A silicon-carbon negative electrode material with a reverse double-gradient element distribution carbon coating layer and a preparation method thereof

Abstract

The application relates to the technical field of lithium ion battery negative electrode material preparation, in particular to a silicon-carbon negative electrode material with a reverse double-gradient element distribution carbon coating layer and a preparation method thereof. A preparation method of a silicon-carbon negative electrode material with a reverse double-gradient element distribution carbon coating layer uses cheap pitch as a high-carbon-content carbon source to perform primary coating on silicon nanoparticles, and then uses low-cost gelatin as a high-nitrogen-content nitrogen source to perform secondary coating on the silicon nanoparticles after the primary pitch coating, so that a carbon coating layer with a gradient nitrogen element distribution from high to low and a gradient carbon element distribution from low to high from the surface to the center of the silicon nanoparticles is formed after sintering. The technical scheme of the application not only has an economic advantage, but also shows remarkable beneficial effects in aspects of improving battery performance, prolonging service life and simplifying a production process and the like.

Description

Technical Field

[0001] This application relates to the field of lithium-ion battery anode material preparation technology, and in particular to a silicon-carbon anode material with a reverse dual-gradient elemental distribution carbon coating layer and its preparation method. Background Technology

[0002] Lithium-ion batteries are widely used in electronic digital products, commercial electric vehicles, and static energy storage due to their advantages such as high energy density, stable charge-discharge cycles, and high coulombic efficiency. However, the energy density of current commercial lithium-ion batteries cannot be further improved due to the limited theoretical specific capacity of traditional graphite anodes. Therefore, there is an urgent need to develop new high-energy-density anode materials to replace traditional graphite anodes and break through the energy density limit of lithium-ion batteries. Among the many alternative anode materials, silicon stands out due to its ultra-high theoretical specific capacity (4200 mAh g / g). -1 It stands out due to its low operating potential (0.4V) and abundant crustal reserves, and is considered an ideal anode material to replace graphite as the next generation of high-energy-density lithium-ion batteries.

[0003] Unlike traditional graphite anodes, silicon anode particles undergo significant volume expansion (>300%) during lithium-ion battery charging and lithium intercalation, forming a lithium-silicon alloy. During discharge, the volume shrinks back down. Therefore, silicon anodes are highly susceptible to particle pulverization and electrode structure cracking and thickening during long-term cycling. Furthermore, electrolyte seeps into the cracks in the silicon particles, causing continuous side reactions and resulting in a continuously thickening solid electrolyte interphase (SEI) on the silicon surface. Ultimately, the electrolyte is continuously consumed, leading to the continuous depletion of active ions and rapid capacity decay. On the other hand, silicon's intrinsic electronic conductivity is low, severely limiting the rate performance of the electrode.

[0004] To address the issues of silicon volume expansion and its low electronic conductivity, researchers have conducted extensive studies. Current research indicates that coating silicon particles with a carbon layer is the optimal solution to these problems. This effectively addresses issues such as electrode structure thickening and cracking caused by the large volume expansion of silicon nanoparticles, inhibits direct contact between silicon nanoparticles and the electrolyte, suppresses the continuous growth of the electrolyte interphase (SEI), and improves electrode conductivity. For example, coating silicon with dopamine and catalyzing its in-situ polymerization in a weakly alkaline environment, followed by high-temperature pyrolysis, yields carbon-coated silicon anode materials. Furthermore, vapor deposition technology allows for the direct growth of silicon within hollow carbon spheres, constructing eggshell-yolk structure carbon-coated silicon anode materials. These methods alleviate the two major problems of silicon anodes and improve electrochemical performance. However, the silicon-carbon composite materials prepared by these methods have a single carbon layer composition, which, while improving electronic conductivity, also inhibits the migration rate of lithium ions to the electrode surface. Moreover, the complex and costly preparation processes still limit their commercial application. Summary of the Invention

