Composite material, preparation method of composite material and battery

Abstract

The invention discloses a composite material, a preparation method of the composite material and a battery, the composite material comprises a graphite inner core, a porous hard carbon layer coating the graphite inner core and a soft carbon layer coating the porous hard carbon layer, the composite material can be used for preparing an electrode of the battery, the performance of the battery is improved, and the service life of the battery is prolonged. And particularly, the quick charging performance of the battery at low temperature is improved.

Description

Technical Field

[0001] This application relates to the field of battery materials technology, specifically to a composite material, a method for preparing the composite material, and a battery. Background Technology

[0002] With the rapid development of portable electronic devices, electric vehicles, and energy systems, batteries, as the core device for energy conversion, are constantly being updated and iterated. Batteries are now widely used in consumer electronics, advanced robotics, grid-scale energy storage, electric vehicles, and other technological fields.

[0003] Electrode materials are one of the key factors determining the overall performance of a battery. Graphite is a common electrode material, possessing excellent electrochemical properties, specifically high theoretical specific capacity and actual reversible capacity, good cycle stability, and high electronic conductivity. Graphite is a cost-effective material; natural graphite is abundant and its mining and processing costs are low. Although the preparation process of artificial graphite is more complex, its cost is controllable after large-scale production, and its overall price is far lower than that of electrode materials such as silicon-carbon. However, low temperatures affect the charging performance of graphite-based batteries. At low temperatures, the viscosity of the electrolyte increases, the diffusion rate of metal ions slows down, and the electrochemical reaction kinetics of the graphite anode decrease, leading to a significant reduction in charging speed. It may even cause metal ions to precipitate on the anode surface, forming metal dendrites, potentially causing short circuits and other safety hazards. Therefore, finding a graphite-based material that can be used to prepare battery electrodes and improve the fast-charging performance of batteries at low temperatures is of great significance to the application and development of batteries. Summary of the Invention

[0004] In view of the shortcomings of the prior art, this application provides a composite material, a method for preparing the composite material, and a battery.

[0005] In a first aspect, this application provides a composite material comprising a graphite core, a porous hard carbon layer covering the graphite core, and a soft carbon layer covering the porous hard carbon layer.

[0006] Secondly, this application provides a method for preparing a composite material, comprising the following steps: S1. Mix graphite particles and porous hard carbon coating agent, and perform a one-time coating treatment on the resulting mixture to obtain one-time coated graphite. S2. The primary coated graphite is mixed with a modified coating agent, and the resulting mixture is subjected to a secondary coating treatment. The modified coating agent is a soft carbon precursor modified with a fluoropolymer, thereby obtaining secondary coated graphite. S3. The secondary coated graphite is subjected to carbonization treatment to obtain the composite material, which includes a graphite core, a porous hard carbon layer covering the graphite core, and a soft carbon layer covering the porous hard carbon layer.

[0007] Thirdly, this application provides a battery comprising a positive electrode and a negative electrode, wherein the material of the positive electrode or the material of the negative electrode comprises a composite material as described in the first aspect, or a composite material prepared by the method for preparing a composite material as described in the second aspect.

[0008] This application provides a composite material, a method for preparing the composite material, and a battery, which have the following technical advantages: The composite material of this application has both a porous hard carbon layer and a soft carbon layer. The porous hard carbon layer has abundant channels to provide reactive sites, and at least some of the channels can penetrate the soft carbon layer, thereby providing channels for electrolyte wetting. This is beneficial to improving the interfacial diffusion and liquid phase diffusion capabilities of metal ions, giving the composite material good fast-charging performance. During the formation of the soft carbon layer, fluorine-containing substances can repair and bridge the defective structures (such as macropores and micropores) in the porous hard carbon layer, thereby reducing the probability of side reactions between the electrode and the electrolyte. This gives the composite material both better fast-charging performance and stability.

[0009] The electrode material includes the composite material of this application or the composite material prepared by the method of this application, which can improve the performance of the battery, especially the fast charging performance of the battery at low temperatures. Attached Figure Description

[0010] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below.

[0011] Figure 1 This is a schematic flowchart illustrating a method for preparing a composite material according to an embodiment of this application.

[0012] Figure 2 This is a microscopic morphology diagram of the composite material in Material Example 1. Detailed Implementation The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0013] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those familiar to those skilled in the art, and the materials or reagents used in the embodiments of this application are commercially available. Furthermore, any methods and materials similar to or equivalent to those described herein may be applied to this application. The preferred embodiments and materials described herein are for illustrative purposes only and do not limit the scope of this application.

[0014] It should be noted that the order of description of the following embodiments is not intended to limit the preferred order of embodiments. Each embodiment of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a rigid limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. In addition, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.

[0015] In the description of this application, the term "comprising" means "including but not limited to".

[0016] The terms “multiple,” “multiple times,” or similar expressions refer to two or more times, such as two, three, four, five, six, etc.

[0017] The term "and / or" encompasses any one of two or more of the related listed items, as well as any and all combinations of the related listed items. These arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. For example, "A and / or B" includes three parallel options: A, B, and A+B.

[0018] The term "inert gas" refers to a class of gases that have stable chemical properties and do not readily react with other substances at room temperature and pressure. These include one or more of nitrogen, helium, neon, argon, krypton, and xenon.

[0019] The term "Dv10 particle size" refers to the particle size value that corresponds to 10% of the cumulative particle volume in the cumulative particle size distribution curve of a particle group.

[0020] The term "Dv50 particle size" refers to the particle size value that corresponds to 50% of the cumulative particle size distribution curve of a particle group. It is also called the "volume median diameter". In other words, when the particles are sorted from smallest to largest, the particle size is Dv50 when the total volume of all particles not larger than a certain particle size accounts for 50% of the total volume of all particles.

[0021] The term "Dv90 particle size" refers to the particle size value that corresponds to 90% of the cumulative particle volume in the cumulative particle size distribution curve of a particle group.

[0022] The term "coating" refers to complete or partial coating. The coating layer's coverage of the coated object (A) can be 80% to 100%, for example, it can be 80%, 85%, 90%, 95%, 100%, or any range or value between the aforementioned two values. The coverage degree refers to the percentage of the surface area of ​​A covered by the coating layer to the total surface area of ​​A. In this application, A can be a single coating of graphite or silicon carbide.

[0023] This application provides a composite material comprising a graphite core, a porous hard carbon layer covering the graphite core, and a soft carbon layer covering the porous hard carbon layer.

