Anode materials, anode slurry and lithium-ion batteries

Abstract

This application relates to anode materials and their preparation methods, and lithium-ion batteries. The anode material includes a silicon-based active material and a coating layer located on at least a portion of the surface of the silicon-based active material. The silicon-based active material includes silicon and lithium silicate. By controlling the type and degree of crystallinity of lithium silicate in the material, the anode material of this application can improve the storage stability of the anode slurry, extend the cycle life of the anode material, increase the adhesion between the anode material and the current collector, and improve the high-temperature storage performance of the cell, thereby improving the cycle performance of the lithium-ion battery.

Description

Negative electrode material, negative electrode slurry and lithium ion battery This application claims priority to the Chinese patent application filed with the State Intellectual Property Office of China on September 22, 2023, with application number 202311231152.8 and application name “Negative electrode material and preparation method thereof, lithium-ion battery”, the entire contents of which are incorporated by reference in this application. The present application relates to the technical field of negative electrode materials, and in particular to negative electrode materials, negative electrode slurry and lithium ion batteries. Lithium-ion batteries have been widely used in portable electronic products and electric vehicles due to their advantages such as high operating voltage, long cycle life, no memory effect, low self-discharge, and environmental friendliness. At present, commercial lithium-ion batteries mainly use graphite-based negative electrode materials, but the theoretical specific capacity of graphite is up to 372mAh / g, which cannot meet the future demand for high energy density of lithium-ion batteries. Although the previous Si had a theoretical capacity of up to 4200mAh / g, its expansion rate reached 300%, which affected the cycle performance and restricted market promotion and application. The corresponding silicon-oxygen material has better cycle performance, but the first efficiency is low. During the first charge, 20~50% of lithium is consumed for SEI film formation, which greatly reduces the first coulomb efficiency. As the first efficiency of positive electrode materials becomes higher and higher, it is particularly important to improve the first efficiency of silicon-oxygen materials. At present, the most effective way to improve the initial effect of silicon oxide materials is to pre-dope them with lithium so that the irreversible lithium consumption phase in the silicon oxide materials can be reacted in advance. The previous industrial method was to directly coat the surface of the electrode with a lithium layer to reduce the lithium consumption of the positive electrode. However, this method has high requirements for the operating environment and has great safety risks, so it is difficult to achieve industrial promotion. Under the current state of technological development, there is a general problem of poor processing performance in the initial effect improvement obtained by pre-lithiation on the silicon oxide material side, which is mainly manifested as follows: the slurry prepared with pre-lithiation silicon oxide negative electrode material has a short stable storage time, and is prone to sedimentation, stratification, and gas production during storage, resulting in uneven distribution of active substances in the coated electrode, large differences in electrode thickness and surface density, and uneven appearance of the electrode, making it impossible to assemble the entire battery; the degree of pre-lithiation is difficult to control, resulting in unstable types and contents of lithium silicates in the silicon oxide material, and the prepared slurry is unstable, which can easily lead to uneven coating of the electrode, further reducing the peeling strength of the electrode, and the active substance is easily peeled off from the current collector; at the same time, due to the introduction of lithium sources and the generation of lithium silicates, the pre-lithiation silicon oxide material will break the original stable structure of the silicon oxide material and shorten the cycle life of the negative electrode material. In a first aspect, the present application provides a negative electrode material, a negative electrode slurry and a lithium ion battery, wherein the negative electrode material comprises a silicon-based active material and a coating layer located on at least a portion of the surface of the silicon-based active material, wherein the silicon-based active material comprises silicon and lithium silicate; Determined by XRD ray diffraction method, in the X-ray diffraction spectrum of the negative electrode material, the peak intensity of the strongest diffraction peak of the negative electrode material in the range of 2θ of 18° to 20° is A1, the peak intensity of the strongest diffraction peak in the range of 2θ of 26° to 27.9° is A2, and the peak intensity of the strongest diffraction peak at 2θ of 32° to 34° is A3, and A1+A2+A3=A; The peak intensity of the strongest diffraction peak of the negative electrode material in the range of 2θ of 16° to 17° is B1, the peak intensity of the strongest diffraction peak in the range of 2θ of 22° to 25.9° is B2, and the peak intensity of the strongest diffraction peak in the range of 2θ of 36° to 38° is B3, B1+B2+B3=B; The peak intensity of the strongest diffraction peak of the negative electrode material in the range of 28° to 30° at 2θ is C1, the peak intensity of the strongest diffraction peak in the range of 46° to 48° at 2θ is C2, and the peak intensity of the strongest diffraction peak in the range of 56° to 58° at 2θ is C3, C1+C2+C3=C; And the relationship between A, B, and C satisfies: 0<(A+B) / C≤10, 0<(A+C) / B≤5. In some embodiments, the negative electrode material is tested using a powder resistivity tester, and the powder conductivity of the negative electrode material at a powder density of ρ1 is measured to be σ1, and the powder conductivity of the negative electrode material at a powder density of ρ2 is measured to be σ2, and the following relationship is satisfied: (σ2-σ1) / (ρ2-ρ1)≤0.8. In some implementations, the relationship between A, B, and C also satisfies: 1≤(B+C) / A≤30. In some embodiments, the silicon-based active material further includes a silicon-oxygen composite. In some embodiments, the molar ratio of oxygen atoms to silicon atoms in the negative electrode material is 0.5-2. In some embodiments, the silicon includes nano-silicon grains, and the average particle size of the nano-silicon grains is 0 nm to 20 nm, and does not include 0 nm. In some embodiments, the coating layer includes a carbon material, and the carbon material includes at least one of amorphous carbon, graphene, graphite, carbon nanotubes, and carbon fibers. In some embodiments, the lithium silicate includes Li 2SiO 3. Li 2Si 2O 5 and Li 4SiO At least one of the 4. In some embodiments, the coating layer includes a carbon material, and the mass content of the carbon material in the negative electrode material is less than or equal to 10%. In some embodiments, the mass content of silicon in the negative electrode material is 20% to 70%. In some embodiments, the mass content of lithium silicate in the negative electrode material is 30% to 75%. In some embodiments, the specific surface area of the negative electrode material is less than or equal to 10 m 2 / g. In some embodiments, the pH value of the negative electrode material is 7.2-11.0. In some embodiments, the active material, carboxymethyl cellulose, conductive carbon black and styrene-butadiene rubber are mixed according to a mass ratio of 95.3:1.3:1.5:1.9 to form a negative electrode slurry with a solid content of 50%, wherein the active material includes the negative electrode material and graphite in a mass ratio of 9:1; the rheological properties of the negative electrode slurry are tested using a German Haake rotational rheometer to obtain a rheological curve of the negative electrode slurry; in the rheological curve, when the shear rate is 0S -1 、150S -1 、300S -1 When , the corresponding shear stresses in the rheological curve are τ0, τ1, τ2, and the relationship between the shear stresses satisfies: 2τ1>(τ2-τ0). In a second aspect, the present application provides a negative electrode slurry comprising the negative electrode material as described in the first aspect. In a third aspect, the present application provides a method for preparing a negative electrode material, comprising the following steps: Silicon oxide SiO x Place in an acid solution for the first surface modification treatment, wherein 0<x<2; The silicon oxide SiO x The mixture with the reducing lithium-containing compound is subjected to a pre-lithiation treatment and a carbon coating treatment at 300° C. to 800° C. to obtain a precursor, wherein 0<x<2; The precursor is subjected to a second surface modification treatment to obtain a negative electrode material, wherein the negative electrode material includes a silicon-based active substance and a coating layer located on at least a portion of the surface of the silicon-based active substance, and the silicon-based active substance includes silicon and lithium silicate. In some embodiments, the acid solution includes at least one of hydrofluoric acid, nitric acid, fluorosulfonic acid, fluoroantimonysulfonic acid, hydrochloric acid, hydrobromic acid, and hydroiodic acid. In some embodiments, the concentration of the acid solution is ≤2 mol / L. In some embodiments, the temperature of the first surface modification treatment is 30°C to 100°C. In some embodiments, the first surface modification treatment is performed for 2 hours to 8 hours. In some embodiments, the preparation method further comprises treating the silicon oxide SiO x Carry out solid-liquid separation, washing and drying. In some embodiments, the preparation method further comprises treating the silicon oxide SiO x Solid-liquid separation, washing and drying are performed, and the drying temperature is 50°C to 180°C. In some embodiments, the silicon oxide is silicon monoxide. In some embodiments, the reducing lithium-containing compound includes at least one of lithium hydride, alkyl lithium, metallic lithium, lithium aluminum hydride, lithium amide, lithium borohydride, and lithium silicon alloy. In some embodiments, the mass ratio of the silicon oxide after the first surface modification treatment to the reducing lithium-containing compound is 1:(0.03-0.2). In some embodiments, the pre-lithiation treatment is performed in a protective atmosphere. In some embodiments, the protective atmosphere includes at least one of nitrogen, helium, neon, argon, krypton, and xenon. In some embodiments, the pre-lithiation treatment time is 3h~9h. In