Silicon carbon material as well as preparation method and application thereof

Abstract

The invention discloses a silicon-carbon material as well as a preparation method and application thereof. The silicon-carbon material comprises nitrogen-doped porous carbon and an amorphous carbon layer coating the nitrogen-doped porous carbon, and pores of the nitrogen-doped porous carbon are filled with boron-doped nano silicon. The nitrogen-doped porous carbon improves the affinity of silane gas while improving the electron conductivity, a high-conductivity and high-density silicon-carbon composite structure is realized, the boron-doped nano silicon and the nitrogen-doped porous carbon form a nano heterojunction site, and the migration rate of lithium ions is improved, so that electrochemical reaction kinetics is improved, and the electrochemical performance of the lithium ion battery is improved. The material has the advantages of high rate and long cycle performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and in particular relates to a silicon-carbon material and a preparation method and application thereof. Background Art

[0002] The negative electrode material is one of the key materials that determines the performance of lithium-ion batteries. However, the mainstream negative electrode material in the current market is graphite, which has a low theoretical specific capacity (372mAh / g). The energy density growth of the battery cell is limited, making it difficult to meet people's demand for long-lasting battery cells. Therefore, the use of silicon negative electrode materials with high specific capacity is an effective way to increase the energy density of lithium-ion batteries. However, the silicon-based materials currently on the market have the disadvantage of poor lithium-ion kinetics and low high-current charge and discharge performance, which affects their fast charging performance. Therefore, in order to improve the fast charging performance of silicon negative electrodes, it is necessary to provide a silicon-based negative electrode material with high energy density and good high-rate charge and discharge characteristics.

[0003] The current technology route for depositing silicon-carbon for silicon-based negative electrode materials has a poor affinity between the raw material porous carbon and silane, resulting in the produced silicon-carbon material containing more pores. These pores will affect the strength and density of the material particles, and bring about the problem of increasingly aggravated side reactions during the cycle of the battery cell, which in turn leads to the deterioration of the battery cell cycle. In addition, the defect of poor affinity makes the processing time of the silane deposition process long and the processing cost increased, which seriously restricts the commercial application process of deposited silicon-carbon materials.

[0004] The porous carbon substrate used for depositing silicon-carbon negative electrode materials is mostly hard carbon material that has not been graphitized at high temperature. Its intrinsic electronic conductivity is low. The defect of low electronic conductivity after compounding with semiconductor silicon limits the electron transfer yield during the electrochemical reaction of the silicon-carbon composite material, and the electrochemical reaction kinetics performance is poor, making it difficult to substantially increase the rate energy density of the battery cell. Summary of the Invention

[0005] The main purpose of the present invention is to provide a silicon-carbon material and a preparation method and application thereof, so as to overcome the deficiencies of the prior art.

[0006] To achieve the aforementioned object of the invention, the technical solutions adopted by the present invention include: An embodiment of the present invention provides a silicon-carbon material, which includes: nitrogen-doped porous carbon and an amorphous carbon layer covering the nitrogen-doped porous carbon, wherein the pores of the nitrogen-doped porous carbon are filled with boron-doped nano-silicon.

[0007] The present invention also provides a method for preparing the aforementioned silicon-carbon material, which comprises: Prepare nitrogen-doped porous carbon by at least one of a template method, a chemical vapor deposition method, and a pyrolysis method; reacting a mixture comprising at least the nitrogen-doped porous carbon, a silicon source gas, and a boron source gas to produce nitrogen-doped porous carbon with pores filled with boron-doped nano-silicon; Furthermore, a carbon source is used to coat the nitrogen-doped porous carbon in which the pores are filled with boron-doped nano-silicon to obtain a silicon-carbon material.

[0008] The embodiments of the present invention also provide the use of the aforementioned silicon-carbon material in preparing a battery negative electrode sheet or a lithium-ion battery.

[0009] An embodiment of the present invention further provides a negative electrode active material for a lithium-ion secondary battery, which includes the aforementioned silicon-carbon material.

[0010] Compared with the prior art, the present invention has the following beneficial effects: (1) The silicon-carbon material of the present invention has high-rate charge and discharge characteristics; (2) The nitrogen-doped porous carbon in the present invention improves the affinity of silane gas while improving the electronic conductivity, thereby achieving a high-conductivity, high-density silicon-carbon composite structure. Boron-doped nano-silicon and nitrogen-doped carbon constitute nano-heterojunction sites, which increases the migration rate of lithium ions, thereby improving the electrochemical reaction kinetics and having the advantages of high rate and long cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments recorded in the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0012] Figure 1 Schematic diagram of the structure of silicon-carbon material in a typical embodiment of the present invention; Figure 2 3 is an electron microscope image of the silicon-carbon material prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0013] In view of the shortcomings of the prior art, the inventors of this case, after long-term research and extensive practice, have proposed the technical solution of the present invention. The technical solution of the present invention will be clearly and completely described below. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making any creative effort shall fall within the scope of protection of the present invention.

[0014] Specifically, as one aspect of the technical solution of the present invention, a silicon-carbon material involved includes: nitrogen-doped porous carbon and an amorphous carbon layer covering the nitrogen-doped porous carbon, wherein the pores of the nitrogen-doped porous carbon are filled with boron-doped nano-silicon.

[0015] The structural diagram of the silicon-carbon material in the present invention is as follows Figure 1 shown.

[0016] The nitrogen-doped porous carbon used in the present invention improves the affinity of silane gas while improving the electronic conductivity, thereby realizing a high-conductivity, high-density silicon-carbon composite structure. The boron-doped nano-silicon and the nitrogen-doped porous carbon constitute nano-heterojunction sites, which increases the migration rate of lithium ions, thereby improving the electrochemical reaction kinetics, and has the advantages of high rate and long cycle performance.

[0017] The preparation methods of nitrogen-doped porous carbon used in the present invention mainly include template method, chemical vapor deposition method and thermal decomposition method. Among them, the template method is to immerse a pre-designed template in a precursor solution containing a nitrogen source, and generate nitrogen-doped carbon material through chemical reaction. The chemical vapor deposition method is to introduce nitrogen-containing gas into a reactor, and generate a chemical reaction at high temperature to generate nitrogen-doped carbon material. The thermal decomposition method is to directly utilize organic matter containing a nitrogen source to thermally decompose at high temperature to generate nitrogen-doped porous carbon material. Boron-doped nanosilicon is to dope nanosilicon by adding a boron-containing gas source to the reactor synchronously or indirectly during the silane cracking process, which can increase the number of carriers in nanosilicon and thus improve electronic conductivity. The amorphous carbon layer can be prepared by carbonization of one or more carbon-containing organic matter such as asphalt, resin, acetylene and benzene.

