Solid electrolyte-coated porous microcrystalline graphite composite material, composite anode and its preparation method and application

Abstract

This invention discloses a solid electrolyte-coated porous microcrystalline graphite composite material, a composite anode, its preparation method, and its applications. The solid electrolyte-coated porous microcrystalline graphite composite material includes porous microcrystalline graphite with a porous structure; an inorganic solid electrolyte with a composite particle size distribution, including aggregates filling the porous structure and coatings distributed between the particles and on the surface of the porous microcrystalline graphite. The composite anode includes a current collector, a solid electrolyte-coated porous microcrystalline graphite composite material disposed on the surface of the current collector, and a metal composited on the surface of the aforementioned composite material. This invention coats the surface of porous microcrystalline graphite with solid electrolytes of different particle sizes, which can significantly improve the ionic conductivity of the material, facilitating uniform metal deposition and dissolution; furthermore, the resulting composite anode exhibits lower expansion, and the porous microcrystalline graphite itself can contribute higher reversible capacity, possessing advantages of high capacity and high compaction.

Description

Technical Field

[0001] This invention relates to the field of negative electrode materials technology, specifically to a solid electrolyte-coated porous microcrystalline graphite composite material and its preparation method, a novel composite negative electrode and its preparation method and application. Background Technology

[0002] With the rapid development of electric vehicles and portable electronic devices, the market demand for high-energy-density batteries is increasing. Lithium metal has an extremely high theoretical specific capacity (3860 mAh / g) and the lowest electrochemical potential (-3.04 V), making it an ideal anode material for realizing high-energy-density batteries. However, lithium metal is prone to forming lithium dendrites during charging and discharging, which not only reduces the battery capacity but may also puncture the separator, causing short circuits or even fires and explosions.

[0003] Microcrystalline graphite, due to its high degree of graphitization and porous structure, possesses a high theoretical specific capacity and excellent charge-discharge performance, offering potential advantages in improving battery energy density. Furthermore, microcrystalline graphite exhibits minimal volume expansion, which helps maintain battery structural stability during charge-discharge processes, reducing material breakage and electrode stripping caused by volume expansion, thereby improving battery cycle stability and extending battery life.

[0004] Patent CN114180568A discloses a pretreatment method for microcrystalline graphite, which involves first-stage calcination of microcrystalline graphite in an ammonia-containing atmosphere, followed by second-stage calcination in a magnesium vapor-containing atmosphere to obtain pretreated microcrystalline graphite. This pretreated microcrystalline graphite exhibits high specific capacity, long cycle life, and good rate performance. However, due to the low processing temperature, the microcrystalline graphite obtained through this pretreatment has an insufficiently rich pore structure, failing to provide ample space for lithium metal deposition. Summary of the Invention

[0005] The main objective of this invention is to provide a solid electrolyte-coated porous microcrystalline graphite composite material and its preparation method, so as to overcome the shortcomings of the prior art.

[0006] Another objective of this invention is to provide a novel composite anode and its preparation method.

[0007] Another object of the present invention is to provide applications of the novel composite negative electrode.

[0008] To achieve the aforementioned objectives, the technical solution adopted by this invention includes:

[0009] This invention provides a solid electrolyte-coated porous microcrystalline graphite composite material, comprising:

[0010] Porous microcrystalline graphite has a porous structure, which includes mesopores and macropores, and at least some of the pores in the porous structure are connected to the outside.

[0011] An inorganic solid electrolyte with a composite particle size distribution includes an aggregate portion filled within the porous structure and a coating portion distributed between the particles of porous microcrystalline graphite and on the surface of the porous microcrystalline graphite. The coating portion is used to close at least a portion of the pores within the porous structure to isolate the aggregate portion distributed within the pores from the outside environment. The aggregate portion includes at least a first inorganic solid electrolyte particle with a first particle size, and the coating portion includes at least a second inorganic solid electrolyte particle with a second particle size, wherein the first particle size is smaller than the second particle size.

[0012] In some embodiments, the mass ratio of the second inorganic solid electrolyte particle to the first inorganic solid electrolyte particle in the particle size-matched inorganic solid electrolyte is 1:1 to 1:10.

[0013] This invention also provides a method for preparing a solid electrolyte-coated porous microcrystalline graphite composite material, comprising:

[0014] Porous microcrystalline graphite is first mixed with first inorganic solid electrolyte particles having a first particle size, so that the first inorganic solid electrolyte particles at least fill the porous structure of the porous microcrystalline graphite to obtain a first inorganic solid electrolyte particle / porous microcrystalline graphite composite material. Then, second inorganic solid electrolyte particles having a second particle size are added, so that the second inorganic solid electrolyte particles are at least distributed between the particles of porous microcrystalline graphite and on the surface of porous microcrystalline graphite to form a coating part, thus obtaining a solid electrolyte coated porous microcrystalline graphite composite material.

[0015] This invention also provides a solid electrolyte-coated porous microcrystalline graphite composite material prepared by the aforementioned method.

[0016] This invention also provides the application of the aforementioned solid electrolyte-coated porous microcrystalline graphite composite material in the preparation of negative electrodes or metal batteries.

[0017] Accordingly, embodiments of the present invention also provide a composite negative electrode, comprising:

[0018] current collector;

[0019] Solid electrolyte-coated porous microcrystalline graphite composite material disposed on the surface of the current collector;

[0020] Metal composite on the surface of the solid electrolyte-coated porous microcrystalline graphite composite material.

[0021] Furthermore, embodiments of the present invention also provide a method for preparing the aforementioned composite negative electrode, comprising:

[0022] A slurry containing a solid electrolyte-coated porous microcrystalline graphite composite material, a binder, a conductive agent, and a solvent is applied to a current collector and dried to obtain a solid electrolyte-coated porous microcrystalline graphite composite material / current collector composite structure.

[0023] A composite negative electrode is prepared by combining the solid electrolyte-coated porous microcrystalline graphite composite material / current collector composite structure with a metal.

[0024] Furthermore, embodiments of the present invention also provide a metal battery, which includes the solid electrolyte coated with a porous microcrystalline graphite composite material or a composite electrode.

[0025] Compared with the prior art, the beneficial effects of the present invention include at least the following:

[0026] 1) The solid electrolyte-coated porous microcrystalline graphite composite material provided by this invention uses inorganic solid electrolytes of different particle sizes to fill and coat porous microcrystalline graphite, which can increase the contact area between the electrode and the electrolyte, improve the physical contact of the interface, and facilitate the efficient transport of electrons and ions. Simultaneously, particle size matching can optimize the lithium-ion transport channels in the solid electrolyte, reduce the porosity between porous microcrystalline graphite materials, improve ion mobility, reduce interfacial polarization, and improve the charge and discharge efficiency of the battery. Furthermore, since inorganic solid electrolytes react with metals to form a solid electrolyte interface layer, particle size matching can make the generated interface layer more uniform, stabilize the electrode structure, and prevent the active material from falling off due to structural damage during charge and discharge, thus affecting the battery's cycle performance and safety.