some embodiments, the coating treatment includes a carbon coating treatment, and the process of the carbon coating treatment includes at least one of a liquid phase coating method, a gas phase coating method, and a solid phase coating method. In some embodiments, the coating process includes a carbon coating process, and the coating material of the carbon coating process includes at least one of amorphous carbon, graphene, graphite, carbon nanotubes, and carbon fibers. In some embodiments, the lithium silicate includes Li 2SiO 3. Li 2Si 2O 5. Li 4SiO At least one of the 4. In some embodiments, the method comprises: x Before the mixture with the reducing lithium-containing compound is subjected to a pre-lithiation treatment at 300°C to 800°C, the silicon oxide SiO x The mixture is mixed with a reducing lithium-containing compound. In some embodiments, the mixing treatment is carried out at a temperature of 60°C to 320°C. In some embodiments, the mixing treatment time is 0.5h~10h. In some embodiments, the equipment required for the mixing process includes at least one of an equipment with a dispersing function and an equipment with a shearing force effect. In some embodiments, the second surface treatment includes at least one of purification treatment, coating treatment, heat treatment, oxidation treatment, and etching treatment. In some embodiments, the temperature of the second surface treatment is 50°C to 900°C. In some embodiments, the second surface treatment time is 0.5h~10h. In some embodiments, the second surface treatment includes placing the precursor in an aluminum hydroxide solution for purification. In a fourth aspect, the present application provides a lithium-ion battery, wherein the lithium-ion battery comprises the negative electrode material described in the first aspect or the negative electrode material prepared by the preparation method described in the second aspect. Compared with the prior art, the technical solution of the present application has at least the following beneficial effects: The negative electrode material provided in the present application includes a silicon-based active material, wherein the silicon-based active material includes silicon and lithium silicate. In the X-ray diffraction spectrum of the negative electrode material, A represents Li in a crystalline state. 2SiO The sum of the peak intensities of different peaks of 3, B represents Li in the crystalline state 2Si 2O 5, C represents the sum of the peak intensities of different peaks of silicon. When the relationship between A, B, and C satisfies: 0<(A+B) / C≤10, 0<(A+C) / B≤5, the Li in the negative electrode material 2SiO 3. Li 2Si 2O 5 and silicon interact with each other and reach a balance. The degree of lithiation on the surface of the negative electrode material is appropriate, so that the processing performance of the negative electrode material is relatively stable. The negative electrode material has a good interface contact with the binder glue. When the negative electrode material is prepared into a negative electrode slurry, the negative electrode material can be evenly dispersed and suspended in the binder glue, so that the prepared negative electrode slurry can be stably stored; in addition, during the charge and discharge process, the battery containing the above-mentioned negative electrode material can also reduce the destructive effect of lithium silicate on the binder, improve the structural stability of the pole piece, and extend the cycle life of the negative electrode material. The negative electrode material provided in the present application, by regulating the type and degree of crystallization of lithium silicate, that is, satisfying the relationship between A, B, and C, reduces the destructive effect of alkaline substances on the binder, improves the structural stability of the pole piece, improves the cycle performance of the battery prepared by the negative electrode material, and extends the cycle life. The negative electrode material preparation method provided in the present application comprises: x The first surface modification treatment is carried out in an acid solution. The acid solution reacts with silicon oxide SiO x The surface is oxidized and etched to form silicon oxide SiO x The surface forms weak defect sites, which can increase the surface modified silicon oxide SiO x The reaction points in the pre-lithiation process make the pre-lithiation reaction more uniform, obtain more lithium silicate growth points, and are conducive to the uniform distribution of lithium silicate inside the negative electrode material particles, which helps to adjust the crystal phase type and content of lithium silicate on the surface of the material. In addition, the surface modified silicon oxide SiO x Pre-lithiation treatment can greatly reduce the catalytic growth of silicon grains by lithium silicate; due to the first surface modification of silicon oxide SiO x The surface has uniformly distributed growth sites, which will contain silicon oxide SiO after the first surface modification treatment. xPre-lithiation treatment with a mixture of reducing lithium-containing compounds can improve the utilization rate of lithium and the uniformity of the distribution of pre-lithiation products. The pre-lithiation products are evenly distributed in the negative electrode material, which is beneficial to buffering the volume change of the silicon-based active substance during the charging and discharging process, maintaining the overall structure of the negative electrode material, extending the cycle life, reducing the regeneration of the SEI film on the surface of the negative electrode material, and improving the initial efficiency of the material; by performing a second surface modification treatment on the precursor, the surface morphology of the negative electrode material can be further adjusted, and the crystal phase type and content of the lithium silicate on the surface of the material can be adjusted. On the one hand, the solid-liquid contact interface between the negative electrode material and the electrolyte can be stabilized, the risk of the negative electrode material being corroded in the electrolyte can be reduced, and the high-temperature storage performance of the battery prepared from the negative electrode material can be improved; on the other hand, the adhesion strength of the binder to the negative electrode material can be improved, the peeling strength of the electrode sheet can be enhanced, the rebound of the electrode sheet can be reduced, and the conductive network of the electrode sheet can be stabilized, thereby improving the cycle life of the battery prepared from the negative electrode material. In order to better understand the technical solution of the present application, the embodiments of the present application are described in detail below with reference to the accompanying drawings. It should be clear that the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application. The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular forms "a", "said" and "the" used in the embodiments of the present application and the attached claims are also intended to include plural forms, unless the context clearly indicates other meanings. It should be understood that the term "and / or" used in this article is only a description of the association relationship between related objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the related objects before and after are in an "or" relationship. In a first aspect, the present application provides a negative electrode material, the negative electrode material comprising a silicon-based active material and a coating layer located on at least a portion of the surface of the silicon-based active material, the silicon-based active material comprising silicon and lithium silicate; The XRD ray diffraction method is used to measure that in the X-ray diffraction spectrum of the negative electrode material, the peak intensity of the strongest diffraction peak of the negative electrode material in the range of 2θ of 18° to 20° is A1, the peak intensity of the strongest diffraction peak in the range of 2θ of 26° to 27.9° is A2, and the peak intensity of the strongest diffraction peak at 2θ of 32° to 34° is A3, and A1+A2+A3=A; The peak intensity of the strongest diffraction peak of the negative electrode material in the range of 2θ of 16° to 17° is B1, the peak intensity of the strongest diffraction peak in the range of 2θ of 22° to 25.9° is B2, and the peak intensity of the strongest diffraction peak in the range of 2θ of 36° to 38° is B3, B1+B2+B3=B; The peak intensity of the strongest diffraction peak of the negative electrode material in the range of 28°~30° at 2θ is C1, the peak intensity of the strongest diffraction peak in the range of 46°~48° at 2θ is C2, and the peak intensity of the strongest diffraction peak in the range of 56°~58° at 2θ is C3, C1+C2+C3=C; And the relationship between A, B, and C satisfies: 0<(A+B) / C≤10, 0<(A+C) / B≤5. The negative electrode material provided in the present application includes a silicon-based active material, and the silicon-based active material includes silicon and lithium silicate. The XRD ray diffraction method is used to measure that in the X-ray diffraction spectrum of the negative electrode material, A represents Li in a crystalline state. 