Composite negative electrode material and preparation method thereof, and lithium ion battery

Abstract

The present application relates to the field of negative electrode materials, providing a composite negative electrode material, a preparation method thereof, and a lithium-ion battery. The composite negative electrode material has a core-shell structure, wherein the core comprises a silicon-based active material, and the shell comprises a connecting layer, a buffer layer, and a protective layer. The connecting layer is coated on the surface of the silicon-based active material, and the buffer layer is filled between the connecting layer and the protective layer. The connecting layer and the buffer layer are connected by a covalent bond. The composite negative electrode material and preparation method of the present application are low-cost, can be produced on a large scale, can reduce the volume expansion of the negative electrode material, and can improve the structural stability and cycle stability of the negative electrode material.

Description

Technical Field

[0001] The present application relates to the technical field of negative electrode materials, and in particular to a composite negative electrode material and a preparation method thereof, and a lithium-ion battery. Background Art

[0002] Lithium-ion batteries are widely used in electric vehicles and consumer electronics due to their high energy density, high output power, long cycle life, and low environmental pollution. To increase battery energy density, research and development of high-capacity anode materials are becoming increasingly mature. However, these anode materials expand significantly when alloying with lithium. During charge and discharge, they pulverize and fall from the current collector, resulting in a loss of electrical contact between the anode material and the current collector. This leads to poor electrochemical performance, capacity fade, and decreased cycle stability, hindering their commercial application. Summary of the Invention

[0003] In view of this, the present application proposes a composite negative electrode material and a preparation method thereof, and a lithium-ion battery, which can reduce volume expansion and improve cycle stability.

[0004] In the first aspect, the present application provides a composite negative electrode material, which has a core-shell structure, wherein the core includes a silicon-based active substance, and the shell includes a connecting layer, a buffer layer and a protective layer. The connecting layer is coated on the surface of the silicon-based active substance, and the buffer layer is filled between the connecting layer and the protective layer. The connecting layer and the buffer layer are connected by a covalent bond.

[0005] In the above scheme, by constructing a connecting layer, a buffer layer and a protective layer on the surface of the silicon-based active material, their synergistic effect can be utilized to effectively alleviate the volume expansion of the silicon-based active material, enhance the structural stability of the silicon-carbon composite negative electrode material, and improve the cycle life; the connecting layer on the surface of the silicon-based active material can greatly improve the conductivity of the material, reduce the occurrence of side reactions, and enhance the lithium ion and electron transmission channels, thereby improving the conductivity of the negative electrode material and improving the material rate performance; the buffer layer filled between the connecting layer and the protective layer is connected to the connecting layer by a covalent bond, which prevents the buffer layer from falling off due to the volume expansion of the silicon-based active material during the charge and discharge process, which is beneficial for the composite negative electrode material to maintain excellent mechanical properties, enhance the structural stability of the composite negative electrode material, and thus enhance the cycle stability.

[0006] In some embodiments, the covalent bond comprises at least one of a carbon-carbon bond, a carbon-oxygen bond, a carbon-nitrogen bond, a carbon-sulfur bond, a carbon-chlorine bond, a fluorine-carbon bond, a nitrogen-oxygen bond, an oxygen-sulfur bond, an oxygen-chlorine bond, and a nitrogen-sulfur bond.

[0007] The present application also provides a composite negative electrode material, which has a core-shell structure, wherein the core includes a silicon-based active substance, and the shell includes a connecting layer, a buffer layer and a protective layer. The connecting layer is coated on the surface of the silicon-based active substance, and the buffer layer is filled between the connecting layer and the protective layer. The average bonding force F between the connecting layer and the buffer layer is greater than 8μN.

[0008] In the above scheme, by constructing a connecting layer, a buffer layer and a protective layer on the surface of the silicon-based active material, their coordinated effect can be utilized to effectively alleviate the volume expansion of the silicon-based active material, enhance the structural stability of the silicon-carbon composite negative electrode material, and improve the cycle life; the connecting layer on the surface of the silicon-based active material can greatly improve the conductivity of the material, reduce the occurrence of side reactions, and enhance the lithium ion and electron transmission channels, thereby improving the conductivity of the negative electrode material and improving the material rate performance; the buffer layer filled between the connecting layer and the protective layer has an average bonding force with the connecting layer greater than 8μN. During the cycle, the buffer layer is not easy to fall off from the connecting layer, which is beneficial for the composite negative electrode material to maintain excellent mechanical properties, enhance the structural stability of the composite negative electrode material, and thus enhance the cycle stability.

[0009] In some embodiments, the connecting layer includes at least one of a polymer, an amorphous carbon material, and a graphitized carbon material.

[0010] In some embodiments, the buffer layer includes a hollow carbon material.

[0011] In some embodiments, the hollow carbon material includes at least one of hollow carbon spheres, hollow carbon rods, and hollow carbon tubes.

[0012] In some embodiments, the hollow carbon material includes hollow carbon spheres, and the diameter of the hollow carbon spheres is 20 nm to 2000 nm.

[0013] In some embodiments, the hollow carbon material comprises hollow carbon spheres, and the wall thickness of the hollow carbon spheres is 5 nm to 500 nm.

[0014] In some embodiments, the hollow carbon material comprises a hollow carbon rod, and the diameter of the hollow carbon rod is 10 nm to 1000 nm.

[0015] In some embodiments, the hollow carbon material comprises a hollow carbon rod, and the length of the hollow carbon rod is 100 nm to 3000 nm.

[0016] In some embodiments, the hollow carbon material comprises a hollow carbon rod, and the wall thickness of the hollow carbon rod is 5 nm to 500 nm.

[0017] In some embodiments, the hollow carbon material comprises a hollow carbon tube, and the length of the hollow carbon tube is 30 nm-20 um.

[0018] In some embodiments, the hollow carbon material comprises a hollow carbon tube, and the wall thickness of the hollow carbon tube is 5 nm to 100 nm.

[0019] In some embodiments, the hollow carbon material includes a hollow carbon tube, and the diameter of the hollow carbon tube is 20 nm to 400 nm.

[0020] In some embodiments, the median particle size D of the silicon-based active material is 50 0.2μm~20μm.

[0021] In some embodiments, the thickness of the buffer layer is about the same as the median particle size D of the silicon-based active material. 50 The ratio is 1:(0.5-10).

[0022] In some embodiments, the protective layer is coated on the surface of the buffer layer.

[0023] In some embodiments, the buffer layer includes a hollow carbon material, and at least a portion of the protective layer fills the gaps between the hollow carbon materials.

[0024] In some embodiments, the protective layer includes at least one of a polymer, an amorphous carbon material, and a graphitized carbon material.

[0025] In some embodiments, the thickness of the connecting layer is 5 nm to 200 nm.

[0026] In some embodiments, the protective layer has a thickness of 5 nm to 500 nm.

[0027] In some embodiments, the graphitized carbon material is modified graphene containing doping elements.

[0028] In some embodiments, the graphitized carbon material is modified graphene containing doping elements, and the number of layers of the modified graphene is less than 10.

[0029] In some embodiments, the graphitized carbon material is modified graphene containing a doping element, and the doping element includes at least one of oxygen, nitrogen, and sulfur.

[0030] In some embodiments, the mass content of the doping element in the graphitized carbon material is 1% to 20%.

[0031] In some embodiments, the polymer includes at least one of a diblock copolymer, a triblock copolymer, and a multiblock copolymer.

[0032] In some embodiments, the mass content of the polymer in the composite negative electrode material is 1% to 20%.

[0033] In some embodiments, the polymer includes at least one of polyacrylic acid, polyacrylonitrile, polyimide, polyurethane, polydopamine, xanthan gum, polypyrrole, polythiophene, polyphenylene vinylene, polyaniline, polyacetylene, and tannic acid.

[0034] The present application also provides a composite negative electrode material, which has a core-shell structure, wherein the core includes a silicon-based active substance, and the shell includes a connecting layer and a protective layer. The connecting layer is coated on the surface of the silicon-based active substance, and the protective layer includes a conductive substrate and a hollow carbon material dispersed in the conductive substrate. The average bonding force F between the connecting layer and the hollow carbon material is greater than 8μN.

[0035] In the above scheme, by constructing a connecting layer and a protective layer on the surface of the silicon-based active material, their synergistic effect is utilized to effectively alleviate the volume expansion of the silicon-based active material, enhance the structural stability of the silicon-carbon composite negative electrode material, and improve the cycle life; the connecting layer on the surface of the silicon-based active material can greatly improve the conductivity of the material, reduce the occurrence of side reactions, and enhance the lithium ion and electron transmission channels, thereby improving the conductivity of the negative electrode material and improving the material rate performance; the conductive substrate in the protective layer can improve the conductivity of the material, and the hollow carbon material dispersed in the conductive substrate can buffer the volume expansion of the silicon-based active material, and the average bonding force between the hollow carbon material and the connecting layer is greater than 8μN. During the cycle, the hollow carbon material is not easy to fall off from the connecting layer, thereby improving the connection stability between the protective layer and the connecting layer, which is beneficial for the composite negative electrode material to maintain excellent mechanical properties, improve the overall structural stability of the composite negative electrode material, and thus improve the cycle stability.

[0036] In some embodiments, the connecting layer includes at least one of a polymer, an amorphous carbon material, and a graphitized carbon material.

[0037] In some embodiments, the hollow carbon material includes at least one of hollow carbon spheres, hollow carbon rods, and hollow carbon tubes.

[0038] In some embodiments, the hollow carbon material includes hollow carbon spheres, and the diameter of the hollow carbon spheres is 20 nm to 2000 nm.

[0039] In some embodiments, the hollow carbon material comprises hollow carbon spheres, and the wall thickness of the hollow carbon spheres is 5 nm to 500 nm.

[0040] In some embodiments, the hollow carbon material comprises a hollow carbon rod, and the diameter of the hollow carbon rod is 10 nm to 1000 nm.

[0041] In some embodiments, the hollow carbon material comprises a hollow carbon rod, and the length of the hollow carbon rod is 100 nm to 3000 nm.

[0042] In some embodiments, the hollow carbon material comprises a hollow carbon rod, and the wall thickness of the hollow carbon rod is 5 nm to 500 nm.

[0043] In some embodiments, the hollow carbon material comprises a hollow carbon tube, and the length of the hollow carbon tube is 30 nm-20 um.

[0044] In some embodiments, the hollow carbon material comprises a hollow carbon tube, and the wall thickness of the hollow carbon tube is 5 nm to 100 nm.

[0045] In some embodiments, the hollow carbon material includes a hollow carbon tube, and the diameter of the hollow carbon tube is 20 nm to 400 nm.

[0046] In some embodiments, the protection layer is coated on the surface of the connecting layer.

[0047] In some embodiments, the conductive substrate includes at least one of a polymer, an amorphous carbon material, and a graphitized carbon material.

[0048] In some embodiments, the thickness of the connecting layer is 5 nm to 200 nm.

[0049] In some embodiments, the protective layer has a thickness of 5 nm to 500 nm.

[0050] In some embodiments, the graphitized carbon material is modified graphene containing doping elements.

[0051] In some embodiments, the graphitized carbon material is modified graphene containing doping elements, and the number of layers of the modified graphene is less than 10.

[0052] In some embodiments, the graphitized carbon material is modified graphene containing a doping element, and the doping element includes at least one of oxygen, nitrogen, and sulfur.

[0053] In some embodiments, the mass content of the doping element in the graphitized carbon material is 1% to 20%.

[0054] In some embodiments, the polymer includes at least one of a diblock copolymer, a triblock copolymer, and a multiblock copolymer.

[0055] In some embodiments, the mass content of the polymer in the composite negative electrode material is 1% to 20%.

[0056] In some embodiments, the polymer includes at least one of polyacrylic acid, polyacrylonitrile, polyimide, polyurethane, polydopamine, xanthan gum, polypyrrole, polythiophene, polyphenylene vinylene, polyaniline, polyacetylene, and tannic acid.

[0057] In some embodiments, the silicon-based active material is a primary particle.

[0058] In some embodiments, the silicon-based active material includes Si, SiO x and silicon alloy, wherein 0 <x<2。

[0059] In some embodiments, the silicon-based active material has a median particle size of 0.2 μm to 20 μm.

[0060] In some embodiments, the mass content of carbon in the composite negative electrode material is 5% to 80%.

[0061] In some embodiments, the mass content of oxygen in the composite negative electrode material is less than 20%.

[0062] In some embodiments, the powder tap density of the composite negative electrode material is 0.2 g / cm 3 ~1.2g / cm 3 .

[0063] In some embodiments, the powder compaction density of the composite negative electrode material is 1.2 g / cm 3 ~1.8g / cm 3 .

[0064] In some embodiments, the median particle size of the composite negative electrode material is 0.2 μm to 20 μm.

[0065] In some embodiments, the specific surface area of ​​the composite negative electrode material is 1.0 m 2 / g~50m 2 / g.

[0066] In some embodiments, the tie layer and the protective layer both comprise a polymer;

[0067] In some embodiments, the connecting layer and the protective layer both include amorphous carbon materials;

[0068] In some embodiments, both the connecting layer and the protective layer include graphitized carbon materials.

[0069] In a second aspect, the present application provides a method for preparing a composite negative electrode material, comprising the following steps:

[0070] forming a connecting layer on the surface of the silicon-based active material, wherein the connecting layer has a modified functional group to obtain a first precursor;

[0071] Performing a polymerization reaction on a mixed slurry comprising the first precursor and a buffer layer material having surface functional groups, and drying the mixture to obtain a second precursor; and

[0072] The second precursor is coated to obtain a composite negative electrode material.

[0073] In the above scheme, a connecting layer with a modified functional group is formed on the surface of the silicon-based active material, and then a buffer layer material with a surface functional group is polymerized with the first precursor so that the connecting layer and the buffer layer material are connected by a covalent bond. This can greatly improve the bonding strength between the buffer layer material and the connecting layer, effectively tightly connecting the connecting layer and the buffer layer material, and ensuring excellent electrical contact after volume expansion. Finally, a coating treatment is performed on the buffer layer, and the protective layer formed further enhances the conductivity and structural integrity of the composite negative electrode material, and can effectively inhibit side reactions with the electrolyte. The composite negative electrode material prepared by the method of this application relies on the high strength and high toughness of the buffer layer material, combined with the synergistic effect of the connecting layer, buffer layer and protective layer on the silicon-based active material, which can effectively alleviate the volume expansion of silicon, improve the conductivity of the silicon negative electrode, enhance the stability of the silicon-carbon composite structure, and thus improve the cycle life and rate performance of this silicon negative electrode material.

[0074] In some embodiments, the silicon-based active material is a primary particle.

[0075] In some embodiments, the silicon-based active material includes Si, SiO x and silicon alloy, wherein 0 <x<2。

[0076] In some embodiments, the silicon-based active material has a median particle size of 0.2 μm to 20 μm.

[0077] In some embodiments, the step of forming a connecting layer on the surface of the silicon-based active substance includes: under a protective atmosphere, depositing a gaseous carbon source on the surface of the silicon-based active substance by vapor deposition to obtain a composite, and using a modifying gas to make the connecting layer on the surface of the composite have modified functional groups.

[0078] In some embodiments, the heating rate of the vapor deposition is 1° C. / min-20° C. / min.

[0079] In some embodiments, the vapor deposition temperature is 600°C to 1000°C.

[0080] In some embodiments, the gaseous carbon source includes at least one of acetylene, methane, toluene, cyclohexane, ethanol, ethylene, and propylene.

[0081] In some embodiments, the concentration of the gaseous carbon source is 0.1 L / min to 10 L / min.

[0082] In some embodiments, the holding time of the vapor deposition is 1 hour to 48 hours.

