WO2025123645A1 - Negative electrode material, negative electrode sheet, and battery - Google Patents

Abstract

A negative electrode material, a negative electrode sheet, and a battery, which relate to the field of negative electrode materials. The negative electrode material comprises a silicon-based material, graphite, and a carbon material located on at least part of the surface of the silicon-based material and/or graphite. Raman mapping is used to test the negative electrode material, and a Raman mapping spectrogram thereof contains a first type of spectral lines having a characteristic peak within the range of 500 cm^-1 to 520 cm^-1 and a second type of spectral lines having no characteristic peak within the range of 500 cm^-1 to 520 cm^-1. By controlling the intensity relationship of the characteristic peaks in the two types of spectral lines, the negative electrode material has a relatively high specific capacity and a good electrolyte wettability, and a prepared negative electrode sheet has a low resistivity.

Description

Negative electrode material, negative electrode sheet, battery

This application claims the priority of Chinese patent application 202311804698.8, filed on December 25, 2023. This application cites the entire text of the above Chinese patent application.

Technical Field

The present application relates to the technical field of negative electrode materials, and in particular to negative electrode materials, negative electrode sheets, and batteries.

Background Art

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.

Therefore, how to improve the wettability and conductivity of silicon-based 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

The purpose of the present application is to provide a negative electrode material, 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.

In a first aspect, the present application provides a negative electrode material, the negative electrode material comprising a silicon-based material and graphite, and a carbon material located on at least a portion of the surface of the silicon-based material and/or graphite;

The negative electrode material is tested by Raman surface scanning, wherein the Raman surface scanning spectrum of the negative electrode material contains a first type of spectrum line with a characteristic peak in the range of 500 cm ^-1 to 520 cm ^-1 and a second type of spectrum line with no characteristic peak in the range of 500 cm ^-1 to 520 cm ^-1 ;

In the first type of spectrum, there is a characteristic peak in the range of 500cm ^-1 to 520cm ^-1 with an intensity of I ₁ , a characteristic peak in the range of 1345cm ^-1 to 1355cm ^-1 with an intensity of I ₂ , and a characteristic peak in the range of 1570cm ^-1 to 1610cm ^-1 with an intensity of I ₃ ;

In the second type of spectral lines, there is a characteristic peak in the range of 1345cm ^-1 to 1355cm ^-1 with an intensity of I ₂ ^' , and there is a characteristic peak in the range of 1570cm ^-1 to 1610cm ^-1 with an intensity of I ₃ ^' ;

in: 0.01≤K≤10.

In a second aspect, the present application provides a negative electrode plate, wherein the negative electrode plate comprises the negative electrode material described in the first aspect; and the resistivity of the negative electrode plate is ≤5Ω·cm.

In a third aspect, the present application provides a battery, comprising the negative electrode material described in the first aspect.

