Negative electrode material and preparation method thereof, negative electrode plate and battery

Abstract

The invention relates to a negative electrode material and a preparation method thereof, a negative electrode plate and a battery, the negative electrode material comprises an active substance and a carbon material located on at least part of the surface of the active substance, and the active substance comprises silicon particles and graphite; in a Raman surface scanning spectrogram of the negative electrode material, the characteristic peak intensity of silicon particles in the negative electrode material in a range of 500 cm <-1 > to 520 cm <-1 > is I1, the characteristic peak intensity of silicon particles in the negative electrode material in a range of 1345 cm <-1 > to 1355 cm <-1 > is I2, and the characteristic peak intensity of silicon particles in the negative electrode material in a range of 1570 cm <-1 > to 1610 cm <-1 > is I3; the characteristic peak intensity of graphite in the negative electrode material in the range of 1345 cm <-1 > to 1355 cm <-1 > is I2 ', the characteristic peak intensity of graphite in the range of 1570 cm <-1 > to 1610 cm <-1 > is I3', and in the negative electrode material, # imgabs0 # 0.01 < = K < = 10. The negative electrode material provided by the invention has relatively high specific capacity and good electrolyte infiltration performance, and the prepared negative electrode plate has relatively low resistivity.

Description

Technical Field

[0001] The present invention relates to the technical field of negative electrode materials, and in particular to negative electrode materials and preparation methods thereof, negative electrode plates and batteries. Background Art

[0002] Lithium-ion batteries have the advantages of high energy density, high cycle life, low environmental pollution and no memory effect, so they are widely used in electric vehicles and consumer electronic products. The negative electrode material is an important component of lithium-ion batteries, which directly affects key indicators such as battery energy density, cycle life and safety performance. At present, commercial lithium-ion batteries mainly use graphite negative electrode materials, but its theoretical specific capacity is only 372mAh / g, which is difficult to meet the needs of high energy density lithium-ion batteries. Silicon-based negative electrode materials have a very high specific capacity as negative electrode materials for lithium-ion batteries and are one of the candidate materials for the next generation of high energy density lithium-ion batteries. However, due to the different morphology, composition, particle size, etc. of silicon, a series of problems will arise after the negative electrode is made, the most obvious of which is the wettability of the electrode in the electrolyte and the decrease in conductivity.

[0003] Therefore, how to improve the wettability and conductivity of silicon-containing negative electrode materials while increasing the specific capacity of negative electrode materials is a technical problem that still needs to be solved. Summary of the invention

[0004] The purpose of the present application is to provide a negative electrode material and a preparation method thereof, a negative electrode plate, and a battery. The negative electrode material of the present application has a higher specific capacity, and can also improve the wettability of the negative electrode material and reduce the resistivity of the negative electrode plate.

[0005] In a first aspect, the present application provides a negative electrode material, the negative electrode material comprising an active substance and a carbon material located on at least a portion of the surface of the active substance, the active substance comprising silicon particles and graphite;

[0006] In the Raman spectrum of the negative electrode material, the silicon particles in the negative electrode material have a Raman spectrum of 500 cm -1 ~520cm -1 The characteristic peak intensity in the range is I 1 , at 1345cm -1 ~1355cm -1 The characteristic peak intensity in the range is I 2 , at 1570cm -1 ~1610cm -1 The characteristic peak intensity in the range is I 3 ;

[0007] The graphite in the negative electrode material has a peak at 1345 cm -1 ~1355cm -1The characteristic peak intensity in the range is I 2 ', at 1570cm -1 ~1610cm -1 The characteristic peak intensity in the range is I 3 ';

[0008] The negative electrode material meets the following requirements:

[0009] In some embodiments, the particle size of the negative electrode material satisfies: 1.0≤(D 05 +D 99 ) / (2*D 50 )≤2.2.

[0010] In some embodiments, the powder conductivity of the negative electrode material under a pressure of 20 kN is greater than 30 S / cm.

[0011] In some embodiments, the silicon particles include at least one of amorphous silicon, crystalline silicon, silicon oxide, and silicate.

[0012] In some embodiments, the graphite includes at least one of natural graphite, artificial graphite, expanded graphite, and oxidized graphite.

[0013] In some embodiments, the median particle size of the negative electrode material is 2 μm to 20 μm.

[0014] In some embodiments, the contact angle of the negative electrode material is greater than 110°.

[0015] In some embodiments, the mass content of silicon particles in the negative electrode material is 1% to 80%, and the mass content of graphite is 20% to 99%.

[0016] In some embodiments, the tap density of the negative electrode material is ≥ 0.7 g / cm 3 .

[0017] In some embodiments, the carbon material includes at least one of amorphous carbon and graphitized carbon.

[0018] In some embodiments, the silicon particles include silicon oxide, the silicon oxide includes silicon element and oxygen element, and the atomic ratio of the silicon element to the oxygen element is 0 to 2, excluding 0.

[0019] In some embodiments, the silicon particles include silicon oxide, the chemical formula of the silicon oxide is SiO x , where 0<x≤2.

[0020] In a second aspect, the present application provides a method for preparing a negative electrode material, comprising the following steps:

[0021] Placing graphite in a modification solution for modification, and drying to obtain modified graphite;

[0022] Using a reaction gas containing a silicon source gas to vapor-deposit the modified graphite to obtain a mixture of silicon-containing particles and modified graphite;

[0023] The mixture is placed at 550° C. to 1000° C. using a gas phase carbon source to perform a gas phase carbon coating treatment to obtain a negative electrode material.

[0024] In some embodiments, the modification step includes placing the graphite in an acid solution or an alkaline solution for modification.

[0025] In some embodiments, the modification step includes placing the graphite in an acid solution or an alkaline solution for modification, wherein the acid solution includes at least one of a hydrochloric acid solution, a sulfuric acid solution, and a nitric acid solution.

[0026] In some embodiments, the modification step includes placing the graphite in an acid solution or an alkaline solution for modification, wherein the alkaline solution includes at least one of a sodium hydroxide solution, a potassium hydroxide solution, and a lithium hydroxide solution.

[0027] In some embodiments, the modification step includes placing the graphite in an acid solution or an alkaline solution for modification, wherein the concentration of the acid solution or the alkaline solution is less than 2 mol / L.

[0028] In some embodiments, the modification step includes placing the graphite in an acid solution or an alkaline solution for modification, the modification time is 10 hours to 48 hours, and the modification temperature is 20° C. to 30° C.

[0029] In some embodiments, the modification step further comprises washing the modified product until the product is washed to neutrality.

[0030] In some embodiments, the drying process is carried out at a temperature of 45°C to 80°C.

[0031] In some embodiments, the drying process lasts for 3 hours to 48 hours.

[0032] In some embodiments, the graphite includes at least one of natural graphite, artificial graphite, expanded graphite, and oxidized graphite.

[0033] In some embodiments, the median particle size of the graphite is 6 μm to 20 μm.

[0034] In some embodiments, the vapor deposition temperature is 300°C to 700°C.

[0035] In some embodiments, the vapor deposition time is 2 hours to 8 hours.

[0036] In some embodiments, the flow rate of the silicon source gas is 0.1 L / min to 15 L / min.