[0024] The composite material of this application embodiment combines a porous hard carbon layer and a soft carbon layer. The porous hard carbon layer has abundant channels to provide reactive sites, and at least some of these channels can penetrate the soft carbon layer, thereby providing channels for electrolyte wetting. This is beneficial for improving the interfacial diffusion and liquid-phase diffusion capabilities of metal ions, giving the composite material excellent fast-charging performance. Furthermore, during the formation of the soft carbon layer, fluorine-containing substances can repair and bridge the defective structures (such as macropores and micropores) in the porous hard carbon layer to regulate the pore structure, thereby reducing the probability of side reactions between the electrode and the electrolyte. This results in the composite material exhibiting both superior fast-charging performance and stability.

[0025] In some embodiments of this application, the mass of the porous hard carbon layer accounts for 0.5% to 2.0% of the total mass of the composite material. For example, it can be 0.5%, 1%, 1.2%, 1.5%, 1.8%, 2%, or any two of the aforementioned values. This can further improve the electrochemical performance of the composite material.

[0026] In some embodiments of this application, the mass of the porous hard carbon layer accounts for 1.0% to 2.0% of the total mass of the composite material, which can further improve the electrochemical performance of the composite material.

[0027] In some embodiments of this application, the mass of the soft carbon layer accounts for 0.5% to 1.5% of the total mass of the composite material. For example, it can be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.5%, or any two of the aforementioned values. This can further improve the electrochemical performance of the composite material.

[0028] In some embodiments of this application, the mass of the soft carbon layer accounts for 1% to 1.5% of the total mass of the composite material, which can further improve the electrochemical performance of the composite material.

[0029] In some embodiments of this application, the fluorine content in the composite material is 0.4% to 1.0%, for example, it can be 0.4%, 0.6%, 0.8%, 1.0% or any two of the aforementioned values, which is beneficial to further improve the size concentration of the pores in the composite material.

[0030] In some embodiments of this application, the D of the composite material V The particle size is 10 μm to 12 μm, for example, it can be 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, or any value between two of the aforementioned values. The specific surface area of ​​the composite material is 1.5 g / cm³. 3 ~4.0 g / cm 3 For example, it could be 1.5 g / cm³. 3 2.0 g / cm 3 3.0 g / cm 3 4.0 g / cm 3 Or the value between any two of the aforementioned values.

[0031] In some embodiments of this application, the D of the composite material V 10. The particle size is 4.0 μm to 7.0 μm, for example, it can be 4.0 μm, 4.5 μm, 5.0 μm, 5.5 μm, 6.0 μm, 6.5 μm, 7.0 μm, or any value between two of the aforementioned values. The D of the composite material... V The particle size of 90 is 18.0 μm to 22.0 μm, for example, it can be 18.0 μm, 19.0 μm, 20.0 μm, 21.0 μm, 22.0 μm or any two of the aforementioned values.

[0032] This application also provides a method for preparing a composite material, which can be used to prepare the composite material as described above, such as... Figure 1 The method for preparing the composite material includes the following steps: S1. Mix graphite particles and porous hard carbon coating agent, and perform a one-time coating treatment on the resulting mixture to obtain one-time coated graphite. S2. The primary coated graphite is mixed with a modified coating agent, and the resulting mixture is subjected to a secondary coating treatment. The modified coating agent is a soft carbon precursor modified with a fluoropolymer, thereby obtaining secondary coated graphite. S3. The secondary coated graphite is subjected to carbonization treatment to obtain the composite material, which includes a graphite core, a porous hard carbon layer covering the graphite core, and a soft carbon layer covering the porous hard carbon layer.

[0033] In the above-mentioned method for preparing composite materials, a porous hard carbon coating agent is first coated on the surface of graphite particles, and then a soft carbon precursor modified with a fluoropolymer is coated. The fluoropolymer can release fluorine gas, which can close and repair the micropores of the inner layer, and the soft carbon precursor can repair the macropores of the inner layer. Then, carbonization treatment is performed to obtain a porous hard carbon layer with abundant pores and a soft carbon layer with relatively few defects on the outer layer. The resulting composite material has good electrochemical performance.

[0034] It should be noted that, compared to first preparing a porous hard carbon layer and then preparing a soft carbon layer, the above-mentioned method for preparing composite materials can avoid the phenomenon of soft carbon precursor blocking the pores of the porous hard carbon layer. Thus, at least some of the pores can penetrate the soft carbon layer, thereby providing channels for electrolyte wetting and improving the interfacial diffusion and liquid phase diffusion capabilities of metal ions. As a result, the prepared composite material has good fast-charging performance.

[0035] In step S1, the graphite particles can be primary or secondary granular graphitized products, and the raw materials for preparing the graphite core can include one or more of the following: pitch, resin, biomass, petroleum coke, pitch coke, and needle coke. The D of the graphite core... V The particle size can be 4 μm to 30 μm, for example, 4 μm to 25 μm, 4 μm to 20 μm, 4 μm to 16 μm, 4 μm to 12 μm or 4 μm to 8 μm.

[0036] In some embodiments of this application, step S1, the step of performing a coating treatment on the obtained mixture, includes: in an inert gas atmosphere, holding the mixture containing the graphite particles and the porous hard carbon coating agent at 400 ℃~500 ℃ for 2 h~4 h, and then holding it at 500 ℃~650 ℃ for 1 h~3 h. In this way, the porous hard carbon coating agent is first softened and granulated at a lower temperature to reduce the graphite orientation index (OI), and then further heat-treated at a higher temperature to remove volatiles, so that the porous hard carbon coating agent coats the graphite core, achieving the effect of solidification and granulation.

[0037] In some embodiments of this application, the porous hard carbon coating agent includes a metal-based organic material and excipients. The metal-based organic material includes one or more of organometallic salts and metal-organic framework materials, and the excipients include one or more of pitch, resin, biomass, and tar. The metal-based organic material can serve as a hard carbon precursor and pore-forming agent. During subsequent carbonization, the metal in the metal-based organic material is removed to form pores, and the remaining organic components form hard carbon. By adding excipients, the uniformity of the porous hard carbon coating agent's coating on the graphite core is improved, and the occurrence rate of agglomerates is reduced.

[0038] In some embodiments of this application, the metal element of the organometallic salt is selected from one or more of Group IA, Group IIA, Group IB, Group IIB, and Group VIII metal elements. For example, the metal element of the organometallic salt is selected from one or more of zinc, lithium, sodium, potassium, magnesium, calcium, copper, iron, and cobalt. The anion of the organometallic salt is selected from C1-C20 organic carboxylate ions, such as gluconate, citrate, acetate, stearate, tartrate, lactate, arachidate, palmitate, oleate, linoleate, and glycolate ions.