[0018] In some preferred embodiments, the particle size D50 of the nitrogen-doped porous carbon is 2 to 20 μm.

[0019] In some preferred embodiments, the content of nitrogen-doped porous carbon in the silicon-carbon material is 10 to 60 wt %.

[0020] Furthermore, the content of nitrogen-doped porous carbon in the silicon-carbon material is 35-55 wt%.

[0021] In some preferred embodiments, the content of nitrogen in the silicon-carbon material is 0.1 to 30 wt %.

[0022] Furthermore, the content of nitrogen in the silicon-carbon material is 1 to 15 wt%.

[0023] In some preferred embodiments, the boron content in the silicon-carbon material is 0.5-5 wt%.

[0024] Furthermore, the boron content in the silicon-carbon material is 1-3 wt%.

[0025] In some preferred embodiments, the content of nano-silicon in the silicon-carbon material is 35-60 wt %.

[0026] In some preferred embodiments, the particle size of the boron-doped nano-silicon is less than 50 nm.

[0027] Furthermore, the particle size of the boron-doped nano-silicon is less than 5 nm.

[0028] In some preferred embodiments, the content of the amorphous carbon layer in the silicon-carbon material is 0.3-30 wt %.

[0029] Furthermore, the content of the amorphous carbon layer in the silicon-carbon material is 0.5-10 wt%.

[0030] In some preferred embodiments, the thickness of the amorphous carbon layer is 20 to 300 nm.

[0031] Furthermore, the thickness of the amorphous carbon layer is 30-80 nm.

[0032] In some preferred embodiments, the amorphous carbon layer is doped with nitrogen.

[0033] The silicon-carbon material in the present invention includes a nitrogen-doped porous carbon substrate (the aforementioned nitrogen-doped porous carbon), boron-doped nanosilicon filled in the pores, and an amorphous carbon layer on the surface. Among them, B-doped nanosilicon plays a major role in contributing to the capacity, and the nitrogen-doped porous carbon and the coating layer play a role in inhibiting the lithiation expansion of nanosilicon and improving the conductivity. It has the advantages of high capacity, low expansion and long cycle time.

[0034] Among them, nitrogen-doped porous carbon substrates can promote the deposition of silanes: because the electronegativity of nitrogen atoms in nitrogen-doped porous carbon is higher than that of carbon atoms, the electron cloud density near the carbon atoms connected to the nitrogen atoms is lower, and SiH4 molecules tend to adsorb on the carbon atoms connected to the nitrogen atoms due to their electron-donating nature. At the same time, nitrogen doping causes a redistribution of the π electron density of the graphene layer, which weakens the π electron conjugation effect of the aromatic carbon layer and increases the adsorption energy of the SiH4 molecules. The above reasons greatly increase the adsorption rate of SiH4 atoms, which is conducive to the efficient utilization of silane molecules and the realization of a dense silicon-carbon particle structure. The increase in the concentration of pyridine-like structures in nitrogen-doped carbon materials is conducive to the formation of localized donor states close to the Fermi level, increasing the density of states on the Fermi surface and greatly reducing the charge transfer activation energy, thereby improving the conductivity of the carbon material. In addition, the increase in defect sites brought about by nitrogen doping can reduce the lithium storage reaction barrier of the carbon material and increase the lithium ion diffusion path, thereby effectively improving the fast charging performance of the material.

[0035] B-doped nano-silicon is evenly distributed in the nitrogen-doped porous carbon substrate. The B-doped nano-silicon and the nitrogen-doped porous carbon substrate form a nanoscale heterojunction site. There are significant differences in the electronic structure and energy band energy levels of silicon and carbon on both sides of the heterojunction site. Electron and hole migration will occur at the interface until the Fermi level reaches equilibrium. During the migration process, an internal electric field is formed at the interface, which increases the migration rate of lithium ions and thus improves the electrochemical reaction kinetics. In addition, B-doped nano-silicon particles can provide holes to increase the number of carriers in semiconductor silicon, thereby improving the electronic conductivity of silicon.

[0036] The design of the above material structure can accelerate the decomposition reaction rate of silane and achieve a dense structure with high tap density; in addition, element doping and heterogeneous structure greatly improve the electron and ion migration rate of the material, and lithium ions are quickly deintercalated, achieving a substantial increase in the power and energy density of silicon negative electrode batteries.

[0037] Another aspect of the embodiments of the present invention further provides a method for preparing the aforementioned silicon-carbon material, which comprises: Prepare nitrogen-doped porous carbon by at least one of a template method, a chemical vapor deposition method, and a pyrolysis method; reacting a mixture comprising at least the nitrogen-doped porous carbon, a silicon source gas, and a boron source gas to produce nitrogen-doped porous carbon with pores filled with boron-doped nano-silicon; Furthermore, a carbon source is used to coat the nitrogen-doped porous carbon in which the pores are filled with boron-doped nano-silicon to obtain a silicon-carbon material.

[0038] In some preferred embodiments, the preparation method specifically includes: allowing an organic monomer containing a carbon-nitrogen bond to undergo a polymerization reaction to obtain a nitrogen-containing organic polymer, and then drying, ball milling, carbonizing, and pore-forming the nitrogen-containing organic polymer to obtain nitrogen-doped porous carbon.

[0039] Furthermore, the organic monomer containing a carbon-nitrogen bond includes any one or more combinations of amine compounds, nitrogen heterocyclic compounds, nitrile compounds, and nitro compounds, but is not limited thereto.

[0040] Furthermore, the organic monomer containing a carbon-nitrogen bond includes any one or more combinations of p-nitroaniline, azobisisobutyronitrile, pyridine, triethylamine, 2-naphthylamine, benzidine, o-aminoazotoluene, ethyleneimine, pyrrolidine, nitrogen mustard, vinblastine, nitrosoamines, and nitrosoamides, and is not limited thereto.

