Negative electrode material, method for preparing same, negative electrode sheet, and battery

Abstract

This application relates to a negative electrode material, a method for preparing the same, a negative electrode sheet, and a battery. The negative electrode material includes an active material and a carbon material located on at least a part of the surface of the active material. The active material includes silicon particles and graphite. In the Raman surface scanning spectrogram of the negative electrode material, the characteristic peak intensity of the silicon particles in the negative electrode material in the range of 500 cm-1 to 520 cm-1 is I1, the characteristic peak intensity in the range of 1345 cm-1 to 1355 cm-1 is I2, and the characteristic peak intensity in the range of 1570 cm-1 to 1610 cm-1 is I3. The characteristic peak intensity of the graphite in the negative electrode material in the range of 1345 cm-1 to 1355 cm-1 is I2', and the characteristic peak intensity in the range of 1570 cm-1 to 1610 cm-1 is I3'. In the negative electrode material, 0.01 ≤ K ≤ 10. The negative electrode material provided by this application has a high specific capacity and good electrolyte infiltration performance, and the prepared negative electrode sheet has a low resistivity.

Description

Technical Field

[0001] The present invention relates to the technical field of anode materials, and particularly to anode materials, their preparation methods, anode plates, and batteries. Background Art

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

[0003] Therefore, how to improve the specific capacity of the anode material while enhancing the wettability and conductivity of the silicon-containing anode material is still a technical problem to be solved at present. Summary of the Invention

[0004] The purpose of the present application is to provide an anode material, its preparation method, anode plate, and battery. The anode material of the present application has a high specific capacity, can also enhance the wettability of the anode material, and reduce the resistivity of the anode plate.

[0005] In the first aspect, the present application provides an anode material, which includes an active material and a carbon material located on at least part of the surface of the active material. The active material includes silicon particles and graphite;

[0006] In the Raman spectrum of the anode material, the characteristic peak intensity of the silicon particles in the anode material is I1 in the range of 500 cm -1 ~520 cm -1 The characteristic peak intensity is I2 in the range of 1345 cm -1 ~1355 cm -1 The characteristic peak intensity is I3 in the range of 1570 cm -1 ~1610 cm -1 ;

[0007] The characteristic peak intensity of the graphite in the anode material is I2' in the range of 1345 cm -1 ~1355 cm -1 The characteristic peak intensity is in the range of 1570 cm -1 ~1610 cm-1 The characteristic peak intensity within the range is I3';

[0008] The negative electrode material satisfies:

[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 ≥ 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, and does not include 0.

[0019] In some embodiments, the silicon particles include silicon oxide, and the chemical general 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, including the following steps:

[0021] Place the graphite in a modification solution for modification treatment, and dry to obtain modified graphite;

[0022] The modified graphite is subjected to chemical vapor deposition using a reaction gas containing a silicon source gas to obtain a mixture of silicon-containing particles and modified graphite;

[0023] The mixture is subjected to chemical vapor carbon coating treatment at 550°C to 1000°C using a gaseous carbon source to obtain a negative electrode material.

[0024] In some embodiments, the step of the modification treatment includes subjecting graphite to a modification treatment in an acid solution or an alkali solution.

[0025] In some embodiments, the step of the modification treatment includes subjecting graphite to a modification treatment in an acid solution or an alkali solution, 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 step of the modification treatment includes subjecting graphite to a modification treatment in an acid solution or an alkali solution, wherein the alkali solution includes at least one of a sodium hydroxide solution, a potassium hydroxide solution, and a lithium hydroxide solution.

[0027] In some embodiments, the step of the modification treatment includes subjecting graphite to a modification treatment in an acid solution or an alkali solution, wherein the concentration of the acid solution or the alkali solution < 2 mol / L.

[0028] In some embodiments, the step of the modification treatment includes subjecting graphite to a modification treatment in an acid solution or an alkali solution, the time of the modification treatment is 10 h to 48 h, and the temperature of the modification treatment is 20°C to 30°C.

[0029] In some embodiments, the step of the modification treatment further includes washing the product after the modification treatment until the product is washed to neutral.

[0030] In some embodiments, the temperature of the drying treatment is 45°C to 80°C.

[0031] In some embodiments, the time of the drying treatment is 3 h to 48 h.

[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 deposition temperature of the chemical vapor deposition is 300°C to 700°C.

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

[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 chemical 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 chemical 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 materials of the silicon source gas include at least one of silane, disilane, trichlorosilane, dichlorosilane, trichlorosilane, tetrachlorosilane, and methylsiloxane.

[0040] In some embodiments, the raw materials of the gaseous carbon source include 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 gaseous carbon source is 0.2 L / min to 18 L / min.

