction is carried out at a temperature of 80-120°C for 2-12 hours. By controlling the heating and stirring temperature and time, the resulting precursor complex can be made more uniform, thereby further improving the pore structure of the porous carbon material and enhancing its electrochemical performance.

[0012] Preferably, the mass ratio of the carbon source to the organic solvent is 1:2 to 10.

[0013] Preferably, the boric acid solution has a mass concentration of 0.5% to 5%.

[0014] In S1, the carbon source is at least one of an organic compound containing multiple hydroxyl and / or multiple carboxyl groups. The types of organic compounds containing multiple hydroxyl and / or multiple carboxyl groups are conventionally selected, and this invention does not impose any special limitations on them. Preferably, the carbon source is selected from at least one of phenolic resin, asphalt, ethylene glycol, glucose, sucrose, and lignin.

[0015] In S1, the type of organic solvent is a conventional choice and can be adjusted according to actual needs; this invention does not impose any special restrictions on it. Preferably, the organic solvent is selected from at least one of anhydrous ethanol, acetone, toluene, xylene, trichloroethylene, and tetrahydrofuran.

[0016] In this invention, the boric acid solution is prepared using conventional methods, such as adding boric acid to a solvent and stirring until completely dissolved. Preferably, the solvent for the boric acid solution is selected from one or more of the following: ethanol, diethyl ether, glycerol, acetone, tetrahydrofuran, isopropylamine, hexane, methanol, benzene, dioxane, acetylacetone, carbon tetrachloride, chloroform, and ethyl acetate.

[0017] This invention controls the appropriate degree of crosslinking reaction by controlling the mass ratio of carbon source to organic solvent and the concentration of boric acid solution, thereby forming a uniform precursor complex, further improving the uniformity of porous carbon materials, and thus improving their electrochemical performance.

[0018] In this invention, the type of metal boride is conventionally selected, and no special limitation is imposed on it. Preferably, the metal boride is selected from at least one of aluminum boride, titanium boride, zirconium boride, and chromium boride.

[0019] In step S2, the heating and pyrolysis temperature and time can be adjusted according to actual needs. Preferably, in step S2, the heating and pyrolysis temperature is 300~1000℃ and the time is 1~10h.

[0020] Preferably, in S2, the protective gas is selected from at least one of nitrogen, argon, and helium.

[0021] In this invention, the types of sulfur-containing organic compounds and elemental phosphorus are conventionally selected, and this invention does not impose any special limitations on them. Preferably, the sulfur-containing organic compound is selected from at least one of thiourea, methanethiol, dimethyl sulfide, and thiophene; preferably, the elemental phosphorus is selected from at least one of red phosphorus, black phosphorus, and purple phosphorus.

[0022] In step S4, the purpose of introducing steam for heating and activation is to remove impurities from the pores of the carbon material and etch the carbon skeleton at high temperature, forming micropores, mesopores, and macropores. The temperature and time can be adjusted according to actual needs. Preferably, in step S4, the heating and activation temperature is 500~1200℃, and the time is 1~10h.

[0023] Preferably, in step S4, the material is pulverized to a D50 of 4~10 μm. By controlling the particle size of the porous carbon material, the material can have high mechanical strength and good adsorption performance, thereby further improving the material's capacity and cycle stability.

[0024] The present invention also proposes a porous carbon material, which is prepared by the aforementioned preparation method.

[0025] The present invention also proposes a silicon-carbon composite material, wherein the silicon-carbon composite material is made using the aforementioned porous carbon material as a substrate; the silicon-carbon composite material has a core-shell structure, wherein the core is a silicon-carbon material with a porous structure, and the outer shell is a carbon layer.

[0026] The preparation method of the silicon-carbon composite material can adopt conventional methods. For example, the preparation method of the silicon-carbon composite material includes: first, passing silicon source gas into the porous carbon material in a protective atmosphere for chemical vapor deposition, and then passing carbon source gas for chemical vapor deposition, thereby obtaining the composite material.

[0027] In this invention, the conditions for chemical vapor deposition using silicon source gas and carbon source gas are conventionally selected.

[0028] Preferably, the conditions for chemical vapor deposition by introducing silicon source gas are: deposition at 400~800℃ for 1~8 hours.

