Negative electrode material and battery

Abstract

A negative electrode material and a battery. The negative electrode material comprises a carbon matrix and an active material, wherein at least a portion of the active material is distributed in the carbon matrix. The surface cleanliness of the negative electrode material is γ, where γ≥60%. The negative electrode material and the battery can alleviate the cycling degradation of the negative electrode material, reduce side reactions between the negative electrode material and an electrolyte, and mitigate the gas generation of the negative electrode material, thereby comprehensively improving the capacity, expansion performance and cycling performance of the negative electrode material.

Description

Anode materials and batteries Cross-references to related applications

[0001] This application claims priority to Chinese patent application filed on January 21, 2025, with application number 202510102544.7 and entitled "Anode Material and Battery". Technical Field

[0002] This application belongs to the field of battery materials technology, and more specifically, relates to negative electrode materials and batteries. Background Technology

[0003] In recent years, with market development, the integration and increasing functionality of power devices, and the growing demand for energy supply, lithium-ion batteries are widely used not only in mobile devices such as smartphones and laptops, but also in electric vehicles and power tools. Developing lithium-ion batteries with higher energy density is the current trend. The positive and negative electrode materials are the core of the battery, determining its operating efficiency. Currently, the commercially available negative electrode material is graphite, whose capacity is nearing its theoretical limit, with limited room for further improvement. Therefore, there is an urgent need to develop a new generation of high-energy-density negative electrode materials.

[0004] Silicon anode materials are widely considered the next-generation battery anode materials, possessing advantages such as high capacity, abundant sources, and relative safety. However, during the fabrication process, small particles adhere to the surface of silicon anode materials. These particles have a large specific surface area and high activation energy, which can easily exacerbate side reactions between the anode material and the electrolyte, leading to accelerated cycle degradation. Furthermore, the anode material also experiences severe volume expansion during cycling, causing pulverization and breakage, further accelerating cycle degradation. Therefore, mitigating cycle degradation, improving cycle stability, and reducing side reactions remain key challenges that need to be addressed. Summary of the Invention

[0005] This application provides a negative electrode material and a battery. The negative electrode material of this application can alleviate the cycle decay of the negative electrode material, reduce side reactions and gas generation, and comprehensively improve the capacity, expansion performance and cycle performance of the negative electrode material.

[0006] In a first aspect, this application provides a negative electrode material, comprising a carbon matrix and an active substance, wherein at least a portion of the active substance is distributed within the carbon matrix;

[0007] The surface cleanliness of the negative electrode material is γ, where γ ≥ 60%. The surface cleanliness of the negative electrode material is measured using the following test method:

[0008] Electron electron microscope images of the negative electrode material were obtained. At 10,000x magnification, the adhesion of microparticles on the surface of 100 negative electrode material particles was randomly observed. Particles with a diameter of 0.1μm to 1μm attached to the surface of the negative electrode material particles were defined as microparticles. Negative electrode material particles with less than 20 microparticles on their surface were defined as clean particles. The number of clean particles in all negative electrode material particles was counted as A. The surface cleanliness of the negative electrode material was γ = A / 100*100%.

[0009] This application provides a battery comprising the negative electrode material described in the first aspect.

[0010] The technical solution of this application has at least the following beneficial effects:

[0011] The large surface area of ​​the micro-powder on the surface of the anode material results in generally higher reactivity of the micro-powder particles, making them more prone to reacting with the electrolyte. This exacerbates side reactions between the anode material and the electrolyte, leading to increased gas production during charge-discharge cycles. Furthermore, due to size differences, the expansion effects of the micro-powder and the main anode material particles are inconsistent during lithium insertion / extraction, causing the anode material to easily break and fracture, further intensifying side reactions between the anode material and the electrolyte. This application controls the surface cleanliness of the anode material to be above 60%, which reduces the micro-powder content on the surface of the anode material, reduces side reactions between the anode material and the electrolyte, reduces the consumption of active lithium ions, effectively reduces gas production, and improves the specific capacity and initial coulombic efficiency of the anode material. In addition, a more balanced expansion effect of the anode material reduces particle breakage, contributing to improved rate performance and cycle performance of batteries made from the anode material. Attached Figure Description

[0012] The present application will be further described below with reference to the accompanying drawings and embodiments.

[0013] Figure 1 is a schematic diagram of the battery structure provided in an embodiment of this application.

[0014] Figure 2 is a SEM image of the negative electrode material prepared in Example 1 of this application.

[0015] Figure 3 is a SEM image of the negative electrode material prepared in Comparative Example 2 of this application. Detailed Implementation

[0016] To better understand the technical solution of this application, the embodiments of this application will be described in detail below with reference to the accompanying drawings.

[0017] It should be understood that the described embodiments are merely some, not all, of the embodiments in this application. All other embodiments obtained by those skilled in the art based on the embodiments in this application without inventive effort are within the scope of protection of this application.

[0018] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms “a,” “the,” and “the” used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0019] It should be understood that the term "and / or" used in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this article generally indicates that the preceding and following related objects have an "or" relationship.

[0020] The negative electrode material provided in this application includes a carbon matrix and an active material, with at least a portion of the active material distributed within the carbon matrix; the surface cleanliness of the negative electrode material is γ, where γ ≥ 60%, and the surface cleanliness of the negative electrode material is measured using the following test method:

[0021] Electron electron microscope images of the negative electrode material were obtained. At 10,000x magnification, the adhesion of microparticles on the surface of 100 negative electrode material particles was randomly observed. Particles with a diameter of 0.1μm to 1μm attached to the surface of the negative electrode material particles were defined as microparticles. Negative electrode material particles with less than 20 microparticles on their surface were defined as clean particles. The number of clean particles in the 100 negative electrode material particles was counted as A. The surface cleanliness of the negative electrode material was γ = A / 100*100%.

[0022] Because the micro-powder on the surface of the negative electrode material has a large specific surface area, the micro-powder particles generally have better reactivity and are more likely to react with the electrolyte, leading to increased side reactions between the negative electrode material and the electrolyte, and increased gas production during charge-discharge cycles. Furthermore, due to size differences, the expansion effects of the micro-powder and the main particles of the negative electrode material are inconsistent during lithium insertion / extraction, causing the negative electrode material to easily shatter and break, further exacerbating side reactions with the electrolyte. This application controls the surface cleanliness of the negative electrode material to above 60%, which can reduce the micro-powder content on the surface of the negative electrode material, reduce side reactions between the negative electrode material and the electrolyte, reduce the consumption of active lithium ions, effectively reduce gas production, and improve the specific capacity and initial coulombic efficiency of the negative electrode material. In addition, the expansion effect of the negative electrode material is more balanced, which can reduce particle shattering and help improve the rate performance and cycle performance of the battery prepared with the negative electrode material.

[0023] In some embodiments, the surface cleanliness of the negative electrode material is γ, where γ ≥ 60%. Specifically, the surface cleanliness γ of the negative electrode material can be 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 98%, or other values ​​within the above range, which are not limited here. When the surface cleanliness is too low, the number of micro-particles adhering to the surface of the negative electrode material increases. These micro-particles have a large specific surface area and high activation energy, intensifying the side reactions between the negative electrode material and the electrolyte, leading to increased gas production. Furthermore, the increase in micro-particles can cause adhesion between the negative electrode material particles, resulting in poor flowability and easy particle agglomeration. This application controls the surface cleanliness of the negative electrode material within the above range, which can reduce the side reactions between the negative electrode material and the electrolyte, reduce the consumption of active lithium ions, improve the specific capacity and initial coulombic efficiency of the negative electrode material, and improve the gas production phenomenon. Preferably, the surface cleanliness γ of the negative electrode material is ≥ 70%.