[0042] In some embodiments, the time for the gaseous carbon coating treatment is 1 h to 6 h.

[0043] In a third aspect, the present application provides a negative electrode sheet, which includes 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 sheet is ≤5 Ω·cm.

[0044] In a fourth aspect, the present application provides a battery, which includes the negative electrode sheet 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 by the present application includes an active material and a carbon material located on at least a part of the surface of the active material. The active material includes silicon particles and graphite. In the Raman surface scanning spectrum, the intensity of the characteristic peak of the silicon particles in the range of 500 cm -1 to 520 cm -1 is I1, the intensity of the characteristic peak in the range of 1345 cm -1 to 1355 cm -1 is I2, and the intensity of the characteristic peak in the range of 1570 cm -1 to 1610 cm -1 is I3. Due to the presence of the carbon material on the surface of the silicon particles, it can be at 1345 cm-1 ~1355 cm -1 range and 1570 cm -1 ~1610 cm -1 range, peaks were detected; for graphite, the characteristic peak intensity in the range of 1345 cm -1 ~1355 cm -1 is I2', and the characteristic peak intensity in the range of 1570 cm -1 ~1610 cm -1 is I3'. I1 / (I2 + I3) can represent the exposure degree of silicon particles in the negative electrode material, and I2 / (I2 + I3) + I2' / (I2' + I3') can represent the total defect degree of carbon materials 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 degree of the surface carbon material is relatively high, the side reaction between the negative electrode material and the electrolyte intensifies, and the thickness of the solid electrolyte interface film on the surface of the negative electrode material also increases accordingly. At this time, although the electrolyte infiltration ability relatively increases, the resistivity of the electrode sheet decreases; in addition, the content of consumed active lithium ions increases, and the initial 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 degree of the surface carbon material is very low, the electrolyte infiltration ability of the negative electrode material decreases, and some active materials are difficult to be formed and activated, which is not conducive to the performance of the active materials. By controlling the ratio of I1 / (I2 + I3) to I2 / (I2 + I3) + I2' / (I2' + I3') within the range of 0.01 - 10 in this application, a balance can be found between the silicon exposure degree and the defect degree of 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, it uses the defect degree of the surface carbon material to improve the electrolyte infiltration ability of the negative electrode material, comprehensively controlling the thickness of the solid electrolyte interface film layer on the material surface. The prepared negative electrode sheet has a lower resistivity, further increasing the stability and durability of the electrode sheet.

[0047] The preparation method of the negative electrode material provided by this application is as follows. First, the graphite is modified to increase the degree of defects of the graphite and reduce the resistivity of the negative electrode sheet. Then, the modified graphite and silicon particles are compounded by chemical vapor deposition to achieve uniform mixing of the silicon particles and the graphite and reduce the segregation phenomenon of the silicon particles. Finally, the mixture of the above two is subjected to chemical vapor carbon coating at 550°C to 1000°C, which can effectively reduce the degree of defects on the surface of the graphite and adjust the degree of defects of the carbon materials on the surfaces of the silicon particles and the graphite, so that the ratio of I1 / (I2+I3) to I2 / (I2+I3)+I2’ / (I2’+I3’) is within the range of 0.01 to 10. A balance can be found between the degree of silicon exposure and the degree of defects of the surface carbon material. On the premise of ensuring a relatively high initial Coulomb efficiency of the negative electrode material, the wettability of the electrolyte of the negative electrode material can be improved by using the degree of defects of the carbon material on the surface of the active substance. In addition, a suitable thickness of the solid electrolyte film layer can be formed by using a small amount of silicon particles exposed on the surface of the negative electrode material, thereby improving the conductivity of the electrode sheet. Brief Description of the Drawings

[0048] The present invention will be further described below with reference to the drawings and embodiments.

[0049] Figure 1 It is a schematic flow chart of the preparation method of the negative electrode material provided by the embodiment of this application.

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

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

[0052] Figure 4 It is the volume-based cumulative particle size distribution width diagram of the negative electrode material prepared in Example 1. Detailed Embodiments

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

[0054] It should be clear that the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

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

[0056] It should be understood that the term "and / or" used herein is only a correlative relationship describing associated objects, indicating that three relationships may exist. For example, A and / or B may represent three situations: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " herein generally represents an "or" relationship between the associated objects before and after.

[0057] In a first aspect, the present application provides a negative electrode material, which includes an active material and a carbon material located on at least a part of the surface of the active material, and the active material includes silicon particles and graphite.