[0029] Preferably, the conditions for chemical vapor deposition by introducing carbon source gas are: deposition at 500~800℃ for 3~8 hours.

[0030] Preferably, the protective gas is selected from at least one of nitrogen, argon, and helium.

[0031] Preferably, the silicon source gas is at least one of silane, ethyl silane, and propane.

[0032] Preferably, the carbon source gas is selected from at least one of acetylene, ethylene, and methane.

[0033] The beneficial effects of this invention are as follows:

[0034] The preparation method of this invention first involves heating and stirring a carbon source with a metal boride and boric acid in a solvent to obtain a precursor composite. Then, through pyrolysis, sulfur and phosphorus doping, steam activation, and pulverization, a porous carbon material is obtained. This method is simple and suitable for large-scale industrial production. The resulting porous carbon material has an optimized pore size distribution and pore structure, more adsorption sites for silanes, stronger adsorption capacity, and can accommodate more silicon. It also exhibits excellent conductivity. When used in the preparation of silicon-carbon composite materials, it can effectively improve battery capacity, charge / discharge efficiency, rate performance, and cycle performance. Attached Figure Description

[0035] Figure 1 This is a SEM image of the porous carbon material prepared in Example 1 of the present invention.

[0036] Figure 2 The electrochemical performance test results of CR2016 coin cells assembled from the silicon-carbon composite material prepared in the embodiments of the present invention and the silicon-carbon material of Comparative Example 1 are shown.

[0037] Figure 3 The results of room temperature cycling tests on 4Ah pouch cells assembled from the silicon-carbon composite material prepared in the embodiments of the present invention and the silicon-carbon material of Comparative Example 1 are shown. Detailed Implementation

[0038] The technical solution of the present invention will now be described in detail through specific embodiments.

[0039] Example 1

[0040] Preparation of porous carbon materials:

[0041] S1. Add 50g of phenolic resin and 30g of ethylene glycol to 200g of anhydrous ethanol and stir at 60℃ for 2h until dissolved. Then add 10g of aluminum boride and a 1% boric acid solution (containing 15g of boric acid). Heat and stir at 80℃ for 3h to obtain precursor complex A.

[0042] S2. Precursor complex A is placed in a tube furnace and heated to 900°C at a heating rate of 5°C / min in a nitrogen atmosphere, and held at that temperature for 2 hours for pyrolysis to obtain product B.

[0043] S3. After mixing product B with thiourea and red phosphorus in a mass ratio of 50:1:1, the mixture was placed in a glass tube and sealed. Then, it was placed in a muffle furnace and heated at 400°C for 12 hours under vacuum to obtain product C.

[0044] S4. In a nitrogen atmosphere, water vapor is introduced into product C, and the product is heated and activated at 800°C for 1 hour. Then, it is pulverized until the D50 is 6 μm to obtain the final product.

[0045] The porous carbon material prepared above was subjected to SEM testing, and the obtained SEM images are shown below. Figure 1 As shown. By Figure 1 As can be seen, the particle size is relatively uniform, with a particle diameter of approximately 5 μm.

[0046] Preparation of silicon-carbon composite materials:

[0047] The porous carbon material prepared above was placed in a fluidized bed reactor, and silane was first introduced and deposited at 500°C for 4 hours. Then acetylene was introduced and deposited at 600°C for 4 hours to obtain the final product.

[0048] The silicon-carbon composite material prepared above was mixed with conductive carbon black (SP) and polyacrylonitrile binder LA133 in a mass ratio of 8:1:1 to obtain a negative electrode slurry. The negative electrode slurry was coated onto copper foil to obtain a negative electrode sheet. A positive electrode slurry was mixed with NCM622, conductive carbon black (SP), and PVDF (polyvinylidene fluoride) in a mass ratio of 8:1:1 to obtain a positive electrode slurry. The positive electrode slurry was coated onto aluminum foil to obtain a positive electrode sheet. CR2016 coin cells were assembled using the above negative and positive electrode sheets. The electrolyte was a 1 mol / L lithium hexafluorophosphate solution, and the solvent was a mixed solvent of EC (ethylene carbonate) and DMC (dimethyl carbonate), with a volume ratio of EC to DMC of 3:7. Electrochemical performance tests were performed. The test results are as follows: Figure 2 As shown in Table 1, at a current density of 0.1C, the battery made of the above silicon-carbon composite material has an initial discharge specific capacity of 2054.9 mAh / g, a charge specific capacity of 1904.7 mAh / g, and an initial coulombic efficiency of 92.7%.