2SiO The sum of the peak intensities of different peaks of 3, B represents Li in the crystalline state 2Si 2O 5, C represents the sum of the peak intensities of different peaks of silicon. When the relationship between A, B, and C satisfies: 0<(A+B) / C≤10, 0<(A+C) / B≤5, the Li in the negative electrode material 2SiO 3. Li 2Si 2O 5 and silicon interact with each other and reach a balance. The degree of lithiation on the surface of the negative electrode material is appropriate, so that the processing performance of the negative electrode material is relatively stable. The negative electrode material has a good interface contact with the binder glue. When the negative electrode material is prepared into a negative electrode slurry, the negative electrode material can be evenly dispersed and suspended in the binder glue, so that the prepared negative electrode slurry can be stably stored; in addition, during the charge and discharge process, the battery containing the above-mentioned negative electrode material can also reduce the destructive effect of lithium silicate in the negative electrode material on the binder, improve the structural stability of the pole piece, and extend the cycle life of the material. The negative electrode material provided in the present application can reduce the destructive effect of alkaline substances on the binder, improve the structural stability of the pole piece, improve the cycle performance of the battery prepared by the negative electrode material, and extend the cycle life by regulating the type and degree of crystallization of the lithium silicate, that is, satisfying the relationship between A, B, and C. Specifically, the value of (A+B) / C can be, for example, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5 and 10, etc., and of course, it can also be other values within the above range, which are not limited here. The value of (A+C) / B can be, for example, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5 and 5, etc., which are not limited here. In some implementations, the relationship between A, B, and C also satisfies: 1≤(B+C) / A≤30. Specifically, the value of (B+C) / A can be, for example, 1, 3, 5, 8, 10, 12, 15, 17, 20, 21, 23, 25, 28, and 30, and of course, it can also be other values within the above range, which is not limited here. Understandably, the negative electrode material is distributed with Li represented by A 2SiO 3. B stands for Li 2Si 2O 5 and C represent three components of silicon; when 1≤(B+C) / A≤30 is satisfied at the same time, the storage performance of the negative electrode slurry made of the negative electrode material will be improved, and the sedimentation, stratification and gas production of the negative electrode slurry during storage will be reduced, so that the active material in the coated electrode is evenly distributed, the thickness and surface density of the electrode are small, and the appearance of the electrode is flat, which is suitable for full battery assembly. In some embodiments, the negative electrode material is tested using a powder resistivity tester, and the powder conductivity of the negative electrode material at a powder density ρ1 is measured to be σ1, and the powder conductivity of the negative electrode material at a powder density ρ2 is measured to be σ2, and the following relationship is satisfied: (σ2-σ1) / (ρ2-ρ1)≤0.8. Specifically, the value of (σ2-σ1) / (ρ2-ρ1) can be 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7 and 0.8, etc., and of course, it can also be other values within the above range, which are not limited here. The above powder density ρ1 and powder conductivity σ1 and powder density ρ2 and powder conductivity σ2 are measured at different pressures respectively. It can be understood that the powder conductivity is related to the surface morphology and internal structure of the negative electrode material, and can reflect the electronic conductivity of the negative electrode material. The increase in lithium silicate in the silicon-based active material after pre-lithiation treatment may reduce the overall electronic conductivity of the negative electrode material. The powder conductivity of the negative electrode material changes with the change of powder density. 2SiO 3. Li 2Si 2O 5 and silicon, and thus balance the relationship between powder conductivity and powder density, ensure the electrical contact between negative electrode material particles, improve the stability of the conductive network between negative electrode material particles, increase the probability of electrical contact between particles during the recycling process, and extend the recycling life of the material. In some embodiments, the molar ratio of oxygen atoms to silicon atoms in the negative electrode material is 0.5-2, specifically 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9 and 2, etc., and of course, it can also be other values within the above range, which is not limited here. In some embodiments, the silicon-based active material further comprises a silicon-oxygen complex, wherein the silicon-oxygen complex comprises oxygen atoms and silicon atoms, and the molar ratio of oxygen atoms to silicon atoms is 0 to 2. The silicon-oxygen complex can be represented by the general formula SiO x (0<x≤2). It can be silicon particles dispersed in SiO The material formed in 2 may also be a material having a tetrahedral structural unit: the silicon atom is located at the center of the tetrahedral structural unit, and the silicon atom and / or oxygen atom is located at the four vertices of the tetrahedral structural unit. In some embodiments, silicon includes nano silicon grains, and the average particle size of the nano silicon grains is 0nm~20nm, and 0nm is not included. Specifically, the average particle size of the nano silicon grains can be 1nm, 3nm, 5nm, 8nm, 10nm, 12nm, 15nm and 20nm, etc., and of course, it can also be other values within the above range, which are not limited here. It can be understood that, under the same silicon content, compared with large-sized crystalline silicon grains, due to the isotropic expansion of silicon, the expansion stress of small-sized silicon grains is more uniform, the silicon grain expansion effect is smaller, and the cycle life is longer, which can be beneficial to improve the cycle performance and rate performance of the negative electrode material. In some embodiments, the coating layer includes a carbon material, and the carbon material includes at least one of amorphous carbon, graphene, graphite, carbon nanotubes, and carbon fibers. In some embodiments, the lithium silicate includes Li 2SiO 3. Li 2Si 2O 5 and Li 4SiO At least one of the 4. In some embodiments, the coating layer includes a carbon material, and the mass content of the carbon material in the negative electrode material is less than or equal to 10%, and can be specifically 0.1%, 1%, 2%, 3%, 5%, 7%, 8%, 9% and 10%. Of course, it can also be other values within the above range, which is not limited here. In some embodiments, the specific surface area of the negative electrode material is less than or equal to 10 m 2 / g, specifically 1m 2 / g, 2m 2 / g, 3m 2 / g, 4m 2 / g, 5m 2 / g, 6m 2 / g, 7m 2 / g, 8m 2 / g, 9m 2 / g and 10m 2 / g, etc., and of course, it can also be other values within the above range, which is not limited here. In some embodiments, the quality content of silicon in the negative electrode material is 20% to 70%, specifically 20%, 24%, 28%, 30%, 35%, 40%, 48%, 52%, 56%, 60%, 63%, 65%, 67% and 70%, etc. Of course, it can also be other values within the above range, which is not limited here. In some embodiments, the mass content of silicate in the negative electrode material is 30% to 75%, specifically 30%, 32%, 35%, 38%, 40%, 45%, 50%, 56%, 60%, 64%, 67%, 70%, 72%, 73% and 75%, etc. Of course, it can also be other values within the above range, which is not limited here. In some embodiments, the pH value of the negative electrode material is 7.2 to 11.0. The pH value of the negative electrode material can be 7.2, 7.6, 7.8, 8, 8.3, 8.5, 8.7, 9.6, 9.9, 10, 10.25, 10.36, 10.47, 10.58, 10.87, 10.98, and 11, etc. Of course, it can also be other values within the above range, which is not limited here. In some embodiments, the active material, carboxymethyl cellulose, conductive carbon black and styrene-butadiene rubber are mixed according to a mass ratio of 95.3:1.3:1.5:1.9 to form a negative electrode slurry with a solid content of 50%, wherein the active material includes a negative electrode material and graphite with a mass ratio of 9:1; the rheological properties of the negative electrode slurry are tested using a German Haake rotational rheometer to obtain a rheological curve of the negative electrode slurry; in the rheological curve, when the shear rate is 0S -1 、150S -1 、300S -1 When , the corresponding shear stresses in the rheological curve are τ0, τ1, τ2, and the relationship between the shear stresses satisfies: 2τ1>(τ2-τ0). It can be understood that the relationship between the shear stress in the rheological curve of the above-mentioned negative electrode slurry is related to the leveling performance, sagging performance and sedimentation performance of the negative electrode material. By defining this relationship, the storage stability of the negative electrode material in the negative electrode slurry can be improved. By defining the shear rate-shear stress, the fluidity and stability of the slurry of the negative electrode material can be improved, the uniformity and consistency of the pole piece can be increased, the bonding strength between the active material and the current collector can be increased, and the active material can be reduced from falling off the current collector. When the rheological curve satisfies the above formula, the negative electrode material has good anti-settling performance, anti-sagging performance and storage stability. In addition, the active material on the pole piece can be evenly attached to the current collector, which is beneficial to improve the peel strength of the pole piece. When 2τ1≤(τ2-τ0), the negative electrode material in the negative electrode slurry is prone to sedimentation, tailing, and stratification, which is not conducive to pole piece coating, and also reduces the consistency of the battery. In a second aspect, the present application provides a negative electrode slurry, comprising the negative electrode material of the first aspect. In some embodiments, the negative electrode slurry is formed by mixing active materials, carboxymethyl cellulose, conductive carbon black and styrene-butadiene rubber in a mass ratio of 95.3:1.3:1.5:1.9, wherein the active material includes negative electrode materials and graphite in a mass ratio of 9:1; the rheological properties of the negative electrode slurry are tested using a German Haake rotational rheometer to obtain a rheological curve of the negative electrode slurry; in the rheological curve, when the shear rate is 0S -1 、150S -1 、300S -1 When , the corresponding shear stresses in the rheological curve are τ0, τ1, τ2, and the relationship between the shear stresses satisfies: 2τ1>(τ2-τ0). In a third aspect, the present application provides a method for preparing a negative electrode material, as shown in FIG1 , comprising the following steps: S100, silicon oxide SiO x Place in an acid solution for the first surface modification treatment, wherein 0<x<2; S200, comprising silicon oxide SiO after the first surface modification treatment x The mixture with the reducing lithium-containing compound is subjected to a pre-lithiation treatment and a coating treatment at 300° C. to 800° C. to obtain a precursor, wherein 0<x<2; S300, subjecting the precursor to a second surface modification treatment to obtain a negative electrode material, wherein the negative electrode material includes a silicon-based active substance and a coating layer located on at least a portion of the surface of the silicon-based active substance, and the silicon-based active substance includes silicon and lithium silicate. The negative electrode material preparation method provided in the present application comprises: x The first surface modification treatment is carried out in an acid solution. The acid solution reacts with silicon oxide SiO x The surface is oxidized and etched to form silicon oxide SiO x The formation of weak defect sites on the surface can increase the SiO x The reaction points in the pre-lithiation process promote a more uniform pre-lithiation reaction, obtain more lithium silicate growth points, and are conducive to the uniform distribution of lithium silicate inside the