[0039] In some embodiments of this application, the organometallic salt includes one or more of zinc gluconate, zinc citrate, potassium acetate, potassium citrate, potassium tartrate, potassium stearate, potassium gluconate, sodium acetate, sodium citrate, sodium tartrate, sodium stearate, sodium gluconate, and calcium gluconate.

[0040] In some embodiments of this application, the metal-organic framework material includes zeolite imidazole ester framework materials, such as one or more of ZIF-8, ZIF-4, ZIF-21, ZIF-25, ZIF-67, ZIF-71, ZIF-90, ZIF-93, ZIF-97 and ZIF-108.

[0041] In some embodiments of this application, the mass ratio between the metal-based organic material and the auxiliary material is (3~6):(1~2). This allows for a more suitable number of pores to be formed and further improves the coating uniformity, thereby further improving the initial coulombic efficiency, cycle performance and kinetic performance of the battery containing the composite material.

[0042] In some embodiments of this application, the preparation method of the modified coating agent in step S2 includes the following steps: mixing a fluoropolymer and a soft carbon precursor to obtain the modified coating agent. The soft carbon precursor includes one or more of asphalt, resin, biomass, and tar; the fluoropolymer includes one or more of fluorinated homopolymers and fluorinated copolymers; and the repeating units of the fluorinated homopolymer and at least one repeating unit of the fluorinated copolymer each independently have the structure shown in the following general formula (I): (Ⅰ); In general formula (I), R1, R2, R3, and R4, each time appearing, are independently selected from hydrogen, a halogen group, an unsubstituted or substituted C1-C30 alkyl group, an unsubstituted or substituted C1-C30 alkoxy group, or a combination of the foregoing groups. R0, each time appearing, is independently selected from -F, -Cl, -Br, -I, a C1-C10 alkyl group, a C1-C10 alkoxy group, -CF3, or a combination of the foregoing groups. At least one of R1, R2, R3, and R4 contains an F atom. The alkyl group of C1 to C30 can be, for example, an alkyl group of C1 to C20, an alkyl group of C1 to C10, or an alkyl group of C1 to C5, and the alkyl group can be a straight-chain alkyl group or a branched alkyl group; the alkoxy group of C1 to C30 can be, for example, an alkoxy group of C1 to C20, an alkoxy group of C1 to C10, or an alkoxy group of C1 to C5, and the alkyl group can be a straight-chain alkoxy group or a branched alkoxy group.

[0043] In some embodiments of this application, the repeating units of the fluorinated homopolymer and at least one repeating unit of the fluorinated copolymer are each independently selected from... -CF2-CF2- , -CH2-CF2- , -CH2-CFH- , -CF2-CF(CF3)- or -CF2-CFCl- And / or fluorinated copolymers also include -CH2-CH2- Repeating units.

[0044] In some embodiments of this application, the fluoropolymer is independently selected from one or more of polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, ethylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer, perfluoroethylene propylene, and chlorotrifluoroethylene. All fluoropolymers are commercially available, and the degree of polymerization of the fluoropolymer is not specifically limited, as long as it can release fluorine gas in the heat treatment step S3. For example, the degree of polymerization of the fluoropolymer can be 100 to 10000.

[0045] In some embodiments of this application, in the step of mixing the fluoropolymer and the soft carbon precursor, the mass ratio between the soft carbon precursor and the fluoropolymer is 1:(0.05~0.1), for example, it can be 1:0.05, 1:0.06, 1:0.07, 1:0.08, 1:0.09, 1:0.1 or any two of the aforementioned values. This makes the number of pores in the porous hard carbon layer more suitable and the size concentration of the pores higher, thereby further improving the fast-charging performance of the prepared composite material.

[0046] In some embodiments of this application, in step S2, the mass ratio between the primary coated graphite and the modified coating agent is 1:(0.1~0.25), for example, it can be 1:0.1, 1:0.15, 1:0.2, 1:0.25 or any two of the aforementioned values. This makes the thickness of the subsequently formed soft carbon layer more suitable, that is, the percentage of the mass of the soft carbon layer to the total mass of the obtained composite material is more suitable (e.g., 0.5%~1.0%), which is more conducive to forming the required pores, and thus further conducive to improving the initial coulombic efficiency of the battery containing the composite material.

[0047] In some embodiments of this application, step S2, the step of mixing the primary coated graphite with the modified coating agent, includes: kneading the primary coated graphite and the modified coating agent, and then drying. Specifically, the primary coated graphite and the modified coating agent are first kneaded at room temperature (e.g., 20°C~30°C), and then kneaded at 100°C~150°C. The kneading time at room temperature can be 0.5 h~1 h and the frequency can be 10 Hz~20 Hz. The kneading time at 100°C~150°C is 5 h~8 h and the frequency is 5 Hz~15 Hz. The purpose of kneading at room temperature is to ensure that the primary coated graphite and the modified coating agent are thoroughly and evenly mixed, and the kneading at 100°C~150°C is to dry the mixture for subsequent heat treatment. In some embodiments of this application, step S2, the step of performing a secondary coating treatment on the obtained mixture, includes: treating the mixture containing primary coated graphite and modified coating agent at 400 ℃ to 850 ℃ for 2 h to 6 h in an inert gas atmosphere.

[0048] In some embodiments of this application, the carbonization temperature in step S3 is 800 ℃ to 1200 ℃.

[0049] This application also provides an electrode sheet, which includes the composite material as described above, or the composite material prepared by the method described above.

[0050] This application also provides a battery comprising a positive electrode and a negative electrode. The material of the positive electrode or the negative electrode comprises a composite material as described above, or a composite material prepared by the method described above. The composite material has both a porous hard carbon layer and a soft carbon layer. The porous hard carbon layer has abundant channels to provide reactive sites, and at least some of the channels can penetrate the soft carbon layer, thereby providing channels for electrolyte wetting. This is beneficial for improving the interfacial diffusion and liquid-phase diffusion capabilities of metal ions (e.g., lithium ions), thereby improving the fast-charging performance of the battery, especially the fast-charging performance at low temperatures. Furthermore, since the outer layer of the composite material is a soft carbon layer, it can compensate for the structural defects caused by the porous hard carbon layer, thereby reducing the probability of side reactions between the electrode and the electrolyte. This is beneficial for improving the initial coulombic efficiency of the battery, as well as improving the cycle performance and high-temperature storage performance of the battery. Based on its geometric shape, the battery in this application embodiment can be a square battery, a cylindrical battery, a button battery, or an irregularly shaped battery. Based on its packaging form, the battery in this application embodiment can be a pouch battery or a hard-case battery. Based on its assembly form, the battery in this application embodiment can be a battery cell, a battery module, or a battery pack. Based on its operating nature and storage method, the battery in this application embodiment can be a primary battery, a secondary battery, or an activated battery. Based on the type of current-carrying ions in the battery, the battery in this application embodiment can be a lithium-ion battery or a sodium-ion battery.

