CN113889609B - Nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite anode material and preparation method thereof - Google Patents

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

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CN113889609B
CN113889609B CN202111139137.1A CN202111139137A CN113889609B CN 113889609 B CN113889609 B CN 113889609B CN 202111139137 A CN202111139137 A CN 202111139137A CN 113889609 B CN113889609 B CN 113889609B
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nitrogen
graphite
zinc oxide
doped silicon
temperature
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CN113889609A (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
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • 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 anode material and a preparation method thereof, wherein graphitized anthracite is used as a graphite substrate, a supercritical fluid method is adopted to conduct intercalation and jack recombination of nitrogen source molecules on the graphite substrate, and nitrogen-doped modified graphite is prepared through hydrothermal reaction; preparing nano silicon dioxide sol by taking silicon tetrachloride which is a byproduct of polysilicon production as a silicon source under the action of an alkaline condition and a stabilizing agent, performing intercalation, jack precipitation and compounding of the nano silicon dioxide sol on nitrogen-doped modified graphite by adopting a supercritical fluid method, and preparing a nitrogen-doped silicon oxide/zinc oxide/graphite compound by performing molten partial reduction on metal zinc powder; the method comprises the steps of taking an organic carbon source as a coating agent, coating and molding a compound by adopting a mixing and kneading and compacting process, and then calcining at high temperature, crushing and screening to obtain the nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite anode material with high tap density and excellent processability.

Description

Nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite anode material and preparation method thereof
Technical Field
The invention relates to the technical field of production of battery anode materials, in particular to a nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite anode 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 the commercial graphite negative electrode material, and the silicon is the negative electrode material with the highest development potential and high specific capacity, but the silicon single serving as the negative electrode material has larger application challenges, and the Li-Si alloying is adopted in the charge and discharge processThe volume expansion change of approximately 300 percent is easy to cause pulverization and deactivation of silicon particles, on the other hand, the poor electrical contact between active particles and a current collector forms an island effect, and a fracture surface repeatedly forms a new SEI film, so that the irreversible capacity loss and the coulomb efficiency of the material are low, and the cycle performance is poor; while the conductivity of silicon is low (10 -5 ～10 -3 S cm -1 ) And has a small ion diffusion coefficient (10 -14 ～10 -13 cm 2 s -1 ) The capacity and the multiplying power performance of the electrode active components are not easily exerted. At present, the modification method for the silicon material mainly comprises nanocrystallization and compounding, but the silicon material is easy to agglomerate after nanocrystallization, a new volume effect can be generated in the circulation process, the problem of the circulation stability of the silicon material cannot be fundamentally solved by simple nanocrystallization treatment, the cost for preparing the nano silicon powder with a special structure and appearance is higher, and the problems of large specific surface area, low tap density and the like caused by the nano effect all affect the wide application of the nano silicon powder in batteries; the compounding is mainly to introduce an active or inactive buffer matrix with good conductivity and small charge-discharge volume effect on the basis of silicon nanocrystallization to reduce the volume effect of a silicon active phase, and improve the cycle stability and the processing performance of the silicon-based material through the physical-chemical property synergistic effect among different components of the material.
The silicon-carbon composite material is the silicon-based material with the most application potential at present, and mainly has two technical routes of simple substance silicon-carbon composite material and silicon oxide-carbon composite material. Wherein, silicon oxide (SiO x 0 < x.ltoreq.2) is an amorphous structure composed of a plurality of uniformly distributed nanoscale Si clusters, siO 2 Clusters and between Si/SiO 2 SiO between two phase interfaces x The transition phases are formed together. The silicon oxide can form a lithiated product Li during the first electrochemical charge/discharge process x Si and inactive phase lithium oxide (Li 2 O) and lithium silicate (Li) 4 SiO 4 ) Inactive phase Li 2 O and Li 4 SiO 4 The matrix surrounds Li x The Si core is used as a good in-situ buffer matrix, can reduce the charge-discharge volume expansion of the active substance to about half of that of pure silicon, and can support and disperse the active phase Li x Si, avoids agglomeration phenomenon in the later circulation process, and simultaneously Li 2 The O matrix can serve as a rapid diffusion channel of lithium ions in the charge and discharge process so as to improve the cycle performance and the rate performance of the material. Therefore, compared with the simple substance silicon-based silicon-carbon composite anode material, the silicon oxide-based silicon-carbon composite anode material has more large-scale application prospect in the power and energy storage fields. On the other hand, however, the silicon oxide forms an inactive phase Li during the first charge and discharge 2 O and Li 4 SiO 4 The matrix, although accelerating microstructure tissue dynamics process, effectively improving electrochemical performance and relieving volume expansion stress, also causes electrochemical active lithium storage phase Li x The reduction of Si reduces the specific capacity and the first coulombic efficiency of the material, and the material still has larger volume expansion effect in the practical application of the finished battery.
The current research on silicon oxide-based silicon carbon composite materials mainly comprises SiO x The method is characterized by comprising the steps of designing a nano particle structure of a body, designing and doping a three-dimensional porous structure of a matrix phase, coating an interface and a surface, and the like, so as to solve the problems of low coulomb efficiency caused by volume expansion and pulverization of a charge-discharge silicon material, unstable interface SEI film formation and high irreversible capacity. Chinese patent CN112018334a discloses a silicon oxide/carbon composite negative electrode material, a preparation method thereof and a lithium ion battery, by micro-nano SiO x The silicon oxide/carbon composite anode material with the secondary particle structure is prepared by mixing, granulating, modifying, carbonizing, sieving and demagnetizing the powder and the carbonaceous binder, and has good capacity and first coulomb efficiency, but the silicon raw material cost is higher, the multiplying power charge-discharge cycle performance is poor, and the capacity attenuation is faster. Chinese patent CN112447958A discloses a preparation method of a nitrogen-doped porous carbon-coated porous silicon dioxide negative electrode material, which comprises the steps of obtaining nitrogen-containing alkali lignin through Mannich reaction, carrying out substitution reaction with 3-chloro-2-hydroxypropyl trimethyl ammonium chloride to obtain positively charged quaternized nitrogen-containing alkali lignin, carrying out electrostatic attraction carbonization with porous silicon dioxide nanospheres to obtain the nitrogen-doped porous carbon-coated porous silicon dioxide negative electrode material with a three-dimensional network structure, wherein the obtained material has excellent theoretical specific capacity, multiplying power performance and excellent performance The preparation method has the advantages of complex process, difficult control of process conditions, poor batch stability and inapplicability to large-scale industrialization.
Disclosure of Invention
The invention aims to solve the technical problems of providing a nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite anode material with high capacity, high multiplying power, long cycle life and low production cost, and a preparation method thereof, which is suitable for large-scale industrialization.