[0037] In some embodiments, an auxiliary carrier gas is further added during the vapor deposition process, and the flow rate of the auxiliary carrier gas is 0.5 L / min to 25 L / min.

[0038] In some embodiments, an auxiliary carrier gas is further added during the vapor deposition process, and the auxiliary carrier gas includes at least one of nitrogen, argon, helium, neon, carbon dioxide, hydrogen and carbon monoxide.

[0039] In some embodiments, the raw material of the silicon source gas includes at least one of monosilane, disilane, monochlorosilane, dichlorosilane, trichlorosilane, tetrachlorosilane and methyl siloxane.

[0040] In some embodiments, the raw material of the gaseous carbon source includes at least one of methane, ethane, ethylene, acetylene, propyne, propylene, propane, formaldehyde, acetaldehyde, methanol, toluene, benzene, styrene and phenol.

[0041] In some embodiments, the flow rate of the gas-phase carbon source is 0.2 L / min to 18 L / min.

[0042] In some embodiments, the vapor phase carbon coating treatment is performed for 1 hour to 6 hours.

[0043] In a third aspect, the present application provides a negative electrode plate, the negative electrode plate comprising the negative electrode material described in the first aspect or the negative electrode material prepared by the preparation method of the negative electrode material described in the second aspect; the resistivity of the negative electrode plate is ≤5Ω*cm.

[0044] In a fourth aspect, the present application provides a battery, comprising the negative electrode plate described in the third aspect.

[0045] Compared with the prior art, the technical solution of the present application has at least the following beneficial effects:

[0046] The negative electrode material provided in the present application comprises an active substance and a carbon material located on at least a portion of the surface of the active substance, wherein the active substance comprises silicon particles and graphite. In the Raman scan spectrum, the silicon particles have a -1 ~520cm -1 The characteristic peak intensity in the range is I 1 , at 1345cm -1 ~1355cm -1 The characteristic peak intensity in the range is I2 , at 1570cm -1 ~1610cm -1 The characteristic peak intensity in the range is I 3 Due to the presence of carbon materials on the surface of silicon particles, it can be -1 ~1355cm -1 Range and 1570cm -1 ~1610cm -1 Peaks were detected in the range of 1345 cm-1 for graphite. -1 ~1355cm -1 The characteristic peak intensity in the range is I 2 ', at 1570cm -1 ~1610cm -1 The characteristic peak intensity in the range is I 3 '. I 1 / (I 2 +I 3 ) can represent the exposure degree of silicon particles in the negative electrode material, I 2 / (I 2 +I 3 )+I 2 ' / (I 2 '+I 3 ') can represent the total defect level of the carbon material on the surface of the negative electrode material. When too much silicon is exposed on the surface of the negative electrode material or the defect level of the surface carbon material is high, the side reaction between the negative electrode material and the electrolyte is intensified, and the thickness of the solid electrolyte film on the surface of the negative electrode material also increases. At this time, although the electrolyte wetting ability is relatively increased, the electrode sheet resistivity decreases; in addition, the consumption of active lithium ions increases, and the first coulomb efficiency of the negative electrode material decreases. When too few silicon particles are exposed on the surface of the negative electrode material or the defect level of the surface carbon material is very low, the electrolyte wetting ability of the negative electrode material decreases, and some active materials are difficult to be activated by formation, which is not conducive to the performance of the active materials. The present application controls I 1 / (I 2 +I 3 ) and I 2 / (I 2 +I 3 )+I 2 ' / (I 2 '+I 3 ') is in the range of 0.01 to 10, which can find a balance between the degree of silicon exposure and the degree of defects in the surface carbon material. On the one hand, it ensures that fewer silicon particles in the negative electrode material are exposed. On the other hand, the degree of defects in the surface carbon material is used to improve the wetting ability of the negative electrode material to the electrolyte, and the thickness of the solid electrolyte film layer on the surface of the material is comprehensively controlled. The prepared negative electrode plate has a lower resistivity, which further increases the stability and durability of the plate.

[0047] The preparation method of the negative electrode material provided by the present application comprises the following steps: firstly, modifying graphite to increase the defect degree of graphite and reduce the resistivity of the negative electrode sheet; then compounding the modified graphite with silicon particles by vapor deposition to achieve uniform mixing of silicon particles and graphite and reduce the segregation of silicon particles; finally, placing the mixture of the two at 550° C. to 1000° C. for vapor phase carbon coating to effectively reduce the defect degree of the graphite surface and adjust the defect degree of the carbon material on the surface of the silicon particles and the surface of the graphite, so that I 1 / (I 2 +I 3 ) and I 2 / (I 2 +I 3 )+I 2 ' / (I 2 '+I 3 ') is in the range of 0.01 to 10, which can find a balance between the degree of silicon exposure and the degree of defects in the surface carbon material. Under the initial condition of ensuring the first coulombic efficiency of the negative electrode material at a high level, the degree of defects in the carbon material on the surface of the active material can be used to improve the electrolyte wetting ability of the negative electrode material. The small amount of silicon particles exposed on the surface of the negative electrode material can also be used to generate a solid electrolyte film layer of appropriate thickness, thereby improving the conductivity of the electrode piece. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0049] Figure 1 A schematic diagram of a process for preparing a negative electrode material provided in an embodiment of the present application.

[0050] Figure 2 The distribution of silicon particles and graphite in the negative electrode material prepared in Example 1 within the scanning range.

[0051] Figure 3 This is the Raman spectrum of the negative electrode material prepared in Example 1.

[0052] Figure 4 This is a volume-based cumulative particle size distribution width diagram of the negative electrode material prepared in Example 1. DETAILED DESCRIPTION

[0053] In order to better understand the technical solution of the present invention, the embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0054] It should be clear that the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0055] The terms used in the embodiments of the present invention are only for the purpose of describing specific embodiments, and are not intended to limit the present invention. The singular forms "a", "said" and "the" used in the embodiments of the present invention and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings.

[0056] It should be understood that the term "and / or" used in this article is only a description of the association relationship of associated 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 associated objects before and after are in an "or" relationship.

[0057] In a first aspect, the present application provides a negative electrode material, the negative electrode material comprising an active substance and a carbon material located on at least a portion of the surface of the active substance, the active substance comprising silicon particles and graphite;

[0058] In the Raman scanning spectrum of the negative electrode material, the silicon particles in the negative electrode material are at 500 cm -1 ~520cm -1 The characteristic peak intensity in the range is I 1 , at 1345cm -1 ~1355cm -1 The characteristic peak intensity in the range is I 2 , at 1570cm -1 ~1610cm -1 The characteristic peak intensity in the range is I 3 ;

[0059] Graphite in the negative electrode material is at 1345cm -1 ~1355cm -1 The characteristic peak intensity in the range is I 2 ', at 1570cm -1 ~1610cm -1 The characteristic peak intensity in the range is I 3 ';

[0060] The negative electrode material meets the following requirements:

[0061] The negative electrode material provided in the present application includes an active material and a carbon material located on at least a portion of the surface of the active material, wherein the active material includes silicon particles and graphite. In the Raman scan spectrum, the silicon particles have a -1 ~520cm -1 The characteristic peak intensity in the range is I 1 , at 1345cm -1 ~1355cm -1 The characteristic peak intensity in the range is I 2 , at 1570cm -1 ~1610cm -1 The characteristic peak intensity in the range is I 3 Due to the presence of carbon materials on the surface of silicon particles, it can be -1 ~1355cm -1 Range and 1570cm -1 ~1610cm -1 Peaks were detected in the range of 1345 cm-1 for graphite. -1 ~1355cm -1 The characteristic peak intensity in the range is I 2 ', at 1570cm -1 ~1610cm -1 The characteristic peak intensity in the range is I 3 '. I 1 / (I 2 +I 3 ) can represent the exposure degree of silicon particles in the negative electrode material, I 2 / (I 2 +I 3 )+I 2 ' / (I 2 '+I 3 ') can represent the total defect level of the carbon material on the surface of the negative electrode material. When too much silicon is exposed on the surface of the negative electrode material or the defect level of the surface carbon material is high, the side reaction between the negative electrode material and the electrolyte is intensified, and the thickness of the solid electrolyte film on the surface of the negative electrode material also increases. At this time, although the electrolyte wetting ability is relatively increased, the electrode sheet resistivity decreases; in addition, the consumption of active lithium ions increases, and the first coulomb efficiency of the negative electrode material decreases. When too few silicon particles are exposed on the surface of the negative electrode material or the defect level of the surface carbon material is very low, the electrolyte wetting ability of the negative electrode material decreases, and some active materials are difficult to be activated by formation, which is not conducive to the performance of the active materials. The present application controls I 1 / (I 2 +I 3 ) and I 2 / (I 2 +I 3 )+I 2 ' / (I2 '+I 3 ') is in the range of 0.01 to 10, which can find a balance between the degree of silicon exposure and the degree of defects in the surface carbon material. On the one hand, it ensures that fewer silicon particles in the negative electrode material are exposed. On the other hand, the degree of defects in the surface carbon material is used to improve the wetting ability of the negative electrode material to the electrolyte, and the thickness of the solid electrolyte film layer on the surface of the material is comprehensively controlled. The prepared negative electrode plate has a lower resistivity, which further increases the stability and durability of the plate.

[0062] In some embodiments, I 1 / (I 2 +I 3 ) and I 2 / (I 2 +I 3 )+I 2 ' / (I 2 '+I 3 The specific value of the ratio of ') can be 0.01, 0.1, 0.2, 0.3, 0.4, 0.5, 0.8, 1.0, 1.5, 2.0, 2.5, 3, 4, 5, 6, 7, 8, 9 or 10, etc., and of course it can also be other values ​​within the above range, which is not limited here. When the ratio is controlled within the above range, an appropriate amount of silicon particles are exposed on the surface of the negative electrode material, the side reaction between the negative electrode material and the electrolyte can be effectively controlled, and the thickness of the solid electrolyte film on the surface of the negative electrode material can also be effectively controlled. At this time, the electrolyte infiltration ability is relatively increased, and the negative electrode material can have a good electrolyte infiltration ability, thereby reducing the resistivity of the negative electrode sheet. Preferably, I 1 / (I 2 +I 3 ) and I 2 / (I 2 +I 3 )+I 2 ' / (I 2 '+I 3 ') is in the range of 0.4 to 10.

[0063] In some embodiments, the silicon particles include at least one of amorphous silicon, crystalline silicon, silicon oxide, and silicate.

[0064] In some embodiments, the silicon particles include silicon oxide, wherein the silicon oxide includes silicon element and oxygen element, and an atomic ratio of the silicon element to the oxygen element is 0 to 2, excluding 0.

[0065] In some embodiments, the silicon particles include silicon oxide, the chemical formula of which is SiO x , where 0<x≤2. Specifically, SiO x Specifically, it can be SiO 0.5、SiO 0.7 、SiO 0.9 、SiO、SiO 1.2 、SiO 1.5 、SiO 1.8 、SiO 1.9 Etc., no limitation is made here.

[0066] Silicon oxide can be represented by the general formula SiO x (0<x≤2). It can be silicon particles dispersed in SiO 2 The material formed may also be a material having a tetrahedral structural unit, wherein the silicon atom is located at the center of the tetrahedral structural unit and the oxygen atoms are located at the four vertices of the tetrahedral structural unit.

[0067] In some embodiments, the median particle size of the silicon particles is 1 nm to 10 μm, specifically 1 nm, 10 nm, 50 nm, 100 nm, 1 μm, 1.8 μm, 2 μm, 2.5 μm, 3 μm, 3.6 μm, 5 μm, 6 μm, 6.5 μm, 7 μm, 7.8 μm, 8.5 μm, 9 μm, 9.8 μm or 10 μm, etc., and of course it can also be other values ​​within the above range, which is not limited here.

[0068] In some embodiments, the silicon particles further include a doping metal M, and M is selected from at least one of Li, Mg, Al, Fe, La, Zn, Ti, Cu and Mn. It is understandable that a small amount of doping metal can be doped into the carbon material or into the silicon-based active material, and the doping metal can improve the conductivity of the negative electrode material and enhance the structural strength of the negative electrode material. Preferably, M is Mg and / or Li.

[0069] In some embodiments, in the negative electrode material, silicon particles and graphite are dispersed with each other in the form of particles.

[0070] In some embodiments, the graphite includes at least one of natural graphite, artificial graphite, expanded graphite and oxidized graphite. Graphite is a material with high conductivity, small volume expansion, high initial efficiency and stable cycle performance. By compounding graphite and silicon particles, the conductivity of the negative electrode material can be comprehensively improved and the expansion can be reduced.

[0071] In some embodiments, the carbon material includes at least one of amorphous carbon and graphitized carbon, and the carbon material is located on the surface of the active material to form a carbon layer. The carbon material can be located on the surface of the silicon particle particles, or on the surface of the graphite particles, or the graphite particles and the silicon particles can be secondary granulated and coated to form secondary particles, which is not limited here. In some embodiments, the thickness of the carbon layer is 1nm to 1000nm, and can specifically be 1nm, 5nm, 10nm, 15nm, 20nm, 50nm, 80nm, 100nm, 150nm, 200nm, 400nm, 500nm, 700nm, 800nm, 900nm, 1000nm, etc., which is not limited here. The thickness of the carbon layer is controlled within the above range, which can increase the conductivity of the negative electrode material, which is conducive to obtaining a negative electrode material with a high specific capacity; and the carbon layer can effectively alleviate the volume expansion of the active material and improve the long cycle performance of the negative electrode material. Preferably, the thickness of the carbon layer is 50 nm to 800 nm; more preferably, the thickness of the carbon layer is 100 nm to 500 nm.

[0072] In some embodiments, the particle size distribution width of the negative electrode material is P, 1.0≤P≤2.2, P=(D 05 +D 99 ) / (2*D 50 ). The specific value of the ratio of P can be 1.0, 1.1, 1.3, 1.5, 1.6, 1.8, 2.0, 2.1 or 2.2, etc., which is not limited here. When the particle size distribution of the positive electrode material is controlled within the above range, it means that the negative electrode material has a wider particle size distribution, which helps to improve the uniform distribution of silicon particles and graphite, is beneficial to improve the gram capacity of the negative electrode material, and helps to improve the conductivity of the negative electrode material. It should be noted that the negative electrode material here is measured based on all particles.