[0058] In the Raman surface scan spectrogram of the negative electrode material, the silicon particles in the negative electrode material have a characteristic peak intensity of I1 in the range of 500 cm -1 ~520 cm -1 The characteristic peak intensity in the range of 1345 cm -1 ~1355 cm -1 is I2, and the characteristic peak intensity in the range of 1570 cm -1 ~1610 cm -1 is I3;

[0059] The graphite in the negative electrode material has a characteristic peak intensity of I2' in the range of 1345 cm -1 ~1355 cm -1 The characteristic peak intensity in the range of 1570 cm -1 ~1610 cm -1 is I3';

[0060] The negative electrode material satisfies:

[0061] The negative electrode material provided by the present application includes an active material and a carbon material located on at least a part of the surface of the active material, and the active material includes silicon particles and graphite. In the Raman surface scan spectrum, the silicon particles have a characteristic peak intensity of I1 in the range of 500 cm -1 ~520 cm -1 The characteristic peak intensity in the range of 1345 cm -1 ~1355 cm -1 is I2, and the characteristic peak intensity in the range of 1570 cm -1 ~1610 cm -1 is I3. Since there is a carbon material on the surface of the silicon particles, it can be at 1345 cm-1 ~1355 cm -1 range and 1570 cm -1 ~1610 cm -1 range; peaks were detected in graphite at 1345 cm -1 ~1355 cm -1 range with the characteristic peak intensity of I2', and at 1570 cm -1 ~1610 cm -1 range with the characteristic peak intensity of I3'. I1 / (I2 + I3) can represent the exposure degree of silicon particles in the negative electrode material, and I2 / (I2 + I3) + I2' / (I2' + I3') can represent the total defect degree of carbon materials 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 degree of the surface carbon material is relatively high, the side reaction between the negative electrode material and the electrolyte intensifies, and the thickness of the solid electrolyte interface film on the surface of the negative electrode material also increases accordingly. At this time, although the electrolyte infiltration ability relatively increases, the resistivity of the electrode sheet decreases; in addition, the content of consumed active lithium ions increases, and the initial Coulombic 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 degree of the surface carbon material is very low, the electrolyte infiltration 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. By controlling the ratio of I1 / (I2 + I3) to I2 / (I2 + I3) + I2' / (I2' + I3') within the range of 0.01 - 10 in this application, a balance can be found between the silicon exposure degree and the defect degree of 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, it uses the defect degree of the surface carbon material to improve the electrolyte infiltration ability of the negative electrode material, comprehensively controlling the thickness of the solid electrolyte interface film on the material surface. The prepared negative electrode sheet has a lower resistivity, further increasing the stability and durability of the electrode sheet.

[0062] In some embodiments, the ratio of I1 / (I2 + I3) to I2 / (I2 + I3) + I2' / (I2' + I3') can specifically 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. Of course, it can also be other values within the above range, which are not limited herein. When the ratio is controlled within the above range, an appropriate amount of silicon particles is 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 interface film on the surface of the negative electrode material can also be effectively controlled. At this time, the electrolyte infiltration ability relatively increases, and the negative electrode material can have a good electrolyte infiltration ability, thereby reducing the resistivity of the negative electrode sheet. Preferably, the ratio of I1 / (I2 + I3) to I2 / (I2 + I3) + I2' / (I2' + I3') is within the range of 0.4 - 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, which includes silicon element and oxygen element, and the atomic ratio of the silicon element to the oxygen element is 0 to 2, and does not include 0.

[0065] In some embodiments, the silicon particles include silicon oxide, and the chemical general formula of the silicon oxide is SiO x , where 0 < x ≤ 2. Specifically, SiO x can specifically be SiO 0.5 , SiO 0.7 , SiO 0.9 , SiO, SiO 1.2 , SiO 1.5 , SiO 1.8 , SiO 1.9 etc., which are not limited herein.

[0066] The silicon oxide can be represented by the general formula SiO x (0 < x ≤ 2). It can be a material formed by silicon particles dispersed in SiO2, or a material having a tetrahedral structural unit, with silicon atoms located at the center of the tetrahedral structural unit and oxygen atoms 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, and specifically can be 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. Of course, it can also be other values within the above range, which are not limited herein.

