Negative electrode material, method for preparing the same, and lithium ion secondary battery

Abstract

The application relates to a negative electrode material and a preparation method thereof, and a lithium ion secondary battery. The negative electrode material comprises a silicon-based active substance, the surface of the silicon-based active substance has a Si-R bond, wherein R comprises at least one of H, COOH, CHO or NH2, and the pH value of the silicon-based active substance is 3-7. The negative electrode material of the application is beneficial to maintaining the interface stability of the silicon-based active substance, reducing the side reaction of the silicon-based active substance, and thus improving the cycle performance of the negative electrode material.

Description

Technical Field

[0001] This invention relates to the field of negative electrode materials technology, and in particular to negative electrode materials and their preparation methods, and lithium-ion secondary batteries. Background Technology

[0002] Lithium-ion batteries possess advantages such as high energy density, long cycle life, low environmental pollution, and no memory effect, making them widely used in electric vehicles and consumer electronics. The rapid development of electric vehicles in recent years has led to a growing demand for higher energy density lithium-ion batteries, prompting researchers to search for battery materials with even higher energy density and better cycle performance. The positive and negative electrode materials are the core of the battery, determining its efficiency. Currently, the commercially available negative electrode material is graphite, whose capacity is nearing its theoretical limit, with limited room for further improvement. Therefore, there is an urgent need to develop a new generation of high-energy-density negative electrode materials. Among them, silicon-based negative electrode materials are widely considered the next-generation battery negative electrode material, possessing advantages such as high capacity, abundant sources, and relative safety.

[0003] However, silicon anodes experience severe volume expansion during cycling, leading to material pulverization and breakage, and rapid battery degradation. To address this issue, multiple solutions exist, including structural design of silicon using nano-sizing and porous technologies; composite coating; and modification of silicon electrodes with novel electrolytes and binders. Nano-sizing is currently one of the mainstream directions. Reducing silicon size to the nanometer scale can decrease silicon expansion and prevent pulverization. However, existing nano-sizing solutions still have many shortcomings in addressing silicon performance issues, and there is significant room for improvement in long-cycle performance. Summary of the Invention

[0004] The purpose of this application is to provide an anode material and its preparation method, as well as a lithium-ion secondary battery. The anode material provided by this application is beneficial to maintaining the interfacial stability of silicon-based active materials, reducing side reactions of silicon-based active materials, and thus improving the cycle performance of the anode material.

[0005] In a first aspect, this application provides a negative electrode material comprising a silicon-based active material having Si-R bonds on its surface, wherein R includes at least one of H, COOH, CHO or NH2, and the pH value of the silicon-based active material is 3 to 7.

[0006] In some embodiments, the average particle size of the silicon-based active material is 1 nm to 500 nm.

[0007] In some embodiments, the silicon-based active material includes at least one of crystalline silicon, silicon oxide, amorphous silicon, silicon alloy, and a composite of crystalline and amorphous silicon.

[0008] In some embodiments, the silicon-based active material includes silicon particles and a silicon oxide layer located on the surface of the silicon particles.

[0009] In some embodiments, the silicon-based active material includes silicon particles and a silicon oxide layer on the surface of the silicon particles, and the mass content of oxygen atoms in the silicon-based active material is 1% to 18% based on 100% of the mass of the silicon-based active material.

[0010] In some embodiments, the negative electrode material further includes carbon material located on at least a portion of the surface of the silicon-based active material.

[0011] In some embodiments, the silicon-based active material in the negative electrode material has a mass content of 99% or greater.

[0012] In some embodiments, the carbon material is present on the surface of the silicon-based active material and / or dispersed between the silicon-based active material.

[0013] In some embodiments, the carbon material includes at least one of amorphous carbon, graphene, graphite, carbon nanotubes, and carbon fibers.

[0014] In some embodiments, the median particle size of the negative electrode material is 1 μm to 10 μm.

[0015] In some embodiments, the specific surface area of ​​the negative electrode material is ≤5m². 2 / g.

[0016] In some embodiments, the silicon-based active material is mixed with ethanol to form a slurry with a solid content of 5% to 30%, and the zeta potential of the slurry is tested using a zeta potential tester, wherein the absolute value of the zeta potential of the slurry is ≥20mV.

[0017] Secondly, this application provides a method for preparing a negative electrode material, comprising the following steps:

[0018] The silicon raw material undergoes a first surface treatment to obtain primary particles with exposed surfaces;

[0019] The primary particles are subjected to surface modification treatment to obtain a silicon-based active material; the negative electrode material includes the silicon-based active material, the surface of the silicon-based active material includes Si-R bonds, wherein R includes at least one of H, COOH, CHO or NH2, and the pH value of the silicon-based active material is 3 to 7.

[0020] In some embodiments, the silicon raw material includes elemental silicon.

[0021] In some embodiments, the silicon raw material comprises elemental silicon, which includes crystalline silicon and / or amorphous silicon.

[0022] In some embodiments, the silicon raw material comprises elemental silicon, wherein the elemental silicon has an average particle size of 1 nm to 100 nm.

[0023] In some embodiments, the silicon raw material comprises elemental silicon, wherein the mass content of silicon element in the elemental silicon is greater than or equal to 97%.

[0024] In some embodiments, the silicon raw material is prepared from a silicon source precursor.

[0025] In some embodiments, the silicon raw material is prepared from a silicon source precursor, which includes at least one of a gaseous silicon source and a liquid silicon source.

[0026] In some embodiments, the silicon raw material is prepared from a silicon source precursor, which includes a gaseous silicon source, and the gaseous silicon source includes at least one of silane, disilane, monochlorosilane, and dichlorosilane.

[0027] In some embodiments, the silicon raw material is prepared from a silicon source precursor, the silicon source precursor including a liquid silicon source, the liquid silicon source including at least one of trichlorosilane or tetrachlorosilane.

[0028] In some embodiments, the first surface treatment includes at least one of a crushing treatment or an etching treatment.

[0029] In some embodiments, the step of performing a first surface treatment on the silicon material includes: etching the silicon material using an etching solution.

[0030] In some embodiments, the step of performing a first surface treatment on the silicon raw material includes: etching the silicon raw material with an etching solution, wherein the etching solution includes at least one of potassium hydroxide solution, ammonium hydroxide solution, tetramethylhydroxylamine solution, hydrofluoric acid solution, buffer oxide etchant BOE, HF / EG solution, and SCl solution.

[0031] In some embodiments, the step of performing a first surface treatment on the silicon raw material includes: etching the silicon raw material with an etching solution, wherein the concentration of hydrogen ions in the etching solution is 1 mol / L to 12 mol / L.

[0032] In some embodiments, the step of performing a first surface treatment on the silicon raw material includes: crushing the silicon raw material to obtain primary particles, wherein the average particle size of the primary particles is 1 μm to 100 μm.

