Composite material, preparation method of composite material, electrode plate and battery

Abstract

The invention discloses a composite material, a preparation method of the composite material, an electrode plate and a battery, the composite material comprises a graphite inner core, a silicon carbon layer coating the graphite inner core and a carbon layer coating the silicon carbon layer, the graphite inner core comprises artificial graphite secondary particles, the silicon carbon layer comprises porous carbon and silicon, and the carbon layer comprises porous carbon and silicon. At least part of silicon is distributed in pores of the porous carbon, and the composite material can be used for preparing an electrode of a battery and is beneficial to improving the performance of the battery.

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, an electrode sheet, 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. Silicon is considered a promising electrode material due to its advantages such as high specific capacity and abundant resources. However, silicon has disadvantages such as significant volume expansion and poor conductivity, which means that the overall performance of batteries containing silicon still needs further improvement.

[0004] Therefore, finding a silicon-based material that can be used to fabricate battery electrodes and improve their electrochemical performance is of great significance to the development of batteries. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this application provides a composite material, a method for preparing the composite material, an electrode sheet, and a battery.

[0006] In a first aspect, this application provides a composite material comprising a graphite core, a silicon-carbon layer covering the graphite core, and a carbon layer covering the silicon-carbon layer; wherein the graphite core comprises artificial graphite secondary particles, the silicon-carbon layer comprises porous carbon and silicon, and at least a portion of the silicon is distributed within the pores of the porous carbon.

[0007] Secondly, this application provides a method for preparing a composite material, comprising the following steps: S1. Provide a mixture comprising a graphite core, a carbon precursor and a template agent, and perform carbonization treatment on the mixture to obtain a material with porous carbon-coated graphite core; S2. The porous carbon-coated graphite core material is subjected to silicon deposition and carbon coating treatment in sequence to obtain a composite material. The graphite core comprises artificial graphite secondary particles.

[0008] Thirdly, this application provides an electrode sheet comprising a composite material as described in the first aspect or a composite material prepared by a method for preparing a composite material as described in the second aspect.

[0009] Fourthly, this application provides a battery including a positive electrode and a negative electrode, wherein the positive electrode or the negative electrode includes an electrode sheet as described in the third aspect.

[0010] This application provides a composite material, a method for preparing the composite material, an electrode sheet, and a battery, which have the following technical advantages: The composite material of this application includes a graphite core and a double coating layer covering the graphite core, which can improve the problems of volume expansion, poor conductivity and insufficient cycle stability of silicon-based electrode materials, while retaining the high conductivity and structural stability of graphite materials, so that the composite material has good electrochemical performance and structural stability.

[0011] In the preparation method of the composite material of this application, a porous carbon coating layer is formed by template method. The porous carbon coating layer has the advantages of uniform pore distribution, high concentration of pore size distribution and uniform pore depth. In addition, the thickness difference of the porous carbon coating layer of different particles and the thickness difference of the porous carbon coating layer of different positions of the same particle are small, thereby improving the uniformity of subsequent silicon deposition, which is conducive to uniformly dispersing the stress generated by silicon volume effect, and further improving the high temperature storage stability and cycle stability of the composite material.

[0012] In the battery of this application, 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 battery capacity, coulombic efficiency and cycle performance. Attached Figure Description

[0013] 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.

[0014] Figure 1 This is a schematic flowchart illustrating a method for preparing a composite material according to an embodiment of this application.

[0015] Figure 2 This is a microscopic morphology diagram of the composite material in Material Example 1.

[0016] Figure 3 This is a silicon element distribution diagram of the composite material in Material Example 1.

[0017] Figure 4 The image shows the microstructure of the composite material in the material comparison example.

[0018] Figure 5 This is a diagram showing the silicon distribution of the composite material in the material comparison example.

[0019] Figure 6 The graph shows the pore distribution characteristics of the porous carbon prepared in Material Example 1 and Material Comparative Example. Detailed Implementation

[0020] 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.

[0021] 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.

[0022] 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.

[0023] In the description of this application, the term "comprising" means "including but not limited to".

[0024] The terms “multiple,” “repeatedly,” or similar expressions refer to two or more times, such as two, three, four, five, six, etc.

[0025] 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.

[0026] 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.

[0027] The term "Dv00 particle size" refers to the smallest particle size in a particle group. It represents the minimum particle size of all particles in the group, meaning that there are no particles smaller than this value within the group. In this application, the Dv00 particle size of the first material refers to the smallest particle size of the first material.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] The term "Dv100 particle size" refers to the particle size within a particle group where all particle sizes are no larger than a certain value. In other words, Dv100 represents the upper limit or maximum particle size within the particle group.

[0032] The term "coverage" refers to complete or partial coverage. The coverage degree of the covering layer on the covered 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 covering layer to the total surface area of ​​A. In this application, A can be a graphite core or a silicon-carbon layer.

[0033] This application provides a composite material comprising a graphite core, a silicon-carbon layer covering the graphite core, and a carbon layer covering the silicon-carbon layer. The graphite core comprises artificial graphite secondary particles, and the silicon-carbon layer comprises porous carbon and silicon, with at least a portion of the silicon distributed within the pores of the porous carbon.

[0034] The composite material of this application includes a graphite core and a double coating layer covering the graphite core, which can improve the problems of volume expansion, poor conductivity and insufficient cycle stability of silicon-based electrode materials, while retaining the high conductivity and structural stability of graphite materials, so that the composite material has good electrochemical performance and structural stability.

[0035] Specifically, artificial graphite secondary particles are secondary agglomerates formed by binding multiple primary graphite particles with a binder (such as pitch or resin) or by high-temperature sintering. The primary graphite particles are nanoscale / submicron-scale graphite single crystals or microcrystalline aggregates formed from easily graphitized carbonaceous precursors through high-temperature graphitization. Artificial graphite secondary particles possess advantages such as high tap density, good crystallinity, high hardness, and high conductivity. Using artificial graphite secondary particles as the graphite core provides structural support, preventing or mitigating electrode pulverization and collapse. Furthermore, the graphite core provides a stable capacitance substrate and serves as the electron transport backbone, which helps reduce electrode resistance.