[0068] In some embodiments, the silicon particles further include a doped metal M, and M is selected from at least one of Li, Mg, Al, Fe, La, Zn, Ti, Cu, and Mn. It can be understood that a small amount of the doped metal can be doped in the carbon material or in the silicon-based active material. The doped metal can improve the conductivity of the negative electrode material and also 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, the silicon particles and graphite are dispersed in 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 graphite oxide. Graphite is a material with high conductivity, small volume expansion, high first efficiency, and stable cycling performance. By compounding graphite and silicon particles, the conductivity of the anode 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 forms a carbon layer on the surface of the active material. The carbon material can be located on the surface of the silicon particle, can also be located on the surface of the graphite particle, or can also form secondary particles by secondary granulation and coating of the graphite particle and the silicon particle, which is not limited herein. In some embodiments, the thickness of the carbon layer is 1 nm to 1000 nm, specifically it can be 1 nm, 5 nm, 10 nm, 15 nm, 20 nm, 50 nm, 80 nm, 100 nm, 150 nm, 200 nm, 400 nm, 500 nm, 700 nm, 800 nm, 900 nm, 1000 nm, etc., which is not limited herein. Controlling the thickness of the carbon layer within the above range can increase the conductivity of the anode material and is beneficial to obtaining an anode material with a high specific capacity; and the carbon layer can effectively relieve the volume expansion of the active material and improve the long cycling performance of the anode 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 anode material is P, 1.0 ≤ P ≤ 2.2, P = (D 05 + D 99 ) / (2 * D 50 ). The ratio of P can specifically 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 herein. When the particle size distribution of the anode material is controlled within the above range, it indicates that the anode material has a relatively wide particle size distribution, which helps to improve the uniform distribution of silicon particles and graphite, is beneficial to increasing the specific capacity per gram of the anode material, and helps to improve the conductivity of the anode material. It should be noted that the anode material here is measured based on all particles.

[0073] It should be noted that the volume-based cumulative particle size distribution measured by the laser diffraction method is used for the particle size distribution determination. D05 represents the particle size corresponding to when the cumulative particle size distribution percentage of the powder reaches 5%, D50 represents the particle size corresponding to when the cumulative particle size distribution percentage reaches 50%, and D99 represents the particle size corresponding to when the cumulative particle size distribution percentage reaches 99%. This application uses (D 05 + D 99 ) / (2 * D 50) To define the particle size distribution of the anode material, the nanoscale silicon particles formed by vapor deposition can be included in the particle size overall planning, which can cover the sizes of the vast majority of anode material particles.

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

[0075] In some embodiments, the powder conductivity of the anode material under a pressure of 20 kN is greater than 30 S / cm, and specifically, it can 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 is not limited herein. Controlling the powder conductivity of the anode material within the above range is beneficial to improving the conductivity of the anode material and reducing the resistivity of the anode electrode sheet.

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

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

[0078] In some embodiments, the tap density of the anode material ≥ 0.7 g / cm 3 . The tap density of the anode material can specifically be 0.7 g / cm 3 , 0.75 g / cm 3 , 0.81 g / cm 3 , 0.85 g / cm 3 , 0.89 g / cm 3 , 0.91 g / cm 3 , 0.95 g / cm 3 , 0.99 g / cm 3 , 1.0 g / cm 3 , 1.05 g / cm 3, 1.1 g / cm 3 , 1.13 g / cm 3 , 1.18 g / cm 3 , 1.2 g / cm 3 , 1.25 g / cm 3 , 1.3 g / cm 3 , 1.38 g / cm 3 or 1.4 g / cm 3 etc., which are not limited herein.

[0079] In some embodiments, the mass content of silicon particles in the negative electrode material is 1% - 80%, and the mass content of graphite is 20% - 99%. Specifically, 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. Of course, it can also be other values within the above range, which are not limited herein. Specifically, the mass content of graphite can be 20%, 30%, 40%, 50%, 55%, 58%, 60%, 65%, 69%, 70%, 80% or 90%, etc. Of course, it can also be other values within the above range, which are not limited herein.

[0080] Second, the present application provides a method for preparing a negative electrode material, as Figure 1 shown, including the following steps:

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

[0082] Step S200, performing chemical vapor deposition on the modified graphite with a reaction gas containing a silicon source gas to obtain a mixture of silicon particle-containing and modified graphite;

[0083] Step S300, performing chemical vapor carbon coating treatment on the mixture with a gaseous carbon source at 550°C - 1000°C to obtain the negative electrode material.

[0084] The preparation method of the negative electrode material provided by the present application first modifies graphite, which can increase the defect degree of graphite and reduce the resistivity of the negative electrode sheet. Then, modified graphite and silicon particles are compounded by chemical vapor deposition, which can achieve uniform mixing of silicon particles and graphite and reduce the segregation phenomenon of silicon particles. Finally, the mixture of the above two is placed at 550°C to 1000°C for chemical vapor carbon coating, which can effectively reduce the defect degree on the surface of graphite and adjust the defect degree of the carbon materials on the surfaces of silicon particles and graphite, so that the ratio of I1 / (I2+I3) to I2 / (I2+I3)+I2’ / (I2’+I3’) is within the range of 0.01 to 10, and a balance can be found between the silicon exposure degree and the defect degree of the surface carbon material. On the premise of ensuring a relatively high initial Coulomb efficiency of the negative electrode material, the defect degree of the carbon material on the surface of the active substance is used to improve the electrolyte infiltration ability of the negative electrode material, and a suitable thickness of the solid electrolyte film layer can also be formed by using a small amount of silicon particles exposed on the surface of the negative electrode material, thereby improving the conductivity of the electrode sheet.