[0083] In some embodiments, the modified gas includes at least one of oxygen, water vapor, ammonia, hydrogen sulfide, phosphine, hydrogen chloride, hydrogen fluoride, hydrogen bromide, nitric oxide, sulfur dioxide, and chlorine.

[0084] In some embodiments, the flow rate of the modified gas is 0.5 L / min to 5 L / min.

[0085] In some embodiments, the modified gas is introduced for a time period of 0.5 h to 10 h.

[0086] In some embodiments, the modified functional group is selected from at least one of a carboxyl group, a carbonyl group, a hydroxyl group, an epoxy group, a nitrogen-containing functional group, a sulfur-containing functional group, a halogen-containing functional group, and derivative functional groups thereof.

[0087] In some embodiments, the protective atmosphere includes at least one of helium, neon, argon, krypton, and xenon.

[0088] In some embodiments, the volume ratio of the protective atmosphere to the gaseous carbon source is 10:(0.5-10).

[0089] In some embodiments, the volume ratio of the protective atmosphere to the modifying gas is 10:(0.1-10).

[0090] In some embodiments, the step of forming a connecting layer on the surface of the silicon-based active substance includes: depositing a gaseous carbon source on the surface of the silicon-based active substance by vapor deposition under a protective atmosphere to obtain a composite; dispersing the composite in a first modified solution containing a first modifier, performing solid-liquid separation, and drying to obtain a first precursor.

[0091] In some embodiments, the first modifier comprises an anionic surfactant.

[0092] In some embodiments, the first modifier includes at least one of cetyltrimethylammonium bromide, sodium cetyl sulfate, polyvinylpyrrolidone, and sodium polystyrene sulfonate.

[0093] In some embodiments, the mass ratio of the complex in the first modification solution to the first modifier is 1:(0.05-1).

[0094] In some embodiments, the solid-liquid separation comprises at least one of centrifugation, normal pressure filtration, and negative pressure filtration.

[0095] In some embodiments, the drying temperature is 60°C to 200°C.

[0096] In some embodiments, the dispersion method includes at least one of mechanical stirring and ultrasonic dispersion.

[0097] In some embodiments, when the first modifier is used to form a connecting layer having a modified functional group, the method further comprises heat-treating the dried product at a temperature of 600° C. to 900° C. for a time of 1 hour to 6 hours.

[0098] It is understood that the method for forming a connecting layer on the surface of the silicon-based active material is not limited to the vapor deposition method, and other known methods, such as liquid phase coating and / or solid phase coating methods, may also be used. In some embodiments, the step of forming a connecting layer on the surface of the silicon-based active material includes: spray drying a mixed coating liquid containing the silicon-based active material and a polymer, so that a connecting layer is formed on the surface of the silicon-based active material, and the connecting layer includes a polymer.

[0099] In some embodiments, the solid content of the silicon-based active material in the mixed coating solution is 5% to 50%.

[0100] In some embodiments, the mixed coating solution includes a polar solvent.

[0101] In some embodiments, the polar solvent includes at least one of water, anhydrous ethanol, methanol, and isopropanol.

[0102] In some embodiments, the mass ratio of the silicon-based active material to the polymer is 10:(0.1-5).

[0103] In some embodiments, the drying temperature of the spray drying is 60°C to 200°C.

[0104] In some embodiments, the polymer includes at least one of a diblock copolymer, a triblock copolymer, and a multiblock copolymer.

[0105] In some embodiments, the polymer includes at least one of polyacrylic acid, polyacrylonitrile, polyimide, polyurethane, polydopamine, xanthan gum, polypyrrole, polythiophene, polyphenylene vinylene, polyaniline, polyacetylene, and tannic acid.

[0106] In some embodiments, the polymer has a modified functional group.

[0107] In some embodiments, in the mixed slurry, the mass ratio of the first precursor to the buffer layer material having surface functional groups is 1:(0.01-2).

[0108] In some embodiments, the solid content of the first precursor in the mixed slurry is 2% to 50%.

[0109] In some embodiments, the solid content of the buffer layer material having surface functional groups in the mixed slurry is 0.5% to 25%.

[0110] In some embodiments, the mixed slurry further includes an active agent.

[0111] In some embodiments, the mass ratio of the first precursor to the active agent in the mixed slurry is 1:(0.1-0.5).

[0112] In some embodiments, the active agent is selected from at least one of polydiallyldimethylammonium chloride, aminopropyltriethoxysilane, a silane coupling agent, hexadecyltrimethylammonium bromide, sodium hexadecyl sulfate, polyvinylpyrrolidone, and sodium polystyrene sulfonate.

[0113] In some embodiments, the drying method is spray drying.

[0114] In some embodiments, the drying method is spray drying, and the temperature of the spray drying is 100°C to 200°C.

[0115] In some embodiments, the drying method is spray drying, and the feed rate of the spray drying is 100 mL / min-1000 mL / min.

[0116] In some embodiments, the preparation step of the buffer layer material having surface functional groups includes: dispersing the buffer layer material in a second modifying solution containing a second modifier for modification, solid-liquid separation, and drying to obtain the buffer layer material having surface functional groups.

[0117] In some embodiments, the second modifier comprises a cationic surfactant.

[0118] In some embodiments, the second modifier includes at least one of polydiallyldimethylammonium chloride, aminopropyltriethoxysilane, and a silane coupling agent.

[0119] In some embodiments, the mass ratio of the buffer layer material to the second modifier in the second modifying solution is 1:(0.5-10).

[0120] In some embodiments, the second modifying solution includes a polar solvent.

[0121] In some embodiments, the polar solvent includes at least one of water, anhydrous ethanol, methanol, and isopropanol.

[0122] In some embodiments, the solid-liquid separation comprises at least one of centrifugation, normal pressure filtration, and negative pressure filtration.

[0123] In some embodiments, the drying temperature is 60°C to 200°C.

[0124] In some embodiments, the dispersion method includes at least one of mechanical stirring and ultrasonic dispersion.

[0125] In some embodiments, the coating treatment includes carbon coating treatment and / or polymer coating treatment.

[0126] In some embodiments, the step of carbon-coating the second precursor includes: introducing a gaseous carbon source into the second precursor, heating the gaseous carbon source until a thermal cracking reaction occurs, so that a protective layer is deposited on the surface of the second precursor, and the protective layer includes at least one of an amorphous carbon material and a graphitized carbon material.

[0127] In some embodiments, the gaseous carbon source includes at least one of acetylene, methane, toluene, cyclohexane, ethanol, ethylene, and propylene.

[0128] In some embodiments, the heating temperature is increased at a rate of 1° C. / min to 20° C. / min.

[0129] In some embodiments, the temperature of the thermal cracking reaction is 600°C to 1000°C.

[0130] In some embodiments, the holding time of the thermal cracking reaction is 1 hour to 48 hours.

[0131] In some embodiments, the concentration of the gaseous carbon source is 0.1 L / min to 10 L / min.

[0132] In some embodiments, the thermal cracking reaction is carried out under a protective atmosphere.

[0133] In some embodiments, the protective atmosphere includes at least one of helium, neon, argon, krypton, and xenon.

[0134] In some embodiments, the volume ratio of the protective atmosphere to the gaseous carbon source is 10:(0.5-10).

[0135] It is understandable that the step of carbon coating the second precursor is not limited to the above-mentioned gas phase coating, and may also be other currently known coating methods, such as liquid phase coating and / or solid phase coating methods.

[0136] In some embodiments, the step of polymer coating the second precursor includes spray drying a mixed coating liquid containing the second precursor and a polymer, so that a protective layer is formed on the surface of the second precursor, and the protective layer includes a polymer.

[0137] In some embodiments, the solid content of the second precursor in the mixed coating liquid is 5% to 50%.

[0138] In some embodiments, the mixed coating solution includes a polar solvent.

[0139] In some embodiments, the polar solvent includes at least one of water, anhydrous ethanol, methanol, and isopropanol.

[0140] In some embodiments, the mass ratio of the second precursor to the polymer is 10:(0.1-5).

[0141] In some embodiments, the drying temperature of the spray drying is 60°C to 200°C.

[0142] In some embodiments, the polymer includes at least one of a diblock copolymer, a triblock copolymer, and a multiblock copolymer.

[0143] In some embodiments, the molecular weight of the polymer is 120,000 g / mol to 550,000 g / mol.

[0144] In some embodiments, the polymer includes at least one of polyacrylic acid, polyacrylonitrile, polyimide, polyurethane, polydopamine, xanthan gum, polypyrrole, polythiophene, polyphenylene vinylene, polyaniline, polyacetylene, and tannic acid.

[0145] In some embodiments, the buffer layer material includes a hollow carbon material.

[0146] In a third aspect, the present application provides a lithium-ion battery, comprising the composite negative electrode material as described in the first aspect or a negative electrode material prepared according to the preparation method of the composite negative electrode material as described in the second aspect.

[0147] Compared with the existing technology, the technical solution of this application has at least the following technical effects:

[0148] The composite negative electrode material provided in the present application constructs a connecting layer, a buffer layer and a protective layer on the surface of a silicon-based active material, and utilizes their coordinated effect to effectively alleviate the volume expansion of the silicon-based active material, enhance the structural stability of the silicon-carbon composite negative electrode material, and improve the cycle life; the connecting layer on the surface of the silicon-based active material can greatly improve the conductivity of the material, reduce the occurrence of side reactions, and enhance the lithium ion and electron transmission channels, thereby improving the conductivity of the negative electrode material and improving the material rate performance; the buffer layer filled between the connecting layer and the protective layer, the buffer layer and the connecting layer are connected by a covalent bond, or the average bonding force between the buffer layer and the connecting layer is greater than 8μN, which is beneficial for the composite negative electrode material to maintain excellent mechanical properties, improve the structural stability of the composite negative electrode material, and thus improve the cycle stability.

[0149] The composite negative electrode material provided by the present application constructs a connecting layer and a protective layer on the surface of the silicon-based active material, and utilizes their synergistic effect to effectively alleviate the volume expansion of the silicon-based active material, enhance the structural stability of the silicon-carbon composite negative electrode material, and improve the cycle life; the connecting layer on the surface of the silicon-based active material can greatly improve the conductivity of the material, reduce the occurrence of side reactions, and enhance the lithium ion and electron transmission channels, thereby improving the conductivity of the negative electrode material and improving the material rate performance; the conductive substrate in the protective layer can improve the conductivity of the material, and the hollow carbon material dispersed in the conductive substrate can buffer the volume expansion of the silicon-based active material, and the average bonding force between the hollow carbon material and the connecting layer is greater than 8μN. During the cycle, the hollow carbon material is not easy to fall off from the connecting layer, thereby improving the connection stability between the protective layer and the connecting layer, preventing the buffer layer from falling off due to the volume expansion of the silicon-based active material during the charge and discharge process, which is beneficial for the composite negative electrode material to maintain excellent mechanical properties, improve the overall structural stability of the composite negative electrode material, and thus improve the cycle stability. The preparation method provided by the present application forms a connecting layer with a modified functional group on the surface of a silicon-based active material, and then polymerizes a buffer layer material with a surface functional group with a first precursor, so that the connecting layer and the buffer layer material are connected by a covalent bond, which can greatly improve the bonding strength between the buffer layer material and the connecting layer, effectively tightly connect the connecting layer and the buffer layer material, and ensure excellent electrical contact after volume expansion; finally, a coating treatment is performed on the buffer layer, and the protective layer formed further enhances the conductivity and structural integrity of the composite negative electrode material, and can effectively inhibit side reactions with the electrolyte. The composite negative electrode material prepared by the method of the present application relies on the high strength and high toughness of the hollow carbon material in the buffer layer, combined with the synergistic effect of the connecting layer, buffer layer and protective layer on the silicon-based active material, which can effectively alleviate the volume expansion of silicon, improve the conductivity of the silicon negative electrode, enhance the stability of the silicon-carbon composite structure, and thus improve the cycle life and rate performance of this silicon negative electrode material. BRIEF DESCRIPTION OF THE DRAWINGS

[0150] Figure 1 A schematic diagram of the structure of the composite negative electrode material provided in this embodiment;

[0151] Figure 2 Another schematic structural diagram of the composite negative electrode material provided in this embodiment;

[0152] Figure 3 A schematic flow chart of a method for preparing a composite negative electrode material provided in this embodiment;

[0153] Figure 4 This is a scanning electron microscope image of the composite negative electrode material provided in Example 1;

[0154] Figure 5 Raman image of the composite negative electrode material provided in Example 1;

[0155] Figure 6 This is a cycle performance curve diagram of the composite negative electrode material provided in Example 1. DETAILED DESCRIPTION

[0156] The following is a preferred implementation of the embodiment of the present invention. It should be noted that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the embodiment of the present invention. These improvements and modifications are also considered to be within the scope of protection of the embodiment of the present invention.

[0157] At present, in lithium-ion batteries, the negative electrode material is one of the key materials that affects its charge and discharge performance. In order to improve the energy density of the battery, the research and development of high-capacity negative electrode materials are becoming increasingly mature. However, these negative electrode materials expand significantly in volume during the alloying process with lithium. The negative electrode material will pulverize and fall from the current collector during the charge and discharge process, causing the negative electrode material to lose electrical contact with the current collector, resulting in poor electrochemical performance, capacity decay, and decreased cycle stability, making it difficult to obtain commercial applications. In order to improve the cycle stability of lithium-ion batteries, the embodiments of the present application provide a composite negative electrode material with low expansion and good stability.

[0158] The present application provides a composite negative electrode material, such as Figure 1 As shown, the composite negative electrode material has a core-shell structure, the core includes a silicon-based active material 10, and the shell includes a connecting layer 21, a buffer layer 22 and a protective layer 23. The connecting layer 21 is coated on the surface of the silicon-based active material 10, and the buffer layer 22 is filled between the connecting layer 21 and the protective layer 23. The connecting layer 21 and the buffer layer 22 are connected by a covalent bond.

[0159] In the above scheme, by constructing a connecting layer, a buffer layer and a protective layer on the surface of the silicon-based active material, their coordinated effect can be utilized to effectively alleviate the volume expansion of the silicon-based active material, enhance the structural stability of the silicon-carbon composite negative electrode material, and improve the cycle life; the connecting layer on the surface of the silicon-based active material can greatly improve the conductivity of the material, reduce the occurrence of side reactions, and enhance the lithium ion and electron transmission channels, thereby improving the conductivity of the negative electrode material and improving the material rate performance; the buffer layer filled between the connecting layer and the protective layer is connected to the connecting layer by a covalent bond, which is beneficial to the composite negative electrode material to maintain excellent mechanical properties and improve the structural stability of the composite negative electrode material.

[0160] In some embodiments, the covalent bond includes at least one of a carbon-carbon bond (CC, C=C), a carbon-oxygen bond (CO, C=O), a carbon-nitrogen bond (CN), a carbon-sulfur bond (CS), a carbon-chlorine bond (C-Cl), a fluorine-carbon bond (CF), a nitrogen-oxygen bond (ON), an oxygen-sulfur bond (OS), an oxygen-chlorine bond (O-Cl), and a nitrogen-sulfur bond (NS).

[0161] In some embodiments, the core is a silicon-based active material, and the silicon-based active material is a primary particle.

[0162] In some embodiments, the silicon-based active material includes Si, SiO x and silicon alloy, wherein 0 <x<2;SiO x Specifically, it can be SiO 0.1 、SiO 0.2 、SiO 0.3 、SiO 0.4 、SiO 0.6 、SiO 0.8 、SiO、SiO 1.2 、SiO 1.5 、SiO 1.8 or SiO 1.9 The silicon alloy may be ferrosilicon alloy particles, silicon-cobalt alloy particles, silicon-nickel alloy particles, silicon-copper alloy particles, silicon-platinum alloy particles or silicon-gold alloy particles.