[0036] Based on the fact that silicon's theoretical specific capacity is far higher than that of graphite, coating a graphite core with a silicon-carbon layer significantly improves the overall specific capacity of the material. The porous carbon in the silicon-carbon layer forms a continuous conductive network, and the channel structure of the porous carbon provides rapid diffusion channels for metal ions (such as lithium ions), thereby improving electron transport efficiency. Silicon is confined within the pores of the porous carbon; the pore space buffers the volume expansion effect of silicon, reduces the aggregation and breakage of silicon particles, and decreases the probability of direct contact between silicon and the electrolyte, thus reducing the incidence of side reactions and improving the interfacial stability between the electrode and the electrolyte.

[0037] Using a carbon layer as a coating layer can reduce electrolyte permeability, further reduce side reactions between the silicon-carbon layer and the electrolyte, and enhance the mechanical strength of the composite material, thus improving the phenomenon of powdering and shedding during cycling. The carbon layer can induce the uniform growth of the solid electrolyte interface (SEI) film on its surface, avoiding the repeated rupture and reconstruction of the SEI film caused by silicon exposure, thereby improving the coulombic efficiency and cycle stability of the battery.

[0038] To further improve the electrochemical performance of the composite material, in some embodiments of this application, the D of the graphite core... V 50 particles with a diameter of 4 μm to 30 μm, D V 00 Particle size greater than 1 μm and D V 100 particles with a diameter less than 50 μm, and D V 90 particle size and D V The difference between 10 particle sizes and D VThe ratio between 50 particles is less than 1.5. Among them, the D of the graphite core... V The particle size can be 4 μm~25 μm, 4 μm~20 μm, or 8 μm~16 μm, D V The particle size can be greater than 1.5 μm, greater than 2 μm, greater than 2.5 μm, or greater than 3 μm. V 100 particle size can be less than 45 μm, less than 40 μm, or less than 35 μm, and D V 90 particle size and D V The difference between 10 particle sizes and D V The ratio between 50 particle sizes can be less than 1.4, less than 1.3, or less than 1.2.

[0039] To further improve the electrochemical performance of the composite material, in some embodiments of this application, the total pore volume of porous carbon in the silicon-carbon layer is 0.01 cm³. 3 / g ~0.5 cm 3 / g, for example, could be 0.01 cm 3 / g, 0.05 cm 3 / g, 0.1cm 3 / g, 0.3 cm 3 / g, 0.5 cm 3 / g or a value between any two of the aforementioned values; and / or, the average pore size of the porous carbon is 1.5 nm to 5.0 nm, for example, it can be 1.5 nm to 1.8 nm, 1.5 nm to 2.0 nm, 1.5 nm to 2.5 nm or 1.5 nm to 3.0 nm.

[0040] In some embodiments of this application, in porous carbon, the percentage of micropores with a pore size of 0.7 nm to 2 nm is not less than 70%, for example, it can be 70% to 80%; and / or, in porous carbon, the percentage of ultrafine pores with a pore size less than 0.7 nm is not greater than 15%, for example, not greater than 12%, not greater than 10%, not greater than 8%, or not greater than 5%; and / or, in porous carbon, the percentage of pores with a pore size greater than 2 nm is not greater than 15%, for example, not greater than 12%, not greater than 10%, not greater than 8%, or not greater than 5%. Micropores with a pore size of 0.7 nm to 2 nm are more conducive to silicon adsorption and deposition. The higher the proportion of ultrafine pores with a pore size less than 0.7 nm, the more silicon can be loaded with a lower coating amount, which is more conducive to controlling the thickness of the silicon-carbon layer and further improving the mass transfer efficiency.

[0041] In some embodiments of this application, the thickness of the silicon-carbon layer is 0.01 μm to 5 μm, for example, it can be 0.05 μm, 0.1 μm, 1 μm, 3 μm, 5 μm or any two of the aforementioned values. Under this condition, the coverage of the graphite core by the silicon-carbon layer is further improved, while the performance advantages of the graphite core are more fully utilized.

[0042] In some embodiments of this application, the mass of the silicon-carbon layer accounts for 1% to 40% of the total mass of the composite material, for example, it can be 1% to 30%, 1% to 20%, 1% to 10%, 1% to 6.4% or 1% to 4%. Under these conditions, the composite material has a high capacity and further improves the structural stability and electrochemical performance of the composite material.

[0043] In some embodiments of this application, the D of the composite material V 50. The particle size is 5 μm to 20 μm, for example, it can be 5 μm, 8 μm, 10 μm, 15 μm, 18 μm, 20 μm, or any value or range between two of the aforementioned values. The D of the composite material... V 00 Particle size greater than 1 μm, for example, greater than 1.5 μm, greater than 2 μm, greater than 2.5 μm, greater than 3 μm, or greater than 3.5 μm. The D of the composite material. V 100 Particle size less than 50 μm, for example less than 48 μm, less than 45 μm, less than 40 μm, or less than 35 μm. The D of the composite material. V 90 particle size and D V The difference between 10 particle sizes and D V The ratio between 50 particle sizes can be less than 1.4, less than 1.3, or less than 1.2.

[0044] In some embodiments of this application, the specific surface area of ​​the composite material is 1 m². 2 / g~100 m 2 / g, for example, could be 1m 2 / g~80 m 2 / g、1 m 2 / g~60 m 2 / g、1 m 2 / g~40 m 2 / g、1 m 2 / g~20 m 2 / g、1 m 2 / g~10 m 2 / g, or 1 m 2 / g~5 m 2 / g.

[0045] In some embodiments of this application, the mass of silicon element accounts for 0.5% to 10% of the total mass of the composite material. For example, it can be 0.5%, 1%, 3%, 5%, 8%, 10%, or any value or range between the aforementioned two values. Under this condition, the capacity of the composite material is further improved, while the volume expansion rate of the composite material during battery charging and discharging is controlled.

[0046] It should be noted that in the composite material, the graphite core and the silicon-carbon layer, as well as the silicon-carbon layer and the carbon layer, are independently combined through one or more of van der Waals forces, physical adsorption, and chemical bonding.

[0047] 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 As shown, the preparation method of the composite material includes the following steps: S1. Provide a mixture comprising a graphite core, a carbon precursor and a template agent, and pre-carbonize and carbonize the mixture to obtain a material with porous carbon-coated graphite core. S2. The porous carbon-coated graphite core material is subjected to silicon deposition and carbon coating treatment in sequence to obtain a composite material.

[0048] The graphite core comprises artificial graphite secondary particles. The graphite core and porous carbon are described separately above. The carbonization process is carried out at a temperature higher than the boiling point of the template agent.