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

The negative electrode material provided in the present application comprises a silicon-based material and graphite, and a carbon material located on at least a portion of the surface of the silicon-based material and/or graphite. The negative electrode material is tested by Raman surface scanning. In the Raman surface scanning spectrum of the negative electrode material, there are first-type spectral lines with characteristic peaks in the range of 500cm ^-1 to 520cm ^-1 and second-type spectral lines without characteristic peaks in the range of 500cm ^-1 to 520cm ^-1 . The first-type spectral lines can represent the Raman spectrum of particles mainly containing silicon-based materials, and the characteristic peak intensity in the range of 500cm ^-1 to 520cm ^-1 is _I1 , the characteristic peak intensity in the range of 1345cm ^-1 to 1355cm ^-1 is _I2 , and the characteristic peak intensity in the range of 1570cm ^-1 to 1610cm ^-1 is _I3 . Due to the presence of carbon material on the surface of the silicon-based material, peaks can be detected in the range of 1345cm-1 to 1355cm ^-1 and in the range of 1570cm ^-1 to 1610cm-1; the second-type spectral lines can represent the Raman spectrum of particles mainly containing graphite, and the characteristic peak intensity in the range of 1345cm ^-1 to 1355cm ^{- 1} is I2. The characteristic peak intensity in the range of 1570cm ^-1 to 1610cm -1 is I ₂ ^' , and the characteristic peak intensity in the range of 1570cm ^-1 to 1610cm ^-1 is I ₃ ^' . I ₁ /(I ₂ +I ₃ ) can indicate the exposure degree of the silicon-based material in the negative electrode material, I ₂ ^' /(I ₂ ^' +I ₃ ^' ) can indicate the defect degree of the graphite surface in the negative electrode material, and I ₂ /(I ₂ +I ₃ )+I ₂ ^' /(I ₂ ^' +I ₃ ^' ) can indicate the total defect degree 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 degree of defect of the surface carbon material is high, during the charge and discharge cycle of the battery prepared from the negative electrode material, the side reaction between the negative electrode material and the electrolyte in the battery 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 infiltration ability is relatively increased, the resistivity of the negative electrode sheet will also increase; in addition, the content of active lithium ions consumed during the battery charge and discharge cycle increases, and the first coulomb efficiency of the negative electrode material decreases. When too little silicon-based material is exposed on the surface of the negative electrode material or the degree of defect of the surface carbon material is very low, the electrolyte infiltration ability of the negative electrode material decreases, and some silicon-based materials and graphite are difficult to be activated by formation, which is not conducive to the electrochemical performance. The present application controls the ratio of I ₁ /(I ₂ +I ₃ ) to I ₂ /(I ₂ +I ₃ )+I ₂ ^' /(I ₂ ^' +I ₃ ^' ) within the range of 0.01 to 10, thereby finding 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 less silicon-based material in the negative electrode material is exposed, and on the other hand, the degree of defects in the surface carbon material is utilized to improve the wettability of the negative electrode material to the electrolyte, and the thickness of the solid electrolyte film layer formed on the surface of the negative electrode material during the charge and discharge process is comprehensively controlled. The prepared negative electrode sheet has a lower resistivity, further increasing the stability and durability of the negative electrode sheet.

BRIEF DESCRIPTION OF THE DRAWINGS

The present application is further described below in conjunction with the accompanying drawings and embodiments.

FIG1 is a schematic flow chart of a method for preparing a negative electrode material provided in an embodiment of the present application.

FIG2 is a diagram showing the distribution of silicon-based materials and graphite in the negative electrode material prepared in Example 1 within the scanning range.

FIG3 is a Raman surface scanning spectrum of the negative electrode material prepared in Example 1.

FIG. 4 is a volume-based cumulative particle size distribution width diagram of the negative electrode material prepared in Example 1.

DETAILED DESCRIPTION

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

It should be clear that the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

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

It should be understood that the term "and/or" used in this article is only a description of the association relationship 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.

In a first aspect, the present application provides a negative electrode material, the negative electrode material comprising a silicon-based material and graphite, and a carbon material located on at least a portion of the surface of the silicon-based material and/or graphite;

The negative electrode material is tested by Raman surface scanning. In the Raman surface scanning spectrum of the negative electrode material, there are first-type spectral lines with characteristic peaks in the range of 500 cm ^-1 to 520 cm ^-1 and second-type spectral lines without characteristic peaks in the range of 500 cm ^-1 to 520 cm ^-1 .

In the first type of spectrum, there is a characteristic peak in the range of 500cm ^-1 to 520cm ^-1 with an intensity of I ₁ , a characteristic peak in the range of 1345cm ^-1 to 1355cm ^-1 with an intensity of I ₂ , and a characteristic peak in the range of 1570cm ^-1 to 1610cm ^-1 with an intensity of I ₃ ;

In the second type of spectral lines, there is a characteristic peak in the range of 1345cm ^-1 to 1355cm ^-1 with an intensity of I ₂ ^' , and there is a characteristic peak in the range of 1570cm ^-1 to 1610cm ^-1 with an intensity of I ₃ ^' ;

in: 0.01≤K≤10.