[0005] To address the aforementioned technical problems, this application provides a silicon-carbon anode material with a reverse dual-gradient elemental distribution carbon coating layer and its preparation method. Inexpensive pitch is used as a high-carbon source to initially coat silicon nanoparticles. Then, low-cost gelatin is used as a high-nitrogen source to secondarily coat the pitch-coated silicon nanoparticles. This results in a carbon coating layer with a gradient nitrogen distribution from high to low and a gradient carbon distribution from low to high from the surface to the center of the silicon nanoparticles after sintering. The decreasing nitrogen distribution from the coating layer surface to the silicon particle center ensures a gradually decreasing electronegativity, facilitating rapid lithium-ion migration to the silicon nanoparticles. The increasing carbon distribution ensures high conductivity and structural stability of the coating layer near the silicon surface, effectively suppressing silicon volume expansion and low conductivity issues. Therefore, the reverse dual-gradient elemental distribution coating layer enhances the diffusion rate of lithium ions to silicon nanoparticles while effectively suppressing silicon volume expansion and ensuring high electrochemical performance of the silicon-carbon anode material. In addition, the raw materials for preparing the coating layer are inexpensive, widely available, and the preparation method is simple, making it suitable for large-scale production.

[0006] In a first aspect, this application provides a method for preparing a silicon-carbon anode material with a reverse dual-gradient elemental distribution carbon coating layer, employing the following technical solution:

[0007] A method for preparing a silicon-carbon anode material with a reverse dual-gradient elemental distribution carbon coating includes the following steps:

[0008] S1. Dissolve coal tar pitch in ethyl acetate and stir until homogeneous to obtain a mixed solution;

[0009] S2. Centrifuge the mixed solution obtained in step S1 at a speed of 200-2000 r / min for 1-5 minutes, filter out the lower layer of insoluble impurities, and keep the filtrate for later use.

[0010] S3. Add silicon nanoparticles to the filtrate after centrifugation and filtration in step S2, stir evenly, and granulate using a nitrogen-circuit dryer to obtain Si@CP powder coated with high carbon content carbon precursor.

[0011] S4. Dissolve the gelatin in deionized water and stir until homogeneous. Then add Si@CP powder and stir at a stirring speed of 200-300 r / min for 1-3 h. After stirring, freeze dry to obtain a mixed powder.

[0012] S5. The mixed powder obtained in step S4 is heat-treated under an inert atmosphere to obtain a silicon-carbon composite material.

[0013] S6. The silicon-carbon composite material obtained in step S5 is ball-milled and sieved to obtain silicon-carbon anode material with a particle size of <15μm.

[0014] By adopting the above technical solution, steps S1 and S2 are the process of preparing a mixed solution. Coal tar pitch is dissolved in ethyl acetate and stirred evenly. Then, the lower layer of insoluble impurities is filtered by centrifugation, and the filtrate is reserved for later use. These two steps are mainly to remove impurities and ensure the purity of subsequent reactions. Step S3 involves adding silicon nanoparticles to the filtrate after centrifugation, stirring evenly, and then granulating using a nitrogen-circuit dryer to obtain Si@CP powder coated with a high-carbon carbon precursor. This step is crucial for achieving one-time coating. By mixing silicon nanoparticles with a high-carbon carbon precursor, carbon elements can be uniformly covered on the surface of the silicon nanoparticles. Step S4 involves dissolving gelatin in deionized water and stirring evenly, then adding Si@CP powder. After stirring at 200-300 r / min for 1-3 h, the mixture is freeze-dried to obtain a mixed powder. This step is crucial for achieving secondary coating. By using gelatin as a high-nitrogen source to perform a secondary coating on the silicon nanoparticles after the initial coating of asphalt, nitrogen can be uniformly coated on the surface of the silicon nanoparticles coated with the carbon precursor. Step S5 involves heat-treating the obtained mixed powder under an inert atmosphere to obtain a silicon-carbon composite material. This step aims to make the coating layer more stable, allowing the carbon precursor and gelatin to better bond and form a stable carbon coating layer through heat treatment. Step S6 involves ball milling and sieving the obtained silicon-carbon composite material to obtain a silicon-carbon anode material with a particle size <15μm. This step is to obtain a silicon-carbon anode material suitable for lithium-ion batteries, and ball milling and sieving ensure that the particle size of the material meets the requirements. In summary, the preparation method of this application forms a carbon coating layer with a gradient nitrogen distribution from high to low and a gradient carbon distribution from low to high from the surface to the center of silicon nanoparticles through two coating processes. This special structure not only ensures the rapid migration of lithium ions to silicon nanoparticles, but also effectively suppresses the volume expansion of silicon, thereby improving the electrochemical performance of silicon-carbon anode materials.