[0049] In the above preparation method, a graphite core is used as the substrate, and a carbon precursor and a template agent are used as coating agents. A porous carbon-coated graphite core material is obtained through coating and carbonization processes. Then, the porous carbon-coated graphite core material undergoes silicon deposition and carbon coating treatment sequentially to obtain a composite material with high specific capacity, long cycle life, and good reaction kinetics. It should be noted that mixing the graphite core, carbon precursor, and template agent first allows the template agent to be uniformly distributed in the carbon precursor and coated on the surface of the graphite core. During the carbonization pore-forming process, the template agent coated on the graphite core surface escapes from the carbon precursor upon heating, forming multiple channels with high pore size uniformity. The high concentration and uniformity of pore size distribution are beneficial for process control and regulation of silicon deposition size consistency during silicon deposition. Furthermore, the formed channels directly connect the surface of the graphite core to the outside, allowing the deposited silicon to directly contact the graphite core, forming an ordered ion migration network, thereby improving the kinetic performance of the silicon-carbon layer and enhancing the conductivity of the composite material.

[0050] The above-mentioned composite material is prepared by using a template method to form a porous carbon coating layer. The resulting porous carbon coating layer has the advantages of uniform pore distribution, high concentration of pore size distribution, and uniform pore depth. Furthermore, the thickness difference of the porous carbon coating layer of different particles and the thickness difference of the porous carbon coating layer of different positions of the same particle are small, thereby improving the uniformity of subsequent silicon deposition. This is beneficial to the uniform dispersion of stress generated by silicon volume effect, and further improves the comprehensive performance of the composite material, especially the high-temperature storage stability and cycle stability of the composite material.

[0051] It should be noted that if an activation method is used to form a porous carbon coating, the activator will erode the binding material inside the artificial graphite secondary particles, thus damaging the graphite core structure and degrading the performance of the artificial graphite secondary particles. Furthermore, due to the etchant effect of the activator on the artificial graphite secondary particles and / or the indiscriminate reaction of the activator with the carbon layer during pore formation, the amount of activator in contact with the carbon layer during the reaction is difficult to control. This results in significant differences in the etching depth of the porous carbon coating on different particles, and even inconsistent etching depths at different locations on the same particle. Consequently, the obtained porous carbon coating suffers from uneven pore distribution, poor pore size uniformity, and uneven pore depth, leading to uneven silicon deposition and an imbalance in stress distribution caused by silicon aggregation. Therefore, the resulting composite material exhibits poor electrochemical performance. Furthermore, the activation method makes it difficult to control the pore depth. If the pore depth is too deep, it will damage the structure of the graphite core. If the pore depth is too shallow, it will be difficult to construct ion migration pathways. As a result, the process control is difficult and the defect rate is high.

[0052] Compared to the activation method for forming porous carbon coatings, the template method of this application does not require the use of an activator, significantly reducing the carbon layer ablation rate, improving the yield and coating uniformity of the porous carbon coating, and the thickness of the porous carbon coating and the pore depth can be flexibly controlled by adjusting the amount of coating agent. This allows for pore formation only in the coating without etching the graphite core, thereby avoiding or reducing the negative impact on the structure and performance of the graphite core.

[0053] For porous carbon prepared by activation method, the percentage of micropores with a pore size of 0.7 nm to 2 nm is no more than 60% of the total number of pores, the percentage of ultrafine micropores with a pore size less than 0.7 nm is 15% to 30% of the total number of pores, and the percentage of pores with a pore size greater than 2 nm is also 15% to 30% of the total number of pores. The relatively small proportion of micropores means that the average pore size of porous carbon can be greater than 3 nm, thus limiting the adsorption and deposition effects of silicon.

[0054] Compared to methods that physically mix graphite cores and silicon-carbon materials to prepare composite materials, the above-mentioned method does not require mixing graphite cores and silicon-carbon materials to form a slurry. This avoids the problems of stratification and poor slurry uniformity caused by the different sedimentation properties of graphite cores and silicon-carbon materials, thereby improving the uniformity of silicon distribution in the silicon-carbon layer and improving the phenomenon of "disconnection" between graphite cores and silicon-carbon materials during cycling, which is beneficial to improving the performance stability of composite materials. It should be noted that the type of carbon precursor in this application is not limited, as long as it can be carbonized after carbonization.

[0055] In some embodiments of this application, the carbon precursor includes one or more of bitumen, resin, biomass, petroleum coke, pitch coke, and needle coke, wherein the resin may be a phenolic resin. As an example, the carbon precursor includes bitumen with a softening point below 200 °C.

[0056] In some embodiments of this application, the template agent includes one or more of metal salts and elemental metals. Elemental metals include, for example, one or more of potassium and sodium, and metal salts include, for example, one or more of potassium nitrate, potassium carbonate, potassium acetate, potassium citrate, potassium tartrate, potassium stearate, potassium gluconate, sodium acetate, sodium citrate, sodium tartrate, sodium stearate, sodium gluconate, zinc gluconate, and calcium gluconate. It should be noted that selecting the aforementioned substances as template agents has advantages: First, by controlling the type and amount of metal salts and / or elemental metals, the pore size range of porous carbon and the proportion of micropores with a pore size of 1 nm to 2 nm can be precisely controlled; second, increasing the pore volume is simple, requiring only an increase in the amount of metal salts and / or elemental metals; third, metal salts and / or elemental metals are compatible with various inexpensive carbon precursors (e.g., phenolic resins, polyacrylonitrile, pitch, coke, etc.), and only require mechanical mixing or solution dispersion with the carbon precursor followed by pyrolysis to form a porous structure, which helps reduce preparation costs.

[0057] In some embodiments of this application, the mass ratio of graphite core to carbon precursor in the mixture is 1:(0.05~0.3), for example, it can be 1:0.05, 1:0.1, 1:0.2, 1:0.3, or any range or value between the aforementioned two values. This allows the thickness of the porous carbon coating layer to be within a more suitable range, thereby further improving the electrochemical performance of the composite material. A mass ratio of carbon precursor to template agent of (3~8):(2~7) allows the porosity and pore size of the porous carbon coating layer to be within a more suitable range, accommodating sufficient silicon and further improving the uniformity of pore size and the structural strength of the porous carbon coating layer, thereby contributing to further improvement in the structural stability and electrochemical performance of the composite material.

[0058] In some embodiments of this application, the mixture further includes a dispersant, which includes one or more of water, methanol, ethanol, isopropanol, tetrahydrofuran, and N,N-dimethylformamide. The mass ratio of the dispersant to the total mass of the mixture is 10% to 95%, for example, it can be 10% to 80%, 10% to 60%, 10% to 40%, or 10% to 20%.

