CN113889609A - Nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite negative electrode material and preparation method thereof - Google Patents

Nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite negative electrode material and preparation method thereof Download PDF

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CN113889609A
CN113889609A CN202111139137.1A CN202111139137A CN113889609A CN 113889609 A CN113889609 A CN 113889609A CN 202111139137 A CN202111139137 A CN 202111139137A CN 113889609 A CN113889609 A CN 113889609A
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nitrogen
graphite
zinc oxide
doped silicon
silicon oxide
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CN113889609B (en
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王兴蔚
侯佼
王北平
侯春平
马勇
贺超
杨丹
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Bolt New Materials Yinchuan Co ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Abstract

The invention provides a nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite negative electrode material and a preparation method thereof, wherein graphitized anthracite is taken as a graphite substrate, a supercritical fluid method is adopted to carry out intercalation and jack compounding of nitrogen source molecules on the graphite substrate, and the nitrogen-doped modified graphite is prepared through hydrothermal reaction; preparing nano silicon dioxide sol under the action of alkaline conditions and a stabilizer by using silicon tetrachloride which is a byproduct in the production of polycrystalline silicon as a silicon source, carrying out intercalation and jack precipitation compounding on the nano silicon dioxide sol on nitrogen-doped modified graphite by adopting a supercritical fluid method, and then partially reducing by melting metal zinc powder to prepare a nitrogen-doped silicon oxide/zinc oxide/graphite compound; and an organic carbon source is used as a coating agent, the compound is coated and formed by adopting a kneading and compacting process, and the nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite anode material with high tap density and excellent processing performance is prepared by high-temperature calcination, crushing and screening.

Description

Nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite negative electrode material and preparation method thereof
Technical Field
The invention relates to the technical field of battery cathode material production, in particular to a nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite cathode material and a preparation method thereof.
Background
The theoretical lithium storage capacity of silicon is up to 4200mAh/g, which is more than 10 times of that of commercial graphite cathode materials, and is a cathode material with the highest specific capacity and the highest development potential, but the single use of silicon as a cathode material has larger application challenges, and the Li-Si alloying has about 300% volume expansion change during the charging and discharging process, so that the silicon particles are easily pulverized and lose activity, on the other hand, the electrical contact between the active particles and a current collector is poor to form an island effect, and a new SEI film is repeatedly formed on a fracture surface, so that the irreversible capacity loss of the material, the coulombic efficiency and the cycle performance are poor; while the conductivity of silicon is low (10)-5～10-3S cm-1) And has a small ion diffusion coefficient (10)-14～10-13cm2 s-1) It is not favorable for the capacity and rate performance of the active components of the electrode. At present, a modification method for silicon materials mainly comprises nanocrystallization and compositing, but the silicon materials are easy to agglomerate after nanocrystallization, a new volume effect can be generated in a circulation process, the problem of circulation stability of the silicon materials cannot be fundamentally solved by pure nanocrystallization, the cost for preparing nano silicon powder with a special structure and morphology is high, and the problems of large specific surface area, low tap density and the like caused by the nano effect influence the wide application of the nano silicon powder in batteries; the compounding is mainly characterized in that on the basis of reducing the volume effect of a silicon active phase by silicon nanocrystallization, an active or inactive buffer matrix with good conductivity and small charge-discharge volume effect is introduced, and the physical and chemical properties of different components of the material are synergistic to improveThe cycling stability and processability of the silicon-based materials.
The silicon-carbon composite material is the silicon-based material with the most application potential at present, and mainly comprises two technical routes of a simple substance silicon-carbon composite material and a silicon oxide-carbon composite material. Wherein, silicon oxide (SiO)xX is more than 0 and less than or equal to 2) is an amorphous structure and is composed of a plurality of uniformly distributed nano-scale Si clusters and SiO2Cluster and inter-Si/SiO2SiO between two phase interfacesxThe transition phases are combined. The silicon oxide can form Li (lithium) product during the first electrochemical charge/discharge processxSi and non-active phase lithium oxide (Li)2O) and lithium silicate (Li)4SiO4) Non-active phase Li2O and Li4SiO4Surrounding Li with a matrixxThe Si core is surrounded by a good in-situ buffer matrix, can reduce the charge-discharge volume expansion of the active material to about half of that of pure silicon, and can support and disperse the active phase LixSi prevents agglomeration in the later cycle, and Li2The O matrix can be used as a rapid diffusion channel of lithium ions in the process of charging and discharging so as to improve the cycle performance and rate capability of the material. Therefore, compared with the simple substance silicon-based silicon-carbon composite cathode material, the silicon oxide-based silicon-carbon composite cathode material has a larger scale application prospect in the fields of power and energy storage. On the other hand, however, silicon oxides form the inactive phase Li during the first charge-discharge process2O and Li4SiO4The matrix, although accelerating the microstructure tissue dynamics process, effectively improving the electrochemical performance and relieving the volume expansion stress, also causes the electrochemical activity lithium storage phase LixThe reduction of Si reduces the specific capacity and the first coulombic efficiency of the material, and meanwhile, the material still faces a larger volume expansion effect in the practical application of the finished battery.
At present, the research on silicon oxide-based silicon-carbon composite materials mainly comprises SiOxThe design of the nano particle structure of the body, the design and doping of the three-dimensional porous structure of the matrix phase, the coating of the interface and the surface and the like are started, so as to solve the problems of low coulombic efficiency caused by volume expansion and pulverization of the charge-discharge silicon material, SEI film formation of an unstable interface and high irreversible capacityTo give a title. Chinese patent CN112018334A discloses a silicon oxide/carbon composite negative electrode material, a preparation method thereof and a lithium ion battery, wherein a micro-nano SiO is usedxThe silicon oxide/carbon composite negative electrode material with good capacity and first coulombic efficiency and a secondary particle structure is prepared by mixing, granulating, modifying, carbonizing and screening the powder and a carbonaceous binder, but the silicon material cost is high, the multiplying power charge-discharge cycle performance is poor and the capacity attenuation is fast. Chinese patent CN112447958A discloses a preparation method of a nitrogen-doped porous carbon-coated porous silicon dioxide cathode material, the method obtains nitrogen-containing alkali lignin through Mannich reaction, the nitrogen-containing alkali lignin and 3-chloro-2-hydroxypropyl trimethyl ammonium chloride undergo substitution reaction to obtain positively charged quaternized nitrogen-containing alkali lignin, and the quaternized nitrogen-containing alkali lignin and porous silicon dioxide nanospheres undergo electrostatic attraction carbonization to obtain the nitrogen-doped porous carbon-coated porous silicon dioxide cathode material in a three-dimensional network structure.
Disclosure of Invention
The invention aims to provide a nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite negative electrode material which has high capacity, high multiplying power, long cycle life and low production cost and is suitable for large-scale industrialization and a preparation method thereof.
The invention provides a preparation method of a nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite negative electrode material, which comprises the following steps:
(1) and (3) nitrogen source compounding: adding a certain amount of graphitized anthracite micro powder into the nitrogen-containing solution, uniformly mixing, injecting into a high-pressure reaction kettle, heating the reaction kettle to a specified temperature, pumping liquid carbon dioxide into the reaction kettle to enable the carbon dioxide in the kettle to reach a set pressure, controlling the temperature and the pressure of materials in the reaction kettle and keeping for a certain time, slowly releasing pressure to discharge the carbon dioxide in the reaction kettle, and repeating the supercritical operation for several times to prepare a pretreated graphite micro powder solution;
(2) nitrogen doping by a hydrothermal method: heating the graphite micro powder solution pretreated in the step (1) to a specified temperature while stirring in a high-pressure reaction kettle under a closed condition, keeping reacting for a certain time, stopping stirring, and naturally cooling to room temperature to obtain a nitrogen-doped modified graphite micro powder solution;
(3) preparing nano silicon dioxide sol: preparing an alkaline aqueous solution with a certain concentration at room temperature, adding a stabilizer into the alkaline aqueous solution under a stirring state, mixing for a certain time till the solution is uniform, then slowly adding silicon tetrachloride to adjust the pH value of the solution to be neutral, continuously keeping stirring and reacting for a certain time, and standing and aging the solution to obtain a nano-silica sol in a stable state;
(4) compounding nano silica sol: uniformly stirring the nano-silica sol prepared in the step (3) and the nitrogen-doped modified graphite micro-powder solution prepared in the step (2) in a high-pressure reaction kettle according to a certain proportion to form a mixed solution, stopping stirring, heating the reaction kettle to a specified temperature, pumping liquid carbon dioxide into the reaction kettle to enable the carbon dioxide in the kettle to reach a set pressure, controlling and keeping the temperature and the pressure of materials in the reaction kettle for a certain time, slowly releasing pressure to discharge the carbon dioxide in the reaction kettle, and washing, removing liquid and drying to prepare a nitrogen-doped silica/graphite compound;
(5) melting and reducing: uniformly mixing metal zinc powder and the nitrogen-doped silicon dioxide/graphite compound prepared in the step (4) according to a certain proportion, then putting the mixture into a high-temperature reaction kettle, stirring and heating the mixture from room temperature to a first constant temperature T1 under the atmosphere of protective gas, preserving heat, continuing stirring and heating the mixture to a second constant temperature T2 after the T1 heat preservation is finished, preserving heat, stirring and cooling the mixture to room temperature after the heat preservation is finished, and obtaining the nitrogen-doped silicon oxide/zinc oxide/graphite compound;
(6) kneading, coating and compacting: uniformly mixing an organic carbon source and the nitrogen-doped silicon oxide/zinc oxide/graphite composite prepared in the step (5) according to a certain proportion, putting the mixture into a kneading machine, kneading and coating the mixture under a heating condition, putting the material into a tablet press after the kneading and cooling are finished, and keeping the material under a specified pressure for a certain time to form an organic carbon source-coated nitrogen-doped silicon oxide/zinc oxide/graphite composite anode material precursor body;
(7) high-temperature calcination: and (4) placing the organic carbon source coated nitrogen-doped silicon oxide/zinc oxide/graphite composite negative electrode material precursor blank prepared in the step (6) in a high-temperature atmosphere furnace, calcining in a protective gas atmosphere, naturally cooling to room temperature in the furnace after calcination, crushing, screening and grading to obtain the final product nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite negative electrode material.