[0049] Using NCM811 as the positive electrode active material and the silicon-carbon composite material prepared in Example 1 as the negative electrode active material, a 4Ah soft-pack battery was assembled by performing the following processes: slurry preparation, coating, rolling, slitting, die-cutting, stacking, electrode tab welding, top-side sealing, baking, and electrolyte injection. The electrolyte consisted of lithium hexafluorophosphate, ethylene fluorocarbonate, and a solvent, with lithium hexafluorophosphate at a concentration of 1 mol / L, ethylene fluorocarbonate at a mass fraction of 10%, and the solvent composed of EC and DMC in a volume ratio of 3:7. After capacity testing, a room-temperature cycling test was conducted at a 1C / 1C current density. The results are as follows: Figure 3 As shown, the capacity retention rate is 80% after 880 full battery cycles.

[0050] Example 2

[0051] Preparation of porous carbon materials:

[0052] S1. Add 60g asphalt and 40g ethylene glycol to 250g anhydrous ethanol and stir at 70℃ for 1.5h until dissolved. Then add 12g aluminum boride and a 2% boric acid solution (containing 20g boric acid). Heat and stir at 85℃ for 2.5h to obtain precursor complex A.

[0053] S2. Precursor complex A was placed in a tube furnace and heated to 950°C at a heating rate of 4°C / min in an argon atmosphere, and held at that temperature for 1.5 h for pyrolysis to obtain product B.

[0054] S3. After mixing product B with thiourea and black phosphorus in a mass ratio of 100:1:1, the mixture was placed in a glass tube and sealed. Then, it was placed in a muffle furnace and heated at 500°C for 10 hours under vacuum to obtain product C.

[0055] S4. In a nitrogen atmosphere, water vapor is introduced into product C, and the product is heated and activated at 850°C for 0.8 h. Then, it is pulverized until the D50 is 7 μm to obtain the final product.

[0056] Preparation of silicon-carbon composite materials:

[0057] The porous carbon material prepared above was placed in a fluidized bed reactor, and silane was first introduced and deposited at 550°C for 4 hours. Then acetylene was introduced and deposited at 600°C for 3 hours to obtain the final product.

[0058] Using the silicon-carbon composite material prepared above, CR2016 coin cells were assembled according to the method in Example 1, and their electrochemical performance was tested. The test results are shown in Table 1. At a current density of 0.1C, the battery made of the above silicon-carbon composite material had an initial discharge specific capacity of 2023.1 mAh / g, a charge specific capacity of 1859.2 mAh / g, and an initial coulombic efficiency of 91.9%.

[0059] Using the silicon-carbon composite material prepared above, a 4Ah soft-pack battery was assembled according to the method in Example 1. After capacity testing, it was subjected to room temperature cycling test at a current density of 1C / 1C. After 870 cycles of the full battery, the capacity retention rate was 80%.

[0060] Example 3

[0061] Preparation of porous carbon materials:

[0062] S1. Add 40g of phenolic resin, 20g of asphalt, and 35g of ethylene glycol to 180g of anhydrous ethanol and stir at 55℃ for 2.5h until dissolved. Then add 8g of aluminum boride and a 0.5% boric acid solution (containing 12g of boric acid). Heat and stir at 75℃ for 3.5h to obtain precursor complex A.

[0063] S2. Precursor complex A was placed in a tube furnace and heated to 850°C at a heating rate of 6°C / min in a nitrogen atmosphere, and held at that temperature for 2.5 h to obtain product B.

[0064] S3. After mixing product B with thiophene and red phosphorus in a mass ratio of 10:1:1, the mixture was placed in a sealed glass tube and then placed in a muffle furnace and heated at 400°C for 12 hours under vacuum to obtain product C.

[0065] S4. In a nitrogen atmosphere, water vapor is introduced into product C, and the product is heated and activated at 750°C for 1.2 hours. Then, it is pulverized until the D50 is 8 μm to obtain the final product.