[0059] In step S1, pre-carbonization is used to achieve curing and densification of the coating layer, remove lightweight components from the carbon precursor, and reduce porosity and cracks within the coating layer. When the carbon precursor is asphalt, pre-carbonization can promote cross-linking and polymerization of asphalt molecules, forming a graphitized disordered carbon structure, transforming the coating layer from a loose, bonded state into a dense, rigid coating. Pre-carbonization and carbonization can be carried out in an inert gas atmosphere.

[0060] In some embodiments of this application, the pre-carbonization temperature is 400 ℃ to 800 ℃, and the pre-carbonization time is 1 h to 20 h.

[0061] In some embodiments of this application, the carbonization temperature is 800 ℃~1200 ℃ and the carbonization time is 1 h~20 h.

[0062] In some embodiments of this application, the step of sequentially performing silicon deposition and carbon coating on the porous carbon-coated graphite core material includes: using the porous carbon-coated graphite core material as a substrate, first introducing silicon source gas for silicon deposition, and then introducing carbon source gas for carbon deposition.

[0063] In some embodiments of this application, the silicon deposition temperature is 300 ℃ to 800 ℃; and / or, the silicon source gas flow rate is 30 L / min to 100 L / min, and the silicon deposition time is 2 h to 8 h.

[0064] In some embodiments of this application, the silicon source gas includes a gaseous silicon source and an inert gas. The volume percentage of the gaseous silicon source to the total volume of the silicon source gas is, for example, 1% to 10%, and the gaseous silicon source includes one or more of silane, silane, monochlorosilane, dichlorosilane, and trichlorosilane.

[0065] In some embodiments of this application, the carbon deposition temperature is 500 ℃ to 1000 ℃; and / or, the carbon source gas flow rate is 20 L / min to 80 L / min, and the carbon deposition time is 2 h to 8 h.

[0066] In some embodiments of this application, the carbon source gas includes a gaseous carbon source and an inert gas. The volume of the gaseous carbon source accounts for 0.5% to 5% of the total volume of the carbon source gas, and the gaseous carbon source includes one or more of methane, ethane, propane, acetylene, ethylene, and propylene.

[0067] It should be noted that, in addition to the above-mentioned vapor phase coating method, one or more of the liquid phase coating method and solid phase coating method can also be used to prepare the carbon layer. Specifically, in step S2, a silicon-carbon layer coating graphite core material is obtained through the silicon deposition step. The carbon source and the silicon-carbon layer coating graphite core material are mixed and then carbonized to obtain a carbon layer. The carbon source includes one or more of solid phase carbon sources and liquid phase carbon sources. The solid phase carbon source includes one or more of solid resin, solid pitch, biomass, petroleum coke, pitch coke, and needle coke. The liquid phase carbon source includes one or more of tar, liquid resin, liquid pitch, and dispersions containing organic matter. The amount of carbon source added can be determined according to the expected thickness of the carbon layer.

[0068] 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.

[0069] This application also provides a battery, which includes a positive electrode and a negative electrode. The positive electrode or negative electrode includes electrode sheets as described above, which can improve the performance of the battery, especially the battery capacity, coulombic efficiency and cycle performance.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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. Taking a sodium-ion battery as an example, the positive electrode active material includes one or more of metal oxides, Prussian compounds, and polyanionic compounds, wherein the chemical formula of the metal oxide is Na. x MO2, where M is a transition metal element, including one or more of Mn, Ni, Cr, Fe, Ti, and V. Suitable examples include Na(Li). 1 / 3 Ti 1 / 6 Mn 1 / 2 O2, NaFeO2 and Na 2 / 3 Ni 1 / 3 Mn 1 / 2 Ti 1 / 6 One or more of O2; the chemical formula of Prussian compounds is Na. x M a (M b (CN)6), M a Including one or more of Fe, Mn, and Ni, M b Suitable examples of Prussian compounds include one or more of Fe and Mn, including Na. x Mn(Fe(CN)6); the chemical formula of the polyanionic compound is Na x A y ((XO m ) n ) z A is a metallic element with a variable valence state, including one or more of Fe and V, X is one or more of P and S, and suitable examples of polyanionic compounds include one or more of Na3V2(PO4)3, NaFePO4, Na2Fe2(SO4)3 and Na4Mn(SO4)2.

[0078] The positive electrode binder includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene-propylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, polyacrylonitrile, and polymethyl methacrylate.

[0079] Positive conductive agents include one or more of carbon black, graphite, graphene, carbon nanotubes, carbon fibers, superconducting carbon, and acetylene black.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] Taking a sodium-ion battery as an example, the metal salt includes sodium salts, which include one or more of sodium hexafluorophosphate, sodium perchlorate, sodium bis(trifluoromethanesulfonyl)imide, sodium bis(fluorosulfonyl)imide, sodium difluorooxalate borate, sodium 4,5-dicyano-2-trifluoromethylimidazolium, sodium 4,5-dicyano-2-pentafluoromethylimidazolium, and sodium fluorosulfonyl (perfluorobutylsulfonyl)imide.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] 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.

[0090] Material Example 1 This embodiment provides a composite material and its preparation method. The composite material includes a graphite core, a silicon-carbon layer covering the graphite core, and a carbon layer covering the silicon-carbon layer. The graphite core is made of secondary graphite particles, and the silicon-carbon layer is made of porous carbon and silicon, with at least a portion of the silicon distributed within the pores of the porous carbon.

[0091] The secondary graphite particles are PQ2-S products from Zhongke Xingcheng. The silicon-carbon layer accounts for 4% of the total mass of the composite material, and the carbon layer accounts for 1% of the total mass of the composite material.

[0092] The method for preparing the composite material in this embodiment includes the following steps S1.1 to S1.3.

[0093] In step S1.1, a carbon precursor, a template agent, and 30 kg of secondary graphite particles are mixed to obtain a mixture. The mixture is then carbonized to obtain a porous carbon-coated graphite core material. The template agent is potassium gluconate, the carbon precursor is conventional bitumen (softening point 200℃), the mass ratio of the carbon precursor to the template agent is 1:1, and the mass ratio of the secondary graphite particles to the carbon precursor is 1:0.1. In the porous carbon-coated graphite core material, the total pore volume of the porous carbon is 0.01 cm³. 3 / g, specific surface area of ​​10 m² 2 / g and an average pore size of 1.8 nm, the pore distribution characteristic curve of porous carbon is as follows: Figure 6 As shown. By Figure 6 It can be seen that in the porous carbon prepared in this embodiment, the number of micropores with a pore size of 0.7 nm to 2 nm accounts for a relatively high percentage of the total number of pores, and it has the advantages of high concentration of pore size distribution and high uniformity of pore size.