[0051] In some embodiments of this application, the negative electrode includes a negative electrode current collector and a negative electrode active material layer disposed on the surface of the negative electrode current collector, wherein the material of the negative electrode active material layer includes the composite material as described above, or the composite material prepared by the method described above.

[0052] The negative electrode current collector includes a first surface and a second surface disposed opposite to each other along its own thickness direction, and at least one of the first surface and the second surface is provided with a negative electrode active material layer. The material of the negative electrode current collector includes copper foil, composite copper foil, or copper mesh.

[0053] In some embodiments of this application, the negative electrode active material layer further includes a negative electrode binder and a negative electrode conductive agent. The negative electrode binder and negative electrode conductive agent can be materials commonly found in the art. Specifically, the negative electrode binder includes one or more of lithium polyacrylate, styrene-butadiene rubber, carboxymethyl cellulose, polyacrylic acid, sodium alginate, polyvinyl alcohol, polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene-propylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, polyacrylonitrile, and polymethyl methacrylate. The negative electrode conductive agent includes one or more of carbon black, graphite, graphene, carbon nanotubes, carbon fibers, superconducting carbon, and acetylene black.

[0054] The preparation method of the negative electrode may include the following steps: mixing and dispersing the negative electrode active material, negative electrode conductive agent, and negative electrode binder in a first dispersion medium to form a negative electrode slurry; then, coating the negative electrode slurry onto a negative electrode current collector, followed by a drying process and a rolling process to obtain the negative electrode. It should be noted that the negative electrode slurry can also be cast on a separate carrier to form a film layer, then the film layer is separated from the carrier, and then the film layer is stacked on the first surface and / or the second surface of the negative electrode current collector. The first dispersion medium includes one or more of N-methylpyrrolidone, acetone, and water.

[0055] In the battery of this application embodiment, the positive electrode includes a positive electrode current collector and a positive electrode active material layer disposed on the surface of the positive electrode current collector. It is understood that the positive electrode current collector includes a third surface and a fourth surface disposed opposite to each other along its own thickness direction, and at least one of the third surface and the fourth surface is provided with a positive electrode active material layer.

[0056] The positive electrode current collector is made of a metal foil or a composite current collector. The metal foil includes aluminum foil, platinum foil, or palladium foil. The composite current collector includes a substrate and a metal layer. The substrate includes a third surface and a fourth surface disposed opposite each other along its thickness direction. At least one of the third surface and the fourth surface has a metal layer. The substrate is made of one or more of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, and polyethylene. The metal layer is made of one or more of aluminum, platinum, palladium, nickel, titanium, and silver.

[0057] The positive electrode active material layer comprises a positive electrode active material, a positive electrode binder, and a positive electrode conductive agent. The positive electrode active material, positive electrode binder, and positive electrode conductive agent can be conventional materials in the art. Taking a lithium-ion battery as an example, the positive electrode active material includes one or more of lithium cobalt oxide, lithium manganese oxide, lithium permanganate, lithium iron phosphate, lithium nickel oxide, lithium manganese phosphate, lithium iron manganese phosphate, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide.

[0058] The positive electrode binder includes one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-hexafluoropropylene copolymer, PVDF-tetrafluoroethylene-propylene copolymer, PVDF-hexafluoropropylene-tetrafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, polyacrylonitrile, and polymethyl methacrylate (PMMA). The positive electrode conductive agent includes one or more of carbon black, graphite, graphene, carbon nanotubes, carbon fibers, superconducting carbon, and acetylene black.

[0059] The preparation method of the positive electrode may include the following steps: mixing and dispersing the positive electrode active material, the positive electrode conductive agent, and the positive electrode binder in a second dispersion medium to form a positive electrode slurry; then, coating the positive electrode slurry onto a positive electrode current collector, followed by a drying process and a rolling process to obtain the positive electrode. It should be noted that the positive electrode slurry can also be cast on a separate carrier to form a film layer, then the film layer is separated from the carrier, and then the film layer is stacked on the third and / or fourth surfaces of the positive electrode current collector. The first dispersion medium includes one or more of N-methylpyrrolidone, acetone, and water.

[0060] It should be noted that the battery in this embodiment may also include other conventional structures. For example, the battery in this embodiment may also include a separator disposed between the positive and negative electrodes. The separator may be a single-layer thin film or a composite membrane with a multi-layer structure. When the separator is a composite membrane, the material of each layer in the composite membrane may be the same or different. The material of the separator includes one or more of glass fiber, non-woven fabric, polyester, Teflon, polyethylene, polypropylene, and polytetrafluoroethylene.

[0061] The electrolyte can be a conventional electrolyte in the art, comprising metal salts and organic solvents. The organic solvents include one or more of the following: ethylene carbonate, propylene carbonate, butyl carbonate, fluoroethylene carbonate, 1,4-butyrolactone, ethylene carbonate, propylene carbonate, propylene sulfite, propyl acetate, propyl propionate, methyl butyrate, butyl acetate, ethyl propionate, ethyl butyrate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate.

[0062] Taking lithium-ion batteries as an example, the metal salts include lithium salts, such as LiPF6, LiClO4, LiBF4, LiSbF6, LiAsF6, LiCF3SO3, Li(CF3SO2)2N, LiC4F9SO3, LiAlO2, LiAlCl4, LiODFB, LiTFSI, LiFSI, LiCl, LiI, and LiN(C x F 2x+1 SO2)(C y F 2y+1 One or more of SO2, wherein x and y are integers from 1 to 20, and the mass of lithium salt accounts for 10% to 15% of the total mass of the electrolyte.

[0063] It should be noted that the positive electrode, negative electrode, and separator can be formed into a battery cell through a winding or stacking process. The electrolyte wets the positive and negative electrodes, and packaging one or more battery cells yields a single battery cell. The battery cell can be packaged using a rigid shell or a pouch. The rigid shell includes a metal shell or a plastic shell with high hardness, while the pouch material includes one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0064] Battery cells can be assembled to form a battery module. Each battery module includes multiple battery cells arranged sequentially along a first direction and secured with fasteners. The first direction can be the length, width, or height of the battery module. It is understood that the battery module also has a housing for accommodating the multiple battery cells.