[0024] In some embodiments, the flowability parameter t of the negative electrode material is ≤80s / 50g. Specifically, the flowability parameter t of the negative electrode material can be 80s / 50g, 75s / 50g, 70s / 50g, 65s / 50g, 60s / 50g, 55s / 50g, 50s / 50g, 45s / 50g, 40s / 50g, 30s / 50g, 20s / 50g, 10s / 50g, 5s / 50g, or any value within the range of any two of the above values, and is not limited here. This application controls the surface cleanliness of the negative electrode material while simultaneously controlling its flowability parameter to below 80s / 50g. During the preparation of the negative electrode slurry, the dispersion of the negative electrode material in the slurry is improved, which can reduce the adhesion or agglomeration between negative electrode material particles, improve the uniformity of the negative electrode material, and effectively reduce the gas generation phenomenon of the negative electrode material. In addition, the appropriate flowability parameter can also improve the volume expansion of the negative electrode material, reduce the problem of local expansion stress concentration within the negative electrode sheet, and make the negative electrode material more evenly distributed within the negative electrode sheet. The expansion stress is effectively released, reducing the occurrence of negative electrode material shedding and cracking, which helps to improve the rate performance and cycle performance of the battery prepared by the negative electrode material.

[0025] When the flowability parameter t of the negative electrode material is too large, the flowability of the negative electrode material particles deteriorates, easily causing particle adhesion or agglomeration, leading to increased gas production. When the flowability parameter t of the negative electrode material is too small, meaning the negative electrode material particles have better flowability, excessively high flowability can lead to uneven coating on the particle surface after coating, increasing side reactions between the negative electrode material and the electrolyte. Preferably, the flowability parameter of the negative electrode material is 10s / 50g ≤ t ≤ 50s / 50g.

[0026] In some implementations, the specific surface area of ​​the negative electrode material is ≤5m². 2 / g, specifically, the specific surface area of ​​the negative electrode material can be 0.1m². 2 / g, 1m 2 / g, 1.5m 2 / g、2m 2 / g, 2.5m 2 / g、3m 2 / g, 3.5m 2 / g、4m 2 / g, 4.5m 2 / g、5m 2 / g or any value within the range of any two of the above values, without limitation. The surface cleanliness of the negative electrode material is good, and the specific surface area of ​​the negative electrode material can be controlled within a small range. However, an excessively small specific surface area will affect the diffusion of lithium ions on the surface of the negative electrode material and the transport within the negative electrode material particles, affecting the wetting ability of the electrolyte. This application controls the specific surface area of ​​the negative electrode material within the above range, which, while reducing side reactions caused by micronized powder, increases the number of lithium ion insertion / extraction sites, improves lithium ion transport efficiency, increases the capacity of the battery prepared with the negative electrode material, and improves rate performance. Preferably, the specific surface area of ​​the negative electrode material is 0.1m². 2 / g~2.5m 2 / g.

[0027] In some embodiments, the gas production value of the negative electrode material is ≤1 mL / g / day, specifically it can be 1 mL / g / day, 0.9 mL / g / day, 0.8 mL / g / day, 0.7 mL / g / day, 0.6 mL / g / day, 0.5 mL / g / day, 0.2 mL / g / day, 0.1 mL / g / day, or 0.01 mL / g / day, or any value within the range of any two of the above values, and is not limited herein. This application can control the gas production value of the negative electrode material within a very small range because the surface cleanliness of the negative electrode material is within the above range, reducing the amount of micropowder on the surface of the negative electrode material particles, significantly reducing the side reactions between the micropowder and the electrolyte, and thus significantly reducing the gas production value of the negative electrode material. Preferably, the gas production value of the negative electrode material is ≤0.2 mL / g / day, more preferably, the gas production value of the negative electrode material is ≤0.1 mL / g / day.

[0028] In some embodiments, the oil absorption value of the negative electrode material is 30 mL / 100g to 80 mL / 100g, specifically 30 mL / 100g, 40 mL / 100g, 50 mL / 100g, 60 mL / 100g, 70 mL / 100g, or 80 mL / 100g, or any value within the range of any two of the above values, and is not limited herein. It is understood that controlling both the surface cleanliness and oil absorption value of the negative electrode material within the above range is beneficial for improving the adsorption and wetting ability of the negative electrode material for the electrolyte, thereby improving the lithium-ion transport efficiency. This ensures the stability of the cycle performance of the battery prepared from the negative electrode material while also improving the rate performance of the negative electrode material.

[0029] In some embodiments, the negative electrode material has pores, and the total pore volume of the negative electrode material is 0.0001 cm³. 3 / g~0.1cm 3 / g, specifically 0.1cm 3 / g, 0.08cm 3 / g, 0.07cm 3 / g, 0.06cm 3 / g, 0.05cm 3 / g, 0.04cm 3 / g, 0.03cm 3 / g, 0.02cm 3 / g, 0.01cm 3 / g, 0.0001cm 3 / g, etc., can also be other values ​​within the above range, and are not limited here. A total pore volume within the above range can improve the specific capacity of the negative electrode material. Furthermore, reserving an appropriate amount of pores in the negative electrode material helps alleviate the volume expansion caused by the lithium insertion / extraction process of active materials such as silicon, which is beneficial for improving the cycle performance of batteries made from negative electrode materials.

[0030] In some implementations, the pores in the negative electrode material include mesopores. According to the standards of the International Union of Pure and Applied Chemistry (IUPAC), porous materials are classified into three categories according to pore size: mesopores: pore size ranges from 2 nm to 50 nm (nanometers), between "micropores" (<2 nm) and "macropores" (>50 nm).

[0031] In some embodiments, the volume percentage of mesopores in the total pore volume of the negative electrode material is 25% to 95%. Specifically, it can be 25%, 30%, 35%, 40%, 50%, 60%, 70%, 75%, 80%, 85%, 90%, 92%, or 95%, etc., and is not limited thereto. Preferably, the volume percentage of mesopores in the total pore volume of the negative electrode material is 80% to 95%.

[0032] It should be noted that the pores in the negative electrode material are mainly mesopores. When the battery made from the negative electrode material is charged and discharged, the mesopores in the negative electrode material can provide a buffer space for the expansion of the silicon material. On the other hand, it ensures the stress dispersion distribution in the negative electrode material. When the negative electrode material is used in lithium-ion batteries, it can improve the specific capacity of the negative electrode material, alleviate the volume expansion of the silicon material, improve the particle strength of the negative electrode material, and reduce the collapse and breakage of the material structure during electrode rolling or cycling. Thus, under the synergistic effect of the above overall structure, the cycle performance and electrochemical performance of the negative electrode material are improved.

[0033] In some embodiments, the median particle size Dv50 of the negative electrode material is 1 μm to 30 μm, specifically it can be 0.1 μm, 1 μm, 5 μm, 7 μm, 10 μm, 12 μm, 15 μm, 18 μm, 19 μm, 20 μm, 30 μm, or any value within the range of any two of the above values, and is not limited herein. Preferably, the median particle size Dv50 of the negative electrode material is 5 μm to 25 μm.

[0034] In some embodiments, the carbon matrix includes at least one of hard carbon, soft carbon, graphite, mesophase carbon microspheres, activated carbon, porous carbon, mesoporous carbon, and carbon gel. It is understood that selecting the above-mentioned materials as the carbon matrix can all serve as a supporting framework and also possesses good electrical conductivity, thereby improving the conductivity of the negative electrode material.

[0035] In some embodiments, taking silicon as an example, the carbon matrix, i.e., the negative electrode material after removing the silicon material, has pores, and at least a portion of the silicon material is located within the pores of the carbon matrix.

[0036] In some embodiments, the average pore size of the anode material after removing silicon is 1.0 nm to 5.2 nm. Specifically, it can be 1.0 nm, 1.8 nm, 2.0 nm, 2.5 nm, 3.0 nm, 3.5 nm, 3.8 nm, 4.0 nm, 4.5 nm, 5.0 nm, 5.2 nm, or any value within the range of any two of the above values, and is not limited here. The anode material after removing silicon is a carbon matrix. If the pore size of the carbon matrix is ​​too small, the gaseous precursor of silicon material is difficult to penetrate into the pores and is prone to agglomerate on the surface of the carbon matrix to form a shell structure, resulting in a decrease in the silicon content inside the anode material and a decrease in the specific capacity of the anode material. If the pore size of the carbon matrix is ​​too large, although it is beneficial for silicon material filling, it will cause uneven distribution of silicon material, silicon segregation and other problems, resulting in uneven expansion of the anode material, excessive local expansion stress, particle breakage, etc., which in turn leads to a decrease in the cycle stability of the anode material. Therefore, controlling the average pore size of the carbon matrix within the above range is beneficial for the composite of the carbon matrix and silicon material. This not only improves the rate performance of the anode material, but also helps to buffer the volume expansion of the silicon material and improve the structural stability of the anode material.