[0033] In some embodiments, the surface modification treatment includes at least one of amination and acid leaching.

[0034] In some embodiments, the surface modification treatment includes an amination treatment, which is carried out in a compound containing an amino group.

[0035] In some embodiments, the surface modification treatment includes an amination treatment, which is carried out in a substance containing amino groups, wherein the amino-containing compound includes at least one of ammonia, ammonium chloride, ammonium sulfate, ammonium bicarbonate, ammonium carbonate, ammonium bisulfate, ammonium nitrate, ammonium fluoride, ammonium iodide, ammonium bromide, ammonium methoxide, or hydrazine.

[0036] In some embodiments, the surface modification treatment includes an acid immersion treatment, which is carried out in a compound containing a carboxyl group.

[0037] In some embodiments, the surface modification treatment includes an acid leaching treatment, which is carried out in a carboxyl-containing compound, the carboxyl-containing compound including at least one of fatty acids and aromatic acids.

[0038] In some embodiments, the surface modification treatment includes an acid immersion treatment, which is carried out in a carboxyl-containing compound, including at least one of formic acid, acetic acid, propionic acid, and octanoic acid.

[0039] In some embodiments, the surface modification treatment includes an acid immersion treatment, which is carried out in a carboxyl-containing compound, including at least one of benzoic acid, phenylacetic acid, phthalic acid, and 3-nitrophthalic acid.

[0040] In some embodiments, the surface modification treatment includes physical treatment.

[0041] In some embodiments, the surface modification treatment includes physical treatment, which includes at least one of ball milling, sand milling, grinding, or air jet milling.

[0042] In some embodiments, the surface modification treatment includes a physical treatment performed under a protective atmosphere.

[0043] In some embodiments, the surface modification treatment includes a physical treatment performed under a protective atmosphere, which includes at least one of nitrogen, helium, neon, argon, krypton, and xenon.

[0044] In some embodiments, the method further includes:

[0045] The silicon-based active material obtained by cooling is subjected to carbon coating treatment to obtain the negative electrode material; the carbon coating treatment includes at least one of solid phase carbon coating, liquid phase carbon coating and gas phase carbon coating.

[0046] In some embodiments, the carbon coating process specifically includes: heating the silicon-based active material obtained by cooling treatment, and then introducing a protective gas and a carbon source gas, wherein the carbon source gas undergoes thermal decomposition to obtain a negative electrode material.

[0047] In some embodiments, the carbon coating process specifically includes: heating the silicon-based active material obtained by cooling treatment, and then introducing a protective gas and a carbon source gas, wherein the carbon source gas undergoes thermal decomposition to obtain a negative electrode material, wherein the carbon source gas is a hydrocarbon.

[0048] In some embodiments, the carbon coating process specifically includes: heating the silicon-based active material obtained by cooling treatment, and then introducing a protective gas and a carbon source gas, wherein the carbon source gas undergoes thermal decomposition to obtain a negative electrode material; wherein the carbon source gas includes at least one of methane, ethylene, acetylene, propyne, propylene, propane, toluene, benzene, styrene and phenol.

[0049] In some embodiments, the carbon coating process specifically includes: heating the silicon-based active material obtained by cooling treatment, and then introducing a protective gas and a carbon source gas, wherein the carbon source gas undergoes thermal decomposition to obtain a negative electrode material; wherein the thermal decomposition temperature is 600℃~1000℃ and the thermal decomposition time is 30min~24h.

[0050] In some embodiments, the carbon coating process specifically includes: carbonizing a mixture obtained by mixing a silicon-based active material obtained by cooling with a solid carbon source to obtain a negative electrode material.

[0051] In some embodiments, the carbon coating process specifically includes: carbonizing a mixture obtained by mixing a silicon-based active material obtained by cooling with a solid carbon source to obtain a negative electrode material; wherein the carbonization temperature is 500℃~1000℃ and the carbonization time is 30min~24h.

[0052] In some embodiments, the carbon coating process specifically includes: carbonizing a mixture obtained by mixing a silicon-based active material obtained by cooling with a solid carbon source to obtain a negative electrode material; wherein the solid carbon source includes at least one of sugars, esters, hydrocarbons, organic acids and polymers.

[0053] In some embodiments, the carbon coating process specifically includes: carbonizing a mixture obtained by mixing a silicon-based active material obtained through cooling treatment with a solid carbon source to obtain a negative electrode material; wherein the solid carbon source includes at least one of polyvinyl chloride, polyvinyl butyral, polyacrylonitrile, polyacrylic acid, polyethylene glycol, polypyrrole, polyaniline, sucrose, glucose, maltose, citric acid, asphalt, furfural resin, epoxy resin, and phenolic resin.

[0054] In some embodiments, the carbon coating process specifically includes: carbonizing a mixture obtained by mixing a silicon-based active material obtained by cooling treatment with a solid carbon source to obtain a negative electrode material; wherein the mass ratio of the solid carbon source to the active material is (10-100):(5-80).

[0055] Thirdly, this application also provides a lithium-ion secondary battery, which includes the negative electrode material described in the first aspect or the negative electrode material prepared by the negative electrode material preparation method described in the second aspect.

[0056] Compared with the prior art, the technical solution of this application has at least the following beneficial effects:

[0057] The negative electrode material provided in this application includes a silicon-based active material. The surface of the silicon-based active material includes Si-R bonds, where R includes at least one of -H, -COOH, -CHO, or -NH2. The Si-R bonds hydrolyze in aqueous solution to release H2. + This can improve the pH value of silicon-based active materials, reduce the situation where the pH value of silicon-based active materials is too acidic or too alkaline, reduce the combination of silicon-based active materials with other elements (especially oxygen), and reduce the impact on the activity of silicon-based active materials.

[0058] In addition, during the production of silicon-based active materials, because silicon-based active materials are nanoscale and have a large specific surface area, they can easily adhere to the human body surface. Controlling the pH value of nanoscale silicon-based active materials within the range of 3 to 7 can reduce the damage to human skin caused by nanoscale silicon-based active materials.

