Negative electrode material and battery

Abstract

The application provides a negative electrode material and a battery. The negative electrode material comprises a silicon-based material and a carbon material, and at least part of the carbon material is located on the surface of the silicon-based material. The specific surface area deviation of the negative electrode material is H, H=(B-A) / A, 0.5 H≤45, A is the theoretical specific surface area of the negative electrode material, and B is the measured specific surface area of the negative electrode material measured by the BET method. The negative electrode material and the battery provided by the application can achieve an ideal balance in cycle performance, capacity performance and rate performance.

Description

Technical Field

[0001] This application relates to the field of negative electrode material technology, specifically to a negative electrode material and a battery. Background Technology

[0002] Electrified new energy vehicles represent the future direction of the automotive market, and their core component is the lithium-ion battery. As the market develops, the demand for high-capacity batteries is increasing, and adopting novel high-specific-capacity positive and negative electrode materials is one of the important methods to improve battery energy density.

[0003] More and more new materials such as metals, oxides, and metal alloys are being used as active materials in anode materials to continuously explore various ways to improve battery energy density. Taking silicon-based anode materials as an example, silicon-based anode materials, as one of the aforementioned active materials, are widely considered the next generation of anode materials. Their ultra-high theoretical specific capacity (4200 mAh / g) and low delithiation potential (<0.5 V), coupled with silicon's slightly higher voltage plateau than graphite, make it less prone to surface lithium plating during charging, resulting in better safety performance and making them highly regarded. However, during charging and discharging, silicon-based materials form an electrolyte film layer through continuous contact with the electrolyte, leading to a significant loss of active lithium ions and accelerated capacity decay of the anode material.

[0004] Therefore, how to construct anode materials with stable solid-liquid reaction interfaces remains a problem that needs to be solved in order to improve the capacity decay of anode materials. Summary of the Invention

[0005] This application proposes a negative electrode material and a battery. By controlling the deviation of the specific surface area of ​​the negative electrode material, it helps to improve the stability of the solid-liquid reaction interface of the negative electrode material, reduce the side reactions generated by the contact between the negative electrode material and the electrolyte, improve the capacity and initial coulombic efficiency of the negative electrode material, and improve the capacity decay of the negative electrode material.

[0006] In a first aspect, this application provides a negative electrode material, the negative electrode material comprising a silicon-based material and a carbon material, wherein at least a portion of the carbon material is located on the surface of the silicon-based material; The specific surface area deviation of the negative electrode material is H, where H = (BA) / A, and 0.5 < H ≤ 45. A is the theoretical specific surface area of ​​the negative electrode material, and B is the measured specific surface area of ​​the negative electrode material obtained by the BET method; wherein, the theoretical specific surface area A is measured in the following way: The anode material was tested using a sphericity meter, and the particle size distribution data and sphericity distribution data were obtained. Based on the particle size distribution data, the frequency distribution data δn and particle size D were obtained. n The particle size D is obtained from the sphericity distribution data map. nand sphericity Q n ; ρ is the true density of the negative electrode material measured using the gas volumetric method. In the sphericity distribution data plot, Q n D n Sphericity data of particles corresponding to particle size; In the particle size distribution data map, D n Frequency distribution data of particles corresponding to particle size. n is the number of valid data sample groups measured by the sphericity meter.

[0007] In some embodiments, the silicon-based material comprises a silicon oxide and a compound of a metal element M, wherein the metal element M is selected from at least one of Li, Mg, Cu, Ni, Fe, Cr, and Zn.

[0008] In some embodiments, the compound of metal element M includes at least one of silicate of metal element M and oxide of metal element M. In some embodiments, the silicon-based material includes silicon and oxygen, and the atomic ratio of oxygen to silicon in the negative electrode material is x, where 0 < x < 2.2.

[0009] In some embodiments, the silicon-based material comprises silicon oxide, the silicon oxide having the general formula SiO. x , 0 < x ≤ 2.

[0010] In some embodiments, the carbon material includes at least one of amorphous carbon, graphite, graphene, carbon nanotubes, and carbon fibers.

[0011] In some embodiments, the oil absorption value of the negative electrode material is 35 mL / 100g to 65 mL / 100g.

[0012] In some embodiments, the metallic element includes at least one of Fe, Cr, and Cu.

[0013] In some embodiments, the Fe element content in the negative electrode material is ≤400ppm by mass.

[0014] In some embodiments, the mass content of Cr in the negative electrode material is ≤200ppm.

[0015] In some embodiments, the mass content of Cu in the negative electrode material is ≤200ppm.

[0016] In some embodiments, the particle size of the negative electrode material satisfies: D 20 -D 10 ≤4μm, D90 -D 80 ≤8μm.

[0017] In some embodiments, the theoretical specific surface area of ​​the negative electrode material is 0.01 m². 2 / g ~12m 2 / g.

[0018] In some embodiments, the measured specific surface area of ​​the negative electrode material is 0.5 m². 2 / g ~30m 2 / g.

[0019] In some embodiments, the pH of the negative electrode material is 5 to 12.

[0020] In some embodiments, the true density ρ of the negative electrode material is 2.0 g / cm³. 3 ~3.4g / cm 3 .

[0021] Secondly, this application provides a battery comprising the negative electrode material described in the first aspect.