[0037] In this application, taking silicon as the active material as an example, the preparation method of the negative electrode material after removing the silicon material includes the following steps: Under stirring, 150 mL of 20% HF acid solution is added dropwise to 10 g of negative electrode material, which will generate SiF4 and H2 gas and release heat. After no gas is generated, the supernatant acid solution is removed by centrifugation. 150 mL of 20% HF acid solution is added to the negative electrode material again, and the mixture is stirred for 12 h. The supernatant acid solution is removed by centrifugation again. Then, the negative electrode material is washed with pure water until neutral and dried to obtain the negative electrode material after removing the silicon material.

[0038] In some embodiments, the specific surface area of ​​the negative electrode material after removing the silicon material is 800 m². 2 / g~2500m 2 / g. Specifically, it could be 800m. 2 / g、1200m 2 / g, 1500m 2 / g、1800m 2 / g、2000m 2 / g、2200m 2 / g or 2500m 2 / g, etc., can also be other values ​​within the above range, and are not limited here.

[0039] In some embodiments, the total pore volume of the negative electrode material after removing the silicon material is 0.4 cm. 3 / g~1.5cm 3 / g. Specifically, it can be 0.4cm.3 / g, 0.6cm 3 / g, 0.9cm 3 / g, 1.0cm 3 / g, 1.2cm 3 / g, 1.3cm 3 / g, 1.4cm 3 / g or 1.5cm 3 / g, etc., can also be other values ​​within the above range, and are not limited here. This application controls the total pore volume of the anode material (i.e., carbon matrix) to be within the above range. The carbon matrix can provide sufficient space to accommodate the silicon material, which can not only improve the specific capacity of the anode material, but also ensure that the anode material can reserve an appropriate amount of pores to alleviate the volume expansion caused by the silicon material during lithium insertion / extraction, which is beneficial to improving the cycle performance of the anode material.

[0040] In some embodiments, the active material includes at least one of non-carbon Group 4A elements. Specifically, the non-carbon Group 4A elements may be at least one of silicon, germanium, tin, lead, and alloys or solid solutions thereof, and the alloys may be silicon-aluminum alloys, silicon-magnesium alloys, etc.

[0041] In some embodiments, the active material includes silicon.

[0042] In some embodiments, the silicon material includes at least one of elemental silicon, silicon-oxygen materials, and silicon alloys.

[0043] In some embodiments, the silicon-oxygen material includes silicon oxide (SiO2). x Where 0 < x ≤ 2, silicon oxide is a silicon-oxygen complex containing oxygen atoms and silicon atoms, with a molar ratio of oxygen atoms to silicon atoms of 0 to 2 (excluding 0). It can be SiO2. 0.2 SiO 0.5 SiO 0.8 SiO, SiO 1.2 SiO 1.5 SiO 1.8 It may be a substance composed of two or more of the following: SiO2, or a substance with the chemical formula SiO2. x The compounds can, of course, be other values ​​within the above range, and this application does not impose any restrictions on them.

[0044] In some embodiments, the elemental silicon includes at least one of crystalline silicon, amorphous silicon, and a composite of crystalline and amorphous silicon. Preferably, the silicon material is amorphous silicon, which expands less than other types of silicon, helping to mitigate the problem of large volume expansion in silicon-carbon anode materials during lithium insertion / extraction.

[0045] In some embodiments, the silicon material comprises silicon particles. The morphology of the silicon particles includes at least one of the following: dot-shaped, spherical, ellipsoidal, and sheet-like.

[0046] In some embodiments, the silicon material further includes elemental silicon and a silicon oxide layer on the surface of the elemental silicon. The silicon oxide layer includes silicon oxide, which has the general formula SiOx, where 0 < x ≤ 2. Specifically, SiOx may be SiO 0.5 SiO 0.7 SiO 0.9 SiO, SiO 1.2 SiO 1.5 SiO 1.8 SiO 1.9 SiO2, etc., are not limited here.

[0047] In some embodiments, the silicon material further includes elemental silicon and a silicon oxide layer on the surface of the elemental silicon. Based on the mass of the silicon material, the mass percentage of oxygen atoms in the silicon material is between 1% and 18%. Specifically, the mass percentage of oxygen atoms in the silicon material can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, or any value within the range of any two of the above values. Controlling the mass percentage of oxygen atoms in the silicon material within the above range is beneficial for forming a stable silicon oxide layer on the surface of the elemental silicon, reducing direct contact between the elemental silicon and the electrolyte, thereby reducing side reactions between the elemental silicon and the electrolyte, and improving the cycle stability of the negative electrode material; it can also maintain the stable activity of the silicon material and increase the specific capacity of the negative electrode material.

[0048] In some embodiments, the silicon material contains ≥99% silicon by mass.

[0049] In some embodiments, the average particle size of the silicon material is 0.1 nm to 100 nm, specifically 0.1 nm, 1 nm, 10 nm, 30 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, or 100 nm, etc., and of course, other values ​​within the above range are also possible, which are not limited herein. Within the above-defined range, the mechanical stress of the silicon material during expansion decreases with the reduction of particle size, and the reduction in size can shorten the electron and ion transport path. At the same time, the reduction in silicon material size increases the gap between adjacent silicon materials, which can reserve space for expansion. It is understood that when the average particle size of the silicon material is within the above range, the battery capacity of the lithium-ion battery can be guaranteed, and irreversible capacity loss can be reduced. Preferably, the average particle size of the silicon material is 1 nm to 50 nm, more preferably, the average particle size of the silicon material is 1 nm to 10 nm.

[0050] In some embodiments, at least a portion of the silicon material is located within the carbon matrix particles. The silicon material's location within the carbon matrix can improve the conductivity of the negative electrode material while simultaneously reducing direct contact between the silicon material and the electrolyte, thus minimizing side reactions.

[0051] In some embodiments, the negative electrode material further includes a coating layer located on at least a portion of the surface of the carbon matrix and / or the active material. Understandably, the coating layer can, on the one hand, reduce the risk of side reactions caused by electrolyte entering the negative electrode material, leading to a decrease in initial coulombic efficiency and initial discharge specific capacity; on the other hand, the coating layer can work synergistically with the carbon matrix to mitigate the volume expansion of the silicon material, reducing the overall volume expansion of the negative electrode material and minimizing the swelling of the electrode sheet fabricated from the negative electrode material.

[0052] In some embodiments, the coating material includes at least one of carbon materials, metal oxides, and nitrides.

[0053] In some embodiments, the carbon material includes at least one of amorphous carbon and graphitized carbon.

[0054] In some embodiments, the coating layer can be a carbon layer with a thickness of 0.1 nm to 3000 nm, specifically 0.1 nm, 0.5 nm, 1 nm, 5 nm, 10 nm, 20 nm, 50 nm, 80 nm, 100 nm, 200 nm, 300 nm, 500 nm, 800 nm, 1000 nm, 2000 nm, or 3000 nm, etc., or other values ​​within the above range, which are not limited here. Controlling the thickness of the carbon layer within the above range is beneficial for maintaining the stability of the particle structure of the anode material during cycling, reducing the exposure of silicon material on the surface of the anode material, reducing the generation of a large amount of SEI during charge and discharge due to exposed silicon material, and improving the specific capacity and electrochemical performance of the anode material. Preferably, the thickness of the carbon layer is 0.5 nm to 1000 nm, more preferably, the thickness of the carbon layer is 5 nm to 500 nm.

[0055] In some embodiments, the metal oxide includes at least one oxide of Sn, Ge, Fe, Cu, Ti, Na, Mg, Al, Ca, and Zn.

[0056] In some embodiments, the nitride includes at least one of titanium nitride, vanadium nitride, cobalt nitride, nickel nitride, and carbon nitride.