[0163] In some embodiments, the median particle size of the silicon-based active material is 0.2 μm to 20 μm; specifically, it can be 0.2 μm, 0.5 μm, 1 μm, 2 μm, 5 μm, 10 μm, 15 μm or 20 μm, which is not limited here.

[0164] In some embodiments, the tie layer includes at least one of a polymer, an amorphous carbon material, and a graphitized carbon material.

[0165] In some embodiments, as Figure 1 As shown, the buffer layer includes a hollow carbon material 221 .

[0166] In some embodiments, as detected by focused ion beam microscopy (FIB-SEM), X-ray photoelectron spectroscopy, electron energy loss spectroscopy or infrared absorption spectrometer, there are multiple covalent bonds at the connection between the hollow carbon material in the connecting layer and the buffer layer, including at least one of a carbon-carbon bond (CC, C=C), a carbon-oxygen bond (CO, C=O), a carbon-nitrogen bond (CN), a carbon-sulfur bond (CS), a carbon-chlorine bond (C-Cl), a fluorine-carbon bond (CF), a nitrogen-oxygen bond (ON), an oxygen-sulfur bond (OS), an oxygen-chlorine bond (O-Cl) and a nitrogen-sulfur bond (NS).

[0167] In the second aspect, the present application provides a composite negative electrode material, which has a core-shell structure. The core includes a silicon-based active substance, and the shell includes a connecting layer, a buffer layer and a protective layer. The connecting layer is coated on the surface of the silicon-based active substance, and the buffer layer is filled between the connecting layer and the protective layer. The average bonding force F between the connecting layer and the buffer layer is greater than 8μN.

[0168] The test method for the average bonding force F between the connecting layer and the buffer layer is: using a nanomechanical testing system and a probe testing system to measure the minimum pulling force required for 5 hollow carbon materials to detach from the connecting layer, and the average value is the average bonding force.

[0169] It can be understood that the greater the average bonding force, the more secure the contact between the buffer layer and the connecting layer can be ensured, thereby avoiding the separation of the hollow carbon material from the connecting layer due to the huge stress generated after lithium embedding in the silicon-based active material, and enhancing electron conduction. The hollow carbon material in the buffer layer can effectively alleviate the volume expansion of silicon. The close bonding between the hollow carbon material and the connecting layer can also reduce material polarization, reduce contact resistance, accelerate lithium ion transmission, and bring high capacity and high rate performance.

[0170] In some embodiments, the buffer layer includes at least one of hollow carbon spheres, hollow carbon rods, and hollow carbon tubes.

[0171] In some embodiments, the hollow carbon material includes a hollow carbon sphere having a diameter of 20 nm to 2000 nm and a wall thickness of 5 nm to 500 nm. The diameter can be 20 nm, 50 nm, 80 nm, 100 nm, 200 nm, 500 nm, 800 nm, 1000 nm, 1500 nm, or 2000 nm, and the wall thickness can be 5 nm, 50 nm, 80 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 450 nm, or 500 nm, without limitation.

[0172] In some embodiments, the hollow carbon material comprises a hollow carbon rod having a diameter of 10 nm to 1000 nm, a length of 100 nm to 3000 nm, and a wall thickness of 5 nm to 500 nm. The diameter can be 10 nm, 50 nm, 80 nm, 100 nm, 200 nm, 500 nm, 600 nm, 700 nm, 850 nm, or 1000 nm, the length can be 100 nm, 200 nm, 400 nm, 500 nm, 800 nm, 1000 nm, 2000 nm, 2500 nm, or 3000 nm, and the wall thickness can be 5 nm, 50 nm, 80 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 450 nm, or 500 nm, without limitation herein.

[0173] In some embodiments, the hollow carbon material includes a hollow carbon tube, wherein the diameter of the hollow carbon tube is 20 nm to 400 nm, the length of the hollow carbon tube is 30 nm to 20 μm, and the wall thickness of the hollow carbon tube is 5 nm to 100 nm. The diameter can be 20 nm, 50 nm, 80 nm, 100 nm, 200 nm, 250 nm, 300 nm, 350 nm, 380 nm, or 400 nm, etc., the length can be 30 nm, 50 nm, 100 nm, 200 nm, 400 nm, 500 nm, 800 nm, 1 μm, 8 μm, 10 μm, 15 μm, or 20 μm, etc., and the wall thickness can be 5 nm, 10 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, or 50 nm, etc., without limitation herein.

[0174] In some embodiments, the thickness of the buffer layer is about the same as the median particle size D of the silicon-based active material. 50 The ratio of is 1:(0.5-10); specifically, it can be 1:0.5, 1:0.7, 1:0.8, 1:0.9, 1:1.0, 1:1.5, 1:2.0, 1:3, 1:5, 1:6, 1:8 or 1:10, etc., which are not limited here. Preferably, the thickness of the buffer layer is about the same as the median particle size D of the silicon-based active material. 50 The ratio is 1:(1~8).

[0175] In some embodiments, the protective layer is coated on the surface of the buffer layer.

[0176] In some embodiments, the protective layer is coated on the surface of the buffer layer, and at least a portion of the protective layer fills the gaps between the hollow carbon materials.

[0177] In some embodiments, the protective layer includes at least one of a polymer, an amorphous carbon material, and a graphitized carbon material.

[0178] In some embodiments, the thickness of the connecting layer is 5 nm to 200 nm, and can be specifically 5 nm, 10 nm, 30 nm, 50 nm, 80 nm, 100 nm, 150 nm, 180 nm or 200 nm, etc., which is not limited here.

[0179] In some embodiments, the thickness of the protective layer is 5 nm to 500 nm, and specifically can be 5 nm, 50 nm, 80 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 450 nm or 500 nm, etc., which is not limited here.

[0180] In some embodiments, the protective layer includes at least one of an amorphous carbon material and a graphitized carbon material, wherein the mass content of the carbon element in the protective layer in the composite negative electrode material is 1% to 50%, preferably 5% to 25%.

[0181] In some embodiments, the protective layer is a carbon layer composed of an amorphous carbon material, the mass content of the carbon layer in the composite negative electrode material is 2% to 25%, and the mass content of oxygen in the carbon layer is less than 5%.

[0182] In some embodiments, the protective layer is a carbon layer composed of a graphitized carbon material, the mass content of the carbon layer in the composite negative electrode material is 2% to 15%, and the mass content of oxygen in the carbon layer is less than 3%.

[0183] In some embodiments, the graphitized carbon material is modified graphene containing a doping element; the doping element includes at least one of oxygen, nitrogen, and sulfur.

[0184] In some embodiments, the graphitized carbon material is modified graphene containing doped elements, and the number of layers of the modified graphene is less than 10. Too many layers of modified graphene will result in an excessively thick protective layer and an excessively high carbon content, which is not conducive to improving the rate performance of the material.

[0185] In some embodiments, the mass content of the doping element in the graphitized carbon material is 1% to 20%; specifically, it can be 1%, 3%, 4%, 5%, 6%, 7%, 10%, 12%, 15%, 18%, or 20%, etc., without limitation herein. The graphitized carbon material with the doping element can significantly enhance its conductivity.

[0186] In some embodiments, the protective layer includes a polymer comprising at least one of a diblock copolymer, a triblock copolymer, and a multiblock copolymer.

[0187] In some embodiments, the mass content of the polymer in the composite negative electrode material is 1% to 20%, specifically 1%, 3%, 5%, 8%, 10%, 12%, 15% or 20%, etc., which is not limited here.

[0188] In some embodiments, the polymer includes at least one of polyacrylic acid, polyacrylonitrile, polyimide, polyurethane, polydopamine, xanthan gum, polypyrrole, polythiophene, polyphenylene vinylene, polyaniline, polyacetylene and tannic acid. The polymer is preferably at least one of polypyrrole, polythiophene, polyaniline, polyaniline and polyacetylene.

[0189] In a third aspect, the present application provides a composite negative electrode material, such as Figure 2 As shown, the composite negative electrode material has a core-shell structure, the core includes a silicon-based active material 10, the shell includes a connecting layer 21 and a protective layer 23, the connecting layer 21 is coated on the surface of the silicon-based active material 10, the protective layer 23 includes a conductive substrate 231 and a hollow carbon material 221 dispersed in the conductive substrate 231, and the average bonding force F between the connecting layer 21 and the hollow carbon material 221 is greater than 8μN.

[0190] In the above scheme, by constructing a connecting layer and a protective layer on the surface of the silicon-based active material, their coordination effect is utilized to effectively alleviate the volume expansion of the silicon-based active material, enhance the structural stability of the silicon-carbon composite negative electrode material, and improve the cycle life; the connecting layer on the surface of the silicon-based active material can greatly improve the conductivity of the material, reduce the occurrence of side reactions, and enhance the lithium ion and electron transmission channels, thereby improving the conductivity of the negative electrode material and improving the material rate performance; the conductive substrate in the protective layer can improve the conductivity of the material, and the hollow carbon material dispersed in the conductive substrate can buffer the volume expansion of the silicon-based active material, and the average bonding force between the hollow carbon material and the connecting layer is greater than 8μN. During the cycle, the hollow carbon material is not easy to fall off from the connecting layer, thereby improving the connection stability between the protective layer and the connecting layer, which is beneficial for the composite negative electrode material to maintain excellent mechanical properties, improve the overall structural stability of the composite negative electrode material, and thus improve the cycle stability.

[0191] In some embodiments, the conductive substrate comprises at least one of a polymer, an amorphous carbon material, and a graphitized carbon material. The selection of the polymer, the amorphous carbon material, and the graphitized carbon material is not further described here and is the same as the composite negative electrode material described in the first aspect.

[0192] In some embodiments, the protection layer is coated on the surface of the connecting layer.

[0193] In some embodiments, both the tie layer and the protective layer comprise a polymer;

[0194] In some embodiments, the connecting layer and the protective layer both include an amorphous carbon material;

[0195] In some embodiments, both the connecting layer and the protective layer include a graphitized carbon material.

[0196] It can be understood that when the connecting layer and the protective layer are made of the same material, the bonding force between the connecting layer and the protective layer is stronger, which is more conducive to fixing the hollow carbon material between the connecting layer and the protective layer, and preventing the hollow carbon material from falling off from the connecting layer during charging and discharging.

[0197] In some embodiments, the mass content of the carbon element in the composite negative electrode material is 5% to 80%. Specifically, it can be 5%, 8%, 10%, 15%, 18%, 20%, 30%, 35%, 40%, 45%, 50%, or 80%, etc., without limitation herein. It should be noted that the carbon in the composite negative electrode material comes from the carbon in the connecting layer, buffer layer, and protective layer.

[0198] In some embodiments, the mass content of oxygen in the composite negative electrode material is less than 20%, and may be 5%, 6%, 8%, 10%, 12%, 15%, 18%, 19%, etc., which are not limited here.

[0199] In some embodiments, the tap density of the composite negative electrode material is 0.2 g / cm 3 ~1.2g / cm 3 , for example 0.2g / cm 3 , 0.3g / cm 3 , 0.5g / cm 3 , 0.6g / cm 3 , 0.7g / cm 3 , 0.8g / cm 3 , 1.0g / cm 3 , 1.2g / cm 3 etc. Preferably 0.5g / cm 3 ~0.8g / cm 3 .

[0200] In some embodiments, the powder compaction density of the composite negative electrode material is 1.2 g / cm 3 ~1.8g / cm 3 , for example 1.2 g / cm 3 , 1.3g / cm 3 , 1.4g / cm 3 , 1.5g / cm 3 , 1.6g / cm 3 or 1.8g / cm 3 etc., preferably 1.45 g / cm 3 ~1.75g / cm 3 .

[0201] In some embodiments, the median particle size of the composite negative electrode material is 0.2 μm to 20 μm. Alternatively, the median particle size of the composite negative electrode material can be 0.2 μm, 0.5 μm, 1 μm, 3 μm, 4 μm, 5 μm, 7 μm, 10 μm, 13 μm, 15 μm, or 20 μm, etc., without limitation herein. The median particle size of the composite negative electrode material is preferably 0.5 μm to 10 μm, more preferably 1 μm to 5 μm.

[0202] The specific surface area ratio of the composite negative electrode material is 1m 2 / g~50m 2 / g. Optionally, the specific surface area ratio of the composite negative electrode material can be 1m 2 / g、5m 2 / g、8m 2 / g、10m 2 / g、15m 2 / g, 20m 2 / g, 25m 2 / g、30m 2 / g、35m 2 / g, 40m 2 / g、45m 2 / g or 50m 2 / g, etc., which are not limited here; it can be understood that the smaller the specific surface area, the better. Too large a specific surface area is likely to lead to the formation of SEI film, consume too much irreversible lithium salt, and reduce the initial efficiency of the battery. Taking into account the cost of the preparation process, the specific surface area is controlled at 2m 2 / g~15m 2 / g.

[0203] This application also provides a method for preparing a composite negative electrode material, such as Figure 3 As shown, the following steps are included:

[0204] S10, forming a connecting layer on the surface of the silicon-based active material, wherein the connecting layer has a modified functional group to obtain a first precursor;

[0205] S20, polymerizing a mixed slurry comprising a first precursor and a buffer layer material having surface functional groups, and drying the mixture to obtain a second precursor; and

[0206] S30, coating the second precursor to obtain a composite negative electrode material.

[0207] The composite negative electrode material prepared by the above method has a core-shell structure, wherein the core includes a silicon-based active material, and the shell includes a connecting layer, a buffer layer and a protective layer. The connecting layer is coated on the surface of the silicon-based active material, and the buffer layer is filled between the connecting layer and the protective layer.

[0208] In this solution, a connecting layer with modified functional groups is formed on the surface of the silicon-based active material, and then a buffer layer material with surface functional groups is polymerized with the first precursor so that the connecting layer and the buffer layer material are connected by covalent bonds. This can greatly improve the bonding strength between the buffer layer material and the connecting layer, effectively tightly connecting the connecting layer and the buffer layer material, and ensuring excellent electrical contact after volume expansion. Finally, a coating treatment is performed on the buffer layer, and the protective layer formed further enhances the conductivity and structural integrity of the composite negative electrode material, and can effectively inhibit side reactions with the electrolyte. The composite negative electrode material prepared by the method of this application relies on the high strength and high toughness of the buffer layer material, combined with the synergistic effect of the connecting layer, buffer layer and protective layer on the silicon-based active material, which can effectively alleviate the volume expansion of silicon, improve the conductivity of the silicon negative electrode, enhance the stability of the silicon-carbon composite structure, and thereby improve the cycle life and rate performance of this silicon negative electrode material.

[0209] The preparation method of the present application is described in detail below with reference to the examples:

[0210] Step S10: forming a connection layer on the surface of the silicon-based active material, wherein the connection layer has a modified functional group, thereby obtaining a first precursor.

[0211] In some embodiments, the silicon-based active material is a primary particle.

[0212] In some embodiments, the silicon-based active material includes Si, SiO x and silicon alloy, wherein 0 <x<2;SiO x Specifically, it can be SiO 0.1 、SiO 0.2 、SiO 0.3 、SiO 0.4 、SiO 0.6 、SiO 0.8 、SiO、SiO 1.2 、SiO 1.5 、SiO 1.8 or SiO 1.9 The silicon alloy may be ferrosilicon alloy particles, silicon-cobalt alloy particles, silicon-nickel alloy particles, silicon-copper alloy particles, silicon-platinum alloy particles or silicon-gold alloy particles.

[0213] In some embodiments, the median particle size D of the silicon-based active material is 50 It is 0.2μm to 20μm; specifically it can be 0.2μm, 0.5μm, 1μm, 2μm, 5μm, 10μm, 15μm or 20μm, which is not limited here.