[0015] Preferably, in step S1, the mass-to-volume ratio of the coal tar pitch to the ethyl acetate is (1-3g):(40-120ml).

[0016] Preferably, in step S1, the process conditions for uniform stirring are: stirring speed 100-500 r / min, stirring time 0.5-5 h.

[0017] Preferably, in step S3, the mass ratio of the silicon nanoparticles to the coal tar pitch is (1-3):(1-3), and the particle size of the silicon nanoparticles is 20-150 nm.

[0018] Preferably, in step S3, the process conditions for achieving uniform mixing are: a mixing speed of 200-600 r / min and a mixing time of 1-3 h.

[0019] By employing the above technical solution, an appropriate stirring speed ensures that the silicon nanoparticles in the mixed solution receive sufficient kinetic energy to achieve uniform dispersion. Too low a stirring speed may lead to uneven mixing, while too high a speed may cause unnecessary shear forces, potentially damaging the structure of the silicon nanoparticles. Sufficient stirring time ensures that each silicon nanoparticle is covered by the carbon precursor, forming a uniform coating layer. Too short a stirring time may result in uneven coating, while too long a stirring time may lead to unnecessary energy waste and equipment wear. By controlling the stirring speed and time, the mixing of silicon nanoparticles and the carbon precursor can be optimized, thereby forming a carbon coating layer with the desired elemental gradient distribution during subsequent drying and heat treatment. This is crucial for the electrochemical performance of the final product, as it directly affects the lithium-ion diffusion rate and electronic conductivity, as well as the structural stability and cycle performance of the silicon-carbon anode material.

[0020] Preferably, in step S4, the mass ratio of the gelatin to the Si@CP powder is (2-4):(1-3); the mass-volume ratio of the gelatin to the deionized water is (2-4g):(40-100ml).

[0021] Preferably, in step S4, the temperature of the nitrogen circulation closed-loop dryer is 80-150°C.

[0022] Preferably, in step S5, the inert atmosphere is either nitrogen or argon.

[0023] Preferably, in step S5, the heat treatment process conditions are: heating to 800-1200℃ at a heating rate of 1-10℃ / min and holding at that temperature for 1-5 hours.

[0024] By employing the above technical solutions, controlling the appropriate heating rate can ensure a uniform distribution of thermal stress within the material, avoiding structural damage caused by excessively rapid temperature increases. Slow heating facilitates a uniform transformation of the material structure, contributing to the formation of a uniform carbon coating layer. 800-1200℃ is a typical carbonization temperature range, capable of converting the organic components in gelatin and coal tar pitch into carbon while maintaining the structural stability of silicon nanoparticles. If the temperature is too low, the organic components may not be completely converted into carbon, while excessively high temperatures may affect the electrochemical performance of the silicon nanoparticles. Holding the material at the target temperature for a period of time ensures sufficient pyrolysis and carbonization of the organic components, as well as the stable formation of the carbon coating layer. Insufficient holding time may lead to incomplete carbonization, while excessively long holding time may result in unnecessary energy consumption and reduced production efficiency. By controlling the heat treatment process conditions, the carbon coating layer in the silicon-carbon composite material can be ensured to have the required reverse dual-gradient elemental distribution, thereby improving the electrochemical performance of the silicon-carbon anode material. This step is also crucial for forming the final product's structure and performance, as it directly affects the conductivity, lithium-ion diffusion rate, volume expansion suppression capability, and cycle stability of the silicon-carbon anode material.