[0041] In some preferred embodiments, the preparation method specifically includes: carbonizing and activating the carbon source material to obtain a porous carbon material, then subjecting the porous carbon material to a gas-phase nitrogen doping treatment, and then heat treating the porous carbon material to obtain nitrogen-doped porous carbon.

[0042] In some preferred embodiments, the preparation method specifically includes: carbonizing and activating the carbon source material to obtain a porous carbon material, then compounding the porous carbon material with a nitrogen-containing compound, and then subjecting it to high-temperature carbonization treatment to obtain nitrogen-doped porous carbon.

[0043] Furthermore, the carbon source material includes natural biomass such as lignin, cellulose or chitosan, protein and natural rubber, and can also be a polymer generated by polymerizing organic monomers by a synthetic method, such as synthetic rubber, synthetic resin, synthetic fiber and other non-biological polymers, or can be any one or more combinations of carbon-containing compounds obtained by processing fossil fuels such as coal, coke, asphalt, etc., and is not limited to these.

[0044] Furthermore, the activating agent used in the activation treatment includes any one or more combinations of steam, carbon dioxide, alkali, alkali metal salt, strong acid, and phosphoric acid, but is not limited thereto.

[0045] Furthermore, the nitrogen-containing compound includes any one or more combinations of HCN, HNO3, N,N-dimethylethanolamine, N,N-dimethylpropylenediamine, urea, dicyandiamide, N,N-dimethylformamide, melamine, and polyaniline, but is not limited thereto.

[0046] In some preferred embodiments, the preparation method specifically includes: placing nitrogen-doped porous carbon in a reaction device and replacing it with a protective gas so that its oxygen content is below 200 ppm, then introducing silicon source gas, boron source gas, and protective gas and reacting at 350-950°C for 1-8 hours to obtain nitrogen-doped porous carbon with boron-doped nano-silicon filled in the pores.

[0047] Furthermore, the silicon source gas includes any one or more combinations of silane, disilane, trisilane, tetrasilane, monochlorosilane, dichlorosilane, trichlorosilane, and tetrachlorosilane, but is not limited thereto.

[0048] Furthermore, the boron source gas includes a compound composed of boron and hydrogen and / or a compound that can be decomposed to produce boron element, but is not limited thereto.

[0049] Furthermore, the protective gas includes any one or more combinations of nitrogen, helium, neon, argon, krypton, and xenon, but is not limited thereto.

[0050] Furthermore, the flow ratio of the silicon source gas, the boron source gas and the protective gas is 10-40:1-15:45-90.

[0051] Furthermore, the flow ratio of the silicon source gas, the boron source gas and the protective gas is 20-30:3-10:60-80.

[0052] In some preferred embodiments, the preparation method specifically includes: placing nitrogen-doped porous carbon with boron-doped nano-silicon filled in the pores in a reaction device and introducing a carbon source gas in a protective atmosphere for thermal cracking to obtain a silicon-carbon material; or, mixing nitrogen-doped porous carbon with boron-doped nano-silicon filled in the pores with a solid carbon source and carbonizing it to obtain a silicon-carbon material; or, mixing nitrogen-doped porous carbon with boron-doped nano-silicon filled in the pores with a liquid dispersant containing a carbon source and drying and carbonizing it to obtain a silicon-carbon material; or, mixing nitrogen-doped porous carbon with boron-doped nano-silicon filled in the pores with a liquid carbon source and carbonizing it to obtain a silicon-carbon material.

[0053] Furthermore, the thermal cracking temperature is 380-1180° C. and the time is 1-6 hours.

[0054] Furthermore, the temperature of the carbonization treatment is 500-1010° C., and the time is 2-8 hours.

[0055] In some more specific embodiments, the method for preparing the silicon-carbon material comprises the following steps: S21. Preparation of nitrogen-doped porous carbon (1) Nitrogen-containing carbon source precursor method: Organic monomers containing carbon-nitrogen bonds (including amines, nitrogen heterocycles, nitriles, nitro compounds, etc.) are dispersed in an organic solvent and polymerized under a certain temperature and catalyst to form nitrogen-containing organic polymers. The nitrogen-containing organic polymers are dried, ball-milled, and carbonized to obtain nitrogen-doped carbon powder, which is then physically or chemically activated to form pores to obtain nitrogen-doped porous carbon materials.

[0056] (2) Chemical vapor deposition method: polymers, biomass, coke and other carbon source materials generated by the polymerization of organic monomers are carbonized and activated to obtain porous carbon materials with rich pores. The porous carbon is then treated with nitrogen doping in the gas phase (ammonia, hydrogen cyanide and amine). For example, ammonia reacts with the carboxylic acid sites in the carbon to form ammonium salts, which are then converted into surface amides, imides and nitriles during heat treatment. At high temperatures, they are even converted into isocyanates. The ether oxygen on the surface of the porous carbon can be converted into imine and pyridine groups by reacting with ammonia, thus obtaining nitrogen-doped porous carbon materials.

[0057] (3) Pyrolysis method: The carbon source undergoes carbonization and activation processes to obtain porous carbon materials with rich pore sizes. The porous carbon material is compounded with nitrogen-containing compounds. After high-temperature carbonization, the nitrogen-containing compounds decompose to generate free radicals (such as NH2, NH and atomic hydrogen and nitrogen). The free radicals will attack the porous carbon material. These free radicals can further etch the porous carbon surface, resulting in increased porosity and forming functional groups such as amides, imides, nitriles, isocyanates, pyridines and quaternary nitrogen, thus obtaining nitrogen-doped porous carbon materials.

[0058] Preferably, the organic monomer containing a carbon-nitrogen bond includes, but is not limited to, one or more of p-nitroaniline, azobisisobutyronitrile, pyridine, triethylamine, 2-naphthylamine, benzidine, o-aminoazotoluene, ethyleneimine, pyrrolidine, nitrogen mustard, vinblastine, nitrosoamines and nitrosoamides.

[0059] Preferably, the activating agent used in the activation process includes, but is not limited to, one or more of water vapor, carbon dioxide, alkali, alkali metal salt, strong acid and phosphoric acid.

[0060] Preferably, the carbon source of the porous carbon can be: a polymer formed by polymerization of organic monomers, biomass including lignin, cellulose and chitosan, and fossil raw materials such as coal, coke and asphalt and their derivatives.