[0022] The technical solution of this application has at least the following beneficial effects: The negative electrode material provided in this application has a theoretical specific surface area (A), which represents the lowest specific surface area of ​​the negative electrode material at a corresponding particle size and sphericity. The negative electrode material particles with the lowest specific surface area have lower surface energy and fewer surface defects. However, this is an ideal state for the negative electrode material particles and is difficult to achieve in practice. Furthermore, the smaller the theoretical specific surface area of ​​the negative electrode material, the fewer sites available for rapid lithium ion adsorption and desorption, resulting in decreased electrolyte wetting ability. This limits the lithium ion insertion / extraction rate on the surface of the negative electrode material during charge and discharge, hindering lithium ion transport and affecting the capacity and rate performance of the negative electrode material. Therefore, a balance needs to be sought between the theoretical and actual specific surface areas of the negative electrode material to ensure that the negative electrode material can possess both high capacity and excellent cycle performance. This application controls the ratio H of the theoretical specific surface area to the actual specific surface area of ​​the negative electrode material to be 0.5 < H ≤ 45, so that the difference between the actual measured specific surface area and the theoretical specific surface area is controlled within a suitable range. This reduces surface defects of the negative electrode material, enables the surface of the negative electrode material to form a stable solid-liquid reaction interface, reduces the occurrence of side reactions between the negative electrode material and the electrolyte, and improves the capacity and initial coulombic efficiency of the negative electrode material. At the same time, it ensures that the surface of the negative electrode material has an appropriate number of active sites for rapid adsorption and desorption of lithium ions, which can improve the charge and discharge performance of the negative electrode material and improve its rate performance. Attached Figure Description

[0023] Figure 1This is a schematic diagram of the apparatus for preparing the negative electrode material provided in the embodiments of this application.

[0024] Figure 2 This is a schematic diagram of the discharge state of a battery provided in an embodiment of this application.

[0025] Figure 3a This is a sphericity distribution data diagram of the negative electrode material prepared in Example 1 of this application.

[0026] Figure 3b This is a table showing the sphericity distribution data of the negative electrode material prepared in Example 1 of this application.

[0027] Figure 4a This is a particle size distribution data diagram of the negative electrode material prepared in Example 1 of this application.

[0028] Figure 4b This is a table showing the particle size distribution data of the negative electrode material prepared in Example 1 of this application. Detailed Implementation

[0029] The following are preferred embodiments of the present invention. It should be noted that those skilled in the art can make several improvements and modifications without departing from the principle of the present invention, and these improvements and modifications are also considered to be within the protection scope of the present invention.

[0030] Specifically, this application provides a negative electrode material, which includes a silicon-based material and a carbon material, with at least a portion of the carbon material located on the surface of the silicon-based material. The silicon-based material includes silicon, oxygen, and metal elements. The specific surface area deviation of the negative electrode material is H, where H = (BA) / A, and 0.5 < H ≤ 45. A is the theoretical specific surface area of ​​the negative electrode material, and B is the measured specific surface area of ​​the negative electrode material obtained by the BET method; wherein, the theoretical specific surface area A is measured in the following way: The anode material was tested using a sphericity meter, and the particle size distribution data and sphericity distribution data were obtained. Based on the particle size distribution data, the frequency distribution data δn and particle size D were obtained. n The particle size D is obtained from the sphericity distribution data map. n and sphericity Q n ; ρ is the true density of the negative electrode material measured using the gas volumetric method. In the sphericity distribution data plot, Q n D n Sphericity data of particles corresponding to particle size; In the particle size distribution data map, Dn Frequency distribution data of particles corresponding to particle size. n is the number of valid data sample groups measured by the sphericity meter.

[0031] In the above scheme, the theoretical specific surface area A of the negative electrode material can represent the minimum specific surface area of ​​the negative electrode material under the corresponding particle size and sphericity. The negative electrode material particles with the lowest specific surface area have lower surface energy and fewer surface defects. However, this is an ideal state for the negative electrode material particles, which is difficult to achieve in practice. Furthermore, the smaller the theoretical specific surface area of ​​the negative electrode material, the fewer sites available for rapid lithium ion adsorption and desorption, resulting in decreased electrolyte wetting ability. During charge and discharge, this limits the lithium ion insertion / extraction rate on the surface of the negative electrode material, hindering lithium ion transport and affecting the capacity and rate performance of the negative electrode material. Therefore, it is necessary to seek a balance between the theoretical and actual specific surface areas of the negative electrode material to ensure that the negative electrode material can have both high capacity and excellent cycle performance. This application controls the ratio H of the theoretical specific surface area to the actual specific surface area of ​​the negative electrode material to be 0.5 < H ≤ 45, so that the difference between the actual measured specific surface area and the theoretical specific surface area is controlled within a suitable range. This reduces surface defects of the negative electrode material, enables the surface of the negative electrode material to form a stable solid-liquid reaction interface, reduces the occurrence of side reactions between the negative electrode material and the electrolyte, and improves the capacity and initial coulombic efficiency of the negative electrode material. At the same time, it ensures that the surface of the negative electrode material has an appropriate number of active sites for rapid adsorption and desorption of lithium ions, which can improve the charge and discharge performance of the negative electrode material and improve its rate performance.

[0032] In some implementations, the specific value of H is 0.51, 1, 2, 5, 10, 12, 15, 20, 22, 25, 30, 33, 35, 38, 40, or 45, etc., and is not limited here. When the H value of the negative electrode material is too large, it indicates that there are too many surface defects and cavities formed by carbon material accumulation, which leads to an aggravation of side reactions between the negative electrode material and the electrolyte, resulting in repeated growth of the SEI film, excessive consumption of lithium ions, and a decrease in the capacity and initial coulombic efficiency of the negative electrode material, as well as a decrease in cycle capacity retention. When the H value of the negative electrode material is too small, it indicates that the surface of the negative electrode material exhibits long-range, continuous, and dense sp2 hybrid carbon material, making the surface of the negative electrode material particles too smooth and dense, making it difficult for the electrolyte to effectively and quickly wet the negative electrode material, hindering lithium ion transport and electron transport, thereby limiting the capacity of the negative electrode material and reducing rate performance. This application controls the H value of the negative electrode material within the above-mentioned range, which is beneficial to reduce surface defects of the negative electrode material, stabilize the solid-liquid interface of the negative electrode material, reduce the occurrence of side reactions between the negative electrode material and the electrolyte, improve the capacity and first coulombic efficiency of the negative electrode material, and improve the rate performance of the negative electrode material.