[0066] Preparation of silicon-carbon composite materials:

[0067] The porous carbon material prepared above was placed in a fluidized bed reactor, and silane was first introduced and deposited at 600°C for 4 hours. Then acetylene was introduced and deposited at 620°C for 4 hours to obtain the final product.

[0068] Using the silicon-carbon composite material prepared above, CR2016 coin cells were assembled according to the method in Example 1, and their electrochemical performance was tested. The test results are shown in Table 1. At a current density of 0.1C, the battery made of the above silicon-carbon composite material had an initial discharge specific capacity of 2011.5 mAh / g, a charge specific capacity of 1856.6 mAh / g, and an initial coulombic efficiency of 92.3%.

[0069] Using the silicon-carbon composite material prepared above, a 4Ah soft-pack battery was assembled according to the method in Example 1. After capacity testing, it was subjected to room temperature cycling test at a current density of 1C / 1C. After 900 cycles of the full battery, the capacity retention rate was 80%.

[0070] Comparative Example 1

[0071] Porous carbon materials were prepared using conventional methods, as detailed below:

[0072] S1. Place 50g of phenolic resin in a tube furnace and heat it to 900℃ in a nitrogen atmosphere at a heating rate of 5℃ / min. Hold the temperature for 2h to carry out pyrolysis and obtain product A.

[0073] S2. In a nitrogen atmosphere, water vapor is introduced into product A, and the product is heated and activated at 800°C for 1 hour. Then, it is pulverized until the D50 is 6 μm to obtain the final product.

[0074] Preparation of silicon-carbon composite materials:

[0075] The porous carbon material prepared above was placed in a fluidized bed reactor, and silane was first introduced and deposited at 500°C for 4 hours. Then acetylene was introduced and deposited at 600°C for 4 hours to obtain the final product.

[0076] Using the silicon-carbon composite material prepared above, CR2016 coin cells were assembled according to the method in Example 1, and their electrochemical performance was tested. The test results are as follows: Figure 2 As shown in Table 1, at a current density of 0.1C, the battery prepared in Comparative Example 1 has an initial discharge specific capacity of 2052.3 mAh / g, a charge specific capacity of 1698.8 mAh / g, and an initial coulombic efficiency of 82.8%.

[0077] Using the silicon-carbon composite material prepared above, a 4Ah pouch cell was assembled according to the method in Example 1. After capacity testing, it was subjected to room temperature cycling tests at 1C / 1C current density, and the results are as follows. Figure 3 As shown, the capacity retention rate is 80% after 750 full battery cycles.

[0078] Comparative Example 2

[0079] Preparation of porous carbon materials:

[0080] S1. Add 50g of phenolic resin and 30g of ethylene glycol to 200g of anhydrous ethanol and stir at 60℃ for 2h until dissolved. Then add 25g of aluminum boride and heat and stir at 80℃ for 3h to obtain precursor complex A.

[0081] S2. Precursor complex A is placed in a tube furnace and heated to 900°C at a heating rate of 5°C / min in a nitrogen atmosphere, and held at that temperature for 2 hours for pyrolysis to obtain product B.

[0082] S3. After mixing product B with thiourea and red phosphorus in a mass ratio of 50:1:1, the mixture was placed in a glass tube and sealed. Then, it was placed in a muffle furnace and heated at 400°C for 12 hours under vacuum to obtain product C.

[0083] S4. In a nitrogen atmosphere, water vapor is introduced into product C, and the product is heated and activated at 800°C for 1 hour. Then, it is pulverized until the D50 is 6 μm to obtain the final product.

[0084] Preparation of silicon-carbon composite materials:

[0085] The porous carbon material prepared above was placed in a fluidized bed reactor, and silane was first introduced and deposited at 500°C for 4 hours. Then acetylene was introduced and deposited at 600°C for 4 hours to obtain the final product.

[0086] Using the silicon-carbon composite material prepared above, CR2016 coin cells were assembled according to the method in Example 1, and their electrochemical performance was tested. The test results are shown in Table 1. At a current density of 0.1C, the battery made of the above silicon-carbon composite material had an initial discharge specific capacity of 1979.9 mAh / g, a charge specific capacity of 1726.5 mAh / g, and an initial coulombic efficiency of 87.2%.