[0061] Preferably, the nitrogen-containing compound may be one or more of HCN, HNO3, N,N-dimethylethanolamine, N,N-dimethylpropylenediamine, urea, dicyandiamide, N,N-dimethylformamide, melamine and polyaniline.

[0062] Compared with chemical vapor deposition and pyrolysis methods, the nitrogen-doped carbon prepared by the nitrogen-containing carbon source precursor method has a higher concentration of pyridine-like structures in its structure, which is conducive to the formation of localized donor states close to the Fermi level, increasing the state density of the Fermi surface, and more significantly improving the conductivity of the material.

[0063] S22, Boron-doped Nano-Si Deposition Nitrogen-doped porous carbon is added to the reaction vessel and replaced with inert gas. After the oxygen content is reduced to below 200 ppm, the temperature is raised to 550°C and kept warm for 5 hours. During this period, silicon source gas, boron source gas and inert gas can be introduced step by step, intermittently or simultaneously for reaction. After the gas introduction is completed, the temperature is kept warm for a period of time to ensure sufficient reaction.

[0064] Preferably, the silicon source gas includes at least one of silane, disilane, trisilane, tetrasilane, monochlorosilane, dichlorosilane, trichlorosilane, and tetrachlorosilane; the boron source gas includes a compound composed of boron and hydrogen, as well as a compound that can decompose to produce elemental boron; and the protective gas includes at least one of nitrogen, helium, neon, argon, krypton, and xenon. The introduction ratio is (10-40 silicon source: 1-15 boron source gas: 45-90 inert gas), preferably 20-30 silicon source: 3-10 boron source gas: 60-80 inert gas. S23, surface carbon coating Under the condition of ensuring the continuous flow of protective gas, the reactor is heated to 800°C, and the diluted carbon source gas is introduced. The carbon source gas is thermally cracked to obtain a negative electrode material (the aforementioned silicon-carbon material) with an amorphous carbon layer coated on the surface; or: the obtained material is mixed with a solid carbon source to obtain a mixture which is carbonized to obtain the negative electrode material; or: the obtained material is added to a liquid dispersant in which the carbon source is dissolved, and the negative electrode material is obtained by drying and carbonizing; or: the obtained material is mixed with a liquid carbon source, and the mixture is carbonized to obtain the negative electrode material.

[0065] Preferably, the carbon coating temperature is 580-980°C, the coating time is 1-6 hours, and the carbon source gas includes at least one of methane, ethane, propane, ethylene, acetylene, gaseous benzene, toluene, xylene, and ethanol; Another aspect of the embodiments of the present invention further provides the use of the aforementioned silicon-carbon material in preparing a battery negative electrode sheet or a lithium-ion battery.

[0066] Another aspect of the embodiments of the present invention further provides a negative electrode active material for a lithium-ion secondary battery, which includes the aforementioned silicon-carbon material.

[0067] The technical solution of the present invention is further described in detail below in conjunction with several preferred embodiments and the accompanying drawings. This embodiment is implemented on the premise of the technical solution of the invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0068] Unless otherwise specified, the experimental materials used in the following examples can be purchased from conventional biochemical reagent companies.

[0069] Example 1 300g of polyethyleneimine was dissolved in 10L of ethanol-water solution, and then 1000g of resorcinol was added to the mixed solution and stirred for reaction. Next, 50g of melamine was dissolved in water, ultrasonically dispersed, and added to the reaction solution, and stirred continuously. 3L of 3M formaldehyde solution was added to the reaction solution and stirred. Subsequently, 250g of potassium hydroxide was added, and stirring and heating were continued to obtain the final solution mixture. The solution was filtered, dried, ball-milled, and carbonized to obtain nitrogen-doped phenolic resin-based carbon microspheres. 1.2kg of porous carbon microsphere powder was added to a rotary kiln, replaced by inert gas, and heated to 850 degrees Celsius at a heating rate of 3°C / min under the condition of continuous inert gas flow, and then water vapor was introduced at a gas flow rate of 3L / min for 2h. The activated porous carbon was crushed and graded to narrow the particle size to obtain nitrogen-doped porous carbon material.

[0070] Take 500g of nitrogen-doped porous carbon powder and place it in a fluidized bed. Pass protective gas to maintain pressure and detect leaks. After the pressure maintenance is completed, pass protective gas at 15L / min, increase the temperature to 650℃ at a rate of 3℃ / min, pass silane gas at a rate of 3L / min, and at the same time, pass borane gas at a rate of 0.5L / min, and keep warm for 5h. After the deposition is completed, turn off the silane gas, keep the protective gas flow conditions unchanged, and increase the temperature to 820℃ at a rate of 3℃ / min. After the temperature stabilizes, pass acetylene gas at a rate of 4L / min, keep warm for 1h, turn off the acetylene gas, and cool to room temperature to obtain silicon-carbon material. The electron microscope image of the prepared silicon-carbon material is shown as follows: Figure 2 shown.

[0071] Example 2 941g of phenol was added to 5L of 2mol / L formaldehyde solution, and 200mL of 12mol / L concentrated hydrochloric acid was added as a catalyst. The polymerization reaction was carried out under the condition of heating in a water bath. After the reaction was completed, the resin carbon powder was obtained by drying, ball milling and carbonization at 1000 degrees Celsius. The carbon powder was added to a rotary kiln and pores were formed by water vapor activation method. The activation temperature was 850℃, the activation time was 2h, and the amount of H2O introduced was 120L. After stopping the introduction of water vapor, 20% concentration of NH4 was introduced into the reactor and the reaction was carried out for 30 minutes to obtain nitrogen-doped porous carbon material.

[0072] 800g of nitrogen-doped porous carbon powder was placed in a fluidized bed and pressure-maintained with protective gas for leak detection. After pressure maintenance, protective gas was introduced at 15L / min, the temperature was raised to 560°C at a rate of 3°C / min, silane gas was introduced at a rate of 3.2L / min, and borane gas was introduced at a rate of 0.6L / min, and the temperature was maintained for 8 hours. After deposition was completed, the silane gas was turned off, the protective gas flow conditions remained unchanged, and the temperature was raised to 950°C at a rate of 3°C / min. After the temperature stabilized, methane gas was introduced at a rate of 3.5L / min. After maintaining the temperature for 2 hours, the methane gas was turned off and the temperature was cooled to room temperature to obtain a silicon-carbon material.