[0027] 2) Compared to traditional graphite materials, the composite electrode made of solid electrolyte-coated porous microcrystalline graphite composite material provided by this invention exhibits lower expansion. Compared to porous carbon composite lithium metal anodes, porous microcrystalline graphite itself can contribute higher reversible capacity, possessing advantages of high capacity and high compaction. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a schematic diagram of the preparation process of a solid electrolyte-coated porous microcrystalline graphite composite material in a typical embodiment of the present invention;

[0030] Figure 2aThis is a schematic diagram of a solid electrolyte-coated porous microcrystalline graphite composite material in a typical embodiment of the present invention;

[0031] Figure 2b It is a morphological diagram of the original porous microcrystalline graphite;

[0032] Figure 3 This is a cross-sectional SEM image of the pulverized microcrystalline graphite powder in Example 1 of the present invention;

[0033] Figure 4 This is a cross-sectional SEM image of the porous microcrystalline graphite obtained after acid treatment in Example 1 of this invention;

[0034] Figure 5 This is a cycle performance diagram of a full battery assembled with a metal negative electrode obtained in Example 2 of the present invention;

[0035] Figure 6 This is a cycle performance diagram of the full battery assembled with the metal negative electrode obtained in Example 4 of the present invention;

[0036] Figure 7 This is a cycle performance diagram of a full cell assembled with a metal negative electrode prepared in Comparative Example 3. Detailed Implementation

[0037] In view of the problems existing in the prior art, after long-term research and a large number of experiments, the inventors of this case proposed the following technical solution, which mainly uses low-cost microcrystalline graphite (earthy graphite) as raw material, preferably high-temperature purification method to remove impurities in graphite, and uses the pores formed after impurity removal to create pores in the microcrystalline graphite material in situ, and then fills and coats the pores and surface of the porous microcrystalline graphite with a solid electrolyte of mixed particle size, so as to obtain an inorganic solid electrolyte coated porous microcrystalline graphite composite material, and further prepares a composite metal electrode, which has the advantages of high capacity and high compaction.

[0038] The following will provide a further explanation of the technical solution, its implementation process, and its principles.

[0039] As one aspect of the technical solution of this invention, a solid electrolyte-coated porous microcrystalline graphite composite material includes:

[0040] Porous microcrystalline graphite has a porous structure, which includes mesopores and macropores, and at least some of the pores in the porous structure are connected to the outside.

[0041] An inorganic solid electrolyte with a composite particle size distribution includes an aggregate portion filled within the porous structure and a coating portion distributed between the particles of porous microcrystalline graphite and on the surface of the porous microcrystalline graphite. The coating portion is used to close at least a portion of the pores within the porous structure to isolate the aggregate portion distributed within the pores from the outside. The aggregate portion includes at least a first inorganic solid electrolyte particle with a first particle size, and the coating portion includes at least a second inorganic solid electrolyte particle with a second particle size, wherein the first particle size is smaller than the second particle size.

[0042] In some embodiments, the agglomeration section includes a first inorganic solid electrolyte particle and a second inorganic solid electrolyte particle, and the content of the first inorganic solid electrolyte particle in the agglomeration section is greater than the content of the second inorganic solid electrolyte particle.

[0043] In some preferred embodiments, the content of the first inorganic solid electrolyte particles in the agglomeration section is more than 50% of the total mass of the inorganic solid electrolyte (i.e., a small amount of second-size inorganic solid electrolyte with smaller particle size is also distributed in the agglomeration section). In this invention, the first inorganic solid electrolyte particles (i.e., small-size inorganic solid electrolyte particles) have a smaller particle size, making it easier to penetrate and fill the small pores of the porous structure. Especially during wet mixing, the small-size particles experience less hydrodynamic resistance and have stronger diffusion capabilities, making it easier to enter the pores. When the pore size of the porous microcrystalline graphite is close to the particle size of the small-size inorganic solid electrolyte particles, they preferentially enter the pores of the porous structure. Furthermore, the first inorganic solid electrolyte particles are non-uniformly distributed in the porous structure, and their enrichment location is mainly related to the pore structure distribution inside the microcrystalline graphite, with a denser distribution in areas with abundant pore structures.

[0044] In some embodiments, the coating layer contains a higher content of second inorganic solid electrolyte particles than the first inorganic solid electrolyte particles, meaning it contains particles of varying sizes, but predominantly large particles. Some small-diameter inorganic solid electrolyte particles may be present in the coating layer due to physical or chemical adsorption during the mixing of the inorganic solid electrolyte and porous microcrystalline graphite, as well as the potential for even smaller pores within the microcrystalline graphite.

[0045] In some more preferred embodiments, the content of the second inorganic solid electrolyte particles in the coating portion is more than 10% and not more than 50% of the total mass of the inorganic solid electrolyte.

[0046] In some preferred embodiments, in the solid electrolyte-coated porous microcrystalline graphite composite material, since the first inorganic solid electrolyte particles (i.e., small-diameter inorganic solid electrolyte particles) are preferentially dispersed in the internal micropores of the porous microcrystalline graphite, ideally the first inorganic solid electrolyte particles are completely filled in the porous structure to form an aggregate, while the second inorganic solid electrolyte particles (i.e., large-diameter inorganic solid electrolyte particles) are all distributed between the porous microcrystalline graphite and coated on its surface to form a coating.

[0047] In some embodiments, the thickness of the coating layer covering the surface of the porous microcrystalline graphite is 1 μm to 5 μm (close to the D of large-particle-size inorganic solid electrolytes). 50 ).

[0048] In some embodiments, the mass ratio of the second inorganic solid electrolyte particle to the first inorganic solid electrolyte particle in the particle size-matched inorganic solid electrolyte is 1:1 to 1:10, preferably 1:1 to 1:5. For example, the mass ratio can be 1:1, 1:2, 2:3, 2:5, 1:4, 1:5, etc., but is not limited to these.

[0049] In some embodiments, the inorganic solid electrolyte with particle size distribution is made of inorganic solid electrolyte, specifically including any one or more combinations of LATP, LLZO, LLTO, NZSP, etc., preferably LATP, whose general chemical formula is Li. 1.3 Al 0.3 Ti 1.7 (PO4)3.

[0050] In some embodiments, the particle size D of the inorganic solid electrolyte with particle size blending 50 Its size ranges from 100 nm to 5 μm.

[0051] Wherein, the first particle size D of the first inorganic solid electrolyte particle 50 The particle size is 200nm to 2μm, preferably 200nm to 1μm. For example, it can be 200nm, 300nm, 600nm, 1μm, etc., but is not limited to these.