Preferably, in the step (1), the graphitized anthracite micro-powder has an average particle size D50 of 6.0-12.0 μm and a carbon content of more than 99.5%, and the anthracite raw material is preferably taixi anthracite; the nitrogen dissolving source in the nitrogen-containing solution in the step (1) is one or more of urea, melamine and ammonium chloride, the solvent in the nitrogen-containing solution is one of deionized water, ethanol, N-methyl pyrrolidone and dimethylformamide, the mass fraction of the nitrogen source in the nitrogen-containing solution is 3-8%, and the mass ratio of the graphitized anthracite micro powder to the solute nitrogen source in the nitrogen-containing solution is 1: (0.05-0.15); in the step (1), the temperature in the high-pressure reaction kettle is controlled to be 31-80 ℃, the pressure is 7-35 MPa, the supercritical retention time of the material in the high-pressure reaction kettle is 1.5-3.0 h, the slow pressure relief time is not less than 2.5h, and the supercritical operation times are 2-4.
Preferably, in the step (2), the stirring speed is 150-850 r/min, the material reaction temperature in the high-pressure reaction kettle is 130-200 ℃, and the material reaction time is 2-6 h.
Preferably, the solute of the alkaline solution in the step (3) is one or more of sodium hydroxide, sodium carbonate, sodium bicarbonate, potassium hydroxide, potassium carbonate and potassium bicarbonate, and the mass fraction of the solute in the alkaline solution is 6.0-25%; the adding amount of the stabilizer in the step (3) is 1.0-3.5% of the mass of the alkaline aqueous solution; the stabilizer is a mixed solvent of a cationic surfactant and a nonionic surfactant, and the mass ratio of the cationic surfactant to the nonionic surfactant is (0.30-0.65): 1; the cationic surfactant is one of hexyl trimethyl ammonium bromide, dodecyl trimethyl ammonium bromide, cationic polyacrylamide, poly (dimethylaminoethyl acrylate), poly (dimethylaminoethyl methacrylate) and polyethyleneimine, and the nonionic surfactant is one of polyvinyl pyrrolidone, polyethylene glycol and alkylphenol polyoxyethylene; the silicon tetrachloride in the step (3) is a byproduct of polycrystalline silicon production with the purity of more than 99.0 percent; in the step (3), the stirring speed is 350-1200 r/min, the stirring and mixing time is 90-150 min, the stirring reaction time is 60-150 min, and the standing and aging time of the solution is 2.5-6.0 h.
Preferably, the mass ratio of the nano silicon dioxide to the nitrogen-doped modified graphite micropowder in the mixed solution in the step (4) is (0.05-0.12): 1; in the step (4), the stirring speed is 300-1000 r/min, and the stirring and mixing time is 60-150 min; and (4) controlling the temperature in the high-pressure reaction kettle in the step (4) to be 31-80 ℃, controlling the pressure to be 7-35 MPa, keeping the supercritical retention time of the materials in the high-pressure reaction kettle to be 3.0-6.5 h, and slowly releasing the pressure for not less than 2.5 h.
Preferably, in the step (5), the first constant temperature T1 is 400-450 ℃, the reaction stage is from room temperature to T1 temperature, the stirring speed is 50-150 r/min, the heating rate is 2-5 ℃/min, and the heat preservation time is 60-150 min; the second constant temperature T2 is 700-900 ℃, the temperature T1 is in a reaction stage from T2, the stirring speed is 40-90 r/min, the heating rate is 2-5 ℃/min, and the heat preservation time is 90-240 min; in the step (5), the molar ratio of the metal zinc powder to the silicon dioxide in the nitrogen-doped silicon dioxide/graphite compound is (0.25-0.65): 1, the average grain diameter D50 of the metallic zinc powder is 50 nm-25 μm, and the mass content is more than 99%; the protective gas in the step (5) is one or more of nitrogen, helium, neon, argon, krypton or xenon, and the flow rate of the protective gas is 0.4-1.2 m3/h。
Preferably, in the step (6), the organic carbon source is one or more of polyvinyl alcohol, polyethylene glycol, phenolic resin, epoxy resin, polyvinylidene fluoride and asphalt, and the mass ratio of the organic carbon source to the nitrogen-doped silicon oxide/zinc oxide/graphite composite is (0.15-0.35): 1; and (3) in the step (6), the kneading temperature is 110-180 ℃, the kneading time is 2-4 h, the green pressing pressure is 7-20 Mpa, and the green pressing time is 0.5-2.0 h.
Preferably, the temperature rise rate of the calcination treatment in the step (7) is 3-5 ℃/min, and the calcination temperature is 750 DEG CThe constant temperature is between 2.5 and 6.0 hours at the temperature of 1000 ℃ below zero; the protective gas in the step (7) is one or more of nitrogen, helium, neon, argon, krypton or xenon, and the flow rate of the protective gas is 0.4-1.2 m3H; the average particle size D50 of the nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite negative electrode material crushed in the step (7) is 14.0-17.0 μm.
The invention also discloses a nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite negative electrode material which consists of the nitrogen-doped silicon oxide/zinc oxide/graphite composite with disordered distribution, amorphous carbon coated on the surface of the nitrogen-doped silicon oxide/zinc oxide/graphite composite and amorphous carbon bridged around the coated nitrogen-doped silicon oxide/zinc oxide/graphite composite.