The negative electrode material provided 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, and the active substance includes a silicon-based material and graphite. The negative electrode material is tested by Raman surface scanning. In the Raman surface scanning spectrum of the negative electrode material, there are first-type spectral lines with characteristic peaks in the range of 500cm ^-1 to 520cm ^-1 and second-type spectral lines without characteristic peaks in the range of 500cm ^-1 to 520cm ^-1 . The first-type spectral lines can represent the Raman spectrum of particles mainly containing silicon-based materials, and the characteristic peak intensity in the range of 500cm ^-1 to 520cm ^-1 is _I1 , the characteristic peak intensity in the range of 1345cm ^-1 to 1355cm ^-1 is _I2 , and the characteristic peak intensity in the range of 1570cm ^-1 to 1610cm ^-1 is _I3 . Due to the presence of carbon material on the surface of the silicon-based material, peaks can be detected in the range of 1345cm-1 to 1355cm ^-1 and in the range of 1570cm ^-1 to 1610cm-1; the second-type spectral lines can represent the Raman spectrum of particles mainly containing graphite, and the characteristic peak intensity in the range of 1345cm ^-1 to 1355cm ^{- 1} is I2. The characteristic peak intensity in the range of 1570cm ^-1 to 1610cm -1 is I ₂ ^' , and the characteristic peak intensity in the range of 1570cm ^-1 to 1610cm ^-1 is I ₃ ^' . I ₁ /(I ₂ +I ₃ ) can indicate the exposure degree of the silicon-based material in the negative electrode material, I ₂ ^' /(I ₂ ^' +I ₃ ^' ) can indicate the defect degree of the graphite surface in the negative electrode material, and I ₂ /(I ₂ +I ₃ )+I ₂ ^' /(I ₂ ^' +I ₃ ^' ) can indicate the carbon material on the surface of the negative electrode material. The total defect level of the 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 in the battery is intensified. During the charge and discharge cycle of the battery prepared from the negative electrode material, the thickness of the solid electrolyte film on the surface of the negative electrode material also increases. At this time, although the electrolyte infiltration ability is relatively increased, the resistivity of the negative electrode sheet will also increase. In addition, the content of active lithium ions consumed increases, and the first coulomb efficiency of the negative electrode material decreases. When too little silicon-based material is exposed on the surface of the negative electrode material or the defect level of the surface carbon material is very low, the electrolyte infiltration ability of the negative electrode material decreases, and some electrochemically active components in the negative electrode material are difficult to be activated by formation, which is not conducive to the performance of the electrochemically active components in the negative electrode material. The present application controls the ratio of I ₁ /(I ₂ +I ₃ ) to I ₂ /(I ₂ +I ₃ )+I ₂ ^' /(I ₂ ^' +I ₃ ^' ) within the range of 0.01 to 10, thereby finding 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 utilized to improve the wettability of the negative electrode material to the electrolyte, and the thickness of the solid electrolyte film layer formed on the surface of the negative electrode material during the charge and discharge process is comprehensively controlled. The prepared negative electrode sheet has a lower resistivity, further increasing the stability and durability of the negative electrode sheet.

In some embodiments, the ratio of I ₁ /(I ₂ +I ₃ ) to I ₂ /(I ₂ +I ₃ )+I ₂ ^' /(I ₂ ^' +I ₃ ^' ) 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 can be other values within the above range, which are not limited here. When the ratio is controlled within the above range, an appropriate amount of silicon-based material 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 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, the ratio of I ₁ /(I ₂ +I ₃ ) to I ₂ /(I ₂ +I ₃ )+I ₂ ^' /(I ₂ ^' +I ₃ ^' ) is in the range of 0.4-10.

