Silicon-carbon particle, negative electrode sheet, and battery

Abstract

The present disclosure relates to the technical field of batteries, and specifically relates to a silicon-carbon particle, a negative electrode sheet, and a battery. The present disclosure provides a silicon-carbon particle. The surface of the silicon-carbon particle is provided with a recessed portion; the number N of recessed portions on the surface of the silicon-carbon particle is greater than or equal to 1; and the diameter of the recessed portions ranges from 0.05 μm to 5 μm; and the depth of the recessed portions ranges from 10 nm to 5 μm. In the present disclosure, recessed portions are provided on the surface of the silicon-carbon particle, so that the cycling stability and the expansion performance of a silicon-based negative electrode material are improved.

Description

Silicon-carbon particles, negative electrode and battery Technical Field

[0001] This disclosure relates to the field of battery technology, specifically to a silicon-carbon particle, a negative electrode, and a battery.

[0002] Background of the Invention

[0003] With the rapid growth in demand from consumer electronics, electric vehicles, and energy storage power stations, traditional graphite materials as battery anodes are no longer sufficient to meet the ever-increasing energy density requirements of lithium-ion batteries. Against this backdrop, employing silicon-based anode materials with higher theoretical lithium storage capacity has become an important approach to further improve the energy density of lithium-ion batteries.

[0004] However, existing silicon-based anode materials suffer from high particle volume expansion and severe surface side reactions during cycling. This leads to the repeated formation of an outer surface reaction (SEI) film during cycling, resulting in an excessively thick SEI film that rapidly consumes active lithium ions, accelerates battery cycle degradation, and affects battery lifespan. Furthermore, the repeatedly formed SEI film on the surface of existing silicon-based anode materials during cycling can detach, causing the silicon anode material to break away from the established conductive network and lose its electrochemical activity. The exposed fresh silicon anode material surface continues to undergo side reactions, forming new SEI films, ultimately significantly reducing the cycle stability and expansion performance of lithium-ion batteries. Summary of the Invention

[0005] The purpose of this disclosure is to overcome the aforementioned problems in the prior art and to provide silicon-carbon particles, anode sheets, and batteries. The silicon-based particles provided in this disclosure have recesses on their surface. Through this structural design, the cycle stability and expansion performance of the battery as a silicon-based anode material can be improved.

[0006] The first aspect of this disclosure provides silicon carbide particles, the surface of which has a recessed portion;

[0007] The number of depressions on the surface of the silicon-carbon particles, N ≥ 1;

[0008] The diameter of the recessed portion is 0.05μm-5μm;

[0009] The depth of the recess is 10nm-5μm.

[0010] A second aspect of this disclosure provides a method for preparing the silicon-carbon particles described in the first aspect of this disclosure, the method comprising:

[0011] A porous carbon substrate is surface treated by immersing it in a potassium hydroxide solution. Then, the surface-treated porous carbon substrate is placed in a vapor deposition furnace, argon gas is introduced and the temperature is raised to 800℃-1200℃, creating depressions on the surface of the porous carbon substrate. Finally, silicon source gas is introduced to deposit nano-silicon in the pores of the porous carbon substrate.

[0012] And / or, a porous carbon matrix is ​​placed in a gas-phase fluidized bed device for surface fluidization collision treatment, in which depressions are generated on the surface of the porous carbon matrix. Then, the material that has undergone the surface fluidization collision treatment is placed in a gas-phase deposition furnace and silicon source gas is introduced to deposit nano-silicon in the pores of the porous carbon matrix.

[0013] And / or, a porous carbon matrix is ​​placed in a ball mill for ball milling surface modification treatment, in which depressions are generated on the surface of the porous carbon matrix. Then, the material that has undergone ball milling surface modification treatment is placed in a vapor deposition furnace and silicon source gas is introduced to deposit nano-silicon in the pores of the porous carbon matrix.

[0014] A third aspect of this disclosure provides a negative electrode sheet comprising the silicon-carbon particles described in the first aspect of this disclosure and / or the silicon-carbon particles prepared by the method described in the second aspect of this disclosure; the negative electrode sheet comprises a negative electrode active coating comprising the silicon-carbon particles; the ratio N of the number of depressions on the surface of the silicon-carbon particles to the elemental silicon content C% in the negative electrode active coating is N / C, which is 0.04-10; and / or, C% is 3%-70%.

[0015] This disclosure provides a battery in a fourth aspect, comprising a negative electrode and an electrolyte, wherein the negative electrode is the negative electrode described in the third aspect of this disclosure; the electrolyte includes a fluorinated additive, wherein the fluorinated additive includes at least one of fluoroethylene carbonate, LiBF4, LiCF3SO3, Li(CF3SO2)2N, LiPO2F2 and LiDFOB.

[0016] Compared with the prior art, the present disclosure has at least the following advantages through the above technical solution:

[0017] This disclosure provides two advantages: first, by creating recesses on the surface of silicon-carbon particles, it can increase the reaction area and reaction sites on the surface of silicon-carbon particles, thereby improving the adhesion and stability between silicon-carbon particles and the surface SEI film; second, it can provide expansion buffer space for silicon-carbon anode materials, improving the expansion performance of the anode, thus greatly improving the cycle stability and expansion performance of silicon-based anode materials.

[0018] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. Attached Figure Description

[0019] Figure 1 shows a SEM image of the outer surface of silicon-carbon particles in an example of this disclosure.

[0020] Figure 2 shows a SEM image of the outer surface of silicon-carbon particles in an example of this disclosure.

[0021] Figure 3 shows a cross-sectional SEM image of silicon-carbon particles in an example of this disclosure.

[0022] Figure 4 shows a cross-sectional SEM image of silicon-carbon particles in an example of this disclosure. Detailed Implementation

[0023] The following provides a detailed description of specific embodiments of this disclosure. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit this disclosure.

[0024] The first aspect of this disclosure provides silicon carbide particles, the surface of which has a recessed portion;

[0025] The number N of the depressions on the surface of the silicon-carbon particles is ≥1, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, or 30; the diameter of the depressions is 0.05μm-5μm, for example, 0.05μm, 0.06μm, 0.07μm, 0.08μm, 0.09μm, 0.1μm, 0.2μm, 0.3μm, 0.4μm, 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1μm, 1.1μm, 1.2μm, 1.3μm. The depth of the recessed portion is 10nm-5μm, for example, 10nm, 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 200nm, 300nm, 400nm, 500nm, 600nm, 70nm, 80nm, 90nm, 100nm, 200nm, 300nm, 400nm, 500nm, 600nm, 700nm, 800nm, 900nm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, or 5μm.