[0057] In some embodiments, the mass percentage of silicon material in the negative electrode material is 30wt% to 65wt%, that is, the mass percentage of silicon element in the negative electrode material is 30wt% to 65wt%, specifically it can be 30wt%, 35wt%, 40wt%, 45wt%, 50wt%, 55wt%, 60wt%, and 65wt%, etc. Of course, it can also be other values ​​within the above range, which are not limited here. Within the above-defined range, the mass percentage of silicon material in the negative electrode material, that is, the mass percentage of silicon element in the negative electrode material is relatively high, which is beneficial to improving the capacity of the negative electrode material.

[0058] In some embodiments, the carbon content in the negative electrode material is 30wt% to 60wt%, specifically 30wt%, 40wt%, 50wt%, 55wt%, or 60wt%, etc., and of course, other values ​​within the above range are also possible, which are not limited here.

[0059] In some embodiments, the mass percentage of oxygen in the negative electrode material is ≤5 wt%. Specifically, the mass percentage of oxygen in the negative electrode material can be 0 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, or 5 wt%, and is not limited thereto. It is understood that if the mass content of oxygen is too high, the active material in the negative electrode material will be partially oxidized. Controlling the mass content of oxygen in the negative electrode material within the above-mentioned range is beneficial for improving the specific capacity of the negative electrode material.

[0060] In some embodiments, the active material includes silicon, and the mass ratio of silicon to carbon in the negative electrode material is 0.8 to 2.0. Specifically, the mass ratio of silicon to carbon in the negative electrode material can be 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, or 2.0, and is not limited thereto.

[0061] This application provides a method for preparing a negative electrode material, including the following steps:

[0062] S10, the porous carbon material is surface cleaned and dried to obtain a carbon matrix, the surface cleanliness of the carbon matrix is ​​≥65%;

[0063] S20, a precursor is obtained by combining a carbon matrix with a silicon material;

[0064] S30, the precursor is coated with a coating material to obtain the negative electrode material, and the surface cleanliness of the negative electrode material is γ≥60%.

[0065] In the above scheme, cleaning the surface of the porous carbon material effectively reduces the content of microparticles on the carbon material surface. This allows the silicon material, during the composite process with the carbon matrix, to more easily penetrate the pores within the carbon matrix, reducing the probability of silicon adhering to the carbon matrix surface. Furthermore, a carbon matrix with a high surface cleanliness results in more uniform coating during the coating process. This coating process further reduces the amount of exposed silicon material on the carbon matrix surface. A uniform coating layer improves the fluidity of the anode material particles, reducing particle adhesion or agglomeration. It also improves structural stability, reducing the collapse and particle breakage of the anode material structure caused by volume expansion during lithium insertion / extraction, effectively reducing side reactions, thereby improving the cycle performance of the anode material, reducing side reactions between the anode material and the electrolyte, and improving gas production.

[0066] Step S10: The porous carbon material is surface-cleaned and dried to obtain a carbon matrix with a surface cleanliness of ≥65%.

[0067] In some embodiments, the surface cleaning treatment includes at least one of flotation treatment and dust removal treatment.

[0068] In some embodiments, the flotation solution used in the flotation process includes a flotation agent and a solvent.

[0069] In some embodiments, the flotation agent includes at least one selected from n-hexane, kerosene, diesel, gasoline, perchloroethylene, trichloroethylene, ethylene glycol ether, oleic acid, sodium alkyl sulfate, mixed amines, pine oil, methyl isobutyl methanol, humic acid, starch, polyacrylamide, sodium tripolyphosphate, and triethanolamine.

[0070] In some embodiments, the solvent includes at least one selected from water, methanol, ethanol, isopropanol, carbon tetrachloride, toluene, benzene, cyclohexane, cyclohexanone, toluenecyclohexanone, chlorobenzene, dichlorobenzene, acetone, methyl ethyl ketone, acetonitrile, pyridine, and phenol.

[0071] In some embodiments, the flotation temperature is 20°C to 80°C, specifically 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, or 80°C, or any value within the range of any two of the above values, and is not limited here.

[0072] In some implementations, the flotation process takes 1 hour to 48 hours, specifically 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 8 hours, 12 hours, 24 hours, 48 ​​hours, or any value within the range of any two of the above values, without limitation.

[0073] In some embodiments, the surface cleaning treatment includes a dust removal treatment, wherein the flue gas velocity of the dust removal treatment is 1L / min to 10L / min, specifically 1L / min, 2L / min, 3L / min, 4L / min, 5L / min, 6L / min, 7L / min, 8L / min, 9L / min or 10L / min or any value within the range of any two of the above values, and is not limited herein.

[0074] In some implementations, the dust removal process takes 1 to 10 hours, specifically 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, or 10 hours, or any value within the range of any two of the above values, without limitation.

[0075] In some embodiments, the temperature for dust removal is 100℃ to 400℃, specifically 400℃, 300℃, 200℃ and 100℃, etc., and of course other values ​​within the above range are also possible, which are not limited here.

[0076] This application controls parameters such as temperature, time, and flotation agent in the surface cleaning process. Through surface cleaning, the number of microparticles on the carbon matrix surface can be reduced, and the surface cleanliness of the carbon matrix can be improved to ≥65%.

[0077] In some embodiments, the surface cleanliness of the carbon matrix is ​​≥65%, specifically 65%, 70%, 75%, 80%, 85%, 90%, 95% or 98%, etc., and of course other values ​​within the above range are also possible, which are not limited here.

[0078] In some embodiments, the carbon matrix has pores, including at least one of micropores, mesopores, and macropores.

[0079] In some embodiments, in the carbon matrix, the volume percentage of pores with a diameter of less than 2 nm in the total pore volume is ≥70%; specifically, it can be 70%, 75%, 80%, 85%, 90%, 95% or 99%, etc., and of course, it can also be other values ​​within the above range, which are not limited here.

[0080] In some embodiments, in the carbon matrix, the volume percentage of pores with a diameter of less than 5 nm in the total pore volume is ≥85%; specifically, it can be 85%, 87%, 89%, 90%, 92%, 95%, 97%, or 99%, etc., and of course, it can also be other values ​​within the above range, which are not limited here.

[0081] In some embodiments, in the carbon matrix, the volume percentage of pores with a pore size of less than 10 nm in the total pore volume is ≥95%; specifically, it can be 95%, 96%, 97%, 98% or 99%, etc., and of course, it can also be other values ​​within the above range, which are not limited here.

[0082] Understandably, when the pore volume ratio of the carbon matrix is ​​controlled within the above range, the pores can accommodate most of the silicon material, reduce silicon segregation formed by silicon deposition on the carbon matrix surface, increase the silicon content and uniformity of silicon distribution in the carbon matrix, and thus improve the specific capacity and mechanical properties of the anode material.

[0083] In some embodiments, the specific surface area of ​​the carbon matrix is ​​800 m². 2 / g~2500m 2 / g. Specifically, it could be 800m. 2 / g, 1000m 2 / g、1200m 2 / g, 1500m 2 / g、1800m 2 / g、2000m 2 / g、2200m 2 / g, or 2500m 2 / g, etc., can also be other values ​​within the above range, and are not limited here.

[0084] In some embodiments, the total pore volume of all pores in the carbon matrix is ​​0.4 cm³. 3 / g~1.5cm 3 / g. Specifically, it can be 0.4cm. 3 / g, 0.5cm 3 / g, 0.6cm 3 / g, 0.9cm 3 / g, 1.0cm 3 / g, 1.2cm 3 / g, 1.3cm 3 / g, 1.4cm 3 / g or 1.5cm 3 / g, etc., and of course, other values ​​within the above range are also possible, and are not limited here. Understandably, the carbon matrix has abundant pores, which can accommodate silicon material and provide space for the volume expansion of the silicon material. Preferably, the total pore volume of all pores in the carbon matrix is ​​0.6 cm³. 3 / g~1.0cm 3 / g.

[0085] S20 involves combining a carbon matrix with a silicon material to obtain a precursor.