[0052] Furthermore, the second particle size D of the second inorganic solid electrolyte particle 50 The (i.e., large particle size) is 2μm~5μm, for example, it can be 2μm, 3μm, 4μm, 5μm, etc., but is not limited to this.

[0053] In some embodiments, the particle size D of the porous microcrystalline graphite 50 The size ranges from 1μm to 50μm, with 4μm to 20μm being preferred.

[0054] In some embodiments, the specific surface area of ​​the porous microcrystalline graphite is 1~100 m². 2 / g, preferably 1~60 m 2 / g.

[0055] In some implementations, the degree of graphitization of the porous microcrystalline graphite is ≤90%.

[0056] In some embodiments, the tap density of the porous microcrystalline graphite is 0.5 g / cm³. 3 ~1.5g / cm 3 .

[0057] In some embodiments, the mass ratio of the inorganic solid electrolyte with the particle size distribution to the porous microcrystalline graphite is 1:2 to 1:30.

[0058] In some embodiments, the particle size of the solid electrolyte-coated porous microcrystalline graphite composite material is 1 μm to 52 μm, preferably 5 μm to 30 μm.

[0059] In some embodiments, the specific surface area of ​​the solid electrolyte-coated porous microcrystalline graphite composite material is 1~20 m². 2 / g.

[0060] In some embodiments, the pore size of the solid electrolyte-coated porous microcrystalline graphite composite material is 10~50 nm.

[0061] In the porous microcrystalline graphite composite material coated with a particle size-matched solid electrolyte of the present invention, the porous microcrystalline graphite material is characterized by a small specific surface area and abundant mesopores and macropores, with the mesopores and macropores mainly distributed inside the microcrystalline graphite. After coating with the particle size-matched inorganic solid electrolyte, the specific surface area of ​​the porous microcrystalline graphite material is reduced, and the external channels contain uniformly dispersed solid electrolyte particles. After coating, it can be ensured that the spaces between the porous microcrystalline graphite material particles are filled with solid electrolytes of different particle sizes. Due to the different particle sizes of the inorganic solid electrolyte, the contact area between the electrode and the electrolyte can be increased after matching, improving the physical contact of the interface and facilitating the efficient transport of electrons and ions. At the same time, the particle size matching can optimize the lithium-ion transport channels in the solid electrolyte, reduce the porosity between the porous microcrystalline graphite materials, improve ion mobility, reduce interfacial polarization, and improve the charge and discharge efficiency of the battery. In addition, since inorganic solid electrolytes react with lithium or sodium metals to form a solid electrolyte interface layer, particle size matching can make the resulting interface layer more uniform, stabilize the electrode structure, and prevent the active material from falling off due to structural damage during charging and discharging, thus affecting the battery's cycle performance and safety.

[0062] As another aspect of the technical solution of the present invention, a method for preparing a solid electrolyte-coated porous microcrystalline graphite composite material includes:

[0063] Porous microcrystalline graphite is first mixed with first inorganic solid electrolyte particles having a first particle size, so that the first inorganic solid electrolyte particles at least fill the porous structure of the porous microcrystalline graphite to obtain a first inorganic solid electrolyte particle / porous microcrystalline graphite composite material. Then, second inorganic solid electrolyte particles having a second particle size are added, so that the second inorganic solid electrolyte particles are at least distributed between the particles of porous microcrystalline graphite and on the surface of porous microcrystalline graphite to form a coating part, thus obtaining a solid electrolyte coated porous microcrystalline graphite composite material.

[0064] In the preparation method of the present invention, porous microcrystalline graphite is first mixed with small-diameter first inorganic solid electrolyte particles, which can preferentially ensure that the small-diameter first inorganic solid electrolyte particles enter the pores of the porous microcrystalline graphite. If it is first mixed with large-diameter second inorganic solid electrolyte particles, it may block the pores of the porous microcrystalline graphite, resulting in the solid electrolyte particles agglomerating into large clumps when mixed with the small-diameter first inorganic solid electrolyte particles.

[0065] This invention coats an inorganic solid electrolyte onto the surface of microcrystalline graphite, which can significantly improve the ionic conductivity of the material and facilitate the uniform deposition and dissolution of metallic lithium or sodium.

[0066] In some implementations, the ratio of the sum of the masses of the first inorganic solid electrolyte particles and the second inorganic solid electrolyte particles to the mass of porous microcrystalline graphite is 1:2 to 1:30.

[0067] In some implementations, the mass ratio of the second inorganic solid electrolyte particle to the first inorganic solid electrolyte particle is 1:1 to 1:10.

[0068] In some embodiments, the preparation method involves mixing porous microcrystalline graphite with the first inorganic solid electrolyte particles or the second inorganic solid electrolyte particles in at least one of the following methods: direct mixing, VC mixing, wet mixing, ball milling, airflow mixing, etc., but is not limited to these methods.

[0069] In some preferred embodiments, the solvent used in the wet mixing process may include at least one of water, ethanol, acetone, formic acid, NMP, etc., more preferably ethanol or water, but is not limited thereto.

[0070] In some preferred embodiments, the wet mixing further includes a dispersant, which may include, but is not limited to, at least one of polyvinylpyrrolidone, sodium dodecylbenzenesulfonate, Tween 80, sodium hydroxyethyl cellulose, sodium citrate, etc.

[0071] In some embodiments, the method for preparing the porous microcrystalline graphite includes:

[0072] Low-graphitization microcrystalline graphite ore is crushed and pulverized to obtain microcrystalline graphite particles.

[0073] In-situ pore-forming was performed on the microcrystalline graphite particles to produce porous microcrystalline graphite.

[0074] The median particle size of the microcrystalline graphite particles is 1 μm to 20 μm.

[0075] In some preferred embodiments, the in-situ pore-forming method includes at least one of high-temperature purification and chemical purification.

[0076] In some more preferred embodiments, the method for preparing the porous microcrystalline graphite specifically includes:

[0077] Low-graphitization microcrystalline graphite ore is crushed and pulverized to a median particle size of 1μm-20μm, and then sieved through a 325-mesh sieve. The pulverizing equipment can be one or more of the following: ball mill, air jet mill, mechanical pulverizer, roller mill, sand mill, etc.

[0078] The above-mentioned pulverized material needs to be purified by high temperature or chemical purification, or a combination of both, to create pores in situ.

[0079] In some preferred embodiments, the high-temperature purification method includes: placing microcrystalline graphite particles in a graphitization device, heating them, and performing the in-situ pore formation.

[0080] Furthermore, the high-temperature purification method may specifically include: feeding the pulverized material into a graphitization furnace and heating the material at a certain heating rate.

[0081] Furthermore, the heating rate is 1℃ / min to 10℃ / min, specifically 1℃ / min, 2℃ / min, 5℃ / min, 10℃ / min, etc., the heating temperature is above 1800℃, preferably controlled at 2200℃ to 2500℃, the heating time is 1h to 20h, preferably 1h to 6h, and the high-temperature purification is carried out in a protective atmosphere, which is formed by one or two of nitrogen and argon.