The invention provides a preparation method of a nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite anode material, which comprises the following steps:
(1) Compounding a nitrogen source: adding a certain amount of graphitized anthracite micropowder into the nitrogen-containing solution, uniformly mixing, injecting the mixture 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 decompressing and discharging the carbon dioxide in the reaction kettle, and repeating the supercritical operation for a plurality of times to obtain a pretreated graphite micropowder solution;
(2) Nitrogen doping by a hydrothermal method: under the airtight condition, heating the graphite micro powder solution pretreated in the step (1) to a specified temperature while stirring, keeping the reaction 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 in a stirring state, mixing for a certain time until the mixture 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 silicon dioxide sol in a stable state;
(4) Nano silicon dioxide sol compounding: 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 and 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 decompressing and discharging the carbon dioxide in the reaction kettle, and washing, removing liquid and drying to prepare the nitrogen-doped silica/graphite compound;
(5) And (3) smelting reduction: 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 from room temperature to a first constant temperature T1 and preserving heat in a protective gas atmosphere, continuously stirring and heating to a second constant temperature T2 and preserving heat after the heat preservation of T1 is finished, stirring and cooling 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, then putting the mixture into a kneader, carrying out kneading cladding treatment on the mixture under a heating condition, putting the materials into a tablet press after cooling after kneading, and maintaining the mixture for a certain time under a specified pressure to form a precursor blank of the nitrogen-doped silicon oxide/zinc oxide/graphite composite anode material coated with the organic carbon source;
(7) High-temperature calcination: and (3) placing the precursor blank of the organic carbon source coated nitrogen-doped silicon oxide/zinc oxide/graphite composite anode material 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 calcining, crushing, screening and grading to obtain the final product nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite anode material.
Preferably, in the step (1), the average particle size D50 of the graphitized anthracite micropowder is 6.0-12.0 μm, the carbon content is more than 99.5%, and the anthracite raw material is preferably teff anthracite; the nitrogen-soluble 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-methylpyrrolidone and dimethylformamide, the mass fraction of the nitrogen source in the nitrogen-containing solution is 3-8%, and the mass ratio of graphitized anthracite micro powder to solute nitrogen source in the nitrogen-containing solution is 1: (0.05-0.15); the temperature in the high-pressure reaction kettle in the step (1) is controlled to be 31-80 ℃, the pressure is 7-35 MPa, the supercritical holding time of materials in the high-pressure reaction kettle is 1.5-3.0 h, the slow pressure release time is not less than 2.5h, and the supercritical operation times are 2-4 times.
Preferably, in the step (2), the stirring rotation 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 aqueous solution is 6.0-25%; the addition 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, a step of; the cationic surfactant is one of hexyl trimethyl ammonium bromide, dodecyl trimethyl ammonium bromide, cationic polyacrylamide, polymethyl amino ethyl acrylate, polymethyl amino ethyl methacrylate and polyethyleneimine, and the nonionic surfactant is one of polyvinylpyrrolidone, polyethylene glycol and alkylphenol ethoxylate; the silicon tetrachloride in the step (3) is a byproduct of polysilicon production with the purity of more than 99.0 percent; in the step (3), the stirring rotation 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 micro powder in the mixed solution in the step (4) is (0.05-0.12): 1, a step of; the stirring rotating speed in the step (4) is 300-1000 r/min, and the stirring and mixing time is 60-150 min; the temperature in the high-pressure reaction kettle in the step (4) is controlled to be 31-80 ℃, the pressure is 7-35 MPa, the supercritical retention time of materials in the high-pressure reaction kettle is 3.0-6.5 h, and the slow pressure release time is not less than 2.5h.
Preferably, in the step (5), the first constant temperature T1 is 400-450 ℃, and the reaction is carried out at the temperature of room temperature to T1The 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 stirring speed is 40-90 r/min, the heating speed is 2-5 ℃/min, and the heat preservation time is 90-240 min in the reaction stage from the temperature T1 to the temperature T2; the molar ratio of the metal zinc powder to the silicon dioxide in the nitrogen doped silicon dioxide/graphite compound in the step (5) is (0.25-0.65): 1, the average grain diameter D50 of the metal zinc powder is 50 nm-25 mu m, and the mass content is more than 99 percent; 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 m 3 /h。
Preferably, in the step (6), the organic carbon source is more than one 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, a step of; in the step (6), the kneading temperature is 110-180 ℃, the kneading time is 2-4 h, the compacting pressure is 7-20 Mpa, and the compacting time is 0.5-2.0 h.
Preferably, the temperature rising speed 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 m 3 /h; the average grain diameter D50 of the nitrogen doped silicon oxide/zinc oxide/graphite/carbon composite anode material crushed in the step (7) is 14.0-17.0 mu m.
The invention also discloses a nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite anode material, which consists of a disordered nitrogen-doped silicon oxide/zinc oxide/graphite composite, 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/oxygenThe zinc/graphite/carbon composite negative electrode material is prepared by taking graphitized anthracite as a graphite substrate, adopting a supercritical fluid method to perform intercalation and jack recombination of nitrogen source molecules on the graphite substrate, and performing hydrothermal reaction to prepare nitrogen doped modified graphite; the method comprises the steps of taking silicon tetrachloride which is a byproduct of polysilicon production as a silicon source, preparing nano silicon dioxide sol under the alkaline condition and the action of a stabilizer consisting of a cationic surfactant and a nonionic surfactant, performing intercalation and jack precipitation compounding of the nano silicon dioxide sol on nitrogen-doped modified graphite by a supercritical fluid method, and performing molten partial reduction on metal zinc powder to prepare nitrogen-doped silicon oxide (SiO) x 0 < x < 2)/zinc oxide/graphite composite; the method comprises the steps of taking an organic carbon source as a coating agent, coating and molding a nitrogen-doped silicon oxide/zinc oxide/graphite composite by adopting a mixing and kneading and compacting process, and then calcining at a high temperature, crushing and screening to prepare the nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite anode material with high tap density and excellent processability. Specifically:
Compared with natural graphite, the graphitized anthracite in the step (1) has the characteristics of porous surface, large graphite layer spacing, mainly microcrystalline graphite distribution as an internal structure and high mechanical strength, and the carbon dioxide fluid has super-solubility, strong diffusivity and unique mass transfer property in a supercritical state, and the nitrogen source is dissolved into the supercritical fluid, so that the carbon dioxide fluid and nitrogen source molecules can simultaneously perform insertion holes and intercalation on the graphitized anthracite; meanwhile, the controllable expansion and reaming preparation of graphitized anthracite can be realized by optimally controlling the decompression rate of carbon dioxide under supercritical pressure, so that a channel and a space are further provided for jack and intercalation compounding 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 peeled into flocculent graphene sheets which are uniformly distributed between and on the surface of the pretreated graphite micro powder, so that the conductivity of the modified graphite can be effectively enhanced;
in the step (2), nitrogen atoms are introduced into the interlayer and surface micropores of the graphite and form covalent bonds under the hydrothermal reaction condition, the radius of the nitrogen atoms is close to that of carbon atoms, but the electronegativity is high, the nitrogen atom doping can keep the crystal structure and pore channels of the graphite, and the extra lone pair electrons of the nitrogen atoms can provide negative charges for a carbon skeleton delocalization system in the crystal structure of the graphite, so that active sites with high electronegativity are generated at the corresponding doping positions of the interlayer and surface micropores of the graphite, the electron transmission performance and chemical reactivity of the nitrogen doped modified graphite can be effectively enhanced, the low-temperature charge-discharge performance of the material is improved, and the uniform precipitation and recombination of the nano silica sol containing the cationic surfactant as a stabilizer in the later stage are facilitated;