[0073] It should be noted that the volume-based cumulative particle size distribution of the particle size distribution determination is measured by laser diffraction method. D05 represents the particle size corresponding to the cumulative particle size distribution percentage of the powder when it reaches 5%, D50 represents the particle size corresponding to the cumulative particle size distribution percentage when it reaches 50%, and D99 represents the particle size corresponding to the cumulative particle size distribution percentage when it reaches 99%. 05 +D 99 ) / (2*D 50 ) is used to define the particle size distribution of the negative electrode material. The nano-scale silicon particles formed by vapor deposition can be included in the particle size planning, which can cover the sizes of most negative electrode material particles.

[0074] When the negative electrode material satisfies 1.0≤P≤2.2, the particle size and quantity matching of large and small particles in the negative electrode material is good, which is conducive to the full dispersion of particles and tends to form small particles embedded in the contact gaps of large particles to form a tightly packed structure, thereby helping to provide the tap density of the negative electrode material. When the ratio is too small, the particle sizes of large and small particles in the material are very close, and there are large pores in the contact between particles, which is not conducive to the formation of a tightly packed structure. When the ratio is too large, the particle size and quantity of large and small particles in the material are quite different, and a large number of small particles tend to agglomerate themselves and are difficult to form a matching tightly packed structure with large particles, and the distribution uniformity decreases.

[0075] In some embodiments, the powder conductivity of the negative electrode material under a pressure of 20 kN is greater than 30 S / cm, and may be 30 S / cm, 31 S / cm, 32 S / cm, 33 S / cm, 35 S / cm, 36 S / cm, 37 S / cm, 38 S / cm or 40 S / cm, etc., which are not limited here. The powder conductivity of the negative electrode material is controlled within the above range, which is conducive to improving the conductivity of the negative electrode material and reducing the resistivity of the negative electrode sheet.

[0076] In some embodiments, the contact angle of the negative electrode material is greater than 110°. In the present application, controlling the contact angle of the negative electrode material within the above range is beneficial to improving the electrolyte wetting ability of the negative electrode material.

[0077] In some embodiments, the median particle size D of the negative electrode material is 50 It is 2μm to 12μm, and specifically can be 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 5μm, 6μm, 8μm, 9μm, 10μm or 12μm, etc., and is not limited here.

[0078] In some embodiments, the tap density of the negative electrode material is ≥ 0.7 g / cm 3 The tap density of the negative electrode material can be specifically 0.7 g / cm 3 , 0.75g / cm 3 、0.81g / cm 3 , 0.85g / cm 3 , 0.89g / cm 3 、0.91g / cm 3 , 0.95g / cm 3 , 0.99g / cm 3 , 1.0g / cm 3 , 1.05g / cm 3 , 1.1g / cm 3 , 1.13g / cm 3 , 1.18g / cm 3 , 1.2g / cm3 , 1.25g / cm 3 , 1.3g / cm 3 , 1.38g / cm 3 or 1.4 g / cm 3 Etc., no limitation is made here.

[0079] In some embodiments, the mass content of silicon particles in the negative electrode material is 1% to 80%, and the mass content of graphite is 20% to 99%. The mass content of silicon particles can be 1%, 2%, 8%, 10%, 12%, 15%, 30%, 50%, 55%, 58%, 60%, 65%, 69%, 70% or 80%, etc., and of course it can also be other values ​​within the above range, which is not limited here. The mass content of graphite can be 20%, 30%, 40%, 50%, 55%, 58%, 60%, 65%, 69%, 70%, 80% or 90%, etc., and of course it can also be other values ​​within the above range, which is not limited here.

[0080] In a second aspect, the present application provides a method for preparing a negative electrode material, such as Figure 1 As shown, the following steps are included:

[0081] Step S100, placing graphite in a modification solution for modification treatment, and drying to obtain modified graphite;

[0082] Step S200, vapor deposition of modified graphite using a reaction gas containing a silicon source gas to obtain a mixture of silicon-containing particles and modified graphite;

[0083] Step S300, using a gas phase carbon source to place the mixture at 550°C to 1000°C for gas phase carbon coating treatment to obtain a negative electrode material.

[0084] The preparation method of the negative electrode material provided by the present application comprises the following steps: firstly, modifying the graphite to increase the defect degree of the graphite and reduce the resistivity of the negative electrode sheet; then, compounding the modified graphite with silicon particles by vapor deposition to achieve uniform mixing of the silicon particles and the graphite and reduce the segregation of the silicon particles; finally, placing the mixture of the two at 550° C. to 1000° C. for vapor phase carbon coating to effectively reduce the defect degree of the graphite surface and adjust the defect degree of the carbon material on the surface of the silicon particles and the surface of the graphite, so that I 1 / (I 2 +I 3 ) and I 2 / (I 2 +I 3 )+I 2 ' / (I 2 '+I 3') is in the range of 0.01 to 10, which can find a balance between the degree of silicon exposure and the degree of defects in the surface carbon material. Under the initial condition of ensuring the first coulombic efficiency of the negative electrode material at a high level, the degree of defects in the carbon material on the surface of the active material can be used to improve the electrolyte wetting ability of the negative electrode material. The small amount of silicon particles exposed on the surface of the negative electrode material can also be used to generate a solid electrolyte film layer of appropriate thickness, thereby improving the conductivity of the electrode piece.

[0085] The following is a detailed introduction to this program:

[0086] Step S100, placing graphite in a modification solution for modification treatment, and drying to obtain modified graphite.

[0087] In some embodiments, the median particle size of graphite is 5 μm to 20 μm, specifically 5 μm, 5 μm, 5 μm, 5 μm, 5 μm, 5 μm, 5 μm or 5 μm, etc., which are not limited here. Controlling the particle size of graphite is beneficial to controlling the particle size of the final negative electrode material and improving the particle structure stability of the negative electrode material. In some embodiments, graphite includes at least one of natural graphite, artificial graphite, expanded graphite and oxidized graphite. Graphite is a material with high conductivity, small volume expansion, high first efficiency and stable cycle performance. By compounding graphite and silicon particles, the conductivity of the negative electrode material can be comprehensively improved and the expansion can be reduced.

[0088] In some embodiments, the modification step includes placing the graphite in an acid solution or an alkaline solution for modification.

[0089] In some embodiments, the acid solution includes at least one of a hydrochloric acid solution, a sulfuric acid solution, and a nitric acid solution.

[0090] In some embodiments, the alkaline solution includes at least one of a sodium hydroxide solution, a potassium hydroxide solution, and a lithium hydroxide solution.

[0091] In some embodiments, the concentration of the acid solution or the alkaline solution is less than 2 mol / L, and can be specifically 1.9 mol / L, 1.85 mol / L, 1.8 mol / L, 1.6 mol / L, 1.5 mol / L, 1.2 mol / L or 1.0 mol / L, etc., which is not limited here.

[0092] In some embodiments, the temperature of the modification treatment is 20° C. to 30° C. The temperature of the modification treatment can be 20° C., 21° C., 22° C., 23° C., 25° C., 28° C., 29° C. or 30° C., etc., and of course, it can also be other values ​​within the above range, which is not limited here.