[0085] The following specifically introduces this solution:

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

[0087] In some embodiments, the median particle size of graphite is 5μm to 20μm, specifically it can be 5μm, 5μm, 5μm, 5μm, 5μm, 5μm, 5μm or 5μm, etc., which is not limited herein. 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 steps of the modification treatment include placing graphite in an acid solution or an alkali solution for modification treatment.

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

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

[0091] In some embodiments, the concentration of the acid solution or the base solution is < 2 mol / L, specifically, it can be 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 herein.

[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. Of course, it can also be other values within the above range, which is not limited herein.

[0093] In some embodiments, the time of the modification treatment is 10 h to 48 h. Specifically, the time of the modification treatment 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 herein.

[0094] In the present application, by controlling the temperature, time of the modification treatment and the concentration of the modification solution, the degree of surface defects of the graphite can be adjusted, which is beneficial to improving the cracking degree of the gas-phase carbon source and the silicon source gas in the subsequent chemical vapor deposition and gas-phase carbon coating processes, making the composite of the graphite particles, the silicon particles and the carbon material more uniform and sufficient, and further adjusting the degree of defects of the carbon material on the surface of the graphite particles.

[0095] In some embodiments, the steps of the modification treatment further include washing the product after the modification treatment until the product is washed to neutral.

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

[0097] In some embodiments, the time of the drying treatment is 3 h to 48 h. The time of the drying treatment can be 3 h, 6 h, 8 h, 12 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 herein.

[0098] Step S200, performing chemical vapor deposition on the modified graphite with a reaction gas containing a silicon source gas to obtain a mixture containing silicon particles and modified graphite.

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

[0100] In some embodiments, the deposition time of chemical 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 are not limited herein.

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

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

[0103] In some embodiments, the auxiliary carrier gas includes at least one of nitrogen, argon, helium, neon, carbon dioxide, hydrogen and carbon monoxide. It can be understood that under the disturbance of the auxiliary carrier gas, the graphite is in a dynamic movement process. The silicon particles formed after the cracking of the silicon source gas come into contact with the dynamic graphite, so as to realize the uniform mixing of the graphite and the silicon particles, which can reduce the self-aggregation of nano-scale particles, and further reduce the excessive local stress during the charge and discharge process of the negative electrode material, reduce particle breakage, and improve the cycle performance of the negative electrode material.

[0104] In some embodiments, the raw materials of the silicon source gas include at least one of silane, disilane, trichlorosilane, 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, it can be 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. Of course, it can also be other values within the above range, which are not limited herein.

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

[0107] In some embodiments, the silicon particles further include a doped metal M, and M is selected from at least one of Li, Mg, Al, Fe, La, Zn, Ti, Cu, and Mn. It can be understood that a small amount of the doped metal can be doped in the carbon material or in the silicon-based active material. The doped metal can improve the conductivity of the negative electrode material and also 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 oxides, the silicon oxides include silicon element and oxygen element, and the atomic ratio of the silicon element to the oxygen element is 0 to 2 and does not include 0.

[0109] In some embodiments, the silicon particles include silicon oxides, and the chemical general formula of the silicon oxides is SiO x , where 0 < x ≤ 2. Specifically, SiO x can specifically be SiO 0.5 , SiO 0.7 , SiO 0.9 , SiO, SiO 1.2 , SiO 1.5 , SiO 1.8 , SiO 1.9 etc., which are not limited herein.

[0110] The silicon oxides can be represented by the general formula SiO x (0 < x ≤ 2). It can be a material formed by silicon particles dispersed in SiO2, or a material having a tetrahedral structural unit, with a silicon atom located at the center of the tetrahedral structural unit and oxygen atoms located at the four vertices of the tetrahedral structural unit.

[0111] In some embodiments, based on the mass of the modified graphite being 100 wt%, the addition amount of the doped metal M in the modified graphite is less than 20 wt%.

[0112] In some embodiments, the silicon particles and graphite in the mixture are dispersed in each other in the form of particles. In step S300, the mixture is subjected to gas-phase carbon coating treatment using a gas-phase carbon source to obtain a negative electrode material.

[0113] In some embodiments, the raw materials of the gas-phase carbon source include 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 gas-phase carbon source is 0.2 L / min to 18 L / min; specifically, it can be 0.2 L / min, 0.5 L / min, 1.0 L / min, 2.0 L / min, 3 L / min, 5 L / min, 6 L / min, 8 L / min, 10 L / min, 15 L / min, or 18 L / min, etc. Of course, it can also be other values within the above range, which are not limited herein.