[0033] In some implementations, the theoretical specific surface area A of the negative electrode material is 0.01 m². 2 / g ~12m 2 / g, specifically 0.01m 2 / g, 0.02 m 2 / g, 0.05 m 2 / g, 0.06 m 2 / g, 0.08 m 2 / g, 0.1 m 2 / g, 0.3 m 2 / g, 0.5 m 2 / g, 0.6m 2 / g, 0.7m 2 / g, 0.8 m 2 / g, 1.0 m 2 / g、2 m 2 / g、3m 2 / g、5m 2 / g、8 m 2 / g、10 m 2 / g or 12m 2 / g, but not limited to the listed values; other unlisted values ​​within this range also apply. Understandably, when the theoretical specific surface area of ​​the negative electrode material is controlled within the above range, the surface area of ​​the negative electrode material particles can be controlled within a suitable range, surface defects of the negative electrode material are significantly reduced, and side reactions between the negative electrode material and the electrolyte can be significantly reduced.

[0034] In some implementations, the measured specific surface area B of the negative electrode material is 0.5 m². 2 / g ~30m 2 / g, specifically 0.5m 2 / g, 1.0 m 2 / g, 1.5 m 2 / g, 1.8 m 2 / g, 2.0 m 2 / g, 2.5 m 2 / g, 3.0 m 2 / g, 3.6 m 2 / g, 4.0 m 2 / g、5 m 2 / g, 5.5 m 2 / g, 6.0 m 2 / g, 7.0 m 2 / g、8.0 m 2 / g, 8.5 m 2 / g, 10.0 m 2 / g, 15.0 m 2 / g, 20.0m 2 / g, 25.0 m 2 / g or 30m 2 / g, but not limited to the listed values; other unlisted values ​​within this range also apply. Understandably, controlling the specific surface area of ​​the anode material within the above range helps reduce side reactions and improve the initial coulombic efficiency.

[0035] In some embodiments, the silicon-based material includes silicon oxide and a compound of a metal element M, wherein the metal element M is selected from at least one of Li, Mg, Cu, Ni, Fe, Cr, and Zn. The compound of the metal element M can be a silicon-lithium alloy, a silicon-magnesium alloy, etc., and is not limited thereto.

[0036] In some embodiments, the atomic ratio of oxygen to silicon in the negative electrode material is x, where 0 < x < 2.2. Specifically, it can be 0.1, 0.2, 0.5, 0.8, 0.9, 1, 1.2, 1.5, 1.8, 1.9, 2.1, 2.185, etc., or other values ​​within the above range.

[0037] In some embodiments, the oxygen-containing and silicon-containing components in the negative electrode material include, but are not limited to, at least one of silicon oxide and silicate.

[0038] In some embodiments, silicon oxide can be represented by the general formula SiO. x (0 < x ≤ 2). Specifically, SiO x Specifically, it can be SiO 0.1 SiO 0.2 SiO 0.3 SiO 0.4 SiO 0.5 SiO 0.8 SiO 0.9 SiO, SiO 1.1 SiO 1.2 SiO 1.5 Alternatively, it can be SiO2, without limitation. Silicon oxide can be a material formed by dispersing silicon particles in SiO2, or it can be a material with tetrahedral structural units, where silicon atoms are located at the center of the tetrahedral structural units, and oxygen atoms and / or silicon atoms are located at the four vertices of the tetrahedral structural units.

[0039] In some embodiments, the silicon-containing component in the negative electrode material can be elemental silicon, silicon oxide, or silicate. Elemental silicon can be amorphous silicon and / or crystalline silicon, and silicate can be magnesium silicate, lithium silicate, etc.

[0040] In some embodiments, the carbon material includes at least one of amorphous carbon and graphitized carbon. The amorphous carbon can be soft carbon and / or hard carbon. Understandably, carbon materials can improve the conductivity of silicon-based active materials.

[0041] In some embodiments, at least a portion of the surface of the negative electrode material has a carbon layer. Understandably, the carbon layer on the surface of the negative electrode material can reduce particle breakage caused by repeated SEI film formation, thereby improving the cycle performance of the negative electrode material and reducing volume expansion due to SEI film formation.

[0042] In some embodiments, the carbon content in the negative electrode material is 1% to 40% by mass; specifically, it can be 2%, 5%, 8%, 10%, 12%, 15%, 18%, 20%, 25%, 28%, 35%, or 40%, etc., and of course, it can also be other values ​​within the above range, which are not limited here.

[0043] In some embodiments, the mass content of silicon in the negative electrode material is 10% to 90%; specifically, it can be 25%, 30%, 40%, 50%, 55%, 60%, 65%, 70%, 85%, 88%, or 90%, etc., and of course, it can also be other values ​​within the above range, which are not limited here.

[0044] In some embodiments, the pH of the negative electrode material is 5-12, specifically 5, 6, 7, 8, 8.5, 9, 9.5, 10, or 12, etc., and is not limited thereto. Controlling the pH value of the negative electrode material helps to reduce gas generation and improve its stability and cycle life. Preferably, the pH value of the negative electrode material is 7-10.

[0045] In some embodiments, the true density ρ of the negative electrode material is 2.0 g / cm³. 3 ~3.4g / cm 3 Specifically, it can be 2.0 g / cm³. 3 2.2 g / cm 3 2.4 g / cm 3 2.6 g / cm 3 2.8 g / cm 3 2.9 g / cm 3 3.0 g / cm 3 3.2g / cm 3 or 3.4m 2 / g, and other unlisted values ​​within this range also apply. Controlling the true density within the above range is beneficial for improving the energy density and rate performance of the anode material.

[0046] In some embodiments, the oil absorption value of the negative electrode material is 35 mL / 100g to 65 mL / 100g, specifically 35 mL / 100g, 38 mL / 100g, 40 mL / 100g, 42 mL / 100g, 45 mL / 100g, 50 mL / 100g, 55 mL / 100g, 60 mL / 100g, or 65 mL / 100g, etc., or other values ​​within the above range, which are not limited here. Controlling the oil absorption value of the negative electrode material within the above range in this application helps the electrolyte to fully wet the negative electrode material, improving its processing performance and cycle stability.