[0214] In some embodiments, the connection layer may be modified by gas phase modification and / or liquid phase modification.

[0215] In some embodiments, step S10 includes: depositing a gaseous carbon source on the surface of a silicon-based active material by vapor deposition under a protective atmosphere to obtain a composite, and using a modifying gas to impart a modified functional group to a connecting layer on the surface of the composite.

[0216] In some embodiments, the heating rate of vapor deposition is 1°C / min-20°C / min, for example, 1°C / min, 3°C / min, 5°C / min, 8°C / min, 10°C / min, 15°C / min or 20°C / min, which is not limited here.

[0217] In some embodiments, the temperature of vapor deposition is 600°C to 1000°C, specifically 400°C, 500°C, 600°C, 700°C, 800°C or 1000°C.

[0218] In some embodiments, the gaseous carbon source includes at least one of acetylene, methane, toluene, cyclohexane, ethanol, ethylene, and propylene.

[0219] In some embodiments, the concentration of the gaseous carbon source is 0.1 L / min to 10 L / min, specifically 0.1 L / min, 1 L / min, 3 L / min, 5 L / min, 8 L / min or 10 L / min, which is not limited here.

[0220] In some embodiments, the holding time of vapor deposition is 1 h to 48 h, specifically 1 h, 2 h, 4 h, 6 h, 8 h, 12 h, 18 h, 24 h or 48 h, which is not limited here.

[0221] In some embodiments, the modifying gas includes at least one of oxygen, water vapor, ammonia, hydrogen sulfide, phosphine, hydrogen chloride, hydrogen fluoride, hydrogen bromide, nitric oxide, sulfur dioxide, and chlorine.

[0222] In some embodiments, the flow rate of the modified gas is 0.5 L / min to 5 L / min, specifically 0.5 L / min, 1 L / min, 2 L / min, 3 L / min, 4 L / min or 5 L / min, which is not limited here.

[0223] In some embodiments, the time for introducing the modified gas is 0.5 h to 10 h, specifically 0.5 h, 2 h, 4 h, 6 h, 8 h or 10 h, which is not limited here.

[0224] In some embodiments, the modifying functional group is selected from at least one of a carboxyl group, a carbonyl group, a hydroxyl group, an epoxy group, a nitrogen-containing functional group, a sulfur-containing functional group, a halogen-containing functional group, and derivative functional groups thereof.

[0225] In some embodiments, the protective atmosphere includes at least one of helium, neon, argon, krypton, and xenon.

[0226] In some embodiments, the volume ratio of the protective atmosphere to the gaseous carbon source is 10:(0.5-10), specifically 10:0.5, 10:1, 10:2, 10:3, 10:4, 10:5, 10:7, 10:8, 10:9 or 10:10, which is not limited here.

[0227] In some embodiments, the volume ratio of the protective atmosphere to the modifying gas is 10:(0.1-10), specifically 10:0.1, 10:1, 10:2, 10:3, 10:4, 10:5, 10:7, 10:8, 10:9 or 10:10, which is not limited here.

[0228] In some embodiments, step S10 includes: under a protective atmosphere, depositing a gaseous carbon source on the surface of a silicon-based active substance by vapor deposition to obtain a composite; dispersing the composite in a first modified solution containing a first modifier, performing solid-liquid separation, drying, and heat treatment to obtain a first precursor.

[0229] The method for preparing the composite is as described above and will not be repeated here.

[0230] In some embodiments, the first modifying agent includes an anionic surfactant.

[0231] In some embodiments, the first modifier includes at least one of cetyltrimethylammonium bromide, sodium cetyl sulfate, polyvinylpyrrolidone, and sodium polystyrene sulfonate.

[0232] In some embodiments, the mass ratio of the complex to the first modifier in the first modification solution is 1:(0.05-1), specifically 1:0.05, 1:0.1, 1:0.2, 1:0.4, 1:0.5, 1:0.7, 1:0.8, 1:0.9 or 1:1, which is not limited here.

[0233] In some embodiments, the first modifying solution includes a polar solvent.

[0234] In some embodiments, the polar solvent includes at least one of water, anhydrous ethanol, methanol, and isopropanol.

[0235] In some embodiments, the dispersion method includes at least one of mechanical stirring and ultrasonic dispersion.

[0236] In some embodiments, solid-liquid separation comprises at least one of centrifugation, normal pressure filtration, and negative pressure filtration.

[0237] In some embodiments, the drying temperature is 60°C to 200°C, specifically 60°C, 80°C, 100°C, 120°C, 150°C, 180°C or 200°C, which is not limited here.

[0238] In some embodiments, forming the connecting layer having the modified functional group using the first modifier further includes heat-treating the dried product at a temperature of 600° C. to 900° C. for a time of 1 hour to 6 hours.

[0239] In some embodiments, the heat treatment temperature can be 600°C, 650°C, 700°C, 720°C, 750°C, 800°C, 850°C, or 900°C, and the heat treatment time can be 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, or 6 hours, which are not limited herein. In some embodiments, step S10 includes spray-drying a mixed coating solution comprising a silicon-based active material and a polymer to form a connecting layer on the surface of the silicon-based active material, wherein the connecting layer comprises a polymer.

[0240] In some embodiments, the solid content of the silicon-based active material in the mixed coating solution is 5% to 50%.

[0241] In some embodiments, the mixed coating fluid includes a polar solvent.

[0242] In some embodiments, the polar solvent includes at least one of water, anhydrous ethanol, methanol, and isopropanol.

[0243] In some embodiments, the mass ratio of the silicon-based active substance to the polymer is 10:(0.1-5), specifically 10:0.1, 10:1, 10:2, 10:3, 10:4 or 10:5, which is not limited here.

[0244] In some embodiments, the drying temperature of spray drying is 60°C to 200°C; specifically, it can be 60°C, 80°C, 100°C, 120°C, 150°C, 180°C or 200°C, which is not limited here.

[0245] In some embodiments, the polymer comprises at least one of a diblock copolymer, a triblock copolymer, and a multiblock copolymer;

[0246] In some embodiments, the polymer includes at least one of polyacrylic acid, polyacrylonitrile, polyimide, polyurethane, polydopamine, xanthan gum, polypyrrole, polythiophene, polyphenylene vinylene, polyaniline, polyacetylene, and tannic acid;

[0247] In some embodiments, the polymer has a modified functional group, and the modified functional group is selected from at least one of a carboxyl group, a carbonyl group, a hydroxyl group, an epoxy group, a nitrogen-containing functional group, a sulfur-containing functional group, a halogen-containing functional group, and derivative functional groups thereof.

[0248] In some embodiments, before S20, the method further includes: dispersing the buffer layer material in a second modifying solution containing a second modifier to perform a modification treatment, performing solid-liquid separation, and drying to obtain the buffer layer material having surface functional groups.

[0249] In some embodiments, the second modifying agent comprises a cationic surfactant.

[0250] In some embodiments, the second modifier includes at least one of polydiallyldimethylammonium chloride, aminopropyltriethoxysilane, and a silane coupling agent;

[0251] In some embodiments, the mass ratio of the buffer layer material to the second modifier in the second modifying solution is 1:(0.5-10); specifically, it can be 1:0.5, 1:0.1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:8 or 1:10, etc.

[0252] In some embodiments, the second modifying solution includes a polar solvent.

[0253] In some embodiments, the polar solvent includes at least one of water, anhydrous ethanol, methanol, and isopropanol.

[0254] In some embodiments, solid-liquid separation comprises at least one of centrifugation, normal pressure filtration, and negative pressure filtration.

[0255] In some embodiments, the drying temperature is 60°C to 200°C, specifically 60°C, 80°C, 100°C, 120°C, 150°C, 180°C or 200°C, which is not limited here.

[0256] In some embodiments, the dispersion method includes at least one of mechanical stirring and ultrasonic dispersion.

[0257] S20, polymerizing a mixed slurry comprising a first precursor and a buffer layer material having surface functional groups, so that the surface functional groups of the buffer layer material are covalently bonded to the modified functional groups of the connecting layer, and drying to obtain a second precursor.

[0258] It should be noted that the buffer layer material can be connected to the connection layer on the surface of the silicon-based active material by self-assembly, electrostatic adsorption, or spray granulation coating.

[0259] In some embodiments, in the mixed slurry, the mass ratio of the first precursor to the buffer layer material having surface functional groups is 1:(0.01-2), specifically 1:0.01, 1:0.02, 1:0.05, 1:0.08, 1:0.1, 1:0.2, 1:0.5, 1:0.8, 1:1, 1:1.5, or 1:2, etc. Preferably, the mass ratio of the first precursor to the buffer layer material having surface functional groups is 1:(0.01-1).

[0260] In some embodiments, the solid content of the first precursor in the mixed slurry is 2% to 50%; specifically, it can be 2%, 5%, 8%, 10%, 15%, 20%, 30%, 40% or 50%, etc., which is not limited here.

[0261] In some embodiments, the solid content of the buffer layer material with surface functional groups in the mixed slurry is 0.5% to 25%; specifically, it can be 0.5%, 2%, 5%, 8%, 10%, 15%, 18%, 20% or 25%, etc., which is not limited here.

[0262] In some embodiments, the buffer layer material includes a hollow carbon material, and the hollow carbon material includes at least one of a hollow carbon sphere, a hollow carbon rod, and a hollow carbon tube.

[0263] In some embodiments, the solid content of the mixed slurry is 5% to 60%, specifically 5%, 2%, 6%, 10%, 20%, 30%, 40%, 50% or 60%, etc., which is not limited here.

[0264] In some embodiments, the mass ratio of the first precursor to the active agent in the mixed slurry is 1:(0.1-0.5); specifically, it can be 1:0.1, 1:0.2, 1:0.3, 1:0.4 or 1:0.5, etc.

[0265] In some embodiments, the mixed slurry is further dispersed and centrifuged, and the dispersion method includes at least one of mechanical stirring and ultrasonic dispersion.

[0266] In some embodiments, the mixed slurry further includes an active agent, which is selected from at least one of polydiallyldimethylammonium chloride, aminopropyltriethoxysilane, a silane coupling agent, hexadecyltrimethylammonium bromide, sodium hexadecyl sulfate, polyvinylpyrrolidone, and sodium polystyrene sulfonate.

[0267] In some embodiments, the mixed slurry further includes a solvent, and the solvent is selected from at least one of water, anhydrous ethanol, methanol, and isopropanol.

[0268] In some embodiments, the drying method is spray drying, and the spray drying temperature is 100°C to 200°C, and can be specifically 100°C, 110°C, 120°C, 150°C, 170°C, 180°C, or 200°C, which is not limited here.

[0269] In some embodiments, the feed rate of spray drying is 100 mL / min-1000 mL / min, specifically 100 mL / min, 200 mL / min, 300 mL / min, 400 mL / min, 600 mL / min, 800 mL / min or 1000 mL / min, etc., which is not limited here.

[0270] S30, coating the second precursor to obtain a composite negative electrode material.

[0271] In some embodiments, the coating treatment includes a carbon coating treatment and / or a polymer coating treatment.

[0272] In some embodiments, the coating process can be performed by vapor deposition, liquid coating, organic matter cracking, etc.

[0273] In some embodiments, the step of carbon coating the second precursor includes: introducing a gaseous carbon source into the second precursor, heating the gaseous carbon source until a thermal cracking reaction occurs, so that a protective layer is deposited on the surface of the second precursor, and the protective layer includes at least one of an amorphous carbon material and a graphitized carbon material.

[0274] In some embodiments, the gaseous carbon source includes at least one of acetylene, methane, toluene, cyclohexane, ethanol, ethylene, and propylene.

[0275] In some embodiments, the heating temperature rise rate is 1°C / min to 20°C / min, specifically 1°C / min, 2°C / min, 3°C / min, 4°C / min, 5°C / min, 8°C / min, 10°C / min, 12°C / min, 15°C / min, 18°C / min, and 20°C / min. Preferably, the heating temperature rise rate is 3°C / min to 5°C / min. The inventors have found through multiple experiments that when the heating rate is controlled at 3°C / min to 5°C / min, the carbonization reaction can be effectively guaranteed and the time to heat to the preset temperature range can be shortened.

[0276] In some embodiments, the temperature of the thermal cracking reaction is 600°C to 1000°C. Specifically, the reaction temperature can be 600°C, 650°C, 700°C, 750°C, 800°C, 890°C, 900°C, 960°C, or 1000°C. The inventors have found through multiple experiments that controlling the reaction temperature within the range of 600°C to 1000°C can improve reaction efficiency, resulting in the formation of a uniform carbon layer on the surface of the second precursor, which can be amorphous carbon. Preferably, the reaction temperature is 700°C to 900°C.

[0277] In some embodiments, the holding time of the thermal cracking reaction is 1 h to 48 h; specifically, it can be 1 h, 4 h, 8 h, 12 h, 16 h, 24 h, 28 h, 32 h, 38 h or 48 h, which is not limited here.

[0278] In some embodiments, the concentration of the gaseous carbon source is 0.1 L / min to 10 L / min; specifically, it can be 0.1 L / min, 0.4 L / min, 0.6 L / min, 0.8 L / min, 1.0 L / min, 2 L / min, 5 L / min, 6 L / min, 8 L / min, 9 L / min or 10 L / min, etc., which is not limited here.

[0279] In some embodiments, the thermal cracking reaction is carried out under a protective atmosphere.

[0280] In some embodiments, the protective atmosphere includes at least one of helium, neon, argon, krypton, and xenon.

[0281] In some embodiments, the volume ratio of the protective atmosphere to the gaseous carbon source is 10:(0.5-10), specifically 10:0.5, 10:1, 10:2, 10:3, 10:5, 10:6.5, 10:7.5, 10:8.5, 10:9 or 10:10, etc., which is not limited here.

[0282] In some embodiments, the step of polymer coating the second precursor includes spray drying a mixed coating liquid containing the second precursor and the polymer, so that a protective layer is formed on the surface of the second precursor, and the protective layer includes the polymer.

[0283] In some embodiments, the solid content of the second precursor in the mixed coating liquid is 5% to 50%, specifically 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45% or 50%, etc., which is not limited here.

[0284] In some embodiments, the mixed coating fluid includes a polar solvent.

[0285] In some embodiments, the polar solvent includes at least one of water, anhydrous ethanol, methanol, and isopropanol.

[0286] In some embodiments, the mass ratio of the second precursor to the polymer is 10:(0.1-5), specifically 10:0.1, 10:1, 10:2, 10:3, 10:4 or 10:5, which is not limited here.

[0287] In some embodiments, the drying temperature of spray drying is 60°C to 200°C, specifically 60°C, 80°C, 100°C, 120°C, 150°C, 180°C or 200°C.

[0288] In some embodiments, the polymer comprises at least one of a diblock copolymer, a triblock copolymer, and a multiblock copolymer.

[0289] In some embodiments, the polymer includes at least one of polyacrylic acid, polyacrylonitrile, polyimide, polyurethane, polydopamine, xanthan gum, polypyrrole, polythiophene, polyphenylene vinylene, polyaniline, polyacetylene, and tannic acid.

[0290] Embodiments of the present invention also provide a lithium-ion battery using the composite negative electrode material provided in the above embodiments of the present invention or a composite negative electrode material prepared using the method for preparing a composite negative electrode material provided in the above embodiments of the present invention. The lithium-ion battery provided in the embodiments of the present invention has the advantages of high capacity, high initial efficiency, long cycle life, excellent rate performance, and low expansion.

[0291] The following further describes the embodiments of the present invention in multiple embodiments. The embodiments of the present invention are not limited to the following specific embodiments. Within the scope of the unchanged main rights, appropriate changes can be made to the implementation.