[0082] Furthermore, the graphitization device (i.e., graphitization furnace) may include, but is not limited to, any one of the following: Atchison graphitization furnace, series graphitization furnace, vacuum graphitization furnace, continuous graphitization furnace, box graphitization furnace, Castner furnace, etc.

[0083] In some preferred embodiments, the chemical purification method includes mixing microcrystalline graphite particles, an acid solution, or an alkaline solution to perform the in-situ pore formation.

[0084] Furthermore, the mass ratio of the microcrystalline graphite particles to the acid solution or alkaline solution is 1:3~10.

[0085] Furthermore, the mixing time is 0.5 to 24 hours.

[0086] Furthermore, the chemical purification method may specifically include: mixing microcrystalline graphite particles (i.e., the pulverized material obtained above), acid solution or alkaline solution in a certain mass ratio (1:3~10), stirring for 0.5~24h, separating solid and liquid, washing with pure water until pH=4~8, and drying.

[0087] Furthermore, the acid contained in the acid solution may include any one or a combination of two or more of hydrochloric acid, hydrofluoric acid, nitric acid, phosphoric acid, and sulfuric acid, but is not limited thereto. The acid content in the acid solution is 5 wt% to 40 wt%.

[0088] Furthermore, the alkaline solution contains any one or a combination of two of potassium hydroxide, sodium hydroxide, etc., but is not limited to these. The concentration of the alkaline solution is 1 mol / L to 6 mol / L.

[0089] As a more preferred embodiment, please refer to Figure 1 As shown, the preparation method of a solid electrolyte-coated porous microcrystalline graphite composite material of the present invention employs both chemical purification and high-temperature purification, and specifically includes the following steps:

[0090] Low-graphitization microcrystalline graphite raw materials are crushed and sieved, retaining the undersize. The undersize is mixed with an acid / alkali solution and stirred for chemical purification to obtain pretreated microcrystalline graphite. The pretreated microcrystalline graphite is then subjected to in-situ high-temperature purification to obtain porous microcrystalline graphite. The porous microcrystalline graphite is mixed with first inorganic solid electrolyte particles having a first particle size (i.e., small particle size) to obtain first inorganic solid electrolyte-doped porous microcrystalline graphite. This first inorganic solid electrolyte-doped porous microcrystalline graphite is then mixed with second inorganic solid electrolyte particles having a second particle size (i.e., large particle size) to obtain a composite material of solid electrolyte-coated porous microcrystalline graphite with a mixture of large and small particle sizes, the structure of which is as follows. Figure 2a As shown, the yellow particles are solid electrolyte particles, while the morphology of the original porous microcrystalline graphite is as follows: Figure 2b As shown.

[0091] In summary, this invention uses low-cost microcrystalline graphite (earthy graphite) as raw material, preferably low-grade, high-impurity raw ore (graphitization degree below 90%) with even lower cost, and preferably uses a high-temperature purification method to remove impurities from the graphite. The pores formed after impurity removal are used to create pores in the microcrystalline graphite material in situ. Compared with conventional porous carbon, porous microcrystalline graphite has a higher degree of graphitization, higher reversible capacity, higher first-time efficiency, and lower cost, which has significant advantages.

[0092] As another aspect of the technical solution of the present invention, it also relates to the application of the solid electrolyte-coated porous microcrystalline graphite composite material in the preparation of negative electrodes or metal batteries.

[0093] Furthermore, another aspect of the present invention provides a composite negative electrode, comprising:

[0094] current collector;

[0095] Solid electrolyte-coated porous microcrystalline graphite composite material disposed on the surface of the current collector;

[0096] Metal composite on the surface of the solid electrolyte-coated porous microcrystalline graphite composite material.

[0097] The metal can be any one of lithium or sodium, but is not limited to this.

[0098] In some embodiments, the compaction density of the composite negative electrode is 1 g / cm³. 3 ~2.5g / cm 3 .

[0099] Compared to traditional graphite materials, the composite anode of this invention, composed of a porous microcrystalline graphite composite material coated with a solid electrolyte, exhibits lower expansion. Furthermore, compared to porous carbon composite lithium metal anodes, porous microcrystalline graphite itself can contribute higher reversible capacity, offering advantages such as high capacity and high compaction.

[0100] Another aspect of the present invention provides a method for preparing the composite negative electrode, comprising:

[0101] A slurry containing a solid electrolyte-coated porous microcrystalline graphite composite material, a binder, a conductive agent, and a solvent is applied to a current collector and dried to obtain a solid electrolyte-coated porous microcrystalline graphite composite material / current collector composite structure.

[0102] A composite negative electrode is prepared by combining the solid electrolyte with a porous microcrystalline graphite composite material / current collector composite structure and a metal.

[0103] In some embodiments, the thickness of the slurry applied to the current collector is 40 μm to 60 μm.

[0104] In some embodiments, the solid electrolyte-coated porous microcrystalline graphite composite material (i.e., inorganic solid electrolyte and porous microcrystalline graphite with mixed particle sizes) accounts for 60 wt% to 95 wt% of the solid matter in the slurry.

[0105] Furthermore, the solid content of the slurry is 8% to 20%, preferably 10%, 11%, 12% or 13%, etc.

[0106] In some embodiments, the binder in the slurry may include any one or a combination of two or more of polyvinylidene fluoride, polyacrylic acid, polyamide, LA133 (aqueous dispersion of acrylonitrile copolymer), polyvinyl alcohol, polyethyleneimine, polyimide, polyethylene, SBR (styrene-butadiene latex), carboxymethyl cellulose, etc., but is not limited thereto.

[0107] Furthermore, the binder accounts for 1 wt% to 10 wt% of the solid matter in the slurry.

[0108] In some embodiments, the conductive agent may include any one or a combination of two or more of SP (conductive carbon black), graphite, acetylene black, carbon nanotubes, graphene, Ketjen black, etc., but is not limited thereto.

[0109] Furthermore, the conductive agent accounts for 1 wt% to 10 wt% of the solid matter in the slurry.

[0110] Furthermore, the solvent may include at least one of NMP (N-methylpyrrolidone), DMF (N,N-dimethylformamide), water, etc., but is not limited thereto.

[0111] In some implementations, the solid electrolyte-coated porous microcrystalline graphite composite / current collector composite structure is composited with a metal by any of the following methods: cold rolling, hot rolling, calendering, extrusion, etc., but not limited to these.

[0112] In some preferred embodiments, the method for preparing the composite negative electrode may specifically include the following steps:

[0113] A slurry is prepared by mixing the solid electrolyte-coated porous microcrystalline graphite composite material, binder, conductive agent and solvent. The slurry is coated on the current collector and dried to obtain an inorganic solid electrolyte composite porous microcrystalline graphite material current collector.