[0025] Secondly, this application provides a silicon-carbon anode material with a reverse dual-gradient elemental distribution carbon coating layer, employing the following technical solution:

[0026] As a general technical concept, this application also provides a silicon-carbon anode material with a reverse dual-gradient elemental distribution carbon coating layer, which is prepared by the above-mentioned method for preparing a silicon-carbon anode material with a reverse dual-gradient elemental distribution carbon coating layer.

[0027] By adopting the above technical solution, the silicon-carbon anode material has a coating layer with a distinct gradient of elemental distribution, and exhibits excellent battery cycle performance in lithium-ion batteries.

[0028] In summary, the beneficial technical effects of this application are as follows:

[0029] 1. Cost-effectiveness: By using inexpensive and readily available raw materials, such as coal tar pitch and gelatin, the method of this application significantly reduces the production cost of silicon-carbon anode materials. These raw materials are not only inexpensive but also widely available, making them easy to procure and use on a large scale.

[0030] 2. Performance Enhancement: The prepared silicon-carbon anode material features a unique reverse dual-gradient elemental distribution. This structural design allows lithium ions to migrate rapidly into the interior of silicon nanoparticles, while the high-carbon inner layer provides excellent electronic conductivity and structural stability. These characteristics work together to significantly improve the battery's electrochemical performance, including high charge-discharge efficiency and excellent cycle stability.

[0031] 3. Structural stability: The coating layer with reverse dual gradient element distribution can effectively suppress the volume expansion of silicon during charging and discharging, reduce material breakage and shedding during cycling, and thus extend the battery's lifespan.

[0032] 4. Simple process: The entire preparation process involves simple steps and mild conditions, and does not require complex equipment or extreme reaction conditions, which is conducive to large-scale production.

[0033] 5. Electrochemical performance: Due to the special coating structure, the prepared silicon-carbon anode material exhibits high lithium-ion diffusion rate and electronic conductivity in electrochemical performance, which is very beneficial for improving the power density and energy density of the battery.

[0034] 6. SEI layer stability: The high carbon content of the coating layer helps to form a stable solid electrolyte interface (SEI) layer, which is crucial for maintaining the stability of the battery during long-term cycling.

[0035] 7. Environmentally friendly: Using low-cost natural materials as precursors not only reduces costs but also minimizes environmental impact, meeting the requirements of sustainable development. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the embodiments will be briefly described below:

[0037] Figure 1 This is a schematic diagram of the silicon-carbon anode material with a reverse dual-gradient elemental distribution coating prepared in this application.

[0038] Figure 2 SEM images and elemental distribution maps of silicon nanoparticles used in all embodiments of this application;

[0039] Figure 3 TEM and STEM images and elemental distribution diagrams of the silicon-carbon composite material prepared in Example 2 of this application;

[0040] Figure 4 This is a graph showing the electrochemical performance of the silicon-carbon anode material prepared in Example 1 of this application;

[0041] Figure 5 This is a graph showing the electrochemical performance of the silicon-carbon anode material prepared in Example 2 of this application;

[0042] Figure 6 This is a graph showing the electrochemical performance of the silicon-carbon anode material prepared in Example 3 of this application;

[0043] Figure 7 This is a graph showing the electrochemical performance of the silicon-carbon anode material prepared in Example 4 of this application;

[0044] Figure 8 This is a graph showing the electrochemical performance of the silicon-carbon anode material prepared in Example 5 of this application;

[0045] Figure 9 This is a graph showing the electrochemical performance of the silicon-carbon anode material prepared in Example 6 of this application. Detailed Implementation

[0046] The embodiments of this application will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of this application. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0047] Example 1

[0048] A method for preparing a silicon-carbon anode material with a reverse dual-gradient elemental distribution carbon coating includes the following steps:

[0049] S1. Dissolve 1g of coal tar pitch (CP) in 80ml of ethyl acetate and stir at 100r / min for 5h to obtain a mixed solution.