The stabilizer in the step (3) adopts 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 negatively influence the dispersibility of the nano silicon dioxide, but because the nitrogen doped modified graphite prepared in the step two is distributed with a large number of active sites with high electronegativity between graphite layers and on surface micropores, the uniformly dispersed cationic surfactant in the nano silicon dioxide sol system can promote the microscopic diffusion movement capability of the nano silicon dioxide between the nitrogen doped modified graphite layers and in the surface micropores, and the composite uniformity and efficiency of the nano silicon dioxide are improved;
in the step (4), the uniform precipitation and compounding of nano silicon dioxide between nitrogen doped modified graphite layers and surface micropores are realized by single supercritical operation by utilizing the super-solubility and strong diffusivity characteristics of the supercritical fluid of carbon dioxide and the electric polarity effect of a cationic surfactant in a nano silicon dioxide sol system;
in the step (5), in the first constant temperature T1 heat preservation stage, the metal zinc powder is stirred, continuously diffused, impregnated and permeated into graphite layers and surface micropores of the nitrogen doped silicon dioxide/graphite composite, and the silicon dioxide and part of the silicon dioxide undergo oxidation-reduction reaction to generate high-capacity active substance nano silicon oxide (SiOx, 0 < x < 2) and zinc oxide, wherein the graphite layers and the surface micropores can be reserved space for charge-discharge expansion of active substances, 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 on the surface micropores along with nano silicon dioxide precipitation under the action of supercritical fluid is carbonized at high temperature, a carbon coating layer with good conductivity is gradually generated on the surfaces of nano silicon oxide and zinc oxide, carbon fibers are formed to connect the coated fusion reduction product with adjacent graphite sheets and the inner surfaces of the surface micropores in series through Van der Waals force, so that the c-axis electronic conductivity of the graphite layers is effectively improved, and the composite material has higher specific capacity and is suitable for high-rate charge and discharge; meanwhile, the oxygen-containing functional group in the stabilizer can further oxidize the metal zinc powder which is not fully reacted in the stage T1 in the process of maintaining the stability of T2, so as to ensure that no metal zinc powder remains in the final product. The theoretical capacity of zinc oxide is as high as 978mAh/g, and the zinc oxide sediment coated on the surface is compounded between graphite layers and on the surface of micropores, so that the zinc oxide sediment is used as an active component of a composite material to show excellent electrochemical performance;
In the step (6), stirring, extruding, splitting and kneading by a kneader, wherein an organic carbon source fully infiltrates and permeates into gaps on the surface of the nitrogen-doped silicon oxide/zinc oxide/graphite compound and graphite layer peeling defects after being softened at high temperature, so as to form paste with high compactness and good shaping; meanwhile, after the paste is cooled, the paste is pressed by a tablet press to further eliminate the friction stress among paste particles so as to improve the compaction density, so that 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 anode material prepared in the step (7) is a secondary granulation particle, macroscopically shows isotropy, can effectively improve the stability of a material structure, and is suitable for embedding and embedding lithium ions in a high-rate charge and discharge process.
The nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite anode material prepared by the method is a secondary granulation particle, and consists of a disordered nitrogen-doped silicon oxide/zinc oxide/graphite composite, 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. Wherein, graphite base material stone The black anthracite is subjected to nitrogen atom doping in the 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 electron transmission performance and chemical reaction activity of a graphite substrate are effectively enhanced, and the low-temperature charge-discharge performance of the material is improved; amorphous carbon-coated high capacity active material nano silicon oxide (SiO x 0 < x < 2) and zinc oxide are compounded between graphite layers and on surface micropores, and carbon fibers are used as a medium to be connected with the inner surfaces of adjacent graphite sheets and the surface micropores in series through Van der Waals force, so that the volume stress of an active substance in the charging and discharging process can be effectively relieved, the c-axis electron conductivity of the graphite layers is improved, and the composite material has higher specific capacity and is suitable for high-rate charging and discharging; the surface of the disordered nitrogen-doped silicon oxide/zinc oxide/graphite composite particles is coated with a compact amorphous carbon coating layer, and the particles are mutually bridged through amorphous carbon to form secondary particles with controllable particle size distribution, so that the composite anode material particles macroscopically show isotropy, and the mechanical strength and the multiplying power circulation stability of the material structure can be effectively improved.
The invention takes graphitized anthracite as a stable structural carrier of the composite material, and silicon tetrachloride as a byproduct of polysilicon production is taken as a silicon source, so that the raw material source is wide, the price is low, and the production cost of the composite material is reduced. The graphitized anthracite has the characteristics of porous surface, large graphite layer spacing, mainly distributed microcrystalline graphite as an internal structure, high mechanical strength and other structural properties, is favorable for easy realization of controllable adjustment in the supercritical fluid expansion reaming modification process, can maximally maintain the original morphology structure of the material, and reduces the generation of graphite layer peeling defects, thereby providing a channel and space with moderate geometric dimensions and stable morphology structure for compounding nitrogen sources and nano silica sol between graphite layers and surface micropores of the material. The nitrogen atoms are doped between graphite layers and on surface micropores to generate a large number of electronegative active sites, so that the electrochemical reaction activity and low-temperature charge-discharge performance of graphitized anthracite are enhanced, and the microscopic diffusion movement capacity of a nano silicon dioxide sol system containing a cationic surfactant as a stabilizer is improved, so that nano silicon dioxide precipitation and recombination is uniform and high in efficiency. The stabilizer in the nano silicon dioxide sol is subjected to composite precipitation in graphite layers and surface micropores along with nano silicon dioxide under the action of a supercritical fluid, amorphous carbon is generated to cover the surfaces of nano silicon oxide and zinc oxide which are zinc powder fusion reduction products after high-temperature pyrolysis, and carbon fibers are formed to connect the fusion reduction products after the cladding with adjacent graphite sheets and the inner surfaces of the surface micropores in series through Van der Waals force, so that on one hand, the charge-discharge characteristics and the first efficiency of the silicon oxide and the zinc oxide are optimized and modified, the interfacial potential energy between active substances is effectively reduced, on the other hand, the silicon oxide and the zinc oxide are firmly bound in the graphite layers and the surface gaps, the volume stress of the silicon oxide and the zinc oxide in the charge-discharge process can be effectively relieved, and the composite material has higher specific capacity and is suitable for high-rate charge-discharge. The kneading cladding and the pressed compact repair and improve the cavity defects of the internal structure of the composite material, and simultaneously effectively improve the compaction density and the mechanical strength of the material, so that the final product has excellent processability and good rate charge-discharge cycling stability. The technological conditions of the invention are easy to control, the production cost is low, and the industrial production is easy to realize.