[0065] Battery modules can be assembled to form a battery pack, with each battery pack containing multiple battery modules. The battery pack also includes a housing for accommodating the multiple battery modules, which can be arranged sequentially along the length or width of the housing. Understandably, the battery pack also includes some conventional components, including a battery management system, buffers, and cooling devices.

[0066] This application also provides an application of the aforementioned battery in electronic devices, electric vehicles, and energy storage systems. The electronic devices, electric vehicles, and energy storage systems respectively employ the aforementioned battery as a power source and / or energy storage component. The electronic devices include mobile phones, computers, digital cameras, camcorders, video game consoles, smart wearable devices, drones, Bluetooth speakers, wireless headphones, security equipment, medical equipment, and aerospace equipment. The electric vehicles include electric cars, electric motorcycles, electric bicycles, electric scooters, and electric balance scooters. The energy storage systems include home energy storage systems, solar energy storage systems, wind energy storage systems, and grid-connected energy storage power stations.

[0067] The technical solutions and effects of this application will be described in detail below through specific embodiments and experimental examples. The following embodiments are only some embodiments of this application and are not intended to limit this application in any specific way.

[0068] Material Example 1 This embodiment provides a composite material and its preparation method. The composite material includes a graphite core, a porous hard carbon layer coated with primary graphite, and a soft carbon layer coated with the porous hard carbon layer. The mass percentage of the porous hard carbon layer in the total mass of the composite material is 2%, and the mass percentage of the soft carbon layer in the total mass of the composite material is 1%. The graphite core is a primary particulate graphitized product with a Dv50 particle size of 7.5 μm.

[0069] The method for preparing the composite material in this embodiment includes the following steps S1.1 to S1.3.

[0070] In step S1.1, the graphite core (primary particulate graphitized product) and porous hard carbon coating agent are mixed, and the resulting mixture is subjected to a primary coating treatment to obtain primary coated graphite with a Dv50 particle size of 9.5 μm. The porous hard carbon coating agent comprises zinc gluconate and pitch, with zinc gluconate accounting for 6% of the total mass of the mixture, pitch accounting for 1% of the total mass of the mixture, and the graphite core weighing 25 kg. The primary coating treatment of the resulting mixture includes: holding the mixture at 450 °C for 3 h under a nitrogen atmosphere, and then holding it at 580 °C for 2 h.

[0071] In step S1.2, the primary coated graphite and the modified coating agent obtained in step S1.1 are mixed together, wherein the mass ratio between the primary coated graphite and the modified coating agent is 1:0.15. The resulting mixture is then subjected to a secondary coating treatment to obtain secondary coated graphite.

[0072] The modified coating agent is a liquid asphalt modified with polytetrafluoroethylene (PTFE). The preparation method of the modified coating agent includes the following steps: 250 g of PTFE emulsion (commercially purchased, solid content 60%) and 3500 g of emulsified asphalt are stirred at high speed for 30 min to obtain the modified coating agent. The kneading and mixing step includes: kneading the primary coated graphite and the modified coating agent at room temperature and a frequency of 15 Hz for 0.5 h, and then kneading at 130 ℃ and a frequency of 10 Hz for 5.5 h. The step of performing a secondary coating treatment on the resulting mixture includes: placing the kneaded and mixed mixture in a rotary kneader, heating it from room temperature to 800 ℃ under a nitrogen protective atmosphere and a rotation frequency of 10 Hz, and holding it at 800 ℃ for 3 h.

[0073] In step S1.3, the secondary coated graphite obtained in step S1.2 is placed in a roller kiln and carbonized under a nitrogen protective atmosphere at a carbonization temperature of 1150 °C for 16 h to obtain the composite material.

[0074] The microstructure of the composite material in this embodiment was observed using a scanning electron microscope (e.g., Figure 2 (As shown). Material Example 2 This embodiment provides a composite material and its preparation method. Compared with the composite material in Material Example 1, the composite material in this embodiment differs in that the mass of the porous hard carbon layer accounts for 1% of the total mass of the composite material, and the mass of the soft carbon layer accounts for 1% of the total mass of the composite material.

[0075] Compared with the preparation method of the composite material in Material Example 1, the difference in the preparation method of the composite material in this example is that in step S1.1, the mass of zinc gluconate accounts for 3% of the total mass of the mixture.

[0076] Material Example 3 This embodiment provides a composite material and its preparation method. Compared with the composite material in Material Example 1, the composite material in this embodiment differs in that the mass of the porous hard carbon layer accounts for 2% of the total mass of the composite material, and the mass of the soft carbon layer accounts for 1% of the total mass of the composite material.

[0077] Compared with the preparation method of the composite material in Material Example 1, the difference in the preparation method of the composite material in this example is that: in step S1.1, the mass of asphalt accounts for 2% of the total mass of the mixture.

[0078] Material Example 4 This embodiment provides a composite material and its preparation method. Compared with the composite material in Material Example 1, the composite material in this embodiment differs in that the mass of the porous hard carbon layer accounts for 2% of the total mass of the composite material, and the mass of the soft carbon layer accounts for 1% of the total mass of the composite material.

[0079] Compared with the preparation method of the composite material in Material Example 1, the difference in the preparation method of the composite material in this example is that "zinc gluconate" in step S1.1 is replaced with "zinc citrate".

[0080] Material Example 5 This embodiment provides a composite material and its preparation method. Compared with the composite material in Material Example 1, the composite material in this embodiment differs in that the mass of the porous hard carbon layer accounts for 2% of the total mass of the composite material, and the mass of the soft carbon layer accounts for 1% of the total mass of the composite material.

[0081] Compared with the preparation method of the composite material in Material Example 1, the difference in the preparation method of the composite material in this example is that "zinc gluconate" in step S1.1 is replaced with "ZIF-8".

[0082] Material Example 6 This embodiment provides a composite material and its preparation method. Compared with the composite material in Material Example 1, the composite material in this embodiment differs in that the mass of the porous hard carbon layer accounts for 2% of the total mass of the composite material, and the mass of the soft carbon layer accounts for 1.5% of the total mass of the composite material.

[0083] Compared with the preparation method of the composite material in Material Example 1, the difference in the preparation method of the composite material in this example is that in step S1.2, the mass ratio between the primary coated graphite and the modified coating agent is 1:0.25.