[0050] S2. Centrifuge the mixed solution obtained in step S1 at 2000 r / min for 3 minutes, filter out the lower layer of insoluble impurities, and keep the filtrate for later use.

[0051] S3. Add 1g of silicon nanoparticles with a particle size of 50nm to the filtrate after centrifugation and filtration in step S2 and stir at a stirring speed of 200r / min for 3h. Granulate using a nitrogen-circulating closed-loop dryer with an inlet temperature set to 80℃ to obtain Si@CP powder coated with carbon precursor with high carbon content.

[0052] S4. Dissolve 2g of gelatin in 100ml of deionized water and stir until homogeneous. Then add 2g of Si@CP powder and stir at 300r / min for 1h. After stirring, freeze dry to obtain a mixed powder.

[0053] S5. The mixed powder obtained in step S4 is heated to 1000℃ at a heating rate of 1℃ / min under a nitrogen atmosphere, and then held at that temperature for 5h to obtain a silicon-carbon composite material.

[0054] S6. The silicon-carbon composite material obtained in step S5 is ball-milled and sieved to obtain a silicon-carbon anode material with a particle size of 10 μm.

[0055] Example 2

[0056] A method for preparing a silicon-carbon anode material with a reverse dual-gradient elemental distribution carbon coating includes the following steps:

[0057] S1. Dissolve 2g of coal tar pitch (CP) in 40ml of ethyl acetate and stir at a stirring speed of 500r / min for 5h to obtain a mixed solution.

[0058] S2. Centrifuge the mixed solution obtained in step S1 at 200 r / min for 3 minutes, filter out the lower layer of insoluble impurities, and keep the filtrate for later use.

[0059] S3. Add 3g of silicon nanoparticles with a particle size of 150nm to the filtrate after centrifugation and filtration in step S2 and stir at a stirring speed of 600r / min for 1h. Granulate using a nitrogen-circulating closed-loop dryer with an inlet temperature set to 120℃ to obtain Si@CP powder coated with carbon precursor with high carbon content.

[0060] S4. Dissolve 3g of gelatin in 40ml of deionized water and stir until homogeneous. Then add 2g of Si@CP powder and stir at 300r / min for 3h. After stirring, freeze dry to obtain a mixed powder.

[0061] S5. The mixed powder obtained in step S4 is heated to 800°C at a heating rate of 5°C / min under a nitrogen atmosphere, and then held at that temperature for 1 hour to obtain a silicon-carbon composite material.

[0062] S6. The silicon-carbon composite material obtained in step S5 is ball-milled and sieved to obtain a silicon-carbon anode material with a particle size of 10 μm.

[0063] Example 3

[0064] A method for preparing a silicon-carbon anode material with a reverse dual-gradient elemental distribution carbon coating includes the following steps:

[0065] S1. Dissolve 3g of coal tar pitch (CP) in 120ml of ethyl acetate and stir at 300r / min for 2.5h to obtain a mixed solution.

[0066] S2. Centrifuge the mixed solution obtained in step S1 at 200 r / min for 3 minutes, filter out the lower layer of insoluble impurities, and keep the filtrate for later use.

[0067] S3. Add 2g of silicon nanoparticles with a particle size of 20nm to the filtrate after centrifugation and filtration in step S2 and stir at a stirring speed of 600r / min for 2h. Granulate using a nitrogen-circulating closed-loop dryer with an inlet temperature set to 150℃ to obtain Si@CP powder coated with carbon precursor with high carbon content.

[0068] S4. Dissolve 4g of gelatin in 80ml of deionized water and stir until homogeneous. Then add 1g of Si@CP powder and stir at 200r / min for 3h. After stirring, freeze dry to obtain a mixed powder.

[0069] S5. The mixed powder obtained in step S4 is heated to 800°C at a heating rate of 10°C / min under an argon atmosphere, and then held at that temperature for 3 hours to obtain a silicon-carbon composite material.

[0070] S6. The silicon-carbon composite material obtained in step S5 is ball-milled and sieved to obtain a silicon-carbon anode material with a particle size of 10 μm.