particles, which helps to adjust the crystal phase type and content of lithium silicate on the surface of the material. x Pre-lithiation treatment can greatly reduce the catalytic growth of lithium silicate on silicon grains, thereby regulating the Li 2SiO 3. Li 2Si 2O 5 and the types, contents and grain growth of the three components of silicon; due to the first surface modification of silicon oxide SiO x The surface has uniformly distributed growth sites, which will contain silicon oxide SiO after the first surface modification treatment. xPre-lithiation treatment with a mixture of reducing lithium-containing compounds can improve the utilization rate of lithium and the uniformity of the distribution of pre-lithiation products. The pre-lithiation products are evenly distributed in the negative electrode material, which is beneficial to buffering the volume change of the silicon-based active substance during the charging and discharging process, maintaining the overall structure of the stable negative electrode material, extending the cycle life, reducing the regeneration of the SEI film on the surface of the negative electrode material, and improving the primary effect of the negative electrode material; by performing a second surface modification treatment on the precursor, the surface morphology of the negative electrode material can be further adjusted, and the crystal phase type and content of the lithium silicate on the surface of the material can be adjusted. On the one hand, it can stabilize the solid-liquid contact interface between the negative electrode material and the electrolyte, reduce the risk of the negative electrode material being corroded in the electrolyte, and improve the high-temperature storage performance of the battery; on the other hand, it can improve the adhesion strength of the binder to the negative electrode material, enhance the peeling strength of the electrode sheet, reduce the rebound of the electrode sheet, and stabilize the conductive network of the electrode sheet, thereby improving the cycle life of the battery prepared from the negative electrode material. The following is a detailed description of the preparation method provided in this scheme: Step S100, silicon oxide SiO x The first surface modification treatment is carried out in an acid solution, wherein 0<x<2. In some embodiments, the silicon oxide is SiO x , where 0<x<2, SiO x Specifically, it can be SiO 0.5 、SiO 0.7 、SiO、SiO 1.2 、SiO 1.4 、SiO 1.6 、SiO 1.8 and SiO 1.9 It should be noted that SiO x The composition of the silicon is relatively complex and can be understood as at least one of amorphous silicon and crystalline silicon uniformly dispersed in SiO 2. At high temperatures, its thermodynamic properties are very unstable and it is easy to undergo reduction reaction with lithium sources to form lithium silicates. In some embodiments, the acid solution includes at least one of hydrofluoric acid, nitric acid, fluorosulfonic acid, fluoroantimonysulfonic acid, hydrochloric acid, hydrobromic acid, and hydroiodic acid. xSurface modification treatment is performed to achieve silicon oxide SiO x Surface oxidation and etching treatment can be performed on silicon oxide SiO x The formation of slight defects on the surface increases the reaction sites of the pre-lithiation process, promotes a more uniform pre-lithiation reaction, obtains more lithium silicate growth sites, and is conducive to the uniform distribution of lithium silicate inside the particles. When the amount of pre-lithiation is fixed, it helps to adjust the crystal phase type and content of lithium silicate. In addition, the use of surface-modified silicon oxide for pre-lithiation treatment can greatly reduce the catalytic growth of lithium silicate on silicon grains. In some embodiments, the concentration of the acid solution is ≤2 mol / L. Specifically, the concentration of the acid solution can be 0.1 mol / L, 0.5 mol / L, 1 mol / L, 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, 1.8 mol / L, 1.9 mol / L, and 2 mol / L, etc., and of course, it can also be other values within the above range, which is not limited here. In some embodiments, the temperature of the first surface modification treatment is 30°C~100°C, specifically 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C and 100°C, etc. Of course, it can also be other values within the above range, which is not limited here. In some embodiments, the time for the first surface modification treatment is 2h~8h, specifically 2h, 3h, 4h, 5h, 6h, 7h and 8h, etc., and of course, it can also be other values within the above range, which is not limited here. In some embodiments, the preparation method further comprises treating the silicon oxide SiO x Carry out solid-liquid separation, washing and drying. In some embodiments, the preparation method further comprises treating the silicon oxide SiO x Solid-liquid separation, washing and drying are performed, and the drying temperature is 50° C. to 180° C. Specifically, the drying temperature can be 50° C., 60° C., 70° C., 80° C., 90° C., 100° C., 110° C., 120° C., 130° C., 140° C., 150° C., 160° C., 170° C. and 180° C., and of course, other values within the above range can also be used, which are not limited here. Step S200, the silicon oxide SiO x The mixture with the reducing lithium-containing compound is subjected to a pre-lithiation treatment and a coating treatment at 300° C. to 800° C. to obtain a precursor, wherein 0<x<2. In the above scheme, the temperature of the pre-lithiation treatment can be 300°C, 350°C, 400°C, 450°C, 500°C, 550°C, 600°C, 650°C, 700°C, 710°C and 800°C, etc., and of course it can also be other values within the above range, which are not limited here. It can be understood that when the temperature of the pre-lithiation treatment is too low, the reducing lithium-containing compound cannot react completely with the silicon oxide, and the remaining silicon oxide will cause the oxygen content in the negative electrode material to be high, which is not conducive to the improvement of the first effect of the negative electrode material; when the temperature of the pre-lithiation treatment is too high, the reducing lithium-containing compound and the silicon oxide react violently, and the speed and amount of lithium silicate generated are fast and large. On the one hand, it will catalyze the growth of silicon grains in the material, so that the recycling performance of the negative electrode material is deteriorated; on the other hand, the fast speed and amount of lithium silicate generated will reduce the stability of the negative electrode slurry, making the negative electrode slurry unable to be stably stored. Controlling the pre-lithiation temperature within this range is beneficial to the reaction between the lithium source and silicon oxide, to balancing the crystal phase type and content of lithium silicate, and to obtaining silicon grains of appropriate size, thereby further improving the slurry storage stability of the material. In some embodiments, the silicon oxide is silicon monoxide. It can be understood that when silicon monoxide is used as the silicon oxide, the problem of unstable processing performance after lithium doping of silicon monoxide to improve the initial effect can be effectively solved. In some embodiments, the reducing lithium-containing compound includes at least one of lithium hydride, alkyl lithium, metallic lithium, lithium aluminum hydride, lithium amide, lithium borohydride, and lithium silicon alloy. It can be understood that the reducing lithium-containing compound is selected as the lithium source for the pre-lithiation treatment. Since the surface of the silicon oxide after the first surface modification has uniformly distributed growth sites, the mixture containing the silicon oxide after the first surface modification treatment and the reducing lithium-containing compound is subjected to pre-lithiation treatment, which can improve the utilization rate of lithium and the uniformity of the distribution of the pre-lithiation product on the surface of the silicon oxide; improving the utilization rate of lithium is conducive to reducing costs and improving the pre-lithiation effect (first effect); the pre-lithiation product is evenly distributed in the negative electrode material, which is conducive to buffering the volume change of the battery prepared by the negative electrode material during the charge and discharge process and improving the cycle performance. In some embodiments, the mass ratio of silicon oxide to the reducing lithium-containing compound after the first surface modification treatment is 1:(0.03~0.2), specifically 1:0.03, 1:0.05, 1:0.08, 1:0.1, 1:0.15 and 1:0.2, etc., and of course it can also be other values within the above range, which is not limited here. In some embodiments, the pre-lithiation treatment is performed in a protective atmosphere. It can be understood that the pre-lithiation treatment in a protective atmosphere can reduce the risk of introducing oxygen elements, ensure the initial effect of the pre-lithiation material, and also help to regulate the composition of lithium silicate, further improving the storage stability of the slurry. In some embodiments, the protective atmosphere includes at least one of nitrogen, helium, neon, argon, krypton, and xenon. In some embodiments, the pre-lithiation treatment time is 3h~9h, specifically 3h, 4h, 5h, 6h, 7h, 8h and 9h, etc., and of course, other values within the above range are also possible, which are not limited here. It can be understood that the pre-lithiation treatment time is within the above range, and the Li 2SiO 3 fully converted into Li 2Si 2O 5. In some embodiments, the lithium silicate includes Li 2SiO 3. Li 2Si 2O 5. Li 4SiO At least one of the 4. In some embodiments, the method further includes mixing the mixture of silicon oxide after the first surface modification treatment and the reductive lithium-containing compound before pre-lithiation treatment of the mixture at 300°C to 800°C. In some embodiments, the temperature of the mixing treatment is 60°C~320°C, specifically 60°C, 70°C, 80°C, 90°C, 100°C, 150°C, 200°C, 250°C, 300°C, 310°C and 320°C, etc., and of course, it can also be other values within the above range, which is not limited here. In some embodiments, the mixing treatment time is 0.5h~10h, specifically 0.5h, 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h and 10h, etc., and of course it can also be other values within the above range, which is not limited here. In some embodiments, the equipment required for the mixing process includes at least one of an equipment with a dispersing function or an equipment with a shearing force. It can be understood that using an equipment with a high-speed dispersing function and a shearing force to mix the mixture containing the silicon oxide after the first surface modification treatment and the reducing lithium-containing compound before pre-lithiation can effectively alleviate the severity of the reaction in the early