[0059] The method for preparing the negative electrode material provided in this application involves a first surface treatment of the silicon raw material, which cleans the surface of the silicon raw material, resulting in exposed primary particles. The crystal lattice terminates at the exposed surface of the primary particles, ensuring that each silicon atom on the outermost layer of the primary particle surface has an unpaired electron, i.e., an unsaturated bond, called a dangling bond. Due to the abundance of dangling bonds on the exposed surface of the primary particles, during the surface modification process, these dangling bonds can act as active sites, recombinating with -H, -COOH, -CHO, or -NH2 to form strong Si-H, Si-COOH, Si-CHO, or Si-NH2 bonds. This reduces the binding of silicon-based active materials with other elements (especially oxygen), thus reducing the impact on the activity of the silicon-based active materials. Furthermore, when the negative electrode material is used in a battery, it readily hydrolyzes and releases H+ upon contact with the electrolyte. + This can improve the pH value of silicon-based active materials, making the pH value of silicon-based active materials 3 to 7, reducing the situation of excessive acidity or alkalinity in the electrolyte system, and improving the cycle performance of the battery. Attached Figure Description

[0060] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0061] Figure 1 A scanning electron microscope (SEM) image of the negative electrode material prepared in Example 1 of this application;

[0062] Figure 2 The image shows the XRD pattern of the negative electrode material prepared in Example 1 of this application.

[0063] Figure 3 The first charge-discharge curve of the negative electrode material prepared in Example 1 of this application;

[0064] Figure 4 The cycling performance curve of the negative electrode material prepared in Example 1 of this application. Detailed Implementation

[0065] To better understand the technical solution of the present invention, the embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0066] It should be understood that the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0067] The terminology used in the embodiments of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms “a,” “the,” and “the” as used in the embodiments of this invention and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0068] It should be understood that the term "and / or" used in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this article generally indicates that the preceding and following related objects have an "or" relationship.

[0069] In a first aspect, this application provides a negative electrode material, wherein the negative electrode material is a silicon-based active material, the surface of the silicon-based active material has Si-R bonds, wherein R includes at least one of H, COOH, CHO or NH2, and the pH value of the silicon-based active material is 3 to 7.

[0070] The negative electrode material provided in this application includes a silicon-based active material. The surface of the silicon-based active material includes Si-R bonds, where R includes at least one of -H, -COOH, -CHO, or -NH2. The Si-R bonds hydrolyze in aqueous solution to release H2. + This can improve the pH value of silicon-based active materials, reduce the situation where the pH value of silicon-based active materials is too acidic or too alkaline, reduce the combination of silicon-based active materials with other elements (especially oxygen), and reduce the impact on the activity of silicon-based active materials.

[0071] In addition, during the production of silicon-based active materials, because silicon-based active materials are nanoscale and have a large specific surface area, they can easily adhere to the human body surface. Controlling the pH value of nanoscale silicon-based active materials within the range of 3 to 7 can reduce the damage to human skin caused by nanoscale silicon-based active materials.

[0072] Specifically, the pH value of the silicon-based active material can be 3, 3.1, 3.2, 3.3, 3.4, 3.5, 3.8, 4, 4.3, 4.5, 4.6, 4.7, 5, 5.3, 5.5, 5.7, 5.8, 5.9, 6 or 7, etc., and is not limited here.

[0073] In some embodiments, the average particle size of the silicon-based active material is 1 nm to 500 nm, specifically 1 nm, 5 nm, 10 nm, 50 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, or 500 nm, etc., and of course, other values ​​within the above range are also possible, and are not limited here. Preferably, the average particle size of the silicon-based active material is 1 nm to 200 nm, and more preferably, the average particle size of the silicon-based active material is 5 nm to 100 nm.

[0074] In some embodiments, the silicon-based active material includes at least one of crystalline silicon, silicon oxide, amorphous silicon, silicon alloy, or a composite of crystalline and amorphous silicon.

[0075] In some embodiments, the silicon-based active material includes silicon particles and a silicon oxide layer located on the surface of the silicon particles.

[0076] In some embodiments, the silicon-based active material includes silicon particles and a silicon oxide layer on the surface of the silicon particles. The mass content of oxygen atoms in the silicon-based active material, calculated as 100% by mass, is 1% to 18%. Specifically, the mass content of oxygen atoms in the silicon-based active material can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, or 18%, etc., and is not limited thereto. Controlling the mass content of oxygen atoms in the silicon-based active material within the above range is beneficial for forming a stable silicon oxide layer on the surface of the silicon particles, reducing direct contact between the silicon particles and the electrolyte, thereby reducing side reactions between the silicon-based active material and the electrolyte, and improving the cycle stability of the negative electrode material. It also ensures stable activity of the silicon-based active material, increasing the specific capacity of the negative electrode material.

[0077] In some embodiments, the negative electrode material further includes carbon material located on at least a portion of the surface of the silicon-based active material.

[0078] In some embodiments, the silicon-based active material in the negative electrode material has a mass content of 99% or greater.

[0079] In some embodiments, the carbon material is present on the surface of the silicon-based active material and / or dispersed between the silicon-based active material.

[0080] In some embodiments, the carbon material includes at least one of amorphous carbon, graphene, graphite, carbon nanotubes, and carbon fibers.

[0081] In some embodiments, the median particle size of the negative electrode material is 1 μm to 10 μm, specifically 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm, etc., and of course, other values ​​within the above range are also possible, and are not limited here. Controlling the median particle size of the negative electrode material within the above range is beneficial to improving the capacity and cycle performance of the negative electrode material.

[0082] In some embodiments, the specific surface area of ​​the negative electrode material is ≤5m². 2 / g, specifically 0.5m 2 / g, 1m 2 / g, 1.5m 2 / g、2m 2 / g, 2.5m 2 / g、3m 2 / g, 3.5m 2 / g、4m 2 / g, 4.5m 2 / g or 5m 2 / g, etc., can also be other values ​​within the above range, and are not limited here. Understandably, controlling the specific surface area of ​​the negative electrode material within the above range is beneficial for suppressing volume expansion and improving the material's cycle performance.

[0083] In some embodiments, the silicon-based active material is mixed with ethanol to form a slurry with a solid content of 5% to 30%. The zeta potential of the slurry is tested using a zeta potential analyzer. The absolute value of the zeta potential of the slurry is ≥20mV, specifically 20mV, 25mV, 30mV, 35mV, 40mV, 45mV, or 50mV, etc., and other values ​​within the above range are also possible, without limitation. It is understood that controlling the absolute value of the zeta potential of the slurry within the above range can improve the dispersibility and stability of the slurry, inhibit particle aggregation and deposition, reduce electrode resistance and polarization, and also improve the interfacial stability of the silicon-based active material, reduce interfacial side reactions of the silicon-based active material, thereby improving the cycle performance of the negative electrode material.

[0084] Secondly, this application provides a method for preparing a negative electrode material, comprising the following steps:

[0085] The silicon raw material undergoes a first surface treatment to obtain primary particles with exposed surfaces;

[0086] The primary particles are subjected to surface modification treatment to obtain a silicon-based active material. The negative electrode material includes the silicon-based active material. The surface of the silicon-based active material includes Si-R bonds, wherein R includes at least one of H, COOH, CHO or NH2, and the pH value of the silicon-based active material is 3 to 7.