[0114] The porous microcrystalline graphite current collector, which is a composite of inorganic solid electrolyte, is combined with lithium or sodium metal to obtain a lithium / sodium metal composite anode.

[0115] Furthermore, another aspect of the present invention provides a metal battery comprising the aforementioned solid electrolyte coated with a porous microcrystalline graphite composite material or a composite electrode.

[0116] Accordingly, the metal battery can be either a lithium battery or a sodium battery.

[0117] By means of the above technical solution, the present invention coats the surface of porous microcrystalline graphite with solid electrolytes of different particle sizes, which can significantly improve the ionic conductivity of the material and facilitate uniform metal deposition and dissolution; and the resulting composite anode has lower expansion, and the porous microcrystalline graphite itself can contribute higher reversible capacity, with the advantages of high capacity and high compaction.

[0118] To make the objectives, technical solutions, and applications of this invention clearer, the technical solutions of this invention will be further described in detail below with reference to several preferred embodiments and accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention. The implementation conditions used in the following embodiments can be further adjusted according to actual needs; implementation conditions not specified are generally conditions in conventional experiments.

[0119] Example 1

[0120] Low-graphitization microcrystalline graphite raw material was crushed and pulverized to a median particle size of 1μm-20μm, then sieved through a 325-mesh sieve, retaining the undersize material. A certain amount of the undersize material was mixed with an acid solution at a mass ratio of 1:3 and stirred for 3 hours. The acid solution was a mixture of nitric acid and hydrochloric acid with a concentration of 15wt%. After stirring, the mixture was separated into solid and liquid phases, washed with water until neutral, and dried to obtain the pretreated microcrystalline graphite. The cross-sectional SEM image of the pulverized microcrystalline graphite material from this step is shown below. Figure 3 As shown, the cross-sectional SEM image of the porous microcrystalline graphite obtained after acid treatment is as follows. Figure 4 As shown.

[0121] Pretreated microcrystalline graphite is placed in a graphite crucible and then placed in a graphitization furnace. The temperature is first raised to 1000℃ at a rate of 10℃ / min, and then raised to 2200℃ at a rate of 5℃ / min. The temperature is then maintained for 6 hours. After the reaction is completed, the temperature is cooled to room temperature to obtain porous microcrystalline graphite material.

[0122] 100g of porous microcrystalline graphite material and 10g of small-particle-size (D) 50The inorganic solid electrolyte LLTO (with a particle size of 500 nm) was dispersed in ethanol, and 0.5 g of dispersant was added and stirred for 30 min. The mixture was then filtered, washed, and dried to obtain a small-particle-size inorganic solid electrolyte porous microcrystalline graphite material. This small-particle-size inorganic solid electrolyte porous microcrystalline graphite material was then mixed with 10 g of a large-particle-size inorganic solid electrolyte (D... 50 The inorganic solid electrolyte-coated porous microcrystalline graphite composite material with a particle size distribution of 4μm was obtained by direct dry mixing of LLTO for 60 min.

[0123] The inorganic solid electrolyte-coated porous microcrystalline graphite composite material with different particle sizes, binder, and conductive agent are mixed at a mass ratio of 93:2:5, and an appropriate amount of pure water is added and stirred to obtain a slurry. The slurry is coated on a current collector and dried to obtain an inorganic solid electrolyte-coated porous microcrystalline graphite current collector.

[0124] The inorganic solid electrolyte-polymerized porous microcrystalline graphite current collector is combined with lithium metal by cold pressing to obtain a lithium metal composite anode.

[0125] Example 2

[0126] This embodiment uses the same scheme as Example 1 to prepare the lithium metal composite anode, except that the small-particle-size inorganic solid electrolyte is replaced with 600nm LATP, and the large-particle-size inorganic solid electrolyte is replaced with 3μm LATP.

[0127] The cycle performance of the full cell assembled with the metal anode obtained in this embodiment is as follows: Figure 5 As shown.

[0128] Example 3

[0129] This embodiment uses the same scheme as Example 1 to prepare the lithium metal composite anode, except that: the small-particle-size inorganic solid electrolyte is 600nm LLZO, and the large-particle-size inorganic solid electrolyte is 4μm LATP.

[0130] Example 4

[0131] Porous microcrystalline graphite was prepared using the same method as in Example 1.

[0132] 100g of porous microcrystalline graphite material and 3g of 600nm LATP were dispersed in an appropriate amount of water, and an appropriate amount of dispersant was added and stirred for 60min. The mixture was then filtered, washed, and dried to obtain a small-particle-size inorganic solid electrolyte porous microcrystalline graphite material. The above small-particle-size inorganic solid electrolyte porous microcrystalline graphite material was then directly dry-mixed with 2g of 3μm LATP for 60min to obtain a composite material of inorganic solid electrolyte coated with porous microcrystalline graphite and varying particle sizes.

[0133] The inorganic solid electrolyte-coated porous microcrystalline graphite composite material with particle size distribution, binder, and conductive agent are mixed at a mass ratio of 93:2:5, and an appropriate amount of pure water is added and stirred to obtain a slurry. The slurry is coated on a current collector and dried to obtain an inorganic solid electrolyte-coated porous microcrystalline graphite current collector.

[0134] The inorganic solid electrolyte-polymerized porous microcrystalline graphite current collector is combined with lithium metal by cold pressing to obtain a lithium metal composite anode.

[0135] The cycle performance of the full cell assembled with the metal anode obtained in this embodiment is as follows: Figure 6 As shown.

[0136] Example 5

[0137] Low-graphitization microcrystalline graphite raw material is crushed and pulverized to a median particle size of 1μm-20μm, then sieved through a 325-mesh sieve, retaining the undersize material. A certain amount of the undersize material is mixed with an alkaline solution at a mass ratio of 1:3 and stirred for 3 hours, wherein the alkaline solution is a 1mol / L NaOH solution. After stirring, the mixture is separated into solid and liquid phases, washed with water until neutral, and dried to obtain the pretreated microcrystalline graphite.

[0138] Pretreated microcrystalline graphite is placed in a graphite crucible and then placed in a graphitization furnace. The temperature is first raised to 1000℃ at a rate of 10℃ / min, and then raised to 2500℃ at a rate of 5℃ / min. The temperature is then maintained for 3 hours. After the reaction is completed, the temperature is cooled to room temperature to obtain porous microcrystalline graphite material.

[0139] The lithium metal composite anode was prepared using the same method as in Example 1, except that the small-particle-size inorganic solid electrolyte was 20g of 600nm LATP and the large-particle-size inorganic solid electrolyte was 4g of 3μm LATP.

