Negative electrode material, negative electrode slurry, and lithium ion battery

Abstract

A negative electrode material and a preparation method therefor, and a lithium ion battery. The negative electrode material comprises a silicon-based active material and a coating layer located on at least part of the surface of the silicon-based active material, and the silicon-based active material comprises silicon and lithium silicate. According to the negative electrode material, by controlling the type and the degree of crystallinity of the lithium silicate in the material, the storage stability of a negative electrode slurry can be improved, the cycle life of the negative electrode material is prolonged, the bonding capacity of the negative electrode material and a current collector is improved, and the high-temperature storage performance of battery cells is improved, thereby improving the cycle performance of the lithium ion battery.

Description

Anode materials, anode slurries and lithium-ion batteries

[0001] 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 into this application. Technical Field

[0002] 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. Background Art

[0003] 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 only 372mAh / g, which cannot meet the demand for high energy density of future lithium-ion batteries. Although the existing Si has a theoretical capacity of up to 4200mAh / g, its expansion rate is 300%, which affects the cycle performance and restricts its market promotion and application. The corresponding silicon oxide material has better cycle performance, but the first efficiency is low. During the first charge, 20-50% of the lithium is consumed for SEI film formation, which greatly reduces the first coulombic efficiency. As the first efficiency of positive electrode materials becomes higher and higher, it is particularly important to improve the first efficiency of silicon oxide materials.

[0004] Currently, the most effective way to improve the initial efficiency of silicon oxide materials is to pre-dope them with lithium, which allows them to react with the irreversible lithium-consuming phase in the silicon oxide material. The current industrial method is to directly coat the electrode surface with a lithium layer to reduce lithium consumption in the positive electrode. However, this method has strict operating environment requirements and poses significant safety risks, making it difficult to commercialize.

[0005] Under the current state of technological development, there is a general problem of poor processing performance in the first-effect improvement obtained by pre-lithiation on the silicon oxide material side, which is mainly manifested as follows: the slurry prepared by using 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 easily leads to uneven coated electrodes, further reducing the peel strength of the electrode, and the active substances are 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.

[0006] Application Contents

[0007] 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;

[0008] Determined by XRD 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 18° to 20° at 2θ is A1, the peak intensity of the strongest diffraction peak in the range of 26° to 27.9° at 2θ is A2, and the peak intensity of the strongest diffraction peak at 32° to 34° at 2θ is A3, and A1+A2+A3=A;

[0009] The peak intensity of the strongest diffraction peak of the negative electrode material in the range of 16° to 17° at 2θ is B1, the peak intensity of the strongest diffraction peak in the range of 22° to 25.9° at 2θ is B2, and the peak intensity of the strongest diffraction peak in the range of 36° to 38° at 2θ is B3, and B1+B2+B3=B;

[0010] 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;

[0011] And the relationship between A, B, and C satisfies: 0<(A+B) / C≤10, 0<(A+C) / B≤5.

[0012] 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.

[0013] In some embodiments, the relationship between A, B, and C further satisfies: 1≤(B+C) / A≤30.

[0014] In some embodiments, the silicon-based active material further includes a silicon-oxygen composite.

[0015] In some embodiments, the molar ratio of oxygen atoms to silicon atoms in the negative electrode material is 0.5-2.

[0016] 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, excluding 0 nm.

[0017] 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.

[0018] In some embodiments, the lithium silicate includes at least one of Li2SiO3, Li2Si2O5, and Li4SiO4.

[0019] 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%.

[0020] In some embodiments, the mass content of silicon in the negative electrode material is 20% to 70%.

[0021] In some embodiments, the mass content of lithium silicate in the negative electrode material is 30% to 75%.

[0022] In some embodiments, the specific surface area of ​​the negative electrode material is less than or equal to 10m 2 / g.

[0023] In some embodiments, the pH value of the negative electrode material is 7.2 to 11.0.

[0024] In some embodiments, the active material, 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 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).

[0025] In a second aspect, the present application provides a negative electrode slurry comprising the negative electrode material as described in the first aspect.

[0026] In a third aspect, the present application provides a method for preparing a negative electrode material, comprising the following steps:

[0027] Silicon oxide SiO x Place in an acid solution for the first surface modification treatment, wherein 0<x<2;

[0028] 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;

[0029] 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.

[0030] 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.

[0031] In some embodiments, the concentration of the acid solution is ≤2 mol / L.

[0032] In some embodiments, the temperature of the first surface modification treatment is 30°C to 100°C.

[0033] In some embodiments, the first surface modification treatment lasts for 2 hours to 8 hours.

[0034] In some embodiments, the preparation method further comprises treating the silicon oxide SiO x Carry out solid-liquid separation, washing and drying.