[0093] In some embodiments, the modification treatment time is 10 h to 48 h. Specifically, the modification treatment time can be 10 h, 13 h, 15 h, 18 h, 20 h, 24 h, 25 h, 28 h, 36 h, 42 h or 48 h, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0094] In the present application, by controlling the temperature, time and concentration of the modification solution of the modification treatment, the degree of surface defects of the graphite can be adjusted, which is beneficial to improve the degree of cracking of the gaseous carbon source and the silicon source gas during the subsequent gas phase deposition and gas phase carbon coating process, so that the composite of the graphite particles with the silicon particles and the carbon material is more uniform and sufficient, and the degree of defects of the carbon material on the surface of the graphite particles can be adjusted.

[0095] In some embodiments, the modification step further comprises washing the modified product until the product is washed to neutrality.

[0096] In some embodiments, the drying temperature is 45° C. to 80° C. The drying temperature can be 45° C., 48° C., 50° C., 54° C., 58° C., 60° C., 65° C., 68° C., 75° C. or 80° C., etc., and of course, it can also be other values ​​within the above range, which is not limited here.

[0097] In some embodiments, the drying time is 3 hours to 48 hours. The drying time can be 3 hours, 6 hours, 8 hours, 12 hours, 15 hours, 18 hours, 20 hours, 24 hours, 25 hours, 28 hours, 36 hours, 42 hours or 48 hours, etc., and of course, it can also be other values ​​within the above range, which is not limited here.

[0098] In step S200, modified graphite is vapor-deposited using a reaction gas containing a silicon source gas to obtain a mixture of silicon-containing particles and modified graphite.

[0099] In some embodiments, the deposition temperature of the vapor deposition is 300° C. to 700° C., and specifically may be 300° C., 350° C., 400° C., 450° C., 500° C., 520° C., 550° C., 600° C., 650° C. or 700° C. It is understood that the above temperature is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0100] In some embodiments, the deposition time of vapor deposition is 2 h to 8 h; specifically, it can be 2 h, 3 h, 4 h, 5 h, 6 h, 7 h or 8 h, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0101] In some embodiments, the flow rate of the silicon source gas is 0.1L / min to 15L / min, specifically 0.1L / min, 0.5L / min, 1.0L / min, 2.0L / min, 3L / min, 5L / min, 6L / min, 8L / min, 10L / min, 12L / min or 15L / min, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0102] In some embodiments, an auxiliary carrier gas is added during the vapor deposition process, and the flow rate of the auxiliary carrier gas is 0.5L / min to 25L / min, specifically 0.5L / min, 1.0L / min, 2.0L / min, 3L / min, 5L / min, 6L / min, 8L / min, 10L / min, 12L / min, or 15L / min, 18L / min, 20L / min or 25L / min, etc. Of course, it can also be other values ​​within the above range, which are not limited here.

[0103] In some embodiments, the auxiliary carrier gas includes at least one of nitrogen, argon, helium, neon, carbon dioxide, hydrogen and carbon monoxide. Understandably, under the disturbance of the auxiliary carrier gas, the graphite is in a dynamic motion process, and the silicon particles formed after the cracking of the silicon source gas contact the dynamic graphite, thereby achieving uniform mixing of the graphite and silicon particles, which can reduce the self-agglomeration of nano-scale particles, thereby reducing the excessive local stress of the negative electrode material during the charge and discharge process, reducing particle breakage, and improving the cycle performance of the negative electrode material.

[0104] In some embodiments, the raw material of the silicon source gas includes at least one of monosilane, disilane, monochlorosilane, dichlorosilane, trichlorosilane, tetrachlorosilane, and methyl siloxane.

[0105] In some embodiments, the median particle size of the silicon particles is 1 nm to 10 μm, specifically 1 nm, 10 nm, 50 nm, 100 nm, 1 μm, 1.8 μm, 2 μm, 2.5 μm, 3 μm, 3.6 μm, 5 μm, 6 μm, 6.5 μm, 7 μm, 7.8 μm, 8.5 μm, 9 μm, 9.8 μm or 10 μm, etc., and of course it can also be other values ​​within the above range, which is not limited here.

[0106] In some embodiments, step S200 includes mixing modified graphite with doped metal M to obtain a composite; and performing vapor deposition on the composite using a reaction gas containing silicon source gas to obtain a mixture of silicon-containing particles, modified graphite and doped metal M.

[0107] In some embodiments, the silicon particles further include a doping metal M, and M is selected from at least one of Li, Mg, Al, Fe, La, Zn, Ti, Cu and Mn. It is understandable that a small amount of doping metal can be doped into the carbon material or into the silicon-based active material, and the doping metal can improve the conductivity of the negative electrode material and enhance the structural strength of the negative electrode material. Preferably, M is Mg and / or Li.

[0108] In some embodiments, the silicon particles include silicon oxide, the silicon oxide includes silicon element and oxygen element, and the atomic ratio of the silicon element to the oxygen element is 0 to 2, and 0 is not included.

[0109] In some embodiments, the silicon particles include silicon oxide, the chemical formula of which is SiO x , where 0<x≤2. Specifically, SiO x Specifically, it can be SiO 0.5 、SiO 0.7 、SiO 0.9 、SiO、SiO 1.2 、SiO 1.5 、SiO 1.8 、SiO 1.9 Etc., no limitation is made here.

[0110] Silicon oxide can be represented by the general formula SiO x (0<x≤2). It can be silicon particles dispersed in SiO 2 The material formed may also be a material having a tetrahedral structural unit, wherein the silicon atom is located at the center of the tetrahedral structural unit and the oxygen atoms are located at the four vertices of the tetrahedral structural unit.

[0111] In some embodiments, based on 100 wt % of the mass of the modified graphite, the amount of the doping metal M added to the modified graphite is less than 20 wt %.

[0112] In some embodiments, the silicon particles and graphite in the mixture are dispersed in the form of particles. Step S300: perform a gas-phase carbon coating treatment on the mixture using a gas-phase carbon source to obtain a negative electrode material.

[0113] In some embodiments, the raw material of the gaseous carbon source includes at least one of methane, ethane, ethylene, acetylene, propyne, propylene, propane, formaldehyde, acetaldehyde, methanol, toluene, benzene, styrene and phenol;

[0114] In some embodiments, the flow rate of the gaseous carbon source is 0.2L / min to 18L / min; specifically, it can be 0.2L / min, 0.5L / min, 1.0L / min, 2.0L / min, 3L / min, 5L / min, 6L / min, 8L / min, 10L / min, 15L / min or 18L / min, etc. Of course, it can also be other values ​​within the above range, which are not limited here.

[0115] In some embodiments, the temperature of the gas phase carbon coating treatment is 550° C. to 1000° C., and specifically can be 550° C., 600° C., 650° C., 700° C., 820° C., 850° C., 900° C., 950° C. or 1000° C. It is understandable that the above temperature is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0116] In some embodiments, the time of the gas phase carbon coating treatment is 1 h to 6 h, specifically 1 h, 2 h, 3 h, 4 h, 5 h or 6 h, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0117] In some embodiments, the vapor phase carbon coating process is performed under a protective atmosphere.