[0026] In this disclosure, the statement that the average number of depressions N on the surface of each silicon-carbon particle is ≥1 means that the average number of depressions on the surface of each silicon-carbon particle is ≥1, and does not mean that the surface of all silicon-carbon particles has depressions. The method for testing the number of depressions on the surface of silicon carbide particles can be obtained by counting after observing the SEM image of the silicon carbide particles. Specifically, the silicon carbide powder is first ultrasonicated, and then a portion of the powder is adhered to the SEM stage. Then, the SEM electron microscope is used for testing. After obtaining the SEM image, a fully observable spherical particle (referring to a spherical silicon carbide particle whose shape and structure are complete and easy to observe) is selected. The total number of observable surface depressions is multiplied by 2 (×2 is because the SEM image can only observe the front of the spherical silicon carbide particle. The number of depressions on the back is not directly observable, so it is assumed that the number of depressions on the back is the same as the number of depressions on the front. Therefore, the total number of observable surface depressions is multiplied by 2 to represent the total number of depressions on the surface of the entire silicon carbide particle). This number is then divided by the number of observed particles to obtain the average number of depressions N on the surface of each silicon carbide particle. This number N needs to be ≥1, where N is an integer and is rounded to the nearest integer. Furthermore, it should be noted that since SEM images can only observe the number of depressions on one side of the silicon carbide particle from a frontal view, and cannot accurately observe the number of depressions on the back side of the same silicon carbide particle, the number of depressions on the surface of the silicon carbide particle disclosed herein only represents the number of depressions on one side of the particle from a frontal view as measured by SEM. Among them, observable depressions located at the edge of one side of the particle from a frontal view are also included in the number of depressions of the silicon carbide particle.

[0027] This disclosure provides a recessed portion on the surface of silicon-carbon particles. On the one hand, the presence of the recessed portion exposes more surface area, increasing the reaction area and reaction sites on the surface of the silicon-carbon particles, improving the specific surface area and surface roughness of the silicon-carbon particles, thereby improving the adhesion and stability between the silicon-carbon particles and the surface SEI film. On the other hand, the recessed portion has an anchoring effect on the SEI film on the surface of the silicon-carbon particles, which can effectively increase the adhesion area between the surface of the silicon-carbon particles and the SEI film, thereby improving the problem of easy detachment of the SEI film on the surface of silicon-carbon particles, reducing the repeated generation of new SEI films, reducing the consumption of active lithium ions, thereby improving the electrochemical performance of lithium-ion batteries, and thus contributing to a significant improvement in the cycle stability and expansion performance of silicon-based anode materials.

[0028] Furthermore, since the recesses have an anchoring effect on the SEI film, the more recesses there are, the stronger the anchoring effect on the SEI film, and the more surface area of ​​the silicon-carbon anode material can be exposed by the recesses. Therefore, by controlling the number of recesses N≥1 on the surface of silicon-carbon particles, this disclosure can further improve the bonding area and anchoring strength between silicon-carbon particles and the SEI film, thereby improving the problem of SEI film detachment on the surface of silicon-carbon particles, reducing the repeated generation of new SEI films, thereby reducing the consumption of active lithium ions, and further improving the cycle stability and expansion performance of silicon-based anode materials.

[0029] Moreover, by controlling the number of average silicon-carbon particle surface depressions N≥1, the contact area between silicon-carbon particles and electrolyte can be increased, which is beneficial for electrolyte wetting and storage. In addition, it is also beneficial to improve the adhesion performance between silicon-carbon particles and binder, increase the adhesion force and adhesion strength between silicon-carbon particles, and help to further improve the structural stability and cycle stability of silicon-carbon anode materials.

[0030] In one example, the number N of the depressions on the surface of the average silicon-carbon particles is 4-20.

[0031] In this disclosure, the diameter of the recess is 0.05 μm-5 μm, and the depth of the recess is 10 nm-5 μm. Controlling the diameter of the recess within this range is beneficial to the film formation stability of the SEI film on the surface of the silicon-carbon particles and prevents SEI film detachment. If the diameter of the recess is >5 μm, the excessively large recess may cause severe damage to the surface of the silicon-carbon particles, easily leading to more severe breakage of the silicon-carbon particles after cycling, resulting in intensified side reactions in the electrolyte and reduced battery cycle stability. More seriously, if the broken silicon-carbon particles produce sharp edges, they may directly puncture the separator, posing a risk of internal short circuits in the battery. If the diameter of the recess is <0.05 μm, its anchoring effect on the SEI film will decrease, and the increased reaction surface area will also be reduced accordingly, failing to effectively improve the adhesion area and adhesion stability between the silicon-carbon particles and the SEI, and the improvement effect on the cycle stability and expansion performance of the silicon-carbon anode material will not be significant. Therefore, it is necessary to control the diameter of the recess within a suitable range.

[0032] In one example, the average diameter of the recess is 0.1 μm-2 μm.

[0033] Similarly, controlling the depth of the recess within this range is also beneficial to the stability of the SEI film on the surface of silicon-carbon particles and prevents the SEI film from detaching. Moreover, the deeper the recess, the more severe the damage to the surface of silicon-carbon particles will be. Therefore, it is necessary to control the depth of the recess within an appropriate range.

[0034] In one example, the average depth of the recess is 50 nm to 1 μm.

[0035] The diameter and depth of the depressions on the surface of the silicon carbide particles can also be determined by statistical analysis of SEM images of the silicon carbide particles. Specifically, the silicon carbide powder is first ultrasonicated, and then a portion of the powder is adhered to the SEM stage. The particles are then tested using an SEM electron microscope to obtain the SEM image. A fully observable spherical particle (referring to a spherical silicon carbide particle whose shape and structure are complete and easy to observe) is selected from the image. The diameter of several groups (generally 3-10 groups) of depressions with complete planar shapes on the particle surface is measured, and the average value is taken as the diameter of the depression on the surface of the silicon carbide particle. The depth of the observable depressions at the edge of the particle surface is also measured, and the average value is taken as the depth of the depression on the surface of the silicon carbide particle.

[0036] In this disclosure, the average particle size of the silicon-carbon particles is 4μm-18μm, for example, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, or 18μm. The method for testing the average particle size of the silicon-carbon particles is as follows: a battery using the silicon-carbon particles as the negative electrode active material is discharged from a fully charged state to empty state. The battery is disassembled, and the negative electrode sheet using the silicon-carbon particles as the negative electrode active material is removed. After rinsing in an electrolyte solvent, the negative electrode powder containing the silicon-carbon particles is obtained. The powder is then observed under a SEM electron microscope in backscatter mode. Thirty complete, light-colored silicon-carbon particles are randomly selected and their diameters are measured. The average value of all test results is then obtained as the average particle size of the silicon-carbon particles.

[0037] In one example, the average particle size of the silicon-carbon particles is 6 μm-15 μm.

[0038] In this disclosure, the median particle size Dv50 of the silicon carbon particles is 5μm-25μm, for example, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm or 16μm, 17μm, 18μm, 19μm, 20μm, 21μm, 22μm, 23μm, 24μm or 25μm. The median particle size Dv50 of the silicon carbon particles can be measured using a Malvern particle size analyzer. The testing procedure is as follows: disperse the silicon carbon particles in deionized water containing a dispersant (such as nonylphenol polyoxyethylene ether, content 0.02wt%-0.03wt%) to form a mixture. Sonicate the mixture for about 2 minutes, and then place it in a Malvern particle size analyzer for testing to obtain the median particle size Dv50 of the silicon carbon particles.