[0035] 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.

[0036] In some embodiments, the silicon oxide is silicon monoxide.

[0037] 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.

[0038] 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).

[0039] In some embodiments, the pre-lithiation treatment is performed in a protective atmosphere.

[0040] In some embodiments, the protective atmosphere includes at least one of nitrogen, helium, neon, argon, krypton, and xenon.

[0041] In some embodiments, the pre-lithiation treatment lasts for 3 hours to 9 hours.

[0042] 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.

[0043] 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.

[0044] In some embodiments, the lithium silicate includes at least one of Li2SiO3, Li2Si2O5, and Li4SiO4.

[0045] In some embodiments, the method comprises the step of treating the silicon oxide SiO x Before the mixture of 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.

[0046] In some embodiments, the mixing process is carried out at a temperature of 60°C to 320°C.

[0047] In some embodiments, the mixing treatment time is 0.5 h to 10 h.

[0048] 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.

[0049] In some embodiments, the second surface treatment includes at least one of purification treatment, coating treatment, heat treatment, oxidation treatment, and etching treatment.

[0050] In some embodiments, the temperature of the second surface treatment is 50°C to 900°C.

[0051] In some embodiments, the second surface treatment lasts for 0.5 h to 10 h.

[0052] In some embodiments, the second surface treatment comprises placing the precursor in an aluminum hydroxide solution for purification.

[0053] 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.

[0054] Compared with the prior art, the technical solution of this application has at least the following beneficial effects:

[0055] The negative electrode material provided by the present application includes a silicon-based active material, wherein the silicon-based active material includes silicon and lithium silicate. The XRD diffraction method is used to determine that in the X-ray diffraction spectrum of the negative electrode material, A represents the sum of the peak intensities of different peak positions of Li2SiO3 in a crystalline state, B represents the sum of the peak intensities of different peak positions of Li2Si2O5 in a crystalline state, and C represents the sum of the peak intensities of different peak positions of silicon. When the relationship between A, B, and C satisfies: 0<(A+B) / C≤10, 0<(A+C) / B≤5, the Li2SiO3, The three components of Li2Si2O5 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, and the negative electrode material has 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 this application satisfies the relationship between A, B, and C by regulating the type and crystallization degree of lithium silicate, thereby reducing the destructive effect of alkaline substances on the binder, improving the structural stability of the pole piece, improving the cycle performance of the battery prepared by the negative electrode material, and extending the cycle life.

[0056] The negative electrode material preparation method provided in this application is to prepare silicon oxide SiO x Place it in acid solution for the first surface modification treatment. The acid solution will react with silicon oxide SiO x The surface is oxidized and etched, and the silicon oxide SiO x The surface forms weak defect sites, which can increase the silicon oxide SiO after surface modification. x The reaction sites in the pre-lithiation process promote a more uniform pre-lithiation reaction, obtain more lithium silicate growth sites, and are conducive to the uniform distribution of lithium silicate inside the negative electrode material particles, and help 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 silicon-based active substances 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 initial effect 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, 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 prepared with the negative electrode material; on the other hand, it can improve the adhesion strength of the binder to the negative electrode material, enhance the peel strength of the electrode sheet, reduce the rebound of the electrode sheet, stabilize the conductive network of the electrode sheet, thereby improving the cycle life of the battery prepared with the negative electrode material. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] The present application is further described below with reference to the accompanying drawings and examples.

[0058] FIG1 is a process flow chart of a method for preparing a negative electrode material provided in this application;

[0059] FIG2 is a graph showing the relationship between the powder density and the powder conductivity of the negative electrode material prepared in Example 1 of the present application. DETAILED DESCRIPTION

[0060] 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.

[0061] It should be clear that the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0062] 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", "an", "the" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms unless the context clearly indicates otherwise.

[0063] It should be understood that the term "and / or" as used herein is merely a description of the relationship between associated objects, indicating that three possible relationships exist. For example, "A and / or B" can represent: A exists alone, A and B exist simultaneously, or B exists alone. Furthermore, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0064] 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, wherein the silicon-based active material comprises silicon and lithium silicate;

[0065] The XRD diffraction spectrum of the negative electrode material is measured by XRD, and the peak intensity of the strongest diffraction peak of the negative electrode material in the range of 18° to 20° at 2θ is A1, the peak intensity of the strongest diffraction peak in the range of 26° to 27.9° at 2θ is A2, and the peak intensity of the strongest diffraction peak at 32° to 34° at 2θ is A3, and A1+A2+A3=A;

[0066] 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;

[0067] 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;

[0068] And the relationship between A, B, and C satisfies: 0<(A+B) / C≤10, 0<(A+C) / B≤5.