In some embodiments, I ₁ /(I ₂ +I ₃ ) ranges from 0.1 to 2.3, and specifically may be 0.1, 0.5, 1, 1.8, 2.0, 2.1, 2.2 or 2.3, etc. Of course, it may also be other values within the above range, which is not limited here.

In some embodiments, I ₂ /(I ₂ +I ₃ ) ranges from 0.1 to 0.8, and specifically may be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7 or 0.8, etc. Of course, it may also be other values within the above range, which is not limited here.

In some embodiments, I ₂ ^' /(I ₂ ^' +I ₃ ^' ) is in the range of 0.1 to 0.61, and specifically can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6 or 0.61, etc., and of course can be other values within the above range, which are not limited here. It can be understood that I ₁ /(I ₂ +I ₃ ) and I ₂ /(I ₂ +I ₃ )+I ₂ ^' /(I ₂ ^' +I ₃ ^' ) are controlled within the above range, which can further improve the electrolyte wettability of the negative electrode material, thereby reducing the resistivity of the negative electrode sheet.

In some embodiments, the silicon-based material includes at least one of amorphous silicon, crystalline silicon, silicon oxide, and silicate.

In some embodiments, the silicon-based material includes silicon oxide, and 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.

In some embodiments, the silicon-based material includes silicon oxide, and the general chemical formula of the silicon oxide is SiO _x , where 0<x≤2. Specifically, SiO _x 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., which are not limited herein.

Silicon oxide can be represented by the general formula SiO _x (0＜x≤2). It can be a material formed by silicon dispersed in SiO ₂ ; or a material having a tetrahedral structural unit, in which the silicon atom is located at the center of the tetrahedral structural unit and the oxygen atoms and/or silicon atoms are located at the four vertices of the tetrahedral structural unit.

In some embodiments, the average particle size of the silicon-based material is 1 nm to 10 μm, and can be 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.

In some embodiments, the silicon-based material further comprises a metal M element, 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 the metal M element can be doped into the carbon material or the silicon-based material, and the metal M element 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.

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

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-based materials, the conductivity of the negative electrode material can be comprehensively improved and the expansion can be reduced.

In some embodiments, the carbon material includes at least one of amorphous carbon and graphitized carbon. The carbon material may be located on the surface of silicon-based material particles, or on the surface of graphite particles, or the graphite particles and silicon-based material particles may be secondary granulated and then carbon-coated to form secondary particles, which is not limited here. In some embodiments, the thickness of the carbon layer is 1nm to 1000nm, and may 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 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.

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 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 are not limited here. When the particle size distribution of the negative 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-based materials and graphite, helps 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 particle size distribution width of the negative electrode material is measured based on all particles.

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

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 a compact stacking structure with small particles embedded in the contact gaps between large particles. This helps to improve the tap density of the negative electrode material. When the ratio is too small, the particle sizes of large and small particles in the negative electrode material are very close, and there are large pores in the contact between the particles, which is not conducive to the formation of a densely packed structure. When the ratio is too large, the particle sizes and numbers of large and small particles in the negative electrode material are quite different, and a large number of small particles tend to agglomerate themselves and are difficult to form a matching densely packed structure with large particles, and the distribution uniformity decreases.

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.

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.

In some embodiments, the median particle size _D50 of the negative electrode material is 2 μm to 12 μm, specifically 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 here.

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 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 is not limited here.

In some embodiments, the mass content of silicon in the negative electrode material is 1% to 80%, and the mass content of carbon is 20% to 99%. The mass content of silicon can be 1%, 2%, 8%, 10%, 12%, 15%, 30%, 50%, 55%, 58%, 60%, 65%, 69%, 70% or 80%, and the mass content of carbon can be 20%, 30%, 40%, 50%, 55%, 58%, 60%, 65%, 69%, 70%, 80% or 90%, and other values within the above range are also possible, which are not limited here. Preferably, the mass content of silicon in the negative electrode material is 3.5% to 31.5%, specifically 3.5%, 10%, 10.1%, 10.2%, 10.3%, 10.5%, 11%, 31.5%, etc. Of course, it can also be other values within the above range, which is not limited here.