[0084] Material Example 7 This embodiment provides a composite material and its preparation method. Compared with the composite material in Material Example 1, the composite material in this embodiment differs in that the mass of the porous hard carbon layer accounts for 2% of the total mass of the composite material, and the mass of the soft carbon layer accounts for 1% of the total mass of the composite material.

[0085] Compared to the preparation method of the composite material in Material Example 1, the difference in the preparation method of the composite material in this example is that the preparation method of the modified coating agent in step S1.2 is different. Compared to the preparation method of the modified coating agent in Material Example 1, the difference in the preparation method of the modified coating agent in this example is that the mass ratio between liquid asphalt and polytetrafluoroethylene is replaced with "1:0.15".

[0086] Material Example 8 This embodiment provides a composite material and its preparation method. Compared with the composite material in Material Example 1, the composite material in this embodiment differs in that the mass of the porous hard carbon layer accounts for 2% of the total mass of the composite material, and the mass of the soft carbon layer accounts for 1% of the total mass of the composite material.

[0087] Compared to the preparation method of the composite material in Material Example 1, the difference in the preparation method of the composite material in this example is that: in step S1.2, the modifying coating agent is liquid asphalt modified with polyvinylidene fluoride. Compared to the preparation method of the modified coating agent in Material Example 1, the difference in the preparation method of the modified coating agent in this example is that: polytetrafluoroethylene is replaced with "polyvinylidene fluoride".

[0088] Material Example 9 This embodiment provides a composite material and its preparation method. Compared with the composite material in Material Example 8, the composite material in this embodiment differs in that the mass of the porous hard carbon layer accounts for 2% of the total mass of the composite material, and the mass of the soft carbon layer accounts for 1% of the total mass of the composite material.

[0089] Compared to the preparation method of the composite material in Material Example 8, the difference in the preparation method of the composite material in this example is that in step S1.2, the modifying coating agent is tar modified with polyvinylidene fluoride. Compared to the preparation method of the modified coating agent in Material Example 8, the difference in the preparation method of the modified coating agent in this example is that liquid asphalt is replaced with "tar", and polytetrafluoroethylene is replaced with "polyvinylidene fluoride".

[0090] Material Example 10 This embodiment provides a composite material and its preparation method. Compared with the composite material in Material Example 1, the composite material in this embodiment differs in that the mass of the porous hard carbon layer accounts for 2% of the total mass of the composite material, and the mass of the soft carbon layer accounts for 1% of the total mass of the composite material.

[0091] Compared with the preparation method of the composite material in Material Example 1, the difference in the preparation method of the composite material in this example is that in step S1.2, "holding at 800 ℃ for 3 h" is replaced with "holding at 800 ℃ for 3 h".

[0092] Material Comparison Example 1 This comparative example provides a composite material and its preparation method. The composite material includes a graphite core and a porous hard carbon layer coated with a single layer of graphite. The graphite core is the same as the graphite core in Material Example 1, and the mass of the porous hard carbon layer accounts for 3% of the total mass of the composite material.

[0093] The preparation method of the composite material in this comparative example includes the following steps: placing the mixture from step S1.1 of material example 1 into a roller kiln and carbonizing it under a nitrogen protective atmosphere at a carbonization temperature of 1150 ℃ and a carbonization time of 16 h.

[0094] Material Comparison Example 2 This comparative example provides a composite material and its preparation method. Compared with the preparation method of the composite material in Material Example 1, the difference in the preparation method of the composite material in this example is that the "modified coating agent" in step S1.2 is replaced with "liquid asphalt (the same as the liquid asphalt in step S1.2)".

[0095] Material Comparison Example 3 This comparative example provides a graphite material, which is the primary particulate graphitized product in Material Example 1.

[0096] Application Example 1 This embodiment provides a lithium-ion battery, which is a pouch battery. The separator is a PE / PPPE composite membrane, and the electrolyte is a 1 mol / L LiPF6 solution. The solvent of the LiPF6 solution is prepared by mixing ethylene carbonate and dimethyl carbonate in a 1:1 volume ratio. The positive electrode includes a positive current collector and a positive active material layer disposed on the surface of the positive current collector. The positive current collector is aluminum foil, and the positive active material layer includes a positive active material, a positive binder, and a positive conductive agent. The positive active material includes lithium iron phosphate, the positive binder includes polyvinylidene fluoride, and the positive conductive agent includes conductive carbon black Super-P. The mass ratio of the positive active material, the positive binder, and the positive conductive agent is 96:2:2.

[0097] The negative electrode includes a negative electrode current collector and a negative electrode active material layer disposed on the surface of the negative electrode current collector. The negative electrode current collector is copper foil, and the material of the negative electrode active material layer includes a negative electrode active substance, a negative electrode binder, and a negative electrode conductive agent. The negative electrode active substance includes the composite material in Material Example 1, the negative electrode binder includes styrene-butadiene rubber and carboxymethyl cellulose, and the negative electrode conductive agent includes conductive carbon black Super-P. The mass ratio of the negative electrode active substance, carboxymethyl cellulose, styrene-butadiene rubber, and negative electrode conductive agent is 95.5:1.5:2:1.

[0098] Application Examples 2-10 The lithium-ion battery in application example m is basically the same as the lithium-ion battery in application example 1, except that in application example m, the negative electrode active material includes the composite material in material example m, where m is a positive integer from 2 to 10.

[0099] Taking Application Example 2 as an example, the difference between the lithium-ion battery in Application Example 1 and the lithium-ion battery in Application Example 2 is that the negative electrode active material includes the composite material from Material Example 2. Similarly, the difference between the lithium-ion battery in Application Example 10 and the lithium-ion battery in Application Example 1 is that the negative electrode active material includes the composite material from Material Example 10.

[0100] Application Comparative Example 1 This comparative example provides a lithium-ion battery. Compared with the lithium-ion battery in Application Example 1, the difference of the lithium-ion battery in this comparative example is that the negative electrode active material includes the composite material in Material Comparative Example 1.

[0101] Application Comparative Example 2 This comparative example provides a lithium-ion battery. Compared with the lithium-ion battery in Application Example 1, the difference of the lithium-ion battery in this comparative example is that the negative electrode active material includes the composite material in Material Comparative Example 2.

[0102] Application Comparative Example 3 This comparative example provides a lithium-ion battery. Compared with the lithium-ion battery in Application Example 1, the difference in this comparative example is that the negative electrode active material includes the graphite material in Material Comparative Example 3.