[0118] In some embodiments, the protective atmosphere includes at least one of nitrogen, helium, neon, and argon.

[0119] In some embodiments, the carbon material is located on the surface of the active material to form a carbon layer. The carbon material can be located on the surface of the silicon particles, or on the surface of the graphite particles, or the graphite particles and the silicon particles can be secondary granulated and coated to form secondary particles, which is not limited here.

[0120] In some embodiments, the thickness of the carbon layer is 1nm to 1000nm, and can be specifically 1nm, 5nm, 10nm, 15nm, 20nm, 50nm, 80nm, 100nm, 150nm, 200nm, 400nm, 500nm, 700nm, 800nm, 900nm, 1000nm, etc., which are not limited here. The thickness of the carbon layer is controlled within the above range, which can increase the conductivity of the negative electrode material and is conducive to obtaining a negative electrode material with a high specific capacity; and the carbon layer can effectively alleviate the volume expansion of the active material and improve the long cycle performance of the negative electrode material. Preferably, the thickness of the carbon layer is 50nm to 800nm; more preferably, the thickness of the carbon layer is 100nm to 500nm.

[0121] In the third aspect, the present application provides a negative electrode sheet, the negative electrode sheet includes the above-mentioned negative electrode material, and the resistivity of the negative electrode sheet is ≤5Ω*cm. The resistivity can be 5Ω*cm, 4.5Ω*cm, 4Ω*cm, 3Ω*cm, 2.8Ω*cm, 2.5Ω*cm, 2.2Ω*cm, 2.0Ω*cm, 1.9Ω*cm, 1.6Ω*cm, 1.2Ω*cm or 1.0Ω*cm, etc., which are not limited here. It can be understood that the resistivity of the negative electrode sheet is within the above range. This is because the electrolyte wetting ability of the negative electrode material is improved, resulting in the electrolyte being able to fully infiltrate the negative electrode material on the negative electrode sheet, so that the electron transmission efficiency is improved, the silicon particles, graphite and carbon materials are in good contact, and the resistivity of the sheet is reduced, so that the sheet has excellent rate performance.

[0122] In a fourth aspect, the present application provides a battery, including the above-mentioned negative electrode material, and the electrochemical device can specifically be a lithium-ion battery, a sodium-ion battery, etc., which is not limited here.

[0123] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

[0124] Example

[0125] Example 1

[0126] (1) Graphite with D50 = 8 μm was placed in a 1 mol / L HCl solution and stirred for 4 h, then allowed to stand at 30°C for 24 h, the solution was removed and rinsed with clean water until neutral, and finally baked in an oven at 80°C for 12 h to obtain modified graphite.

[0127] (2) The modified graphite is placed in a fluidized bed reactor, monosilane gas is introduced, the monosilane gas flow rate is 5 L / min, the carrier gas (argon) rate is set to 7.5 L / min, and the reaction is carried out at 400° C. for 6 hours to obtain a mixture of silicon particles and graphite particles.

[0128] (3) The temperature of the fluidized bed reactor was adjusted to 800° C., the gas introduced was switched to methane with a gas flow rate of 8 L / min, and the gas phase carbon coating treatment was performed for 4 h. The material was cooled to room temperature and discharged to obtain the negative electrode material.

[0129] The negative electrode material prepared in the present application includes an active substance and a non-graphite carbon material located on at least a portion of the surface of the active substance, the active substance includes silicon and graphite, and the carbon material includes amorphous carbon.

[0130] Figure 2 The distribution of silicon particles and graphite in the scanning range of the negative electrode material prepared in Example 1 is shown in FIG. Figure 3This is the Raman spectrum of the negative electrode material prepared in Example 1. Other parameters of the negative electrode material are shown in Table 1.

[0131] Example 2

[0132] (1) Graphite with D50 = 6 μm was placed in a 1 mol / L HCl solution and stirred for 4 h, then allowed to stand at 30°C for 24 h, the solution was removed and rinsed with clean water until neutral, and finally baked in an oven at 80°C for 12 h to obtain modified graphite.

[0133] (2) The modified graphite is placed in a fluidized bed reactor, monosilane gas is introduced, the monosilane gas flow rate is 5 L / min, the carrier gas (argon) rate is set to 7.5 L / min, and the reaction is carried out at 500° C. for 6 h to obtain a mixed powder of silicon particles and graphite particles.

[0134] (3) The temperature of the fluidized bed reactor was adjusted to 600° C., the gas introduced was switched to methane with a gas flow rate of 8 L / min, and the gas phase carbon coating treatment was performed for 2 h. The material was cooled to room temperature and discharged to obtain the negative electrode material.

[0135] The negative electrode material prepared in the present application includes an active substance and a carbon material located on at least a portion of the surface of the active substance, the active substance includes silicon and graphite, and the carbon material includes amorphous carbon.

[0136] Other parameters of the negative electrode materials are shown in Table 1.

[0137] Example 3

[0138] (1) Artificial graphite with D50 = 12 μm was placed in a 1 mol / L HCl solution and stirred for 4 h, then allowed to stand at 30°C for 24 h, the solution was removed and rinsed with clean water until neutral, and finally baked in an oven at 80°C for 12 h to obtain modified graphite.

[0139] (2) The modified graphite is placed in a fluidized bed reactor, monosilane gas is introduced, the monosilane gas flow rate is 5 L / min, the carrier gas (argon) rate is set to 7.5 L / min, and the reaction is carried out at 400° C. for 6 h to obtain a mixed powder of silicon particles and graphite particles.

[0140] (3) The temperature of the fluidized bed reactor was adjusted to 800° C., the gas introduced was switched to methane with a gas flow rate of 8 L / min, and the gas phase carbon coating treatment was performed for 4 h. The material was cooled to room temperature and discharged to obtain the negative electrode material.

[0141] The negative electrode material prepared in this embodiment includes an active material and a carbon material located on at least a portion of the surface of the active material. The active material includes silicon particles and graphite. The silicon particles are simple silicon.

[0142] Other parameters of the negative electrode materials are shown in Table 1.

[0143] Example 4

[0144] (1) Natural flake graphite with a D50 of 10 μm was placed in a 1 mol / L HCl solution and stirred for 4 h, then allowed to stand at 30°C for 24 h, the solution was removed and rinsed with clean water until neutral, and finally baked in an oven at 80°C for 12 h to obtain modified graphite.

[0145] (2) The modified graphite is placed in a fluidized bed reactor, monosilane gas is introduced, the monosilane gas flow rate is 6 L / min, the carrier gas (argon) rate is set to 7.5 L / min, and the reaction is carried out at 400° C. for 8 h to obtain a mixed powder of silicon particles and graphite particles.

[0146] (3) The temperature of the fluidized bed reactor was adjusted to 700° C., the gas introduced was switched to methane with a gas flow rate of 8 L / min, and the gas phase carbon coating treatment was performed for 6 h. The material was cooled to room temperature and discharged to obtain the negative electrode material.

[0147] The negative electrode material prepared in this embodiment includes an active material and a carbon material located on at least a portion of the surface of the active material. The active material includes silicon particles and graphite. The silicon particles are simple silicon.

[0148] Other parameters of the negative electrode materials are shown in Table 1.