The invention has the beneficial effects that:
1. the silicon source used in the invention is silicon tetrachloride which is a byproduct of polysilicon production, the price is low, and the production cost of the composite anode material can be effectively reduced; meanwhile, a new thought is provided for energy-saving and environment-friendly treatment of the byproduct in the production of the polysilicon, and the high-value utilization of the silicon tetrachloride byproduct is facilitated.
2. According to the invention, by utilizing the structural characteristics of porous surface of graphitized anthracite, large interlayer spacing of graphite, mainly microcrystalline graphite distribution in an internal structure, high mechanical strength and the like, and adopting a supercritical fluid binding hydrothermal synthesis method to introduce nitrogen atom doping into the interlayer and surface micropores of graphitized anthracite to form covalent bonds, a large number of active sites with high electronegativity are generated at corresponding doping positions, so that the electrochemical reaction activity and low-temperature charge-discharge performance of graphitized anthracite are enhanced, and the microscopic diffusion movement capability of uniformly precipitating and compounding a nano silica sol system containing a cationic surfactant as a stabilizer between the interlayer and the surface micropores of nitrogen-doped graphitized anthracite is improved.
3. According to the invention, 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 used as a medium to be connected with adjacent graphite sheets 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 charging and discharging process can be effectively relieved, the c-axis electronic conductivity of the graphite layers is improved, and the composite material has higher specific capacity and is suitable for high-rate charging and discharging;
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 image of graphitized anthracite coal of 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 scheme of the invention easier to understand, the technical scheme of the invention is clearly and completely described by adopting a specific embodiment mode.
1. The specific embodiment is as follows:
example 1:
(1) The mass ratio of graphitized anthracite micropowder to nitrogen-containing liquid nitrogen source solute is 1: adding graphitized anthracite micropowder with the average particle diameter D50 of 6 mu m into a 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 and keeping for 1.5 hours, slowly decompressing for 5 hours, discharging carbon dioxide, and repeating the supercritical operation for 4 times to obtain a pretreated graphite micropowder 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 maintaining the reaction for 2 hours, 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 hexyl trimethyl ammonium bromide and the mass ratio of 0.30:1 of polyvinylpyrrolidone into the sodium hydroxide aqueous solution 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 maintaining stirring and reacting for 60min, and standing and ageing the solution for 2.5h to obtain a nano silicon dioxide sol in a stable state;
(4) Adding quantitative nano silica sol into a high-pressure reaction kettle containing nitrogen-doped modified graphite micro powder solution according to the mass ratio of silica to nitrogen-doped modified graphite in the mixed solution of 0.05:1, 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 ensure that the pressure of carbon dioxide in the kettle reaches 35MPa, controlling the temperature and the pressure of the reaction kettle to be unchanged and keeping for 3.0h, slowly decompressing for 5h to discharge carbon dioxide, and washing, dehydrating and drying the product to obtain the nitrogen-doped silica/graphite compound;
(5) According to the molar ratio of metal zinc powder to silicon dioxide in the nitrogen-doped silicon dioxide/graphite compound of 0.25:1, uniformly mixing metal zinc powder with average grain diameter D50 of 50nm with the nitrogen-doped silicon dioxide/graphite compound, and then putting into a high-temperature reaction kettle, wherein the flow rate of nitrogen is 0.4m 3/ In the atmosphere, the stirring rotating speed is 50r/min, the temperature is raised to 400 ℃ from the room temperature at the heating speed of 2 ℃/min, the temperature is kept for 150min, after the temperature is kept, the stirring rotating speed is 40r/min, the temperature is raised to 700 ℃ at the heating speed of 2 ℃/min, the temperature is kept for 240min, the reaction kettle is naturally cooled to the room temperature, and the stirring is stopped to obtain the 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 materials, and compacting for 2.0 hours under a pressure of 7Mpa to obtain a precursor blank of the organic carbon source coated nitrogen-doped silicon oxide/zinc oxide/graphite composite anode material;
(7) Placing the precursor blank of the organic carbon coated nitrogen doped silicon oxide/zinc oxide/graphite composite anode material in a high-temperature atmosphereFurnace with nitrogen flow of 0.4m 3 And (3) calcining for 6 hours at the temperature rising speed of 3 ℃/min to 750 ℃, naturally cooling the material to room temperature after calcining, crushing, screening and grading to obtain the nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite anode material with the average particle size D50 of 14.0 mu m.
Example 1 a nitrogen doped silicon oxide/zinc oxide/graphite/carbon composite negative electrode material was obtained for physical and chemical property testing. The specific surface area of the cathode material is 1.63m 2 Per gram, the tap density of the powder of the negative electrode material is 1.04g/cm 3 The initial discharge capacity of 0.1C is 421.4mAh/g, the initial efficiency is 92.3%, the capacity retention rate of 1C charge and discharge 100 weeks is 90.4%, the capacity retention rate of-20 ℃/25 ℃ is 72.1%, and the test results are summarized in Table 1.
Example 2:
(1) The mass ratio of graphitized anthracite micropowder to nitrogen-containing liquid nitrogen source solute is 1: adding graphitized anthracite micropowder with the average particle diameter D50 of 8 mu m into 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 and keeping for 2.0 hours, slowly decompressing for 4.5 hours, discharging carbon dioxide, and repeating the supercritical operation for 4 times to obtain pretreated graphite micropowder 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 maintaining the reaction for 3 hours, and naturally cooling to room temperature after stirring 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 fraction of 1.5% of sodium carbonate aqueous solution and the mass ratio of 0.37:1 of dodecyl trimethyl ammonium bromide to polyethylene glycol at the rotating speed of 520r/min, 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 maintaining stirring and reacting for 78min, and standing and ageing the solution for 3.0h to obtain a nano silicon dioxide sol in a stable state;
(4) Adding quantitative nano silica sol into a high-pressure reaction kettle containing nitrogen-doped modified graphite micro powder solution according to the mass ratio of silica to nitrogen-doped modified graphite in the mixed solution of 0.07:1, 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 carbon dioxide in the kettle to reach 28MPa, controlling the temperature and the pressure of the reaction kettle to be unchanged and keeping for 3.5h, slowly decompressing for 4.5h to discharge carbon dioxide, and washing, dehydrating and drying the product to obtain the nitrogen-doped silica/graphite compound;
(5) 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, uniformly mixing the metal zinc powder with the average grain diameter D50 of 500nm with the nitrogen-doped silicon dioxide/graphite compound, and then putting the mixture into a high-temperature reaction kettle, wherein the flow of helium is 0.6m 3/ In the atmosphere, the stirring rotating speed is 70r/min, the temperature is raised to 410 ℃ from the room temperature at the heating speed of 2 ℃/min, the heat is preserved for 132min, after the heat preservation is finished, the stirring rotating speed is 50r/min, the temperature is raised to 740 ℃ at the heating speed of 2 ℃/min, the heat is preserved for 210min, the reaction kettle is naturally cooled to the room temperature, and the stirring is stopped to obtain the 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 a temperature of 120 ℃, cooling the materials, and compacting for 1.5 hours under a pressure of 10Mpa to obtain a precursor blank of the organic carbon source coated nitrogen-doped silicon oxide/zinc oxide/graphite composite anode material;
(7) Placing a 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 controlling the flow of helium to be 0.6m 3 And (3) calcining for 5 hours at a temperature rising speed of 3 ℃/min to 800 ℃, naturally cooling the material to room temperature after calcining, crushing, screening and grading to obtain the nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite anode material with an average particle size D50 of 14.0 mu m.