[0140] Example 6

[0141] Low-graphitization microcrystalline graphite raw materials are crushed and pulverized to a median particle size of 1μm-20μm, then sieved through a 325-mesh sieve, retaining the sieve-through material. This material is placed in a graphite crucible and then in a graphitization furnace. The temperature is first increased to 1000℃ at a rate of 10℃ / min, then increased to 2500℃ at a rate of 5℃ / min, and held at this temperature for 6 hours. After the reaction is complete, the material is cooled to room temperature to obtain porous microcrystalline graphite material.

[0142] The porous microcrystalline graphite and solid electrolyte were combined using the same method as in Example 4 to obtain a lithium metal composite anode.

[0143] Example 7

[0144] Porous microcrystalline graphite was prepared using the same method as in Example 1, except that high-temperature graphitization was not performed.

[0145] The lithium metal composite anode was prepared using the same method as in Example 2.

[0146] Example 8

[0147] The porous microcrystalline graphite and lithium metal composite anode was prepared using the same method as in Example 5, except that the high-temperature treatment process was as follows: the temperature was raised to 1800°C at a rate of 5°C / min and held for 6 hours.

[0148] The small-particle-size inorganic solid electrolyte is 30g 1μm LATP, and the large-particle-size inorganic solid electrolyte is 7.5g 3μmL ATP.

[0149] Example 9

[0150] This embodiment uses the same scheme as Example 5 to prepare lithium metal composite anode, except that the sieved material and alkaline solution are mixed at a mass ratio of 1:10.

[0151] Example 10

[0152] This embodiment uses the same scheme as Example 5 to prepare lithium metal composite anode, except that a certain amount of sieved material and alkaline solution are mixed at a mass ratio of 1:3 and stirred for 0.5 hours.

[0153] Example 11

[0154] This embodiment uses the same scheme as Example 5 to prepare lithium metal composite anode, except that a certain amount of sieved material and alkaline solution are mixed at a mass ratio of 1:3 and stirred for 24 hours.

[0155] Example 12

[0156] This embodiment uses the same scheme as Example 6 to prepare lithium metal composite anode, except that: the temperature is first raised to 1000℃ at a heating rate of 1℃ / min, and then raised to 2500℃ at a heating rate of 5℃ / min, and held at that temperature for 6 hours.

[0157] Example 13

[0158] This embodiment uses the same scheme as Example 1 to prepare lithium metal composite anode, except that: the small-particle-size inorganic solid electrolyte is 30g of 500nm LLTO, and the large-particle-size inorganic solid electrolyte is 20g of 3μm LLTO.

[0159] Example 14

[0160] This embodiment uses the same scheme as Example 1 to prepare lithium metal composite anode, except that: the small-particle-size inorganic solid electrolyte is 2.33g of 500nm LLTO, and the large-particle-size inorganic solid electrolyte is 1g of 3μm LLTO.

[0161] Example 15

[0162] This embodiment uses the same scheme as Example 8 to prepare the lithium metal composite anode, except that: the small-particle-size inorganic solid electrolyte is 10g 600nm LATP, and the large-particle-size inorganic solid electrolyte is 1g 3μm LATP.

[0163] Comparative Example 1

[0164] The lithium metal composite anode was prepared using the same scheme as in Example 1, except that the small-particle-size inorganic solid electrolyte was 2g of 600nm LATP and the large-particle-size inorganic solid electrolyte was 8g of 3μm LATP.

[0165] Comparative Example 2

[0166] The lithium metal composite anode was prepared using the same method as in Example 1, except that the small-particle-size inorganic solid electrolyte was 10g of 600nm LATP, and the large-particle-size inorganic solid electrolyte was not used.

[0167] Comparative Example 3

[0168] The lithium metal composite anode was prepared using the same method as in Example 1, except that the large-particle-size inorganic solid electrolyte was 10g 3μm LATP, and the small-particle-size inorganic solid electrolyte was not used.

[0169] The cycle performance of the full cell assembled from the metal anode prepared in this comparative example is as follows: Figure 7 As shown.

[0170] Comparative Example 4

[0171] The lithium metal composite anode was prepared using the same scheme as in Example 1, except that the porous microcrystalline graphite material was replaced with the sieved undersize material, and acid treatment and high-temperature purification were not performed.

[0172] The present invention also tested the specific surface area and pore size distribution of the inorganic solid electrolyte composite porous microcrystalline graphite materials obtained in Examples 1-15 and Comparative Examples 1-4 using a Gaobo BK300C specific surface area analyzer and a Microt TriStar-3030 pore size analyzer, a Malvern 3000 laser particle size analyzer, a Zeiss SEM 460 thermal field emission scanning electron microscope and an Oxford Ultim Max170 energy dispersive spectrometer, and a Blue Electric M340A test cabinet for electrochemical performance testing. Battery assembly was carried out in a Braun glove box in Germany.

[0173] The coin cell was specifically fabricated using methods known in the art: NCM polycrystalline silicon was used as the positive electrode, the aforementioned lithium metal composite negative electrode was used as the negative electrode, a conventional carbonate electrolyte was used, Celgard 2400 was used as the separator, and a 2032 coin cell casing was used for the outer shell. The coin cell was then assembled. The testing conditions were as follows: at room temperature, it was first charged and discharged at a constant rate of 0.1C for two weeks, with a voltage range of 2.75-4.2V, and then cycled using a 1C / 1C charge and discharge regime.

[0174] Results Analysis: As shown in Table 1, the particle size and specific surface area of ​​the composite materials prepared using different purification methods and with different particle sizes and types of solid electrolytes showed significant differences. In particular, when the purification method for porous microcrystalline graphite was changed from a combination of chemical and high-temperature purification to a single purification method, the specific surface area of ​​the resulting composite material decreased significantly. This is because the presence of impurities, insufficiently dispersed particles, and closed micropores or mesopores in the microcrystalline graphite, obtained through a single purification method or without purification treatment, reduced the porosity and thus affected the specific surface area of ​​the material. From Examples 1-15 and the capacity retention rate of Comparative Example 4, it can be seen that the composite material with a larger specific surface area maintained a capacity retention rate of over 80% after 150 cycles, while the battery assembled from the unpurified material only maintained a capacity retention rate of 68.5%. This may be because in materials with smaller specific surface areas, due to the limited pore structure, ions require longer particle sizes to reach the active sites. This not only increases the diffusion resistance of ions but may also lead to a decrease in the interfacial stability between the material and the electrolyte, resulting in significant performance degradation during cycling. Comparative examples 5, 10, and 11 show that the amount of alkali solution and the stirring time have a certain impact on the specific surface area of ​​the material. When the amount of alkali solution is too large or the stirring time is too short, problems such as difficulty in removing impurities or insufficient reaction may occur, affecting the pore structure and electrochemistry of the material. Examples 8, 13, 14, and Comparative Example 1 show that, in addition to the microcrystalline graphite processing technology, the amount of inorganic solid electrolyte added also has a certain impact on its cycle performance. When the amount of small-particle-size inorganic solid electrolyte is within a suitable range, the assembled full battery can cycle 150 times. However, when the content of small-particle-size inorganic solid electrolyte is low, it leads to obvious gaps between large and small particles, reducing the effective lithium-ion transport channels and affecting the lithium-ion transport rate. Furthermore, an unsuitable ratio of large and small particle sizes can also affect the overall structure of the material, resulting in loose connections between active materials, low utilization, and consequently affecting the performance of the electrode and the battery.