The preparation principle of the invention is as follows: the invention provides a nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite negative electrode material and a preparation method thereof, wherein graphitized anthracite is used as a graphite substrate, a supercritical fluid method is adopted to carry out intercalation and jack compounding of nitrogen source molecules on the graphite substrate, and the nitrogen-doped modified graphite is prepared through hydrothermal reaction; preparing nano silicon dioxide sol under the action of alkaline condition and a stabilizing agent consisting of a cationic surfactant and a nonionic surfactant by using silicon tetrachloride which is a byproduct in polysilicon production as a silicon source, performing intercalation and jack precipitation compounding on the nano silicon dioxide sol by adopting a supercritical fluid method to perform nitrogen-doped modified graphite, and performing partial reduction through melting metal zinc powder to prepare nitrogen-doped silicon oxide (SiO)xX is more than 0 and less than 2)/zinc oxide/graphite compound; the organic carbon source is used as a coating agent, the nitrogen-doped silicon oxide/zinc oxide/graphite compound is coated and molded by adopting a kneading and compacting process, and the nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite anode material with high tap density and excellent processing performance is prepared by high-temperature calcination, crushing and screening. Specifically, the method comprises the following steps:
compared with natural graphite, the graphitized anthracite in the step (1) has the structural performance characteristics of porous surface, large graphite layer spacing, high mechanical strength and high mechanical strength of the internal structure mainly comprising microcrystalline graphite distribution, and the carbon dioxide has super-solubility, strong diffusivity and unique mass transfer property in a supercritical state; meanwhile, the pressure release rate of the carbon dioxide under the supercritical pressure is optimally controlled, controllable layer expanding and hole expanding preparation can be realized on the graphitized anthracite, a channel and a space are further provided for the combination of the jack and the intercalation of a nitrogen source, and the carbon dioxide can be recycled for multiple times. On the other hand, a small amount of microcrystalline graphite in the graphitized anthracite is stripped into flocculent graphene sheets which are uniformly distributed among the layers and on the surface of the pretreated graphite micro-powder, so that the conductivity of the modified graphite can be effectively enhanced;
introducing nitrogen atoms into graphite layers and surface micropores to form covalent bonds under the hydrothermal reaction condition of the pretreated graphite micropowder compounded by the nitrogen source intercalation and the jacks, wherein the radius of the nitrogen atoms is close to that of carbon atoms, but the electronegativity is high, the crystal structure and pore channels of the graphite can be maintained by doping the nitrogen atoms, and the extra lone pair electrons of the nitrogen atoms can provide negative charges for a carbon skeleton delocalized system in the graphite crystal structure, so that active sites with high electronegativity are generated at the corresponding doping positions between the graphite layers and the surface micropores, thereby not only effectively enhancing the electron transmission performance and the chemical reaction activity of the nitrogen-doped modified graphite and improving the low-temperature charge-discharge performance of the material, but also being beneficial to promoting the uniform precipitation compounding of nano-silica sol containing a cationic surfactant as a stabilizer at the later stage;
in the step (3), the stabilizer is a mixed solvent of a cationic surfactant and a nonionic surfactant, and the silicon dioxide belongs to an atomic crystal, so that the cationic surfactant does not have negative influence on the dispersibility of the nano-silicon dioxide, but a large number of active sites with high electronegativity are distributed between graphite layers and surface micropores of the nitrogen-doped modified graphite prepared in the step two, and the cationic surfactant uniformly dispersed in a nano-silicon dioxide sol system can promote the micro-diffusion movement capability of the nano-silicon dioxide between the nitrogen-doped modified graphite layers and in the surface micropores, so that the compounding uniformity and efficiency of the nano-silicon dioxide are improved;
in the step (4), by utilizing the super-solubility and strong diffusivity characteristics of the carbon dioxide supercritical fluid and the electric polarity action of the cationic surfactant in the nano-silica sol system, uniform precipitation compounding of the nano-silica between the nitrogen-doped modified graphite layers and surface micropores is realized through single supercritical operation;
in the heat preservation stage at the first constant temperature T1 in the step (5), the metal zinc powder is stirred and continuously diffused, impregnated and permeated into the graphite interlayer and surface micropores of the nitrogen-doped silicon dioxide/graphite compound in a molten state, and the metal zinc powder and part of the nano silicon dioxide are subjected to oxidation-reduction reaction to generate high-capacity active substance nano silicon oxide (SiOx, x is more than 0 and less than 2) and zinc oxide, and the graphite interlayer and surface micropores can reserve space for charge-discharge expansion of the active substance, so that the volume stress of the composite material in the charge-discharge process is effectively relieved; in the second constant temperature T2 heat preservation stage, the stabilizer which is compounded between graphite layers and surface micropores along with the precipitation of the nano silicon dioxide is carbonized at high temperature under the action of the supercritical fluid, a carbon coating layer with good conductivity is gradually generated on the surfaces of the nano silicon oxide and the zinc oxide, and the coated fusion reduction product is connected with adjacent graphite sheet layers and the inner surfaces of the surface micropores in series through Van der Waals force to form carbon fibers, so that the c-axis electronic conductivity of the graphite layer is effectively improved, and the composite material has high specific capacity and is suitable for large-rate charge and discharge; meanwhile, the oxygen-containing functional group in the stabilizer can further oxidize the metal zinc powder which is not completely reacted in the T1 stage in the T2 stabilizing process so as to ensure that no metal zinc powder remains in the final product. The theoretical capacity of the zinc oxide is up to 978mAh/g, and the zinc oxide sediment coated on the surface is compounded between graphite layers and surface micropores to ensure that the zinc oxide sediment is taken as an active component of a composite material to show excellent electrochemical performance;
in the step (6), through stirring, extruding, splitting and kneading of a kneading machine, an organic carbon source is fully infiltrated and permeated into surface gaps of the nitrogen-doped silicon oxide/zinc oxide/graphite compound and stripping defects of a graphite layer after being softened at a high temperature to form a paste with high compactness and good shaping; meanwhile, after the paste is cooled, the paste is subjected to compaction treatment by a tablet press, so that the friction stress among particles of the paste is further eliminated, the compaction density is improved, the mechanical strength of secondary particles of a final product can be effectively enhanced, and the composite material has good circulation stability;
the nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite negative electrode material prepared in the step (7) is secondary granulated particles, macroscopically shows isotropy, can effectively improve the stability of the material structure, and is suitable for embedding and embedding lithium ions in the high-rate charge-discharge process.
The nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite negative electrode material prepared by the invention is secondary granulated particles and consists of a nitrogen-doped silicon oxide/zinc oxide/graphite compound which is distributed in a disordered manner, amorphous carbon coated on the surface of the nitrogen-doped silicon oxide/zinc oxide/graphite compound and amorphous carbon bridging around the coated nitrogen-doped silicon oxide/zinc oxide/graphite compound. The graphitized anthracite coal with the graphite substrate is doped with nitrogen atoms in graphite layers and surface micropores to form covalent bonds, so that a large number of active sites with high electronegativity are generated at corresponding doping positions, the electronic transmission performance and the chemical reaction activity of the graphite substrate are effectively enhanced, and the low-temperature charge and discharge performance of the material is improved; amorphous carbon coated high capacity active material nano silicon oxide (SiO)xX is more than 0 and less than 2) and zinc oxide are compounded between graphite layers and surface micropores, and carbon fibers are taken as a medium and are connected with adjacent graphite sheet layers and the inner surfaces of the surface micropores in series through Van der Waals force, so that the volume stress of an active substance in the charge-discharge process can be effectively relieved, the c-axis electronic conductivity of the graphite layer is improved, and the composite material has higher specific capacity and is suitable for large-rate charge-discharge; the surfaces of the nitrogen-doped silicon oxide/zinc oxide/graphite compound particles which are distributed in a disordered way are coated with compact amorphous carbon coating layers, and the particles are bridged with each other through amorphous carbon to form secondary particles with controllable particle size distribution, so that the composite anode material particles are macroscopically isotropic, and the mechanical strength and the multiplying power circulation stability of the material structure can be effectively improved.
The method takes the graphitized anthracite as a stable structure carrier of the composite material, takes the silicon tetrachloride which is a byproduct in the production of the polycrystalline silicon as a silicon source, has wide raw material sources and low price, and is beneficial to reducing the production cost of the composite material. The graphitized anthracite has the structural performance characteristics of porous surface, large graphite layer spacing, microcrystalline graphite distribution as a main internal structure, high mechanical strength and the like, is favorable for easily realizing controllable adjustment in the supercritical fluid expanding, reaming and modifying process, can keep the original morphology structure of the material to the maximum extent, and reduces the generation of graphite layer stripping defects, thereby providing channels and spaces with proper geometric dimensions and stable morphology structures for the compounding of a nitrogen source and nano silica sol between graphite layers and surface micropores of the graphite source and the nano silica sol. Nitrogen atoms are doped between graphite layers and surface micropores to generate a large number of electronegative active sites, so that the electrochemical reaction activity and the low-temperature charge and discharge performance of the graphitized anthracite are enhanced, and the capability of microcosmic diffusion movement of a nano-silica sol system containing a cationic surfactant as a stabilizer is improved, so that the nano-silica precipitation compounding is uniform and high in efficiency. The stabilizer in the nano silicon dioxide sol is deposited in graphite layers and surface micropores along with the nano silicon dioxide under the action of a supercritical fluid, after the nano silicon dioxide sol is pyrolyzed at high temperature, amorphous carbon is generated to be coated on the surfaces of zinc powder fusion reduction products, namely nano silicon oxide and zinc oxide, and carbon fibers are formed to connect the coated fusion reduction products, adjacent graphite sheets and the inner surfaces of the surface micropores in series through Van der Waals force. The kneading coating and the pressed compact effectively improve the material compaction density and the mechanical strength while repairing and improving the defects of the internal structure cavity of the composite material, so that the final product has excellent processing performance and good multiplying power charge-discharge cycle stability. The invention has the advantages of easy control of process conditions, low production cost and easy industrial production.
The invention has the beneficial effects that:
1. the silicon source used in the invention is silicon tetrachloride which is a byproduct in the production of polycrystalline silicon, and the price is low, so that the production cost of the composite cathode material can be effectively reduced; meanwhile, a new idea is provided for energy-saving and environment-friendly treatment of the byproducts in the production of the polysilicon, and the high-value utilization of the silicon tetrachloride byproducts is facilitated.
2. According to the invention, by utilizing the structural characteristics that the graphitized anthracite is porous on the surface, the graphite layer spacing is large, the distribution of microcrystalline graphite is taken as the main internal structure, the mechanical strength is high and the like, and the supercritical fluid is combined with the hydrothermal synthesis method to introduce nitrogen atoms into the graphite layers and surface micropores of the graphitized anthracite to dope and form covalent bonds, so that a large number of active sites with high electronegativity are generated at corresponding doping positions, and the micro diffusion motion capability of uniformly precipitating and compounding the nano silicon dioxide sol system containing a cationic surfactant as a stabilizer between the graphite layers and the surface micropores of the graphitized anthracite is improved while the electrochemical reaction activity and the low-temperature charge and discharge performance of the graphitized anthracite are enhanced.