[0292] Example 1

[0293] A method for preparing a composite negative electrode material comprises the following steps:

[0294] (1) Silicon with a median particle size of 2 μm was placed in a rotary atmosphere furnace. Under the protection of an argon atmosphere, the temperature was increased to 900°C at a heating rate of 3°C / min. Then, 0.5 L / min of acetylene gas was introduced so that the volume ratio of argon to acetylene in the rotary atmosphere furnace was 9:1. After keeping the temperature for 3 hours, the acetylene gas was turned off. Ammonia gas was introduced at a rate of 1.5 L / min so that the volume ratio of argon to ammonia in the rotary atmosphere furnace was 10:1. After keeping the temperature for 3 hours, the ammonia gas was turned off and the mixture was cooled to obtain a composite. 10 g of the composite and hexadecyltrimethylammonium bromide were dispersed in 200 ml of deionized water at a mass ratio of 10:2, stirred for 30 minutes, ultrasonicated for 10 minutes, and centrifuged to obtain a first precursor.

[0295] (2) 1g of hollow carbon spheres with a diameter of 100nm and 1g of polydiallyldimethylammonium chloride were dissolved in 100ml of deionized water, stirred for 30 minutes, ultrasonicated for 20 minutes, and centrifuged to obtain surface hydroxylated hollow carbon sphere material. 10g of the first precursor was dissolved in 100ml of deionized water and stirred for 10 minutes to obtain solution E. 1g of the modified hollow carbon spheres was dispersed in 100ml of deionized water and stirred for 10 minutes to obtain solution F. Solution E was slowly dripped into solution F, and continued to stir rapidly for 40 minutes, and then centrifuged to obtain the second precursor.

[0296] (3) 10 g of the second precursor was dissolved in 100 g of anhydrous ethanol, 1 g of polyacrylic acid was added, and mechanical stirring was performed for 30 minutes. The composite negative electrode material was obtained by spray drying while controlling the drying temperature at 100°C.

[0297] The composite negative electrode material prepared in this embodiment has a core-shell structure, wherein the core includes silicon, the outer shell includes a connecting layer, a buffer layer and a protective layer, the connecting layer is an amorphous carbon material layer, the amorphous carbon material layer is coated on the surface of the silicon particles, the buffer layer includes hollow carbon spheres, the protective layer is a polymer layer (polyacrylic acid), the buffer layer is filled between the connecting layer and the protective layer, and the amorphous carbon material layer and the hollow carbon spheres of the buffer layer are connected by covalent bonds (carbon-nitrogen bonds).

[0298] The median particle size of the composite negative electrode material is 2.5 μm and the specific surface area is 5 m 2 / g, the tap density of the powder is 0.9g / cm 3 , the powder compaction density is 1.65g / cm 3 The mass content of oxygen element in the composite negative electrode material is 5%, the mass content of carbon element in the composite negative electrode material is 25%, the thickness of the connecting layer is 50nm, the thickness of the buffer layer is 500nm, the thickness of the protective layer is 30nm, and the mass content of the protective layer in the composite negative electrode material is 5%.

[0299] Figure 4 This is a scanning electron microscope image of the composite negative electrode material of this embodiment; the surface of the composite negative electrode material has a spherical carbon structure and is wrapped with a dense carbon layer.

[0300] Figure 5 is the XRD pattern of the composite negative electrode material of this embodiment, as shown in Figure 5 As shown, the XRD pattern of the composite negative electrode material shows that the three strong peaks at 28.4°, 47.3° and 56.1° correspond to the three strong peaks of silicon (JCPDS No. 27-1402), and there is basically no impurity phase.

[0301] Figure 6 The cycle performance curve of the composite negative electrode material of this embodiment is as follows: Figure 6As shown, the material has excellent cycle performance. The charge and discharge current is 1000mA / g. After 500 cycles at a current of 0.25C, there is still a capacity of 1068mAh / g, and the capacity retention rate reaches 81%.

[0302] Example 2

[0303] A method for preparing a composite negative electrode material comprises the following steps:

[0304] (1) Silicon with a median particle size of 2.5 μm was placed in a rotary atmosphere furnace. Under the protection of an argon atmosphere, the temperature was increased to 950°C at a heating rate of 3°C / min. Then, 0.5 L / min of acetylene gas was introduced so that the volume ratio of argon to acetylene in the rotary atmosphere furnace was 9:1. After keeping the temperature for 4 hours, the acetylene gas was turned off and 1.5 L / min of hydrogen sulfide was introduced so that the volume ratio of argon to hydrogen sulfide in the rotary atmosphere furnace was 5:1. After keeping the temperature for 3 hours, the mixture was cooled to obtain a composite. 10 g of the composite and hexadecyltrimethylammonium bromide were dispersed in 200 ml of deionized water at a mass ratio of 10:1, stirred for 30 minutes, ultrasonicated for 10 minutes, and centrifuged to obtain a second precursor.

[0305] (2) 1 g of hollow carbon spheres with a diameter of 200 nm and 2 g of polydiallyldimethylammonium chloride were dissolved in 100 ml of deionized water, stirred for 30 minutes, and then ultrasonicated for 20 minutes. The mixture was centrifuged and dried to obtain a surface carboxylated hollow carbon sphere material. 10 g of the first precursor was dissolved in 100 ml of deionized water and stirred for 10 minutes to obtain solution E. 2 g of the modified hollow carbon spheres were dispersed in 100 ml of deionized water and stirred for 10 minutes to obtain solution F. Solution E was slowly dripped into solution F, and after continuous rapid stirring for 40 minutes, the mixture was centrifuged and dried to obtain the second precursor.

[0306] (3) 10 g of the second precursor was dissolved in 100 g of deionized water, 1 g of polyacrylonitrile was added, and mechanical stirring was performed for 30 minutes. The composite negative electrode material was obtained by spray drying with the drying temperature controlled at 120°C.

[0307] The composite negative electrode material prepared in this embodiment has a core-shell structure, the core includes silicon, the shell includes a connecting layer, a buffer layer and a protective layer, the connecting layer is an amorphous carbon material layer, the amorphous carbon material layer is coated on the surface of the silicon particles, the buffer layer includes hollow carbon spheres, the protective layer is a polymer layer (polyacrylonitrile), the buffer layer is filled between the connecting layer and the protective layer, and the amorphous carbon material layer and the hollow carbon spheres of the buffer layer are connected by covalent bonds (carbon-sulfur bonds).

[0308] After testing, the median particle size of the obtained silicon-carbon composite negative electrode material is 2.8μm and the specific surface area is 2m 2 / g, the tap density of the powder is 1.0g / cm 3, the powder compaction density is 1.5g / cm 3 The mass content of oxygen element in the composite negative electrode material is 4%, the mass content of carbon element in the composite negative electrode material is 30%, the thickness of the connecting layer is 60nm, the thickness of the buffer layer is 800nm, the thickness of the protective layer is 20nm, and the mass content of the protective layer in the composite negative electrode material is 8%.

[0309] Example 3

[0310] (1) Silicon with a median particle size of 2.5 μm was placed in a rotary atmosphere furnace, and heated to 950°C at a heating rate of 3°C / min under the protection of an argon atmosphere. Then, 0.5 L / min of acetylene gas was introduced so that the volume ratio of argon to acetylene in the rotary atmosphere furnace was 9:1. After keeping the temperature for 4 hours, the acetylene gas was turned off, and 2.5 L / min of hydrogen chloride was introduced so that the volume ratio of argon to hydrogen chloride in the rotary atmosphere furnace was 8:1. After keeping the temperature for 4 hours, the mixture was cooled to obtain a composite. 10 g of the composite and polyvinyl pyrrolidone were dispersed in 200 ml of anhydrous ethanol at a mass ratio of 10:3, stirred for 30 minutes, ultrasonicated for 10 minutes, and centrifuged to obtain a first precursor.

[0311] (2) 1 g of hollow carbon tubes with a diameter of 50 nm and a length of 1000 nm and 2 g of aminopropyltriethoxysilane were dissolved in 100 ml of deionized water, stirred for 30 minutes, ultrasonicated for 20 minutes, and centrifuged to obtain a hollow carbon tube material with amino groups. 10 g of the first precursor was dissolved in 100 ml of deionized water and stirred for 10 minutes to obtain solution E. 2 g of the modified hollow carbon tubes were dispersed in 100 ml of deionized water and stirred for 10 minutes to obtain solution F. Solution E was slowly dripped into solution F, and after continuous rapid stirring for 40 minutes, centrifuged to obtain the second precursor.

[0312] (3) 10 g of the second precursor was dissolved in 100 g of anhydrous ethanol, 3 g of tannic acid was added, and mechanical stirring was performed for 30 minutes. The composite negative electrode material was obtained by spray drying with the drying temperature controlled at 120°C.

[0313] The composite negative electrode material prepared in this embodiment has a core-shell structure, wherein the core includes silicon, the outer shell includes a connecting layer, a buffer layer and a protective layer, the connecting layer is an amorphous carbon material layer, the amorphous carbon material layer is coated on the surface of the silicon particles, the buffer layer includes hollow carbon tubes, the protective layer is a polymer layer (polytannic acid), the buffer layer is filled between the connecting layer and the protective layer, and the amorphous carbon material layer and the hollow carbon spheres of the buffer layer are connected by covalent bonds (carbon-chlorine bonds).

[0314] The composite negative electrode material prepared in this embodiment has a core-shell structure, wherein the core includes silicon, the shell includes a connecting layer and a protective layer, the connecting layer is an amorphous carbon material layer, and the protective layer includes polytannic acid and hollow carbon tubes dispersed in the polytannic acid.

[0315] After testing, the median particle size of the composite negative electrode material is 4.5μm and the specific surface area is 8m 2 / g, the tap density of the powder is 1.1g / cm 3 , the powder compaction density is 1.7g / cm 3 The mass content of oxygen element in the composite negative electrode material is 7%, the mass content of carbon element in the composite negative electrode material is 35%, the thickness of the connecting layer is 60nm, the thickness of the buffer layer is 700nm, the thickness of the protective layer is 45nm, and the mass content of the protective layer in the composite negative electrode material is 15%.

[0316] Example 4

[0317] (1) Silicon with a median particle size of 2 μm was placed in a rotary atmosphere furnace. Under the protection of an argon atmosphere, the temperature was increased to 900°C at a heating rate of 3°C / min. Then, 0.5 L / min of acetylene gas was introduced so that the volume ratio of argon to acetylene in the rotary atmosphere furnace was 9:1. After keeping the temperature for 3 hours, the acetylene gas was turned off. Ammonia gas was introduced at a rate of 1.5 L / min so that the volume ratio of argon to ammonia in the rotary atmosphere furnace was 4:1. After keeping the temperature for 3 hours, the ammonia gas was turned off. The first precursor was obtained by cooling.

[0318] (2) 10 g of the first precursor and 0.5 g of hollow carbon tubes (50 nm in diameter and 1000 nm in length) were dissolved in 200 ml of anhydrous ethanol. 2 g of polyvinyl pyrrolidone was added, stirred for 30 minutes, and then ultrasonicated for 10 minutes to obtain a mixed slurry. The mixed slurry was sphericalized by spray granulation under drying conditions at 130°C to obtain the second precursor.

[0319] (3) 10 g of the second precursor was dissolved in 100 g of anhydrous ethanol, 1 g of polyacrylic acid was added, and mechanical stirring was performed for 30 minutes. The composite negative electrode material was obtained by spray drying while controlling the drying temperature at 100°C.

[0320] The composite negative electrode material prepared in this embodiment has a core-shell structure, wherein the core includes silicon, the outer shell includes a connecting layer, a buffer layer and a protective layer, the connecting layer is an amorphous carbon material layer, the amorphous carbon material layer is coated on the surface of the silicon particles, the buffer layer includes hollow carbon tubes, the protective layer is a polymer layer (polyacrylic acid), the buffer layer is filled between the connecting layer and the protective layer, and the amorphous carbon material layer and the hollow carbon spheres of the buffer layer are connected by covalent bonds (carbon-nitrogen bonds).

[0321] The composite negative electrode material prepared in this embodiment has a core-shell structure, wherein the core includes silicon, the shell includes a connecting layer and a protective layer, the connecting layer is an amorphous carbon material layer, and the protective layer includes polyacrylic acid and hollow carbon tubes dispersed in the polyacrylic acid.

[0322] The median particle size of the composite negative electrode material is 3.5 μm and the specific surface area is 15 m 2 / g, the powder tap density is 0.88g / cm 3 The compacted density of the powder is 1.36 g / cm 3 The mass content of oxygen element in the composite negative electrode material is 11%, the mass content of carbon element in the composite negative electrode material is 21%, the thickness of the connecting layer is 50nm, the thickness of the buffer layer is 300nm, the thickness of the protective layer is 33nm, and the mass content of the protective layer in the composite negative electrode material is 5%.

[0323] Example 5

[0324] (1) Silicon with a median particle size of 3 μm was placed in a rotary atmosphere furnace. Under the protection of an argon atmosphere, the temperature was increased to 800°C at a heating rate of 5°C / min. Then, 0.5 L / min of acetylene gas was introduced so that the volume ratio of argon to acetylene in the rotary atmosphere furnace was 9:1. After keeping the temperature for 3 hours, the acetylene gas was turned off. Ammonia gas was introduced at a rate of 2.5 L / min so that the volume ratio of argon to ammonia in the rotary atmosphere furnace was 6:1. After keeping the temperature for 3 hours, the ammonia gas was turned off and the furnace was cooled to obtain a first precursor.

[0325] (2) 10 g of the first precursor and 0.5 g of hollow carbon tubes (80 nm in diameter and 1100 nm in length) were dissolved in 200 ml of anhydrous ethanol. 2 g of polyvinyl pyrrolidone was added, stirred for 30 minutes, and then ultrasonicated for 10 minutes to obtain a mixed slurry. The mixed slurry was sphericalized by spray granulation under drying conditions at 130°C to obtain the second precursor.

[0326] (3) 10 g of the second precursor was dissolved in 100 g of anhydrous ethanol, 1 g of polyacrylonitrile was added, and mechanical stirring was performed for 30 minutes. The composite negative electrode material was obtained by spray drying with the drying temperature controlled at 100°C.

[0327] The composite negative electrode material prepared in this embodiment has a core-shell structure, wherein the core includes silicon, the shell includes a connecting layer, a buffer layer and a protective layer, the connecting layer is an amorphous carbon material layer, the amorphous carbon material layer is coated on the surface of the silicon particles, the buffer layer includes hollow carbon tubes, the protective layer is a polymer layer (polyacrylonitrile), the buffer layer is filled between the connecting layer and the protective layer, and the amorphous carbon material layer and the hollow carbon spheres of the buffer layer are connected by covalent bonds (carbon-nitrogen bonds).

[0328] The composite negative electrode material prepared in this embodiment has a core-shell structure, wherein the core includes silicon, the shell includes a connecting layer and a protective layer, the connecting layer is an amorphous carbon material layer, and the protective layer includes polyacrylonitrile and hollow carbon tubes dispersed in the polyacrylonitrile.

[0329] After testing, the median particle size of the obtained silicon-carbon composite negative electrode material is 5μm and the specific surface area is 19m2 / g, the tap density of the powder is 0.98g / cm 3 , the powder compaction density is 1.4g / cm 3 The mass content of oxygen element in the composite negative electrode material is 23%, the mass content of carbon element in the composite negative electrode material is 29%, the thickness of the connecting layer is 66nm, the thickness of the buffer layer is 200nm, the thickness of the protective layer is 25nm, and the mass content of the protective layer in the composite negative electrode material is 5%.