[0039] In one example, the median particle size Dv50 of the silicon-carbon particles is 8 μm-20 μm.

[0040] The smaller the average particle size of silicon-carbon particles, the larger the proportion of the surface area of ​​the depressions on the surface of the silicon-carbon particles to the total surface area of ​​the silicon-carbon particles. This results in greater surface roughness for individual silicon-carbon particles, which enhances the anchoring effect and increases the reaction sites. However, it also causes more severe surface damage. Therefore, the average particle size of silicon-carbon particles should not be too small. On the other hand, when the average particle size of silicon-carbon particles is large, the proportion of the surface area of ​​the depressions on the surface of the silicon-carbon particles to the total surface area of ​​the silicon-carbon particles is smaller. This reduces the surface roughness of individual silicon-carbon particles and weakens the anchoring effect. In the later stages of cycling, there is still a risk of the SEI film detaching from the surface of the silicon-carbon particles. Therefore, it is necessary to reasonably control the average particle size of silicon-carbon particles.

[0041] In the median particle size Dv50 of silicon-carbon particles, Dv50 refers to the particle size corresponding to a cumulative particle size distribution volume percentage of 50%. In other words, the volume percentage of particles larger than this value is 50%, and the volume percentage of particles smaller than this value is also 50%. Therefore, by controlling the median particle size Dv50 of silicon-carbon particles, the contact area between the silicon-carbon anode material and the electrolyte can be better controlled. This is beneficial for improving the wettability of the electrolyte to the anode active material and the electrolyte storage capacity of the anode active material. Furthermore, controlling the median particle size Dv50 also helps improve the adhesion performance between silicon-carbon particles and the binder, increasing the adhesion force and bonding strength between silicon-carbon particles, which contributes to further improving the structural stability and electrochemical performance of the silicon-carbon anode material.

[0042] In this disclosure, the average sphericity of the silicon-carbon particles is 0.5-1. For example, it is 0.5, 0.65, 0.75, 0.8, 0.85, 0.86, 0.87, 0.88, 0.89, 0.9, 0.95, 0.96, 0.97, 0.98, 0.99, or 1. The testing method for the average sphericity of the silicon-carbon particles in this disclosure may include the following steps: First, disassemble the lithium-ion battery, remove the negative electrode sheet, and soak and rinse it with dimethyl carbonate solvent to remove lithium salt and electrolyte solvent from the negative electrode sheet. After drying, obtain the cross-section of the negative electrode sheet by argon ion cutting. In the backscattered electron microscope mode, the silicon-carbon particles exhibit a brighter contrast, while the graphite particles are darker. Therefore, the sphericity can be determined using image processing software (such as Image Pro). Plus) The images of each bright particle in the SEM backscatter mode photograph of the negative electrode at a certain magnification (e.g., 2500x) are calculated to obtain the perimeter and area of ​​each silicon-carbon particle. The equivalent radius r1 of the perimeter and the equivalent radius r2 of the area of ​​each particle are calculated respectively. Then the sphericity of each particle is b = r2 / r1. The sphericity of each particle is then weighted and averaged to obtain the average sphericity of the silicon-carbon particles in the cross section of the negative electrode.

[0043] In one example, the average sphericity of the silicon-carbon particles is 0.85-1.

[0044] In this disclosure, the elemental silicon content, based on the total mass of the silicon-carbon particles, is 35%-80%, for example, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, or 80%. The mass content of elemental silicon in the silicon-carbon particles can be obtained through cross-sectional SEM-EDS analysis of the silicon-carbon particles. By maintaining the elemental silicon content in the silicon-carbon particles within the range of 35%-80%, the energy density of the battery can be improved by leveraging the high theoretical lithium storage capacity of silicon. Furthermore, it avoids the exacerbated volume expansion caused by excessive silicon content, further ensuring the structural stability of the silicon-carbon particles and the cycle stability of the battery.

[0045] In this disclosure, the silicon-carbon particles comprise a porous carbon matrix and nano-silicon dispersed within the pores of the porous carbon matrix. The nano-silicon has a grain size of 1 nm to 100 nm, for example, 1 nm, 3 nm, 5 nm, 6 nm, 8 nm, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, or 100 nm. Anode sheets and batteries employing the aforementioned specially structured silicon-carbon particles can better mitigate the volume change of silicon-carbon particles in the later stages of cycling, further improving the cycle performance and expansion performance of the battery.

[0046] Furthermore, after the silicon-carbon particles are subjected to a pressure of 377 MPa, the rate of change of their median particle size Dv50 is ≤15%, for example, 15%, 14%, 13%, 12%, 11%, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, or 0%. The rate of change of the median particle size Dv50 after the silicon-carbon particles are subjected to a pressure of 377 MPa refers to the ratio of the difference between the median particle size Dv50 before and after the pressure of 377 MPa to the median particle size Dv50 before the pressure of 377 MPa. In this disclosure, the specific steps for "the silicon carbide particles being subjected to a pressure of 377 MPa" are as follows: Take 1 g of silicon carbide particles (the median particle size Dv50 before being subjected to a pressure of 377 MPa is known), apply a pressure of 377 MPa using a powder compactor (e.g., a Sansi Zongheng 300kN microcomputer-controlled electronic powder compaction tester) and maintain the pressure for 30 s, then release the pressure and take out the powder, measure the median particle size Dv50 of the sampled silicon carbide particles after being subjected to a pressure of 377 MPa, and calculate the rate of change of the median particle size Dv50 using the aforementioned formula.

[0047] This disclosure allows for the selection of silicon-carbon particles with higher compressive strength by controlling the variation rate of the median particle size Dv50 of silicon-carbon particles to no more than 15%. This ensures that the silicon-carbon particles used as a negative electrode active material are not easily damaged after being rolled on the electrode sheet, thereby avoiding the decrease in structural stability of the silicon-carbon particle surface caused by the presence of recesses, and improving the structural stability and cycle performance of the silicon-carbon negative electrode material. Moreover, because of the high compressive strength of silicon-carbon particles, the compaction density of the negative electrode sheet containing the silicon-carbon negative electrode material can also be increased, thereby effectively improving the energy density of the lithium-ion battery.

[0048] In one instance, the median particle size Dv50 of the silicon-carbon particles changed by 2%–8% after being subjected to a pressure of 377 MPa.

[0049] In this disclosure, the sphericity change rate of the silicon-carbon particles after being subjected to a pressure of 377 MPa is ≤10%, for example, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, or 0%. The sphericity change rate of the silicon-carbon particles after being subjected to a pressure of 377 MPa refers to the ratio of the difference in sphericity before and after being subjected to the pressure to the sphericity before being subjected to the pressure. By controlling the sphericity change rate of the silicon-carbon particles to not exceed 10% after rolling, the silicon-carbon particles can maintain their original relatively regular spherical morphology after rolling, possessing a relatively stable structure, thereby increasing the compactness of the silicon-carbon particles and improving the density of the silicon-carbon anode material.

[0050] In one instance, the sphericity of the silicon-carbon particles changed by 1%–4% after being subjected to a pressure of 377 MPa.