3. According to the invention, the amorphous carbon-coated high-capacity active substance nano silicon oxide (SiOx, x is more than 0 and less than 2) and zinc oxide are compounded between graphite layers and surface micropores, and carbon fibers are taken as a medium and are connected with adjacent graphite sheet layers and the inner surfaces of the surface micropores in series through van der Waals force, so that the volume stress of the active substance in the charge-discharge process can be effectively relieved, the c-axis electronic conductivity of the graphite layer is improved, and the composite material not only has higher specific capacity but also is suitable for large-rate charge-discharge;
4. the preparation method of the invention is simple, easy to control, low in cost and easy for industrial production.
Drawings
FIG. 1 is an SEM photograph of graphitized anthracite coal as a graphite substrate in example 4;
fig. 2 is an SEM image of the nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite anode material prepared in example 4.
Detailed Description
In order to make the technical solution of the present invention easier to understand, the technical solution of the present invention is now clearly and completely described by using the specific embodiments.
The first embodiment is as follows:
example 1:
(1) according to the mass ratio of the graphitized anthracite micro powder to the nitrogen source solute of the nitrogen-containing solution being 1: 0.05, adding graphitized anthracite micro powder with the average particle size D50 of 6 microns into urea aqueous solution with the mass fraction of 3%, uniformly mixing, injecting into a high-pressure reaction kettle, heating the reaction kettle to 31 ℃, pumping liquid carbon dioxide into the reaction kettle to enable the pressure of the carbon dioxide in the kettle to reach 35MPa, controlling the temperature and the pressure of the reaction kettle to be unchanged, keeping the temperature and the pressure for 1.5 hours, slowly releasing the pressure for 5 hours, discharging the carbon dioxide, and repeating the supercritical operation for 4 times to prepare pretreated graphite micro powder solution;
(2) sealing the high-pressure reaction kettle, heating the pretreated graphite micro powder solution to 200 ℃ at the rotating speed of 150r/min, continuously keeping the reaction for 2 hours, then stirring, and naturally cooling to room temperature to obtain a nitrogen-doped modified graphite micro powder solution;
(3) preparing a sodium hydroxide aqueous solution with the mass fraction of 6.0% at room temperature, adding a combined stabilizer with the mass fraction of 1.0% of the sodium hydroxide aqueous solution and the mass ratio of 0.30:1 to polyethylene pyrrolidone at the rotating speed of 350r/min, stirring and mixing for 150min, slowly adding silicon tetrachloride with the purity of more than 99.0% to adjust the pH value of the solution to be neutral, continuously keeping stirring and reacting for 60min, and standing and aging the solution for 2.5h to obtain a stable nano silicon dioxide sol;
(4) adding a certain amount of nano silica sol into a high-pressure reaction kettle containing nitrogen-doped modified graphite micropowder solution according to the mass ratio of 0.05:1 of silica to nitrogen-doped modified graphite in the mixed solution, mixing for 60min at the rotating speed of 1000r/min, stopping stirring and heating the reaction kettle to 31 ℃, pumping liquid carbon dioxide into the reaction kettle to enable the pressure of the carbon dioxide in the kettle to reach 35MPa, controlling the temperature and the pressure of the reaction kettle to be unchanged and keeping for 3.0h, slowly releasing pressure for 5h to discharge the carbon dioxide, washing, removing liquid and drying the product to obtain a nitrogen-doped silica/graphite composite;
(5) metal zinc powder with the average grain diameter D50 of 50nm is doped with nitrogen according to the molar ratio of the metal zinc powder to the silicon dioxide content in the nitrogen-doped silicon dioxide/graphite compound of 0.25:1After uniformly mixing the mixed silicon dioxide/graphite compound, putting the mixture into a high-temperature reaction kettle, and keeping the nitrogen flow at 0.4m3/heating the mixture from room temperature to 400 ℃ at a heating rate of 2 ℃/min under the atmosphere of h, keeping the temperature for 150min, heating the mixture to 700 ℃ at a heating rate of 2 ℃/min at a stirring speed of 40r/min after the heat preservation is finished, naturally cooling the reaction kettle to room temperature after the heat preservation is finished for 240min, and stopping stirring to obtain a nitrogen-doped silicon oxide/zinc oxide/graphite compound;
(6) uniformly mixing polyvinyl alcohol and a nitrogen-doped silicon oxide/zinc oxide/graphite compound according to a mass ratio of 0.15:1, kneading and coating for 4 hours at a temperature of 110 ℃, cooling the material, and pressing the material under a pressure of 7MPa for 2.0 hours to obtain an organic carbon source-coated nitrogen-doped silicon oxide/zinc oxide/graphite composite anode material precursor blank;
(7) placing the precursor blank of the organic carbon source-coated nitrogen-doped silicon oxide/zinc oxide/graphite composite anode material in a high-temperature atmosphere furnace, wherein the nitrogen flow is 0.4m3Heating to 750 ℃ at the heating rate of 3 ℃/min in the atmosphere of/h, calcining for 6h, naturally cooling the calcined material to room temperature, crushing, screening and grading to obtain the nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite negative electrode material with the average particle size D50 of 14.0 mu m.
The nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite anode material obtained in example 1 was tested for physical and chemical properties. The specific surface area of the anode material is 1.63m2The tap density of the negative electrode material powder is 1.04g/cm3The first discharge capacity at 0.1C is 421.4mAh/g, the first efficiency is 92.3%, the cycle capacity retention rate at 100 cycles of 1C charge and discharge is 90.4%, the capacity retention rate at-20 ℃/25 ℃ is 72.1%, and the test results are summarized in Table 1.
Example 2:
(1) according to the mass ratio of the graphitized anthracite micro powder to the nitrogen source solute of the nitrogen-containing solution being 1: 0.08, adding graphitized anthracite micro powder with the average particle size D50 of 8 microns into a melamine ethanol solution with the mass fraction of 4%, uniformly mixing, injecting into a high-pressure reaction kettle, heating the reaction kettle to 45 ℃, pumping liquid carbon dioxide into the reaction kettle to enable the pressure of the carbon dioxide in the kettle to reach 28MPa, controlling the temperature and the pressure of the reaction kettle to be unchanged, keeping the temperature and the pressure for 2.0 hours, slowly releasing the pressure for 4.5 hours, discharging the carbon dioxide, and repeating the supercritical operation for 4 times to prepare a pretreated graphite micro powder solution;
(2) sealing the high-pressure reaction kettle, heating the pretreated graphite micro powder solution to 180 ℃ at the rotating speed of 290r/min, continuously keeping the reaction for 3 hours, then stirring, and naturally cooling to room temperature to obtain a nitrogen-doped modified graphite micro powder solution;
(3) preparing a sodium carbonate aqueous solution with the mass fraction of 10.0% at room temperature, adding a combined stabilizer with the mass ratio of dodecyl trimethyl ammonium bromide to polyethylene glycol of 0.37:1, the mass fraction of which is 1.5% of the sodium carbonate aqueous solution, stirring and mixing for 138min, slowly adding silicon tetrachloride with the purity of more than 99.0% to adjust the pH value of the solution to be neutral, continuously keeping stirring and reacting for 78min, and standing and aging the solution for 3.0h to obtain a stable nano-silica sol;
(4) adding a certain amount of nano silica sol into a high-pressure reaction kettle containing nitrogen-doped modified graphite micropowder solution according to the mass ratio of 0.07:1 of the silica to the nitrogen-doped modified graphite in the mixed solution, mixing for 78min at the rotating speed of 860r/min, stopping stirring and heating the reaction kettle to 40 ℃, pumping liquid carbon dioxide into the reaction kettle to enable the pressure of the carbon dioxide in the kettle to reach 28MPa, controlling the temperature and the pressure of the reaction kettle to be unchanged and keeping the temperature and the pressure for 3.5h, slowly releasing the pressure for 4.5h to discharge the carbon dioxide, washing, removing the liquid and drying the product to obtain a nitrogen-doped silica/graphite composite;
(5) uniformly mixing the metal zinc powder with the average grain diameter D50 of 500nm and the nitrogen-doped silicon dioxide/graphite compound according to the molar ratio of the metal zinc powder to the silicon dioxide content in the nitrogen-doped silicon dioxide/graphite compound of 0.33:1, putting the mixture into a high-temperature reaction kettle, and feeding the mixture into the high-temperature reaction kettle under the condition that the flow of helium gas is 0.6m3/heating the mixture from room temperature to 410 ℃ at a heating rate of 2 ℃/min under the atmosphere of h, keeping the temperature for 132min, heating the mixture to 740 ℃ at a heating rate of 2 ℃/min at a stirring speed of 50r/min after the heat preservation is finished, naturally cooling the reaction kettle to room temperature after the heat preservation is carried out for 210min, and stopping stirring to obtain a nitrogen-doped silicon oxide/zinc oxide/graphite compound;
(6) uniformly mixing polyvinyl alcohol and a nitrogen-doped silicon oxide/zinc oxide/graphite compound according to a mass ratio of 0.19:1, kneading and coating for 4 hours at the temperature of 120 ℃, cooling the material, and pressing the cooled material under the pressure of 10MPa for 1.5 hours to obtain an organic carbon source-coated nitrogen-doped silicon oxide/zinc oxide/graphite composite anode material precursor body;
(7) placing the precursor blank of the organic carbon source-coated nitrogen-doped silicon oxide/zinc oxide/graphite composite anode material in a high-temperature atmosphere furnace, and keeping the flow of helium at 0.6m3Heating to 800 ℃ at the heating rate of 3 ℃/min in the atmosphere of/h, calcining for 5h, naturally cooling the calcined material to room temperature, crushing, screening and grading to obtain the nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite negative electrode material with the average particle size D50 of 14.0 mu m.
The nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite anode material obtained in example 2 was tested for physical and chemical properties. The specific surface area of the negative electrode material is 1.57m2The tap density of the negative electrode material powder is 1.07g/cm3The first discharge capacity at 0.1C is 451.3mAh/g, the first efficiency is 91.3%, the cycle capacity retention rate at 100 cycles of 1C charge and discharge is 90.2%, the capacity retention rate at-20 ℃/25 ℃ is 71.5%, and the test results are summarized in Table 1.
Example 3:
(1) according to the mass ratio of the graphitized anthracite micro powder to the nitrogen source solute of the nitrogen-containing solution being 1: 0.10, adding graphitized anthracite micro powder with the average particle size D50 of 9 microns into 5% ammonium chloride N-methyl pyrrolidone solution, uniformly mixing, injecting into a high-pressure reaction kettle, heating the reaction kettle to 55 ℃, pumping liquid carbon dioxide into the reaction kettle to enable the pressure of the carbon dioxide in the kettle to reach 21MPa, controlling the temperature and the pressure of the reaction kettle to be unchanged, keeping the temperature and the pressure for 2.0 hours, slowly releasing pressure for 4.0 hours, discharging the carbon dioxide, and repeating the supercritical operation for 3 times to prepare a pretreated graphite micro powder solution;
(2) sealing the high-pressure reaction kettle, heating the pretreated graphite micro powder solution to 170 ℃ at the rotating speed of 330r/min, continuously keeping the reaction for 4 hours, then stirring, and naturally cooling to room temperature to obtain a nitrogen-doped modified graphite micro powder solution;
(3) preparing a sodium bicarbonate aqueous solution with the mass fraction of 15.0% at room temperature, adding a combined stabilizer with the mass ratio of cationic polyacrylamide and alkylphenol ethoxylates of which the mass fraction is 2.0% of the sodium hydroxide aqueous solution at the rotating speed of 690r/min, stirring and mixing for 126min, slowly adding silicon tetrachloride with the purity of more than 99.0% to adjust the pH value of the solution to be neutral, continuously keeping stirring and reacting for 96min, and standing and aging the solution for 4.5h to obtain a stable nano-silica sol;
(4) adding a certain amount of nano silica sol into a high-pressure reaction kettle containing nitrogen-doped modified graphite micropowder solution according to the mass ratio of 0.08:1 of the silica to the nitrogen-doped modified graphite in the mixed solution, mixing for 96min at the rotating speed of 720r/min, stopping stirring and heating the reaction kettle to 50 ℃, pumping liquid carbon dioxide into the reaction kettle to enable the pressure of the carbon dioxide in the kettle to reach 21MPa, controlling the temperature and the pressure of the reaction kettle to be unchanged and keeping for 4.0h, slowly releasing pressure for 4.0h to discharge the carbon dioxide, washing, removing liquid and drying the product to obtain a nitrogen-doped silica/graphite composite;
(5) uniformly mixing the metal zinc powder with the average grain diameter D50 of 5 mu m and the nitrogen-doped silicon dioxide/graphite compound according to the molar ratio of the metal zinc powder to the silicon dioxide content in the nitrogen-doped silicon dioxide/graphite compound of 0.41:1, putting the mixture into a high-temperature reaction kettle, and putting the mixture into the high-temperature reaction kettle under the condition that the neon gas flow is 0.8m3/heating the mixture from room temperature to 420 ℃ at a heating rate of 3 ℃/min under the atmosphere of h, keeping the temperature for 114min, heating the mixture to 780 ℃ at a heating rate of 3 ℃/min at a stirring speed of 60r/min after the heat preservation is finished, naturally cooling the reaction kettle to room temperature after the heat preservation is carried out for 180min, and stopping stirring to obtain a nitrogen-doped silicon oxide/zinc oxide/graphite compound;
(6) uniformly mixing polyvinyl alcohol and a nitrogen-doped silicon oxide/zinc oxide/graphite compound according to a mass ratio of 0.23:1, kneading and coating at 140 ℃ for 3h, cooling the material, and pressing under 14MPa for 1.5h to obtain an organic carbon source-coated nitrogen-doped silicon oxide/zinc oxide/graphite composite anode material precursor blank;
(7) placing the precursor body of the organic carbon source-coated nitrogen-doped silicon oxide/zinc oxide/graphite composite cathode material in a high-temperature atmosphere furnace, wherein the flow of neon is 0.8m3Heating to 850 ℃ at the heating rate of 4 ℃/min in the atmosphere of/h, calcining for 4.5h, naturally cooling the calcined material to room temperature, crushing, sieving and grading to obtain the nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite negative electrode material with the average particle size D50 of 15.0 mu m.
The nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite anode material obtained in example 3 was tested for physical and chemical properties. The specific surface area of the negative electrode material is 1.47m2The tap density of the negative electrode material powder is 1.08g/cm3The first discharge capacity at 0.1C is 466.1mAh/g, the first efficiency is 91.2%, the cycle capacity retention rate at 100 cycles of 1C charge and discharge is 89.7%, the capacity retention rate at-20 ℃/25 ℃ is 72.0%, and the test results are summarized in Table 1.
Example 4:
(1) according to the mass ratio of the graphitized anthracite micro powder to the nitrogen source solute of the nitrogen-containing solution being 1: 0.10, adding graphitized anthracite micro powder with the average particle size D50 of 9 microns into 6 mass percent urea dimethyl amide solution, uniformly mixing, injecting into a high-pressure reaction kettle, heating the reaction kettle to 55 ℃, pumping liquid carbon dioxide into the reaction kettle to enable the pressure of the carbon dioxide in the kettle to reach 21MPa, controlling the temperature and the pressure of the reaction kettle to be unchanged and keeping for 2.5 hours, slowly releasing pressure for 4.0 hours to discharge the carbon dioxide, and repeating the supercritical operation for 3 times to prepare a pretreated graphite micro powder solution;
(2) sealing the high-pressure reaction kettle, heating the pretreated graphite micro powder solution to 160 ℃ at the rotating speed of 470r/min, continuously keeping the reaction for 4 hours, then stirring, and naturally cooling to room temperature to obtain a nitrogen-doped modified graphite micro powder solution;
(3) preparing a potassium hydroxide aqueous solution with the mass fraction of 15.0% at room temperature, adding a composite stabilizer with the mass fraction of 2.5% of sodium hydroxide aqueous solution and the mass ratio of poly (dimethylaminoethyl acrylate) to poly (vinylpyrrolidone) of 0.51:1 at the rotating speed of 860r/min, stirring and mixing for 114min, slowly adding silicon tetrachloride with the purity of more than 99.0% to adjust the pH value of the solution to be neutral, continuously keeping stirring and reacting for 114min, and standing and aging the solution for 4.5h to obtain a stable nano-silica sol;
(4) adding a certain amount of nano silica sol into a high-pressure reaction kettle containing the nitrogen-doped modified graphite micropowder solution according to the mass ratio of 0.09:1 of the silica to the nitrogen-doped modified graphite in the mixed solution, mixing for 114min at the rotating speed of 580r/min, stopping stirring and heating the reaction kettle to 60 ℃, pumping liquid carbon dioxide into the reaction kettle to enable the pressure of the carbon dioxide in the kettle to reach 21MPa, controlling the temperature and the pressure of the reaction kettle to be unchanged and keeping for 5.0h, slowly releasing pressure for 4.0h to discharge the carbon dioxide, washing, removing liquid and drying the product to obtain a nitrogen-doped silica/graphite composite;
(5) uniformly mixing the metallic zinc powder with the average grain diameter D50 of 10 mu m and the nitrogen-doped silicon dioxide/graphite compound according to the molar ratio of the content of silicon dioxide in the metallic zinc powder and the nitrogen-doped silicon dioxide/graphite compound of 0.49:1, putting the mixture into a high-temperature reaction kettle, and adding the mixture into the reaction kettle under the condition that the argon flow is 0.8m3/heating the mixture from room temperature to 430 ℃ at a heating rate of 4 ℃/min under an atmosphere of h, keeping the temperature for 96min, heating the mixture to 820 ℃ at a heating rate of 4 ℃/min at a stirring speed of 70r/min after the heat preservation is finished, naturally cooling the reaction kettle to room temperature after the temperature is kept for 150min, and stopping stirring to obtain a nitrogen-doped silicon oxide/zinc oxide/graphite compound;
(6) uniformly mixing polyvinyl alcohol and a nitrogen-doped silicon oxide/zinc oxide/graphite compound according to a mass ratio of 0.27:1, kneading and coating for 3h at the temperature of 150 ℃, and compacting under the pressure of 14MPa for 1.0h after cooling the material to obtain an organic carbon source-coated nitrogen-doped silicon oxide/zinc oxide/graphite composite anode material precursor blank;
(7) placing the precursor body of the organic carbon source-coated nitrogen-doped silicon oxide/zinc oxide/graphite composite anode material in a high-temperature atmosphere furnace, wherein the flow of argon is 0.8m3Heating to 900 ℃ at the heating rate of 4 ℃/min in the atmosphere of/h, calcining for 4h, naturally cooling the calcined material to room temperature, crushing, screening and grading to obtain the nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite negative electrode material with the average particle size D50 of 16.0 mu m.
The nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite anode material obtained in example 4 was tested for physical and chemical properties. The specific surface area of the negative electrode material is 1.43m2G, powder of negative electrode materialTap density of 1.12g/cm3The first discharge capacity at 0.1C is 480.3mAh/g, the first efficiency is 91.7%, the cycle capacity retention rate at 100 cycles of 1C charge and discharge is 89.8%, the capacity retention rate at-20 ℃/25 ℃ is 70.9%, and the test results are summarized in Table 1.
Example 5:
(1) according to the mass ratio of the graphitized anthracite micro powder to the nitrogen source solute of the nitrogen-containing solution being 1: 0.12, adding graphitized anthracite micro powder with the average particle size D50 of 10 microns into 7% of melamine ethanol solution, uniformly mixing, injecting into a high-pressure reaction kettle, heating the reaction kettle to 65 ℃, pumping liquid carbon dioxide into the reaction kettle to enable the pressure of the carbon dioxide in the kettle to reach 14MPa, controlling the temperature and the pressure of the reaction kettle to be unchanged, keeping the temperature and the pressure for 2.5 hours, slowly releasing the pressure for 3.0 hours, discharging the carbon dioxide, and repeating the supercritical operation for 2 times to prepare a pretreated graphite micro powder solution;
(2) sealing the high-pressure reaction kettle, heating the pretreated graphite micro powder solution to 150 ℃ at the rotating speed of 610r/min, continuously keeping the reaction for 5 hours, then stirring, and naturally cooling to room temperature to obtain a nitrogen-doped modified graphite micro powder solution;
(3) preparing a potassium carbonate aqueous solution with the mass fraction of 20.0% at room temperature, adding dimethylaminoethyl methacrylate and polyethylene glycol with the mass fraction of 3.0% of a sodium hydroxide aqueous solution at the rotating speed of 1030r/min, wherein the mass ratio of the dimethylaminoethyl methacrylate to the polyethylene glycol is 0.58: 1, stirring and mixing for 102min, slowly adding silicon tetrachloride with the purity of more than 99.0 percent to adjust the pH value of the solution to be neutral, continuously keeping stirring and reacting for 132min, and standing and aging the solution for 5.5h to obtain the nano-silica sol in a stable state.
(4) Adding a certain amount of nano silica sol into a high-pressure reaction kettle containing nitrogen-doped modified graphite micropowder solution according to the mass ratio of 0.10:1 of the silica to the nitrogen-doped modified graphite in the mixed solution, mixing for 132min at the rotating speed of 440r/min, stopping stirring and heating the reaction kettle to 70 ℃, pumping liquid carbon dioxide into the reaction kettle to enable the pressure of the carbon dioxide in the kettle to reach 14MPa, controlling the temperature and the pressure of the reaction kettle to be unchanged and keeping for 6.0h, slowly releasing pressure for 3.0h to discharge the carbon dioxide, washing, removing liquid and drying the product to obtain a nitrogen-doped silica/graphite composite;
(5) uniformly mixing the metallic zinc powder with the average grain diameter D50 of 15 mu m and the nitrogen-doped silicon dioxide/graphite compound according to the molar ratio of the content of silicon dioxide in the metallic zinc powder and the nitrogen-doped silicon dioxide/graphite compound of 0.57:1, putting the mixture into a high-temperature reaction kettle, and adding the mixture into the kettle at the krypton gas flow of 1.0m3/heating the mixture from room temperature to 440 ℃ at a heating rate of 5 ℃/min under an atmosphere of h, keeping the temperature for 78min, heating the mixture to 860 ℃ at a heating rate of 5 ℃/min at a stirring speed of 80r/min after the heat preservation is finished, naturally cooling the reaction kettle to room temperature, and stopping stirring to obtain a nitrogen-doped silicon oxide/zinc oxide/graphite compound;
(6) uniformly mixing polyvinyl alcohol and a nitrogen-doped silicon oxide/zinc oxide/graphite compound according to a mass ratio of 0.31:1, kneading and coating for 2h at the temperature of 170 ℃, and compacting under the pressure of 17MPa for 1.0h after cooling the material to obtain an organic carbon source-coated nitrogen-doped silicon oxide/zinc oxide/graphite composite anode material precursor blank;
(7) placing the precursor body of the organic carbon source-coated nitrogen-doped silicon oxide/zinc oxide/graphite composite anode material in a high-temperature atmosphere furnace at the krypton gas flow of 1.0m3Heating to 950 ℃ at the heating rate of 5 ℃/min in the atmosphere of/h, calcining for 3.5h, naturally cooling the calcined material to room temperature, crushing, sieving and grading to obtain the nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite negative electrode material with the average particle size D50 of 17.0 mu m.
The nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite anode material obtained in example 5 was tested for physical and chemical properties. The specific surface area of the negative electrode material is 1.38m2The tap density of the negative electrode material powder is 1.15g/cm3The first discharge capacity at 0.1C is 494.9mAh/g, the first efficiency is 90.5%, the cycle capacity retention rate at 100 cycles of 1C charge and discharge is 88.5%, the capacity retention rate at-20 ℃/25 ℃ is 70.1%, and the test results are summarized in Table 1.
Example 6:
(1) according to the mass ratio of the graphitized anthracite micro powder to the nitrogen source solute of the nitrogen-containing solution being 1: 0.15, adding graphitized anthracite micro powder with the average particle size D50 of 12 microns into ammonium chloride aqueous solution with the mass fraction of 8%, uniformly mixing, injecting into a high-pressure reaction kettle, heating the reaction kettle to 80 ℃, pumping liquid carbon dioxide into the reaction kettle to enable the pressure of the carbon dioxide in the kettle to reach 7MPa, controlling the temperature and the pressure of the reaction kettle to be unchanged and keeping the temperature and the pressure for 3.0 hours, slowly releasing the pressure for 2.5 hours to discharge the carbon dioxide, and repeating the supercritical operation for 2 times to prepare pretreated graphite micro powder solution;
(2) sealing the high-pressure reaction kettle, heating the pretreated graphite micro powder solution to 130 ℃ at the rotating speed of 850r/min, continuously keeping the reaction for 6 hours, then stirring, and naturally cooling to room temperature to obtain a nitrogen-doped modified graphite micro powder solution;
(3) preparing a 25.0 mass percent aqueous solution of potassium bicarbonate at room temperature, adding a combined stabilizer with a mass percent of 3.5 percent of sodium hydroxide aqueous solution and a mass ratio of hexyltrimethylammonium bromide to polyvinyl pyrrolidone of 0.65:1 at a rotating speed of 1200r/min, stirring and mixing for 90min, slowly adding silicon tetrachloride with a purity of more than 99.0 percent to adjust the pH value of the solution to be neutral, continuously keeping stirring and reacting for 150min, and standing and aging the solution for 6.0h to obtain a stable nano-silica sol;
(4) adding a certain amount of nano silica sol into a high-pressure reaction kettle containing nitrogen-doped modified graphite micropowder solution according to the mass ratio of 0.12:1 of the silica to the nitrogen-doped modified graphite in the mixed solution, mixing for 150min at the rotating speed of 300r/min, stopping stirring and heating the reaction kettle to 80 ℃, pumping liquid carbon dioxide into the reaction kettle to enable the pressure of the carbon dioxide in the kettle to reach 7MPa, controlling the temperature and the pressure of the reaction kettle to be unchanged and keeping for 6.5h, slowly releasing pressure for 2.5h to discharge the carbon dioxide, washing, removing liquid and drying the product to obtain a nitrogen-doped silica/graphite composite;
(5) uniformly mixing metal zinc powder with the average particle size D50 of 25 mu m and the nitrogen-doped silicon dioxide/graphite compound according to the molar ratio of the metal zinc powder to the silicon dioxide content in the nitrogen-doped silicon dioxide/graphite compound of 0.65:1, putting the mixture into a high-temperature reaction kettle, and adding the mixture into the reaction kettle at the xenon flow of 1.2m3/heating the mixture from room temperature to 450 ℃ at a heating rate of 5 ℃/min under the atmosphere of h, keeping the temperature for 60min, heating the mixture at a heating rate of 5 ℃/min according to a stirring speed of 90r/min after the temperature is kept,heating to 900 ℃, preserving the temperature for 90min, naturally cooling the reaction kettle to room temperature, and stopping stirring to obtain a nitrogen-doped silicon oxide/zinc oxide/graphite compound;
(6) uniformly mixing polyvinyl alcohol and a nitrogen-doped silicon oxide/zinc oxide/graphite compound according to a mass ratio of 0.35:1, kneading and coating for 2 hours at the temperature of 180 ℃, cooling the material, and pressing the cooled material under the pressure of 20MPa for 0.5 hour to obtain an organic carbon source-coated nitrogen-doped silicon oxide/zinc oxide/graphite composite anode material precursor blank;
(7) placing an organic carbon source-coated nitrogen-doped silicon oxide/zinc oxide/graphite composite anode material precursor blank in a high-temperature atmosphere furnace, wherein the flow of xenon is 1.2m3Heating to 1000 ℃ at the heating rate of 5 ℃/min in the atmosphere of/h, calcining for 2.5h, naturally cooling the calcined material to room temperature, crushing, sieving and grading to obtain the nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite negative electrode material with the average particle size D50 of 17.0 mu m.
The nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite anode material obtained in example 6 was tested for physical and chemical properties. The specific surface area of the negative electrode material is 1.27m2The tap density of the negative electrode material powder is 1.17g/cm3The first discharge capacity at 0.1C is 519.5mAh/g, the first efficiency is 90.3%, the cycle capacity retention rate at 100 cycles of 1C charge and discharge is 87.4%, the capacity retention rate at-20 ℃/25 ℃ is 69.7%, and the test results are summarized in Table 1.
Comparative example:
(1) and (2) taking ethanol as a solvent and polyethylene glycol as a grinding aid, carrying out wet grinding on the nano silicon dioxide with the purity of more than 99.9 percent and the average particle size D50 of 2 mu m by using a rod pin type nano sand mill, using a zirconia ball with the diameter of 0.1mm as a grinding medium, and washing, removing liquid and drying after grinding to obtain the nano silicon dioxide with the particle size of less than 50 nm.
(2) Graphitized anthracite fine powder with the average particle size D50 of 9 mu m, nano silicon dioxide and metallic zinc powder with the average particle size D50 of 10 mu m are mixed according to the mass ratio of 1: 0.09: 0.04, mixing uniformly, putting into a high-temperature reaction kettle, and keeping the argon flow at 0.8m3/h, stirring at a speed of 110r/min, heating from room temperature to 430 ℃ at a temperature rise rate of 4 ℃/min, keeping the temperature for 96min, and keeping the temperatureAfter the reaction is finished, heating to 820 ℃ at the heating rate of 4 ℃/min according to the stirring speed of 70r/min, preserving the temperature for 150min, naturally cooling the reaction kettle to room temperature, and stopping stirring to obtain the silicon oxide/zinc oxide/graphite compound.
(3) Uniformly mixing polyvinyl alcohol and the silicon oxide/zinc oxide/graphite composite according to the mass ratio of 0.27:1, kneading and coating for 3h at the temperature of 150 ℃, cooling the material, and compacting for 1.0h at the pressure of 14MPa to obtain the precursor blank of the silicon oxide/zinc oxide/graphite composite anode material coated with the organic carbon source.
(4) Placing the silicon oxide/zinc oxide/graphite composite anode material precursor blank coated with the organic carbon source in a high-temperature atmosphere furnace at the argon flow rate of 0.8m3Heating to 900 ℃ at the heating rate of 4 ℃/min in the atmosphere of/h, calcining for 4h, naturally cooling the calcined material to room temperature, crushing, screening and grading to obtain the silicon oxide/zinc oxide/graphite/carbon composite negative electrode material with the average particle size D50 of 16.0 mu m.
The material prepared in the comparative example has a specific surface area of 1.50m2(iv) g, powder tap density 1.10g/cm3. The material prepared by the comparative example is used as a negative active material of a simulated battery to carry out electrochemical performance test, the 0.1C first discharge capacity is 433.4mAh/g, the first efficiency is 77.8 percent, the 100-week circulation capacity retention rate is more than or equal to 57.2 percent, and the-20 ℃/25 ℃ capacity retention rate is 44.6 percent. The test results are shown in Table 1.
The silicon source of the comparative example is commercial silicon dioxide, nitrogen doping modification and supercritical fluid intercalation composite are not adopted, and the components, the proportion and the process of other substances are the same as those of the example 4.
Second, performance characterization method
1. Physical property characterization: the method is used for preparing the nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite negative electrode material, and a Zeiss GeminiSEM 500 field emission scanning electron microscope is used for observing the appearance of the composite negative electrode material; testing the tap density of the composite cathode material powder by using an Auto tap type tap density instrument of the American Congta company; testing the specific surface area of the composite anode material by using a JW-DX type specific surface area tester of the Jingwei Gaobao company; the charging electrical property of the composite negative electrode material is tested by a CT2001A type blue dot battery test system of blue electric company in Wuhan city.
2. And (3) electrical property characterization: pole pieces were made from the negative electrode material samples of examples 1-6 and comparative example, and half cell testing was performed. According to the active substance: SP: CMC: SBR 95: 2: 1.5: 1.5 pulping, uniformly mixing, coating on a Cu film, drying for 10 hours at 110 ℃, rolling and punching, using a metal lithium sheet as a counter electrode, using FEC: EC: EMC 1: 2: 7 as electrolyte, and preparing into CR2032 button experimental cell in a German Braun MBRAUN glove box protected by high-purity argon. At room temperature (25 ℃), measuring 0.1C first discharge capacity mAh/g and first efficiency% within a charge-discharge voltage range of 0.003-2.0V, performing 1C charge-discharge cycle test after 0.1C charge-discharge activation for 2 weeks, and calculating by utilizing the ratio of the 1C discharge capacity at the 100 th week to the 1C discharge capacity at the 1 st week of the composite negative electrode material to obtain a 100-week cycle capacity retention rate; under room temperature (25 ℃), the charge-discharge voltage range is 0.003-2.0V, after activation for 2 weeks at 0.1C, a 0.1C charge-discharge cycle test is carried out at the temperature of-20 ℃, and the capacity retention rate at-20 ℃/25 ℃ is calculated by utilizing the ratio of the 0.1C discharge capacity at 1 week at-20 ℃ to the 0.1C discharge capacity at 1 week at 25 ℃.
Third, performance characterization results and analysis
FIG. 1 is an SEM photograph of graphitized anthracite coal as a graphite substrate in example 4; fig. 2 is an SEM image of the nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite anode material prepared in example 4. As shown in figure 1, micropores are distributed on the surface of the graphitized anthracite, the pore size distribution of the micropores is about 20-200 nm, and the special morphology structure of the micropores greatly facilitates the diffusion of supercritical fluid between graphite layers and the micropores on the surface, thereby effectively promoting the intercalation and the jack compounding of nitrogen source molecules and nano-silica sol; as shown in fig. 2, the nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite negative electrode material with the secondary granulation structure has a smooth surface and no micropores exposed, which indicates that the surface of the material is uniformly and densely coated, and can effectively prevent organic solvent molecules from being inserted into the graphite sheet layer of the internal graphite substrate, thereby improving the cycling stability of the material.
Table 1: physical and chemical property test results of the samples of examples and comparative examples
Figure BDA0003283235680000251
Table 1 shows the results of the physical property and chemical property tests of the samples of examples 1 to 6 and comparative examples, and it can be seen from table 1 that the first efficiency of the nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite anode material prepared in examples 1 to 6 is greater than 90%, the capacity retention rate of 100 cycles of charge and discharge at 1C is greater than 87%, and the capacity retention rate of-20 ℃/25 ℃ is greater than 69.5%. The silicon source of the comparative example is commercial silicon dioxide, nitrogen doping modification and supercritical fluid intercalation composite are not adopted, and the components, the proportion and the process of other substances are the same as those of the example 4. The first efficiency, the rate charge-discharge cycle performance and the low-temperature performance of the prepared sample are not as good as the test results of the sample in the example 4. Therefore, the first efficiency, the multiplying power charge-discharge cycle performance and the low-temperature performance of the cathode material can be improved by adopting nitrogen doping modification and supercritical fluid intercalation jack compounding.
It should be noted that the embodiments described herein are only some embodiments of the present invention, and not all implementations of the present invention, and the embodiments are only examples, which are only used to provide a more intuitive and clear understanding of the present invention, and are not intended to limit the technical solutions of the present invention. All other embodiments, as well as other simple substitutions and various changes to the technical solutions of the present invention, which can be made by those skilled in the art without inventive work, are within the scope of the present invention without departing from the spirit of the present invention.