[0069] The negative electrode material provided by the present application includes a silicon-based active material, which includes silicon and lithium silicate. The XRD diffraction method is used to determine that in the X-ray diffraction spectrum of the negative electrode material, A represents the sum of the peak intensities of different peak positions of Li2SiO3 in a crystalline state, B represents the sum of the peak intensities of different peak positions of Li2Si2O5 in a crystalline state, and C represents the sum of the peak intensities of different peak positions of silicon. When the relationship between A, B, and C satisfies: 0<(A+B) / C≤10, 0<(A+C) / B≤5, the Li2SiO3, Li2S in the negative electrode material are The three components of i2O5 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, and the negative electrode material has 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, the battery containing the above-mentioned negative electrode material can also reduce the destructive effect of the lithium silicate in the negative electrode material on the binder during the charge and discharge process, improve the structural stability of the pole piece, and extend the cycle life of the material. The negative electrode material provided in this application can reduce the destructive effect of alkaline substances on the binder by regulating the type and degree of crystallization of the lithium silicate, that is, satisfying the relationship between A, B, and C, and 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.

[0070] 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, and other values ​​within the above range are also possible, without limitation. The value of (A+C) / B can be, for example, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, and 5, without limitation.

[0071] In some embodiments, the relationship between A, B, and C further 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 other values ​​within the above range are also possible, which is not limited here.

[0072] It can be understood that the negative electrode material is distributed with three components: Li2SiO3 represented by A, Li2Si2O5 represented by B, and silicon represented by C; 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, the appearance of the electrode is flat, and it is suitable for full battery assembly.

[0073] 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, other values ​​within the above range can also be used, which are not limited here. The above powder density ρ1 and powder conductivity σ1, as well as the powder density ρ2 and powder conductivity σ2, are measured at different pressures.

[0074] It can be understood that the powder conductivity is related to the apparent morphology and internal structure of the negative electrode material, and can reflect the electronic conductivity of the negative electrode material. The silicon-based active material after pre-lithiation treatment may reduce the overall electronic conductivity of the negative electrode material due to the increase of lithium silicate. The powder conductivity of the negative electrode material changes with the change of powder density. The present application controls the balance between the three components of Li2SiO3, Li2Si2O5 and silicon, and then balances the relationship between powder conductivity and powder density, ensures electrical contact between negative electrode material particles, improves the stability of the conductive network between negative electrode material particles, increases the probability of electrical contact between particles during the cycle, and extends the cycle life of the material.

[0075] In some embodiments, the molar ratio of oxygen atoms to silicon atoms in the negative electrode material is 0.5 to 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. Of course, it can also be other values ​​within the above range, which is not limited here.

[0076] In some embodiments, the silicon-based active material further comprises a silicon-oxygen composite, wherein the silicon-oxygen composite comprises oxygen atoms and silicon atoms, and the molar ratio of oxygen atoms to silicon atoms is 0 to 2. The silicon-oxygen composite can be represented by the general formula SiO x (0<x≤2). It can be a material formed by dispersing silicon particles in SiO2, or a material having a tetrahedral structural unit: the silicon atom is located at the center of the tetrahedral structural unit, and the silicon atoms and oxygen atoms are located at the four vertices of the tetrahedral structural unit.

[0077] In some embodiments, silicon includes nano-silicon grains, and the average particle size of the nano-silicon grains is 0nm to 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 is not limited here. It can be understood that when the silicon content is the same, 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 improving the cycle performance and rate performance of the negative electrode material.

[0078] In some embodiments, the coating layer includes a carbon material including at least one of amorphous carbon, graphene, graphite, carbon nanotubes, and carbon fibers.

[0079] In some embodiments, the lithium silicate includes at least one of Li2SiO3, Li2Si2O5, and Li4SiO4.

[0080] 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%, 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.

[0081] 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.

[0082] In some embodiments, the mass 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.

[0083] 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.

[0084] 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 specifically 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, other values ​​within the above range are also possible and are not limited here.

[0085] In some embodiments, the active material, 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 material includes a 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).

[0086] 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 negative electrode material slurry can be improved, the uniformity and consistency of the electrode sheet 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 good storage stability. In addition, the active material on the electrode sheet can be evenly attached to the current collector, which is beneficial to improving the peel strength of the electrode sheet. 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 electrode sheet coating and also reduces the consistency of the battery.

[0087] 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 material, 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 comprises negative electrode material and graphite in a mass ratio of 9:1; a German Haake rotational rheometer is used to test the rheological properties of the negative electrode slurry 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).