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

[0116] In some embodiments, the time of the gas-phase carbon coating treatment is 1 h to 6 h, specifically, it can be 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 are not limited herein.

[0117] In some embodiments, the gas-phase carbon coating treatment is carried out 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 particle grains, or on the surface of the graphite grains, or the graphite grains and silicon particle grains can be granulated again to form secondary particles, which are not limited herein.

[0120] In some embodiments, the thickness of the carbon layer is 1 nm to 1000 nm, specifically, it can be 1 nm, 5 nm, 10 nm, 15 nm, 20 nm, 50 nm, 80 nm, 100 nm, 150 nm, 200 nm, 400 nm, 500 nm, 700 nm, 800 nm, 900 nm, 1000 nm, etc., which is not limited herein. Controlling the thickness of the carbon layer within the above range can increase the conductivity of the negative electrode material, which is beneficial 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.

[0121] In a third aspect, the present application provides a negative electrode sheet, which includes the above-mentioned negative electrode material, and the resistivity of the negative electrode sheet is ≤5 Ω·cm. The resistivity can specifically be 5 Ω·cm, 4.5 Ω·cm, 4 Ω·cm, 3 Ω·cm, 2.8 Ω·cm, 2.5 Ω·cm, 2.2 Ω·cm, 2.0 Ω·cm, 1.9 Ω·cm, 1.6 Ω·cm, 1.2 Ω·cm or 1.0 Ω·cm, etc., which is not limited herein. It can be understood that the resistivity of the negative electrode sheet is within the above range because the electrolyte infiltration 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, improving the electron transfer efficiency, ensuring good contact between silicon particles, graphite and carbon materials, and reducing the resistivity of the electrode sheet, thereby enabling the electrode sheet to have excellent rate performance.

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

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

[0124] Examples

[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 left standing at 30 °C for 24 h. After removing the solution, it was 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 was placed in a fluidized bed reactor, and silane gas was introduced. The flow rate of silane gas was 5 L / min, the speed of the carrier gas (argon) was set at 7.5 L / min, and the reaction was carried out at 400 °C for 6 h to obtain a mixture of silicon particles and graphite particles.

[0128] (3) Adjust the temperature of the fluidized bed reactor to 800°C, switch the inlet gas to methane, the gas flow rate is 8 L / min, and perform gas phase carbon coating treatment for 4 hours. Cool to room temperature and discharge 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 negative electrode material prepared in Example 1 within the scanning range is shown in FIG. Figure 3 This is the Raman spectrum of the negative electrode material prepared in Example 1. Other parameters of the negative electrode material are detailed 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. After removing the solution, the graphite was 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 was placed in a fluidized bed reactor, monosilane gas was introduced, the monosilane gas flow rate was 5 L / min, the carrier gas (argon) rate was set to 7.5 L / min, and the reaction was carried out at 500°C for 6 hours to obtain a mixed powder of silicon particles and graphite particles.

[0134] (3) Adjust the temperature of the fluidized bed reactor to 600°C, switch the gas introduced to methane with a gas flow rate of 8 L / min, perform gas-phase carbon coating for 2 hours, cool to room temperature and discharge 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 detailed in Table 1.

[0137] Example 3

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

[0139] (2) Place the modified graphite in a fluidized bed reactor, introduce silane gas with a flow rate of 5 L / min, set the speed of the carrier gas (argon) at 7.5 L / min, and react at 400 °C for 6 h to obtain a mixed powder of silicon particles and graphite particles.

[0140] (3) Adjust the temperature of the fluidized bed reactor to 800 °C, switch the introduced gas to methane with a flow rate of 8 L / min, perform gas-phase carbon coating treatment for 4 h, cool to room temperature and discharge to obtain the negative electrode material.

[0141] The negative electrode material prepared in this example includes active substances and carbon materials located on at least part of the surface of the active substances. The active substances include silicon particles and graphite, and the silicon particles are elemental silicon.

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

[0143] Example 4

[0144] (1) Place natural flake graphite with D50 = 10 μm in a 1 mol / L HCl solution, stir for 4 h, then let it stand at 30 °C for 24 h. After removing the solution, rinse with clear water until neutral, and finally bake in an oven at 80 °C for 12 h to obtain modified graphite.

[0145] (2) Place the modified graphite in a fluidized bed reactor, introduce silane gas with a flow rate of 6 L / min, set the speed of the carrier gas (argon) at 7.5 L / min, and react at 400 °C for 8 h to obtain a mixed powder of silicon particles and graphite particles.

[0146] (3) Adjust the temperature of the fluidized bed reactor to 700 °C, switch the introduced gas to methane with a flow rate of 8 L / min, perform gas-phase carbon coating treatment for 6 h, cool to room temperature and discharge to obtain the negative electrode material.