[0087] The method for preparing the negative electrode material provided in this application involves a first surface treatment of the silicon raw material, which cleans the surface of the silicon raw material, resulting in exposed primary particles. The crystal lattice terminates at the exposed surface of the primary particles, ensuring that each silicon atom on the outermost layer of the primary particle surface has an unpaired electron, i.e., an unsaturated bond, called a dangling bond. Due to the abundance of dangling bonds on the exposed surface of the primary particles, during the surface modification process, these dangling bonds can act as active sites, recombinating with -H, -COOH, -CHO, or -NH2 to form strong Si-H, Si-COOH, Si-CHO, or Si-NH2 bonds. This reduces the binding of silicon-based active materials with other elements (especially oxygen), thus reducing the impact on the activity of the silicon-based active materials. Furthermore, when the negative electrode material is used in a battery, it readily hydrolyzes and releases H+ upon contact with the electrolyte. + This can improve the pH value of silicon-based active materials, making the pH value of silicon-based active materials 3 to 7, reducing the situation of excessive acidity or alkalinity in the electrolyte system, and improving the cycle performance of the battery.

[0088] In some embodiments, the silicon raw material includes elemental silicon.

[0089] In some embodiments, the silicon raw material comprises elemental silicon, which includes crystalline silicon and / or amorphous silicon.

[0090] In some embodiments, the silicon raw material includes elemental silicon, the average particle size of which is 1nm to 100nm, specifically 1nm, 5nm, 10nm, 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm or 100nm, etc., and of course, other values ​​within the above range are also possible, which are not limited here.

[0091] In some embodiments, the silicon raw material comprises elemental silicon, wherein the mass content of silicon element in the elemental silicon is greater than or equal to 97%.

[0092] In some embodiments, the silicon raw material is prepared from a silicon source precursor.

[0093] In some embodiments, the silicon raw material is prepared from a silicon source precursor, which includes at least one of a gaseous silicon source and a liquid silicon source.

[0094] In some embodiments, the silicon raw material is prepared from a silicon source precursor, which includes a gaseous silicon source, and the gaseous silicon source includes at least one of silane, disilane, monochlorosilane, and dichlorosilane.

[0095] In some embodiments, the silicon raw material is prepared from a silicon source precursor, the silicon source precursor including a liquid silicon source, the liquid silicon source including at least one of trichlorosilane or tetrachlorosilane.

[0096] In some embodiments, the first surface treatment includes at least one of a crushing treatment or an etching treatment.

[0097] In some embodiments, the step of performing a first surface treatment on the silicon material includes: etching the silicon material using an etching solution.

[0098] In some embodiments, the step of performing a first surface treatment on the silicon raw material includes: etching the silicon raw material with an etching solution, wherein the etching solution includes at least one of potassium hydroxide solution, ammonium hydroxide solution, tetramethylhydroxylamine solution, hydrofluoric acid solution, buffer oxide etchant BOE, HF / EG solution, and SCl solution.

[0099] Specifically, buffered oxide etchant BOE is a mixture of HF and NH4F in different proportions, where HF is the main etching solution and NH4F acts as a buffer. Concentrated HF etches silicon raw materials too quickly. Buffered oxide etchant BOE has advantages such as high etching rate, easy etching control, and high dissolving power. Using buffered oxide etchant BOE to etch silicon raw materials is beneficial for controlling the etching rate.

[0100] Specifically, the HF / EG solution is a mixture of 49% hydrofluoric acid and ethylene glycol in a ratio of approximately 4:96.

[0101] Specifically, SC1 solution is a mixture of ammonium hydroxide, hydrogen peroxide, and water. At 60℃~70℃, SC1 (ammonium hydroxide: hydrogen peroxide: water = 1:2:50) exhibits a low etching rate for silicon raw materials, approximately... It allows for precise control of the etching rate of silicon raw materials.

[0102] In some embodiments, the step of performing the first surface treatment on the silicon raw material includes: etching the silicon raw material with an etching solution, wherein the concentration of hydrogen ions in the etching solution is 1 mol / L to 12 mol / L, specifically 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, 5 mol / L, 6 mol / L, 7 mol / L, 8 mol / L, 9 mol / L, 10 mol / L, 11 mol / L, or 12 mol / L, etc., and of course, other values ​​within the above range are also possible, which are not limited here.

[0103] In some embodiments, the step of performing a first surface treatment on the silicon raw material includes: crushing the silicon raw material to obtain primary particles, wherein the average particle size of the primary particles is 1μm to 100μm, specifically 1μm, 5μm, 10μm, 20μm, 30μm, 40μm, 50μm, 60μm, 70μm, 80μm, 90μm or 100μm, etc., and of course, other values ​​within the above range are also possible, which are not limited here.

[0104] In some embodiments, the surface modification treatment includes at least one of amination and acid leaching.

[0105] In some embodiments, the surface modification treatment includes an amination treatment, which is carried out in a compound containing an amino group.

[0106] In some embodiments, the surface modification treatment includes an amination treatment, which is carried out in a substance containing amino groups, wherein the amino-containing compound includes at least one of ammonia, ammonium chloride, ammonium sulfate, ammonium bicarbonate, ammonium carbonate, ammonium bisulfate, ammonium nitrate, ammonium fluoride, ammonium iodide, ammonium bromide, ammonium methoxide, or hydrazine.

[0107] In some embodiments, the surface modification treatment includes an acid immersion treatment, which is carried out in a compound containing a carboxyl group.

[0108] In some embodiments, the surface modification treatment includes an acid leaching treatment, which is carried out in a carboxyl-containing compound, the carboxyl-containing compound including at least one of fatty acids and aromatic acids.

[0109] In some embodiments, the surface modification treatment includes an acid immersion treatment, which is carried out in a carboxyl-containing compound, including at least one of formic acid, acetic acid, propionic acid, and octanoic acid.

[0110] In some embodiments, the surface modification treatment includes an acid immersion treatment, which is carried out in a carboxyl-containing compound, including at least one of benzoic acid, phenylacetic acid, phthalic acid, and 3-nitrophthalic acid.

[0111] In some embodiments, the surface modification treatment includes physical treatment.

[0112] In some embodiments, the surface modification treatment includes physical treatment, which includes at least one of ball milling, sand milling, grinding, or air jet milling.

[0113] In some embodiments, the surface modification treatment includes a physical treatment performed under a protective atmosphere.

[0114] In some embodiments, the protective atmosphere includes at least one of nitrogen, helium, neon, argon, krypton, and xenon.

[0115] In some embodiments, the method further includes:

[0116] The silicon-based active material obtained by cooling is subjected to carbon coating treatment to obtain a negative electrode material; the carbon coating treatment includes at least one of solid phase carbon coating, liquid phase carbon coating and gas phase carbon coating.