[0087] Using the silicon-carbon composite material prepared above, a 4Ah soft-pack battery was assembled according to the method in Example 1. After capacity testing, it was subjected to room temperature cycling test at a 1C / 1C current density. After 770 cycles of the full battery, the capacity retention rate was 80%.

[0088] Comparative Example 3

[0089] Preparation of porous carbon materials:

[0090] S1. Add 50g of phenolic resin and 30g of ethylene glycol to 200g of anhydrous ethanol, stir at 60℃ for 2h until dissolved, then add a 3% boric acid solution (containing 25g of boric acid), heat and stir at 80℃ for 3h to obtain precursor complex A;

[0091] S2. Precursor complex A is placed in a tube furnace and heated to 900°C at a heating rate of 5°C / min in a nitrogen atmosphere, and held at that temperature for 2 hours for pyrolysis to obtain product B.

[0092] S3. After mixing product B with thiourea and red phosphorus in a mass ratio of 50:1:1, the mixture was placed in a glass tube and sealed. Then, it was placed in a muffle furnace and heated at 400°C for 12 hours under vacuum to obtain product C.

[0093] S4. In a nitrogen atmosphere, water vapor is introduced into product C, and the product is heated and activated at 800°C for 1 hour. Then, it is pulverized until the D50 is 6 μm to obtain the final product.

[0094] Preparation of silicon-carbon composite materials:

[0095] The porous carbon material prepared above was placed in a fluidized bed reactor, and silane was first introduced and deposited at 500°C for 4 hours. Then acetylene was introduced and deposited at 600°C for 4 hours to obtain the final product.

[0096] Using the silicon-carbon composite material prepared above, CR2016 coin cells were assembled according to the method in Example 1, and their electrochemical performance was tested. The test results are shown in Table 1. At a current density of 0.1C, the battery made of the above silicon-carbon composite material had an initial discharge specific capacity of 2003.5 mAh / g, a charge specific capacity of 1769.1 mAh / g, and an initial coulombic efficiency of 88.3%.

[0097] Using the silicon-carbon composite material prepared above, a 4Ah soft-pack battery was assembled according to the method in Example 1. After capacity testing, it was subjected to room temperature cycling test at a current density of 1C / 1C. After 750 cycles of the full battery, the capacity retention rate was 80%.

[0098] Comparative Example 4

[0099] Preparation of porous carbon materials:

[0100] S1. Add 50g of phenolic resin and 30g of ethylene glycol to 200g of anhydrous ethanol and stir at 60℃ for 2h until dissolved. Then add 10g of aluminum boride and a 1% boric acid solution (containing 15g of boric acid). Heat and stir at 80℃ for 3h to obtain precursor complex A.

[0101] S2. Precursor complex A is placed in a tube furnace and heated to 900°C at a heating rate of 5°C / min in a nitrogen atmosphere, and held at that temperature for 2 hours for pyrolysis to obtain product B.

[0102] S3. In a nitrogen atmosphere, water vapor is introduced into product B, and the product is heated and activated at 800°C for 1 hour. Then, it is pulverized until the D50 is 6 μm to obtain the final product.

[0103] Preparation of silicon-carbon composite materials:

[0104] The porous carbon material prepared above was placed in a fluidized bed reactor, and silane was first introduced and deposited at 500°C for 4 hours. Then acetylene was introduced and deposited at 600°C for 4 hours to obtain the final product.

[0105] Using the silicon-carbon composite material prepared above, CR2016 coin cells were assembled according to the method in Example 1, and their electrochemical performance was tested. The test results are shown in Table 1. At a current density of 0.1C, the battery made of the above silicon-carbon composite material had an initial discharge specific capacity of 2018.4 mAh / g, a charge specific capacity of 1792.3 mAh / g, and an initial coulombic efficiency of 88.8%.

[0106] Using the silicon-carbon composite material prepared above, a 4Ah soft-pack battery was assembled according to the method in Example 1. After capacity testing, it was subjected to room temperature cycling test at a current density of 1C / 1C. After 780 cycles of the full battery, the capacity retention rate was 80%.