[0051] The sphericity of silicon carbide particles represents their spherical state. The higher the sphericity, the closer the silicon carbide particles are to a sphere. The testing method is as follows: Using image processing software (such as Image Pro Plus), analyze the image of each particle in a SEM photograph of silicon carbide particles at a certain magnification (e.g., 2500x) to obtain the perimeter and area of ​​each particle. Calculate the equivalent radius r1 of the perimeter and the equivalent radius r2 of the area of ​​each particle. Then, the sphericity S of each particle is calculated as r2 / r1. The sphericity of each particle is then weighted and averaged to obtain the average sphericity of the silicon carbide particles. Finally, the average sphericity before and after being subjected to a pressure of 377 MPa is calculated to obtain the sphericity change rate (%) of the silicon carbide particles. The sphericity change rate (%) of silicon carbide particles is calculated as: (Average sphericity of silicon carbide particles before rolling - Average sphericity of silicon carbide particles after rolling) / Average sphericity of silicon carbide particles before rolling × 100%.

[0052] The second aspect of this disclosure provides a method for preparing the silicon-carbon particles described in the first aspect of this disclosure. The method includes: immersing a porous carbon matrix in a potassium hydroxide solution for surface treatment; then placing the surface-treated porous carbon matrix in a vapor deposition furnace, introducing argon gas and raising the temperature to 800°C-1200°C (e.g., 800°C, 900°C, 1000°C, 1100°C, or 1200°C), creating depressions on the surface of the porous carbon matrix; and finally introducing a silicon source gas to deposit nano-silicon within the pores of the porous carbon matrix.

[0053] Specifically, 30g of porous carbon is soaked in potassium hydroxide solution with a concentration of 0.8mol / L-2mol / L (e.g., 0.8mol / L, 0.9mol / L, 1mol / L, 1.1mol / L, 1.2mol / L, 1.3mol / L, 1.4mol / L, 1.5mol / L, 1.6mol / L, 1.7mol / L, 1.8mol / L, 1.9mol / L, or 2mol / L) for 6h-12h (e.g., 6h, 7h, 8h, 9h, 1...). After 0h, 11h, or 12h, the porous carbon is removed, washed, and dried. It is then placed in a vapor deposition furnace. Argon gas is first introduced, and the temperature is raised to 800-1200℃ (e.g., 800℃, 900℃, 1000℃, 1100℃, or 1200℃) and held for 2-5h (e.g., 2h, 3h, 4h, or 5h) to create surface pits. The furnace temperature is then controlled to 400-500℃ (e.g., 400℃, 410℃, 420℃, 430℃, 440℃, 450℃, 460℃, 470℃). 480℃, 490℃, or 500℃), followed by the introduction of silane gas at a flow rate of 100sccm-500sccm (e.g., 100sccm, 200sccm, 300sccm, 400sccm, or 500sccm) for 2h-8h (e.g., 2h, 3h, 4h, 5h, 6h, 7h, or 8h); after completion, the silane introduction is stopped, and the temperature is raised to 500℃-600℃ (e.g., 500℃, 510℃, 520℃, 530℃, 540℃, 550℃). An acetylene gas flow rate of 80 sccm-150 sccm (e.g., 80 sccm, 90 sccm, 100 sccm, 110 sccm, 120 sccm, 130 sccm, 140 sccm, or 150 sccm) is introduced at a temperature of 500℃, 560℃, 570℃, 580℃, 590℃, or 600℃. The acetylene cracking time is controlled at 0.5h-2h (e.g., 0.5h, 1h, 1.5h, or 2h). The acetylene is then stopped and the temperature is lowered to obtain silicon-carbon particles with depressions on the surface.

[0054] The second aspect of this disclosure provides a method for preparing the silicon-carbon particles described in the first aspect of this disclosure. The method includes: placing a porous carbon matrix into a gas-phase fluidized bed apparatus for surface fluidization collision treatment, thereby generating depressions on the surface of the porous carbon matrix; then placing the material that has undergone the surface fluidization collision treatment into a vapor deposition furnace and introducing silicon source gas to deposit nano-silicon within the pores of the porous carbon matrix.

[0055] Specifically, 60g of porous carbon is placed in a gas-phase fluidized bed apparatus and fluidized at high speed at room temperature for 1-5 hours (e.g., 1 hour, 2 hours, 3 hours, 4 hours, or 5 hours). After fluidization and collision, the surface of the particles develops depressions. 30g of the fluidized product is then placed in a CVD vapor deposition furnace. Argon gas is first introduced, and the temperature is raised to 400℃-500℃ (e.g., 400℃, 410℃, 420℃, 430℃, 440℃, 450℃, 460℃, 470℃, 480℃, 490℃, or 500℃). Subsequently, a flow rate of 100sccm-500sccm (e.g., 100sccm, 150sccm, 200sccm, 250sccm, 300sccm, 350sccm, 400sccm, 450sccm, or 500sccm) is introduced. Silicate gas is introduced for 2-8 hours (e.g., 2h, 3h, 4h, 5h, 6h, 7h, or 8h). After the silane is introduced, the silane is stopped, and the temperature is raised to 500℃-600℃ (e.g., 500℃, 510℃, 520℃, 530℃, 540℃, 550℃, 560℃, 570℃, 580℃, 590℃, or 600℃). Acetylene gas is introduced at a flow rate of 80sccm-150sccm (e.g., 80sccm, 90sccm, 100sccm, 110sccm, 120sccm, 130sccm, 140sccm, or 150sccm), and the acetylene cracking time is controlled to be 0.5h-2h (e.g., 0.5h, 1h, 1.5h, or 2h). The acetylene is then stopped and the temperature is lowered, which yields silicon-carbon particles with surface depressions.

[0056] The second aspect of this disclosure provides a method for preparing the silicon-carbon particles described in the first aspect of this disclosure. The method includes: placing a porous carbon matrix into a ball mill for ball milling surface modification treatment, thereby creating depressions on the surface of the porous carbon matrix; then placing the material that has undergone ball milling surface modification treatment into a vapor deposition furnace and introducing silicon source gas to deposit nano-silicon within the pores of the porous carbon matrix.

[0057] Specifically, 50g of porous carbon is placed in a ball mill for low-speed ball milling surface modification. The zirconia balls have a diameter of 1mm, the ball-to-material ratio is 1:25, the planetary ball mill speed is 10rpm-50rpm (e.g., 10rpm, 20rpm, 30rpm, 40rpm, or 50rpm), and the milling time is 20min-40min (e.g., 20min, 25min, 30min, 35min, or 40min). 30g of the ball-milled surface-modified product is then placed in a CVD vapor deposition furnace. Argon gas is first introduced and the temperature is raised to 400℃-500℃ (e.g., 400℃, 410℃, 420℃, 430℃, 440℃, 450℃, 460℃, 470℃, 480℃, 490℃, or 500℃). Subsequently, an argon gas flow rate of 100sccm-500sccm (e.g., 100sccm, 200sccm, 3 ... Introduce silane gas at 00 sccm, 400 sccm, or 500 sccm for 2-8 hours (e.g., 2h, 3h, 4h, 5h, 6h, 7h, or 8h); after this, stop introducing silane and raise the temperature to 500℃-600℃ (e.g., 500℃, 510℃, 520℃, 530℃, 540℃, 550℃, 560℃, 570℃, 580℃, 590℃, or 600℃), and then introduce... Acetylene gas with a flow rate of 80 sccm-150 sccm (e.g., 80 sccm, 90 sccm, 100 sccm, 110 sccm, 120 sccm, 130 sccm, 140 sccm or 150 sccm), and acetylene cracking time controlled at 0.5 h-2 h (e.g., 0.5 h, 1 h, 1.5 h or 2 h), followed by stopping the acetylene flow and cooling, can yield silicon-carbon particles with surface depressions.