[0088] In a third aspect, the present application provides a method for preparing a negative electrode material, as shown in FIG1 , comprising the following steps:

[0089] S100, silicon oxide SiO x Place in an acid solution for the first surface modification treatment, wherein 0<x<2;

[0090] S200, containing 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;

[0091] S300 , performing a second surface modification treatment on the precursor to obtain a negative electrode material, wherein the negative electrode 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, and the silicon-based active material includes silicon and lithium silicate.

[0092] The negative electrode material preparation method provided in this application is to prepare silicon oxide SiO x Place it in acid solution for the first surface modification treatment. The acid solution will react with silicon oxide SiO x The surface is oxidized and etched, and the silicon oxide SiO x The formation of weak defect sites on the surface can increase the silicon oxide SiO after the first surface modification treatment. 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. In addition, the surface modified silicon oxide SiO xPre-lithiation treatment can greatly reduce the catalytic growth of silicon grains by lithium silicate, thereby regulating the type, content and grain growth of the three components of Li2SiO3, Li2Si2O5 and silicon in the negative electrode material; 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. x Pre-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 silicon-based active substances during the charging and discharging process, maintaining the overall structure of the stable negative electrode material, extending the cycle life, reducing the regeneration of SEI film on the surface of the negative electrode material, and improving the initial 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 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 peel strength of the electrode sheet, reduce the electrode sheet rebound, stabilize the electrode sheet conductive network, thereby improving the cycle life of the battery prepared with the negative electrode material.

[0093] The following is a detailed description of the preparation method provided in this scheme:

[0094] Step S100: silicon oxide SiO x The first surface modification treatment is performed in an acid solution, wherein 0<x<2.

[0095] 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 lithium ions is relatively complex and can be understood as being composed of at least one of amorphous silicon and crystalline silicon uniformly dispersed in SiO2. At high temperatures, its thermodynamic properties are very unstable and it easily undergoes a reduction reaction with a lithium source to form lithium silicate.

[0096] 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.x Surface modification treatment is performed to achieve silicon oxide SiO x Surface oxidation and etching can be done on silicon oxide SiO x The formation of subtle defects on the surface increases the number of reaction sites during the pre-lithiation process, promoting a more uniform pre-lithiation reaction and obtaining more lithium silicate growth sites, which facilitates the uniform distribution of lithium silicate within the particles. With a fixed pre-lithiation amount, this helps to adjust the crystal phase type and content of the lithium silicate. Furthermore, using surface-modified silicon oxide for pre-lithiation treatment can significantly reduce the catalytic growth of silicon grains by lithium silicate.

[0097] 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. Of course, other values ​​within the above range are also possible and are not limited here.

[0098] In some embodiments, the temperature of the first surface modification treatment is 30°C to 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.

[0099] In some embodiments, the time for the first surface modification treatment is 2 hours to 8 hours, specifically 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours and 8 hours, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0100] In some embodiments, the preparation method further comprises treating the silicon oxide SiO x Carry out solid-liquid separation, washing and drying.

[0101] 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 is not limited here.

[0102] Step S200, the silicon oxide SiO xThe 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.

[0103] In the above scheme, the temperature of the pre-lithiation treatment can be specifically 300°C, 350°C, 400°C, 450°C, 500°C, 550°C, 600°C, 650°C, 700°C, 710°C and 800°C, etc. Of course, it can also be other values ​​within the above range, which is 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 efficiency 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, causing the cycle performance of the negative electrode material to deteriorate; on the other hand, the 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 conducive to the reaction between the lithium source and silicon oxide, balancing the crystal phase type and content of lithium silicate, and obtaining silicon grains of appropriate size, thereby further improving the slurry storage stability of the material.

[0104] In some embodiments, the silicon oxide is silicon monoxide. It is understandable that when silicon monoxide is used as the silicon oxide, the problem of unstable processing performance after the initial effect of lithium doping of silicon monoxide can be effectively solved.

[0105] 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 silicon oxide surface; 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.

[0106] 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. Of course, it can also be other values ​​within the above range, which is not limited here.

[0107] In some embodiments, the pre-lithiation treatment is performed in a protective atmosphere. Understandably, performing the pre-lithiation treatment in a protective atmosphere can reduce the risk of oxygen introduction, ensure the initial efficiency of the pre-lithiation material, and also help control the composition of the lithium silicate, further improving the storage stability of the slurry.

[0108] In some embodiments, the protective atmosphere includes at least one of nitrogen, helium, neon, argon, krypton, and xenon.

[0109] In some embodiments, the pre-lithiation treatment time is 3 hours to 9 hours, specifically 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, and 9 hours, etc., and of course other values ​​within the above range are also possible and are not limited herein. It can be understood that the pre-lithiation treatment time within the above range can fully calcine and fully convert Li2SiO3 into Li2Si2O5.