Example 2 a nitrogen doped silicon oxide/zinc oxide/graphite/carbon composite negative electrode material was obtained for physical and chemical property testing. The specific surface area of the negative electrode material is 1.57m 2 /g, negativeThe tap density of the polar material powder is 1.07g/cm 3 The initial discharge capacity of 0.1C is 451.3mAh/g, the initial efficiency is 91.3%, the capacity retention rate of 1C in 100 weeks of charge and discharge is 90.2%, the capacity retention rate of-20 ℃/25 ℃ is 71.5%, and the test results are summarized in Table 1.
Example 3:
(1) The mass ratio of graphitized anthracite micropowder to nitrogen-containing liquid nitrogen source solute is 1:0.10, adding graphitized anthracite micropowder with the average particle diameter D50 of 9 mu m into an ammonium chloride N-methylpyrrolidone solution with the mass fraction of 5%, 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 2.0h, slowly decompressing for 4.0h, discharging carbon dioxide, and repeating the supercritical operation for 3 times to obtain a pretreated graphite micropowder 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 maintaining the reaction for 4 hours, and naturally cooling to room temperature after stirring to obtain a nitrogen-doped modified graphite micro powder solution;
(3) Preparing sodium bicarbonate aqueous solution with the mass fraction of 15.0% at room temperature, adding a combined stabilizer with the mass fraction of 2.0% of the sodium hydroxide aqueous solution and the mass ratio of 0.44:1 of the cationic polyacrylamide to the alkylphenol polyoxyethylene ether 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 maintaining stirring and reacting for 96min, standing and aging the solution for 4.5h to obtain nano silicon dioxide sol in a stable state;
(4) Adding quantitative nano silica sol into a high-pressure reaction kettle containing nitrogen-doped modified graphite micro powder solution according to the mass ratio of silica to nitrogen-doped modified graphite in the mixed solution of 0.08:1, 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 ensure that the pressure of carbon dioxide in the kettle reaches 21MPa, controlling the temperature and the pressure of the reaction kettle to be unchanged and keeping for 4.0h, slowly decompressing for 4.0h to discharge carbon dioxide, and washing, dehydrating and drying the product to obtain the nitrogen-doped silica/graphite compound;
(5) According to the mole ratio of the metal zinc powder to the silicon dioxide in the nitrogen doped silicon dioxide/graphite compound of 0.41:1, uniformly mixing the metal zinc powder with the average grain diameter D50 of 5 mu m with the nitrogen doped silicon dioxide/graphite compound, and then putting the mixture into a high-temperature reaction kettle, wherein the neon flow is 0.8m 3/ In the atmosphere, the stirring rotating speed is 90r/min, the temperature is raised to 420 ℃ from room temperature at a heating speed of 3 ℃/min, the temperature is kept for 114min, after the temperature is kept, the stirring rotating speed is 60r/min, the temperature is raised to 780 ℃ at a heating speed of 3 ℃/min, the temperature is kept for 180min, the reaction kettle is naturally cooled to the room temperature, and the stirring is stopped to obtain the 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 for 3 hours at 140 ℃, cooling the materials, and compacting for 1.5 hours under 14Mpa pressure to obtain a precursor blank of the organic carbon source coated nitrogen-doped silicon oxide/zinc oxide/graphite composite anode material;
(7) Placing the precursor blank of the organic carbon coated nitrogen doped silicon oxide/zinc oxide/graphite composite anode material in a high-temperature atmosphere furnace, and enabling the neon gas flow to be 0.8m 3 Calcining for 4.5 hours at a temperature rising speed of 4 ℃/min to 850 ℃, naturally cooling the material to room temperature after calcining, crushing, screening and grading to obtain the nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite anode material with an average particle size D50 of 15.0 mu m.
Example 3 a nitrogen doped silicon oxide/zinc oxide/graphite/carbon composite negative electrode material was obtained for physical and chemical property testing. The specific surface area of the negative electrode material is 1.47m 2 Per gram, the tap density of the powder of the cathode material is 1.08g/cm 3 The initial discharge capacity of 0.1C is 466.1mAh/g, the initial efficiency is 91.2%, the capacity retention rate of 1C charge and discharge 100 weeks is 89.7%, the capacity retention rate of-20 ℃/25 ℃ is 72.0%, and the test results are summarized in Table 1.
Example 4:
(1) The mass ratio of graphitized anthracite micropowder to nitrogen-containing liquid nitrogen source solute is 1:0.10, adding graphitized anthracite micropowder with the average particle diameter D50 of 9 mu m into urea dimethyl amide solution with the mass fraction of 6%, 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 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 decompressing for 4.0 hours, discharging carbon dioxide, and repeating the supercritical operation for 3 times to obtain pretreated graphite micropowder 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 maintaining the reaction for 4 hours, and naturally cooling to room temperature after stirring 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 combined stabilizer with the mass fraction of 2.5% of the sodium hydroxide aqueous solution and the mass ratio of 0.51:1 of the dimethylaminoethyl polyacrylate to the polyvinylpyrrolidone 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 maintaining stirring and reacting for 114min, and standing and ageing the solution for 4.5h to obtain a stable nano silicon dioxide sol;
(4) Adding quantitative nano silica sol into a high-pressure reaction kettle containing nitrogen-doped modified graphite micro powder solution according to the mass ratio of 0.09:1 of the silicon dioxide 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 ensure that the pressure of the carbon dioxide in the kettle reaches 21MPa, controlling the temperature and the pressure of the reaction kettle to be unchanged and keeping for 5.0h, slowly decompressing for 4.0h to discharge carbon dioxide, and washing, dehydrating and drying the product to obtain the nitrogen-doped silicon dioxide/graphite compound;
(5) According to the mole ratio of the metal zinc powder to the silicon dioxide content in the nitrogen-doped silicon dioxide/graphite compound of 0.49:1, uniformly mixing the metal zinc powder with the average grain diameter D50 of 10 mu m with the nitrogen-doped silicon dioxide/graphite compound, and then putting the mixture into a high-temperature reaction kettle, wherein the argon flow is 0.8m 3/ In the atmosphere of h, the stirring rotating speed is 110r/min, the temperature is raised from room temperature to 430 ℃ at a heating speed of 4 ℃/min, the temperature is kept for 96min, and after the temperature is kept, the stirring rotating speed is used70r/min, heating to 820 ℃ at a heating rate of 4 ℃/min, preserving heat for 150min, 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 0.27:1, kneading and coating for 3 hours at a temperature of 150 ℃, and compacting for 1.0 hour under a pressure of 14Mpa after the materials are cooled to obtain a precursor blank of the organic carbon source coated nitrogen-doped silicon oxide/zinc oxide/graphite composite anode material;
(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 controlling the argon flow to be 0.8m 3 And (3) calcining for 4 hours at the temperature rising speed of 4 ℃/min to 900 ℃ in the atmosphere, naturally cooling the material to room temperature after the calcining is finished, crushing, screening and grading to obtain the nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite anode material with the average particle size D50 of 16.0 mu m.