[0330] Example 6

[0331] (1) Silicon with a median particle size of 6 μm was placed in a rotary atmosphere furnace. Under the protection of an argon atmosphere, the temperature was increased to 900°C at a heating rate of 3°C / min. Then, 0.5 L / min of acetylene gas was introduced so that the volume ratio of argon to acetylene in the rotary atmosphere furnace was 9:1. After keeping the temperature for 3 h, the acetylene gas was turned off. 3.5 L / min of hydrogen fluoride was introduced so that the volume ratio of argon to hydrogen fluoride in the rotary atmosphere furnace was 2:1. After keeping the temperature for 8 h, the hydrogen fluoride was turned off. The product was cooled to obtain a first precursor.

[0332] (2) 10 g of the first precursor and 0.5 g (50 nm in diameter, 1000 nm in length) of hydroxylated hollow carbon tubes were dissolved in 200 ml of anhydrous ethanol, 2 g of polyvinyl pyrrolidone was added, stirred for 30 minutes, and then ultrasonicated for 10 minutes to obtain a mixed slurry. The mixed slurry was sphericalized by spray granulation under drying conditions at 130°C to obtain a second precursor.

[0333] (3) Take 100 g of the second precursor and place it in a rotary atmosphere furnace. Under the protection of argon atmosphere, heat it to 900 °C at a heating rate of 3 °C / min, then introduce 0.5 L / min of methane gas so that the volume ratio of argon to acetylene in the rotary atmosphere furnace is 9:1. After keeping the temperature for 6 h, turn off the acetylene gas and cool it to obtain a composite negative electrode material.

[0334] The composite negative electrode material prepared in this embodiment has a core-shell structure, wherein the core includes silicon, and the outer shell includes a connecting layer and a protective layer. The connecting layer is an amorphous carbon material layer, and the connecting layer is coated on the surface of the silicon particles; the protective layer includes an amorphous carbon material and hollow carbon tubes dispersed in the amorphous carbon material, and the amorphous carbon material layer and the hollow carbon tubes are connected by a covalent bond (carbon-fluorine bond).

[0335] The median particle size of the composite negative electrode material is 8 μm and the specific surface area is 11 m 2 / g, the tap density of the powder is 0.98g / cm 3 , the powder compaction density is 1.3g / cm 3The mass content of oxygen element in the composite negative electrode material is 8%, the mass content of carbon element in the composite negative electrode material is 32%, the thickness of the connecting layer is 50nm, the thickness of the protective layer is 350nm, and the mass content of the protective layer in the composite negative electrode material is 14%.

[0336] Example 7

[0337] The preparation steps are the same as those in Example 1. The only difference from Example 1 is that step (1) is not modified with ammonia. The specific operation of step (1) in this example is:

[0338] Silicon with a median particle size of 6 μm was placed in a rotary atmosphere furnace and heated to 900°C at a heating rate of 3°C / min under argon atmosphere. Then, 0.5 L / min of acetylene gas was introduced so that the volume ratio of argon to acetylene in the rotary atmosphere furnace was 9:1. After keeping warm for 3 hours, the acetylene gas was turned off and cooled to obtain a complex; 10 g of the complex and hexadecyltrimethylammonium bromide were dispersed in 200 ml of deionized water in a mass ratio of 10:2, stirred for 30 minutes, and then ultrasonicated for 10 minutes. The product obtained after centrifugal drying was placed in a vacuum reactor, heated to 700°C, and kept warm for 3 hours to obtain the first precursor after surface amino modification.

[0339] The composite negative electrode material prepared in this embodiment has a core-shell structure, wherein the core includes silicon, the outer shell includes a connecting layer, a buffer layer and a protective layer, the connecting layer is an amorphous carbon material layer, the amorphous carbon material layer is coated on the surface of the silicon particles, the buffer layer includes hollow carbon spheres, the protective layer is a polymer layer (polyacrylic acid), the buffer layer is filled between the connecting layer and the protective layer, and the amorphous carbon material layer and the hollow carbon spheres of the buffer layer are connected by covalent bonds (carbon-nitrogen bonds).

[0340] The median particle size of the composite negative electrode material is 2.2 μm and the specific surface area is 4.8 m 2 / g, the tap density of the powder is 0.92g / cm 3 The compacted density of the powder is 1.59g / cm 3 The mass content of oxygen element in the composite negative electrode material is 7%, the mass content of carbon element in the composite negative electrode material is 23%, the thickness of the connecting layer is 60nm, the thickness of the buffer layer is 550nm, the thickness of the protective layer is 50nm, and the mass content of the protective layer in the composite negative electrode material is 5.2%.

[0341] Example 8

[0342] The preparation steps are the same as those in Example 1, and the only difference from Example 1 is that SiO is used as the silicon-based active material.

[0343] The composite negative electrode material prepared in this embodiment has a core-shell structure, wherein the core includes SiO, the shell includes a connecting layer, a buffer layer and a protective layer, the connecting layer is an amorphous carbon material layer, the amorphous carbon material layer is coated on the surface of the silicon particles, the buffer layer includes hollow carbon spheres, the protective layer is a polymer layer (polyacrylic acid), the buffer layer is filled between the connecting layer and the protective layer, and the amorphous carbon material layer and the hollow carbon spheres in the buffer layer are connected by covalent bonds (carbon-nitrogen bonds).

[0344] The median particle size of the composite negative electrode material is 2.6 μm and the specific surface area is 5.3 m 2 / g, the tap density of the powder is 0.97g / cm 3 The compacted density of the powder is 1.64g / cm 3 The mass content of oxygen element in the composite negative electrode material is 19%, the mass content of carbon element in the composite negative electrode material is 22%, the thickness of the connecting layer is 54nm, the thickness of the buffer layer is 500nm, the thickness of the protective layer is 40nm, and the mass content of the protective layer in the composite negative electrode material is 8%.

[0345] Example 9

[0346] The preparation steps are the same as those in Example 1, and the only difference from Example 1 is that lithium silicon alloy is used as the silicon-based active material.

[0347] The composite negative electrode material prepared in this embodiment has a core-shell structure, wherein the core includes a lithium-silicon alloy, the outer shell includes a connecting layer, a buffer layer and a protective layer, the connecting layer is an amorphous carbon material layer, the amorphous carbon material layer is coated on the surface of the silicon particles, the buffer layer includes hollow carbon spheres, the protective layer is a polymer layer (polyacrylic acid), the buffer layer is filled between the connecting layer and the protective layer, and the amorphous carbon material layer and the hollow carbon spheres in the buffer layer are connected by covalent bonds (carbon-nitrogen bonds).

[0348] The median particle size of the composite negative electrode material is 3.1 μm and the specific surface area is 6.1 m 2 / g, the tap density of the powder is 1.01g / cm 3 The compacted density of the powder is 1.72g / cm 3 The mass content of oxygen element in the composite negative electrode material is 12%, the mass content of carbon element in the composite negative electrode material is 28%, the thickness of the connecting layer is 50nm, the thickness of the buffer layer is 600nm, the thickness of the protective layer is 60nm, and the mass content of the protective layer in the composite negative electrode material is 8.5%.

[0349] Example 10

[0350] (1) Silicon with a median particle size of 6 μm was placed in a 1 mol / L nickel acetate solution and ultrasonicated for 30 minutes to obtain a dispersion. The slurry was dried by spray drying to obtain a silicon precursor with a nickel acetate modified surface. The precursor was placed in a rotary atmosphere furnace and heated to 900°C at a heating rate of 3°C / min under argon atmosphere. 0.5 L / min of toluene vapor and 1.5 L / min of ammonia were introduced to make the volume ratio of argon to toluene in the rotary atmosphere furnace 9:1. After keeping the temperature for 3 hours, the ammonia was turned off and the mixture was cooled to obtain a composite. 10 g of the composite and hexadecyltrimethylammonium bromide were dispersed in 200 ml of deionized water at a mass ratio of 10:2, stirred for 30 minutes, ultrasonicated for 10 minutes, and centrifuged to obtain the first precursor.

[0351] (2) 1g of hollow carbon spheres with a diameter of 100nm and 1g of polydiallyldimethylammonium chloride were dissolved in 100ml of deionized water, stirred for 30 minutes, and then ultrasonicated for 20 minutes. The mixture was centrifuged and dried to obtain a hollow carbon sphere material with hydroxyl groups on the surface. 10g of the first precursor was dissolved in 100ml of deionized water and stirred for 10 minutes to obtain solution E. 1g of the modified hollow carbon spheres was dispersed in 100ml of deionized water and stirred for 10 minutes to obtain solution F. Solution E was slowly dripped into solution F, and after continuous rapid stirring for 40 minutes, the mixture was centrifuged and dried to obtain the second precursor.

[0352] (3) 10 g of the second precursor was dissolved in 100 g of anhydrous ethanol, 1 g of polyacrylic acid was added, and mechanical stirring was performed for 30 minutes. The composite negative electrode material was obtained by spray drying while controlling the drying temperature at 100°C.

[0353] The composite negative electrode material prepared in this embodiment has a core-shell structure, wherein the core includes silicon, the shell includes a connecting layer, a buffer layer and a protective layer, the connecting layer is a graphitized carbon material layer, wherein the graphitized carbon material includes graphene, the graphitized carbon material layer is coated on the surface of the silicon particles, the buffer layer includes hollow carbon spheres, and the protective layer is a polymer layer (polyacrylic acid). The buffer layer is filled between the connecting layer and the protective layer, and the graphitized carbon material layer and the hollow carbon spheres in the buffer layer are connected by covalent bonds (carbon-nitrogen bonds).

[0354] The median particle size of the composite negative electrode material is 2.4 μm and the specific surface area is 5.6 m 2 / g, the powder tap density is 0.88g / cm 3 The compacted density of the powder is 1.63 g / cm 3 The mass content of oxygen element in the composite negative electrode material is 4.6%, the mass content of carbon element in the composite negative electrode material is 22%, the thickness of the connecting layer is 5nm, the thickness of the buffer layer is 500nm, the thickness of the protective layer is 30nm, and the mass content of the protective layer in the composite negative electrode material is 5%.

[0355] Example 11

[0356] (1) Silicon with a median particle size of 6 μm is placed in a 0.1 mol / L solution of triblock copolymer P123 (polyethylene oxide-polypropylene oxide-polyethylene oxide), with a mass ratio of silicon to polymer P123 being 10:1. Ultrasonic treatment is performed for 60 min to obtain a mixed coating liquid, wherein the solid content of the mixed coating liquid is 40%. The slurry is dried by spray drying at 100°C to obtain a first precursor, which includes silicon and a polymer connecting layer coated on the surface of the silicon. The polyethylene oxide-polypropylene oxide-polyethylene oxide used in this step itself has phenolic hydroxyl, carboxyl and carbonyl modified functional groups.

[0357] (2) 1 g of hollow carbon spheres with a diameter of 100 nm and 1 g of polydiallyldimethylammonium chloride were dissolved in 100 ml of deionized water, stirred for 30 minutes, and then ultrasonicated for 20 minutes. The mixture was centrifuged and dried to obtain a hollow carbon sphere material with surface hydroxylation modification. 10 g of the first precursor was dissolved in 100 ml of deionized water and stirred for 10 minutes to obtain solution E. 1 g of the modified hollow carbon spheres was dispersed in 100 ml of deionized water and stirred for 10 minutes to obtain solution F. Solution E was slowly dripped into solution F, and the mixture was continuously stirred rapidly for 40 minutes. The mixture was then centrifuged and dried to obtain the second precursor.

[0358] (3) 10 g of the second precursor was dissolved in 100 g of anhydrous ethanol, 1 g of polyacrylic acid was added, and mechanical stirring was performed for 30 minutes. The composite negative electrode material was obtained by spray drying while controlling the drying temperature at 100°C.

[0359] The composite negative electrode material prepared in this embodiment has a core-shell structure, wherein the core includes silicon, the shell includes a connecting layer, a buffer layer and a protective layer, the connecting layer is a polymer layer, the polymer layer is coated on the surface of the silicon particles, the buffer layer includes hollow carbon spheres, the protective layer is a polymer layer (polyacrylic acid), the buffer layer is filled between the connecting layer and the protective layer, and the polymer layer and the hollow carbon spheres in the buffer layer are connected by covalent bonds (carbon-oxygen bonds).

[0360] The composite negative electrode material prepared in this embodiment has a core-shell structure, wherein the core includes silicon, the shell includes a connecting layer and a protective layer, the connecting layer is a polymer layer, and the protective layer includes polyacrylic acid and hollow carbon spheres dispersed in the polyacrylic acid.

[0361] The median particle size of the composite negative electrode material is 2.6 μm and the specific surface area is 5.7 m 2 / g, the tap density of the powder is 0.89g / cm 3 The compacted density of the powder is 1.61g / cm 3The mass content of oxygen element in the composite negative electrode material is 4.9%, the mass content of carbon element in the composite negative electrode material is 27%, the thickness of the connecting layer is 20nm, the thickness of the buffer layer is 500nm, the thickness of the protective layer is 30nm, and the mass content of the protective layer in the composite negative electrode material is 5%.

[0362] Comparative Example 1

[0363] (1) Disperse 10 g of silicon material with a median particle size of 2 μm and hexadecyltrimethylammonium bromide in a mass ratio of 10:2 in 200 ml of deionized water, stir for 30 minutes, ultrasonicate for 10 minutes, and centrifuge to obtain the modified silicon material. Dissolve 1 g of hollow carbon spheres with a diameter of 100 nm and 1 g of polydiallyldimethylammonium chloride in 100 ml of deionized water, stir for 30 minutes, ultrasonicate for 20 minutes, and centrifuge to obtain the modified hollow carbon sphere material. Dissolve 10 g of the modified silicon material in 100 ml of deionized water and stir for 10 minutes to obtain solution E1. Disperse 1 g of the modified hollow carbon spheres in 100 ml of deionized water and stir for 10 minutes to obtain solution F1. Slowly drip solution E1 into solution F, continue to stir rapidly for 40 minutes, and centrifuge to obtain the composite product H1.

[0364] (2) 10 g of the composite H1 was dissolved in 100 g of anhydrous ethanol, 1 g of polyacrylic acid was added, and mechanical stirring was performed for 30 minutes. The composite negative electrode material was obtained by spray drying with the drying temperature controlled at 100°C.

[0365] The composite negative electrode material prepared in this comparative example includes silicon, a buffer layer and a protective layer coated on the surface of the silicon, the buffer layer is hollow carbon spheres, the protective layer is polypropylene, and there is no connecting layer on the surface of the silicon.

[0366] After testing, the median particle size of the composite negative electrode material is 2.2μm and the specific surface area is 8.5m 2 / g, the tap density of the powder is 0.8g / cm 3 , the powder compaction density is 1.1g / cm 3 The mass content of oxygen element in the composite negative electrode material is 25%, the mass content of carbon element in the composite negative electrode material is 15%, the thickness of the buffer layer is 500nm, and the mass content of the protective layer in the composite negative electrode material is 3%.

[0367] Comparative Example 2

[0368] (1) Silicon with a median particle size of 2 μm was placed in a rotary atmosphere furnace. Under the protection of an argon atmosphere, it was heated to 900°C at a heating rate of 3°C / min. Then, 0.5 L / min of acetylene gas was introduced so that the volume ratio of argon to acetylene in the rotary atmosphere furnace was 9:1. After keeping the temperature for 3 hours, the acetylene gas was turned off to obtain the first precursor.

[0369] (2) 10 g of the first precursor was dissolved in 100 ml of deionized water and stirred for 10 minutes to obtain solution E. 1 g of hollow carbon spheres was dispersed in 100 ml of deionized water and stirred for 10 minutes to obtain solution F. Solution E was slowly added dropwise to solution F and stirred rapidly for 40 minutes. The mixture was then centrifuged and dried to obtain the second precursor.