[0086] This application uses a vapor-phase active material precursor to perform vapor-phase deposition on a carbon matrix. The active material generated by the vapor-phase active material precursor can fill the pores of the carbon matrix, reduce the specific surface area, reduce problems such as breakage and cracking of the negative electrode material during the rolling process, and improve the processing performance and cycle performance of the negative electrode material.

[0087] In some embodiments, the gas-phase active material precursor includes a gaseous silicon source.

[0088] In some embodiments, the gaseous silicon source includes at least one of silane, hexane, and propane.

[0089] In some embodiments, the concentration of the gas-phase active material precursor is 5% to 30%, specifically 5%, 8%, 10%, 12%, 15%, 18%, 20%, 23%, 26%, 28%, or 30%, etc. Of course, other values ​​within the above range are also possible, and this application does not impose any restrictions on them.

[0090] In some embodiments, the temperature of vapor deposition is 400°C to 800°C, specifically 400°C, 500°C, 600°C, 700°C and 800°C, etc., and of course other values ​​within the above range are also possible, which are not limited here.

[0091] In some embodiments, the holding time for vapor deposition is 2h to 25h, specifically 2h, 5h, 10h, 15h, 20h and 25h, etc., and of course other values ​​within the above range are also possible, which are not limited here.

[0092] This application controls the temperature, time, and concentration of the vapor phase active material precursor during vapor deposition, thereby controlling the mass ratio of silicon to carbon in the composite, resulting in a negative electrode material prepared from the composite that has both high capacity and high first-pass efficiency.

[0093] S30, the precursor is coated with a coating material to obtain a negative electrode material, wherein the surface cleanliness of the negative electrode material is γ≥60%.

[0094] In some embodiments, the coating material includes at least one of carbon materials, metal oxides, and nitrides.

[0095] In some embodiments, step S30 involves carbon coating the precursor with a coating material, the carbon coating process including at least one of solid-phase carbon coating, liquid-phase carbon coating, and gas-phase carbon coating.

[0096] In some embodiments, the carbon coating process is gas-phase carbon coating, and the steps include: introducing a carbon source gas into the precursor body, and thermally decomposing the carbon source gas to obtain the negative electrode material.

[0097] In some implementations, the carbon source gas is a hydrocarbon.

[0098] In some embodiments, the carbon source gas includes at least one of methane, ethane, propane, ethylene, acetylene, gaseous benzene, gaseous toluene, gaseous xylene, gaseous ethanol, and gaseous acetone.

[0099] In some embodiments, the concentration of the carbon source gas is 5% to 20%, specifically 5%, 8%, 10%, 12%, 15%, 18%, or 20%, etc., and of course, other values ​​within the above range are also possible, which are not limited herein. Generally, the carbon source gas is mixed with a protective atmosphere before being introduced. For example, when the concentration of the carbon source gas is 15%, it can be a mixture of argon and methane with a volume ratio of 85:15.

[0100] In some embodiments, the thermal decomposition temperature is 400℃ to 800℃. Optionally, the temperature can be 400℃, 500℃, 600℃, 700℃, and 800℃, or other values ​​within the range, which can be selected according to actual needs and are not limited here. Preferably, the thermal decomposition temperature is 500℃ to 650℃.

[0101] In some embodiments, the holding time for thermal pyrolysis is 0.5h to 18h. The specific holding time can be 0.5h, 1.5h, 3h, 5h, 6h, 7h, 8h, 10h, and 18h, or other values ​​within this range, and can be selected according to actual needs. No limitation is made here. Preferably, the holding time for thermal pyrolysis is 1h to 2h.

[0102] In some embodiments, the coating material includes a metal oxide, and the step of coating the precursor includes: mixing the precursor with the coating material and then performing heat treatment.

[0103] In some embodiments, the metal oxide layer is made of at least one of oxides of Sn, Ge, Fe, Si, Cu, Ti, Na, Mg, Al, Ca, and Zn.

[0104] In some embodiments, the nitride layer is made of at least one of titanium nitride, vanadium nitride, cobalt nitride, nickel nitride, and carbon nitride.

[0105] This application provides a method for preparing a negative electrode material, including the following steps:

[0106] Step S11: Composite carbon matrix with silicon material to obtain precursor;

[0107] Step S21: The precursor is coated with a coating material to obtain a silicon-carbon composite.

[0108] Step S31: The silicon-carbon composite is subjected to surface cleaning treatment and dried to obtain a negative electrode material. The surface cleanliness of the negative electrode material is γ≥60%.

[0109] It should be noted that the surface cleaning treatment method is the same as the surface cleaning treatment method in the preparation method of the second aspect above, and will not be described in detail here.

[0110] This invention also provides a battery. Figure 1 is a schematic diagram of the discharge state of the battery provided in this embodiment. As shown in Figure 1, the battery includes a casing and an electrode assembly. The electrode assembly includes a positive electrode 1, a negative electrode 2, and a separator 3, with the separator 3 disposed between the positive electrode 1 and the negative electrode 2. The electrode assembly can be a stacked structure, formed by alternately stacking the positive electrode 1, the separator 3, and the negative electrode 2. In other embodiments, the electrode assembly can also be a wound structure, formed by sequentially stacking and winding the positive electrode, the separator, and the negative electrode.

[0111] In some embodiments, the positive electrode 1 includes a positive current collector 101 and a positive active layer 102 disposed on at least one surface of the positive current collector 101.

[0112] In some embodiments, the positive current collector 101 may be made of aluminum foil or nickel foil, or any composite current collector disclosed in the prior art, such as, but not limited to, current collectors formed by combining the aforementioned conductive foil (aluminum foil or nickel foil, etc.) with a polymer substrate. The positive active layer 102 comprises a positive active material, which includes compounds that reversibly insert and deintercalate metal ions.

[0113] In some embodiments, the positive electrode active material may include lithium transition metal composite oxides, sodium transition metal composite oxides, etc. The lithium transition metal composite oxide contains lithium and at least one element selected from cobalt, manganese, and nickel.

[0114] In some embodiments, the positive electrode active material may include, but is not limited to, lithium cobalt oxide (LiCoO2), lithium nickel manganese cobalt ternary materials (NCM), lithium manganese oxide (LiMn2O4), and lithium nickel manganese oxide (LiNi). 0.5 Mn 1.5 At least one of lithium iron phosphate (LiFePO4) or lithium iron phosphate (LiFePO4).

[0115] In some embodiments, the negative electrode 2 includes a negative electrode current collector 201 and a negative electrode active material layer 202 disposed on at least one surface of the negative electrode current collector.

[0116] In some embodiments, the negative electrode current collector 201 can be at least one of copper foil, nickel foil, stainless steel foil, titanium foil, or carbon-based current collector, or any composite current collector disclosed in the prior art, such as, but not limited to, current collectors formed by combining the aforementioned conductive foil and polymer substrate. The negative electrode active material layer 202 includes a negative electrode material, which is the negative electrode material described in the first aspect or the negative electrode material prepared by the aforementioned preparation method. The battery provided in this application embodiment has the advantages of high capacity, high initial efficiency, long cycle life, excellent rate performance, and low expansion. The battery can be a lithium-ion battery, a sodium-ion battery, a solid electrolyte battery, etc., and is not limited thereto.

[0117] The embodiments of the present invention will be further described below with reference to several examples. However, the embodiments of the present invention are not limited to the specific embodiments described below. Appropriate modifications can be made within the scope of the original claims.

[0118] Example 1

[0119] (1) Commercial porous carbon was used as raw material and graded to obtain a carbon matrix precursor with a median particle size Dv50 of 8.6 μm. The carbon matrix precursor was then subjected to flotation treatment with n-hexane as the flotation agent, flotation temperature of 25℃ and flotation time of 24h. The upper and lower liquids were then separated and dried to obtain a carbon matrix with a surface cleanliness of 78%.

[0120] (2) Place the carbon matrix in a CVD (Chemical Vapor Deposition) device, then introduce silane into the CVD device, control the silane concentration to 19%, raise the temperature to 480℃, and react for 10h to obtain the precursor;

[0121] (3) The precursor is placed in a reactor and a mixture of methane and propylene with a volume ratio of 100:5 is introduced under nitrogen protection. The concentration of the mixed gas is 12%. The reactor is heat-treated at 620°C and kept at that temperature for 2 hours to obtain the negative electrode material.