[0094] The steps for carbonizing the mixture include: placing the mixture in a vertical reactor under a nitrogen atmosphere, raising the temperature from room temperature to 500 ℃ and holding it at 500 ℃ for 2 h, then cooling the material and placing it in a roller kiln, raising the temperature to 1150 ℃ and holding it at 1150 ℃ for 3 h.

[0095] In step S1.2, 10 kg of the porous carbon-coated graphite core material is placed in a chemical vapor deposition furnace. After purging and removing oxygen and detecting leaks, the temperature is raised to 500 °C. Using the porous carbon-coated graphite core material as the deposition substrate, a silicon source gas composed of silane and nitrogen (carrier gas) is introduced. The volume percentage of silane in the silicon source gas is 4%, the flow rate of the silicon source gas is 60 L / min, and the gas introduction time is 1 h. The silane decomposes to form silicon, which is deposited in the pores of the porous carbon, thus obtaining a silicon-carbon layer-coated graphite core material.

[0096] In step S1.3, the chemical vapor deposition furnace is heated to 600 °C. The material with the silicon-carbon layer covering the graphite core is used as the deposition substrate. A carbon source gas composed of acetylene and nitrogen (carrier gas) is introduced. The volume percentage of acetylene in the carbon source gas is 10%, the flow rate of the carbon source gas is 40 L / min, and the gas introduction time is 1 h, so as to coat carbon on the surface of the silicon-carbon layer to form a carbon layer. Then, the composite material is obtained by sieving.

[0097] The microstructure of the composite material in this embodiment was observed using a scanning electron microscope (e.g., Figure 2 As shown in the figure, the elemental distribution of the composite material was analyzed using scanning electron microscopy combined with energy dispersive spectroscopy (EDS). Figure 3 The silicon elemental distribution diagram of the composite material is shown. Figure 3 As shown, silicon in the composite material exhibits good uniformity of distribution. Material Example 2 This embodiment provides a composite material and its preparation method. The composite material includes a graphite core, a silicon-carbon layer covering the graphite core, and a carbon layer covering the silicon-carbon layer. The graphite core is made of secondary graphite particles, and the silicon-carbon layer is made of porous carbon and silicon, with at least a portion of the silicon distributed within the pores of the porous carbon. The graphite core is the same as that in Material Example 1. The silicon-carbon layer accounts for 2.4% of the total mass of the composite material, and the carbon layer accounts for 1% of the total mass of the composite material.

[0098] 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 ratio between the carbon precursor and the template agent is 3:7.

[0099] Material Example 3 This embodiment provides a composite material and its preparation method. The composite material includes a graphite core, a silicon-carbon layer covering the graphite core, and a carbon layer covering the silicon-carbon layer. The graphite core is made of secondary graphite particles, and the silicon-carbon layer is made of porous carbon and silicon, with at least a portion of the silicon distributed within the pores of the porous carbon. The graphite core is the same as that in Material Example 1. The silicon-carbon layer accounts for 6.4% of the total mass of the composite material, and the carbon layer accounts for 1% of the total mass of the composite material.

[0100] 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 ratio between the carbon precursor and the template agent is 8:2.

[0101] Material Example 4 This embodiment provides a composite material and its preparation method. The composite material includes a graphite core, a silicon-carbon layer covering the graphite core, and a carbon layer covering the silicon-carbon layer. The graphite core is made of secondary graphite particles, and the silicon-carbon layer is made of porous carbon and silicon, with at least a portion of the silicon distributed within the pores of the porous carbon. The graphite core is the same as that in Material Example 1. The silicon-carbon layer accounts for 2% of the total mass of the composite material, and the carbon layer accounts for 1% of the total mass of the composite material.

[0102] 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 ratio between the secondary graphite particles and the carbon precursor is 1:0.05.

[0103] Material Example 5 This embodiment provides a composite material and its preparation method. The composite material includes a graphite core, a silicon-carbon layer covering the graphite core, and a carbon layer covering the silicon-carbon layer. The graphite core is made of secondary graphite particles, and the silicon-carbon layer is made of porous carbon and silicon, with at least a portion of the silicon distributed within the pores of the porous carbon. The graphite core is the same as that in Material Example 1. The silicon-carbon layer accounts for 12% of the total mass of the composite material, and the carbon layer accounts for 1% of the total mass of the composite material.

[0104] 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 ratio between the graphite secondary particles and the carbon precursor is 1:0.3.

[0105] Material Example 6 This embodiment provides a composite material and its preparation method. The composite material includes a graphite core, a silicon-carbon layer covering the graphite core, and a carbon layer covering the silicon-carbon layer. The graphite core is made of secondary graphite particles, and the silicon-carbon layer is made of porous carbon and silicon, with at least a portion of the silicon distributed within the pores of the porous carbon. The graphite core is the same as that in Material Example 1. The silicon-carbon layer accounts for 4% of the total mass of the composite material, and the carbon layer accounts for 1% of the total mass of the composite material.

[0106] 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 template agent is potassium citrate.

[0107] Material Example 7 This embodiment provides a composite material and its preparation method. The composite material includes a graphite core, a silicon-carbon layer covering the graphite core, and a carbon layer covering the silicon-carbon layer. The graphite core is made of secondary graphite particles, and the silicon-carbon layer is made of porous carbon and silicon, with at least a portion of the silicon distributed within the pores of the porous carbon. The graphite core is the same as that in Material Example 1. The silicon-carbon layer accounts for 4% of the total mass of the composite material, and the carbon layer accounts for 1% of the total mass of the composite material.

[0108] 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 template agent is potassium acetate.

[0109] Material Example 8 This embodiment provides a composite material and its preparation method. The composite material includes a graphite core, a silicon-carbon layer covering the graphite core, and a carbon layer covering the silicon-carbon layer. The graphite core is made of secondary graphite particles, and the silicon-carbon layer is made of porous carbon and silicon, with at least a portion of the silicon distributed within the pores of the porous carbon. The graphite core is the same as that in Material Example 1. The silicon-carbon layer accounts for 4% of the total mass of the composite material, and the carbon layer accounts for 1% of the total mass of the composite material.