Claims (9)

1. A preparation method of a nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite negative electrode material is characterized by comprising the following steps:
(1) and (3) nitrogen source compounding: adding a certain amount of graphitized anthracite micro powder into the nitrogen-containing solution, uniformly mixing, injecting into a high-pressure reaction kettle, heating the reaction kettle to a specified temperature, pumping liquid carbon dioxide into the reaction kettle to enable the carbon dioxide in the kettle to reach a set pressure, controlling the temperature and the pressure of materials in the reaction kettle and keeping for a certain time, slowly releasing pressure to discharge the carbon dioxide in the reaction kettle, and repeating the supercritical operation for several times to prepare a pretreated graphite micro powder solution;
(2) nitrogen doping by a hydrothermal method: heating the graphite micro powder solution pretreated in the step (1) to a specified temperature while stirring in a high-pressure reaction kettle under a closed condition, keeping reacting for a certain time, stopping stirring, and naturally cooling to room temperature to obtain a nitrogen-doped modified graphite micro powder solution;
(3) preparing nano silicon dioxide sol: preparing an alkaline aqueous solution with a certain concentration at room temperature, adding a stabilizer into the alkaline aqueous solution under a stirring state, mixing for a certain time till the solution is uniform, then slowly adding silicon tetrachloride to adjust the pH value of the solution to be neutral, continuously keeping stirring and reacting for a certain time, and standing and aging the solution to obtain a nano-silica sol in a stable state;
(4) compounding nano silica sol: uniformly stirring the nano-silica sol prepared in the step (3) and the nitrogen-doped modified graphite micro-powder solution prepared in the step (2) in a high-pressure reaction kettle according to a certain proportion to form a mixed solution, stopping stirring, heating the reaction kettle to a specified temperature, pumping liquid carbon dioxide into the reaction kettle to enable the carbon dioxide in the kettle to reach a set pressure, controlling and keeping the temperature and the pressure of materials in the reaction kettle for a certain time, slowly releasing pressure to discharge the carbon dioxide in the reaction kettle, and washing, removing liquid and drying to prepare a nitrogen-doped silica/graphite compound;
(5) melting and reducing: uniformly mixing metal zinc powder and the nitrogen-doped silicon dioxide/graphite compound prepared in the step (4) according to a certain proportion, then putting the mixture into a high-temperature reaction kettle, stirring and heating the mixture from room temperature to a first constant temperature T1 under the atmosphere of protective gas, preserving heat, continuing stirring and heating the mixture to a second constant temperature T2 after the T1 heat preservation is finished, preserving heat, stirring and cooling the mixture to room temperature after the heat preservation is finished, and obtaining the nitrogen-doped silicon oxide/zinc oxide/graphite compound;
(6) kneading, coating and compacting: uniformly mixing an organic carbon source and the nitrogen-doped silicon oxide/zinc oxide/graphite composite prepared in the step (5) according to a certain proportion, putting the mixture into a kneading machine, kneading and coating the mixture under a heating condition, putting the material into a tablet press after the kneading and cooling are finished, and keeping the material under a specified pressure for a certain time to form an organic carbon source-coated nitrogen-doped silicon oxide/zinc oxide/graphite composite anode material precursor body;
(7) high-temperature calcination: and (4) placing the organic carbon source coated nitrogen-doped silicon oxide/zinc oxide/graphite composite negative electrode material precursor blank prepared in the step (6) in a high-temperature atmosphere furnace, calcining in a protective gas atmosphere, naturally cooling to room temperature in the furnace after calcination, crushing, screening and grading to obtain the final product nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite negative electrode material.
2. The method for preparing the nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite negative electrode material according to claim 1, wherein the average particle size D50 of the graphitized anthracite fine powder in the step (1) is 6.0-12.0 μm, the carbon content is more than 99.5%, and the anthracite raw material is preferably taixi anthracite;
the nitrogen source solute in the nitrogen-containing solution in the step (1) is one or more of urea, melamine and ammonium chloride, the solvent in the nitrogen-containing solution is one of deionized water, ethanol, N-methylpyrrolidone and dimethylformamide, the mass fraction of the nitrogen source in the nitrogen-containing solution is 3-8%, and the mass ratio of the graphitized anthracite fine powder to the solute nitrogen source in the nitrogen-containing solution is 1: (0.05-0.15);
in the step (1), the temperature in the high-pressure reaction kettle is controlled to be 31-80 ℃, the pressure is 7-35 MPa, the supercritical retention time of the material in the high-pressure reaction kettle is 1.5-3.0 h, the slow pressure relief time is not less than 2.5h, and the supercritical operation times are 2-4.
3. The preparation method of the nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite negative electrode material as claimed in claim 1, wherein the stirring speed in the step (2) is 150-850 r/min, the reaction temperature of the materials in the high-pressure reaction kettle is 130-200 ℃, and the reaction time of the materials is 2-6 h.
4. The method for preparing the nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite negative electrode material according to claim 1, wherein the solute of the alkaline solution in the step (3) is one or more of sodium hydroxide, sodium carbonate, sodium bicarbonate, potassium hydroxide, potassium carbonate and potassium bicarbonate, and the mass fraction of the solute in the alkaline solution is 6.0-25%;
the adding amount of the stabilizer in the step (3) is 1.0-3.5% of the mass of the alkaline aqueous solution; the stabilizer is a mixed solvent of a cationic surfactant and a nonionic surfactant, and the mass ratio of the cationic surfactant to the nonionic surfactant is (0.30-0.65): 1; the cationic surfactant is one of hexyl trimethyl ammonium bromide, dodecyl trimethyl ammonium bromide, cationic polyacrylamide, poly (dimethylaminoethyl acrylate), poly (dimethylaminoethyl methacrylate) and polyethyleneimine, and the nonionic surfactant is one of polyvinyl pyrrolidone, polyethylene glycol and alkylphenol polyoxyethylene;
the silicon tetrachloride in the step (3) is a byproduct of polycrystalline silicon production with the purity of more than 99.0 percent;
in the step (3), the stirring speed is 350-1200 r/min, the stirring and mixing time is 90-150 min, the stirring reaction time is 60-150 min, and the standing and aging time of the solution is 2.5-6.0 h.
5. The method for preparing the nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite negative electrode material according to claim 1, wherein the mass ratio of the nano silicon dioxide to the nitrogen-doped modified graphite micropowder in the mixed solution in the step (4) is (0.05-0.12): 1;
in the step (4), the stirring speed is 300-1000 r/min, and the stirring and mixing time is 60-150 min;
and (4) controlling the temperature in the high-pressure reaction kettle in the step (4) to be 31-80 ℃, controlling the pressure to be 7-35 MPa, keeping the supercritical retention time of the materials in the high-pressure reaction kettle to be 3.0-6.5 h, and slowly releasing the pressure for not less than 2.5 h.
6. The method for preparing the nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite negative electrode material according to claim 1, wherein in the step (5), the first constant temperature T1 is 400-450 ℃, the reaction stage is from room temperature to T1 temperature, the stirring speed is 50-150 r/min, the heating rate is 2-5 ℃/min, and the heat preservation time is 60-150 min; the second constant temperature T2 is 700-900 ℃, the temperature T1 is in a reaction stage from T2, the stirring speed is 40-90 r/min, the heating rate is 2-5 ℃/min, and the heat preservation time is 90-240 min;
in the step (5), the molar ratio of the metal zinc powder to the silicon dioxide in the nitrogen-doped silicon dioxide/graphite compound is (0.25-0.65): 1, the average grain diameter D50 of the metallic zinc powder is 50 nm-25 μm, and the mass content is more than 99%;
the protective gas in the step (5) is one or more of nitrogen, helium, neon, argon, krypton or xenon, and the flow rate of the protective gas is 0.4-1.2 m3/h。
7. The method for preparing the nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite negative electrode material of claim 1, wherein the organic carbon source in the step (6) is one or more of polyvinyl alcohol, polyethylene glycol, phenolic resin, epoxy resin, polyvinylidene fluoride and asphalt, and the mass ratio of the organic carbon source to the nitrogen-doped silicon oxide/zinc oxide/graphite composite material is (0.15-0.35): 1;
and (3) in the step (6), the kneading temperature is 110-180 ℃, the kneading time is 2-4 h, the green pressing pressure is 7-20 Mpa, and the green pressing time is 0.5-2.0 h.
8. The preparation method of the nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite anode material according to claim 1, wherein the temperature rise rate of the calcination treatment in the step (7) is 3-5 ℃/min, the calcination temperature is 750-1000 ℃, and the constant temperature time is 2.5-6.0 h;
the protective gas in the step (7) is one or more of nitrogen, helium, neon, argon, krypton or xenon, and the flow rate of the protective gas is 0.4-1.2 m3/h；
The average particle size D50 of the nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite negative electrode material crushed in the step (7) is 14.0-17.0 μm.
9. A nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite negative electrode material is characterized in that: the nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite negative electrode material is prepared by the preparation method of any one of claims 1 to 8, and the nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite negative electrode material consists of a nitrogen-doped silicon oxide/zinc oxide/graphite compound which is distributed randomly, amorphous carbon which is coated on the surface of the nitrogen-doped silicon oxide/zinc oxide/graphite compound and amorphous carbon which is bridged around the coated nitrogen-doped silicon oxide/zinc oxide/graphite compound.
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