[0370] (3) 10 g of the second precursor was dissolved in 100 g of anhydrous ethanol, 1 g of polyacrylic acid was added, and mechanical stirring was performed for 30 minutes. The composite negative electrode material was obtained by spray drying while controlling the drying temperature at 100°C.

[0371] The composite negative electrode material prepared in this embodiment has a core-shell structure, wherein the core includes silicon, the shell includes a connecting layer, a buffer layer and a protective layer, the connecting layer is an amorphous carbon material layer, the amorphous carbon material layer is coated on the surface of the silicon particles, the buffer layer includes hollow carbon spheres, the protective layer is a polymer layer (polyacrylic acid), and the buffer layer is filled between the connecting layer and the protective layer.

[0372] The median particle size of the composite negative electrode material is 2.9 μm and the specific surface area is 9 m 2 / g, the tap density of the powder is 0.8g / cm 3 , the powder compaction density is 1.5g / cm 3 The mass content of oxygen element in the composite negative electrode material is 12%, the mass content of carbon element in the composite negative electrode material is 20%, the thickness of the connecting layer is 10nm, the thickness of the buffer layer is 400nm, the thickness of the protective layer is 40nm, and the mass content of the protective layer in the composite negative electrode material is 22%.

[0373] Test method:

[0374] 1) Median particle size of negative electrode material:

[0375] The median particle size test method refers to GB / T 19077-2016. It can be conveniently measured using a laser particle size analyzer, such as the Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0376] 2) Test method for specific surface area of ​​negative electrode material:

[0377] At constant temperature and low temperature, after measuring the adsorption amount of gas on the solid surface at different relative pressures, the monolayer adsorption amount of the sample is obtained based on the Brownauer-Ettel-Taylor adsorption theory and its formula (BET formula), thereby calculating the specific surface area of ​​the material.

[0378] 3) Test method for tap density:

[0379] Using a vibrator, weigh a certain amount of sample and vibrate 3000 times at 300 times / min to test the tap density.

[0380] 4) Test methods for oxygen content and carbon content:

[0381] The oxygen content was measured by Fourier transform infrared spectroscopy, and the carbon content was tested by thermogravimetric analysis.

[0382] 5) Test method for the size of hollow carbon materials:

[0383] The size of the hollow carbon materials was measured by atomic force microscopy (AFM) and high magnification transmission electron microscopy (HRTEM).

[0384] 6) Test method for thickness of connecting layer and protective layer:

[0385] The material was sectioned using a FIB-SEM device, and the average thickness of the connecting layer and the protective layer was measured in the SEM.

[0386] 7) Test method for bonding strength between hollow carbon material and connecting layer:

[0387] The maximum pulling force (F) required for a single hollow carbon material to be separated from the connecting layer was measured by a nanomechanical testing system and a probe testing system. In this embodiment and the comparative example, the bonding strength at 5 positions was tested, and the average value was calculated.

[0388] After the above tests, the composite negative electrode materials prepared in Examples 1 to 11 and Comparative Examples 1 to 2 have sample numbers S1 to S11 and R1 to R2, respectively. The performance parameters of the composite negative electrode materials are shown in Table 1:

[0389] Table 1

[0390]

[0391] 9) Electrochemical testing:

[0392] The negative electrode material was mixed with sodium carboxymethyl cellulose, styrene-butadiene rubber, conductive graphite (KS-6) and carbon black (SP) in a ratio of 92:2:2:2:2 to prepare a slurry, uniformly coated on copper foil and dried to form a negative electrode sheet, which was assembled into a button battery in an argon atmosphere glove box. The separator used was a polypropylene microporous membrane, the electrolyte used was 1 mol / L lithium hexafluorophosphate (the solvent was a mixed slurry of ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate), and the counter electrode used was a metal lithium sheet.

[0393] The above 13 groups of batteries were subjected to a discharge specific capacity test on a Blue Power CT2001A battery test system. The battery was discharged from the open circuit voltage to a voltage of 0.01V at 0.01C, and the specific capacity was the discharge specific capacity.

[0394] The above 13 groups of batteries were tested for their initial coulombic efficiency on a Blue Power CT2001A battery testing system with a charge and discharge current of 0.05C, and the initial coulombic efficiency was measured.

[0395] The above 13 groups of batteries were cycled for 100 cycles on a Blue Power CT2001A battery testing system with a charge and discharge current of 0.2C. After 100 cycles, the post-cycle battery capacity and post-cycle capacity retention rate were calculated.

[0396] Among them, the capacity retention rate after 100 cycles at 0.2C = 100th cycle discharge capacity / third cycle discharge capacity * 100%,

[0397] The expansion ratio of the electrode film after 100 cycles at 0.2C = (thickness of the electrode film after the 100th cycle - initial thickness of the electrode film) / initial thickness of the electrode film * 100%. The results are shown in Table 2.

[0398] Table 2 Parameter performance comparison of each battery

[0399]

[0400]

[0401] The composite negative electrode material of the present application has the advantages of low expansion and good cycle stability.

[0402] As shown in Table 2, the negative electrode materials prepared in Examples 1 to 11 are characterized by forming a connecting layer having a modified functional group on the surface of the silicon-based active material, and then subjecting the hollow carbon material having the surface functional group to a polymerization reaction with the first precursor, so that the connecting layer and the hollow carbon material are connected by a covalent bond. This can greatly improve the bonding strength between the hollow carbon material and the connecting layer, effectively tightly connecting the connecting layer and the hollow carbon material, and ensuring excellent electrical contact after volume expansion; the formed protective layer further enhances the conductivity and structural integrity of the composite negative electrode material, and can effectively inhibit side reactions caused by contact with the electrolyte; it is beneficial for the composite negative electrode material to maintain excellent mechanical properties, improve the structural stability of the composite negative electrode material, and thus improve the cycle stability.

[0403] During the preparation process of the negative electrode material of Comparative Example 1, no connecting layer was formed on the surface of the silicon element, and the hollow carbon spheres were attached to the surface of the silicon element particles, resulting in decreased connection stability. During the cycle, the expansion stress of the silicon particles caused the hollow carbon spheres to disconnect from the silicon, resulting in decreased electrical contact, decreased capacity retention rate of the material, and a significant increase in expansion rate.

[0404] During the preparation of the negative electrode material of Comparative Example 2, the connecting layer was not modified, and the hollow carbon material could not be connected to the connecting layer through a covalent bond. The two were connected by intermolecular forces, and the connection stability decreased. During the cycle, the expansion stress of the silicon particles easily caused the hollow carbon balls to disconnect from the silicon, the electrical contact decreased, the capacity retention rate of the material decreased, and the expansion rate increased significantly.

[0405] Although the present application is disclosed as above with preferred embodiments, it is not intended to limit the claims. Any person skilled in the art may make several possible changes and modifications without departing from the concept of the present application. Therefore, the scope of protection of the present application shall be based on the scope defined by the claims of the present application.

Claims

1. A composite negative electrode material, characterized in that The composite negative electrode material has a core-shell structure, wherein the core includes a silicon-based active material, and the shell includes a connecting layer, a buffer layer, and a protective layer. The connecting layer is coated on the surface of the silicon-based active material, and the buffer layer is filled between the connecting layer and the protective layer. The connecting layer includes at least one of an amorphous carbon material and a graphitized carbon material; and the buffer layer includes a hollow carbon material. The connecting layer and the buffer layer are connected via a covalent bond, wherein the covalent bond includes at least one of a carbon-oxygen bond, a carbon-nitrogen bond, a carbon-sulfur bond, a carbon-chlorine bond, and a fluorine-carbon bond.

2. A composite negative electrode material, characterized in that The composite negative electrode material has a core-shell structure, wherein the core includes a silicon-based active material, and the shell includes a connecting layer, a buffer layer, and a protective layer. The connecting layer is coated on the surface of the silicon-based active material, and the buffer layer is filled between the connecting layer and the protective layer. The average bonding force F between the connecting layer and the buffer layer is greater than 8 μN. The connecting layer includes at least one of an amorphous carbon material and a graphitized carbon material; and the buffer layer includes a hollow carbon material.

3. The composite negative electrode material according to claim 1 or 2, characterized in that Contains at least one of the following features (1) to (23): (1) The hollow carbon material includes at least one of hollow carbon spheres, hollow carbon rods, and hollow carbon tubes; (2) The hollow carbon material includes hollow carbon spheres, and the diameter of the hollow carbon spheres is 20 nm to 2000 nm; (3) The hollow carbon material comprises a hollow carbon sphere, and the wall thickness of the hollow carbon sphere is 5 nm to 500 nm; (4) The hollow carbon material comprises a hollow carbon rod, and the diameter of the hollow carbon rod is 10 nm to 1000 nm; (5) The hollow carbon material comprises a hollow carbon rod, and the length of the hollow carbon rod is 100 nm to 3000 nm; (6) The hollow carbon material comprises a hollow carbon rod, and the wall thickness of the hollow carbon rod is 5 nm to 500 nm; (7) The hollow carbon material comprises a hollow carbon tube, and the length of the hollow carbon tube is 30 nm-20 μm; (8) The hollow carbon material comprises a hollow carbon tube, and the wall thickness of the hollow carbon tube is 5 nm to 100 nm; (9) The hollow carbon material comprises a hollow carbon tube, and the diameter of the hollow carbon tube is 20 nm to 400 nm; (10) The median particle size D of the silicon-based active material 50 0.2µm~20µm; (11) The thickness of the buffer layer and the median particle size D of the silicon-based active material 50 The ratio is 1:(0.5-10); (12) The protective layer is coated on the surface of the buffer layer; (13) At least a portion of the protective layer is filled in the gaps between the hollow carbon materials; (14) The protective layer comprises at least one of a polymer, an amorphous carbon material, and a graphitized carbon material; (15) The thickness of the connecting layer is 5 nm to 200 nm; (16) The thickness of the protective layer is 5 nm to 500 nm; (17) The protective layer comprises a graphitized carbon material, wherein the graphitized carbon material is modified graphene containing a doping element; (18) The protective layer comprises a graphitized carbon material, wherein the graphitized carbon material is modified graphene containing a doping element, and the number of layers of the modified graphene is less than 10; (19) The protective layer comprises a graphitized carbon material, wherein the graphitized carbon material is modified graphene containing a doping element, wherein the doping element comprises at least one of oxygen, nitrogen and sulfur; (20) The protective layer comprises a graphitized carbon material, wherein the graphitized carbon material is modified graphene containing a doping element, and the mass content of the doping element in the graphitized carbon material is 1% to 20%; (21) The protective layer comprises a polymer, wherein the polymer comprises at least one of a diblock copolymer, a triblock copolymer, and a multiblock copolymer; (22) The protective layer comprises a polymer, and the mass content of the polymer in the composite negative electrode material is 1% to 20%; (23) The protective layer includes a polymer, and the polymer includes at least one of polyacrylic acid, polyacrylonitrile, polyimide, polyurethane, polydopamine, xanthan gum, polypyrrole, polythiophene, polyphenylene vinylene, polyaniline, polyacetylene and tannic acid.

4. A composite negative electrode material, characterized in that The composite negative electrode material has a core-shell structure, the core includes a silicon-based active material, the shell includes a connecting layer and a protective layer, the connecting layer is coated on the surface of the silicon-based active material, the connecting layer includes at least one of an amorphous carbon material and a graphitized carbon material; the protective layer includes a conductive substrate and a hollow carbon material dispersed in the conductive substrate, and the average bonding force F between the connecting layer and the hollow carbon material is greater than 8μN.

5. The composite negative electrode material according to claim 4, characterized in that Contains at least one of the following features (1) to (20): (1) The hollow carbon material includes at least one of hollow carbon spheres, hollow carbon rods, and hollow carbon tubes; (2) The hollow carbon material includes hollow carbon spheres, and the diameter of the hollow carbon spheres is 20 nm to 2000 nm; (3) The hollow carbon material comprises a hollow carbon sphere, and the wall thickness of the hollow carbon sphere is 5 nm to 500 nm; (4) The hollow carbon material comprises a hollow carbon rod, and the diameter of the hollow carbon rod is 10 nm to 1000 nm; (5) The hollow carbon material comprises a hollow carbon rod, and the length of the hollow carbon rod is 100 nm to 3000 nm; (6) The hollow carbon material comprises a hollow carbon rod, and the wall thickness of the hollow carbon rod is 5 nm to 500 nm; (7) The hollow carbon material comprises a hollow carbon tube, and the length of the hollow carbon tube is 30 nm-20 μm; (8) The hollow carbon material comprises a hollow carbon tube, and the wall thickness of the hollow carbon tube is 5 nm to 100 nm; (9) The hollow carbon material comprises a hollow carbon tube, and the diameter of the hollow carbon tube is 20 nm to 400 nm; (10) The protective layer is coated on the surface of the connecting layer; (11) The conductive substrate comprises at least one of a polymer, an amorphous carbon material, and a graphitized carbon material; (12) The thickness of the connecting layer is 5 nm to 200 nm; (13) The thickness of the protective layer is 5 nm to 500 nm; (14) The connecting layer comprises a graphitized carbon material, wherein the graphitized carbon material is modified graphene containing a doping element; (15) The connecting layer comprises a graphitized carbon material, wherein the graphitized carbon material is modified graphene containing a doping element, and the number of layers of the modified graphene is less than 10; (16) The connecting layer comprises a graphitized carbon material, wherein the graphitized carbon material is modified graphene containing a doping element, wherein the doping element comprises at least one of oxygen, nitrogen and sulfur; (17) The connecting layer comprises a graphitized carbon material, wherein the graphitized carbon material is modified graphene containing a doping element, and the mass content of the doping element in the graphitized carbon material is 1% to 20%; (18) The connecting layer comprises a polymer, wherein the polymer comprises at least one of a diblock copolymer, a triblock copolymer, and a multiblock copolymer; (19) The connecting layer comprises a polymer, and the mass content of the polymer in the composite negative electrode material is 1% to 20%; (20) The connecting layer includes a polymer, and the polymer includes at least one of polyacrylic acid, polyacrylonitrile, polyimide, polyurethane, polydopamine, xanthan gum, polypyrrole, polythiophene, polyphenylene vinylene, polyaniline, polyacetylene and tannic acid.

6. The composite negative electrode material according to any one of claims 1, 2 or 4, characterized in that: Contains at least one of the following features (1) to (11): (1) The silicon-based active material is a primary particle; (2) The silicon-based active material includes Si, SiO x and silicon alloy, wherein 0 <x<2; (3) The median particle size of the silicon-based active material is 0.2µm to 20µm; (4) The mass content of carbon element in the composite negative electrode material is 5% to 80%; (5) The mass content of oxygen in the composite negative electrode material is less than 20%; (6) The tap density of the composite negative electrode material is 0.2 g / cm 3 ~1.2g / cm 3 ; (7) The powder compaction density of the composite negative electrode material is 1.2 g / cm 3 ~1.8g / cm 3 ; (8) The median particle size of the composite negative electrode material is 0.2µm~20µm; (9) The specific surface area of ​​the composite negative electrode material is 1.0 m 2 / g~50m 2 / g; (10) Both the connecting layer and the protective layer comprise amorphous carbon materials; (11) Both the connecting layer and the protective layer include graphitized carbon material.