[0058] In this invention, the method for preparing the silicon-carbon particles can be any one or more of the three methods described above.

[0059] A third aspect of this disclosure provides a negative electrode sheet comprising the silicon-carbon particles described in the first aspect of this disclosure and / or the silicon-carbon particles prepared by the method described in the second aspect of this disclosure. The negative electrode sheet includes a negative electrode active coating comprising the silicon-carbon particles. The ratio N / C of the average number N of the depressions on the surface of the silicon-carbon particles to the elemental silicon content C% in the negative electrode active coating is 0.04-10, for example, 0.04, 0.06, 0.08, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10. Furthermore, it should be noted that when substituting the elemental silicon content C% in the negative electrode active coating into the ratio N / C calculation, a dimensionless value is used, for example, C = 40, N = 20, and the ratio N / C = 0.5.

[0060] In one example, the ratio N / C of the average number of depressions N on the surface of each silicon-carbon particle to the elemental silicon content C% in the negative electrode active coating is 2-6.

[0061] In this disclosure, the elemental silicon content (C%) in the negative electrode active coating is 3%-70%, for example, 3%, 5%, 7%, 9%, 10%, 20%, 30%, 40%, 50%, 60%, or 70%. The elemental silicon content (C%) in the negative electrode active coating can be measured using inductively coupled plasma emission (ICP).

[0062] In one example, the elemental silicon content (C%) in the negative electrode active coating is 4%-50%.

[0063] The elemental silicon in the negative electrode active coating originates from silicon-carbon particles. If the silicon content (C) in the negative electrode active coating is too high, it indicates a large content of silicon-carbon particles, which can easily cause the negative electrode active coating to expand, and severe expansion can even lead to battery failure. By providing at least one recess on the surface of the silicon-carbon particles, the silicon content in the negative electrode active coating can be reduced accordingly. Therefore, when the ratio N / C of the average number of recesses on the surface of each silicon-carbon particle to the silicon content (C) in the negative electrode active coating is within a suitable range, it can ensure that the silicon content (C) in the negative electrode active coating is not excessive, thus suppressing negative electrode expansion and improving battery energy density. It can also avoid excessive defects on the surface of the silicon-carbon particles due to too many recesses, and prevent damage after multiple cycles. Furthermore, it can prevent the repeated formation of new SEI films on the surface of the negative electrode active coating, thereby improving battery cycle performance. Moreover, the recess structure provides expansion buffer space for the silicon-carbon negative electrode material, which is beneficial for improving the expansion performance of the negative electrode.

[0064] In one example, the negative electrode active coating further includes a carbon-based negative electrode material, which includes at least one of artificial graphite, natural graphite, mesophase carbon microspheres, hard carbon, and soft carbon.

[0065] In one example, the negative electrode active coating further includes a negative electrode conductive agent and a negative electrode binder, wherein the negative electrode conductive agent includes at least one of conductive carbon black (SuperP) and single-walled carbon nanotubes (SWCNTs), and the negative electrode binder includes at least one of sodium carboxymethyl cellulose (CMC-Na) and styrene-butadiene rubber.

[0066] In one example, based on the total weight of the negative electrode active coating, the weight content of the silicon-carbon particles is 2%-50% (e.g., 2%, 3%, 4%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or 50%), and the weight content of the carbon-based negative electrode material is 47%-97% (e.g., 47%, 48%, 49%, 50%, 55%, 60%, 65%, 7%). The negative electrode conductive agent has a weight content of 0.2%-3% (e.g., 0.2%, 0.3%, 0.4%, 0.5%, 1%, 1.5%, 2%, 2.5%, or 3%), and the negative electrode binder has a weight content of 0.5%-4% (e.g., 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, or 4%).

[0067] This disclosure provides a battery in a fourth aspect, the battery comprising a negative electrode and an electrolyte, wherein the negative electrode is the negative electrode described in the third aspect of this disclosure; the electrolyte comprises a fluorinated additive, the fluorinated additive comprising at least one selected from fluoroethylene carbonate, LiBF4, LiCF3SO3, Li(CF3SO2)2N, LiPO2F2, and LiDFOB. Silicon-carbon particles, as the silicon-carbon negative electrode material in the negative electrode active coating of the battery negative electrode, can effectively improve the cycle capacity retention rate and cycle expansion rate of the battery.

[0068] In this disclosure, the battery is fully charged and disassembled after 500 cycles at 25°C, with a charge / discharge cutoff voltage of 3.0V-4.53V, and under 1C charging and 1C discharging conditions. The average thickness of the SEI film on the surface of the silicon-carbon particles is 100nm-800nm, for example, 100, 200nm, 210nm, 220nm, 230nm, 240nm, 250nm, 300nm, 350nm, 400nm, 450nm, 500nm, 550nm, 600nm, 650nm, 700nm, 750nm, or 800nm. The average thickness of the SEI film on the surface of the silicon-carbon particles can be calculated by observing the cross-sectional SEM image of the silicon-carbon particles. Specifically, the negative electrode sheet in the battery after the above cycle is disassembled, and the powder of the negative electrode active layer of the negative electrode sheet is first ultrasonicated. After ultrasonication, some of the powder is adhered to the SEM stage and then tested using an SEM electron microscope. After obtaining the SEM image, the fully observable spherical particles in the image (referring to spherical silicon-carbon particles whose shape and structure are complete and easy to observe) are taken, and the SEI film thickness at different positions on their surface is measured. The average value is calculated, which is the average thickness of the SEI film on the surface of the silicon-carbon particles.

[0069] In one example, the average thickness of the SEI film on the surface of the silicon-carbon particles is 300 nm to 700 nm.

[0070] In this disclosure, the battery is fully charged and disassembled after 500 cycles at 25°C, with a charge / discharge cutoff voltage of 3.0V-4.53V, and a 1C charge / discharge condition. The fluorine content in the SEI film on the surface of the silicon-carbon particles is 1%-15%, for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, or 15%. The fluorine content in the SEI film on the surface of the silicon-carbon particles can be measured by EDS energy-dispersive X-ray spectroscopy. The source of the fluorine in the SEI film on the surface of the silicon-carbon particles is the fluorine-containing additive in the electrolyte. The presence of fluoride in the SEI film is beneficial for improving the stability of the SEI film in the electrolyte and the lithium-ion diffusion capacity during charge and discharge. Therefore, this disclosure can further enhance the improvement effect by controlling the fluoride content in the SEI film on the surface of silicon-carbon particles, thereby improving the stability of the SEI film in the electrolyte, preventing it from falling off from the silicon-carbon particles, and also improving the lithium-ion diffusion capacity during charge and discharge. This allows for the construction of a stable and highly conductive network, thereby improving the cycle stability and expansion performance of the lithium-ion battery.