[0103] Performance Test 1 The composite materials in Material Examples 1 to 10, Material Comparative Example 1 and Material Comparative Example 2 were subjected to performance tests. The performance test items included the particle size, specific surface area and fluorine content of the composite materials.

[0104] The particle size was measured according to the method described in GB-T-19077-2024. The instrument used was a Malvern Panaco Zetasizer Ultra dynamic scattering particle size analyzer.

[0105] The method for detecting specific surface area, pore volume, and pore size distribution includes the following steps: degassing the composite material sample to be tested in a vacuum environment (pressure -0.1 MPa) at 200℃ for 10 h; then, obtaining the nitrogen adsorption-desorption isotherm of the sample at 77 K using a Micromeritcs Tristar 3030 instrument; next, calculating the specific surface area using the Brunauer-Emmett-Teller method and adsorption curve branch data in the relative pressure range of 0.005~1, and analyzing the pore volume and pore size distribution from the adsorption curves. The model for analyzing the pore volume and pore size distribution is the DensityFunction Theory model.

[0106] The fluorine content of the composite material was detected using X-ray photoelectron spectroscopy (XPS).

[0107] The test results are shown in Table 1 below: Table 1

[0108] As shown in Table 1, the Dv50 particle size of the composite materials in Material Examples 1 to 10 is 10.78 μm to 11.45 μm, and the specific surface area is 1.72 m². 2 / g~3.66 m 2 The composite material in Material Comparative Example 1 and Material Comparative Example 2 has a Dv50 particle size of 11.13 μm to 11.45 μm and a specific surface area greater than 4 m². The fluorine content is 0.40% to 0.81%. 2 / g and a fluorine content of 0.

[0109] This illustrates that in the preparation process of the composite material in the embodiments of this application, a soft carbon layer is prepared by using a soft carbon precursor modified with a fluoropolymer. The soft carbon precursor modified with a fluoropolymer releases fluorine-containing gas during heat treatment, which bridges and repairs the defective structures (such as macropores and micropores) in the porous hard carbon layer, thereby making the obtained composite material fluorine-containing and reducing the specific surface area of ​​the composite material.

[0110] Performance Test 2 The performance of the lithium-ion batteries in Application Examples 1 to 10 and Application Comparative Examples 1 to 3 was tested respectively.

[0111] The method for testing the fast-charging performance of lithium-ion batteries at low temperatures includes the following steps: At room temperature, the lithium-ion battery under test is fully charged at a rate of 0.5C, then discharged at 0.5C to 50% SOC, and then the lithium-ion battery under test is transferred to -20℃ and placed for 2 hours; then, at -20℃, the open-circuit voltage (U1, V) at 50% SOC is recorded; subsequently, a pulse discharge current of 0.3C is applied to the battery for 10 seconds, and the voltage value (U2, V) at the moment of discharge end is obtained; the DC internal resistance (DCR, Ω) of the lithium-ion battery under test at low temperature is calculated, DCR = (U1 - U2) / I, where I represents the pulse current value.

[0112] The method for testing the high-temperature storage performance of lithium-ion batteries includes the following steps: First, under a constant temperature environment of 25 ℃, the lithium-ion battery under test is tested using a Blue Electric testing device. Charging and discharging are performed at a current density of 0.5C, with the first charge, first discharge, and second charge occurring within a voltage range of 3.0 V to 4.2 V. The capacity of the second charge is obtained as the initial capacity. After storing the lithium-ion battery at 60 ℃ for 14 days, it is tested again using the Blue Electric testing device, following the same testing method. The capacity of the second charge is obtained as the actual capacity after 14 days of storage. Finally, the lithium-ion battery is stored at 60 ℃ for another 14 days, and then tested again using the Blue Electric testing device, following the same testing method. The capacity of the second charge is obtained as the actual capacity after 28 days of storage. The capacity retention rate of lithium-ion batteries after 14 days of storage and after 28 days of storage are calculated. The capacity retention rate of lithium-ion batteries after 14 days of storage (%) = actual capacity after 14 days of storage / initial capacity × 100%, and the capacity retention rate of lithium-ion batteries after 28 days of storage (%) = actual capacity after 28 days of storage / initial capacity × 100%.

[0113] The test results are shown in Table 2 below: Table 2

[0114] As shown in Table 2, compared to the lithium-ion batteries in Comparative Examples 1 to 3, the lithium-ion batteries in Application Examples 1 to 10 exhibit both good low-temperature fast-charging performance and high-temperature storage stability. Specifically, compared to the lithium-ion batteries in Comparative Examples 1 to 3, the lithium-ion batteries in Application Examples 1 to 10 have lower DCR, and their capacity retention remains at a high level after 14 and 28 days of storage at 60 °C.

[0115] This indicates that the negative electrode active material of a lithium-ion battery includes a composite material, which comprises a graphite core, a porous hard carbon layer covering the graphite core, and a soft carbon layer covering the porous hard carbon layer. The porous hard carbon layer has abundant channels to provide reactive sites, and at least some of the channels can penetrate the soft carbon layer, thereby providing channels for electrolyte wetting. This is beneficial to improving the interfacial diffusion and liquid phase diffusion capabilities of lithium ions, thus enhancing the fast-charging performance of the lithium-ion battery. Furthermore, the outer layer of the composite material is a soft carbon layer, which can compensate for the structural defects caused by the porous hard carbon layer, thereby reducing the probability of side reactions between the electrode and the electrolyte. This allows the lithium-ion battery to have both good fast-charging performance and high-temperature storage stability.

[0116] The negative electrode active material of the lithium-ion battery in Comparative Example 1 includes a graphite core and a porous hard carbon layer covering the graphite core. Although it can improve the fast charging performance to a certain extent, the overall performance of the lithium-ion battery is poor due to the large number of defects in the porous hard carbon layer.

[0117] The negative electrode active material of the lithium-ion battery in Comparative Example 2 includes a graphite core, a porous hard carbon layer covering the graphite core, and a soft carbon layer covering the porous hard carbon layer. The soft carbon layer is prepared using conventional pitch. During the formation of the soft carbon layer, the soft carbon precursor can repair the large pores of the inner layer, but the micropores of the inner layer cannot be repaired. The porous hard carbon layer still has many defect structures, resulting in poor overall performance of the lithium-ion battery.

[0118] The negative electrode active material of the lithium-ion battery in Comparative Example 3 includes primary particulate graphitized material. Since the primary particulate graphitized material has fewer defects, the lithium-ion battery in Comparative Example 3 has good high-temperature storage performance. However, the fast-charging performance of the uncoated primary particulate graphitized material is poor. Therefore, the overall performance of the lithium-ion battery is worse than that of the lithium-ion batteries in Application Examples 1 to 10.