[0110] 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 template agent is potassium carbonate.

[0111] Material Example 9 This embodiment provides a composite material and its preparation method. The composite material includes a graphite core, a silicon-carbon layer covering the graphite core, and a carbon layer covering the silicon-carbon layer. The graphite core is made of secondary graphite particles, and the silicon-carbon layer is made of porous carbon and silicon, with at least a portion of the silicon distributed within the pores of the porous carbon. The graphite core is the same as that in Material Example 1. The silicon-carbon layer accounts for 4% of the total mass of the composite material, and the carbon layer accounts for 1% of the total mass of the composite material.

[0112] 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 template agent is potassium nitrate.

[0113] Material Example 10 This embodiment provides a composite material and its preparation method. The composite material includes a graphite core, a silicon-carbon layer covering the graphite core, and a carbon layer covering the silicon-carbon layer. The graphite core is made of secondary graphite particles, and the silicon-carbon layer is made of porous carbon and silicon, with at least a portion of the silicon distributed within the pores of the porous carbon. The graphite core is the same as that in Material Example 1. The silicon-carbon layer accounts for 4% of the total mass of the composite material, and the carbon layer accounts for 1% of the total mass of the composite material.

[0114] 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 template agent is elemental potassium.

[0115] Material Example 11 This embodiment provides a composite material and its preparation method. The composite material includes a graphite core, a silicon-carbon layer covering the graphite core, and a carbon layer covering the silicon-carbon layer. The graphite core is made of secondary graphite particles, and the silicon-carbon layer is made of porous carbon and silicon, with at least a portion of the silicon distributed within the pores of the porous carbon. The graphite core is the same as that in Material Example 1. The silicon-carbon layer accounts for 4% of the total mass of the composite material, and the carbon layer accounts for 1% of the total mass of the composite material.

[0116] 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 template agent is sodium gluconate.

[0117] Material Example 12 This embodiment provides a composite material and its preparation method. The composite material includes a graphite core, a silicon-carbon layer covering the graphite core, and a carbon layer covering the silicon-carbon layer. The graphite core is made of secondary graphite particles, and the silicon-carbon layer is made of porous carbon and silicon, with at least a portion of the silicon distributed within the pores of the porous carbon. The graphite core is the same as that in Material Example 1. The silicon-carbon layer accounts for 4% of the total mass of the composite material, and the carbon layer accounts for 1% of the total mass of the composite material.

[0118] 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 template agent is zinc gluconate.

[0119] Material Example 13 This embodiment provides a composite material and its preparation method. The composite material includes a graphite core, a silicon-carbon layer covering the graphite core, and a carbon layer covering the silicon-carbon layer. The graphite core is made of secondary graphite particles, and the silicon-carbon layer is made of porous carbon and silicon, with at least a portion of the silicon distributed within the pores of the porous carbon. The graphite core is the same as that in Material Example 1. The silicon-carbon layer accounts for 4% of the total mass of the composite material, and the carbon layer accounts for 1% of the total mass of the composite material.

[0120] 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 gas supply time of the silicon source gas is replaced with 2 h.

[0121] Material Example 14 This embodiment provides a composite material and its preparation method. The composite material includes a graphite core, a silicon-carbon layer covering the graphite core, and a carbon layer covering the silicon-carbon layer. The graphite core is made of secondary graphite particles, and the silicon-carbon layer is made of porous carbon and silicon, with at least a portion of the silicon distributed within the pores of the porous carbon. The graphite core is the same as that in Material Example 1. The silicon-carbon layer accounts for 4% of the total mass of the composite material, and the carbon layer accounts for 1% of the total mass of the composite material.

[0122] 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 gas supply time of the carbon source gas is replaced with 30 min.

[0123] Material comparison This comparative example provides a composite material and its preparation method. The composite material includes a graphite core, a silicon-carbon layer covering the graphite core, and a carbon layer covering the silicon-carbon layer. The graphite core is made of secondary graphite particles, and the silicon-carbon layer is made of porous carbon and silicon, with at least a portion of the silicon distributed within the pores of the porous carbon. The graphite core is the same as that in Material Example 1. The silicon-carbon layer accounts for 4% of the total mass of the composite material, and the carbon layer accounts for 1.5% of the total mass of the composite material.

[0124] The preparation method of the composite material in this comparative example includes the following steps S2.1 to S2.3.

[0125] In step S2.1, a carbon precursor (the same as the carbon precursor in Material Example 1) and 30 kg of secondary graphite particles (the same as the secondary graphite particles in Material Example 1) are mixed to obtain a mixture. The mixture is then placed in a vertical tubular furnace under an argon-nitrogen atmosphere. The temperature is first raised from room temperature to 500 °C and held at 500 °C for 2 h, followed by activation with steam at 800 °C for 3 h to obtain a porous carbon-coated graphite core material. In the obtained porous carbon-coated graphite core material, the total pore volume of the porous carbon is 0.01 cm³. 3 / g, specific surface area is 5.6m² 2 / g and an average pore size of 3.49nm, the pore distribution characteristic curve of porous carbon is as follows: Figure 6 As shown. By Figure 6 It can be seen that in the porous carbon prepared in this comparative example, the number of micropores with a pore size of 0.7 nm to 2 nm accounts for a low percentage of the total number of pores, and there are phenomena of uneven pore distribution and poor pore size uniformity. In step S2.2, 10 kg of the porous carbon-coated graphite core material obtained in step S2.1 is placed in a chemical vapor deposition furnace. After purging and removing oxygen and detecting leaks, the temperature is raised to 500 °C. The porous carbon-coated graphite core material is used as the deposition substrate. A silicon source gas composed of silane and nitrogen (carrier gas) is introduced. The volume percentage of silane in the silicon source gas is 4%, the flow rate of the silicon source gas is 60 L / min, and the gas introduction time is 1 h. The silane decomposes to form silicon and deposits on the first intermediate to obtain a silicon-carbon layer-coated graphite core material.

[0126] In step S1.3, the chemical vapor deposition furnace is heated to 600 °C. The material with the silicon-carbon layer covering the graphite core is used as the deposition substrate. A carbon source gas composed of acetylene and nitrogen (carrier gas) is introduced. The volume percentage of acetylene in the carbon source gas is 10%, the flow rate of the carbon source gas is 40 L / min, and the gas introduction time is 1 h, so as to coat carbon on the surface of the silicon-carbon layer to form a carbon layer. Then, the composite material is obtained by sieving.