In a second aspect, an embodiment of the present application provides a method for preparing a negative electrode material, comprising the following steps:

Placing graphite in a modification solution containing an acid solution or an alkali solution for modification treatment, wherein the concentration of the acid solution or the alkali solution is less than 2 mol/L, the modification treatment temperature is 20° C. to 30° C., the modification treatment time is 10 h to 48 h, 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 a silicon-based material and the modified graphite, wherein the vapor-deposition process is carried out in a fluidized bed reactor and an auxiliary carrier gas is added during the vapor-deposition process;

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.

The preparation method of the negative electrode material provided by the present application first modifies graphite to improve the defect degree of graphite; then composites the modified graphite with a silicon-based material by vapor deposition to achieve uniform mixing of the silicon-based material and the modified graphite, thereby reducing the segregation of the silicon-based material; finally, the mixture of the two is placed at 550°C to 1000°C for vapor phase carbon coating, thereby effectively reducing the defect degree of the graphite surface and adjusting the defect degree of the carbon material on the surface of the silicon-based material and the surface of the graphite. The degree of depression is adjusted so that the ratio of I ₁ /(I ₂ +I ₃ ) to I ₂ /(I ₂ +I ₃ )+I ₂ ^' /(I ₂ ^' +I ₃ ^' ) is in the range of 0.01 to 10, and a balance can be found between the degree of silicon exposure and the degree of defects in the surface carbon material. Under the premise of ensuring that the first coulombic efficiency of the negative electrode material is at a high level in the early stage, the degree of defects in the carbon materials on the surface of silicon-based materials and graphite is used to improve the electrolyte wetting ability of the negative electrode material. The small amount of silicon-based material exposed on the surface of the negative electrode material can also be used to generate a solid electrolyte film layer of suitable thickness during the charge and discharge cycle, thereby improving the conductivity of the electrode sheet.

The following is a detailed introduction to this solution, as shown in Figure 1, which includes the following steps:

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

In some embodiments, the median particle size of graphite is 6 μm to 20 μm, preferably 6 μm to 12 μm, specifically 6 μm, 8 μm, 10 μm, 12 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-based materials, the conductivity of the negative electrode material can be comprehensively improved and the expansion can be reduced.

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

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

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

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.

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.

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.

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

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

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.

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.

Step S200, vapor deposition of modified graphite is performed using a reaction gas containing a silicon source gas to obtain a mixture of a silicon-based material and modified graphite.

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.

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.

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.

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, 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.

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 the silicon-based material, 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.

In some embodiments, the raw material of the silicon source gas includes at least one of monosilane, disilane, monochlorosilane, dichlorosilane, trichlorosilane, tetrachlorosilane, and methylsiloxane.

In some embodiments, the median particle size of the silicon-based material 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.

In some embodiments, step S200 includes mixing modified graphite with a raw material containing metal M to obtain a composite; and vapor-depositing the composite using a reaction gas containing a silicon source gas to obtain a mixture of silicon-based material, modified graphite and doped metal M.

In some embodiments, the silicon-based material further includes a metal M element, where 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 the metal M element can be doped into the carbon material, or When doped in the silicon-based active material, the metal M element 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.

In some embodiments, the silicon-based material includes silicon oxide, and 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.

In some embodiments, the silicon-based material includes silicon oxide, and the general chemical formula of silicon oxide is SiO _x , where 0<x≤2. Specifically, SiO _x 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., which are not limited herein.

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 SiO ₂ ; or it can be a material with a tetrahedral structural unit, with the silicon atom located at the center of the tetrahedral structural unit and oxygen atoms and/or silicon atoms located at the four vertices of the tetrahedral structural unit.