[0117] In the above technical solution, carbon coating treatment is applied to the surface of silicon-based active material to form a coating layer. This can reduce the side reactions caused by electrolyte entering the interior of the negative electrode material, which leads to a decrease in the initial coulombic efficiency and specific capacity. It can further solve the problem of large volume expansion of the negative electrode material, improve the conductivity of the negative electrode material, and thus reduce the overall volume expansion of the negative electrode material and reduce the swelling of the electrode sheet.

[0118] In some embodiments, the carbon coating process specifically includes: heating the silicon-based active material obtained by cooling treatment, and then introducing a protective gas and a carbon source gas, wherein the carbon source gas undergoes thermal decomposition to obtain a negative electrode material.

[0119] In some embodiments, the carbon coating process specifically includes: heating the silicon-based active material obtained by cooling treatment, and then introducing a protective gas and a carbon source gas, wherein the carbon source gas undergoes thermal decomposition to obtain a negative electrode material, wherein the carbon source gas is a hydrocarbon.

[0120] In some embodiments, the carbon coating process specifically includes: heating the silicon-based active material obtained by cooling treatment, and then introducing a protective gas and a carbon source gas, wherein the carbon source gas undergoes thermal decomposition to obtain a negative electrode material; wherein the carbon source gas includes at least one of methane, ethylene, acetylene, propyne, propylene, propane, toluene, benzene, styrene and phenol.

[0121] In some embodiments, the carbon coating process specifically includes: heating the silicon-based active material obtained by cooling treatment, and then introducing a protective gas and a carbon source gas, wherein the carbon source gas undergoes thermal decomposition to obtain a negative electrode material; wherein the thermal decomposition temperature is 600℃~1000℃ and the thermal decomposition time is 30min~24h.

[0122] Specifically, the temperature of thermal decomposition can be 600℃, 650℃, 700℃, 750℃, 800℃, 850℃, 900℃, 950℃ or 1000℃, etc., and the time of thermal decomposition can be 30min, 1h, 3h, 5h, 8h, 10h, 12h, 15h, 18h, 20h or 24h, etc., without limitation.

[0123] In some embodiments, the carbon coating process specifically includes: carbonizing a mixture obtained by mixing a silicon-based active material obtained by cooling with a solid carbon source to obtain a negative electrode material.

[0124] In some embodiments, the carbon coating process specifically includes: carbonizing a mixture obtained by mixing a silicon-based active material obtained by cooling with a solid carbon source to obtain a negative electrode material; wherein the carbonization temperature is 500℃~1000℃ and the carbonization time is 30min~24h.

[0125] The specific temperature for carbonization treatment can be 500℃, 600℃, 700℃, 800℃, 900℃ or 1000℃, etc., and the specific time for carbonization treatment can be 30min, 1h, 3h, 5h, 8h, 10h, 12h, 15h, 18h, 20h or 24h, etc., without any limitation here.

[0126] In some embodiments, the carbon coating process specifically includes: carbonizing a mixture obtained by mixing a silicon-based active material obtained by cooling with a solid carbon source to obtain a negative electrode material; wherein the solid carbon source includes at least one of sugars, esters, hydrocarbons, organic acids and polymers.

[0127] In some embodiments, the carbon coating process specifically includes: carbonizing a mixture obtained by mixing a silicon-based active material obtained through cooling treatment with a solid carbon source to obtain a negative electrode material; wherein the solid carbon source includes at least one of polyvinyl chloride, polyvinyl butyral, polyacrylonitrile, polyacrylic acid, polyethylene glycol, polypyrrole, polyaniline, sucrose, glucose, maltose, citric acid, asphalt, furfural resin, epoxy resin, and phenolic resin.

[0128] In some embodiments, the carbon coating process specifically includes: carbonizing a mixture obtained by mixing a silicon-based active material obtained by cooling with a solid carbon source to obtain a negative electrode material; wherein the mass ratio of the solid carbon source to the silicon-based active material is (10-100):(5-80), specifically it can be 10:5, 10:10, 10:20, 10:30, 20:50, 30:70, 40:60, 50:60, 80:70, 90:70 or 100:80, etc., and of course it can also be other values ​​within the above range, which are not limited here.

[0129] Thirdly, this application also provides a lithium-ion secondary battery, which includes the negative electrode material described in the first aspect or the negative electrode material prepared by the negative electrode material preparation method described in the second aspect.

[0130] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

[0131] Example

[0132] Example 1

[0133] (1) Weigh 0.5 kg of commercially available nano-silicon (median particle size of 45 nm), add it to the prepared acid solution (HF and HCl in a volume ratio of 1:15), react for 1 h, and then dry to obtain primary particles with a pure surface.

[0134] (2) Add the primary particles from step (1) to 1000g of butanol, stir and disperse, then add 10g of acetic acid, reflux at 50°C for 6h under argon protection, and dry to obtain silicon-based active material with Si-COOH bond on the surface.

[0135] (3) The silicon-based active material and glucose were mixed at a mass ratio of 100:44, and then heat-treated at 880°C for 5 hours to obtain the negative electrode material.

[0136] The negative electrode material prepared in this embodiment includes a silicon-based active material with Si-COOH bonds on its surface and a carbon material located on at least a portion of the surface of the silicon-based active material. The median particle size of the negative electrode material is 5.8 μm, and the specific surface area is 3.1 m². 2 / g.

[0137] Figure 1 The image shows a scanning electron microscope (SEM) image of the negative electrode material prepared in Example 1.

[0138] Figure 2 The XRD pattern of the negative electrode material prepared in Example 1 is shown below. Figure 2As shown in the figure, silicon peaks can be observed in the negative electrode material.

[0139] Figure 3 The first charge-discharge curve of the negative electrode material prepared in Example 1 is shown below. Figure 3 As shown, the anode material has a high initial charge-discharge capacity and a high initial coulombic efficiency.

[0140] Figure 4 The cycling performance curve of the negative electrode material prepared in Example 1 is shown below. Figure 4 As shown, the anode material exhibits excellent cycle performance, with a capacity retention rate of 94.0% after 100 cycles.

[0141] Example 2

[0142] (1) Weigh 10 kg of metallic silicon (median particle size of 25 μm), with a silicon content of 99%, add it to an argon gas protector, place it in a plasma reactor, heat it to 2400℃, and then cool it rapidly to obtain primary particles with a pure surface.

[0143] (2) Continue to introduce a mixture of hydrogen and nitrogen (ammonia to nitrogen volume ratio of 1:15) into the plasma reactor of step (1), raise the temperature to 600°C, keep it at the temperature for 2 hours, and obtain the silicon-based active material with Si-H bonds on the surface.

[0144] (3) The silicon-based active material and glucose were mixed at a mass ratio of 100:44, and then heat-treated at 880°C for 5 hours to obtain the negative electrode material.