[0122] In this embodiment, the negative electrode material includes a carbon matrix and a silicon material, with the silicon material dispersed in the carbon matrix. As shown in Figure 2, the negative electrode material prepared in this embodiment has a low number of microparticles on its surface, and the surface cleanliness γ of the negative electrode material is ≥60%. Other parameters of the negative electrode material are shown in Tables 1 and 2.

[0123] Example 2

[0124] Unlike Example 1:

[0125] (1) Using commercially available porous carbon 1 as raw material, it is graded to obtain porous carbon 2. Then, porous carbon 2 is subjected to flotation treatment with n-hexane as the flotation agent, flotation temperature of 25°C, and flotation time of 18h. Then, the upper and lower liquids are separated and dried to obtain a carbon matrix with a surface cleanliness of 70%.

[0126] In this embodiment, the negative electrode material includes a carbon matrix and a silicon material, with the silicon material dispersed in the carbon matrix. Other parameters of the negative electrode material are shown in Tables 1 and 2.

[0127] Example 3

[0128] Unlike Example 1:

[0129] (1) Using commercially available porous carbon 1 as raw material, it is graded to obtain porous carbon 2. Then, porous carbon 2 is subjected to flotation treatment. The flotation agent is n-pentanol, the flotation temperature is 25℃, and the flotation time is 24h. Then, the upper and lower liquids are separated and dried to obtain a carbon matrix with a surface cleanliness of 78%.

[0130] The subsequent steps are the same as in Example 1.

[0131] In this embodiment, the negative electrode material includes a carbon matrix and a silicon material, with the silicon material dispersed in the carbon matrix. Other parameters of the negative electrode material are shown in Tables 1 and 2.

[0132] Example 4

[0133] Unlike Example 1:

[0134] (1) Using commercially available porous carbon 1 as raw material, it is graded to obtain porous carbon 2. Then, the porous carbon 2 is subjected to electrostatic dust removal treatment. Under the drive of carrier gas, the temperature is set to 230℃, the flue gas flow rate is 3L / min, and the electrostatic dust removal treatment is carried out for 3.5h to obtain a carbon matrix with a surface cleanliness of 89%.

[0135] The subsequent steps are the same as in Example 1.

[0136] In this embodiment, the negative electrode material includes a carbon matrix and a silicon material, with the silicon material dispersed in the carbon matrix. Other parameters of the negative electrode material are shown in Tables 1 and 2.

[0137] Example 5

[0138] (1) Using commercially available porous carbon 1 as raw material, the porous carbon 2 is obtained by fractionation.

[0139] (2) Place porous carbon 2 in CVD, then introduce silane into the CVD equipment, control the silane concentration to 19%, raise the temperature to 480℃, react for 10h, and obtain the precursor;

[0140] (3) The precursor was placed in a reactor and methane gas with a concentration of 24% was introduced. The mixture was heat-treated at 680°C for 4 hours to obtain a silicon-carbon composite.

[0141] (4) The silicon-carbon composite was subjected to flotation treatment with kerosene as the flotation agent for 48 hours. Then it was separated, dried, and the negative electrode material was obtained.

[0142] In this embodiment, the negative electrode material includes a carbon matrix and a silicon material, with the silicon material dispersed in the carbon matrix. Other parameters of the negative electrode material are shown in Tables 1 and 2.

[0143] Example 6

[0144] Unlike Example 1, the preparation method further includes:

[0145] (4) The product obtained in step (3) is subjected to flotation treatment. The flotation agent is n-hexane, the flotation solution is water, the volume ratio of water to n-hexane is 100:1, the flotation time is 20h, the flotation temperature is 25℃, and then the particles of the upper and lower layers are separated and collected, dried, and the negative electrode material is obtained.

[0146] In this embodiment, the negative electrode material includes a carbon matrix and a silicon material, with the silicon material dispersed in the carbon matrix. Other parameters of the negative electrode material are shown in Tables 1 and 2.

[0147] Example 7

[0148] Commercially available porous carbon 1 was used as raw material and graded to obtain porous carbon 2. The porous carbon 2 was then subjected to flotation treatment with water as solvent and kerosene as flotation agent. The flotation temperature was 25℃ and the flotation time was 20h. The upper and lower liquids were then separated and dried to obtain a carbon matrix with a surface cleanliness of 65%.

[0149] The subsequent steps are the same as in Example 1.

[0150] Example 8

[0151] (1) Using commercially available porous carbon 1 as raw material, it is graded to obtain porous carbon 2. Then, porous carbon 2 is subjected to flotation treatment with isopropanol as solvent, gasoline as flotation agent, flotation temperature of 25°C, and flotation time of 48h. Then, the upper and lower liquids are separated and dried to obtain a carbon matrix with a surface cleanliness of 76%.

[0152] (2) Place the carbon matrix in CVD, then introduce silane into the CVD equipment, control the silane concentration to 19%, raise the temperature to 480℃, and react for 10h to obtain the precursor;

[0153] (3) The precursor is placed in a reactor and methane gas with a concentration of 15% is introduced. The reactor is then heat-treated at 620°C for 5 hours to obtain the negative electrode material.

[0154] The subsequent steps are the same as in Example 1.

[0155] Example 9

[0156] Unlike Example 4:

[0157] (1) Using commercially available porous carbon 1 as raw material, it is graded to obtain porous carbon 2. Then, the porous carbon 2 is subjected to electrostatic dust removal treatment. Under the drive of carrier gas, the temperature is set to 230℃, the flue gas flow rate is 1L / min, and the electrostatic dust removal treatment is carried out for 3.5h to obtain a carbon matrix with a surface cleanliness of 65%.

[0158] Example 10

[0159] The difference from Example 6 is:

[0160] (4) The negative electrode material is subjected to flotation treatment. The solvent is acetone, the flotation agent is oleic acid, the flotation solution is water, the volume ratio of water to n-hexane is 100:1, the flotation time is 28h, the flotation temperature is 25℃, and then the particles of the upper and lower layers are separated and collected, dried, and the negative electrode material is obtained.

[0161] Example 11

[0162] The difference from Example 1 is that: (1) commercial porous carbon 1 is used as raw material, graded to obtain porous carbon 2, porous carbon 2 is subjected to flotation treatment, the flotation agent is n-hexane, the flotation time is 24h, and then the upper and lower liquids are separated, dried, and a carbon matrix with a surface cleanliness of 65% is obtained.

[0163] Comparative Example 1

[0164] The difference from Example 1 is:

[0165] (1) Using commercially available porous carbon 1 as raw material, it is graded to obtain porous carbon 2. Then, porous carbon 2 is subjected to flotation treatment with n-hexane as the flotation agent, flotation temperature of 25℃, and flotation time of 10h. Then, the upper and lower liquids are separated and dried to obtain a carbon matrix with a surface cleanliness of 58%.

[0166] In this comparative example, the negative electrode material includes a carbon matrix and a silicon material, with the silicon material dispersed in the carbon matrix. Other parameters of the negative electrode material are shown in Tables 1 and 2.

[0167] Comparative Example 2

[0168] The difference from Example 1 is:

[0169] (1) Commercially available porous carbon was used as raw material and graded to obtain a carbon matrix. As shown in Figure 3, the negative electrode material prepared in Comparative Example 2 had a large number of micro-powder particles on its surface, and the surface cleanliness γ of the negative electrode material was <60%.

[0170] Performance testing

[0171] (1) Test method for surface morphology of negative electrode material:

[0172] The surface morphology of the negative electrode material particles was observed using a Hitachi S4800 scanning electron microscope to obtain electron electron microscope images of the negative electrode material. At 10,000 magnification, the adhesion of microparticles on the surface of 100 negative electrode material particles was randomly observed. Particles with a diameter of 0.1 μm to 1 μm attached to the surface of the negative electrode material particles were defined as microparticles. Negative electrode material particles with less than 20 microparticles on their surface were defined as clean particles. The number of clean particles in the 100 negative electrode material particles was counted as A. The surface cleanliness of the negative electrode material was γ = A / 100*100%.