[0071] In one example, the fluorine content in the SEI film on the surface of the silicon-carbon particles is 6%-13%.

[0072] In one example, the battery is a lithium-ion battery.

[0073] In one example, the battery further includes a positive electrode, a separator, and an electrolyte.

[0074] In one example, the positive electrode sheet includes a positive current collector and a positive active coating located on one or both sides of the surface of the positive current collector, the positive active coating including a positive active material, a positive conductive agent and a positive binder.

[0075] In one example, the positive electrode active material includes at least one of lithium cobalt oxide, nickel-cobalt-manganese ternary materials, lithium iron phosphate, and lithium manganese iron phosphate.

[0076] In one example, the positive conductive agent includes at least one of acetylene black and carbon nanotubes (CNTs).

[0077] In one example, the negative electrode binder includes at least one of polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and polyacrylic acid (PAA).

[0078] In one example, the electrolyte also includes lithium salts, carbonate solvents, and other additives.

[0079] In one example, the lithium salt includes at least one of LiPF6, LiBF4, LiSbF6, LiClO4, LiCF3SO3, LiAlO4, LiAlCl4, Li(CF3SO2)2N, LiBOB, LiPO2F2, and LiDFOB.

[0080] In one example, the carbonate solvent includes at least one of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC).

[0081] In one example, the other additives include one or more of 1,3-propanesulfonyl lactone (PS), 1,3-acrylonitrile lactone (PST), ethylene ethylene carbonate (VEC), adiponitrile (ADN), succinic anhydride (SN), and 1,3,6-hexanetrionitrile (HTCN).

[0082] In one example, based on the total weight of the electrolyte, the lithium salt content is 12%-35% by weight (e.g., 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, or 35%), and the carbonate solvent content is 10%-60% by weight (e.g., 10%, 15%, 20%, 25%, 30%). The other additives are present in a weight content of 3%-20% (e.g., 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, or 20%), and the fluorinated additives are present in a weight content of 3%-35% (e.g., 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 15%, 20%, 25%, 30%, or 35%).

[0083] The present disclosure will be described in detail below through embodiments. The embodiments described in this disclosure are only some embodiments of this disclosure, and not all embodiments. Based on the embodiments in this disclosure, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this disclosure.

[0084] In the following examples, unless otherwise specified, all materials used are commercially available analytical grade.

[0085] The following examples illustrate the battery of this disclosure.

[0086] Example 1

[0087] Silicon-carbon particles, a negative electrode containing the silicon-carbon particles, and a lithium-ion battery are prepared according to the following method:

[0088] (1) Preparation of ingredients

[0089] Porous carbon: 60g, particle size Dv10 6.0μm, Dn50 10μm, Dv100 28μm, sphericity S=0.99;

[0090] Silane gases: methanesilane, acetylene gas;

[0091] SiC material: 10 parts by weight;

[0092] Graphite: 86.5 parts by weight of artificial graphite;

[0093] Negative electrode conductive agent: SuperP 0.2 parts by weight; SWCNTs 0.1 parts by weight

[0094] Negative electrode binder: 1.6 parts by weight of sodium carboxymethyl cellulose and 1.6 parts by weight of styrene-butadiene rubber;

[0095] Negative electrode current collector: copper foil thickness is 6μm;

[0096] (2) Preparation of silicon-carbon particles

[0097] 30g of porous carbon was soaked in a 1.5mol / L potassium hydroxide solution for 12h, then removed, washed and dried. The porous carbon was then placed in a vapor deposition furnace, argon gas was first introduced and the temperature was raised to 1000℃ and held for 3h to create surface pits. The temperature was then lowered to 400℃, and then silane gas at a flow rate of 200sccm was introduced for 5h each time. After the end of the process, the silane gas was stopped, the temperature was raised to 550℃, and acetylene gas at a flow rate of 120sccm was introduced. The acetylene decomposition time was controlled to be 1h, and then the acetylene was stopped and the temperature was lowered to obtain the silicon-carbon particles of this embodiment.

[0098] The SEM image of the outer surface of the silicon-carbon particle is shown in Figure 1. The number of depressions on one side of the silicon-carbon particle is 7. Therefore, the number of depressions on the other side is considered to be the same as the number of depressions on the observable surface. The number N of depressions on the surface of the silicon-carbon particle is 14. The diameter of the depression is 0.5 μm and the depth of the depression is 0.3 μm.

[0099] Furthermore, the average particle size of the silicon-carbon particles is 7 μm; the median particle size Dv50 of the silicon-carbon particles is 9 μm; the median particle size Dv50 changes by 5% and the sphericity changes by 3% after being subjected to a pressure of 377 MPa.

[0100] (3) Preparation of negative electrode

[0101] The silicon-carbon particles, artificial graphite, sodium carboxymethyl cellulose, styrene-butadiene rubber, SuperP, and single-walled carbon nanotubes (SWCNTs) obtained in step (2) were mixed in a ratio of 10:86.5:1.6:1.6:0.2:0.1. Deionized water was added, and a negative electrode slurry was obtained under vacuum stirring. The negative electrode slurry was uniformly coated on both sides of a negative electrode current collector with a thickness of [thickness value missing]. The areal density of the negative electrode slurry coated on the surface of the negative electrode current collector was 11.0 mg / cm³. 2 The negative electrode current collector coated with negative electrode slurry was transferred to an 80℃ oven and dried for 12 hours, and then rolled (with the compaction density controlled at 1.4-1.8 g / cm³). 3 Within the specified range, the material is cut to obtain the negative electrode sheet.

[0102] Among them, the elemental silicon content C% in the negative electrode active coating of the test negative electrode sheet is 4.9%; at this time, the ratio N of the number of depressions on the surface of silicon-carbon particles to the elemental silicon content C% in the negative electrode active coating is 2.86.

[0103] (4) Preparation of lithium-ion batteries

[0104] 1) Preparation of positive electrode sheet

[0105] Lithium cobalt oxide (LCO), polyvinylidene fluoride (PVDF), acetylene black, and carbon nanotubes (CNTs) were mixed in a mass ratio of 96:2:1.5:0.5. N-methylpyrrolidone was added, and the mixture was stirred under vacuum until a homogeneous positive electrode slurry was formed. The positive electrode slurry was then uniformly coated onto an aluminum foil with a thickness of 12 μm. The coated aluminum foil was baked in an oven, then dried in an oven at 120°C for 8 hours. Afterward, it was rolled and slit to obtain the desired positive electrode sheet. The positive electrode sheet was smaller than the negative electrode sheet, and its reversible capacity per unit area was 5% lower than that of the negative electrode sheet.

[0106] 2) Preparation of negative electrode sheet

[0107] The negative electrode sheet used in the above embodiment.