Example 4 a nitrogen doped silicon oxide/zinc oxide/graphite/carbon composite negative electrode material was obtained for physical and chemical property testing. The specific surface area of the negative electrode material is 1.43m 2 Per gram, the tap density of the powder of the cathode material is 1.12g/cm 3 The initial discharge capacity of 0.1C is 480.3mAh/g, the initial efficiency is 91.7%, the capacity retention rate of 1C in 100 weeks after charge and discharge is 89.8%, the capacity retention rate of-20 ℃/25 ℃ is 70.9%, and the test results are summarized in Table 1.
Example 5:
(1) The mass ratio of graphitized anthracite micropowder to nitrogen-containing liquid nitrogen source solute is 1: adding graphitized anthracite micropowder with the average particle diameter D50 of 10 mu m into melamine ethanol solution with the mass fraction of 7%, 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 and keeping for 2.5 hours, slowly decompressing for 3.0 hours, discharging carbon dioxide, and repeating the supercritical operation for 2 times to obtain pretreated graphite micropowder 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 maintaining the reaction for 5 hours, and naturally cooling to room temperature after stirring 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, and adding a polymethyl methacrylate with the mass fraction of 3.0% of a sodium hydroxide aqueous solution into the aqueous solution at the rotating speed of 1030r/min, wherein the mass ratio of the polymethyl methacrylate to the polyethylene glycol is 0.58:1, slowly adding silicon tetrachloride with the purity of more than 99.0 percent to adjust the pH value of the solution to be neutral after stirring and mixing for 102min, continuously keeping stirring and reacting for 132min, and standing and aging the solution for 5.5h to obtain the nano silicon dioxide sol in a stable state.
(4) Adding quantitative nano silica sol into a high-pressure reaction kettle containing nitrogen-doped modified graphite micro powder solution according to the mass ratio of 0.10:1 of silica to 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 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 decompressing for 3.0h to discharge carbon dioxide, and washing, dehydrating and drying the product to obtain the nitrogen-doped silica/graphite compound;
(5) According to the mole ratio of metal zinc powder to silicon dioxide in the nitrogen doped silicon dioxide/graphite compound of 0.57:1, uniformly mixing metal zinc powder with average grain diameter D50 of 15 mu m with the nitrogen doped silicon dioxide/graphite compound, and then feeding into a high-temperature reaction kettle, wherein the krypton gas flow is 1.0m 3/ In the atmosphere, the stirring rotation speed is 130r/min, the temperature is raised to 440 ℃ from room temperature at a heating speed of 5 ℃/min, the temperature is kept for 78min, after the temperature is kept, the stirring rotation speed is 80r/min, the temperature is raised to 860 ℃ at a heating speed of 5 ℃/min, the temperature is kept for 120min, the reaction kettle is naturally cooled to the room temperature, and the stirring is stopped to obtain the 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 2 hours at 170 ℃, cooling the materials, and compacting for 1.0 hour under 17Mpa pressure 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 flow rate of krypton is 1.0m 3 And (3) calcining for 3.5 hours at a temperature rising speed of 5 ℃/min to 950 ℃, naturally cooling the material to room temperature after calcining, crushing, screening and grading to obtain the nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite anode material with an average particle size D50 of 17.0 mu m.
Example 5 a nitrogen doped silicon oxide/zinc oxide/graphite/carbon composite negative electrode material was obtained for physical and chemical property testing. The specific surface area of the cathode material is 1.38m 2 Per gram, the tap density of the powder of the negative electrode material is 1.15g/cm 3 The initial discharge capacity of 0.1C is 494.9mAh/g, the initial efficiency is 90.5%, the capacity retention rate of 1C charge and discharge 100 weeks is 88.5%, the capacity retention rate of-20 ℃/25 ℃ is 70.1%, and the test results are summarized in Table 1.
Example 6:
(1) The mass ratio of graphitized anthracite micropowder to nitrogen-containing liquid nitrogen source solute is 1:0.15, adding graphitized anthracite micropowder with the average particle diameter D50 of 12 mu m into an 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 for 3.0h, slowly decompressing for 2.5h, discharging carbon dioxide, and repeating the supercritical operation for 2 times to obtain a pretreated graphite micropowder 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 maintaining the reaction for 6 hours, and naturally cooling to room temperature after stirring to obtain a nitrogen-doped modified graphite micro powder solution;
(3) Preparing a potassium bicarbonate aqueous solution with the mass fraction of 25.0% at room temperature, adding a combined stabilizer with the mass fraction of 3.5% of hexyl trimethyl ammonium bromide and the mass ratio of 0.65:1 of polyvinylpyrrolidone in the sodium hydroxide aqueous solution at the rotating speed of 1200r/min, stirring and mixing for 90min, slowly adding silicon tetrachloride with the purity of more than 99.0% to adjust the pH value of the solution to be neutral, continuously maintaining stirring and reacting for 150min, and standing and ageing the solution for 6.0h to obtain a stable nano silicon dioxide sol;
(4) Adding quantitative nano silica sol into a high-pressure reaction kettle containing nitrogen-doped modified graphite micro powder solution according to the mass ratio of 0.12:1 of the silicon dioxide 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 ensure that the pressure of the carbon dioxide in the kettle reaches 7MPa, controlling the temperature and the pressure of the reaction kettle to be unchanged and keeping for 6.5h, slowly decompressing for 2.5h to discharge carbon dioxide, and washing, dehydrating and drying the product to obtain the nitrogen-doped silicon dioxide/graphite compound;
(5) According to the molar ratio of metal zinc powder to silicon dioxide in the nitrogen-doped silicon dioxide/graphite compound of 0.65:1, uniformly mixing the metal zinc powder with the average grain diameter D50 of 25 mu m with the nitrogen-doped silicon dioxide/graphite compound, and then putting the mixture into a high-temperature reaction kettle, wherein the xenon gas flow rate is 1.2m 3/ In the atmosphere, the stirring rotating speed is 150r/min, the temperature is raised to 450 ℃ from room temperature at a heating speed of 5 ℃/min, the temperature is kept for 60min, after the temperature is kept, the stirring rotating speed is 90r/min, the temperature is raised to 900 ℃ at a heating speed of 5 ℃/min, the temperature is kept for 90min, the reaction kettle is naturally cooled to the room temperature, and the stirring is stopped to obtain the 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 180 ℃, cooling the materials, and compacting for 0.5 hour under 20Mpa pressure to obtain a precursor blank of the organic carbon source coated nitrogen-doped silicon oxide/zinc oxide/graphite composite anode material;
(7) Placing a 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 xenon flow is 1.2m 3 And (3) calcining for 2.5 hours at a temperature rising speed of 5 ℃/min to 1000 ℃, naturally cooling the calcined material to room temperature, crushing, screening and grading to obtain the nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite anode material with an average particle size D50 of 17.0 mu m.