stage of pre-lithiation, help to regulate the lithium silicate component to meet the requirements of this application, thereby improving the storage stability of the slurry and the bonding ability of the active material in the pole piece. In some embodiments, before subjecting the mixture comprising the silicon oxide subjected to the first surface modification treatment and the reducing lithium-containing compound to a pre-lithiation treatment, the method further comprises subjecting the silicon oxide subjected to the first surface modification treatment to a coating treatment. It can be understood that the coating treatment can be carried out before the mixture of silicon oxide after the first surface modification treatment and the reducing lithium-containing compound is pre-lithiated, or it can be carried out after the mixture of silicon oxide after the first surface modification treatment and the reducing lithium-containing compound is pre-lithiated, and there is no limitation here. It should be noted that when the coating treatment is carried out before the mixture of silicon oxide after the first surface modification treatment and the reducing lithium-containing compound is pre-lithiated, the coating treatment needs to be carried out before the mixture of silicon oxide after the first surface modification treatment and the reducing lithium-containing compound is mixed. In some embodiments, the coating treatment includes a carbon coating treatment, and the process of the carbon coating treatment includes at least one of a liquid phase coating method, a gas phase coating method, and a solid phase coating method. In some embodiments, the coating treatment includes a carbon coating treatment, and the coating material of the carbon coating treatment includes at least one of amorphous carbon, graphene, graphite, carbon nanotubes and carbon fibers. Preferably, the coating material of the carbon coating is amorphous carbon. It can be understood that amorphous carbon is produced by high-temperature cracking and has a certain degree of graphitization. Using amorphous carbon to coat the surface of silicon oxide can improve the conductivity of the negative electrode material on the one hand, and on the other hand, the amorphous carbon produced by high-temperature cracking has a relatively developed void structure. Coating it on the surface of silicon oxide can inhibit the volume expansion of the negative electrode material, which is beneficial to improving the recycling performance of the negative electrode material. In step S300, the precursor is subjected to a second surface modification treatment to obtain a negative electrode material, wherein the negative electrode material includes a silicon-based active substance and a coating layer located on at least a portion of the surface of the silicon-based active substance, and the silicon-based active substance includes silicon and lithium silicate. In some embodiments, the second surface modification treatment includes at least one of purification treatment, coating treatment, heat treatment, oxidation treatment, and etching treatment. In some embodiments, the coating treatment may specifically be a secondary carbon coating treatment, a polymer coating treatment, or an inorganic coating treatment, etc., which is not limited herein. In a specific implementation, the heat treatment is combined with other methods, such as polymer coating treatment and etching treatment, which are not limited here. In some embodiments, the temperature of the second surface modification treatment is 50°C~900°C, specifically 50°C, 100°C, 200°C, 300°C, 400°C, 500°C, 600°C, 700°C, 800°C and 900°C, etc. Of course, it can also be other values within the above range, which is not limited here. In some embodiments, the time for the second surface modification treatment is 0.5h~10h, specifically 0.5h, 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h and 10h, etc., and of course it can also be other values within the above range, which is not limited here. In some embodiments, the second surface modification treatment includes placing the precursor in an aluminum hydroxide solution for purification. It can be understood that since the coatings on the aluminum foil and the separator in the battery system are of the same origin, placing the precursor in an aluminum hydroxide solution for purification can make the composed battery system more compatible. In the above preparation method, if the surface modification treatment is excessive, it will lead to too many pre-lithium reaction sites on the surface of silicon oxide, and the lithium source will react violently on the surface of the negative electrode material to generate more Li 2SiO 3 Even Li 4SiO 4. In this way 2Si 2O 5 content will be very low; if the surface modification treatment is too weak, the pre-lithiation reaction sites on the surface of silicon oxide are insufficient, the content of lithium silicate generated is small, and the pre-lithiation effect cannot be exerted. In addition, the reaction temperature and reaction time during the pre-lithiation process will also affect the product composition of the negative electrode material after pre-lithiation. If the reaction temperature is too high and the reaction time is too long, it will cause Li 2SiO 3 content is high. If the reaction temperature is too low and the reaction time is too short, it will lead to Li 2Si 2O The content of 5 is high. In general, it is necessary to control the appropriate active site, temperature and time, and combine the three to prepare the negative electrode material that meets the requirements. In a fourth aspect, the present application provides a lithium-ion battery, wherein the lithium-ion battery comprises the negative electrode material of the first aspect or the negative electrode material prepared by the preparation method of the second aspect. The above are only preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application should be included in the scope of protection of the present application. Example Example 1 (1) Silicon monoxide (SiO) is placed in a mixed acid solution of nitric acid and hydrochloric acid with a concentration of 1 mol / L, stirred and dispersed at 50° C. for 4 h, then filtered and washed with pure water, and the obtained product is dried at 80° C. to obtain silicon monoxide (SiO) after surface modification. (2) A mixture of 1000 g of surface-modified silicon monoxide (SiO) and 200 g of lithium hydride is placed in a high-speed disperser, argon gas is introduced, the temperature is raised to 80° C., and the mixture is dispersed at 2000 rpm for 1 h for mixing. The mixture is cooled to room temperature and then loaded into a crucible. The crucible is placed in a box furnace for pre-lithiation treatment at 500° C. for 4 h, and the temperature is lowered to 25° C. to obtain a silicon-based active material. Then, 2% wt of amorphous carbon is coated on the surface of the silicon-based active material by a liquid phase coating method to obtain a precursor. (3) Place the precursor in Al(OH) 3, the precursor was purified at 40°C for 2h, the residual alkaline liquid on the surface of the precursor was removed by filtration and washing, and then 2%wt of amorphous carbon was coated on the surface of the precursor by a liquid phase coating method to obtain a negative electrode material. The negative electrode material prepared in this embodiment includes a silicon-based active material and a carbon material located on at least a portion of the surface of the silicon-based active material, the silicon-based active material includes silicon and lithium silicate, and the silicon includes nano silicon grains; the negative electrode material is measured by XRD ray diffraction method, and the relationship between A, B, and C in the negative electrode material is calculated by X-ray diffraction spectrum of the negative electrode material to satisfy: (A+B) / C=4.6, (A+C) / B=2.1, (B+C) / A=12.3. FIG. 2 is a relationship diagram between powder density and powder conductivity of the negative electrode material prepared in this embodiment. It can be concluded from FIG. 2 that the relationship between ρ1, ρ2, σ1, and σ2 satisfies: (σ2-σ1) / (ρ2-ρ1)=0.32, and the relationship between shear forces in the rheological curve satisfies 2τ1>(τ2-τ0). The negative electrode material prepared in this embodiment can be stably stored for more than 72 hours after being prepared into negative electrode slurry. Example 2 The negative electrode material was prepared in a method substantially the same as that in Example 1, except that: (2) 2%wt of amorphous carbon was coated on the surface of 1000g of surface-modified silicon monoxide (SiO) by a liquid phase coating method, and then 200g of lithium hydride was weighed and placed in a high-speed disperser. Argon was introduced, the temperature was raised to 80°C, and the mixture was dispersed at 2000 rpm for 1h for mixing. The mixture was cooled to room temperature and then loaded into a crucible. The crucible was placed in a box furnace for pre-lithiation treatment at 500°C for 4h, and then the temperature was lowered to 25°C to obtain a precursor. The remaining operations are the same as those in Example 1. The negative electrode material prepared in this embodiment includes a silicon-based active material and a carbon material located on at least a portion of the surface of the silicon-based active material, the silicon-based active material includes silicon and lithium silicate, and the silicon includes nano silicon grains; the negative electrode material is measured by XRD ray diffraction method, and the relationship between A, B, and C in the negative electrode material is calculated by X-ray diffraction spectrum of the negative electrode material to satisfy: (A+B) / C=5.1, (A+C) / B=2.0, (B+C) / A=10.3, the relationship between ρ1, ρ2, σ1, and σ2 satisfies: (σ2-σ1) / (ρ2-ρ1)=0.33, and the relationship between shear forces in the rheological curve satisfies 2τ1>(τ2-τ0). The negative electrode material prepared in this embodiment can be stably stored for more than 72 hours after being prepared into negative electrode slurry. Example 3 The negative electrode material was prepared in a method substantially the same as that in Example 1, except that: (2) A mixture of 1000 g of surface-modified silicon monoxide (SiO) and 150 g of metallic lithium was placed in a high-speed disperser, argon gas was introduced, the temperature was raised to 80° C., and the mixture was dispersed at 2000 rpm for 1 h for mixing. The mixture was cooled to room temperature and then loaded into a crucible. The crucible was placed in a box furnace for pre-lithiation treatment at 500° C. for 4 h, and the temperature was lowered to 25° C. to obtain a silicon-based active material. Then, 2% wt of amorphous carbon was coated on the surface of the silicon-based active material by a liquid phase coating method to obtain a precursor. The remaining operations are the same as those in Example 1. The negative electrode material