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

In some embodiments, the silicon-based material and the graphite in the mixture are dispersed with each other in the form of particles.

Step S300, using a gas-phase carbon source to perform a gas-phase carbon coating treatment on the mixture to obtain a negative electrode material.

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;

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.

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.

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.

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

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

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-based material particles, or on the surface of the graphite particles, or the graphite particles and the silicon-based material 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 1 nm to 1000 nm, and specifically 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 are not limited here. Controlling the thickness of the carbon layer within the above range can increase the conductivity of the negative electrode material, which is beneficial 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.

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 specifically 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-based material, graphite and carbon material are in good contact, and the resistivity of the sheet is reduced, so that the sheet has excellent rate performance.

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.

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

Example

Example 1

(1) 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.

(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.

(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.

The negative electrode material prepared in the present application includes silicon-based material and graphite, and carbon material located on at least a portion of the surface of the silicon-based material and/or graphite, the active substance includes silicon element and graphite, and the carbon material includes amorphous carbon.

FIG2 is a diagram showing the distribution of silicon-based materials and graphite in the scanning range of the negative electrode material obtained in Example 1, and FIG3 is a Raman surface scanning spectrum of the negative electrode material obtained in Example 1. The spectrum with a peak at the displacement of 500-520 cm ^- 1 corresponds to the spectrum of particles mainly composed of silicon-based materials, and the spectrum without a peak at 500-520 cm ^-1 corresponds to the spectrum of particles mainly composed of graphite. FIG4 is a volume-based cumulative particle size distribution width diagram of the negative electrode material obtained in Example 1. Other parameters of the negative electrode material are detailed in Table 1-2.

Example 2

(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.

(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.

(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.

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.

Other parameters of negative electrode materials are shown in Table 1-2.

Example 3

(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.

(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.

(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.

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 a silicon-based material and graphite. The silicon-based material contains silicon alone.

Other parameters of negative electrode materials are shown in Table 1-2.

Example 4

(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.

(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.

(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.

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 a silicon-based material and graphite. The silicon-based material contains silicon alone.

Other parameters of negative electrode materials are shown in Table 1-2.

Example 5

The difference from Example 1 is:

(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.

Example 6

The difference from Example 1 is:

(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.

Example 7

The difference from Example 1 is:

(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-based material and graphite particles.

Example 8

The difference from Example 1 is:

(2) The modified graphite is placed in a fluidized bed reactor, dimethylsiloxane gas is introduced, the methylsiloxane 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-based material and graphite particles, wherein the silicon-based material includes at least one of silicon element and silicon oxide.

Example 9

The difference from Example 1 is:

(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.

Example 10

The difference from Example 1 is:

(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.

Embodiment 11

The difference from Example 1 is:

(1) Graphite with D50 = 8 μm is 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 is 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% is added to obtain a mixture of silicon-based material and graphite particles, wherein the silicon-based material includes lithium silicate.

Example 12

The difference from Example 1 is:

(1) Graphite with D50 = 8 μm was placed in a 1.5 mol/L HCl solution and stirred for 8 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.

Comparative Example 1

The difference from Example 1 is:

(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.

(2) The modified graphite is placed in a fluidized bed reactor, monosilane 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.

(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.

Comparative Example 2

The difference from Example 1 is:

Skip step (1) and go directly to step (2).

The parameters of the negative electrode materials are detailed in Table 1-2.

Comparative Example 3

The difference from Example 12 is:

(3) The temperature of the fluidized bed reactor was adjusted to 300° 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.

Test Method

(1) Particle size of negative electrode materials and silicon-based materials:

The particle size test method of negative electrode material 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 Co., Ltd. in the United Kingdom. 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 5%, D50 represents the particle size corresponding to the cumulative particle size distribution percentage reaching 50% (i.e., the median particle size), and D80 represents the particle size corresponding to the cumulative particle size distribution percentage reaching 80%.