[0145] The negative electrode material prepared in this embodiment includes a silicon-based active material with Si-H bonds on its surface and a carbon material located on at least a portion of the surface of the silicon-based active material. The median particle size of the negative electrode material is 7.9 μm, and the specific surface area is 3.0 m². 2 / g.

[0146] Example 3

[0147] (1) Weigh 10 kg of metallic silicon (median particle size of 12 μm), with a silicon content of 99%, place the silicon powder in HF vapor for 2 h, and then vacuum dry to obtain primary particles.

[0148] (2) Add the primary particles from step (1) into a high-energy ball mill, add anhydrous ethanol and formaldehyde to form a slurry, control the solid content of the slurry to be 33%, the ball-to-material ratio to be 10:1, set the speed of the ball mill to 300 rpm, and continue ball milling for 30 hours to obtain silicon-based active material with Si-CHO bonds on the surface.

[0149] (3) The silicon-based active material and glucose were mixed at a mass ratio of 100:44, and then heat-treated at 880°C for 5 hours to obtain the negative electrode material.

[0150] The negative electrode material prepared in this embodiment includes a silicon-based active material with Si-CHO bonds on its surface and a carbon material located on at least a portion of the surface of the silicon-based active material. The median particle size of the negative electrode material is 4.6 μm, and the specific surface area is 4.1 m². 2 / g.

[0151] Example 4

[0152] (1) Weigh 5 kg of metallic silicon (median particle size of 5 μm), with a silicon content of 99%, and add it to the prepared acid solution (HF and HCl in a volume ratio of 1:20). Perform acid washing and stirring treatment for 10 h, then wash with water until neutral, and vacuum dry to obtain primary particles.

[0153] (2) Add the primary particles to the sand mill, add acetone and acetic acid in a volume ratio of 100:1 to form a slurry, control the solid content of the slurry to be 25%, the ball-to-material ratio to be 12:1, set the speed of the sand mill to 350 rpm, and continue sand milling for 30 hours to obtain silicon-based active material with Si-COOH bonds on the surface.

[0154] (3) The silicon-based active material and glucose were mixed at a mass ratio of 100:44, and then heat-treated at 880°C for 5 hours to obtain the negative electrode material.

[0155] The negative electrode material prepared in this embodiment includes a silicon-based active material with Si-COOH bonds on its surface and a carbon material located on at least a portion of the surface of the silicon-based active material. The median particle size of the negative electrode material is 9.1 μm, and the specific surface area is 2.8 m². 2 / g.

[0156] Example 5

[0157] (1) In a chemical vapor deposition apparatus, a mixture of silane and nitrogen gas (the volume ratio of silane to nitrogen is 1:15) is introduced and heated to 500℃ and held for 2 hours to obtain primary particles.

[0158] (2) Continue to introduce a mixture of ammonia and nitrogen into the chemical vapor deposition equipment, wherein the volume ratio of ammonia to nitrogen is 0.5:10, and heat to 800℃ and hold for 3 hours to obtain silicon-based active material with Si-NH2 bonds on the surface.

[0159] (3) Continue to introduce a mixture of carbon source gas and nitrogen into the chemical vapor deposition equipment, wherein the volume ratio of carbon source gas to nitrogen is 100:40, and heat to 1000℃ and hold for 5 hours to obtain the negative electrode material.

[0160] The negative electrode material prepared in this embodiment includes a silicon-based active material with Si-NH2 bonds on its surface and a carbon material located on the surface of the silicon-based active material. The median particle size of the negative electrode material is 2.9 μm, and the specific surface area is 3.3 m². 2 / g.

[0161] Example 6

[0162] Unlike Example 1, in step (3), a liquid phase carbon coating process is used to coat the silicon-based active material to obtain the negative electrode material.

[0163] The negative electrode material prepared in this embodiment includes a silicon-based active material with Si-COOH bonds on its surface and a carbon material located on at least a portion of the surface of the silicon-based active material. The median particle size of the negative electrode material is 6.5 μm, and the specific surface area is 2.8 m². 2 / g.

[0164] Example 7

[0165] Unlike Example 1, in step (3), a gas-phase carbon coating process is used to coat the silicon-based active material to obtain the negative electrode material.

[0166] The negative electrode material prepared in this embodiment includes a silicon-based active material with Si-COOH bonds on its surface and a carbon material located on at least a portion of the surface of the silicon-based active material. The median particle size of the negative electrode material is 6.0 μm, and the specific surface area is 3.5 m². 2 / g.

[0167] Comparative Example 1

[0168] The negative electrode material was prepared in basically the same way as in Example 1, except that HF ​​was not added for treatment in step (1).

[0169] Comparative Example 2

[0170] The negative electrode material was prepared in basically the same way as in Example 1, except that acetic acid was not added in step (2) for treatment.

[0171] Comparative Example 3

[0172] Silicon particles with a median particle size of 50 nm were placed in a chemical vapor deposition (CVD) apparatus. A mixture of carbon source gas and nitrogen gas was introduced into the CVD apparatus, with a volume ratio of carbon source gas to nitrogen gas of 100:40. The mixture was heated to 1000 °C and held for 5 hours to obtain the anode material.

[0173] Test method:

[0174] (1) Test method for Si-R bonds on the surface of silicon-based active materials:

[0175] Fourier transform infrared spectroscopy was used to test the Si-R valence bonds on the surface of silicon-based active materials.

[0176] (2) Method for testing the pH value of silicon-based active materials:

[0177] Tested according to ISO 3071-1980 method.

[0178] (3) Test method for the absolute value of the zeta potential of the slurry:

[0179] Silicon-based active materials were mixed with ethanol to form a slurry with a solid content of 5% to 30%. The zeta potential value of the slurry was tested using an Omec NS-90Z nanoparticle size and potential analyzer.

[0180] (4) Method for testing the average particle size of silicon-based active materials:

[0181] The particle size distribution range of the composite anode material was tested using a Malvern laser particle size analyzer.

[0182] (5) Test method for the mass content of oxygen atoms in silicon-based active materials:

[0183] The range of oxygen content in the negative electrode material was tested using an oxygen, nitrogen, and hydrogen analyzer.

[0184] (6) Test method for specific surface area of ​​negative electrode material:

[0185] The dynamic specific surface area was measured using the JW-DX dynamic specific surface area rapid analyzer from Beijing Jingwei Gaobo Science and Technology Co., Ltd., and the unit is m2 / g.