[0173] (2) Flowability parameters of the negative electrode material:

[0174] The flowability parameters of the negative electrode material particles were tested according to GB / T 1482-2022 "Standard for Determination of Flowability of Metal Powders - Funnel Method (Hall Flowmeter)" to obtain the flowability parameter t.

[0175] (3) Test method for the specific surface area of ​​the negative electrode material or the negative electrode material after removing silicon material:

[0176] Specific surface area was measured using a Microtonic TriStar 3000 surface area and pore size analyzer (USA). The static volumetric method was followed according to GB / T19587-2017, "Determination of Specific Surface Area of ​​Solid Substances by Gas Adsorption BET Method". First, a specific surface area tube (dried at high temperature) was weighed (M1). A certain amount of sample (1 / 2 to 2 / 3 of the tube volume) was then added and degassed at 300℃ for one hour. After cooling, the tube weight (M2) was measured; the sample mass is M2-M1. The sample mass was entered into the computer, and the instrument was used for testing. The instrument automatically completed the test, read the data, and recorded the results. It is important to note that after heating the sample to 300℃ and purging with nitrogen for 1 hour, it was cooled to room temperature, and N2 purging was required again during the cooling process. The sampling range was 0.05-0.30 g / cm³. 3 Take a point every 0.05.

[0177] (4) Test method for oil absorption value of negative electrode material:

[0178] The measurement was performed according to GB / T 3780.2-2017 "Carbon Black Part 2: Determination of Oil Absorption Value" or the equipment instruction manual. The oil absorption value was measured using an ASAHI S-500 oil absorption value tester from ASAHISOUKEN (Japan). The oil absorption value (O) is the amount of linseed oil added when the torque generated by the change in viscosity characteristics reaches 70% of the maximum torque. The unit is mL / 100g.

[0179] (5) Gas generation test of negative electrode material:

[0180] Carboxymethyl cellulose (CMC) was dispersed in water at a mass ratio of 1.4% and then glued. After uniform dispersion, 10g of glue solution was mixed with 10g of negative electrode material to obtain a slurry. The slurry was then placed in an aluminum-plastic film bag, and the mass of the slurry was recorded. The bag was then sealed to form a sealed aluminum-plastic film bag.

[0181] The sealed aluminum-plastic film bag was fixed at the bottom of the container and completely submerged in water. The volume of the aluminum-plastic film bag was recorded. After a fixed time (24h), the volume of the aluminum-plastic film bag was recorded again. The gas production of the silicon anode material was calculated based on the change in the volume of the aluminum-plastic film, in mL / g.

[0182] (6) Test method for pore volume of negative electrode material or negative electrode material after silicon removal:

[0183] Etching process:

[0184] While stirring, 150 mL of 20% HF acid solution was added dropwise to 10 g of anode material. This produced SiF4 and H2 gases and released heat. After no more gas was produced, the supernatant acid solution was removed by centrifugation. Another 150 mL of 20% HF acid solution was added to the anode material, and the mixture was stirred for 12 h. The supernatant acid solution was removed by centrifugation again. The anode material was then washed with pure water until neutral and dried to obtain the anode material after removing the silicon material.

[0185] The tests were conducted using an ASAP2460 instrument from Micron Technology, USA. The pore volume V was determined using the BJH Desorption Cumulative Volume of Pores model. The average pore size and pore volume of the material are calculated within the pore size range. The pore volume ratio can be calculated according to the proportion of the pore volume of micropores (0-2nm), mesopores (2-50nm), and macropores (>50nm) to the total pore volume.

[0186] (7) Test method for median particle size of negative electrode materials:

[0187] The particle size distribution test method refers to GB / T 19077-2016. A laser particle size analyzer can be used to conveniently determine the cumulative particle size distribution based on volume, such as the Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK. Dv50 represents the particle size corresponding to a cumulative particle size distribution percentage of 50%, i.e., the median particle size.

[0188] (8) Test method for average particle size of silicon materials:

[0189] The particle size of 20 silicon materials was randomly tested using a high-powered microscope, and then the average particle size of the multiple silicon materials was calculated, which is the average particle size of the silicon material.

[0190] (9) Coating thickness:

[0191] The material was cross-sectioned using a FIB-SEM device. Ten particles were randomly selected from the SEM, and the coating thickness of each particle was measured three times to obtain the average coating thickness.

[0192] (10) Types of silicon materials:

[0193] The type of silicon material is identified by measuring diffraction peaks using an X-ray diffractometer (XRD).

[0194] (11) Test of silicon content in anode materials:

[0195] The sample was burned in an oxygen atmosphere using a box-type atmosphere furnace (model: SA2-9-17TP) to allow silicon and silicon suboxide in the sample to react and become silicon dioxide. The carbon was then burned and turned into carbon dioxide, which was then discharged. The mass content of silicon in the negative electrode material was calculated by weighing.

[0196] (12) Test of carbon content in negative electrode material:

[0197] Using a Bruker / Elter G4 ICARUS HF / CS-i infrared carbon-sulfur analyzer, the sample was burned in a high-temperature, oxygen-rich environment. The carbon contained in the sample was oxidized into carbon dioxide, which then entered the infrared detector along with the carrier gas. The carbon content was quantitatively calculated by statistically analyzing the changes in the intensity of the infrared absorption wavelength of the carbon dioxide signal.

[0198] (13) Test of oxygen content in negative electrode material:

[0199] The oxygen content in the negative electrode material was tested using an ONH2000 elemental analyzer. Test procedure: 5 mg ± 0.5 mg of the sample was weighed using a 0.0001 g / mL balance. The sample was wrapped with aluminum foil as a flux and placed in a graphite crucible under a helium atmosphere. The crucible was heated to approximately 2300°C to melt the oxygen. The oxygen in the sample was released as carbon monoxide or carbon dioxide. After separation from other gaseous products, the oxygen was introduced into an infrared detector for measurement. A standard sample with a similar oxygen content to the sample was selected for instrument calibration. Each sample was tested twice in parallel, and the average value was taken. Other settings: degassing time 45 s, degassing power 5.8 kW, rinsing time 20 s, stabilization time 40 s, infrared integration delay 2 s, analysis time 60 s, analysis power 5.5 kW.

[0200] (14) Test the electrochemical performance of the negative electrode material:

[0201] A: Capacity efficiency testing method:

[0202] A negative electrode slurry was prepared by mixing negative electrode material, conductive carbon black, and polyacrylic acid (PPA) in a mass ratio of 75:15:10. This slurry was then coated onto copper foil and dried to form the negative electrode sheet. A coin cell was assembled using a lithium metal sheet as the counter electrode in an argon-filled glove box. The coin cell was then charged and discharged at a current density of 0.1C within a charge-discharge range of 0.005V–1.5V to obtain its initial discharge specific capacity and initial coulombic efficiency (ICE).

[0203] B: Finished product cycle testing method:

[0204] The prepared negative electrode material, conductive agent, and binder were dissolved and mixed in a solvent at a mass ratio of 94:1:5, with the solid content controlled at 50%. This mixture was then coated onto a copper foil current collector, vacuum dried, and the negative electrode sheet was obtained. Next, a ternary positive electrode sheet prepared using conventional mature processes, a 1 mol / L LiPF6 / ethyl cellulose + dimethyl carbonate + methyl ethyl carbonate (v / v = 1:1:1) electrolyte, a polypropylene separator (Celgard 2400), and a casing were assembled into an 18650 cylindrical cell using conventional manufacturing processes. The charge-discharge tests of the cylindrical cells were conducted on the LAND battery testing system of Wuhan Jinno Electronics Co., Ltd. Under normal temperature conditions, constant current charge-discharge at 0.2C, and charge-discharge voltage limited to 2.75–4.2V, cycle performance tests were performed. After 500 cycles, the 500-cycle capacity retention rate was obtained.

[0205] The capacity measured by 10C constant current charge-discharge is divided by the capacity measured by 1C constant current charge-discharge to test the 10C / 1C capacity retention rate.