[0110] In some embodiments, the lithium silicate includes at least one of Li2SiO3, Li2Si2O5, and Li4SiO4.

[0111] In some embodiments, the method further includes mixing the mixture of silicon oxide after the first surface modification treatment and the reducing lithium-containing compound before pre-lithiation treatment of the mixture at 300°C to 800°C.

[0112] In some embodiments, the temperature of the mixing treatment is 60°C to 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. Of course, it can also be other values ​​within the above range, which is not limited here.

[0113] In some embodiments, the mixing treatment time is 0.5h to 10h, specifically 0.5h, 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h and 10h, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0114] In some embodiments, the equipment required for the mixing process includes at least one of a dispersion device and a shearing device. It is understood that using a high-speed dispersion device and a shearing device to mix the mixture comprising 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 stages of pre-lithiation, facilitate the regulation of the lithium silicate composition to meet the requirements of this application, and thereby improve the storage stability of the slurry and the bonding ability of the active material in the electrode.

[0115] 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.

[0116] 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.

[0117] 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.

[0118] 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.

[0119] 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 pyrolysis and has a certain degree of graphitization. Using amorphous carbon to coat the surface of silicon oxide can, on the one hand, improve the conductivity of the negative electrode material. On the other hand, the amorphous carbon produced by high-temperature pyrolysis has a relatively developed void structure. Coating it on the surface of silicon oxide can suppress the volume expansion of the negative electrode material, which is beneficial to improving the cycle performance of the negative electrode material.

[0120] 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 material and a coating layer located on at least a portion of the surface of the silicon-based active material, and the silicon-based active material includes silicon and lithium silicate.

[0121] In some embodiments, the second surface modification treatment includes at least one of a purification treatment, a coating treatment, a heat treatment, an oxidation treatment, and an etching treatment.

[0122] 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 here.

[0123] In a specific embodiment, the heat treatment is combined with other methods, such as polymer coating and etching, which are not limited here.

[0124] In some embodiments, the temperature of the second surface modification treatment is 50°C to 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.

[0125] In some embodiments, the time for the second surface modification treatment is 0.5h to 10h, specifically 0.5h, 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h and 10h, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0126] In some embodiments, the second surface modification treatment includes purifying the precursor in an aluminum hydroxide solution. It is understood that since the coatings on the aluminum foil and the separator in the battery cell system are of the same origin, purifying the precursor in an aluminum hydroxide solution can improve the compatibility of the resulting battery cell system.

[0127] 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 the silicon oxide, and the lithium source will react violently on the surface of the negative electrode material to generate more Li2SiO3 or even Li4SiO4, so that the content of Li2Si2O5 will be particularly low; if the surface modification treatment is too weak, the pre-lithium reaction sites on the surface of the silicon oxide will be insufficient, and the content of lithium silicate generated will be small, and the pre-lithium effect will not 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, the content of Li2SiO3 will be high. If the reaction temperature is too low and the reaction time is too short, the content of Li2Si2O5 will be high. Overall, it is necessary to control the appropriate active sites, appropriate temperature and time, and combine the three to prepare a negative electrode material that meets the requirements.

[0128] In a fourth aspect, the present application provides a lithium-ion battery, which comprises the negative electrode material of the first aspect or the negative electrode material prepared by the preparation method of the second aspect.

[0129] The above are only preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application should be included in the scope of protection of the present application.

[0130] Example

[0131] Example 1

[0132] (1) Silicon monoxide (SiO) 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. The resulting product was dried at 80°C to obtain surface-modified silicon monoxide (SiO).

[0133] (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 hour 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 500° C. for 4 hours, and then cooled 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.

[0134] (3) The precursor was placed in Al(OH)3 and purified at 40°C for 2h. The residual alkali solution on the surface of the precursor was removed by filtration and washing. Then, 2%wt of amorphous carbon was coated on the surface of the precursor by liquid phase coating method to obtain a negative electrode material.

[0135] 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 diffraction method, and the relationship between A, B, and C in the negative electrode material is calculated through the 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. Figure 2 is a relationship diagram between the powder density and powder conductivity of the negative electrode material prepared in this embodiment. It can be concluded from Figure 2 that the relationship between ρ1, ρ2, σ1, and σ2 satisfies: (σ2-σ1) / (ρ2-ρ1)=0.32, and the relationship between the shear forces in the rheological curve satisfies 2τ1>(τ2-τ0).

[0136] The negative electrode material prepared in this embodiment can be stably stored for more than 72 hours after being prepared into negative electrode slurry.