[0047] In some implementations, the particle size of the negative electrode material satisfies: D 20 -D 10 ≤4μm, D 90 -D 80 ≤8μm; D 20 -D 10 Specifically, it can be 1μm, 1.5μm, 2μm, 2.5μm, 3.5μm, or 4μm, etc., D 90 -D 80 Specifically, the micrometer size can be 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, or 8 μm, etc., and is not limited here. This application controls D 20 -D 10 ≤4μm, and D 90 -D 80 ≤8μm indicates that the particle size distribution of the negative electrode material is suitable. The matching of smaller and larger particles results in a higher compaction density and a relatively uniform particle size distribution, which is beneficial for improving the ion conduction efficiency, rate performance, and cycle performance of the negative electrode material. If D 20 -D 10 ≤4μm, D 90 -D 80 >8μm indicates that the particle size distribution of the negative electrode material is shifted towards larger particle sizes. If D 20 -D 10 >4μm, D 90 -D 80 ≤8μm indicates that the particle size distribution of the negative electrode material is shifted towards smaller particle sizes. Both of these situations will lead to an increase in the particle size range of the negative electrode material. Small particles have shorter lithium-ion diffusion paths, while large particles have longer diffusion paths. This increases the difference in lithium-ion diffusion paths between negative electrode material particles and reduces the rate performance of the negative electrode material.

[0048] In some embodiments, the Fe content in the total dissolved solution of the negative electrode material is ≤400ppm, specifically 400ppm, 300ppm, 250ppm, 200ppm, 150ppm, 100ppm, 50ppm or 10ppm, etc., which are not limited here.

[0049] In some embodiments, the Cr content in the total dissolved solution of the negative electrode material is ≤200ppm, specifically 200ppm, 180ppm, 150ppm, 100ppm, 50ppm or 10ppm, etc., which are not limited here.

[0050] In some embodiments, the Cu in the total dissolved solution of the negative electrode material is ≤200ppm, specifically 200ppm, 180ppm, 150ppm, 100ppm, 50ppm or 10ppm, etc., which are not limited here.

[0051] Understandably, metal impurity ions such as iron, copper, and chromium can cause self-discharge, and deposited iron ions can easily puncture the separator, causing micro-short circuits and safety issues. Furthermore, the deposition of metal impurity ions will prevent the formation of an effective passivation layer on the electrode surface, leading to damage to the entire battery. Therefore, controlling the content of the aforementioned Fe, Cr, and Cu metal impurities is beneficial for improving the cycle stability and safety of the negative electrode material.

[0052] This application also provides a method for preparing a negative electrode material, the method comprising the following steps S10~S20: S100 involves placing silicon powder and silicon oxide raw materials in two separate chambers of a vacuum furnace, evacuating the two chambers to below 20 Pa, and then heating them.

[0053] In some embodiments, each of the two chambers 10 has two oppositely arranged air outlets 11, and the air outlets of the two chambers are connected by a closable air guide pipe 20. A cooling ring 30 is provided in the cooling chamber, and the air guide pipe 20 is also connected to the air inlet of the cooling ring 30. Figure 1 This is a schematic diagram of the structure of the anode material preparation apparatus provided in the embodiments of this application, as shown below. Figure 1 As shown, the evaporated gas from silicon powder and silicon-oxygen raw materials is blown vertically into the mixing chamber, and then introduced into the gas inlet at the center of the low-temperature cooling ring 30. The cooling ring 30 is composed of 5 to 15 layers of stacked annular cooling plates. The evaporated gas passes through the gas channel at the center of the cooling ring 30. Most of the evaporated gas does not directly contact the surface of the cooling plates of the cooling ring 30, but is cooled by heat exchange. The cooled and condensed products fall naturally into the collection chamber 40 in the form of particles.

[0054] This application employs a cooling ring to cool the mixed gas, which reduces the adhesion and agglomeration of cooling products on the cooling plate. During the cooling process, high-pressure inert gas is also introduced into the gas channel of the cooling ring. The precursor particles collide with each other under the influence of the high-pressure inert gas, causing the precursor particles that are stuck together during rapid cooling to disintegrate on their own, thus facilitating the obtaining of precursor particles with rounded and smooth surfaces.

[0055] In some embodiments, the silicon-oxygen raw material is SiO2.

[0056] In some embodiments, the silicon-oxygen raw material further includes a doped metal M, which is selected from at least one of elemental metals and metal oxides.

[0057] In some embodiments, the dopant metal M is selected from at least one of Li, Mg, Cu, Ni, Fe, Cr and Zn.

[0058] In some embodiments, the mass ratio of the doped metal M to the total mass of silicon dioxide and silicon powder is 1:(5~99), specifically 1:5, 1:6, 1:7, 1:8, 1:10, 1:15, 1:20, 1:25, 1:30, 1:50, 1:60, 1:70, 1:80, 1:90 or 1:99, etc. Of course, other values ​​within the above range are also possible, and are not limited here.

[0059] S200 raises the temperature of the two chambers to 1300℃~1600℃, and the gas is quickly discharged into the cooling ring for deposition to obtain an intermediate. The temperature of the cooling ring is controlled to be -25℃~15℃.

[0060] In some embodiments, the heating process temperature can be 1300°C, 1400°C, 1500°C, 1550°C, 1575°C, or 1600°C. It is understood that the above temperatures are not limited to the listed values, and other unlisted values ​​within this range also apply.

[0061] In the above technical solution, ensuring that steam is generated in both chambers helps to accelerate the steam generation efficiency. The rapid convection and mixing of the gas before deposition helps to improve the uniformity of the deposition.

[0062] In some embodiments, the coolant used in the cooling ring is a mixture containing one or more of the following: silicone oil, ethylene glycol, isopropanol, water, ethanol, and kerosene.