[0147] The negative electrode material prepared in this example includes active substances and carbon materials located on at least part of the surface of the active substances. The active substances include silicon particles and graphite, and the silicon particles are elemental silicon.

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

[0149] Example 5

[0150] The difference from Example 1 is:

[0151] (1) Place graphite with D50 = 8 μm in a 1.8 mol / L NaOH solution, stir for 4 h, then let it stand at 30 °C for 24 h. After removing the solution, rinse with clear water until neutral, and finally bake in an oven at 70 °C for 12 h to obtain modified graphite.

[0152] Example 6

[0153] The difference from Example 1 is that:

[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. After removing the solution, it was 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 that:

[0157] (2) The modified graphite was placed in a fluidized bed reactor, monochlorosilane gas was introduced, the monochlorosilane gas flow rate was 15 L / min, the carrier gas (argon) rate was set to 25 L / min, and the reaction was 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 that:

[0160] (2) The modified graphite is placed in a fluidized bed reactor, and a siloxane gas is introduced at a flow rate of 5 L / min and a carrier gas (argon) rate of 7.5 L / min. The reaction is carried out at 400° C. for 6 h 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 that:

[0163] (3) Adjust the temperature of the fluidized bed reactor to 800°C, switch the inlet gas to acetylene, the gas flow rate is 18 L / min, and perform gas phase carbon coating treatment for 2 hours. Cool to room temperature and discharge to obtain the negative electrode material.

[0164] Example 10

[0165] The difference from Example 1 is that:

[0166] (3) Adjust the temperature of the fluidized bed reactor to 1000°C, switch the gas introduced to methane, with a gas flow rate of 0.2 L / min, perform gas-phase carbon coating treatment for 6 hours, cool to room temperature and discharge to obtain the negative electrode material.

[0167] Embodiment 11

[0168] The difference from Example 1 is that:

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

[0170] Comparative Example 1

[0171] Differing from Example 1:

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

[0173] (2) The modified graphite was placed in a fluidized bed reactor, and silane gas was introduced. The gas flow rate was 5 L / min, the carrier gas velocity was set at 7.5 L / min, and the reaction was 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, the gas flow rate was 8 L / min, and the gas-phase carbon coating treatment was carried out for 2 h. After cooling to room temperature, the product was discharged to obtain the negative electrode material.

[0175] Comparative Example 2

[0176] Differing from Example 1:

[0177] Step (1) was not carried out, and step (2) was directly carried out

[0178] The parameters of the negative electrode material are shown in Table 1.

[0179] Testing Method

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

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

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

[0183] Reference is made to GB / T 5162-2006 / ISO 3953:1993 "Metal powders - Determination of tap density." Tests were performed using a Quantachrome tap density analyzer (Quantachrome DAT-4-220) from Anton Paar (Shanghai) Trading Co., Ltd. The tap density, T, is the value after 1000 vibrations, with a charge of 60 g, and is expressed in g / cm². 3 .

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

[0185] The powder conductivity of the material was tested according to the equipment and methods specified in BTRTC / ZY / 02-093, "Powder Conductivity Test Operation Instructions." The testing equipment was from Mitsubishi Chemical, Japan. Test parameters included: -3 initial resistance magnitude, 10V voltage limit, and sample thickness of 3-5mm at 20kN pressure. Pressure settings were 4, 8, 12, 16, and 20kN. Electrode radius was 0.7mm, and sample radius was 10mm.

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

[0187] The Raman spectrum of the powder was measured using a Renishaw In Via confocal Raman microscope from Japan. The test parameters were: laser wavelength 532nm, test range 120um×120um, step size 4um. The test results were processed using the instrument's own software. When processing the data, the baseline of the Raman spectrum curves at all points was first removed. By adjusting the peak search parameters, the peak at 500cm was detected. -1 ~520cm -1 The first characteristic peak is at 1345cm -1 ~1355cm -1 There is a second characteristic peak in the range of 1570cm -1 ~1610cm -1 The third characteristic peak is found in the range, and then the peak intensity of each peak is obtained. In particular, the baseline is removed based on the standard that the processed baseline is close to 0, and the other processing steps are based on the initial parameters of the software.

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

[0189] The negative electrode plate 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 plate was placed in a glove box, and 5 mL of electrolyte was dropped onto the 5 cm × 5 cm negative electrode plate using a pipette, and the time taken for the electrolyte to be completely absorbed was recorded.