Example 6 a nitrogen doped silicon oxide/zinc oxide/graphite/carbon composite negative electrode material was obtained for physical and chemical property testing. The specific surface area of the negative electrode material is 1.27m 2 Per gram, the tap density of the powder of the cathode material is 1.17g/cm 3 The first discharge capacity of 0.1C is 519.5mAh/g, the first efficiency is 90.3%, the capacity retention rate of 1C in 100 weeks of charge and discharge is 87.4%, the capacity retention rate of-20 ℃/25 ℃ is 69.7%, and the test results are summarized in Table 1.
Comparative example:
(1) Ethanol is used as a solvent, polyethylene glycol is used as a grinding aid, a rod pin type nano sand mill is used for carrying out wet grinding on the nano silicon dioxide with the purity of more than 99.9% and the average particle size D50 of 2 mu m, a grinding medium adopts zirconia balls with the diameter of 0.1mm, and the nano silicon dioxide with the particle size of less than 50nm is obtained through washing, liquid removal and drying after the grinding is finished.
(2) Graphitized anthracite micro powder with an average particle size D50 of 9 mu m, nano silicon dioxide and metal zinc powder with an average particle size D50=10mu m are mixed according to a mass ratio of 1:0.09:0.04 is put into a high temperature reaction kettle after being evenly mixed, and the flow rate of argon is 0.8m 3/ And in the atmosphere, the stirring rotating speed is 110r/min, the temperature is raised to 430 ℃ from room temperature at a heating speed of 4 ℃/min, the temperature is kept for 96min, after the temperature is kept, the stirring rotating speed is 70r/min, the temperature is raised to 820 ℃ at a heating speed of 4 ℃/min, the temperature is kept for 150min, the reaction kettle is naturally cooled to the room temperature, and the stirring is stopped to obtain the silicon oxide/zinc oxide/graphite compound.
(3) Uniformly mixing polyvinyl alcohol and a silicon oxide/zinc oxide/graphite composite according to a mass ratio of 0.27:1, kneading and coating for 3 hours at a temperature of 150 ℃, cooling the materials, and compacting for 1.0 hour under a pressure of 14Mpa to obtain a precursor blank of the silicon oxide/zinc oxide/graphite composite anode material coated by an organic carbon source.
(4) Placing a precursor blank of the silicon oxide/zinc oxide/graphite composite anode material coated by an organic carbon source in a high-temperature atmosphere furnace, and controlling the argon flow to be 0.8m 3 And (3) calcining for 4 hours at the temperature rising speed of 4 ℃/min to 900 ℃ in the atmosphere, naturally cooling the material to room temperature after the calcining is finished, crushing, screening and grading to obtain the silicon oxide/zinc oxide/graphite/carbon composite anode material with the average particle size D50 of 16.0 mu m.
The material prepared in comparative example has a specific surface area of 1.50m 2 Per gram, the tap density of the powder is 1.10g/cm 3 . The material prepared in the comparative example is used as a negative electrode active material of a simulated battery, and electrochemical performance test is carried out, wherein the first discharge capacity of 0.1C is 433.4mAh/g, the first efficiency is 77.8%, the 100-cycle capacity retention rate is more than or equal to 57.2%, and the capacity retention rate of-20 ℃/25 ℃ is 44.6%. The test results are shown in Table 1.
Comparative example silicon source was commercial silicon dioxide, nitrogen doping modification and supercritical fluid intercalation and intercalation jack compounding were not employed, and other material components, proportions and processes were the same as in example 4.
2. Performance characterization method
1. Characterization of physical properties: the nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite anode material is prepared by the method, and the morphology of the composite anode material is observed by a Zeiss GeminiSEM 500 field emission scanning electron microscope; testing the tap density of the composite anode material powder by using an Auto tap type tap density meter of the company Kang Da in the United states; testing the specific surface area of the composite anode material by using a JW-DX specific surface area tester of a fine micro-high Bo company; the buckling electrical properties of the composite negative electrode material were tested by using a CT2001A blue-spot battery test system from Wuhan City blue electric company.
2. And (3) electrical property characterization: pole pieces were made with samples of the negative electrode materials of examples 1-6 and comparative examples, and half cell tests were performed. The active substances are as follows: SP: CMC: sbr=95: 2:1.5:1.5 pulping, uniformly mixing, coating on a Cu film, drying at 110 ℃ for 10 hours, rolling and punching, using a metal lithium sheet as a counter electrode, and using FEC: EC: emc=1: 2:7, preparing a CR2032 button type experimental battery in a high-purity argon protected Braun MBRAUN glove box. At room temperature (25 ℃), the charging and discharging voltage range is 0.003-2.0V, the primary discharging capacity mAh/g of 0.1C is measured, the primary efficiency is measured, 1C charging and discharging cycle test is carried out after 0.1C charging and discharging activation for 2 weeks, and the 100-week cycle capacity retention rate is calculated by using the ratio of the 1C discharging capacity of the composite anode material at the 100 th week to the 1C discharging capacity at the 1 th week; and (3) at room temperature (25 ℃), carrying out 0.1C charge-discharge cycle test at-20 ℃ after 0.003-2.0V charge-discharge voltage range and 0.1C activation for 2 weeks, and calculating to obtain the capacity retention rate of-20 ℃/25 ℃ by using the ratio of the 0.1C discharge capacity of the composite anode material at-20 ℃ at the 1 st week to the 0.1C discharge capacity of the composite anode material at the 25 ℃ at the 1 st week.
3. Performance characterization results and analysis
FIG. 1 is an SEM image of graphitized anthracite coal of 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 graphitized anthracite, the pore size of the micropores is distributed at about 20-200 nm, and the special morphology structure of the graphitized anthracite is extremely beneficial to the diffusion of supercritical fluid between graphite layers and on the micropores on the surface, so that the intercalation and jack recombination of nitrogen source molecules and nano silica sol are effectively promoted; as shown in fig. 2, the nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite anode material with the secondary granulation structure has smooth surface and no micropore exposure, which indicates that the surface coating of the material is uniform and compact, and can effectively prevent organic solvent molecules from being inserted into graphite sheets of an internal graphite substrate, thereby improving the circulation stability of the material.