[0127] The microstructure of the composite material in this comparative example was observed using a scanning electron microscope (e.g., Figure 4 As shown in the figure, the elemental distribution of the composite material was analyzed using scanning electron microscopy combined with EDS. Figure 5 The silicon elemental distribution diagram of the composite material is shown. Figure 5 It can be seen that the composite material has the problem of uneven distribution of silicon element and obvious silicon agglomerates. Application Example 1 This embodiment provides a lithium-ion battery and its preparation method. The lithium-ion battery in this embodiment is a CR2032 button cell, in which a lithium metal sheet is used as the counter electrode. The separator is a glass fiber membrane (Whatman GF / D). The electrolyte is a 1 mol / L LiPF6 solution, and the solvent of the LiPF6 solution is prepared by mixing ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a volume ratio of 1:1:1. The working electrode includes an electrode current collector and an electrode active material layer disposed on the surface of the electrode current collector. The electrode current collector is an aluminum foil (9 μm thick). The electrode active material layer includes an electrode active substance, an electrode binder, and an electrode conductive agent. The electrode active substance is the composite material in Material Example 1. The electrode binder is styrene-butadiene rubber and carboxymethyl cellulose. The electrode conductive agent is conductive carbon black Super-P.

[0128] The preparation method of the working electrode includes the following steps: First, the composite material in Material Example 1 is mixed in a mass ratio of 94.5:2.5:1.5:1.5 of styrene-butadiene rubber:carboxymethyl cellulose:conductive carbon black. Then, ultrapure water is added and stirred evenly to form a slurry. Next, the slurry is coated on the surface of aluminum foil. Then, the aluminum foil coated with slurry is placed in a vacuum drying oven and dried at 90 °C for 24 h. After being pressed by a 5T roller, it is pressed into a circular electrode sheet with a diameter of 12 mm by a tablet press to obtain the working electrode.

[0129] The lithium-ion battery in this embodiment is assembled in a glove box, the gas atmosphere inside the glove box includes argon, and the total content of water and oxygen inside the glove box is less than 0.01 ppm.

[0130] Application Examples 2-14 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 electrode active material is the composite material in material example m, where m is a positive integer from 2 to 14.

[0131] 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 electrode active material is the composite material from Material Example 2. Similarly, the difference between the lithium-ion battery in Application Example 14 and the lithium-ion battery in Application Example 1 is that the electrode active material is the composite material from Material Example 14.

[0132] Application of comparative examples 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 electrode active material is the composite material in the material comparative example.

[0133] Performance Test 1 The composite materials in Material Examples 1 to 14 and the material comparative examples were subjected to performance tests. The performance test items included D50 particle size, resistivity and specific surface area.

[0134] The particle size was determined according to the method described in GB-T-19077-2024. The instrument used was a Malvern Panaco Zetasizer Ultra dynamic scattering particle size analyzer.

[0135] The resistivity detection method is in accordance with GB / T 45324-2025, including the following steps: Take out the clean test mold, use a brush to remove residual powder in the mold cavity, and ensure that the inner wall is smooth and free of oil stains; use a spatula to evenly fill the pretreated sample into the mold cavity, and gently tap the side wall of the mold to reduce sample delamination; place the mold into the pressure platform of the tester and start the automatic compaction program: set the target pressure (5 MPa~30 MPa), and the constant pressure time is 30 s~60 s to ensure that the sample forms a dense and uniform test layer, record the resistance value under different pressures, and obtain the resistivity at 30 MPa. The method for detecting the specific surface area, pore volume, and pore size distribution of composite materials includes the following steps: The composite material sample to be tested is degassed for 10 h in a vacuum environment (pressure -0.1 MPa) at 200 ℃; then, the nitrogen adsorption-desorption isotherm of the sample at 77 K is obtained using a MicromeritcsTristar 3030 instrument; next, the specific surface area is calculated using the Brunauer-Emmett-Teller method and adsorption curve branching data within the relative pressure P / P0 range of 0.005~1, and the pore volume and pore size distribution are analyzed from the adsorption curves. The model for analyzing the pore volume and pore size distribution is the DensityFunctionTheory model.

[0136] The test results are shown in Table 1 below: Table 1

[0137] As shown in Table 1, the composite materials in Material Examples 1 to 14 have a D50 particle size of 13.66 μm to 17.67 μm, a resistivity of 0.21 Ω / cm to 2.11 Ω / cm at 30 MPa, and a specific surface area of ​​1.53 m². 2 / g~2.59m 2 / g. Compared to the resistivity of the composite material in the material comparison example, the resistivity of the composite material in the material comparison example is higher.

[0138] Therefore, the template method of this application for preparing silicon-carbon layers in composite materials has the advantages of high pore size distribution concentration, uniform pore distribution, uniform silicon distribution, and no damage to the structure of the graphite core. The formed pores directly connect the surface of the graphite core to the outside, and the deposited silicon can directly contact the graphite core to form an ordered ion migration network, which is beneficial to improving the conductivity of the composite material.

[0139] Performance Test 2 The performance of the lithium-ion batteries in Application Examples 1 to 14 and the Comparative Application Examples was tested respectively.

[0140] The method for detecting the initial coulombic efficiency and specific capacity includes the following steps: Under a constant temperature environment of 25 ℃, a Blue Electric testing device is used for testing. The battery is charged and discharged at a current density of 0.1C (1C=300 mA / g), and the charge-discharge cycle is repeated twice within a voltage range of 0.01 V to 2.00 V. During the test, the initial charge specific capacity and initial discharge specific capacity of each lithium-ion battery are obtained, as well as the second discharge specific capacity, which is then used as the specific capacity. The initial coulombic efficiency (ICE, %) of each lithium-ion battery is calculated as: Initial Coulombic Efficiency (ICE, %) = Initial Charge Specific Capacity / Initial Discharge Specific Capacity × 100%.

[0141] The cycle performance test method includes the following steps: Under a constant temperature environment of 25 ℃, the test is conducted using a Blue Electric test device, with a current density of 0.5C for charge and discharge, and 50 charge and discharge cycles within a voltage range of 0.001 V to 2.0 V. The initial discharge specific capacity of each lithium-ion battery at 0.5C and the remaining discharge specific capacity after 50 cycles are obtained, and the capacity retention rate (%) of each lithium-ion battery is calculated as: (remaining discharge specific capacity after 50 cycles / initial discharge specific capacity at 0.5C) × 100%.