[0149] Example 5

[0150] The difference from Example 1 is:

[0151] (1) Graphite with D50 = 8 μm was placed in a 1.8 mol / L NaOH solution and stirred for 4 h, then allowed to stand at 30°C for 24 h, the solution was removed and rinsed with clean water until neutral, and finally baked in an oven at 70°C for 12 h to obtain modified graphite.

[0152] Example 6

[0153] The difference from Example 1 is:

[0154] (1) Graphite with D50 = 8 μm was placed in a 1 mol / L HCl solution and stirred for 4 h, then allowed to stand at 25°C for 10 h, the solution was removed and rinsed with clean water until neutral, and finally baked in an oven at 80°C for 12 h to obtain modified graphite.

[0155] Example 7

[0156] The difference from Example 1 is:

[0157] (2) The modified graphite is placed in a fluidized bed reactor, monochlorosilane gas is introduced, the monochlorosilane gas flow rate is 15 L / min, the carrier gas (argon) rate is set to 25 L / min, and the reaction is carried out at 300° C. for 8 hours to obtain a mixture of silicon particles and graphite particles.

[0158] Example 8

[0159] The difference from Example 1 is:

[0160] (2) The modified graphite is placed in a fluidized bed reactor, and a siloxane gas is introduced, the siloxane gas flow rate is 5 L / min, and the carrier gas (argon) rate is set to 7.5 L / min. The reaction is carried out at 400° C. for 6 hours to obtain a mixture of silicon particles and graphite particles, wherein the silicon particles include at least one of silicon element and silicon oxide.

[0161] Example 9

[0162] The difference from Example 1 is:

[0163] (3) The temperature of the fluidized bed reactor was adjusted to 800° C., the gas introduced was switched to acetylene with a gas flow rate of 18 L / min, and the gas phase carbon coating treatment was performed for 2 h. The material was cooled to room temperature and discharged to obtain the negative electrode material.

[0164] Example 10

[0165] The difference from Example 1 is:

[0166] (3) The temperature of the fluidized bed reactor was adjusted to 1000° C., the gas introduced was switched to methane with a gas flow rate of 0.2 L / min, and the gas phase carbon coating treatment was performed for 6 h. The material was cooled to room temperature and discharged to obtain the negative electrode material.

[0167] Embodiment 11

[0168] The difference from Example 1 is:

[0169] (1) Graphite with D50 = 8 μm was placed in a 1 mol / L HCl solution and stirred for 4 h, then allowed to stand at 30°C for 24 h, the solution was removed and rinsed with clean water until neutral, and finally baked in an oven at 80°C for 12 h to obtain modified graphite, and lithium metal powder (D50 = 1 μm) with a mass percentage of 5 wt% was added.

[0170] Comparative Example 1

[0171] The difference from Example 1 is:

[0172] (1) Graphite with D50 = 10 μm was placed in a 1 mol / L HCl solution and stirred for 4 h, then allowed to stand at 30°C for 24 h, the solution was removed and rinsed with clean water until neutral, and finally baked in an oven at 80°C for 12 h to obtain modified graphite.

[0173] (2) The modified graphite is placed in a fluidized bed reactor, silane gas is introduced, the gas flow rate is 5 L / min, the carrier gas speed is set to 7.5 L / min, and the reaction is carried out at 300° C. for 6 h to obtain a mixed powder of silicon particles and graphite particles.

[0174] (3) The temperature of the fluidized bed reactor was adjusted to 500° C., the gas introduced was switched to methane with a gas flow rate of 8 L / min, and the gas phase carbon coating treatment was performed for 2 h. The material was cooled to room temperature and discharged to obtain the negative electrode material.

[0175] Comparative Example 2

[0176] The difference from Example 1 is:

[0177] Skip step (1) and go directly to step (2)

[0178] The parameters of the negative electrode materials are detailed in Table 1.

[0179] Test Method

[0180] (1) Particle size of negative electrode material:

[0181] The particle size test method refers to GB / T 19077-2016. It can be conveniently measured with a laser particle size analyzer, such as the Mastersizer 3000 laser particle size analyzer of Malvern Instruments Ltd. in the UK. The particle size distribution range of the negative electrode material is tested by Malvern laser particle size analyzer (Mastersizer 3000), and the volume-based cumulative particle size distribution of the particle size distribution is measured by laser diffraction method. D05 represents the particle size corresponding to the cumulative particle size distribution percentage of the powder reaching 05%, D50 represents the particle size corresponding to the cumulative particle size distribution percentage reaching 50%, and D80 represents the particle size corresponding to the cumulative particle size distribution percentage reaching 80%.

[0182] (2) Test method for tap density of negative electrode materials:

[0183] Refer to GB / T 5162-2006 / ISO 3953:1993 "Determination of tap density of metal powders", and use the Quantachrome tap density analyzer (Quantachrome DAT-4-220) of Anton Paar (Shanghai) Trading Co., Ltd. for testing. The tap density T is the value after 1000 vibrations, the loading amount is 60g, and the unit is g / cm 3 .

[0184] (3) Powder conductivity test of negative electrode materials

[0185] According to the equipment and methods of BTRTC / ZY / 02-093 "Powder Conductivity Test Operation Instructions", the powder conductivity of the material is tested. 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 must ensure that the sample thickness is 3 to 5mm under a pressure of 20KN. The pressure settings are 4, 8, 12, 16, and 20KN. The Electrode radius is 0.7mm and the Sample radius is 10mm.

[0186] (4) Raman test of negative electrode materials:

[0187] The Raman spectrum of the powder was tested using the In Via micro-confocal Raman spectrometer from Renishaw of Japan. The test parameters were: laser wavelength 532nm, test range 120um×120um, step length 4um. The test results were processed using the software that came with the test instrument. When processing the data, the baseline of the Raman spectrum curve of all the points was first removed, and the peak search parameters were adjusted at 500cm -1 ~520cm -1 The first characteristic peak in the range is at 1345cm -1 ~1355cm -1 There is a second characteristic peak in the range of 1570cm -1 ~1610cm -1 There is a third characteristic peak in the range, and then the peak intensity of each peak is obtained. In particular, the baseline after processing is around 0 as the standard for baseline removal, and the other processing steps use the initial parameters of the software.

[0188] (5) Liquid absorption capacity test of negative electrode materials

[0189] A negative electrode sheet was prepared according to the ratio of negative electrode material: sodium carboxymethyl cellulose (MAC350HC): conductive carbon black: styrene-butadiene rubber (451B) = 95.3:1.3:1.5:1.9. The negative electrode sheet was placed in a glove box, and 5 mL of electrolyte was dripped onto the 5 cm×5 cm negative electrode sheet using a pipette, and the time taken for the electrolyte to be completely absorbed was recorded.

[0190] (6) Resistivity test of negative electrode:

[0191] The negative electrode sheet was made according to the ratio of negative electrode material: sodium carboxymethyl cellulose (MAC350HC): conductive carbon black: styrene-butadiene rubber (451B) = 95.3:1.3:1.5:1.9. A 50 cm × 50 cm square block was taken, and 9 points were randomly tested using a sheet resistance meter, and the average value was taken as the resistivity of the measured material.

[0192] The test results are shown in Table 1.