prepared in this embodiment includes a silicon-based active material and a carbon material located on at least a portion of the surface of the silicon-based active material, the silicon-based active material includes silicon and lithium silicate, and the silicon includes nano-silicon grains; the negative electrode material is measured by XRD ray diffraction method, and the relationship between A, B, and C in the negative electrode material is calculated by X-ray diffraction spectrum of the negative electrode material to satisfy: (A+B) / C=4.1, (A+C) / B=2.2, (B+C) / A=8.8, the relationship between ρ1, ρ2, σ1, and σ2 satisfies: (σ2-σ1) / (ρ2-ρ1)=0.46, and the relationship between shear forces in the rheological curve satisfies 2τ1>(τ2-τ0). The negative electrode material prepared in this embodiment can be stably stored for more than 72 hours after being prepared into negative electrode slurry. Example 4 (1) Silicon oxide (SiO 1.5 ) was placed in a mixed acid solution of nitric acid and hydrochloric acid with a concentration of 1 mol / L, stirred and dispersed at 50°C for 4 hours, then filtered and washed with pure water, and the obtained product was dried at 80°C to obtain silicon oxide (SiO 1.5 ). (2) 1000 g of surface-modified silicon oxide (SiO 1.5 ) and 100g of alkyl lithium are placed in a high-speed disperser, argon is introduced, the temperature is raised to 80°C, and the mixture is dispersed at 2000 rpm for 1 hour for mixing. The mixture is cooled to room temperature and then loaded into a crucible. The crucible is placed in a box furnace for pre-lithiation treatment at 500°C for 4 hours, and the temperature is lowered to 25°C to obtain a silicon-based active substance. Then, 2%wt of amorphous carbon is coated on the surface of the silicon-based active substance by a liquid phase coating method to obtain a precursor. (3) Place the precursor in Al(OH) 3, the precursor was purified at 40°C for 2h, the residual alkaline liquid on the surface of the precursor was removed by filtration and washing, and then 2%wt of amorphous carbon was coated on the surface of the precursor by a liquid phase coating method to obtain a negative electrode material. The negative electrode material prepared in this embodiment includes a silicon-based active material and a carbon material located on at least a portion of the surface of the silicon-based active material, the silicon-based active material includes silicon and lithium silicate, and the silicon includes nano-silicon grains; the negative electrode material is measured by XRD ray diffraction method, and the relationship between A, B, and C in the negative electrode material is calculated by X-ray diffraction spectrum of the negative electrode material to satisfy: (A+B) / C=2.5, (A+C) / B=1.8, (B+C) / A=1.2, the relationship between ρ1, ρ2, σ1, and σ2 satisfies: (σ2-σ1) / (ρ2-ρ1)=0.52; the relationship between shear forces in the rheological curve satisfies 2τ1>(τ2-τ0). The negative electrode material prepared in this embodiment can be stably stored for more than 72 hours after being prepared into negative electrode slurry. Example 5 The negative electrode material was prepared in a method substantially the same as that in Example 1, except that: (1) Silicon monoxide (SiO) is placed in a mixed acid solution of nitric acid and hydrochloric acid with a concentration of 2 mol / L, stirred and dispersed at 50° C. for 4 h, then filtered and washed with pure water, and the obtained product is dried at 80° C. to obtain silicon monoxide (SiO) after surface modification. The remaining operations are the same as those in Example 1. The negative electrode material prepared in this embodiment includes a silicon-based active material and a carbon material located on at least a portion of the surface of the silicon-based active material, the silicon-based active material includes silicon and lithium silicate, and the silicon includes nano silicon grains; the negative electrode material is measured by XRD ray diffraction method, and the relationship between A, B, and C in the negative electrode material is calculated by X-ray diffraction spectrum of the negative electrode material to satisfy: (A+B) / C=2.8, (A+C) / B=1.5, (B+C) / A=1.9, the relationship between ρ1, ρ2, σ1, and σ2 satisfies: (σ2-σ1) / (ρ2-ρ1)=0.61, and the relationship between shear forces in the rheological curve satisfies 2τ1>(τ2-τ0). The negative electrode material prepared in this embodiment can be stably stored for more than 72 hours after being prepared into negative electrode slurry. Example 6 The negative electrode material was prepared in a method substantially the same as that in Example 1, except that: (2) A mixture of 1000 g of surface-modified silicon monoxide (SiO) and 200 g of lithium hydride was placed in a high-speed disperser, argon was introduced, the temperature was raised to 80° C., and the mixture was dispersed at 2000 rpm for 1 h for mixing. The mixture was cooled to room temperature and then placed in a crucible. The crucible was placed in a box furnace for pre-lithiation treatment at 300° C. for 5 h, and the temperature was lowered to 25° C. to obtain a silicon-based active material. Then, 2% wt of amorphous carbon was coated on the surface of the silicon-based active material by a liquid phase coating method to obtain a precursor. The remaining operations were the same as those in Example 1. The negative electrode material prepared in this embodiment includes a silicon-based active material and a carbon material located on at least a portion of the surface of the silicon-based active material, the silicon-based active material includes silicon and lithium silicate, and the silicon includes nano silicon grains; the negative electrode material is measured by XRD ray diffraction method, and the relationship between A, B, and C in the negative electrode material is calculated by X-ray diffraction spectrum of the negative electrode material to satisfy: (A+B) / C=10, (A+C) / B=1.0, (B+C) / A=30, the relationship between ρ1, ρ2, σ1, and σ2 satisfies: (σ2-σ1) / (ρ2-ρ1)=0.46, and the relationship between shear forces in the rheological curve satisfies 2τ1>(τ2-τ0). The negative electrode material prepared in this embodiment can be stably stored for more than 72 hours after being prepared into negative electrode slurry. Example 7 The negative electrode material was prepared in a method substantially the same as that in Example 1, except that: (2) A mixture of 1000 g of surface-modified silicon monoxide (SiO) and 200 g of lithium hydride is placed in a high-speed disperser, argon gas is introduced, the temperature is raised to 80° C., and the mixture is dispersed at 2000 rpm for 1 h for mixing. The mixture is cooled to room temperature and then loaded into a crucible. The crucible is placed in a box furnace for pre-lithiation treatment at 800° C. for 4 h, and the temperature is lowered to 25° C. to obtain a silicon-based active material. Then, 2% wt of amorphous carbon is coated on the surface of the silicon-based active material by a liquid phase coating method to obtain a precursor. The remaining operations are the same as those in Example 1. The negative electrode material prepared in this embodiment includes a silicon-based active material and a carbon material located on at least a portion of the surface of the silicon-based active material, the silicon-based active material includes silicon and lithium silicate, and the silicon includes nano silicon grains; the negative electrode material is measured by XRD ray diffraction method, and the relationship between A, B, and C in the negative electrode material is calculated by X-ray diffraction spectrum of the negative electrode material to satisfy: (A+B) / C=1.3, (A+C) / B=5, (B+C) / A=29.3, the relationship between ρ1, ρ2, σ1, and σ2 satisfies: (σ2-σ1) / (ρ2-ρ1)=0.5, and the relationship between shear forces in the rheological curve satisfies 2τ1>(τ2-τ0). The negative electrode material prepared in this embodiment can be stably stored for more than 72 hours after being prepared into negative electrode slurry. Comparative Example 1 The difference from Example 1 is that: In this embodiment, except that in step (2), the crucible is placed in a box furnace for pre-lithiation treatment at 200° C. for 5 h, other operating conditions and raw materials are the same as those in Example 1. The negative electrode material prepared in this comparative example includes a silicon-based active material and a carbon material located on at least a portion of the surface of the silicon-based active material, wherein the silicon-based active material includes silicon and lithium silicate; the negative electrode material is measured by XRD ray diffraction method, and the relationship between A, B, and C in the negative electrode material is calculated by X-ray diffraction spectrum of the negative electrode material to satisfy: (A+B) / C=8, (A+C) / B=13, (B+C) / A=40, the relationship between ρ1, ρ2, σ1, and σ2 satisfies: (σ2-σ1) / (ρ2-ρ1)=0.9, and the relationship between shear forces in the rheological curve satisfies 2τ1>(τ2-τ0). The negative electrode material prepared in this comparative example cannot be stably stored after being prepared into negative electrode slurry. Comparative Example 2 The difference from Example 1 is that: In this embodiment, except that in step (2), the crucible is placed in a box furnace for pre-lithiation treatment at 900° C. for 2 h, other operating conditions and raw materials are the same as those in Example 1. The negative electrode material prepared in this comparative example includes a silicon-based active substance and a carbon material located on at least a portion of the surface of the silicon-based active substance, wherein the silicon-based active substance includes silicon and lithium silicate; the negative electrode material is measured by XRD ray diffraction method, and the relationship between A, B, and C in the negative electrode material is calculated by the X-ray diffraction spectrum of the negative electrode material to satisfy: (A+B) / C=1.8, (A+C) / B=18, (B+C) / A=30, the relationship between ρ1, ρ2, σ1, and σ2 satisfies: (σ2-σ1) / (ρ2-ρ1)=0.96, and the relationship between shear forces in the rheological curve satisfies 2τ1<(τ2-τ0). The negative electrode material prepared in this comparative example cannot be stably stored after being prepared into negative electrode slurry. Comparative Example 3 The difference from Example 1 is that: In this comparative example, the process of step (1) of Example 1 is not performed, and other operating conditions and raw materials are the same as those of Example 1. The negative electrode material prepared in this comparative example includes a silicon-based active substance and a carbon material located on at least a portion of the surface of the silicon-based active substance, wherein the silicon-based active substance includes silicon and lithium silicate; the negative electrode material is measured by XRD ray diffraction method, and the relationship between A, B, and