[0108] 3) Diaphragm

[0109] A polyethylene diaphragm with a thickness of 8μm was selected.

[0110] 4) Electrolyte

[0111] In an argon-filled glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), EC / PC / PP / PA were mixed uniformly in a mass ratio of 10 / 15 / 55 / 20. Then, lithium hexafluorophosphate (LiPF6) at a total mass content of 14.38% was quickly added as a lithium salt. After dissolving, fluoroethylene carbonate at a total mass content of 5% was added, along with 1,3-propanesulfonyl lactone (PS) at 4%, 1,3,6-hexanetrionitrile (HTCN) at 2%, adiponitrile (ADN) at 2%, and succinic anion at 1%. The mixture was stirred until homogeneous. After passing the tests for moisture and free acid, the desired electrolyte was obtained.

[0112] 5) Preparation of lithium-ion batteries

[0113] The positive electrode sheet from step 1), the separator from step 3), and the negative electrode sheet from step 2) are stacked in sequence, ensuring that the separator is positioned between the positive and negative electrodes to provide isolation. Then, the cells are wound to obtain a bare cell. The bare cell is placed in an aluminum-plastic film casing, and the electrolyte from step 4) is injected into the dried bare cell. After vacuum sealing, settling, formation, shaping, and sorting, the desired lithium-ion battery is obtained.

[0114] Example 2

[0115] This embodiment 2 is based on embodiment 1, with the only difference being the change in (2) the preparation of silicon carbon particles. Specifically, 60g of porous carbon is placed in a gas-phase fluidized bed device and fluidized at room temperature and high speed for 3 hours. After the particles undergo fluidization collision, the surface of the particles is concave. 30g of the product after fluidization collision is placed in a CVD vapor deposition furnace. Argon gas is first introduced and the temperature is raised to 400°C. Then, silane gas with a flow rate of 200 sccm is introduced for 5 hours each. After the end, the silane is stopped and the temperature is raised to 550°C. Acetylene gas with a flow rate of 120 sccm is introduced and the acetylene cracking time is controlled to be 1 hour. The acetylene is then stopped and the temperature is lowered to obtain the silicon carbon particles of this embodiment. For details, please refer to Table 1.

[0116] Example 3

[0117] This embodiment 2 is based on embodiment 1, with the only difference being the change in (2) the preparation of silicon carbon particles. Specifically, 50g of porous carbon is placed in a ball mill for low-speed ball milling surface modification. The diameter of the zirconia balls is 1mm, the ball-to-material ratio is 1:25, the planetary ball mill speed is 10rpm, and the ball milling time is 30min. 30g of the ball-milled product is placed in a CVD vapor deposition furnace. Argon gas is first introduced and the temperature is raised to 400℃. Then, silane gas with a flow rate of 200sccm is introduced for 5h each. After the end, the silane is stopped and the temperature is raised to 550℃. Acetylene gas with a flow rate of 120sccm is introduced and the acetylene cracking time is controlled to be 1h. The acetylene is then stopped and the temperature is lowered to obtain the silicon carbon particles of this embodiment. For details, please refer to Table 1.

[0118] Example 4 group

[0119] Example 4 was carried out with reference to Example 2, the only difference being that the preparation of silicon carbon particles (2) was changed. Specifically, the fluidization temperature, fluidization gas flow rate and fluidization time of the gas phase fluidized bed equipment were adjusted so that the number N of the depressions on the surface of the silicon carbon particles, the diameter and depth of the depressions were changed. For details, please refer to Table 1.

[0120] Example 5 group

[0121] Example 5 was carried out with reference to Example 2, the only difference being that (1) the composition preparation was changed, specifically: the particle size of the porous carbon raw material was changed, so that the average particle size and median particle size Dv50 of the silicon carbon particles were changed, as detailed in Table 1.

[0122] Example 6 group

[0123] Example 6 was carried out with reference to Example 2, the only difference being that the preparation of the negative electrode sheet (3) was changed. Specifically, the amount of silicon carbon particles added to the negative electrode active coating was changed, so that the content of elemental silicon C% in the negative electrode active coating was changed. For details, please refer to Table 1.

[0124] Example 7 group

[0125] Example 7 was carried out with reference to Example 2, the only difference being that the preparation of silicon-carbon particles (2) was changed. Specifically, the number N of the depressions on the surface of the silicon-carbon particles, the diameter and depth of the depressions, and the content of elemental silicon C% in the negative electrode active coating were changed. For details, please refer to Table 1.

[0126] Comparative Example 1

[0127] Comparative Example 1 was carried out in accordance with Example 2, except that the preparation of silicon carbon particles (2) was changed. Specifically, instead of placing the raw porous carbon into a gas-phase fluidized bed to prepare the depressions, 30g of porous carbon was directly placed into a CVD vapor deposition furnace. Argon gas was first introduced and the temperature was raised to 400°C. Then, silane gas with a flow rate of 200 sccm was introduced for 5 hours each. After the end, the silane was stopped and the temperature was raised to 550°C. Acetylene gas with a flow rate of 120 sccm was introduced and the acetylene cracking time was controlled to be 1 hour. The acetylene was stopped and the temperature was lowered to obtain silicon carbon particles without depressions. The SEM image of the outer surface of the silicon carbon particles is shown in Figure 2.

[0128] Comparative Example 2

[0129] Comparative Example 2 was carried out in accordance with Example 2, except that the preparation of silicon carbon particles (2) was changed. Specifically, the fluidization temperature, fluidization gas flow rate and fluidization time of the gas phase fluidized bed equipment were adjusted so that the number of depressions on the surface of the silicon carbon particles N=1 and the diameter of the depressions =7μm. For details, please refer to Table 1.

[0130] Comparative Example 3

[0131] Comparative Example 3 was carried out in accordance with Example 2, except that the preparation of silicon carbon particles (2) was changed. Specifically, the fluidization temperature, fluidization gas flow rate and fluidization time of the gas phase fluidized bed equipment were adjusted so that the number of depressions on the surface of silicon carbon particles N=1 and the depth of the depressions =7000nm. For details, please refer to Table 1.

[0132] Table 1

[0133] In Table 1, the silicon-carbon particles of Comparative Example 1 do not have recesses, so the depth and diameter of the recesses are not specified and are represented by " / ".

[0134] Test case

[0135] 1) Capacity retention test after cycling:

[0136] At room temperature, the batteries prepared in the above examples and comparative examples were charged to 4.53V at a constant current and constant voltage of 0.5C or 3C, cut off at 0.05C, and then discharged to 3.0V at 0.5C. After 500 cycles, the capacity retention rate after 500 cycles was calculated using the following formula: Battery capacity retention rate (%) = Termination capacity / Initial capacity * 100%.

[0137] 2) Post-cycle expansion rate test:

[0138] At room temperature, the batteries prepared in the above examples and comparative examples were charged to 4.53V at a constant current and constant voltage of 0.5C or 3C, cut off at 0.05C, and then discharged to 3.0V at 0.5C. After cycling for 500 cycles, the battery expansion rate (%) was calculated using the following formula: Battery expansion rate (%) = (THK1 - THK0) / THK0 × 100%; where THK0 is the thickness of the battery at the initial 3.85V measured by 600g PPG, and THK1 is the thickness of the fully charged battery after cycling.