[0175] Table 1. Performance of composite materials and full cells prepared in Examples 1-15 and Comparative Examples 1-4

[0176] ;

[0177] In addition, the inventors of this case also conducted experiments with other raw materials and conditions listed in this specification, referring to Examples 1-15, and achieved the same technical effect.

[0178] It should be understood that the above are merely specific application examples of the present invention and do not constitute any limitation on the scope of protection of the present invention. All technical solutions formed by equivalent transformations or equivalent substitutions fall within the scope of protection of the present invention.

Claims

1. A solid electrolyte-coated porous microcrystalline graphite composite material, characterized in that, include: Porous microcrystalline graphite has a porous structure, which includes mesopores and macropores, and at least some of the pores in the porous structure are connected to the outside. An inorganic solid electrolyte with a composite particle size distribution includes an aggregate portion filled within a porous structure and a coating portion distributed between particles of porous microcrystalline graphite and on the surface of the porous microcrystalline graphite. The coating portion is used to seal at least a portion of the pores within the porous structure, thereby isolating the inorganic solid electrolyte distributed within the pores from the external environment. The aggregate portion includes first inorganic solid electrolyte particles with a first particle size and second inorganic solid electrolyte particles with a second particle size, and the content of the first inorganic solid electrolyte particles in the aggregate portion is greater than the content of the second inorganic solid electrolyte particles. The coating portion includes first inorganic solid electrolyte particles with a first particle size and second inorganic solid electrolyte particles with a second particle size, and the content of the second inorganic solid electrolyte particles in the coating portion is greater than the content of the first inorganic solid electrolyte particles. The first particle size D of the first inorganic solid electrolyte particles... 50 The second particle size D of the second inorganic solid electrolyte particle is 200 nm to 2 μm. 50 The particle size is 2μm to 5μm, and the first particle size is smaller than the second particle size; The mass ratio of the second inorganic solid electrolyte particle to the first inorganic solid electrolyte particle in the particle size-blended inorganic solid electrolyte is 1:1 to 1:10, and the material of the particle size-blended inorganic solid electrolyte includes any one or more combinations of LATP, LLZO, LLTO, and NZSP.

2. The solid electrolyte-coated porous microcrystalline graphite composite material according to claim 1, characterized in that: The content of the first inorganic solid electrolyte particles in the agglomeration section is more than 50% of the total mass of the inorganic solid electrolyte.

3. The solid electrolyte-coated porous microcrystalline graphite composite material according to claim 1, characterized in that: The content of the second inorganic solid electrolyte particles in the coating part is more than 10% and not more than 50% of the total mass of the inorganic solid electrolyte.

4. The solid electrolyte-coated porous microcrystalline graphite composite material according to claim 1, characterized in that: The thickness of the covering part is 1μm~5μm.

5. The solid electrolyte-coated porous microcrystalline graphite composite material according to claim 1, characterized in that: The mass ratio of the second inorganic solid electrolyte particles to the first inorganic solid electrolyte particles in the inorganic solid electrolyte with the specified particle size distribution is 1:1 to 1:

5.

6. The solid electrolyte-coated porous microcrystalline graphite composite material according to claim 1, characterized in that: The inorganic solid electrolyte with the specified particle size is made of LATP.

7. The solid electrolyte-coated porous microcrystalline graphite composite material according to claim 1, characterized in that: The particle size D of the inorganic solid electrolyte with particle size blending 50 Its size ranges from 100 nm to 5 μm.

8. The solid electrolyte-coated porous microcrystalline graphite composite material according to claim 1, characterized in that: The first particle size D of the first inorganic solid electrolyte particle 50 Its wavelength ranges from 200 nm to 1 μm.

9. The solid electrolyte-coated porous microcrystalline graphite composite material according to claim 1, characterized in that: The particle size D of the porous microcrystalline graphite 50 The range is from 1μm to 50μm.

10. The solid electrolyte-coated porous microcrystalline graphite composite material according to claim 9, characterized in that: The particle size D of the porous microcrystalline graphite 50 The range is 4μm to 20μm.

11. The solid electrolyte-coated porous microcrystalline graphite composite material according to claim 1, characterized in that: The specific surface area of ​​the porous microcrystalline graphite is 1~100 m². 2 / g.

12. The solid electrolyte-coated porous microcrystalline graphite composite material according to claim 11, characterized in that: The specific surface area of ​​the porous microcrystalline graphite is 1~60 m². 2 / g.

13. The solid electrolyte-coated porous microcrystalline graphite composite material according to claim 1, characterized in that: The degree of graphitization of the porous microcrystalline graphite is ≤90%.

14. The solid electrolyte-coated porous microcrystalline graphite composite material according to claim 1, characterized in that: The tap density of the porous microcrystalline graphite is 0.5 g / cm³. 3 ~1.5g / cm 3 .

15. The solid electrolyte-coated porous microcrystalline graphite composite material according to claim 1, characterized in that: The mass ratio of the inorganic solid electrolyte with the specified particle size to the porous microcrystalline graphite is 1:2 to 1:

30.

16. The solid electrolyte-coated porous microcrystalline graphite composite material according to claim 1, characterized in that: The particle size of the solid electrolyte-coated porous microcrystalline graphite composite material is 1 μm to 52 μm.

17. The solid electrolyte-coated porous microcrystalline graphite composite material according to claim 16, characterized in that: The particle size of the solid electrolyte-coated porous microcrystalline graphite composite material is 5μm~30μm.

18. The solid electrolyte-coated porous microcrystalline graphite composite material according to claim 1, characterized in that: The specific surface area of ​​the solid electrolyte-coated porous microcrystalline graphite composite material is 1~20 m². 2 / g.

19. The solid electrolyte-coated porous microcrystalline graphite composite material according to claim 1, characterized in that: The pore size of the solid electrolyte-coated porous microcrystalline graphite composite material is 10~50 nm.

20. The solid electrolyte-coated porous microcrystalline graphite composite material according to claim 1, characterized in that: In the solid electrolyte-coated porous microcrystalline graphite composite material, first inorganic solid electrolyte particles fill the porous structure to form an aggregate, and second inorganic solid electrolyte particles are distributed between the particles of porous microcrystalline graphite and on the surface of porous microcrystalline graphite to form a coating.