[0073] Example 3 1882g of phenol was added to 10L of 2mol / L formaldehyde solution, 400mL of 12mol / L concentrated hydrochloric acid was added as a catalyst, and the polymerization reaction was carried out under the condition of water bath heating. After the reaction was completed, the resin carbon powder was obtained by drying, ball milling and carbonization at 1000 degrees Celsius. The carbon powder was added to a rotary kiln and pores were formed by water vapor activation method with an activation temperature of 900℃ and an activation time of 2h. After the water vapor was stopped, the material was removed after the temperature dropped to room temperature. The obtained porous carbon powder was immersed in 5L of ethanol solution dissolved with 126g of melamine and 60g of urea. The solution was dried and carbonized at 600℃ to obtain nitrogen-doped porous carbon material.

[0074] Take 500g of nitrogen-doped porous carbon powder and place it in a rotary kiln with argon at 20L / min for 2h. After the exhaust is completed, the temperature is then raised to 650℃ at a rate of 5L / min and kept stable for 1h. After the temperature stabilizes, high-purity silane gas (99.9999%) is introduced at a flow rate of 2L / min, and diborane gas is introduced at an air intake rate of 0.2L / min. The speed is controlled to 5r / min, kept warm for 7h, and then the silane and borane gases are turned off. Then the temperature is raised to 700℃ at 2℃ / min, and acetylene gas is introduced at a rate of 2L / min while the protective gas is continuously introduced, and kept warm for 2h. Then the acetylene gas is turned off, and the temperature is lowered to room temperature under the protective gas condition to obtain a silicon-carbon material.

[0075] Example 4 4 kg of needle coke was added to a rotary kiln and oxidized in air at 250°C for 4 hours. It was then pyrolyzed at 1250°C in an N2 atmosphere for 1 hour. The temperature was then lowered to 850°C, and the N2 flow rate was switched to CO2 (3 l / min). This activation process lasted for 16.5 hours. 10% NH4 was then introduced into the reactor, and the reaction continued for 120 minutes to produce a nitrogen-doped porous carbon material.

[0076] 1000g of nitrogen-doped porous carbon powder was placed in a fluidized bed and pressure-maintained with protective gas for leak detection. After pressure maintenance, protective gas was introduced at 20L / min, the temperature was raised to 650°C at a rate of 3°C / min, silane gas was introduced at a rate of 10L / min, and borane gas was introduced at a rate of 2L / min, and the temperature was maintained for 3 hours. After deposition, the silane and borane gases were turned off, the protective gas flow conditions remained unchanged, and the temperature was raised to 920°C at a rate of 3°C / min. After the temperature stabilized, acetylene gas was introduced at a rate of 8L / min. After maintaining the temperature for 2 hours, the acetylene gas was turned off and the temperature was cooled to room temperature to obtain a silicon-carbon material.

[0077] Example 5 1882g of phenol was added to 10L of 2mol / L formaldehyde solution, 400mL of 12mol / L concentrated hydrochloric acid was added as a catalyst, and the polymerization reaction was carried out under the condition of water bath heating. After the reaction was completed, the resin carbon powder was obtained by drying, ball milling and carbonization at 1000 degrees Celsius. The carbon powder was added to a rotary kiln and pores were formed by water vapor activation method with an activation temperature of 900℃ and an activation time of 2h. After the water vapor was stopped, the material was removed after the temperature dropped to room temperature. The obtained porous carbon powder was immersed in 5L of ethanol solution dissolved with 126g of melamine and 60g of urea. The solution was dried and carbonized at 600℃ to obtain nitrogen-doped porous carbon material.

[0078] Take 500g of nitrogen-doped porous carbon powder and place it in a rotary kiln with argon at 20L / min for 2h. After the exhaust is completed, the temperature is then raised to 650℃ at a rate of 5L / min and kept stable for 1h. After the temperature stabilizes, high-purity silane gas (99.9999%) is introduced at a flow rate of 2L / min, and diborane gas is introduced at an air intake rate of 0.2L / min. The speed is controlled to 5r / min, and the temperature is kept warm for 7h, and then the silane and borane gases are turned off. The temperature is then raised to 700℃ at 2℃ / min, and acetylene gas is introduced at a rate of 2L / min while the protective gas is continuously introduced, and NH4 is introduced at 0.5L / min, and the temperature is kept warm for 2h. Then the acetylene gas and NH4 are turned off, and the temperature is lowered to room temperature under the protective gas condition to obtain a silicon-carbon material.

[0079] Example 6 300g of polyethyleneimine was dissolved in 10L of ethanol-water solution, and then 1000g of resorcinol was added to the mixed solution and stirred for reaction. Next, 50g of melamine was dissolved in water, ultrasonically dispersed, and added to the reaction solution, and stirred continuously. 3L of 3M formaldehyde solution was added to the reaction solution and stirred. Subsequently, 250g of potassium hydroxide was added, and stirring and heating were continued to obtain the final solution mixture. The solution was filtered, dried, ball-milled, and carbonized to obtain nitrogen-doped phenolic resin-based carbon microspheres. 1.2kg of porous carbon microsphere powder was added to a rotary kiln, replaced by inert gas, and heated to 850 degrees Celsius at a heating rate of 3°C / min under the condition of continuous inert gas flow, and then water vapor was introduced at a gas flow rate of 3L / min for 2h. The activated porous carbon was crushed and graded to narrow the particle size to obtain nitrogen-doped porous carbon material.

[0080] 500g of nitrogen-doped porous carbon powder was placed in a fluidized bed and pressure-maintained with protective gas. After pressure maintenance, protective gas was introduced at a rate of 15L / min, and the temperature was raised to 650°C at a rate of 3°C / min. Silane gas was introduced at a rate of 3L / min, and borane gas was introduced at a rate of 0.5L / min. The temperature was maintained for 5 hours. After deposition, the silane gas was turned off, and the protective gas flow conditions remained unchanged. The temperature was raised to 820°C at a rate of 3°C / min. After the temperature stabilized, acetylene gas was introduced at a rate of 4L / min and ammonia gas at a rate of 0.5L / min. After maintaining the temperature for 1 hour, the acetylene and ammonia gases were turned off and the temperature was lowered to room temperature to obtain a silicon-carbon material.