[0139] 3) Thickness of the SEI film on the particle surface after cycling:

[0140] At room temperature, the batteries prepared in the above examples and comparative examples were charged to 4.53V at a constant current and voltage of 0.5C or 3C, cut off at 0.05C, and then discharged to 3.0V at 0.5C. The batteries were cycled for 500 cycles. After cycling, the cells were disassembled in a fully charged state, and the electrodes with intact appearance were sealed and stored. The cross-section of the negative electrode was polished with Ar particles and observed in SEM backscatter mode. The light-colored areas of the particles were Si, a high atomic number element, and the dark-colored areas were SEI, a by-reaction product composed of low atomic number elements. The state of SEI on the particle surface was observed using SEM, and the thickness of the SEI film on the particle surface was measured (after taking values ​​from multiple points, the average value was calculated). The unit is nm.

[0141] 4) Characterization of fluorine content in the SEI film on the particle surface after cycling:

[0142] At room temperature, the batteries prepared in the above examples and comparative examples were charged to 4.53V at a constant current and constant voltage of 0.5C or 3C, cut off at 0.05C, and then discharged to 3.0V at 0.5C. The batteries were cycled for 500 cycles. After cycling, the cells were disassembled in a fully charged state, and the electrodes with intact appearance were taken. The CP electrodes were subjected to EDS (elemental analysis) surface scanning using SEM. The scanning results showed that the SEI layer on the particle surface contained a large amount of F element, and the mass content of fluorine element in the SEI film was obtained (in %).

[0143] The test results of the above test cases are recorded in Table 2.

[0144] Table 2

[0145] According to the test methods described above, the batteries prepared in the above examples and comparative examples were charged at room temperature with a constant current and constant voltage of 0.5C or 3C to 4.53V, cut off at 0.05C, and then discharged at 0.5C to 3.0V. After cycling for 500 cycles, the cross-sectional SEM morphology of the silicon-carbon particles in Example 1 is shown in Figure 3. The SEI film did not peel off. The cross-sectional SEM morphology of the silicon-carbon particles in Comparative Example 1 is shown in Figure 4. The SEI film is thicker, and the SEI film is fractured and peeled off near the outer side.

[0146] The preferred embodiments of this disclosure have been described in detail above; however, this disclosure is not limited thereto. Within the scope of the technical concept of this disclosure, various simple modifications can be made to the technical solutions of this disclosure, including combining the various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in this disclosure and are all within the protection scope of this disclosure.

Claims

1. A silicon-carbon particle, characterized in that, The silicon-carbon particles have recesses on their surface; On average, the number of depressions on the surface of each silicon-carbon particle is N≥1; The average diameter of the recess is 0.05μm-5μm; The average depth of the recess is 10 nm to 5 μm.

2. The silicon-carbon particles according to claim 1, characterized in that, The average number N of the depressions on the surface of each silicon-carbon particle is 4-20.

3. The silicon-carbon particles according to claim 1 or 2, characterized in that, The average diameter of the recess is 0.1 μm-2 μm; and / or the average depth of the recess is 50 nm-1 μm.

4. The silicon-carbon particles according to any one of claims 1-3, characterized in that, The average particle size of the silicon carbide particles is 4μm-18μm; preferably 6μm-15μm. And / or, the median particle size Dv50 of the silicon-carbon particles is 5μm-25μm; preferably 8μm-20μm.

5. The silicon-carbon particles according to any one of claims 1-4, characterized in that, The average sphericity of the silicon-carbon particles is 0.5-1; preferably 0.85-1.

6. The silicon-carbon particles according to any one of claims 1-5, characterized in that, The elemental silicon content is 35%-80% based on the total mass of the silicon-carbon particles. And / or, the silicon-carbon particles comprise a porous carbon matrix and nano-silicon dispersed within the pores of the porous carbon matrix, wherein the grain size of the nano-silicon is 1 nm to 100 nm.

7. The silicon-carbon particles according to claim 4, characterized in that, The median particle size Dv50 change rate of the silicon-carbon particles after being subjected to a pressure of 377 MPa is ≤15%; preferably 2%-8%.

8. The silicon-carbon particles according to claim 5, characterized in that, The sphericity change rate of the silicon-carbon particles after being subjected to a pressure of 377 MPa is ≤10%; preferably 1%-4%.

9. A method for preparing silicon-carbon particles according to any one of claims 1-8, characterized in that, The method includes: immersing a porous carbon substrate in a potassium hydroxide solution for surface treatment, then placing the surface-treated porous carbon substrate into a vapor deposition furnace, introducing argon gas and raising the temperature to 800℃-1200℃, creating depressions on the surface of the porous carbon substrate, and finally introducing silicon source gas to deposit nano-silicon within the pores of the porous carbon substrate.

10. A method for preparing silicon-carbon particles according to any one of claims 1-8, characterized in that, A porous carbon matrix is ​​placed in a gas-phase fluidized bed apparatus for surface fluidization collision treatment, which creates depressions on the surface of the porous carbon matrix. The material that has undergone the surface fluidization collision treatment is then placed in a gas-phase deposition furnace and silicon source gas is introduced to deposit nano-silicon within the pores of the porous carbon matrix.

11. A method for preparing silicon-carbon particles according to any one of claims 1-8, characterized in that, A porous carbon matrix is ​​placed in a ball mill for ball milling surface modification treatment, which produces depressions on the surface of the porous carbon matrix. Then, the material that has undergone ball milling surface modification treatment is placed in a vapor deposition furnace and silicon source gas is introduced to deposit nano-silicon in the pores of the porous carbon matrix.

12. A negative electrode sheet, characterized in that, The negative electrode comprises silicon-carbon particles according to any one of claims 1-8 and / or silicon-carbon particles prepared by the method according to any one of claims 9-11; The negative electrode sheet includes a negative electrode active coating, and the negative electrode active coating includes the silicon-carbon particles; the ratio N / C of the average number of depressions on the surface of each silicon-carbon particle to the elemental silicon content C% in the negative electrode active coating is 0.04-10; Preferably, C% is 3%-70%.

13. A battery, characterized in that, The battery includes a negative electrode and an electrolyte, wherein the negative electrode is the negative electrode as described in claim 12; The electrolyte includes a fluorinated additive, which includes at least one of fluoroethylene carbonate, LiBF4, LiCF3SO3, Li(CF3SO2)2N, LiPO2F2, and LiDFOB.

14. The battery according to claim 13, characterized in that, The battery was fully charged and disassembled after 300 cycles at 25°C, with a charge / discharge cutoff voltage of 3.0V-4.53V, and under 1C charging and 1C discharging conditions. The average thickness of the SEI film on the surface of the silicon-carbon particles is 100nm-800nm; preferably 300nm-700nm.

15. The battery according to any one of claims 13 or 14, characterized in that, The fluorine content in the SEI film on the surface of the silicon-carbon particles is 1%-15%.

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