Average particle size of silicon-based materials: Observe silicon-based material particles through field emission scanning electron microscopy or transmission electron microscopy, directly measure the particle sizes of 5-10 silicon-based material particles through a scale, and take the average value of the particle sizes as the average particle size of the silicon-based material.

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

With reference to GB/T 5162-2006/ISO 3953:1993 “Determination of tap density of metal powders”, the test was conducted using the Quantachrome tap density analyzer (Quantachrome DAT-4-220) of Anton Paar (Shanghai) Trading Co., Ltd. The tap density T is the value after 1000 vibrations, the loading amount is 60g, and the unit is g/cm ³ .

(3) Powder conductivity test of negative electrode materials

According to the equipment and methods of BTRTC/ZY/02-093 "Powder Conductivity Test Operation Instructions" of BTR Company, the powder conductivity of the material was 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 pressures are set to 4kN, 8kN, 12kN, 16kN, and 20kN respectively. The electrode radius is 0.7mm and the sample radius is 10mm.

(4) Raman test of negative electrode materials:

The Raman spectrum of the powder was tested using the In Via micro-confocal Raman spectrometer of Renishaw of Japan, and 200 Raman spectrum curves were tested. The test parameters are: laser wavelength 532nm, test range 120μm×120μm, step length 4μm. The test results were processed using the software provided by the test instrument. When processing the data, the Raman spectrum curves of all points were first baselined, and the peak-to-peak intensity of each peak was obtained by adjusting the peak-finding parameters. The first type of spectrum line is the one with characteristic peaks in the range of 500cm ^-1 to 520cm ^-1 , and the second type of spectrum line is the one without characteristic peaks in the range of 500cm ^-1 to 520cm ^-1 . It is specially noted that the baseline removal is based on the standard that the processed baseline is near 0, and the other processing steps use the initial parameters of the software. In the processed spectrum, when the peak-to-peak intensity of the highest peak in the range of 500cm ^-1 to 520cm ^-1 is less than or equal to 100, it is considered that there is no target characteristic peak.

(5) Liquid absorption capacity test of negative electrode materials

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.

(6) Contact angle test method of negative electrode material:

The contact angle of the negative electrode material to water was tested by the sessile drop method. The sample powder to be tested was placed in the groove containing the powder and pressed tightly, and then tested by a contact angle meter (Shanghai Xuanyi Chuangxi Industrial Equipment Co., Ltd., XG-CAMB3).

(7) Resistivity test of negative electrode:

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.

(8) Capacity and initial efficiency test

The negative electrode materials prepared in Examples 1 to 12 and Comparative Examples 1 to 3 were assembled into button cells: negative electrode plates were 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.

The battery assembly was carried out in an argon glove box, with metal lithium sheet as the negative electrode, the electrolyte was 1 mol/L lithium hexafluorophosphate LiPF6 + ethylene carbonate (EC) + methyl ethyl carbonate (EMC), the separator was a polyethylene/propylene composite microporous membrane, and the electrochemical performance was carried out on a battery testing instrument with a charge and discharge voltage of 0.01 to 1.5V.

The battery cycle life is the number of charge and discharge cycles when the capacity retention rate decays to 80%.

First coulombic efficiency = first cycle discharge capacity/first cycle charge capacity.

Table 1 is a table of Raman data test results of negative electrode materials, and Table 2 is a table of negative electrode material and battery performance test results.

Table 1 Raman data test results of negative electrode materials

Table 2 Negative electrode materials and battery performance test results

According to the data in Table 1, the negative electrode materials prepared in Examples 1 to 12 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.

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, 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.

In the negative electrode material of Comparative Example 2, the graphite was not modified during the preparation process, which may lead to poor subsequent coating and modification effects. The surface morphology of silicon particles and graphite particles is too different, which greatly increases the resistivity of the electrode.