[0137] Example 2

[0138] The negative electrode material was prepared in a manner substantially the same as in Example 1, except that:

[0139] (2) 2% wt of amorphous carbon was coated on the surface of 1000 g of surface-modified silicon monoxide (SiO) by a liquid phase coating method. Then, 200 g 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 1 hour 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 500°C for 4 hours, and then cooled to 25°C to obtain a precursor.

[0140] The remaining operations are the same as those in Example 1.

[0141] 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 X-ray diffraction spectrum of the negative electrode material is calculated to show that the relationship between A, B, and C in the negative electrode material satisfies: (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 the shear forces in the rheological curve satisfies 2τ1>(τ2-τ0).

[0142] The negative electrode material prepared in this embodiment can be stably stored for more than 72 hours after being prepared into negative electrode slurry.

[0143] Example 3

[0144] The negative electrode material was prepared in a manner substantially the same as in Example 1, except that:

[0145] (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 was introduced, the temperature was raised to 80°C, and the mixture was dispersed at 2000 rpm for 1 hour 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 500°C for 4 hours, and then cooled 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.

[0146] The remaining operations are the same as those in Example 1.

[0147] 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 diffraction method, and the X-ray diffraction spectrum of the negative electrode material is calculated to show that the relationship between A, B, and C in the negative electrode material satisfies: (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 the shear forces in the rheological curve satisfies 2τ1>(τ2-τ0).

[0148] The negative electrode material prepared in this embodiment can be stably stored for more than 72 hours after being prepared into negative electrode slurry.

[0149] Example 4

[0150] (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 h, then filtered and washed with pure water, and the obtained product was dried at 80 ° C to obtain silicon oxide (SiO 1.5 ).

[0151] (2) 1000g 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 placed in 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.

[0152] (3) The precursor was placed in Al(OH)3 and purified at 40°C for 2h. The residual alkali solution on the surface of the precursor was removed by filtration and washing. Then, 2%wt of amorphous carbon was coated on the surface of the precursor by liquid phase coating method to obtain a negative electrode material.

[0153] 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 diffraction method, and the X-ray diffraction spectrum of the negative electrode material is calculated to show that the relationship between A, B, and C in the negative electrode material satisfies: (A+B) / C=2.5, (A+C) / B=1.8, (B+C) / A=1.2, and the relationship between ρ1, ρ2, σ1, and σ2 satisfies: (σ2-σ1) / (ρ2-ρ1)=0.52; the relationship between the shear forces in the rheological curve satisfies 2τ1>(τ2-τ0).

[0154] The negative electrode material prepared in this embodiment can be stably stored for more than 72 hours after being prepared into negative electrode slurry.

[0155] Example 5

[0156] The negative electrode material was prepared in a manner substantially the same as in Example 1, except that:

[0157] (1) Silicon monoxide (SiO) was 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. The resulting product was dried at 80°C to obtain surface-modified silicon monoxide (SiO).

[0158] The remaining operations are the same as those in Example 1.

[0159] 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 X-ray diffraction spectrum of the negative electrode material is calculated to show that the relationship between A, B, and C in the negative electrode material satisfies: (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 the shear forces in the rheological curve satisfies 2τ1>(τ2-τ0).

[0160] The negative electrode material prepared in this embodiment can be stably stored for more than 72 hours after being prepared into negative electrode slurry.

[0161] Example 6

[0162] The negative electrode material was prepared in a manner substantially the same as in Example 1, except that:

[0163] (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, purged with argon, heated to 80° C., and 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 then cooled to 25° C. to obtain a silicon-based active material. 2% wt of amorphous carbon was then coated on the surface of the silicon-based active material using a liquid phase coating method to obtain a precursor. The remaining operations were the same as in Example 1.

[0164] 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 diffraction method, and the X-ray diffraction spectrum of the negative electrode material is calculated to obtain the relationship between A, B, and C in the negative electrode material: (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 the shear forces in the rheological curve satisfies 2τ1>(τ2-τ0).

[0165] The negative electrode material prepared in this embodiment can be stably stored for more than 72 hours after being prepared into negative electrode slurry.

[0166] Example 7

[0167] The negative electrode material was prepared in a manner substantially the same as in Example 1, except that:

[0168] (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 hour 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 800° C. for 4 hours, 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.

[0169] The remaining operations are the same as those in Example 1.

[0170] 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 X-ray diffraction spectrum of the negative electrode material is calculated to show that the relationship between A, B, and C in the negative electrode material satisfies: (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 the shear forces in the rheological curve satisfies 2τ1>(τ2-τ0).

[0171] The negative electrode material prepared in this embodiment can be stably stored for more than 72 hours after being prepared into negative electrode slurry.