[0190] (6) Measurement of the resistivity of the negative electrode plate:

[0191] The negative electrode plate 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. A 50 cm × 50 cm square block was taken, and 9 points were randomly measured 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 Test results of the performance of the negative electrode material

[0194]

[0195] According to the data in Table 1, it can be seen that the K value of the negative electrode materials prepared in Examples 1 to 10 of the present application is controlled within the range of 0.01 to 10, and a balance can be found between the degree of silicon exposure and the degree of defects of 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, it uses the degree of defects of the surface carbon material to improve the wettability of the negative electrode material to the electrolyte. The prepared negative electrode plate has a lower resistivity, further increasing the stability of the electrode plate.

[0196] For the negative electrode material of Comparative Example 1, the temperature of gas-phase carbon coating was too low during the preparation process, resulting in the K value of the negative electrode material deviating from the range of 0.01 to 10. Too many silicon particles were exposed on the surface of the negative electrode material, and the wettability of the negative electrode material to the electrolyte decreased. Compared with Example 1, the resistivity of the electrode plate prepared from the negative electrode material also increased significantly.

[0197] For 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 decreased compared with Example 1, and the degree of defects of the carbon material on the surface of the negative electrode material was too large. Although the wettability of the negative electrode material to the electrolyte was greatly improved, the side reaction between the negative electrode material and the electrolyte was aggravated, 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 plate.

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

Claims

1. A negative electrode material, characterized in that, The negative electrode material includes an active material and a carbon material located on at least a part of the surface of the active material. The active material includes silicon particles and graphite. The silicon particles and the graphite are dispersed with each other in the form of particles. The carbon material exists on at least a part of the surface of the silicon particles, and the carbon material exists on at least a part of the surface of the graphite; In the Raman mapping spectrum of the negative electrode material, the characteristic peak intensity of silicon particles in the negative electrode material in the range of 500 cm -1 to 520 cm -1 is I1, the characteristic peak intensity in the range of 1345 cm -1 to 1355 cm -1 is I2, and the characteristic peak intensity in the range of 1570 cm -1 to 1610 cm -1 is I3; The intensity of the characteristic peak of graphite in the negative electrode material within the range of 1345 cm -1 to 1355 cm -1 is I2', and the intensity of the characteristic peak within the range of 1570 cm -1 to 1610 cm -1 is I3'; In the negative electrode material, 0.01 ≤ K ≤ 10; The contact angle of the negative electrode material is greater than 110°, and the resistivity of the negative electrode sheet containing the negative electrode material is ≤5Ω*cm.

2. The negative electrode material according to claim 1, characterized in that, The particle size distribution width of the negative electrode material is P, and P = (D 05 + D 99 ) / (2 * D 50 ), and 1.0 ≤ P ≤ 2.

2.

3. The negative electrode material according to claim 1, wherein 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 (6): (1) The silicon particles include at least one of amorphous silicon, crystalline silicon, silicon oxide, and silicate; (2) The graphite includes 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 mass content of the silicon particles in the negative electrode material is 1% to 80%, and the mass content of the graphite is 20% to 99%; (5) The tap density of the negative electrode material ≥ 0.7 g / cm 3 ; (6) 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 element and oxygen element, and the atomic ratio of the silicon element to the oxygen element is 0 to 2 and does not include 0; (2) The silicon particles include silicon oxide, and the chemical general formula of the silicon oxide is SiO x , where 0 < x ≤ 2.

6. A method for preparing the negative electrode material according to any one of claims 1 to 5, characterized in that, The method includes the following steps: Placing the graphite in a modification solution for modification treatment, and drying to obtain modified graphite; Performing chemical vapor deposition on the modified graphite with a reaction gas containing a silicon source gas to obtain a mixture containing silicon particles and modified graphite; Performing chemical vapor carbon coating treatment on the mixture at 550°C to 1000°C with a gaseous carbon source to obtain the negative electrode material.

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

8. The preparation method according to claim 6, characterized in that, The method includes at least one of the following features (1) to (11): (1) The graphite includes 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 chemical vapor deposition is 300 °C to 700 °C; (4) The deposition time of the chemical vapor deposition is 2 h to 8 h; (5) The flow rate of the silicon source gas is 0.1 L / min to 15 L / min; (6) An auxiliary carrier gas is further added during the chemical vapor deposition, and the flow rate of the auxiliary carrier gas is 0.5 L / min to 25 L / min; (7) An auxiliary carrier gas is further added during the chemical vapor deposition, 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 silane, disilane, trichlorosilane, 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 gaseous carbon source is 0.2 L / min to 18 L / min; (11) The time of the gaseous carbon coating treatment is 1 h to 6 h.

9. A negative electrode plate, characterized in that, The negative electrode sheet includes the negative electrode material according to any one of claims 1 to 5 or the negative electrode material prepared by the preparation method of the negative electrode material according to any one of claims 6 to 8.

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

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