[0063] In some embodiments, the operating temperature of the cooling ring is -25℃ to 15℃, specifically -25℃, -20℃, -15℃, -5℃, 5℃, 10℃ or 15℃, etc., and of course, other values ​​within the above range are also possible, which are not limited here.

[0064] Step S300: Introduce an inert gas to perform shaping and modification on the intermediate to obtain a precursor.

[0065] During the cooling process, a high-pressure inert gas is also introduced into the gas channel of the cooling ring. The intermediate particles collide with each other under the drive of the high-pressure inert gas, causing the agglomerated intermediate particles generated during the rapid cooling process to dissociate themselves, which is beneficial to obtaining precursor particles with a smooth and round surface.

[0066] In some embodiments, the pressure of the inert gas is 0.1 MPa to 2 MPa. Specifically, it can be 0.1 MPa, 0.5 MPa, 0.8 MPa, 1.0 MPa, 1.2 MPa, 1.5 MPa, 1.8 MPa or 2 MPa, etc. Of course, it can also be other values within the above range, which are not limited herein.

[0067] In some embodiments, the introduction time of the inert gas is 0.5 h to 8 h. Specifically, it can be 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 4 h, 5 h, 6 h, 7 h or 8 h, etc. Of course, it can also be other values within the above range, which are not limited herein.

[0068] Step S400: Perform carbon coating treatment on the precursor to obtain the negative electrode material.

[0069] It can be understood that in the technical solution of doping metal M, during the carbon coating process, the metal M element reacts with the silicon oxide to obtain the oxygen released by the silicon oxide and generate SiO y and the silicate of metal M, where 0 < y < 1. Thereby, the initial Coulomb efficiency of the negative electrode material can be improved.

[0070] In one embodiment, the carbon coating treatment is specifically at least one of solid-phase carbon coating, liquid-phase carbon coating and gas-phase carbon coating.

[0071] Specifically, the steps of the carbon coating treatment specifically include: heating the active material obtained by the cooling treatment, introducing a protective gas and a carbon source gas, and performing carbon coating with the carbon source gas to obtain the negative electrode material.

[0072] In some embodiments, the carbon source gas used for gas-phase carbon coating includes hydrocarbons.

[0073] In some embodiments, the carbon source gas includes at least one of methane, acetylene, ethylene, ethane, propane, propylene, propyne, acetone and benzene.

[0074] In some embodiments, the chemical vapor deposition apparatus includes at least one of a rotary chemical vapor deposition reactor, a plasma-enhanced chemical vapor deposition reactor, a chemical vapor deposition tube furnace, and a fluidized bed. Specifically, the chemical vapor deposition apparatus is at least one of a rotary furnace and a box furnace.

[0075] In some embodiments, the carbon coating temperature is 600℃~1100℃, specifically 600℃, 700℃, 800℃, 900℃, 1000℃, 1050℃ or 1100℃, etc., and of course other values ​​within the above range are also possible, which are not limited here.

[0076] In some embodiments, the carbon coating time is 2h-20h, specifically 2h, 3h, 4h, 6h, 8h, 10h, 12h, 15h, 18h or 20h, etc., and of course other values ​​within the above range are also possible, which are not limited here.

[0077] In some implementations, a carbon source gas is introduced under a protective gas atmosphere.

[0078] In some embodiments, the protective gas includes at least one of nitrogen, helium, neon, argon, krypton, and xenon.

[0079] Furthermore, the method also includes: screening and demagnetizing the carbonized material to obtain the negative electrode material.

[0080] In some embodiments, the screening method is any one of a fixed screen, drum screen, resonant screen, roller screen, vibrating screen, and chain screen, and the screening mesh is 100 to 500 mesh. Specifically, the screening mesh can be 100 mesh, 200 mesh, 250 mesh, 325 mesh, 400 mesh, 500 mesh, etc. Preferably, the screening mesh is 250 mesh. Controlling the median particle size of the negative electrode material within the above range is beneficial to improving the processing performance of the negative electrode material.

[0081] In some implementations, the demagnetizing equipment is any one of a permanent magnet drum magnetic separator, an electromagnetic iron remover, and a pulsed high-gradient magnetic separator. Demagnetization is to ultimately control the magnetic content of the negative electrode material, thereby avoiding the impact of magnetic materials on the discharge effect of the lithium-ion battery and the safety of the battery during use.

[0082] Thirdly, embodiments of the present invention also provide a battery. Figure 2 This is a schematic diagram of the discharge state of the battery provided in the embodiments of this application, such as... Figure 2As shown, 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.

[0083] 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.

[0084] In some embodiments, the positive electrode 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 electrode active layer 102 contains a positive electrode active material, which includes compounds that can reversibly insert and deintercalate metal ions.

[0085] 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.

[0086] 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).

[0087] 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.

[0088] In some embodiments, the negative electrode current collector 201 may 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.

[0089] The battery provided in this application 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-state electrolyte battery, etc., and is not limited thereto.

[0090] The embodiments of the present invention will be further described below with reference to several examples.

[0091] Test method: 1) Test method for the theoretical specific surface area of ​​negative electrode materials: The anode material was tested using a QICPIC(M3) sphericity analyzer manufactured by SYMPA TEC. Particle size distribution and sphericity distribution data were obtained. Frequency distribution data were then derived from the particle size distribution data, with particle sizes ranging from 0.44 μm to 38.35 μm. Particle size D1~D n Based on the sphericity distribution data, particle sizes ranging from 0.44 μm to 38.35 μm were obtained, resulting in particle sizes D1~D2. n and sphericity Q1~Q n D1~D n Similar to the data in the particle size distribution map, particle size, sphericity, and frequency distribution with a frequency distribution of 0 are discarded as invalid data. For example... Figure 4b Frequency distribution data for medium particle sizes Dn of 0.44 μm and 38.35 μm Since the value is 0 and there is no corresponding sphericity data, it is invalid data. Therefore, the number of valid data sample groups n is 17. ρ is the true density of the negative electrode material measured using the gas volumetric method. In the sphericity distribution data plot, Q n D n Sphericity data of particles corresponding to particle size; In the particle size distribution data map, D n Frequency distribution data of particles corresponding to particle size. , where n is the number of valid data sample groups measured by the sphericity analyzer.