[0081] Comparative Example 1 Dissolve 1000g of resorcinol in 30L of ethanol-water solution, continue stirring and add 1.5L of 3M formaldehyde solution to the solution. Then add 250g of potassium hydroxide, continue stirring and heating to obtain the final solution mixture. The solution is filtered, dried, ball-milled, and carbonized to obtain carbon microspheres. Add 1.5kg of carbon microsphere powder into a rotary kiln, replace it with inert gas, and heat it to 850 degrees Celsius at a heating rate of 3℃ / min under the condition of continuous inert gas introduction. Then, introduce water vapor at a gas flow rate of 3L / min for 2h. The activated porous carbon is crushed and graded to narrow the particle size to obtain a porous carbon material.

[0082] 500g of porous carbon powder was placed in a fluidized bed and pressure-maintained with protective gas for leak detection. After pressure maintenance, protective gas was introduced at 15L / min, the temperature was raised to 650°C at a rate of 3°C / min, silane gas was introduced at a rate of 3L / min, and the temperature was maintained for 5 hours. After deposition, the silane gas was turned off, the protective gas flow conditions remained unchanged, and the temperature was raised to 820°C at a rate of 3°C / min. After the temperature stabilized, acetylene gas was introduced at a rate of 4L / min. After maintaining the temperature for 1 hour, the acetylene gas was turned off and the temperature was cooled to room temperature to obtain a silicon-carbon negative electrode material.

[0083] Comparative Example 2 941g of phenol was added to 5L of 2mol / L formaldehyde solution, and 200mL of 12mol / L concentrated hydrochloric acid was added as a catalyst. The polymerization reaction was carried out under heating in a water bath. After the reaction was completed, the resin carbon powder was obtained through drying, ball milling and carbonization at 1000 degrees Celsius. The carbon powder was added to a rotary kiln and pores were formed by water vapor activation. The activation temperature was 850°C, the activation time was 2h, and the amount of H2O introduced was 120L. The water vapor was stopped to obtain a nitrogen-doped porous carbon material.

[0084] 800g of porous carbon powder was placed in a fluidized bed and pressure-maintained with protective gas for leak detection. After pressure maintenance, protective gas was introduced at 15L / min, the temperature was raised to 560°C at a rate of 3°C / min, silane gas was introduced at a rate of 3.2L / min, and the temperature was maintained for 8 hours. After deposition, the silane gas was turned off, the protective gas flow conditions remained unchanged, and the temperature was raised to 950°C at a rate of 3°C / min. After the temperature stabilized, methane gas was introduced at a rate of 3.5L / min. After maintaining the temperature for 2 hours, the methane gas was turned off and the temperature was cooled to room temperature to obtain a silicon-carbon negative electrode material.

[0085] Comparative Example 3 1882g of phenol was added to 10L of a 2mol / L formaldehyde solution, and 400mL of 12mol / L concentrated hydrochloric acid was added as a catalyst. The polymerization reaction was carried out under heating in a water bath. After the reaction was completed, the resin carbon powder was obtained through drying, ball milling, and carbonization at 1000 degrees Celsius. The carbon powder was added to a rotary kiln and pores were formed by water vapor activation at 900°C for 2 hours. After the water vapor was stopped, the material was removed after the temperature dropped to room temperature to obtain a porous carbon material.

[0086] Take 500g of porous carbon powder and place it in a rotary kiln with argon at 20L / min for 2h. After the exhaust is completed, the temperature is then raised to 650℃ at a rate of 5L / min and kept stable for 1h. After the temperature stabilizes, high-purity silane gas (99.9999%) is introduced at a flow rate of 2L / min and a controlled speed of 5r / min. The temperature is kept for 7h, and then the silane gas is turned off. The temperature is then raised to 700℃ at 2℃ / min. While the protective gas is continuously introduced, acetylene gas is introduced at a rate of 2L / min, and the temperature is kept for 2h. The acetylene gas is then turned off and the temperature is lowered to room temperature under the protective gas condition to obtain a silicon-carbon negative electrode material.

[0087] Comparative Example 4 4 kg of needle coke was added into a rotary kiln, oxidized at 250 ° C in air for 4 hours, and then pyrolyzed in a N2 atmosphere at 1250 ° C for 1 hour. The temperature was then lowered to 850 ° C, and the N2 flow rate was switched to CO2 (3l / min). The activation process lasted for 16.5 hours to obtain a porous carbon material.

[0088] 1000g of porous carbon powder was placed in a fluidized bed and pressure-maintained with protective gas. After pressure maintenance, protective gas was introduced at a rate of 20 L / min. The temperature was raised to 650°C at a rate of 3°C / min. Silane gas was introduced at a rate of 10 L / min, and borane gas was introduced at a rate of 2 L / min. The temperature was maintained for 3 hours. After deposition, the silane and borane gases were turned off. The protective gas flow conditions remained unchanged, and the temperature was raised to 920°C at a rate of 3°C / min. After the temperature stabilized, acetylene gas was introduced at a rate of 8 L / min. After maintaining the temperature for 2 hours, the acetylene gas was turned off and the temperature was cooled to room temperature to obtain a silicon-carbon material.

[0089] Comparative Example 5 1882g of phenol was added to 10L of a 2mol / L formaldehyde solution, and 400mL of 12mol / L concentrated hydrochloric acid was added as a catalyst. The polymerization reaction was carried out under heating in a water bath. After the reaction was completed, the resin carbon powder was obtained through drying, ball milling, and carbonization at 1000 degrees Celsius. The carbon powder was added to a rotary kiln and pores were formed by water vapor activation at 900°C for 2 hours. After the water vapor was stopped, the material was removed after the temperature dropped to room temperature to obtain a porous carbon material.

[0090] Take 500g of porous carbon powder and place it in a rotary kiln with argon gas at 20L / min for 2h. After the exhaust is completed, the temperature is then raised to 650°C at a rate of 5L / min and kept stable for 1h. After the temperature stabilizes, high-purity silane gas (99.9999%) is introduced at a flow rate of 2L / min and a control speed of 5r / min. The temperature is kept warm for 7h, and the silane gas is then turned off. The temperature is then raised to 700°C at a rate of 2°C / min. While the protective gas is continuously introduced, acetylene gas is introduced at a rate of 2L / min, and NH4 is introduced at a rate of 0.5L / min. The temperature is kept warm for 2h, and then the acetylene gas and NH4 are turned off. The temperature is lowered to room temperature under the protective gas condition to obtain a silicon-carbon material.