C in the negative electrode material is calculated by the X-ray diffraction spectrum of the negative electrode material to satisfy: (A+B) / C=2.1, (A+C) / B=6.2, (B+C) / A=6.9, the relationship between ρ1, ρ2, σ1, and σ2 satisfies: (σ2-σ1) / (ρ2-ρ1)=0.72, and the relationship between shear forces in the rheological curve satisfies 2τ1<(τ2-τ0). The negative electrode material prepared in this comparative example cannot be stably stored after being prepared into negative electrode slurry. Comparative Example 4 The difference from Example 1 is that: This comparative example does not carry out the process of step (3) of Example 1, and other operating conditions and raw materials are the same as those of Example 1. The negative electrode material prepared in this comparative example includes a silicon-based active substance and a carbon material located on at least a portion of the surface of the silicon-based active substance, wherein the silicon-based active substance includes silicon and lithium silicate; the negative electrode material is measured by XRD ray diffraction method, and the relationship between A, B, and C in the negative electrode material is calculated by the X-ray diffraction spectrum of the negative electrode material to satisfy: (A+B) / C=1.8, (A+C) / B=7.0, (B+C) / A=19, the relationship between ρ1, ρ2, σ1, and σ2 satisfies: (σ2-σ1) / (ρ2-ρ1)=0.96, and the relationship between shear forces in the rheological curve satisfies 2τ1<(τ2-τ0). The negative electrode material prepared in this comparative example cannot be stably stored after being prepared into negative electrode slurry. Test method: (1) XRD test method of negative electrode material: The XRD spectrum of the material was tested using the German Bruker AXS D8-Focus equipment. Equipment test parameters: CuKα ray, divergence slit 1.0°, anti-scattering slit 2.0°, receiving slit 9.6°, voltage range 40KV, current 40mA, scanning range 10-90°, scanning step (scanstep) 0.01313, scanning mode is continuous, each step scanning time is 10.2s, and calculation wavelength is 1.5406Å. Calculate the value of A / B / C and the average particle size of silicon grains. (2) Test method for powder conductivity and powder density of negative electrode materials: The test equipment comes from Mitsubishi Chemical of Japan. The test parameters are: the initial resistance magnitude can be selected as -3, the voltage limit can be selected as 10V, and the sample quality should ensure that the sample thickness is 3~5mm under the pressure of 20KN. The pressure is set to 4, 8, 12, 16, 20KN, the Electroderadius is 0.7mm, and the Sampleradius is 10mm. The powder density and powder conductivity corresponding to different pressures are measured. (3) Testing method of rheological curve of negative electrode slurry: Active materials, carboxymethyl cellulose, conductive carbon black and styrene-butadiene rubber are mixed in a mass ratio of 95.3:1.3:1.5:1.9 to form a negative electrode slurry with a solid content of 50%, wherein the active materials include negative electrode materials and graphite in a mass ratio of 9:1; the rheological properties of the negative electrode slurry are tested using a German Haake rotational rheometer to obtain the rheological curve of the negative electrode slurry. (4) Power-off 50-cycle performance test: According to the equipment and methods used in the operating instructions of BTRTC / ZY / 01-020 "Button Battery Method Operating Instructions" of BTR Company: PAA is selected as a binder to prepare a 5% solid content glue solution, and then the negative electrode active material and conductive agent are added according to the mass ratio of negative electrode active material: conductive agent (SP): binder (PAA) = 75:15:10, and a high-speed disperser is used to evenly disperse to form a negative electrode slurry, and the slurry is evenly coated on a copper foil with a thickness of 10um, and then dried, rolled, punched, and dried again to obtain the negative electrode. The positive electrode uses a lithium sheet, and the button battery is assembled in the order of shell, gasket, nickel sheet, lithium sheet, diaphragm, negative electrode, and shell. Among them, the counter electrode uses a metal lithium sheet, and the diaphragm is a PP-PE-PP composite film with a diameter of 19.2mm; the electrolyte component ratio is EC / EMC / DMC=1 / 1 / 1, and the lithium salt (LiPF6) concentration is 1.05mol / L. Using button battery charging and discharging equipment, in the first week, 0.1C discharge to 0.01V, 0.01C discharge to 0.01V, 0.01C discharge to 0.005V, 0.1C charge to 1.5V; in the second week, 0.2C discharge to 0.01V, 0.02C discharge to 0.01V, 0.02C discharge to 0.005V, 0.2C charge to 1.5V; in the third week, 0.5C discharge to 0.01V, 0.02C discharge to 0.005V, 0.02C charge to 1.5V. 0.5C discharge in equal steps to 0.01V, 0.05C discharge to 0.005V, 0.5C charge to 1.5V; from the 4th to the 50th week, 1C discharge to 0.01V, 0.1C discharge in equal steps to 0.01V, 0.1C discharge to 0.005V, 1C charge to 1.5V; in the 51st week, 0.1C discharge to 0.01V, 0.01C discharge in equal steps to 0.01V, 0.01C discharge to 0.005V, 0.01C charge to 1.5V. (5) Negative electrode slurry storage stability assessment method: Active materials, carboxymethyl cellulose, conductive carbon black and styrene-butadiene rubber were mixed in a mass ratio of 95.3:1.3:1.5:1.9 to form a negative electrode slurry with a solid content of 50%, wherein the active materials included negative electrode materials and graphite in a mass ratio of 9:1, and then the negative electrode slurry was allowed to stand at 25°C to observe changes in viscosity, fluidity, solid content, fineness, coating conditions, etc. during the standing process of the slurry. If the viscosity increases or decreases, it means that the slurry may have particle aggregation or dispersion, which is not conducive to the stability of the slurry; if obvious stratification and fluid thickening occur, it means that the slurry has reduced dispersibility, poor fluidity, and reduced stability; if the solid content changes significantly, particles will aggregate or precipitate in the slurry, affecting its stability; if larger particles aggregate or the fineness of the particles changes significantly, the stability of the slurry will decrease; the slurry is coated on the substrate, and the uniformity and adhesion of the coating are observed. If the coating is uneven, falls off or cracks, it means that the slurry has poor stability. (6) Test method for specific capacity: Use button battery charging and discharging equipment, 0.1C constant current charging to 10mV, then 0.02C constant current charging to 5mV, and 0.1C constant current discharging to 1.5V cutoff. The above test results are detailed in Table 1. Table 1 Test results of embodiments and proportions Based on the above examples and comparative examples, it can be seen that Examples 1 to 7 control the Li 2SiO 3. Li 2Si 2O 5 and the balance between the three components of silicon can improve the lithiation uniformity of the negative electrode material, improve the processing performance of the negative electrode material, and thus improve the storage stability of the negative electrode slurry made of the negative electrode material; at the same time, by controlling the Li 2SiO 3. Li 2Si 2O 5 and the balance between the three components of silicon can increase the Li 2Si 2O 5 content, reducing the destructive effect of lithium silicate on the binder, improving the stability of the electrode, improving the cycle performance of the negative electrode material, and extending the cycle life. Compared with Example 1, the temperature of the pre-lithiation treatment of the negative electrode material in Comparative Example 1 is too low. During the pre-lithiation process, the lithium source cannot react completely with silicon monoxide, and the oxygen content in the prepared negative electrode material is high, resulting in a low initial efficiency of the negative electrode material. Compared with Example 1, the temperature of the pre-lithiation treatment of the negative electrode material in Comparative Example 2 is too high. During the pre-lithiation process, the lithium source and silicon monoxide react violently, and lithium silicate is generated at a fast rate and in large quantities. On the one hand, it catalyzes the growth of silicon grains in the negative electrode material, resulting in degradation of the material's recycling performance; on the other hand, it reduces the storage stability of the negative electrode slurry made of the negative electrode material, making it impossible to stably store the slurry for a long time. Compared with Example 1, the negative electrode material of Comparative Example 3 does not perform surface modification on silicon monoxide, the reaction sites of the pre-lithium process are reduced, the pre-lithium reaction is uneven, the growth sites of lithium silicate are reduced, and the lithium silicate inside the negative electrode material particles is unevenly distributed, which is not conducive to the regulation of the crystal phase type and content of lithium silicate, resulting in the Li 2SiO 3. Li 2Si 2O 5 and the imbalance in the relative relationship between the three components of silicon reduce the storage performance of the negative electrode slurry made of the negative electrode material. The negative electrode slurry cannot be stored stably for a long time. The slurry is prone to sedimentation, stratification and gas production during storage, which makes the active material distribution in the coated electrode uneven. Moreover, the lithium silicate in the negative electrode material has a great destructive effect on the binder, which reduces the structural stability of the electrode and leads to a decrease in the recycling performance of the negative electrode material. Compared with Example 1, the negative electrode material of Comparative Example 4 does not perform a second surface treatment on the precursor. On the one hand, the interface stability of the negative electrode material is poor, the performance stability of the formed SEI film is reduced, and the corrosion risk of the negative electrode material in the electrolyte is increased. On the other hand, the adhesion strength of the binder to the negative electrode material is weakened, the peel strength of the electrode piece is reduced, the electrode piece is easy to rebound, the stability of the electrode piece conductive network is reduced, and the recycling performance of the negative electrode material is reduced. S100-S300: Steps The present application is further described below in conjunction with the accompanying drawings and embodiments. FIG1 is a process flow chart of a method for preparing a negative electrode material provided in the present application; FIG. 2 is a graph showing the relationship between the powder density and powder conductivity of the negative electrode material prepared in Example 1 of the present application. S100-S300: Steps