7. A method for preparing a composite negative electrode material, characterized in that: The following steps are involved: forming a connecting layer on the surface of the silicon-based active material, and using a modifying gas to impart a modified functional group to the connecting layer to obtain a first precursor, wherein the connecting layer comprises at least one of an amorphous carbon material and a graphitized carbon material, and the modified functional group is selected from at least one of a carboxyl group, a carbonyl group, an epoxy group, a nitrogen-containing functional group, a sulfur-containing functional group, a halogen-containing functional group, and derivative functional groups thereof; Performing a polymerization reaction on a mixed slurry comprising the first precursor and a buffer layer material having surface functional groups, wherein the buffer layer material comprises a hollow carbon material, and drying the mixture to obtain a second precursor; and The second precursor is coated to obtain a composite negative electrode material.

8. The method for preparing a composite negative electrode material according to claim 7, characterized in that: The preparation method comprises at least one of the following features (1) to (32): (1) The silicon-based active material is a primary particle; (2) The silicon-based active material includes Si, SiO x and silicon alloy, wherein 0 <x<2; (3) The median particle size of the silicon-based active material is 0.2µm to 20µm; (4) The step of forming a connecting layer on the surface of the silicon-based active material comprises: depositing a gaseous carbon source on the surface of the silicon-based active material by vapor deposition under a protective atmosphere to obtain a composite, and using a modifying gas to allow the connecting layer on the surface of the composite to have a modified functional group; (5) The step of forming a connecting layer on the surface of the silicon-based active material comprises: depositing a gaseous carbon source on the surface of the silicon-based active material by vapor deposition under a protective atmosphere to obtain a composite, and using a modified gas to make the connecting layer on the surface of the composite have a modified functional group, wherein the heating rate of the vapor deposition is 1°C / min-20°C / min; (6) The step of forming a connecting layer on the surface of the silicon-based active material comprises: depositing a gaseous carbon source on the surface of the silicon-based active material by vapor deposition under a protective atmosphere to obtain a composite, and using a modified gas to make the connecting layer on the surface of the composite have a modified functional group, wherein the temperature of the vapor deposition is 600°C to 1000°C; (7) The step of forming a connecting layer on the surface of the silicon-based active material comprises: depositing a gaseous carbon source on the surface of the silicon-based active material by vapor deposition under a protective atmosphere to obtain a composite, and using a modified gas to make the connecting layer on the surface of the composite have a modified functional group, wherein the gaseous carbon source comprises at least one of acetylene, methane, toluene, cyclohexane, ethanol, ethylene and propylene; (8) The step of forming a connecting layer on the surface of the silicon-based active material comprises: depositing a gaseous carbon source on the surface of the silicon-based active material by vapor deposition under a protective atmosphere to obtain a composite, and using a modified gas to make the connecting layer on the surface of the composite have modified functional groups, wherein the concentration of the gaseous carbon source is 0.1 L / min to 10 L / min; (9) The step of forming a connecting layer on the surface of the silicon-based active material comprises: depositing a gaseous carbon source on the surface of the silicon-based active material by vapor deposition under a protective atmosphere to obtain a composite, and using a modified gas to make the connecting layer on the surface of the composite have modified functional groups, wherein the vapor deposition is carried out for a holding time of 1 hour to 48 hours; (10) The step of forming a connecting layer on the surface of the silicon-based active material comprises: depositing a gaseous carbon source on the surface of the silicon-based active material by vapor deposition under a protective atmosphere to obtain a composite, and using a modifying gas to make the connecting layer on the surface of the composite have a modified functional group, wherein the modifying gas comprises at least one of oxygen, water vapor, ammonia, hydrogen sulfide, phosphine, hydrogen chloride, hydrogen fluoride, hydrogen bromide, nitric oxide, sulfur dioxide and chlorine; (11) The step of forming a connecting layer on the surface of the silicon-based active material comprises: depositing a gaseous carbon source on the surface of the silicon-based active material by vapor deposition under a protective atmosphere to obtain a composite, and using a modifying gas to make the connecting layer on the surface of the composite have a modified functional group, wherein the flow rate of the modifying gas is 0.5 L / min to 5 L / min; (12) The step of forming a connecting layer on the surface of the silicon-based active material comprises: depositing a gaseous carbon source on the surface of the silicon-based active material by vapor deposition under a protective atmosphere to obtain a composite, and using a modified gas to make the connecting layer on the surface of the composite have a modified functional group, wherein the time for introducing the modified gas is 0.5 h to 10 h; (13) The step of forming a connecting layer on the surface of the silicon-based active material comprises: depositing a gaseous carbon source on the surface of the silicon-based active material by vapor deposition under a protective atmosphere to obtain a composite, and using a modified gas to make the connecting layer on the surface of the composite have a modified functional group, wherein the protective atmosphere comprises at least one of helium, neon, argon, krypton and xenon; (14) The step of forming a connecting layer on the surface of the silicon-based active material comprises: depositing a gaseous carbon source on the surface of the silicon-based active material by vapor deposition under a protective atmosphere to obtain a composite, and using a modified gas to make the connecting layer on the surface of the composite have a modified functional group, wherein the volume ratio of the protective atmosphere to the gaseous carbon source is 10:(0.5-10); (15) The step of forming a connecting layer on the surface of the silicon-based active material comprises: depositing a gaseous carbon source on the surface of the silicon-based active material by vapor deposition under a protective atmosphere to obtain a composite, and using a modifying gas to make the connecting layer on the surface of the composite have a modified functional group, wherein the volume ratio of the protective atmosphere to the modifying gas is 10:(0.1-10); (16) The step of forming a connecting layer on the surface of the silicon-based active material comprises: depositing a gaseous carbon source on the surface of the silicon-based active material by vapor deposition under a protective atmosphere to obtain a composite; dispersing the composite in a first modifying solution containing a first modifier, performing solid-liquid separation, and drying to obtain a first precursor; (17) The step of forming a connecting layer on the surface of the silicon-based active material comprises: depositing a gaseous carbon source on the surface of the silicon-based active material by vapor deposition under a protective atmosphere to obtain a composite; dispersing the composite in a first modifying solution containing a first modifier, performing solid-liquid separation, and drying to obtain a first precursor, wherein the first modifier comprises an anionic surfactant; (18) The step of forming a connecting layer on the surface of the silicon-based active material comprises: depositing a gaseous carbon source on the surface of the silicon-based active material by vapor deposition under a protective atmosphere to obtain a composite; dispersing the composite in a first modified solution containing a first modifier, performing solid-liquid separation, and drying to obtain a first precursor, wherein the first modifier comprises at least one of hexadecyltrimethylammonium bromide, sodium hexadecyl sulfate, polyvinylpyrrolidone, and sodium polystyrene sulfonate; (19) The step of forming a connecting layer on the surface of the silicon-based active material comprises: depositing a gaseous carbon source on the surface of the silicon-based active material by vapor deposition under a protective atmosphere to obtain a composite; dispersing the composite in a first modifying solution containing a first modifier, performing solid-liquid separation, and drying to obtain a first precursor, wherein the mass ratio of the composite in the first modifying solution to the first modifier is 1:(0.05-1); (20) The step of forming a connecting layer on the surface of the silicon-based active material comprises: depositing a gaseous carbon source on the surface of the silicon-based active material by vapor deposition under a protective atmosphere to obtain a composite; dispersing the composite in a first modified solution containing a first modifier, performing solid-liquid separation, and drying to obtain a first precursor, wherein the solid-liquid separation comprises at least one of centrifugation, normal pressure filtration, and negative pressure filtration; (21) The step of forming a connecting layer on the surface of the silicon-based active material comprises: depositing a gaseous carbon source on the surface of the silicon-based active material by vapor deposition under a protective atmosphere to obtain a composite; dispersing the composite in a first modified solution containing a first modifier, performing solid-liquid separation, and drying to obtain a first precursor, wherein the drying temperature is 60°C to 200°C; (22) The step of forming a connecting layer on the surface of the silicon-based active material comprises: depositing a gaseous carbon source on the surface of the silicon-based active material by vapor deposition under a protective atmosphere to obtain a composite; dispersing the composite in a first modified solution containing a first modifier, performing solid-liquid separation, and drying to obtain a first precursor, wherein the dispersion method comprises at least one of mechanical stirring and ultrasonic dispersion; (23) When the first modifier is used to form a connecting layer having a modified functional group, the method further comprises heat-treating the dried product at a temperature of 600° C. to 900° C. for a time of 1 hour to 6 hours; (24) The step of forming a connecting layer on the surface of the silicon-based active material comprises: spray drying a mixed coating liquid containing the silicon-based active material and a polymer, so that a connecting layer is formed on the surface of the silicon-based active material, wherein the connecting layer comprises a polymer; (25) The step of forming a connecting layer on the surface of the silicon-based active material comprises: spray drying a mixed coating liquid containing the silicon-based active material and a polymer, so that a connecting layer is formed on the surface of the silicon-based active material, wherein the connecting layer comprises a polymer, wherein the solid content of the silicon-based active material in the mixed coating liquid is 5% to 50%; (26) The step of forming a connecting layer on the surface of the silicon-based active material comprises: spray drying a mixed coating liquid containing the silicon-based active material and a polymer, so that a connecting layer is formed on the surface of the silicon-based active material, wherein the connecting layer comprises a polymer, and wherein the mixed coating liquid comprises a polar solvent; (27) The step of forming a connecting layer on the surface of the silicon-based active material comprises: spray drying a mixed coating liquid containing the silicon-based active material and a polymer, so that a connecting layer is formed on the surface of the silicon-based active material, wherein the connecting layer comprises a polymer, wherein the polar solvent comprises at least one of water, anhydrous ethanol, methanol and isopropanol; (28) The step of forming a connecting layer on the surface of the silicon-based active material comprises: spray drying a mixed coating liquid containing the silicon-based active material and a polymer, so that a connecting layer is formed on the surface of the silicon-based active material, wherein the connecting layer comprises a polymer, wherein the mass ratio of the silicon-based active material to the polymer is 10:(0.1-5); (29) The step of forming a connecting layer on the surface of the silicon-based active material comprises: spray drying a mixed coating liquid containing the silicon-based active material and a polymer, so that a connecting layer is formed on the surface of the silicon-based active material, wherein the connecting layer comprises a polymer, wherein the drying temperature of the spray drying is 60°C to 200°C; (30) The step of forming a connecting layer on the surface of the silicon-based active material comprises: spray drying a mixed coating liquid containing the silicon-based active material and a polymer, so that a connecting layer is formed on the surface of the silicon-based active material, wherein the connecting layer comprises a polymer, wherein the polymer comprises at least one of a diblock copolymer, a triblock copolymer, and a multiblock copolymer; (31) The step of forming a connecting layer on the surface of the silicon-based active material comprises: spray-drying a mixed coating liquid containing the silicon-based active material and a polymer, so that a connecting layer is formed on the surface of the silicon-based active material, wherein the connecting layer comprises a polymer, wherein the polymer comprises at least one of polyacrylic acid, polyacrylonitrile, polyimide, polyurethane, polydopamine, xanthan gum, polypyrrole, polythiophene, polyphenylene vinylene, polyaniline, polyacetylene and tannic acid; (32) The step of forming a connecting layer on the surface of the silicon-based active material comprises: spray-drying a mixed coating liquid containing the silicon-based active material and a polymer, so that a connecting layer is formed on the surface of the silicon-based active material, wherein the connecting layer comprises a polymer, wherein the polymer has a modified functional group.

9. The method for preparing a composite negative electrode material according to claim 7 or 8, characterized in that: The preparation method comprises at least one of the following features (1) to (20): (1) In the mixed slurry, the mass ratio of the first precursor to the buffer layer material having surface functional groups is 1:(0.01-2); (2) The solid content of the first precursor in the mixed slurry is 2% to 50%; (3) The solid content of the buffer layer material having surface functional groups in the mixed slurry is 0.5% to 25%; (4) The mixed slurry also includes an active agent; (5) The mixed slurry further includes an active agent, and the mass ratio of the first precursor to the active agent in the mixed slurry is 1:(0.1-0.5); (6) The mixed slurry further includes an active agent, which is selected from at least one of polydiallyldimethylammonium chloride, aminopropyltriethoxysilane, a silane coupling agent, hexadecyltrimethylammonium bromide, sodium hexadecyl sulfate, polyvinylpyrrolidone, and sodium polystyrene sulfonate; (7) The drying method is spray drying; (8) The drying method is spray drying, and the spray drying temperature is 100°C to 200°C; (9) The drying method is spray drying, and the feed rate of the spray drying is 100 mL / min-1000 mL / min; (10) The steps of preparing the buffer layer material having surface functional groups include: dispersing the buffer layer material in a second modifying solution containing a second modifier, performing a modification treatment, performing solid-liquid separation, and drying to obtain the buffer layer material having surface functional groups; (11) The step of preparing a buffer layer material having surface functional groups comprises: dispersing the buffer layer material in a second modifying solution containing a second modifying agent, performing a modification treatment, performing solid-liquid separation, and drying to obtain the buffer layer material having surface functional groups, wherein the second modifying agent comprises a cationic surfactant; (12) The step of preparing a buffer layer material having surface functional groups comprises: dispersing the buffer layer material in a second modifying solution containing a second modifier, performing a modification treatment, performing solid-liquid separation, and drying to obtain the buffer layer material having surface functional groups, wherein the second modifier comprises at least one of polydiallyldimethylammonium chloride, aminopropyltriethoxysilane, and a silane coupling agent; (13) The step of preparing a buffer layer material having surface functional groups comprises: dispersing the buffer layer material in a second modifying solution containing a second modifier, performing a modification treatment, performing solid-liquid separation, and drying to obtain the buffer layer material having surface functional groups, wherein the mass ratio of the buffer layer material to the second modifier in the second modifying solution is 1:(0.5-10); (14) The step of preparing a buffer layer material having surface functional groups comprises: dispersing the buffer layer material in a second modifying solution containing a second modifier to perform a modification treatment, performing solid-liquid separation, and drying to obtain the buffer layer material having surface functional groups, wherein the second modifying solution comprises a polar solvent; (15) The step of preparing a buffer layer material having surface functional groups comprises: dispersing the buffer layer material in a second modifying solution containing a second modifier, performing a modification treatment, performing solid-liquid separation, and drying to obtain the buffer layer material having surface functional groups, wherein the polar solvent comprises at least one of water, anhydrous ethanol, methanol, and isopropanol; (16) The coating treatment includes carbon coating treatment and / or polymer coating treatment; (17) performing a carbon coating treatment on the second precursor, comprising: introducing a gaseous carbon source into the second precursor, heating the gaseous carbon source until a thermal cracking reaction occurs, so that a protective layer is deposited on the surface of the second precursor, wherein the protective layer comprises at least one of an amorphous carbon material and a graphitized carbon material; (18) The step of coating the second precursor with a polymer comprises: spray drying a mixed coating liquid comprising the second precursor and a polymer, so that a protective layer is formed on the surface of the second precursor, wherein the protective layer comprises a polymer; (19) The step of coating the second precursor with a polymer comprises spray drying a mixed coating liquid containing the second precursor and a polymer, so that a protective layer is formed on the surface of the second precursor, wherein the protective layer comprises a polymer, wherein the polymer comprises at least one of polyacrylic acid, polyacrylonitrile, polyimide, polyurethane, polydopamine, xanthan gum, polypyrrole, polythiophene, polyphenylene vinylene, polyaniline, polyacetylene and tannic acid; (20) The step of subjecting the second precursor to polymer coating treatment comprises: spray-drying a mixed coating liquid comprising the second precursor and a polymer, so that a protective layer is formed on the surface of the second precursor, wherein the protective layer comprises a polymer, wherein the mass ratio of the second precursor to the polymer is 10:(0.1-5).

10. A lithium ion battery, characterized in that: The negative electrode material comprises the composite negative electrode material according to any one of claims 1 to 6 or the negative electrode material prepared according to the method for preparing the composite negative electrode material according to any one of claims 7 to 9.

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