[0107] Table 1

[0108] Initial discharge specific capacity / mAh / g Initial charge specific capacity / mAh / g Initial coulombic efficiency Example 1 2054.9 1904.7 92.7% Example 2 2023.1 1859.2 91.9% Example 3 2011.5 1856.6 92.3% Comparative Example 1 2052.3 1698.8 82.8% Comparative Example 2 1979.9 1726.5 87.2% Comparative Example 3 2003.5 1769.1 88.3% Comparative Example 4 2018.4 1792.3 88.8%

[0109] Therefore, the present invention first reacts carbon source with metal borides and boric acid in a solvent by heating and stirring to obtain a precursor composite, and then through pyrolysis, sulfur and phosphorus doping and steam activation. The above processes have a synergistic effect, which can effectively optimize the pore structure of porous carbon materials, so that the silicon-carbon composite material prepared by the porous carbon material can effectively improve the battery capacity, charge and discharge efficiency, rate performance and cycle performance.

[0110] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing porous carbon materials, characterized in that, Includes the following steps: S1. Dissolve the carbon source in an organic solvent, then add a metal boride and a boric acid solution, heat and stir to react, and obtain precursor complex A, wherein the mass ratio of metal boride, boric acid and carbon source is 1:1~20:1~20; the carbon source is at least one of organic compounds containing multiple hydroxyl and / or multiple carboxyl groups. S2. The precursor complex A is heated and pyrolyzed in a protective atmosphere to obtain product B; S3. The product B is mixed with a sulfur-containing organic compound and elemental phosphorus, and then heated under vacuum at 400-800°C for 8-16 hours to obtain product C; the mass ratio of product B, sulfur-containing organic compound, and elemental phosphorus is 100:1-10:1-10. S4. In a protective atmosphere, water vapor is introduced into the product C for heating and activation, and then the product is pulverized to obtain the porous carbon material.

2. The method for preparing porous carbon materials according to claim 1, characterized in that, In S1, the temperature of the heating and stirring reaction is 80~120℃, and the time is 2~12h; The mass ratio of the carbon source to the organic solvent is 1:2~10; The boric acid solution has a mass concentration of 0.1% to 5%.

3. The method for preparing porous carbon materials according to claim 1, characterized in that, The carbon source is selected from at least one of phenolic resin, asphalt, ethylene glycol, glucose, sucrose, and lignin; the metal boride is selected from at least one of aluminum boride, titanium boride, zirconium boride, and chromium boride.

4. The method for preparing porous carbon materials according to claim 1, characterized in that, In S2, the heating and pyrolysis temperature is 300~1000℃ and the time is 1~10h; in S2, the protective gas is selected from at least one of nitrogen, argon and helium.

5. The method for preparing porous carbon materials according to claim 1, characterized in that, The sulfur-containing organic compound is selected from at least one of thiourea, methanethiol, dimethyl sulfide, and thiophene; the elemental phosphorus is selected from at least one of red phosphorus, black phosphorus, and purple phosphorus.

6. The method for preparing porous carbon materials according to claim 1, characterized in that, In S4, the heating activation temperature is 500~1200℃ and the time is 1~10h; in S4, the protective gas is selected from at least one of nitrogen, argon and helium.

7. A porous carbon material, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 6.

8. A silicon-carbon composite material, characterized in that, The silicon-carbon composite material is prepared using the porous carbon material described in claim 7 as a substrate; the silicon-carbon composite material has a core-shell structure, with the core being a silicon-carbon material with a porous structure and the outer shell being a carbon layer.

9. The silicon-carbon composite material according to claim 8, characterized in that, The method for preparing the silicon-carbon composite material includes: first, introducing a silicon source gas for chemical vapor deposition in a protective atmosphere, and then introducing a carbon source gas for chemical vapor deposition, thereby obtaining the composite material.

10. The silicon-carbon composite material according to claim 9, characterized in that, The conditions for chemical vapor deposition by introducing silicon source gas are: deposition at 400~800℃ for 1~8h; The conditions for chemical vapor deposition with carbon source gas are: deposition at 500~800℃ for 3~8h; The protective gas is selected from at least one of nitrogen, argon, and helium.

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