[0142] The test results are shown in Table 2 below: Table 2

[0143] As shown in Table 2, the lithium-ion batteries in Application Examples 1 to 14 exhibit superior overall performance compared to the lithium-ion batteries in the comparative examples. Specifically, the lithium-ion batteries in Application Examples 1 to 14 have an ICE (Internal Capacity Efficiency) of 92.97%–95.40%, a specific capacity of 381 mAh / g–388 mAh / g, and a capacity retention rate of 92.17%–95.43%. In contrast, the lithium-ion batteries in the comparative examples have an ICE below 90% and a capacity retention rate below 90%.

[0144] Therefore, it can be seen that the electrode material, including the composite material of the embodiments of this application or the composite material prepared by the method of preparing composite material, can improve the performance of the battery, especially the battery capacity, coulombic efficiency and cycle performance. The lithium-ion battery in the comparative example has poor overall performance because: since the activator has an etching effect on the binding material inside the artificial graphite secondary particles, the activator will destroy the structure of the graphite core, resulting in the deterioration of the performance of the artificial graphite secondary particles; in addition, the porous carbon coating layer prepared by the activation method has problems such as uneven pore distribution, poor pore size uniformity and uneven pore depth, which leads to uneven silicon deposition and easy occurrence of uneven stress distribution due to silicon aggregation.

[0145] The foregoing has provided a detailed description of a composite material, a method for preparing the composite material, an electrode sheet, 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 only 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 silicon-carbon layer covering the graphite core, and a carbon layer covering the silicon-carbon layer; wherein the graphite core includes artificial graphite secondary particles, the silicon-carbon layer includes porous carbon and silicon, and at least a portion of the silicon is distributed within the pores of the porous carbon.

2. The composite material according to claim 1, characterized in that, The silicon-carbon layer satisfies at least one of the following conditions: (1) The thickness of the silicon-carbon layer is 0.01 μm to 5 μm; (2) The total pore volume of the porous carbon is 0.01 cm³. 3 / g ~0.5 cm 3 / g; (3) The average pore size of the porous carbon is 1.5 nm to 5.0 nm; optionally, the average pore size of the porous carbon is 1.5 nm to 2.0 nm. (4) In the porous carbon, the percentage of micropores with a pore size of 0.7 nm to 2 nm is not less than 70% of the total number of pores; optionally, the percentage of micropores with a pore size of 0.7 nm to 2 nm is 70% to 80% of the total number of pores. (5) In the porous carbon, the percentage of ultrafine pores with a pore size less than 0.7 nm in the total number of pores is no more than 15%; (6) The mass of the silicon carbon layer accounts for 1% to 40% of the total mass of the composite material.

3. The composite material according to claim 1, characterized in that, The composite material satisfies at least one of the following conditions: (1) D of the composite material V 50 particles with a diameter of 5 μm to 20 μm, D V 00 Particle size greater than 1 μm and D V 100 Particle size less than 50μm, D V 90 particle size and D V The difference between 10 particle sizes and D V The ratio between 50 particle sizes is less than 1.5; (2) The specific surface area of ​​the composite material is 1 m². 2 / g ~100 m 2 / g; (3) The mass percentage of silicon in the composite material is 0.5% to 10%.

4. A method for preparing a composite material, characterized in that, Includes the following steps: S1. Provide a mixture comprising a graphite core, a carbon precursor and a template agent, and pre-carbonize and carbonize the mixture to obtain a material with porous carbon-coated graphite core. S2. The porous carbon-coated graphite core material is subjected to silicon deposition and carbon coating treatment in sequence to obtain a composite material. The graphite core comprises artificial graphite secondary particles, and the carbonization treatment temperature is higher than the boiling point of the template agent.

5. The method for preparing the composite material according to claim 4, characterized in that, At least one of the following conditions must be met: (1) The carbon precursor includes one or more of asphalt, resin, biomass, petroleum coke, pitch coke and needle coke. (2) The template agent includes one or more of metal salts and elemental metals; optionally, the elemental metals include one or more of potassium and sodium, and the metal salts include one or more of potassium nitrate, potassium carbonate, potassium acetate, potassium citrate, potassium tartrate, potassium stearate, potassium gluconate, sodium acetate, sodium citrate, sodium tartrate, sodium stearate, sodium gluconate, zinc gluconate, and calcium gluconate. (3) In the mixture, the mass ratio between the graphite core and the carbon precursor is 1:(0.05~0.3), and the mass ratio between the carbon precursor and the template agent is (3~8):(2~7).

6. The method for preparing the composite material according to claim 4, characterized in that, The pre-carbonization temperature is 400 ℃~800 ℃, and the pre-carbonization time is 1 h~20 h; The carbonization treatment temperature is 800 ℃~1200 ℃, and the carbonization treatment time is 1 h~20 h.

7. The method for preparing the composite material according to claim 4, characterized in that, The steps of sequentially performing silicon deposition and carbon coating on the porous carbon-coated graphite core material include: using the porous carbon-coated graphite core material as a substrate, first introducing silicon source gas for silicon deposition, and then introducing carbon source gas for carbon deposition.

8. The method for preparing the composite material according to claim 7, characterized in that, At least one of the following conditions must be met: (1) The temperature of silicon deposition is 300 ℃~800 ℃; (2) The flow rate of the silicon source gas is 30 L / min to 100 L / min, and the silicon deposition time is 2 h to 8 h; (3) The silicon source gas includes a gaseous silicon source and an inert gas; optionally, the volume of the gaseous silicon source accounts for 1% to 10% of the total volume of the silicon source gas, and the gaseous silicon source includes one or more of silane, silane, monochlorosilane, dichlorosilane and trichlorosilane.

9. The method for preparing the composite material according to claim 7, characterized in that, At least one of the following conditions must be met: (1) The carbon deposition temperature is 500 ℃~1000 ℃; (2) The flow rate of the carbon source gas is 20 L / min to 80 L / min, and the carbon deposition time is 2 h to 8 h; (3) The carbon source gas includes a gaseous carbon source and an inert gas; optionally, the volume of the gaseous carbon source accounts for 0.5% to 5% of the total volume of the carbon source gas, and the gaseous carbon source includes one or more of methane, ethane, propane, acetylene, ethylene and propylene.

10. An electrode sheet, characterized in that, This includes composite materials as described in any one of claims 1 to 3, or composite materials prepared by any one of claims 4 to 9.

11. A battery, characterized in that, It includes a positive electrode and a negative electrode, wherein the positive electrode or the negative electrode includes the electrode sheet as described in claim 10.

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