Table 1: results of physical and chemical Properties testing of examples and comparative examples samples
Table 1 shows the results of physical and chemical property tests of samples of examples 1 to 6 and comparative examples, and it can be seen from Table 1 that the nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite anode materials prepared in examples 1 to 6 have a first efficiency of > 90%, a 1C charge/discharge 100 cycle capacity retention rate of > 87%, and a-20 ℃/25 ℃ capacity retention rate of > 69.5%. Comparative example silicon source was commercial silicon dioxide, nitrogen doping modification and supercritical fluid intercalation and intercalation jack compounding were not employed, and other material components, proportions and processes were the same as in example 4. The first efficiency, the multiplying power charge-discharge cycle performance and the low temperature performance of the prepared sample are not equal to those of the sample of the example 4. Therefore, the first efficiency, the multiplying power charge-discharge cycle performance and the low-temperature performance of the anode 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, not all the implementation manners of the present invention, and the embodiments are only exemplary, and are only used for providing a more visual and clear way of understanding the present disclosure, not limiting the technical solution described in the present invention. All other embodiments, and other simple alternatives and variations of the inventive solution, which would occur to a person skilled in the art without departing from the inventive concept, are within the scope of the invention.

Claims (9)

1. The preparation method of the nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite anode material is characterized by comprising the following steps of:
(1) Compounding a nitrogen source: adding a certain amount of graphitized anthracite micropowder into the nitrogen-containing solution, uniformly mixing, injecting the mixture into a high-pressure reaction kettle, heating the reaction kettle to a specified temperature, pumping liquid carbon dioxide into the reaction kettle to enable 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 decompressing and discharging carbon dioxide in the reaction kettle, and repeating the operations of heating, pumping carbon dioxide and decompressing for a plurality of times to obtain a pretreated graphite micropowder solution;
(2) Nitrogen doping by a hydrothermal method: under the airtight condition, heating the graphite micro powder solution pretreated in the step (1) to a specified temperature while stirring, keeping the reaction 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 in a stirring state, mixing for a certain time until the mixture 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 silicon dioxide sol in a stable state;
(4) Nano silicon dioxide sol compounding: 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 and 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 decompressing and discharging the carbon dioxide in the reaction kettle, and washing, removing liquid and drying to prepare the nitrogen-doped silica/graphite compound;
(5) And (3) smelting reduction: 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 from room temperature to a first constant temperature T1 and preserving heat in a protective gas atmosphere, continuously stirring and heating to a second constant temperature T2 and preserving heat after the T1 preserving heat is finished, stirring and cooling to room temperature after the preserving heat 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, then putting the mixture into a kneader, carrying out kneading cladding treatment on the mixture under a heating condition, putting the materials into a tablet press after cooling after kneading, and maintaining the mixture for a certain time under a specified pressure to form a precursor blank of the nitrogen-doped silicon oxide/zinc oxide/graphite composite anode material coated with the organic carbon source;
(7) High-temperature calcination: and (3) placing the precursor blank of the organic carbon source coated nitrogen-doped silicon oxide/zinc oxide/graphite composite anode material 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 calcining, crushing, screening and grading to obtain the final product nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite anode material.
2. The method for preparing a nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite anode material according to claim 1, wherein the average particle diameter D50 of graphitized anthracite micropowder in the step (1) is 6.0-12.0 μm, the carbon content is more than 99.5%, and the anthracite raw material is selected from 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 graphitized anthracite micro powder to the solute nitrogen source in the nitrogen-containing solution is 1: (0.05-0.15);
the temperature in the high-pressure reaction kettle in the step (1) is controlled to be 31-80 ℃, the pressure is 7-35 MPa, the supercritical holding time of materials in the high-pressure reaction kettle is 1.5-3.0 h, the slow pressure release time is not less than 2.5h, and the supercritical operation times are 2-4 times.
3. The method for preparing a nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite anode material according to claim 1, wherein the stirring speed in the step (2) 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.
4. The method for preparing a nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite anode 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 aqueous solution is 6.0-25%;
the addition 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, a step of; the cationic surfactant is one of hexyl trimethyl ammonium bromide, dodecyl trimethyl ammonium bromide, cationic polyacrylamide, polymethyl amino ethyl acrylate, polymethyl amino ethyl methacrylate and polyethyleneimine, and the nonionic surfactant is one of polyvinylpyrrolidone, polyethylene glycol and alkylphenol ethoxylate;
The silicon tetrachloride in the step (3) is a byproduct of polysilicon production with the purity of more than 99.0 percent;
in the step (3), the stirring rotation 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 a nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite anode material according to claim 1, wherein the mass ratio of nano silicon dioxide to nitrogen-doped modified graphite micro powder in the mixed solution in the step (4) is (0.05-0.12): 1, a step of;
the stirring rotating speed in the step (4) is 300-1000 r/min, and the stirring and mixing time is 60-150 min;
the temperature in the high-pressure reaction kettle in the step (4) is controlled to be 31-80 ℃, the pressure is 7-35 MPa, the supercritical retention time of materials in the high-pressure reaction kettle is 3.0-6.5 h, and the slow pressure release time is not less than 2.5h.
6. The method for preparing a nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite anode material according to claim 1, wherein in the step (5), the first constant temperature T1 is 400-450 ℃, the reaction period from room temperature to T1 temperature 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 stirring speed is 40-90 r/min, the heating speed is 2-5 ℃/min, and the heat preservation time is 90-240 min in the reaction stage from the temperature T1 to the temperature T2;
The molar ratio of the metal zinc powder to the silicon dioxide in the nitrogen doped silicon dioxide/graphite compound in the step (5) is (0.25-0.65): 1, the average grain diameter D50 of the metal zinc powder is 50 nm-25 mu m, and the mass content is more than 99 percent;
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 m 3 /h。
7. The method for preparing a nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite anode material according to claim 1, wherein in the step (6), the organic carbon source is more than one 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, a step of;
in the step (6), the kneading temperature is 110-180 ℃, the kneading time is 2-4 h, the compacting pressure is 7-20 Mpa, and the compacting time is 0.5-2.0 h.
8. The method for preparing a 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 m 3 /h；
The average grain diameter D50 of the nitrogen doped silicon oxide/zinc oxide/graphite/carbon composite anode material crushed in the step (7) is 14.0-17.0 mu m.
9. A nitrogen doped silicon oxide/zinc oxide/graphite/carbon composite anode material, characterized in that: the nitrogen-doped silicon oxide/zinc oxide/graphite/carbon composite anode 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 anode material consists of nitrogen-doped silicon oxide/zinc oxide/graphite composite in 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.
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