[0092] The test conditions and parameters in the aforementioned test were set as follows: Sample retention tank configuration: 0.1mm / 0.2mm Measurement range configuration: 0.6μm~375μm; Sample dispersant: water; Auxiliary dispersant: ethanol; Dispersion method: Stir and disperse, then sonicate externally for 3 minutes; Test cycle: 2 times; Test duration: 60 seconds per test; Sample test snap count: 3; Pump speed: 200 rpm; Mixer speed: 500 rpm; Photo frequency: 100Hz.

[0093] 2) Test method for the measured specific surface area of ​​negative electrode materials: According to GB / T 19587-2017 "Determination of Specific Surface Area of ​​Solid Substances by Gas Adsorption BET Method", the specific operating steps are as follows: Weigh a certain amount of negative electrode material sample and place it into a special bubble tube for specific surface area analysis. Degas the bubble tube containing the negative electrode material using nitrogen at 300℃ in a degassing station. After degassing, cool it to room temperature. Weigh the actual mass of the negative electrode material sample. Then, install the special bubble tube containing the negative electrode material sample into a specific surface area and pore size analyzer (e.g., any one of Micromeritics TriStar 3000, Micromeritics TriStar 3020, or Micromeritics TriStar 3030). Input the actual mass of the negative electrode material sample and begin measuring the specific surface area of ​​the negative electrode material with an opening pore size greater than or equal to 2 nm. The sampling range is 0.05 g / cm³. 3 ~0.3g / cm 3 Take a point every 0.05cm.

[0094] 3) Particle size of the negative electrode material: The particle size distribution test method is based on GB / T 19077-2016. It can be conveniently determined using a laser particle size analyzer, such as the Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK. The cumulative volumetric particle size distribution is obtained from the test.

[0095] 4) Testing the mass content of carbon in the negative electrode material: The carbon content was measured according to Appendix A of GB / T 38823-2020, "Test Method for Carbon Content". An infrared carbon-sulfur analyzer was used for measurement.

[0096] 5) Testing the mass content of oxygen in the negative electrode material: The oxygen content was tested using an oxygen, nitrogen, and hydrogen analyzer.

[0097] 6) Test method for complete dissolution of negative electrode materials: 0.100g of the negative electrode material was placed in a clean platinum crucible and then calcined in a muffle furnace under air atmosphere at 750°C for 4 hours until the carbon elements were completely burned off. The cooled residue was then reacted thoroughly with a mixture of 4mL HNO3 and 6mL HF. The platinum crucible containing this solution was then placed on a 350°C hot plate until the hydrofluoric acid evaporated without emitting white smoke. 6mL of concentrated HCl was then added, and the mixture was heated until the residue was completely dissolved and diluted to a 100mL plastic volumetric flask. Finally, the mass content of Fe, Cr, and Cu elements in the material was determined using an ICP spectrometer (Agilent 5800VDV ICP-OES).

[0098] 7) True density testing method for negative electrode materials: The true density of the negative electrode material was measured using the gas volumetric method.

[0099] 8) pH test of negative electrode material: Take 10 g of negative electrode material, add 10 g of water, stir for 30 min, and measure the pH value of the solid-liquid separated liquid.

[0100] 9) Oil absorption value The test was conducted according to GB / T 3780.2-2017 "Carbon Black Part 2: Determination of Oil Absorption Value". A 40g sample was placed in a mixing chamber, and linseed oil was dripped onto the sample at a constant rate while simultaneously agitated by two motor-driven rotary blades. As the sample absorbed more linseed oil, the mixture changed from a free-flowing state to a semi-plastic agglomerate. During this process, the viscosity of the mixture gradually increased and reached a peak. The measurement endpoint was the amount of linseed oil added when the torque generated by the change in viscosity characteristics reached a set value or a constant percentage of the maximum torque obtained from the torque curve. The oil absorption value (mL / 100g) of the sample was calculated. The testing equipment was an ASAHI S-500 oil absorption value tester manufactured by ASAHISOUKEN, Japan.

[0101] 10) Button cell battery test The prepared negative electrode material, conductive carbon black, and polyacrylic acid binder were dissolved in a solvent at a mass ratio of 75:15:10 and mixed. The mixture was then coated onto a copper foil current collector and vacuum dried to obtain the negative electrode sheet. A lithium metal sheet was used as the counter electrode, and the cells were assembled into a coin cell in an argon-filled glove box. Charge-discharge tests were conducted at a current density of 0.1C, within a charge-discharge range of 0.01-1.5V.

[0102] 11) Electrochemical performance testing The prepared negative electrode material was mixed with graphite (artificial graphite S360 series) at a ratio of 10:90, and then mixed with sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR) binder, Super-P conductive agent, and KS-6 conductive agent at a mass ratio of 92:2:2:4 to form a slurry. The slurry was coated on copper foil and then vacuum dried and rolled to prepare a negative electrode sheet. The counter electrode was a lithium sheet. A 1 mol / L LiPF6 / ethylene carbonate + dimethyl carbonate + methyl ethyl carbonate (v / v=1:1:1) electrolyte and a Celgard 2400 separator were assembled into a coin cell.

[0103] Cyclic performance testing employed a constant current charge-discharge experiment at 30mA, with the charge-discharge voltage limited to 0–1.5V. The LAND battery testing system from Wuhan Jinno Electronics Co., Ltd. was used for testing. At room temperature, the coin cells were cycled once each at 0.1C, 0.2C, and 0.5C, followed by 47 cycles at 1C. The 50-cycle capacity retention rate was obtained by dividing the capacity at week 50 by the capacity at week 1. The 0.1C capacity divided by the 1C capacity was used to evaluate the product's rate performance.