[0091] Comparative Example 6 300g of polyethyleneimine was dissolved in 10L of ethanol-water solution, and then 1000g of resorcinol was added to the mixed solution and stirred for reaction. Next, 50g of melamine was dissolved in water, ultrasonically dispersed, and added to the reaction solution, and stirred continuously. 3L of 3M formaldehyde solution was added to the reaction solution and stirred. Subsequently, 250g of potassium hydroxide was added, and stirring and heating were continued to obtain the final solution mixture. The solution was filtered, dried, ball-milled, and carbonized to obtain nitrogen-doped phenolic resin-based carbon microspheres. 1.2kg of porous carbon microsphere powder was added to a rotary kiln, replaced by inert gas, and heated to 850 degrees Celsius at a heating rate of 3°C / min under the condition of continuous inert gas flow, and then water vapor was introduced at a gas flow rate of 3L / min for 2h. The activated porous carbon was crushed and graded to narrow the particle size to obtain nitrogen-doped porous carbon material.

[0092] 500g of nitrogen-doped porous carbon powder was placed in a fluidized bed and pressure-maintained with protective gas for leak detection. After pressure maintenance, protective gas was introduced at 15L / min, the temperature was raised to 650°C at a rate of 3°C / min, silane gas was introduced at a rate of 3L / min, and the temperature was maintained for 5h. After deposition, the silane gas was turned off, the protective gas flow conditions remained unchanged, and the temperature was raised to 820°C at a rate of 3°C / min. After the temperature stabilized, acetylene gas and ammonia gas were introduced at a rate of 4L / min and 0.5L / min, respectively. After maintaining the temperature for 1h, the acetylene and ammonia gases were turned off and the temperature was cooled to room temperature to obtain a silicon-carbon material.

[0093] The silicon-carbon negative electrode materials prepared in the above examples and comparative examples were subjected to a buckle test and a cycle test. The electrochemical performance was measured in a 2032 buckle test. The specific test conditions were as follows: the silicon-carbon negative electrode material, conductive agent SP, and binder la133 were mixed in a ratio of 75:10:15, and an appropriate amount of water was added to obtain a slurry. The slurry was coated on copper foil and dried. After that, an electrode sheet was obtained using a punching machine. A lithium sheet was used as the counter electrode, the electrolyte used was 1 mol / L LiPF6, and the solvent composition was EC:EMC = 3:7. 5 wt.% FEC film-forming additive was added to the electrolyte. Celgard 2400 polyethylene film was used as the separator. The material specific capacity test charge and discharge range was 0.005V-1.5V, and the test current was 0.1C. The cycle test was 0.1C discharge to 50mV and 0.1C charge to 1.5V, and the cycle test was 50 cycles. The rate test conditions are as follows: the material is mixed with fast-charging graphite, and the mixed material capacity is 480mAh / g. The constant current discharge is gradually reduced from 0.1C to 0.02C. The constant rate discharge gradient is: 0.2C discharge and double charge for 5 weeks; 0.5C discharge and double charge for 5 weeks; 1C discharge and double charge for 5 weeks; 2C discharge and double charge for 5 weeks; 3C discharge and double charge for 5 weeks; 0.5C discharge and double charge for 5 weeks; 1C discharge and double charge for 5 weeks. The specific test results are shown in Table 1.

[0094] The true density of the material was tested using a G-DenPyc 3900M true density meter produced by Guoyi.

[0095] The 20kN resistivity of the material was tested using the Ruikewei intelligent FT-3110 four-probe resistivity tester.

[0096] Table 1 Performance test

[0097] Conclusion: From the power-off data, it can be seen that the reversible capacity range of nitrogen-doped Examples 1-6 is 2067.9-2121.8 mAh / g, and the first efficiency is 90.9%-91.2%. Compared with the reversible capacity range of Comparative Examples 1-6 of 1917.0-2013.1 mAh / g and the first efficiency of 90.1%-91.3%, the reversible capacity and first efficiency of nitrogen-doped silicon-carbon materials will be slightly improved. The reason is that the kinetic performance is improved by doping in the material, and the capacity of the active material is fully released, which makes both the reversible capacity and the first efficiency improved. The true density of nitrogen-doped examples 1-6 is 1.99-2.13 g / cc, and the 50-week capacitance retention rate is 23.1-28.1%, while the true density of comparative examples 1-6 is 1.73-1.91 g / cc, and the 50-week capacitance retention rate is 14.8-19.8%. The reason is that the nitrogen-doped carbon material improves the interfacial affinity with silane, making the nano-silicon deposition denser, avoiding loose and porous structures, and improving the material particle strength. Therefore, the cracking of the material during the cycle is alleviated, and the cycle performance is significantly improved. The resistivity of nitrogen-doped examples 1-6 under 20kN pressure conditions is 1.511-2.356 E+00Ω·cm, and the 2C buckle capacitance retention rate is 21.5-25.9%, while the resistivity of comparative examples 1-6 under 20kN pressure conditions is 3.211-5.285 E+00Ω·cm, and the 2C buckle capacitance retention rate is 14.8-18.6%. This is because the nitrogen-doped pyridine doping structure in the carbon substrate forms a localized donor state close to the Fermi level, which increases the state density of the Fermi surface, thereby improving the conductivity of the material; in addition, the increase in the number of carriers of boron-doped nano-silicon increases the electronic conductivity, and the nano-heterojunction sites bring about an increase in ionic conductivity. The above structural design greatly improves the electrochemical reaction kinetics of the material, thereby significantly improving the rate performance.

[0098] In addition, the inventors of this case also referred to the aforementioned embodiments and conducted experiments using other raw materials, process operations, and process conditions described in this specification, and obtained relatively ideal results.

[0099] It should be understood that the technical solution of the present invention is not limited to the above-mentioned specific implementation cases. Any technical variations made according to the technical solution of the present invention without departing from the scope of protection of the purpose of the present invention and the claims shall fall within the scope of protection of the present invention.