[0172] Comparative Example 1

[0173] The difference from Example 1 is that:

[0174] In this embodiment, except that the crucible is placed in a box furnace for pre-lithiation treatment at 200° C. for 5 h in step (2), other operating conditions and raw materials are the same as those in Example 1.

[0175] 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 X-ray diffraction spectrum of the negative electrode material is calculated to obtain the relationship between A, B, and C in the negative electrode material: (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 the shear forces in the rheological curve satisfies 2τ1>(τ2-τ0).

[0176] The negative electrode material prepared in this comparative example cannot be stably stored after being prepared into negative electrode slurry.

[0177] Comparative Example 2

[0178] The difference from Example 1 is that:

[0179] In this embodiment, except that the crucible is placed in a box furnace for pre-lithiation treatment at 900° C. for 2 h in step (2), other operating conditions and raw materials are the same as those in Example 1.

[0180] 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 X-ray diffraction spectrum of the negative electrode material is calculated to obtain the relationship between A, B, and C in the negative electrode material: (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 the shear forces in the rheological curve satisfies 2τ1<(τ2-τ0).

[0181] The negative electrode material prepared in this comparative example cannot be stably stored after being prepared into negative electrode slurry.

[0182] Comparative Example 3

[0183] The difference from Example 1 is that:

[0184] This comparative example does not carry out the process of step (1) of Example 1, and other operating conditions and raw materials are the same as those of Example 1.

[0185] 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 X-ray diffraction spectrum of the negative electrode material is calculated to show that the relationship between A, B, and C in the negative electrode material satisfies: (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 the shear forces in the rheological curve satisfies 2τ1<(τ2-τ0).

[0186] The negative electrode material prepared in this comparative example cannot be stably stored after being prepared into negative electrode slurry.

[0187] Comparative Example 4

[0188] The difference from Example 1 is that:

[0189] 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.

[0190] 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 X-ray diffraction spectrum of the negative electrode material is calculated to show that the relationship between A, B, and C in the negative electrode material satisfies: (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 the shear forces in the rheological curve satisfies 2τ1<(τ2-τ0).

[0191] The negative electrode material prepared in this comparative example cannot be stably stored after being prepared into negative electrode slurry.

[0192] Test method:

[0193] (1) XRD test method of negative electrode material:

[0194] The XRD patterns of the materials were measured using a German Bruker AXSD8-Focus instrument. Instrument test parameters: CuKα radiation, divergence slit 1.0°, anti-scattering slit 2.0°, receiving slit 9.6°, voltage range 40 kV, current 40 mA, scanning range 10-90°, scanning step 0.01313, scanning mode continuous, scanning time per step 10.2 s, calculated wavelength Calculate the value of A / B / C and the average particle size of the silicon grains.

[0195] (2) Test method for the powder conductivity and powder density of the negative electrode material:

[0196] The test equipment is from Mitsubishi Chemical of Japan. Test parameters include an initial resistance magnitude of -3, a voltage limit of 10V, and sample quality, ensuring a sample thickness of 3 to 5mm at a pressure of 20kN. Pressure settings were 4, 8, 12, 16, and 20kN, with an electrode radius of 0.7mm and a sample radius of 10mm. The corresponding powder density and conductivity were measured at different pressures.

[0197] (3) Testing method of rheological curve of negative electrode slurry:

[0198] 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%, wherein the active material included 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 Haake rotational rheometer to obtain the rheological curve of the negative electrode slurry.

[0199] (4) 50-week cycle performance test with power off:

[0200] The equipment and methods used follow the BTRTC / ZY / 01-020 "Button Cell Method Operating Instructions": PAA is used as a binder to prepare a 5% solids solution. The negative electrode active material and conductive agent are then added in a mass ratio of 75:15:10 (negative electrode active material: conductive agent (SP): binder (PAA). A high-speed disperser is used to evenly disperse the mixture to form a negative electrode slurry. The slurry is then evenly coated onto 10µm thick copper foil, dried, rolled, punched, and dried again to produce the negative electrode. The positive electrode is a lithium sheet. The button cell is assembled in the following order: casing, gasket, nickel sheet, lithium sheet, separator, negative electrode, and casing. The counter electrode is a metallic lithium sheet, and the separator is a 19.2mm diameter PP-PE-PP composite film. The electrolyte composition ratio is 1:1:1 (EC / EMC / DMC), and the lithium salt (LiPF6) concentration is 1.05 mol / L. Using button battery charging and discharging equipment, in the first week, discharge at 0.1C to 0.01V, discharge at 0.01C in a stepwise decreasing manner to 0.01V, discharge at 0.01C to 0.005V, and charge at 0.1C to 1.5V; in the second week, discharge at 0.2C to 0.01V, discharge at 0.02C in a stepwise decreasing manner to 0.01V, discharge at 0.02C to 0.005V, and charge at 0.2C to 1.5V; in the third week, discharge at 0.5C to 0.01V, 0. Discharge at 0.5C in a stepwise decreasing manner to 0.01V, discharge at 0.05C to 0.005V, and charge at 0.5C to 1.5V; from the 4th to the 50th week, discharge at 1C to 0.01V, discharge at 0.1C in a stepwise decreasing manner to 0.01V, discharge at 0.1C to 0.005V, and charge at 1C to 1.5V; in the 51st week, discharge at 0.1C to 0.01V, discharge at 0.01C in a stepwise decreasing manner to 0.01V, and discharge at 0.01C to 0.005V.