[0104] The negative electrode materials prepared in each embodiment and comparative example were used as negative electrode precursors. The mass ratio of precursor, conductive agent (Super-P), and binder (CMC+SBR) in the electrode coating was 92:4:4. The counter electrode was a lithium sheet. Coin cells were assembled using a 1 mol / L LiPF6 / EC+DMC+EMC (v / v = 1:1:1) electrolyte and a Celgard 2400 separator. The first charge-discharge cycle of these cells was conducted, with the charge-discharge regime being... Charging: 0.1C to 10mV CC, 0.02C to 5mV CC; Discharging: 0.1C to 1.5V CC.

[0105] The embodiments of this application will be further described below with reference to several examples. However, the embodiments of this application are not limited to the specific embodiments described below. Appropriate modifications can be made within the scope of the main claims.

[0106] Example 1 A method for preparing a negative electrode material includes the following steps: (1) Take a mixture of silicon and silicon dioxide and place it in a vacuum furnace. The vacuum furnace has a high-temperature chamber and a low-temperature chamber. The high-temperature chamber and the low-temperature chamber are connected by a gas guide pipe that can be closed and isolated. The gas guide pipe is also connected to the inlet of the cooling ring to blow the gas vertically to the low-temperature cooling ring. The cooling ring is cooled by coolant. Evacuate to a vacuum degree of less than 20 Pa and heat to 1450 °C to form vapor. The vaporized atomic clusters are guided through the gas guide pipe to be blown into the inlet of the cooling ring. The temperature of the cooling ring is -10 °C. After the reaction is completed, cut off the vacuum pump and isolate the gas guide pipe. High-pressure inert gas is introduced with a gas source pressure of 1.3 MPa. The intermediate particles in the cooling chamber collide with each other under the action of the high-pressure inert gas, so that the intermediate particles in the sticky state generated during the rapid cooling process are dissociated by themselves. After introducing inert gas for 2.5 h, the inert gas is turned off. After standing for 4 h, the cooling chamber is opened to take out the material and the precursor particles with round and smooth surfaces are obtained.

[0107] (2) The precursor was carbon coated at 950°C for 4 hours using CVD method. The gaseous carbon source was methane and the carrier gas was nitrogen to obtain the negative electrode material.

[0108] Figure 3a This is a sphericity distribution data diagram of the negative electrode material prepared in Example 1 of this application. Figure 3b This is a table showing the sphericity distribution data of the negative electrode material obtained in Example 1 of this application. Figure 4a This is a particle size distribution data diagram of the negative electrode material prepared in Example 1 of this application. Figure 4b This is a table showing the particle size distribution data of the negative electrode material prepared in Example 1 of this application. According to... Figures 3a to 4b The calculated deviation H of the specific surface area of ​​the negative electrode material is 15.79.

[0109] According to the preparation steps of Example 1, Examples 2 to 15 were prepared, and the specific process parameters of each example are shown in Table 1.

[0110] Comparative Example 1 The difference from Example 1 is that the time for introducing high-pressure inert gas is changed to 12 hours, while the rest remains the same.

[0111] Comparative Example 2 The difference from Example 1 is that the cooling ring temperature is 25°C and the carbon source gas used for carbon coating is kerosene vapor.

[0112] Comparative Example 3 The difference from Example 1 is that, (1) Take a mixture of silicon and silicon dioxide and place it in a vacuum furnace. The vacuum furnace has a high-temperature chamber and a low-temperature chamber. The high-temperature chamber and the low-temperature chamber are connected by a gas guide pipe that can be closed and isolated. The gas guide pipe is also connected to a cooling plate, which is cooled by a coolant. Evacuate the vacuum to a vacuum degree of less than 20 Pa and heat it to 1450 °C to vaporize it. The vaporized atomic clusters are guided by the gas guide pipe to blow the gas vertically to the low-temperature cooling plate. The temperature of the cooling plate is -10 °C. After the reaction is completed, cut off the vacuum pump and isolate the gas guide pipe. After cooling for 4 hours, open the cooling chamber to take out the material and obtain the precursor particles.

[0113] Table 1. Preparation process parameters of negative electrode materials The negative electrode materials prepared in the examples and comparative examples were subjected to various performance tests, and the results of the above performance tests are shown in Tables 2 and 3.

[0114] Table 2. Summary of Performance Test Results Table 3. Summary of Performance Test Results The anode material of this application controls the theoretical specific surface area to satisfy 0.5 < H ≤ 45, so that the actual measured specific surface area can be closer to the theoretical specific surface area, reducing surface defects of the anode material, enabling the surface of the anode material to form a stable solid-liquid reaction interface, reducing the occurrence of side reactions between the anode material and the electrolyte, improving the capacity and initial coulombic efficiency of the anode material, and improving the capacity decay of the anode material.

[0115] According to the test data of Examples 1 to 3, whether the raw material is doped with metal or not, as long as the H value is controlled within the above range, the negative electrode material has good capacity and first coulombic efficiency.

[0116] Based on the test data from Examples 1 and 4, it can be seen that increasing the heating temperature leads to excessively rapid vapor evaporation, causing the gas to be quickly discharged into the cooling ring for deposition. This reduces the smoothness of the precursor particle surface, resulting in an increase in the ratio of the theoretical specific surface area to the actual specific surface area of ​​the carbon-coated anode material. Compared to Example 1, the surface defects of the anode material particles increase, side reactions increase, and the capacity and initial coulombic efficiency of the anode material decrease slightly compared to Example 1. The cycle retention rate and rate performance also decrease slightly compared to the examples.

[0117] According to the test data of Examples 1 and 5-8, by changing the temperature of the cooling ring and the pressure of the inert gas, as long as the temperature of the cooling ring and the pressure of the gas source are controlled within a suitable range, the specific surface deviation of the negative electrode material can also be controlled within a suitable range. However, the test data shows that the temperature of the cooling ring has a significant impact on the specific surface deviation of the particles.