[0186] (7) Electrochemical performance testing:

[0187] The negative electrode materials, conductive agent, and binder of Examples 1-7 and Comparative Examples 1-3 prepared above were dissolved in deionized water at a mass ratio of 94:1:5, and the solid content was controlled at 50%. The mixture was then coated onto a copper foil current collector, vacuum dried, and a negative electrode sheet was obtained. Then, a ternary positive electrode sheet (lithium nickel cobalt manganese oxide NCM523) prepared using conventional mature processes, a 1 mol / L lithium hexafluorophosphate LiPF6 / (ethylene carbonate EC + dimethyl carbonate DMC + ethyl methyl carbonate EMC) (v / v = 1:1:1) electrolyte, a Celgard 2400 separator, and a casing were assembled into an 18650 cylindrical cell using conventional manufacturing processes. The charge-discharge tests of the cylindrical cells were conducted on the LAND battery testing system of Wuhan Jinno Electronics Co., Ltd., under room temperature conditions, with a constant current charge-discharge of 0.2C and a charge-discharge voltage limited to 2.75–4.2V. The initial specific capacity, first charge capacity, and first discharge capacity were obtained. Initial Coulomb efficiency = First discharge capacity / First charge capacity.

[0188] The test results are detailed in Tables 1 and 2.

[0189] Table 1 Performance parameters of silicon-based active materials in each embodiment and comparative example

[0190]

[0191] Table 2. Electrochemical performance test results of each embodiment and comparative example.

[0192] Initial specific capacity (mAh / g) First-time coulomb efficiency (%) Capacity retention rate after 100 cycles (%) Example 1 1845 88.4 87.9 Example 2 1811 87.4 88.1 Example 3 1784 87.1 89.0 Example 4 1819 89.4 88.2 Example 5 1842 90.3 87.7 Example 6 1811 88.0 88.5 Example 7 1801 89.1 89.9 Comparative Example 1 1696 84.4 83.1 Comparative Example 2 1513 81.4 82.3 Comparative Example 3 814 70.4 80.4

[0193] According to the test data in Tables 1 and 2, the negative electrode materials prepared in Examples 1 to 7 include silicon-based active materials. The surface of the silicon-based active materials includes Si-R bonds, where R includes at least one of -H, -COOH, -CHO, or -NH2. The Si-R bonds will hydrolyze in aqueous solution to release H. + This can improve the pH value of silicon-based active materials, reduce the situation where the pH value of silicon-based active materials is too acidic or too alkaline, reduce the combination of silicon-based active materials with other elements (especially oxygen), and reduce the impact on the activity of silicon-based active materials.

[0194] Compared to Example 1, the negative electrode material in Comparative Example 1 did not have HF added to treat the silicon raw material during preparation. Therefore, the surface of the silicon raw material could not be cleaned properly, and an oxide layer was present on the surface of the primary particles. The presence of the oxide layer made it difficult for the primary particles to form dangling bonds, and they could not combine to form Si-COOH valence bonds, or the number of Si-COOH valence bonds formed was very small. The primary particles easily reacted with oxygen to form inactive silicon oxide, which reduced the specific capacity of the negative electrode material. After the negative electrode material was applied to the battery, the pH value of the silicon-based active material could not be improved, the side reactions between it and the electrolyte were aggravated, the consumption of active lithium ions increased, and the battery's initial efficiency and cycle performance were significantly reduced.

[0195] Compared with Example 1, in the preparation process of the negative electrode material in Comparative Example 2, acetic acid was not added to treat the primary particles, which prevented the formation of Si-COOH bonds on the surface of the silicon-based active material. The primary particles easily reacted with oxygen to form inactive silicon oxide, resulting in a decrease in the specific capacity of the negative electrode material. After the negative electrode material was applied to the battery, the pH value of the silicon-based active material could not be improved, the side reactions between it and the electrolyte were aggravated, the consumption of active lithium ions increased, and the battery's initial efficiency and cycle performance were significantly reduced.

[0196] Compared to Example 1, in Comparative Example 3, silicon particles were directly composited with carbon materials without undergoing a first surface treatment and surface modification treatment. As a result, Si-R bonds could not be formed on the surface of the silicon particles, and the silicon particles were extremely prone to reacting with oxygen to form inactive silicon oxide, which led to a significant decrease in the specific capacity of the negative electrode material. After the negative electrode material was applied to the battery, the pH value of the silicon particles could not be improved, the side reactions between the silicon particles and the electrolyte were aggravated, the consumption of active lithium ions increased, and the battery's initial efficiency and cycle performance were significantly reduced.

Claims

1. A negative electrode material, characterized in that, The negative electrode material includes a silicon-based active material, the surface of which has Si-R bonds, wherein R includes at least one of H, COOH, CHO or NH2, the pH value of which is 3 to 7, the silicon-based active material includes silicon particles and a silicon oxide layer on the surface of which the silicon particles are located, and the mass content of oxygen atoms in which the silicon-based active material is 1% to 12.1% based on 100% of the mass of the silicon-based active material.

2. The negative electrode material according to claim 1, characterized in that, It includes at least one of the following features (1) to (2): (1) The average particle size of the silicon-based active material is 1 nm to 500 nm; (2) The silicon-based active material includes at least one of crystalline silicon, silicon oxide, amorphous silicon, silicon alloy, and a composite of crystalline silicon and amorphous silicon.

3. The negative electrode material according to claim 1, characterized in that, The negative electrode material also includes carbon material located on at least a portion of the surface of the silicon-based active material.

4. The negative electrode material according to claim 3, characterized in that, It includes at least one of the following features (1) to (6): (1) The mass content of the silicon-based active material in the negative electrode material is greater than or equal to 99%; (2) The carbon material exists on the surface of the silicon-based active material and / or is dispersed between the silicon-based active materials; (3) The carbon material includes at least one of amorphous carbon, graphene, graphite, carbon nanotubes and carbon fibers; (4) The median particle size of the negative electrode material is 1µm~10µm; (5) The specific surface area of ​​the negative electrode material is ≤5m². 2 / g; (6) The silicon-based active material is mixed with ethanol to form a slurry with a solid content of 5% to 30%, and the zeta potential of the slurry is tested using a zeta potential analyzer. The absolute value of the zeta potential of the slurry is ≥20mV.

5. A method for preparing the negative electrode material as described in claim 1, characterized in that, Includes the following steps: The silicon raw material undergoes a first surface treatment to obtain primary particles with exposed surfaces. The first surface treatment includes at least one of crushing or etching. The primary particles are surface modified to obtain a silicon-based active material; the negative electrode material includes the silicon-based active material, the surface of the silicon-based active material includes Si-R bonds, wherein R includes at least one of H, COOH, CHO or NH2, the pH value of the silicon-based active material is 3 to 7, the silicon-based active material includes silicon particles and a silicon oxide layer located on the surface of the silicon particles, and the mass content of oxygen atoms in the silicon-based active material is 1% to 12.1% based on 100% of the mass of the silicon-based active material.