[0193] Table 1 Negative electrode material performance test results

[0194]

[0195] According to the data in Table 1, the negative electrode materials prepared in Examples 1 to 10 of the present application control the K value within the range of 0.01 to 10, and can find a balance between the degree of silicon exposure and the degree of defects in the surface carbon material. On the one hand, it ensures that fewer silicon particles in the negative electrode material are exposed, and on the other hand, the degree of defects in the surface carbon material is used to improve the wetting ability of the negative electrode material to the electrolyte. The prepared negative electrode plate has a lower resistivity, further increasing the stability of the plate.

[0196] For the negative electrode material of Comparative Example 1, the gas phase carbon coating temperature is too low during the preparation process, resulting in the K value of the negative electrode material being out of the range of 0.01 to 10, too many silicon particles exposed on the surface of the negative electrode material, and the electrolyte wetting ability of the negative electrode material is reduced. Compared with Example 1, the resistivity of the electrode sheet prepared from the negative electrode material is also greatly increased.

[0197] In the negative electrode material of Comparative Example 2, the graphite was not modified during the preparation process, the K value of the negative electrode material was lower than that of Example 1, and the degree of defects of the carbon material on the surface of the negative electrode material was too large. Although the electrolyte infiltration ability of the negative electrode material was greatly improved, the side reaction between the negative electrode material and the electrolyte was intensified, and the thickness of the solid electrolyte film on the surface of the negative electrode material was too large, resulting in a significant increase in the resistivity of the electrode sheet.

[0198] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A negative electrode material, characterized in that: The negative electrode material includes an active substance and a carbon material located on at least a portion of the surface of the active substance, wherein the active substance includes silicon particles and graphite; In the Raman scanning spectrum of the negative electrode material, the silicon particles in the negative electrode material have a wavelength of 500 cm -1 ~520cm -1 The characteristic peak intensity in the range is I1, at 1345cm -1 ~1355cm -1 The characteristic peak intensity in the range is I2, at 1570cm -1 ~1610cm -1 The characteristic peak intensity in the range is I3; The graphite in the negative electrode material has a peak at 1345 cm -1 ~1355cm -1 The characteristic peak intensity in the range is I2', at 1570cm -1 ~1610cm -1 The characteristic peak intensity in the range is I3'; In the negative electrode material, 2. The negative electrode material according to claim 1, characterized in that The particle size distribution width of the negative electrode material is P, P = (D 05 +D 99 ) / (2*D 50 ), and 1.0≤P≤2.

2.

3. The negative electrode material according to claim 1, characterized in that The powder conductivity of the negative electrode material under a pressure of 20 kN is greater than 30 S / cm.

4. The negative electrode material according to any one of claims 1 to 3, characterized in that The negative electrode material includes at least one of the following features (1) to (7): (1) The silicon particles include at least one of amorphous silicon, crystalline silicon, silicon oxide and silicate; (2) The graphite comprises at least one of natural graphite, artificial graphite, expanded graphite and oxidized graphite; (3) The median particle size of the negative electrode material is 2 μm to 20 μm; (4) The contact angle of the negative electrode material is greater than 110°; (5) The mass content of silicon particles in the negative electrode material is 1% to 80%, and the mass content of graphite is 20% to 99%; (6) The tap density of the negative electrode material is ≥ 0.7 g / cm 3 ; (7) The carbon material includes at least one of amorphous carbon and graphitized carbon.

5. The negative electrode material according to any one of claims 1 to 3, characterized in that: The negative electrode material includes at least one of the following features (1) to (2): (1) The silicon particles include silicon oxide, the silicon oxide includes silicon and oxygen, and the atomic ratio of the silicon to the oxygen is 0 to 2, excluding 0; (2) The silicon particles include silicon oxide, and the chemical formula of the silicon oxide is SiO x , where 0<x≤2.

6. A method for preparing a negative electrode material, characterized in that: The following steps are involved: Placing graphite in a modification solution for modification, and drying to obtain modified graphite; Using a reaction gas containing a silicon source gas to vapor-deposit the modified graphite to obtain a mixture of silicon-containing particles and modified graphite; The mixture is placed at 550° C. to 1000° C. using a gas phase carbon source to perform a gas phase carbon coating treatment to obtain a negative electrode material.

7. The preparation method according to claim 6, characterized in that: The method comprises at least one of the following features (1) to (8): (1) The modification step comprises placing the graphite in an acid solution or an alkaline solution for modification; (2) The modification step includes placing the graphite in an acid solution or an alkaline solution for modification, wherein the acid solution includes at least one of a hydrochloric acid solution, a sulfuric acid solution, and a nitric acid solution; (3) The modification step includes placing the graphite in an acid solution or an alkaline solution for modification, wherein the alkaline solution includes at least one of a sodium hydroxide solution, a potassium hydroxide solution, and a lithium hydroxide solution; (4) The modification step includes placing the graphite in an acid solution or an alkaline solution for modification, wherein the concentration of the acid solution or the alkaline solution is less than 2 mol / L; (5) The modification step includes placing the graphite in an acid solution or an alkaline solution for modification, the modification time is 10 hours to 48 hours, and the modification temperature is 20° C. to 30° C.; (6) The modification step further comprises washing the modified product until the product is washed to neutrality; (7) The drying temperature is 45°C to 80°C; (8) The drying time is 3 hours to 48 hours.

8. The preparation method according to claim 6, characterized in that: The method comprises at least one of the following features (1) to (11): (1) The graphite comprises at least one of natural graphite, artificial graphite, expanded graphite and oxidized graphite; (2) The median particle size of the graphite is 6 μm to 20 μm; (3) The deposition temperature of the vapor deposition is 300° C. to 700° C.; (4) The deposition time of the vapor deposition is 2h to 8h; (5) The flow rate of the silicon source gas is 0.1 L / min to 15 L / min; (6) An auxiliary carrier gas is also added during the vapor deposition process, and the flow rate of the auxiliary carrier gas is 0.5 L / min to 25 L / min; (7) An auxiliary carrier gas is also added during the vapor deposition process, and the auxiliary carrier gas includes at least one of nitrogen, argon, helium, neon, carbon dioxide, hydrogen and carbon monoxide; (8) The raw material of the silicon source gas includes at least one of monosilane, disilane, monochlorosilane, dichlorosilane, trichlorosilane, tetrachlorosilane and methyl siloxane; (9) The raw material of the gaseous carbon source includes at least one of methane, ethane, ethylene, acetylene, propyne, propylene, propane, formaldehyde, acetaldehyde, methanol, toluene, benzene, styrene and phenol; (10) The flow rate of the gas phase carbon source is 0.2 L / min to 18 L / min; (11) The time of the gas phase carbon coating treatment is 1 hour to 6 hours.

9. A negative electrode plate, characterized in that: The negative electrode plate comprises the negative electrode material according to any one of claims 1 to 5 or the negative electrode material prepared by the method for preparing the negative electrode material according to any one of claims 6 to 8, and the resistivity of the negative electrode plate is ≤5Ω*cm.

10. A lithium ion battery, characterized in that: The lithium-ion battery comprises the negative electrode material according to any one of claims 1 to 5 or the negative electrode material prepared by the method for preparing the negative electrode material according to any one of claims 6 to 8.

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