[0118] According to the test data of Examples 6 and 9-12, the longer the inert gas is introduced, the smoother and more rounded the particle surface becomes, and the specific surface deviation gradually decreases.

[0119] According to the test data of Examples 1 and 13-15, the increase of carbon coating time or temperature has little effect on the specific surface deviation of the negative electrode material. This may be because the coating amount of carbon coating layer is not much different. The main factor affecting the specific surface deviation is the smoothness and roundness of the particle surface of the core silicon-based material.

[0120] Compared to Example 1, Comparative Example 1 involved an excessively long inert gas introduction time. This resulted in overly smooth and rounded precursor particle surfaces, leading to a denser and more uniform carbon layer after coating. Consequently, the specific surface area deviation of the anode material was too low, resulting in fewer surface defects. This made it more difficult for lithium ions to penetrate the carbon coating layer on the silicon-based material, leading to insufficient capacity utilization and deteriorated rate performance. Because it was more difficult for lithium ions to penetrate the carbon coating layer on the silicon-based material, the lithium intercalation depth of the battery prepared with the anode material fluctuated more during each cycle, affecting the stability of the solid-liquid reaction interface of the anode material and causing deterioration in cycle performance.

[0121] Compared to Example 1, Comparative Example 2 has an excessively high cooling ring temperature, which prevents the precursor vapor from quickly condensing into dense solid particles with closed edge structures. Instead, a loose structure is formed by a slow accumulation process. This type of loose structure is more fragile and more easily broken by inert gas, resulting in a large number of open holes and uneven structures. This leads to an increase in surface defects of the carbon layer after carbon coating, an increase in side reactions during charging and discharging, excessive consumption of lithium ions, and thickening of the SEI film, resulting in a significant decrease in both capacity and cycle performance.

[0122] Compared to Example 1, Comparative Example 3 did not use a cooling ring to cool the vapor. The precursor vapor was directly blown onto the cooling plate, causing the precursor to quickly agglomerate and fail to form a dense, small-particle structure. The condensed lumps continuously adsorbed newly condensed precursors through surface adsorption, thus generating loose, large-lump materials. These materials have a large number of pore structures and surface defects. Therefore, the specific surface area deviation of the prepared negative electrode material is too high, and there are too many defects on the surface of the negative electrode material particles, which in turn form more reactive sites. During charging and discharging, a large number of side reactions occur, leading to excessive consumption of lithium ions, thickening of the SEI film, and failure to fully utilize the capacity. The first-efficiency and cycle retention rate of the negative electrode material are significantly lower than those of Example 1.

[0123] Although this application discloses preferred embodiments as described above, it is not intended to limit the claims. Any person skilled in the art can make several possible changes and modifications without departing from the concept of this application. Therefore, the scope of protection of this application should be determined by the scope defined in the claims of this application.

Claims

1. A negative electrode material, characterized in that, The negative electrode material includes silicon-based material and carbon material, with at least a portion of the carbon material located on the surface of the silicon-based material; The specific surface area deviation of the negative electrode material is H. 0.5 < H ≤ 45 A is the theoretical specific surface area of ​​the negative electrode material, and B is the measured specific surface area of ​​the negative electrode material obtained by the BET method; wherein, the theoretical specific surface area A is measured in the following way: The anode material was tested using a sphericity meter, and the particle size distribution data and sphericity distribution data were obtained. Frequency distribution data were then obtained from the particle size distribution data. Particle size D n The particle size D is obtained from the sphericity distribution data map. n and sphericity Q n ; , To determine the true density of the negative electrode material using the gas volumetric method, In the sphericity distribution data plot, Q n D n Sphericity data of particles corresponding to particle size; In the particle size distribution data map, D n Frequency distribution data of particles corresponding to particle size. n is the number of valid data sample groups measured by the sphericity meter.

2. The negative electrode material according to claim 1, characterized in that, The silicon-based material includes silicon oxide and a compound of metal element M, wherein the metal element M is selected from at least one of Li, Mg, Cu, Ni, Fe, Cr and Zn.

3. The negative electrode material according to claim 2, characterized in that, The compound of the metal element M includes at least one of the silicates of the metal element M and the oxides of the metal element M.

4. The negative electrode material according to claim 1, characterized in that, The silicon-based material comprises silicon and oxygen, wherein the atomic ratio of oxygen to silicon in the negative electrode material is x, where 0 < x < 2.2; and / or, the silicon-based material comprises silicon oxide, wherein the general formula of the silicon oxide is... , 0 < x ≤ 2.

5. The negative electrode material according to claim 1, characterized in that, The carbon material includes at least one of amorphous carbon, graphitized carbon, graphite, graphene, carbon nanotubes, and carbon fibers.

6. The negative electrode material according to claim 1, characterized in that, The oil absorption value of the negative electrode material is 35 mL / 100g to 65 mL / 100g.

7. The negative electrode material according to claim 2, characterized in that, The metallic element includes at least one of Fe, Cr, and Cu, and satisfies at least one of the following characteristics: (1) The mass content of Fe element in the negative electrode material is ≤400ppm; (2) The mass content of Cr element in the negative electrode material is ≤200ppm; (3) The mass content of Cu element in the negative electrode material is ≤200ppm.

8. The negative electrode material according to any one of claims 1 to 7, characterized in that, The particle size of the negative electrode material satisfies: D 20 -D 10 ≤4μm, D 90 -D 80 ≤8μm.

9. The negative electrode material according to any one of claims 1 to 7, characterized in that, The negative electrode material satisfies at least one of the following characteristics: (1) The theoretical specific surface area of ​​the negative electrode material is 0.01 m². 2 / g ~12m 2 / g; (2) The measured specific surface area of ​​the negative electrode material is 0.5 m². 2 / g ~30m 2 / g; (3) The pH of the negative electrode material is 5~12; (4) The true density ρ of the negative electrode material is 2.0 g / cm³. 3 ~3.4g / cm 3 .

10. A battery, characterized in that, Includes the negative electrode material as described in any one of claims 1 to 9.

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