[0119] The foregoing has provided a detailed description of a composite material, a method for preparing the composite material, and a battery provided in the embodiments of this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the embodiments above are merely for the purpose of helping to understand the technical solutions and core ideas of this application. Those skilled in the art should understand that modifications can still be made to the technical solutions described in each of the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A composite material, characterized in that, The composite material includes a graphite core, a porous hard carbon layer covering the graphite core, and a soft carbon layer covering the porous hard carbon layer.

2. The composite material according to claim 1, characterized in that, At least one of the following conditions must be met: (1) The mass of the porous hard carbon layer accounts for 0.5% to 2.0% of the total mass of the composite material; (2) The fluorine content in the composite material is 0.4%~1.0%; (3) The specific surface area of ​​the composite material is 1.5 g / cm³. 3 ~4.0 g / cm 3 ; (4) The mass of the soft carbon layer accounts for 0.5% to 1.5% of the total mass of the composite material; (5) D of the composite material V 50. The particle size is 10 μm to 12 μm; optionally, the D of the composite material... V The particle size of the composite material is 4.0 μm to 7.0 μm; the D of the composite material is... V The particle size of 90 ranges from 18.0 μm to 22.0 μm.

3. A method for preparing a composite material, characterized in that, Includes the following steps: S1. Mix graphite particles and porous hard carbon coating agent, and perform a one-time coating treatment on the resulting mixture to obtain one-time coated graphite. S2. The primary coated graphite is mixed with a modified coating agent, and the resulting mixture is subjected to a secondary coating treatment. The modified coating agent is a soft carbon precursor modified with a fluoropolymer, thereby obtaining secondary coated graphite. S3. The secondary coated graphite is subjected to carbonization treatment to obtain the composite material, which includes a graphite core, a porous hard carbon layer covering the graphite core, and a soft carbon layer covering the porous hard carbon layer.

4. The method for preparing the composite material according to claim 3, characterized in that, The step of performing a primary coating treatment on the obtained mixture includes: in an inert gas atmosphere, holding the mixture containing the graphite particles and the porous hard carbon coating agent at 400 ℃~500 ℃ for 2 h~4 h, and then holding it at 500 ℃~650 ℃ for 1 h~3 h. The step of performing a secondary coating treatment on the obtained mixture includes: treating the mixture containing the primary coated graphite and the modified coating agent at 400 ℃~850 ℃ for 2 h~6 h in an inert gas atmosphere; In step S3, the carbonization temperature is 800 ℃~1200 ℃.

5. The method for preparing the composite material according to claim 3, characterized in that, In step S2, the step of mixing the primary coated graphite with the modified coating agent includes: kneading the primary coated graphite and the modified coating agent together and drying.

6. The method for preparing the composite material according to claim 3, characterized in that, In step S1, the mass percentage of the porous hard carbon coating agent to the total mass of the resulting mixture is 4% to 8%. In step S2, the mass ratio between the primary coated graphite and the modified coating agent is 1:(0.1~0.25).

7. The method for preparing the composite material according to claim 3, characterized in that, The porous hard carbon coating agent comprises a metal-based organic material and an additive. The metal-based organic material includes one or more of organometallic salts and metal-organic framework materials, and the additive includes one or more of asphalt, resin, biomass, and tar, and satisfies at least one of the following conditions: (1) The mass ratio between the metal-based organic material and the auxiliary material is (3~6):(1~2); (2) The metal element of the organometallic salt is selected from one or more of Group IA, Group IIA, Group IB, Group IIB and Group VIII metal elements, and the anion of the organometallic salt is selected from C1 to C20 organic carboxylate ions; optionally, the metal element of the organometallic salt is selected from one or more of zinc, lithium, sodium, potassium, magnesium, calcium, copper, iron and cobalt, and the anion of the organometallic salt is selected from one or more of gluconate ion, citrate ion, acetate ion, stearate ion, tartrate ion, lactate ion, arachidate ion, palmitate ion, oleate ion, linoleate ion and glycolate ion. (3) The metal-organic framework material includes zeolite imidazole ester framework material; optionally, the zeolite imidazole ester framework material includes one or more of ZIF-8, ZIF-4, ZIF-21, ZIF-25, ZIF-67, ZIF-71, ZIF-90, ZIF-93, ZIF-97 and ZIF-108.

8. The method for preparing the composite material according to claim 3, characterized in that, The preparation method of the modified coating agent includes the steps of: mixing a fluoropolymer and a soft carbon precursor to obtain the modified coating agent; The soft carbon precursor includes one or more of asphalt, resin, biomass, and tar; the fluoropolymer includes one or more of fluorinated homopolymers and fluorinated copolymers, wherein the repeating unit of the fluorinated homopolymer and at least one repeating unit of the fluorinated copolymer each independently has the structure shown in the following general formula (I): (Ⅰ)； In general formula (Ⅰ), R1, R2, R3 and R4 are each independently selected from hydrogen, halogen groups, unsubstituted or substituted C1 to C30 alkyl groups, unsubstituted or substituted C1 to C30 alkoxy groups, or combinations of the foregoing groups, each time R0 appears independently selected from -F, -Cl, -Br, -I, C1 to C10 alkyl groups, C1 to C10 alkoxy groups, -CF3, or combinations of the foregoing groups; Furthermore, at least one of R1, R2, R3, and R4 contains an F atom.

9. The method for preparing the composite material according to claim 8, characterized in that, The modified coating agent satisfies at least one of the following conditions: (1) The repeating units of the fluorinated homopolymer and at least one repeating unit of the fluorinated copolymer are each independently selected from... -CF2-CF2- , -CH2-CF2- , -CH2-CFH- , -CF2-CF(CF3)- or -CF2-CFCl- And / or the fluorinated copolymer also includes -CH2-CH2- Repeating units; (2) The fluoropolymers are each independently selected from one or more of polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, ethylene-tetrafluoroethylene copolymer, ethylene-trifluorochloroethylene copolymer, perfluoroethylene propylene, and polytrifluorochloroethylene; (3) The mass ratio between the soft carbon precursor and the fluoropolymer is 1:(0.05~0.1).

10. A battery, characterized in that, It includes a positive electrode and a negative electrode, wherein the material of the positive electrode or the material of the negative electrode includes the composite material as described in claim 1 or 2, or the composite material prepared by the method of preparing the composite material as described in any one of claims 3 to 9.

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