[0201] (5) Negative electrode slurry storage stability assessment method:

[0202] 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 consisted of negative electrode material and graphite in a mass ratio of 9:1. The negative electrode slurry was then allowed to stand at 25°C, and changes in viscosity, fluidity, solids content, fineness, and coating quality were observed during the standing period. An increase or decrease in viscosity indicates that the slurry may be experiencing particle aggregation or dispersion, which is detrimental to slurry stability. Significant stratification and fluid thickening indicate reduced dispersibility, poor fluidity, and decreased stability. A significant change in solids content may lead to particle aggregation or precipitation in the slurry, affecting its stability. Large particle aggregation or significant changes in particle fineness will lead to reduced slurry stability. The slurry was applied to a substrate and the coating uniformity and adhesion were observed. If the coating was uneven, flaking, or cracking, it indicates poor slurry stability.

[0203] (6) Test method for specific capacity:

[0204] 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.

[0205] The above test results are detailed in Table 1.

[0206] Table 1 Test results of embodiments and ratios

[0207] From the above embodiments and comparative examples, it can be seen that embodiments 1 to 7 can improve the lithiation uniformity of the negative electrode material and the processing performance of the negative electrode material by controlling the balance relationship between the three components of Li2SiO3, Li2Si2O5 and silicon in the negative electrode material, thereby improving the storage stability of the negative electrode slurry prepared from the negative electrode material; at the same time, by controlling the balance relationship between the three components of Li2SiO3, Li2Si2O5 and silicon in the negative electrode material, the content of Li2Si2O5 in the negative electrode material can be increased, the destructive effect of lithium silicate on the binder can be reduced, the stability of the electrode sheet can be improved, the cycle performance of the negative electrode material can be improved, and the cycle life can be extended.

[0208] 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.

[0209] 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 quickly and in large quantities. On the one hand, it catalyzes the growth of silicon grains in the negative electrode material, resulting in deterioration of the material's cycle performance; on the other hand, it reduces the storage stability of the negative electrode slurry made from the negative electrode material, making the slurry unable to be stored stably for a long time.

[0210] 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 an imbalance in the relative relationship between the three components of Li2SiO3, Li2Si2O5 and silicon in the negative electrode material, reducing the storage performance of the negative electrode slurry made of the negative electrode material, and the negative electrode slurry cannot be stored stably for a long time. The slurry is prone to sedimentation, stratification, and gas production during storage, resulting in uneven distribution of active substances in the coated electrode sheet, and the lithium silicate in the negative electrode material has a large destructive effect on the binder, reducing the structural stability of the electrode sheet, resulting in a decrease in the cycle performance of the negative electrode material.

[0211] Compared with Example 1, the negative electrode material of Comparative Example 4 does not undergo 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 conductive network of the electrode piece is reduced, and the cycle performance of the negative electrode material is reduced.

Claims

1. A negative electrode material, characterized in that: The negative electrode 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, wherein the silicon-based active material includes 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 the following conditions at the same time: 0<(A+B) / C≤10, 0<(A+C) / B≤5.

2. The negative electrode material according to claim 1, characterized in that 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.

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

4. The negative electrode material according to claim 1, characterized in that The silicon-based active material also includes silicon-oxygen composites.

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

6. The negative electrode material according to claim 1, characterized in that The silicon in the negative electrode material includes nano silicon crystal particles, and the average particle size of the nano silicon crystal particles is 0nm to 20nm, and 0nm is not included.

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

8. The negative electrode material according to claim 1, characterized in that 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%.

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

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

11. The negative electrode material according to claim 1, characterized in that The specific surface area of ​​the negative electrode material is less than or equal to 10m 2 / g.

12. The negative electrode material according to claim 1, characterized in that 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, characterized in that: Active material, 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 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).

14. A negative electrode slurry, characterized in that: The negative electrode slurry comprises the negative electrode material according to any one of claims 1 to 13.

15. A lithium ion battery, characterized in that: The lithium-ion battery comprises the negative electrode material according to any one of claims 1 to 13.

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