6. The preparation method according to claim 5, characterized in that, The preparation method includes at least one of the following features (1) to (8): (1) The silicon raw material includes elemental silicon; (2) The silicon raw material includes elemental silicon, which includes crystalline silicon and / or amorphous silicon; (3) The silicon raw material includes elemental silicon, and the average particle size of the elemental silicon is 1 nm to 100 nm; (4) The silicon raw material includes elemental silicon, wherein the mass content of silicon element in the elemental silicon is greater than or equal to 97%; (5) The silicon raw material is prepared from a silicon source precursor; (6) The silicon raw material is prepared from a silicon source precursor, and the silicon source precursor includes at least one of a gas phase silicon source and a liquid phase silicon source; (7) The silicon raw material is prepared from a silicon source precursor, the silicon source precursor includes a gaseous silicon source, and the gaseous silicon source includes at least one of silane, silane, monochlorosilane and dichlorosilane; (8) The silicon raw material is prepared from a silicon source precursor, the silicon source precursor includes a liquid silicon source, and the liquid silicon source includes at least one of trichlorosilane or tetrachlorosilane.

7. The preparation method according to claim 5, characterized in that, The preparation method includes at least one of the following features (1) to (15): (1) The step of performing the first surface treatment on the silicon raw material includes: etching the silicon raw material with an etching solution; (2) The step of performing the first surface treatment on the silicon raw material includes: etching the silicon raw material with an etching solution, wherein the etching solution includes at least one of potassium hydroxide solution, ammonium hydroxide solution, tetramethylhydroxylamine solution, hydrofluoric acid solution, buffer oxide etchant BOE, HF / EG solution and SC1 solution; (3) The step of performing the first surface treatment on the silicon raw material includes: etching the silicon raw material with an etching solution, wherein the concentration of hydrogen ions in the etching solution is 1 mol / L to 12 mol / L; (4) The step of performing the first surface treatment on the silicon raw material includes: crushing the silicon raw material to obtain primary particles, wherein the average particle size of the primary particles is 1μm~100μm; (5) The surface modification treatment includes at least one of amination treatment and acid leaching treatment; (6) The surface modification treatment includes an amination treatment, which is carried out in a compound containing an amino group; (7) The surface modification treatment includes an amination treatment, which is carried out in a substance containing an amino group, wherein the compound containing an amino group includes at least one of ammonia, ammonium chloride, ammonium sulfate, ammonium bicarbonate, ammonium carbonate, ammonium bisulfate, ammonium nitrate, ammonium fluoride, ammonium iodide, ammonium bromide, ammonium methoxide or hydrazine. (8) The surface modification treatment includes acid immersion treatment, which is carried out in a compound containing carboxyl groups; (9) The surface modification treatment includes acid immersion treatment, which is carried out in a compound containing a carboxyl group, the compound containing a carboxyl group including at least one of fatty acids and aromatic acids; (10) The surface modification treatment includes acid immersion treatment, which is carried out in a compound containing a carboxyl group, the compound containing a carboxyl group including at least one of formic acid, acetic acid, propionic acid and octanoic acid; (11) The surface modification treatment includes acid immersion treatment, which is carried out in a compound containing a carboxyl group, the compound containing a carboxyl group including at least one of benzoic acid, phenylacetic acid, phthalic acid and 3-nitrophthalic acid; (12) The surface modification treatment includes physical treatment; (13) The surface modification treatment includes physical treatment, which includes at least one of ball milling, sand milling, grinding or air jet milling; (14) The surface modification treatment includes physical treatment, which is carried out under a protective atmosphere; (15) The surface modification treatment includes a physical treatment, which is carried out under a protective atmosphere, the protective atmosphere including at least one of nitrogen, helium, neon, argon, krypton and xenon.

8. The preparation method according to any one of claims 5 to 7, characterized in that, The method further includes: The silicon-based active material obtained by cooling is subjected to carbon coating treatment to obtain the negative electrode material; the carbon coating treatment includes at least one of solid phase carbon coating, liquid phase carbon coating and gas phase carbon coating.

9. The preparation method according to claim 8, characterized in that, The preparation method includes at least one of the following features (1) to (9): (1) The carbon coating process specifically includes: heating the silicon-based active material obtained by cooling treatment, and then introducing a protective gas and a carbon source gas, wherein the carbon source gas undergoes thermal decomposition to obtain a negative electrode material; (2) The carbon coating process specifically includes: heating the silicon-based active material obtained by cooling treatment, and then introducing a protective gas and a carbon source gas. The carbon source gas is thermally decomposed to obtain a negative electrode material, wherein the carbon source gas is a hydrocarbon. (3) The carbon coating process specifically includes: heating the silicon-based active material obtained by cooling treatment, and then introducing a protective gas and a carbon source gas. The carbon source gas is thermally decomposed to obtain a negative electrode material. The carbon source gas includes at least one of methane, ethylene, acetylene, propyne, propylene, propane, toluene, benzene, styrene and phenol. (4) The carbon coating process specifically includes: heating the silicon-based active material obtained by cooling treatment, and then introducing a protective gas and a carbon source gas. The carbon source gas undergoes thermal decomposition to obtain the negative electrode material. The thermal decomposition temperature is 600℃~1000℃ and the thermal decomposition time is 30min~24h. (5) The carbon coating process specifically includes: carbonizing the mixture obtained by mixing the silicon-based active material obtained by cooling treatment with the solid carbon source to obtain the negative electrode material; (6) The carbon coating process specifically includes: carbonizing the mixture obtained by cooling the silicon-based active material and the solid carbon source to obtain the negative electrode material; wherein the carbonization temperature is 500℃~1000℃ and the carbonization time is 30min~24h. (7) The carbon coating process specifically includes: carbonizing a mixture obtained by mixing a silicon-based active material obtained by cooling treatment with a solid carbon source to obtain a negative electrode material; wherein the solid carbon source includes at least one of sugars, esters, hydrocarbons, organic acids and polymers. (8) The carbon coating process specifically includes: carbonizing a mixture obtained by mixing a silicon-based active material obtained by cooling treatment with a solid carbon source to obtain a negative electrode material; wherein the solid carbon source includes at least one of polyvinyl chloride, polyvinyl butyral, polyacrylonitrile, polyacrylic acid, polyethylene glycol, polypyrrole, polyaniline, sucrose, glucose, maltose, citric acid, asphalt, furfural resin, epoxy resin and phenolic resin; (9) The carbon coating process specifically includes: carbonizing the mixture obtained by cooling the silicon-based active material and the solid carbon source to obtain the negative electrode material; wherein the mass ratio of the solid carbon source to the silicon-based active material is (10~100): (5~80).

10. A lithium-ion secondary battery, characterized in that, The lithium-ion secondary battery includes the negative electrode material according to any one of claims 1 to 4 or the negative electrode material prepared by the method according to any one of claims 5 to 9.

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