21. The method for preparing a solid electrolyte-coated porous microcrystalline graphite composite material according to any one of claims 1-20, characterized in that, include: Porous microcrystalline graphite is first mixed with first inorganic solid electrolyte particles having a first particle size, so that the first inorganic solid electrolyte particles at least fill the porous structure of the porous microcrystalline graphite to obtain a first inorganic solid electrolyte particle / porous microcrystalline graphite composite material. Then, second inorganic solid electrolyte particles having a second particle size are added, so that the second inorganic solid electrolyte particles are at least distributed between the particles of porous microcrystalline graphite and on the surface of porous microcrystalline graphite to form a coating part, thus obtaining a solid electrolyte coated porous microcrystalline graphite composite material.

22. The preparation method according to claim 21, characterized in that: The ratio of the sum of the masses of the first inorganic solid electrolyte particles and the second inorganic solid electrolyte particles to the mass of porous microcrystalline graphite is 1:2 to 1:

30.

23. The preparation method according to claim 21, characterized in that: The mass ratio of the second inorganic solid electrolyte particle to the first inorganic solid electrolyte particle is 1:1 to 1:

10.

24. The preparation method according to claim 21, characterized in that: The method of mixing porous microcrystalline graphite with the first inorganic solid electrolyte particles or the second inorganic solid electrolyte particles includes at least one of direct mixing, VC mixing, wet mixing, ball milling, and air-flow mixing.

25. The preparation method according to claim 24, characterized in that: The solvent used in the wet mixing process includes at least one of water, ethanol, acetone, formic acid, and NMP.

26. The preparation method according to claim 25, characterized in that: The solvent used in the wet mixing process is ethanol or water.

27. The preparation method according to claim 25, characterized in that: The wet mixing process also includes the addition of a dispersant, which includes at least one of polyvinylpyrrolidone, sodium dodecylbenzenesulfonate, Tween 80, sodium hydroxyethyl cellulose, and sodium citrate.

28. The preparation method according to claim 21, characterized in that, The method for preparing the porous microcrystalline graphite includes: Low-graphitization microcrystalline graphite ore is crushed and pulverized to obtain microcrystalline graphite particles. In-situ pore-forming was performed on the microcrystalline graphite particles to produce porous microcrystalline graphite.

29. The preparation method according to claim 28, characterized in that: The median particle size of the microcrystalline graphite particles is 1 μm to 20 μm.

30. The preparation method according to claim 28, characterized in that: The in-situ pore-forming method includes at least one of high-temperature purification and chemical purification. The high-temperature purification method includes: placing microcrystalline graphite particles in a graphitization device, heating them to perform in-situ pore formation; wherein the heating rate is 1℃ / min ~ 10℃ / min, the heating temperature is above 1800℃, the heating time is 1h ~ 20h, and the high-temperature purification is carried out in a protective atmosphere, which is formed by one or two of nitrogen and argon. The graphitization apparatus includes any one of the following: Atchison graphitization furnace, in-line graphitization furnace, vacuum graphitization furnace, continuous graphitization furnace, box-type graphitization furnace, and Castner furnace. The chemical purification method includes: mixing microcrystalline graphite particles, an acid solution, or an alkaline solution to perform in-situ pore formation, wherein the mass ratio of the microcrystalline graphite particles to the acid solution or alkaline solution is 1:3~10, and the mixing time is 0.5~24h; the acid solution contains any one or a combination of two or more of hydrochloric acid, hydrofluoric acid, nitric acid, phosphoric acid, and sulfuric acid; the alkaline solution contains any one or a combination of two of potassium hydroxide and sodium hydroxide, the acid content in the acid solution is 5 wt%~40 wt%, and the concentration of the alkaline solution is 1 mol / L~6 mol / L.

31. The preparation method according to claim 30, characterized in that: In the high-temperature purification method, the heating temperature is 2200℃~2500℃, and the heating time is 1h~6h.

32. The use of the solid electrolyte-coated porous microcrystalline graphite composite material according to any one of claims 1-20 in the preparation of a negative electrode or metal battery.

33. A composite negative electrode, characterized in that, include: current collector; The solid electrolyte-coated porous microcrystalline graphite composite material according to any one of claims 1-20 is disposed on the surface of the current collector; Metal composite on the surface of the solid electrolyte-coated porous microcrystalline graphite composite material.

34. The composite negative electrode according to claim 33, characterized in that: The metal includes either lithium or sodium.

35. The composite negative electrode according to claim 33, characterized in that: The compaction density of the composite negative electrode is 1 g / cm³. 3 ~2.5g / cm 3 .

36. The method for preparing the composite negative electrode according to any one of claims 33-35, characterized in that, include: A slurry containing a solid electrolyte-coated porous microcrystalline graphite composite material, a binder, a conductive agent, and a solvent is applied to a current collector and dried to obtain a solid electrolyte-coated porous microcrystalline graphite composite material / current collector composite structure. A composite negative electrode is prepared by combining the solid electrolyte with a porous microcrystalline graphite composite material / current collector composite structure and a metal.

37. The preparation method according to claim 36, characterized in that: The thickness of the slurry applied to the current collector is 40μm~60μm.

38. The preparation method according to claim 36, characterized in that: The solid electrolyte-coated porous microcrystalline graphite composite material accounts for 60wt% to 95wt% of the solid matter in the slurry, and the solid content of the slurry is 8% to 20%.

39. The preparation method according to claim 36, characterized in that: The adhesive includes any one or a combination of two or more of the following: polyvinylidene fluoride, polyacrylic acid, polyamide, acrylonitrile copolymer aqueous dispersion, polyvinyl alcohol, polyethyleneimine, polyimide, polyethylene, styrene-butadiene latex, and carboxymethyl cellulose.

40. The preparation method according to claim 36, characterized in that: The binder accounts for 1 wt% to 10 wt% of the solid matter in the slurry.

41. The preparation method according to claim 36, characterized in that: The conductive agent includes any one or a combination of two or more of conductive carbon black, graphite, acetylene black, carbon nanotubes, graphene, and Ketjen black.

42. The preparation method according to claim 36, characterized in that: The conductive agent accounts for 1 wt% to 10 wt% of the solid matter in the slurry.

43. The preparation method according to claim 36, characterized in that: The solvent includes at least one of N-methylpyrrolidone, N,N-dimethylformamide, and water.

44. The preparation method according to claim 36, characterized in that: The method of combining the solid electrolyte-coated porous microcrystalline graphite composite material / current collector composite structure with the metal includes any one of cold rolling, hot rolling, calendering, and extrusion.

45. A metal battery, characterized in that, Includes the solid electrolyte-coated porous microcrystalline graphite composite material according to any one of claims 1-20 or the composite negative electrode according to any one of claims 33-35.

46. ​​The metal battery according to claim 45, characterized in that: The metal battery includes any one of lithium battery and sodium battery.

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