[0206] The test results of Examples 1 to 11 (abbreviated as S1 to S11) and Comparative Examples 1 to 2 (abbreviated as D1 to D2) prepared according to the above method are shown in Tables 1 to 2.

[0207] Table 1. Performance parameters of the negative electrode materials in each embodiment and comparative example

[0208] Table 2. Battery performance tests for each embodiment and comparative example

[0209] According to the test data from Examples 1 to 11, this application can reduce the content of micropowder on the surface of the negative electrode material by controlling the surface cleanliness of the negative electrode material, thereby reducing the side reactions between the negative electrode material and the electrolyte, reducing the consumption of active lithium ions, and improving the specific capacity and initial coulombic efficiency of the negative electrode material. A negative electrode material with high surface cleanliness can reduce the adhesion or agglomeration between particles, improve the uniformity of the negative electrode material, and further reduce the gas generation phenomenon of the negative electrode material. This enables the negative electrode material to have high initial discharge specific capacity and initial coulombic efficiency, excellent rate performance and cycle performance.

[0210] According to the test data from Examples 1 and 2, due to the shortened flotation time in Example 2, the surface cleanliness of the carbon matrix decreased, and the surface cleanliness of the anode material after the carbon matrix and silicon material were combined also decreased. The gas production value of the anode material increased compared to Example 1, while the 500-cycle retention rate of the anode material decreased.

[0211] According to the test data of Examples 1 and 3-4, as long as the surface cleanliness and flowability parameters of the negative electrode material are controlled within a reasonable range, the negative electrode material can have good rate performance and cycle performance, and the gas production value can be controlled at a low level.

[0212] Based on the test data from Examples 1 and 5 or 6, it can be seen that in Example 5, the silicon-carbon composite was subjected to flotation treatment, which improved the surface cleanliness of the negative electrode material. In Example 6, the negative electrode material prepared in Example 1 was subjected to a second flotation treatment, which further improved the surface cleanliness of the negative electrode material and further reduced its flowability parameters. The flowability of the negative electrode material particles was better, the gas production value of the negative electrode material reached its lowest state, and the initial discharge specific capacity of the negative electrode material decreased slightly, but the 500-cycle capacity and the 10C / 1C capacity retention rate were improved.

[0213] Based on the test data from Examples 1, 7, and 9, it can be seen that the surface cleanliness of the carbon matrix is ​​slightly lower than that of Example 1, leading to a decrease in the surface cleanliness of the negative electrode material. This results in an increase in microparticles on the surface of the negative electrode material, and a slight decrease in the initial coulombic efficiency, 500-cycle capacity, and 10C / 1C capacity retention rate. Preferably, the surface cleanliness γ ≥ 70%, and the flowability parameter t ≤ 50s / 50g.

[0214] According to the test data of Examples 1 and 11, the porous carbon was not graded. The carbon matrix particles without grading were not uniform, which increased the fluidity coefficient of the prepared anode material, i.e., the fluidity was worse. Some particles agglomerated and clumped together, which led to a decrease in the first discharge specific capacity of the anode material. The first coulombic efficiency, 500-cycle capacity and 10C / 1C capacity retention rate also decreased.

[0215] According to the test data of Example 1 and Comparative Example 1, the flotation treatment time of porous carbon is too short, the surface cleanliness of the carbon matrix is ​​low, and after the carbon matrix is ​​combined with silicon material, the surface cleanliness of the anode material further decreases, the gas production value of the anode material is too high, which is not conducive to the cycle stability of the anode material, and the capacity retention rate of the anode material also decreases significantly.

[0216] According to the test data of Example 1 and Comparative Example 2, the porous carbon was only graded and not surface cleaned. Although the flow parameters of the negative electrode material could meet the requirements, the gas production of the negative electrode material increased significantly due to the increase of micro powder on the surface of the negative electrode material. The side reaction with the electrolyte was aggravated, the first discharge specific capacity of the negative electrode material decreased, and the first coulombic efficiency, 500-cycle capacity and 10C / 1C capacity retention rate also decreased significantly.

[0217] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A negative electrode material, characterized in that, It includes a carbon matrix and an active substance, with at least a portion of the active substance distributed within the carbon matrix; The surface cleanliness of the negative electrode material is γ, where γ ≥ 60%. The surface cleanliness of the negative electrode material is measured using the following test method: Electron electron microscope images of the negative electrode material were obtained. At 10,000x magnification, the adhesion of microparticles on the surface of 100 negative electrode material particles was randomly observed. Particles with a diameter of 0.1μm to 1μm attached to the surface of the negative electrode material particles were defined as microparticles. Negative electrode material particles with less than 20 microparticles on their surface were defined as clean particles. The number of clean particles in the 100 negative electrode material particles was counted as A. The surface cleanliness γ of the negative electrode material was defined as A / 100*100%.

2. The negative electrode material according to claim 1, characterized in that, The negative electrode material has at least one of the following characteristics: (1) γ is 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 98% or any value within the range of any two of the above values; (2) γ≥70%.

3. The negative electrode material according to claim 1, characterized in that, The negative electrode material has at least one of the following characteristics: (1) The flowability parameter of the negative electrode material is t≤80s / 50g; (2) The flowability parameter of the negative electrode material is 10s / 50g≤t≤50s / 50g.

4. The negative electrode material according to claim 1, characterized in that, The negative electrode material has at least one of the following characteristics: (1) The specific surface area of ​​the negative electrode material is ≤5m². 2 / g; (2) The specific surface area of ​​the negative electrode material is 0.1–2.5 m². 2 / g.

5. The negative electrode material according to claim 1, characterized in that, The negative electrode material has at least one of the following characteristics: (1) The gas production value of the negative electrode material is ≤1 mL / g / day; (2) The gas production value of the negative electrode material is ≤0.1mL / g / day.

6. The negative electrode material according to claim 1, characterized in that, The oil absorption value of the negative electrode material is 30mL / 100g to 80mL / 100g.

7. The negative electrode material according to claim 1, characterized in that, The negative electrode material has pores, and the total pore volume of the negative electrode material is ≤0.1cm. 3 / g.

8. The negative electrode material according to claim 1, characterized in that, The pores of the negative electrode material include mesopores, and the volume of the mesopores accounts for 25% to 95% of the total pore volume of the negative electrode material.

9. The negative electrode material according to claim 1, characterized in that, The negative electrode material has at least one of the following characteristics: (1) The negative electrode material further includes a coating layer, which is located on at least a portion of the surface of the carbon matrix and / or the active material; (2) The negative electrode material further includes a coating layer, the thickness of which is 0.1 nm to 3000 nm; (3) The negative electrode material further includes a coating layer, the material of which includes at least one of carbon materials, metal oxides and nitrides.

10. The negative electrode material according to any one of claims 1 to 9, characterized in that, The negative electrode material has at least one of the following characteristics: (1) The carbon matrix includes at least one of hard carbon, soft carbon, graphite, mesophase carbon microspheres, activated carbon, porous carbon, mesoporous carbon and carbon gel; (2) The active material includes silicon material, which includes at least one of elemental silicon, silicon-oxygen material and silicon alloy; (3) The active material includes silicon material, and the silicon material includes amorphous silicon; (4) The active material includes silicon material, and the average particle size of the silicon material is 1 nm to 100 nm.

11. The negative electrode material according to any one of claims 1 to 7, characterized in that, The negative electrode material has at least one of the following characteristics: (1) The mass percentage of oxygen in the negative electrode material is ≤5wt%; (2) The carbon content in the negative electrode material is 30wt% to 60wt% by mass; (3) The active material includes silicon material, and the mass percentage of silicon element in the negative electrode material is 30wt% to 65wt%; (4) The active material includes silicon material, and the mass ratio of silicon to carbon in the negative electrode material is 0.8 to 2.

0.

12. The negative electrode material according to claim 1, characterized in that, The median particle size Dv50 of the negative electrode material is 1 μm to 30 μm.

13. A battery, characterized in that, The battery comprises the negative electrode material as described in any one of claims 1 to 12.

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