Claims

1. A silicon-carbon material, characterized in that: include: Nitrogen-doped porous carbon and an amorphous carbon layer covering the nitrogen-doped porous carbon, wherein the pores of the nitrogen-doped porous carbon are filled with boron-doped nano-silicon.

2. The silicon-carbon material according to claim 1, wherein: The particle size D50 of the nitrogen-doped porous carbon is 2 to 20 μm; And / or, the content of nitrogen-doped porous carbon in the silicon-carbon material is 10 to 60 wt%; And / or, the content of nitrogen in the silicon-carbon material is 0.1 to 30 wt%; And / or, the boron content in the silicon-carbon material is 0.5-5 wt%; And / or, the content of nano-silicon in the silicon-carbon material is 35-60wt%; And / or, the particle size of the boron-doped nano-silicon is less than 50 nm; And / or, the content of the amorphous carbon layer in the silicon-carbon material is 0.3 to 30 wt%; and / or, the thickness of the amorphous carbon layer is 20 to 300 nm; And / or, the amorphous carbon layer is doped with nitrogen.

3. The silicon-carbon material according to claim 2, characterized in that: The content of nitrogen-doped porous carbon in the silicon-carbon material is 35 to 55 wt %; And / or, the content of nitrogen in the silicon-carbon material is 1 to 15 wt%; And / or, the content of boron in the silicon-carbon material is 1 to 3 wt%; And / or, the particle size of the boron-doped nano-silicon is less than 5 nm; And / or, the content of the amorphous carbon layer in the silicon-carbon material is 0.5-10 wt%; And / or, the thickness of the amorphous carbon layer is 30-80 nm.

4. The method for preparing a silicon-carbon material according to any one of claims 1 to 3, wherein: include: Prepare nitrogen-doped porous carbon by at least one of a template method, a chemical vapor deposition method, and a pyrolysis method; reacting a mixture comprising at least the nitrogen-doped porous carbon, a silicon source gas, and a boron source gas to produce nitrogen-doped porous carbon with pores filled with boron-doped nano-silicon; Furthermore, a carbon source is used to coat the nitrogen-doped porous carbon in which the pores are filled with boron-doped nano-silicon to obtain a silicon-carbon material.

5. The preparation method according to claim 4, characterized in that Specifically include: causing an organic monomer containing a carbon-nitrogen bond to undergo a polymerization reaction to obtain a nitrogen-containing organic polymer, and then subjecting the nitrogen-containing organic polymer to drying, ball milling, carbonization, and pore formation to obtain nitrogen-doped porous carbon; And / or, the preparation method specifically comprises: carbonizing and activating a carbon source material to obtain a porous carbon material, then subjecting the porous carbon material to a gas-phase nitrogen doping treatment, and then subjecting the porous carbon material to a heat treatment to obtain nitrogen-doped porous carbon; And / or, the preparation method specifically includes: carbonizing and activating the carbon source material to obtain a porous carbon material, then compounding the porous carbon material with a nitrogen-containing compound, and then subjecting it to a high-temperature carbonization treatment to obtain nitrogen-doped porous carbon.

6. The preparation method according to claim 5, characterized in that: The organic monomer containing a carbon-nitrogen bond includes any one or more combinations of amine compounds, nitrogen heterocyclic compounds, nitrile compounds, and nitro compounds; And / or, the carbon source material includes any one or more combinations of natural biomass, non-biological polymers, and carbon-containing compounds obtained by processing fossil fuels; wherein the natural biomass includes any one or more combinations of lignin, cellulose, chitosan, protein, and natural rubber; the non-biological polymer includes any one or more combinations of synthetic rubber, synthetic resin, and synthetic fiber; the carbon-containing compounds obtained by processing fossil fuels include carbon-containing compounds obtained by processing coal, coke, or asphalt; And / or, the activating agent used in the activation treatment includes any one or more combinations of steam, carbon dioxide, alkali, alkali metal salt, strong acid, and phosphoric acid; And / or, the nitrogen-containing compound includes any one or more combinations of HCN, HNO3, N,N-dimethylethanolamine, N,N-dimethylpropylenediamine, urea, dicyandiamide, N,N-dimethylformamide, melamine, and polyaniline.

7. The preparation method according to claim 4, characterized in that Specifically include: The nitrogen-doped porous carbon is placed in a reaction apparatus and replaced with a protective gas to reduce the oxygen content to below 200 ppm. Then, silicon source gas, boron source gas, and protective gas are introduced and reacted at 350-950° C. for 1-8 hours to obtain nitrogen-doped porous carbon with boron-doped nano-silicon filled in the pores. And / or, the preparation method specifically comprises: placing nitrogen-doped porous carbon with boron-doped nano-silicon in its pores in a reaction device and introducing a carbon source gas in a protective atmosphere for thermal cracking to obtain a silicon-carbon material; Alternatively, nitrogen-doped porous carbon with boron-doped nano-silicon in its pores is mixed with a solid carbon source and subjected to carbonization treatment to obtain a silicon-carbon material; alternatively, nitrogen-doped porous carbon with boron-doped nano-silicon in its pores is mixed with a liquid dispersant containing a carbon source and dried and carbonized to obtain a silicon-carbon material; alternatively, nitrogen-doped porous carbon with boron-doped nano-silicon in its pores is mixed with a liquid carbon source and subjected to carbonization treatment to obtain a silicon-carbon material.

8. The preparation method according to claim 7, characterized in that: The silicon source gas includes any one or more of silane, disilane, trisilane, tetrasilane, monochlorosilane, dichlorosilane, trichlorosilane, and tetrachlorosilane; And / or, the boron source gas includes a compound composed of boron and hydrogen and / or a compound that can be decomposed to produce boron element; And / or, the protective gas includes any one or more combinations of nitrogen, helium, neon, argon, krypton, and xenon; And / or, the flow ratio of the silicon source gas, the boron source gas and the protective gas is 10-40:1-15:45-90; And / or, the thermal cracking temperature is 380-1180°C and the time is 1-6h; And / or, the carbonization treatment temperature is 500-1010° C. and the time is 2-8 hours.

9. Use of the silicon-carbon material according to any one of claims 1 to 3 in preparing a battery negative electrode sheet or a lithium-ion battery.

10. A negative electrode active material for a lithium ion secondary battery, characterized in that: The invention comprises the silicon-carbon material according to any one of claims 1 to 3.

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