For the negative electrode material of Comparative Example 3, the temperature of the gas-phase carbon coating treatment during the preparation process is too low, the degree of defects of the carbon material on the surface of the negative electrode material is relatively high, the K value of the negative electrode material is significantly lower than the K value of the embodiment, its electrolyte wettability is good, and the thickness of the electrolyte membrane is too large, resulting in a significant increase in the resistivity of the electrode sheet.

In addition, by comparing the test results of Example 1 and Example 11, it can be found that doping metal into the silicon-based material can improve the conductivity and tap density of the negative electrode material.

The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims (15)

A negative electrode material, characterized in that the negative electrode material comprises a silicon-based material and graphite, and a carbon material located on at least a portion of the surface of the silicon-based material and/or graphite; The negative electrode material is tested by Raman surface scanning, wherein the Raman surface scanning spectrum of the negative electrode material contains a first type of spectrum line with a characteristic peak in the range of 500 cm ^-1 to 520 cm ^-1 and a second type of spectrum line with no characteristic peak in the range of 500 cm ^-1 to 520 cm ^-1 ; In the first type of spectrum, there is a characteristic peak in the range of 500cm ^-1 to 520cm ^-1 with an intensity of I ₁ , a characteristic peak in the range of 1345cm ^-1 to 1355cm ^-1 with an intensity of I ₂ , and a characteristic peak in the range of 1570cm ^-1 to 1610cm ^-1 with an intensity of I ₃ ; In the second type of spectral lines, there is a characteristic peak in the range of 1345cm ^-1 to 1355cm ^-1 with an intensity of I ₂ ', and there is a characteristic peak in the range of 1570cm ^-1 to 1610cm ^-1 with an intensity of I ₃ '; in, 0.01≤K≤10. The negative electrode material according to claim 1, characterized in that the particle size distribution width of the negative electrode material is P, wherein P=(D ₀₅ +D ₉₉ )/(2*D ₅₀ ), and 1.0≤P≤2.2. 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. The negative electrode material according to claim 1 is characterized in that the silicon-based material comprises at least one of amorphous silicon, crystalline silicon, silicon oxide and silicate. The negative electrode material according to claim 1, characterized in that the graphite comprises at least one of natural graphite, artificial graphite, expanded graphite and oxidized graphite. The negative electrode material according to claim 1, characterized in that, in the negative electrode material, I ₁ /(I ₂ +I ₃ ) is in the range of 0.1 to 2.3, and/or I ₂ /(I ₂ +I ₃ ) is in the range of 0.1 to 0.8, and/or I ₂ '/(I ₂ '+I ₃ ') is in the range of 0.1 to 0.61. The negative electrode material according to claim 1 is characterized in that the mass content of silicon element in the negative electrode material is 1% to 80%, and/or the mass content of carbon element is 20% to 99%. The negative electrode material according to claim 1, characterized in that the tap density of the negative electrode material is ≥ 0.7 g/cm ³ . The negative electrode material according to claim 1, characterized in that the carbon material comprises at least one of amorphous carbon and graphitized carbon. The negative electrode material according to claim 1, characterized in that 0.4≤K≤10. The negative electrode material according to claim 4 is characterized in that the silicon-based material includes 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. The negative electrode material according to claim 4, characterized in that the silicon-based material comprises silicon oxide, and the general chemical formula of the silicon oxide is SiO _x , wherein 0＜x≤2. The negative electrode material according to claim 1 is characterized in that the silicon-based material further comprises a metal M element, and the M is selected from at least one of Li, Mg, Al, Fe, La, Zn, Ti, Cu, and Mn. A negative electrode plate, characterized in that the negative electrode plate comprises the negative electrode material according to any one of claims 1 to 13, and the resistivity of the negative electrode plate is ≤5Ω·cm. A lithium-ion battery, characterized in that the lithium-ion battery comprises the negative electrode material according to any one of claims 1 to 13.