Claims

1. A negative electrode material, wherein, The negative electrode material comprises a silicon-based active material and a coating layer located on at least a portion of the surface of the silicon-based active material. The silicon-based active material comprises silicon and lithium silicate. Using XRD diffraction, the X-ray diffraction pattern of the negative electrode material shows that the peak intensity of the strongest diffraction peak in the 2θ range of 18°~20° is A1, the peak intensity of the strongest diffraction peak in the 2θ range of 26°~27.9° is A2, and the peak intensity of the strongest diffraction peak in the 2θ range of 32°~34° is A3, where A1+A2+A3=A; the peak intensity of the strongest diffraction peak in the 2θ range of 16°~17° is B1, the peak intensity of the strongest diffraction peak in the 2θ range of 22°~25.9° is B2, and the peak intensity of the strongest diffraction peak in the 2θ range of 36°~38° is B3, where B1+B2+B3=B. The peak intensity of the strongest diffraction peak of the negative electrode material in the range of 2θ 28°~30° is C1, the peak intensity of the strongest diffraction peak in the range of 2θ 46°~48° is C2, and the peak intensity of the strongest diffraction peak in the range of 2θ 56°~58° is C3, C1+C2+C3=C; and the relationship between A, B, and C simultaneously satisfies: 0<(A+B) / C≤10, 0<(A+C) / B≤5.

2. The negative electrode material according to claim 1, wherein, The negative electrode material was tested using a powder resistivity tester. The powder conductivity of the negative electrode material at powder density ρ1 was measured as σ1, and the powder conductivity of the negative electrode material at powder density ρ2 was measured as σ2, and the following relationship was satisfied: (σ2-σ1) / (ρ2-ρ1)≤0.

8.

3. The negative electrode material according to claim 1, wherein, The relationship between A, B, and C also satisfies: 1≤(B+C) / A≤30.

4. The negative electrode material according to claim 1, wherein, The silicon-based active material also includes silicon oxide complexes.

5. The negative electrode material according to claim 1, wherein, The molar ratio of oxygen atoms to silicon atoms in the negative electrode material is 0.5 to 2.

6. The negative electrode material according to claim 1, wherein, The silicon in the negative electrode material includes nano-silicon grains, the average particle size of which is 0nm~20nm, but does not include 0nm.

7. The negative electrode material according to claim 1, wherein, The lithium silicate includes at least one of Li2SiO3, Li2Si2O5 and Li4SiO4.

8. The negative electrode material according to claim 1, wherein, The coating layer comprises carbon material, and the mass content of the carbon material in the negative electrode material is less than or equal to 10%.

9. The negative electrode material according to claim 1, wherein, The silicon content in the negative electrode material is 20% to 70% by mass.

10. The negative electrode material according to claim 1, wherein, The lithium silicate content in the negative electrode material is 30% to 75% by mass.

11. The negative electrode material according to claim 1, wherein, The specific surface area of ​​the negative electrode material is less than or equal to 10 m² / g.

12. The negative electrode material according to claim 1, wherein, The pH value of the negative electrode material is 7.2~11.

0.

13. The negative electrode material according to any one of claims 1 to 12, wherein, An active material, carboxymethyl cellulose, conductive carbon black, and styrene-butadiene rubber were mixed in a mass ratio of 95.3:1.3:1.5:1.9 to form a negative electrode slurry with a solid content of 50%. The active material included the negative electrode material and graphite in a mass ratio of 9:

1. The rheological properties of the negative electrode slurry were tested using a German Hacker rotational rheometer to obtain the rheological curve of the negative electrode slurry. In the rheological curve, when the shear rate is 0 s⁻¹, 150 s⁻¹, and 300 s⁻¹, the corresponding shear stresses are τ₀, τ₁, and τ₂, and the relationship between the shear stresses satisfies: 2τ₁>(τ₂-τ₀).

14. A negative electrode slurry, wherein, The negative electrode slurry includes the negative electrode material as described in any one of claims 1 to 13.

15. A lithium-ion battery, wherein, The lithium-ion battery comprises a negative electrode material as described in any one of claims 1 to 13.

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