[0071] Example 4

[0072] A method for preparing a silicon-carbon anode material with a reverse dual-gradient elemental distribution carbon coating includes the following steps:

[0073] S1. Dissolve 2g of coal tar pitch (CP) in 80ml of ethyl acetate and stir at a stirring speed of 500r / min for 0.5h to obtain a mixed solution;

[0074] S2. Centrifuge the mixed solution obtained in step S1 at a speed of 200-2000 r / min for 1-5 minutes, filter out the lower layer of insoluble impurities, and keep the filtrate for later use.

[0075] S3. Add 1g of silicon nanoparticles with a particle size of 150nm to the filtrate after centrifugation and filtration in step S2 and stir at a stirring speed of 200r / min for 3h. Granulate using a nitrogen-circulating closed-loop dryer with an inlet temperature set to 150℃ to obtain Si@CP powder coated with carbon precursor with high carbon content.

[0076] S4. Dissolve 2g of gelatin in 100ml of deionized water and stir until homogeneous. Then add 3g of Si@CP powder and stir at 300r / min for 1h. After stirring, freeze dry to obtain a mixed powder.

[0077] S5. The mixed powder obtained in step S4 is heated to 1000℃ at a heating rate of 1℃ / min under a nitrogen atmosphere, and then held at that temperature for 1h to obtain a silicon-carbon composite material.

[0078] S6. The silicon-carbon composite material obtained in step S5 is ball-milled and sieved to obtain a silicon-carbon anode material with a particle size of 10 μm.

[0079] Example 5

[0080] A method for preparing a silicon-carbon anode material with a reverse dual-gradient elemental distribution carbon coating includes the following steps:

[0081] S1. Dissolve 1g of coal tar pitch (CP) in 40ml of ethyl acetate and stir at a stirring speed of 100r / min for 5h to obtain a mixed solution.

[0082] S2. Centrifuge the mixed solution obtained in step S1 at 1000 r / min for 5 minutes, filter out the lower layer of insoluble impurities, and keep the filtrate for later use.

[0083] S3. Add 1g of silicon nanoparticles with a particle size of 150nm to the filtrate after centrifugation and filtration in step S2 and stir at a stirring speed of 400r / min for 2h. Granulate using a nitrogen-circulating closed-loop dryer with an inlet temperature set to 150℃ to obtain Si@CP powder coated with carbon precursor with high carbon content.

[0084] S4. Dissolve 3g of gelatin in 40ml of deionized water and stir until homogeneous. Then add 1g of Si@CP powder and stir at 250r / min for 2h. After stirring, freeze dry to obtain a mixed powder.

[0085] S5. The mixed powder obtained in step S4 is heated to 1000℃ at a heating rate of 10℃ / min under a nitrogen atmosphere, and then held at that temperature for 1h to obtain a silicon-carbon composite material.

[0086] S6. The silicon-carbon composite material obtained in step S5 is ball-milled and sieved to obtain a silicon-carbon anode material with a particle size of 10 μm.

[0087] Example 6

[0088] A method for preparing a silicon-carbon anode material with a reverse dual-gradient elemental distribution carbon coating includes the following steps:

[0089] S1. Dissolve 3g of coal tar pitch (CP) in 100ml of ethyl acetate and stir at a stirring speed of 400r / min for 0.5h to obtain a mixed solution;

[0090] S2. Centrifuge the mixed solution obtained in step S1 at 200 r / min for 1 minute, filter out the lower layer of insoluble impurities, and keep the filtrate for later use.

[0091] S3. Add 3g of silicon nanoparticles with a particle size of 20nm to the filtrate after centrifugation and filtration in step S2 and stir at a stirring speed of 300r / min for 3h. Granulate using a nitrogen-circulating closed-loop dryer with an inlet temperature set to 80℃ to obtain Si@CP powder coated with carbon precursor with high carbon content.

[0092] S4. Dissolve 4g of gelatin in 80ml of deionized water and stir until homogeneous. Then add 3g of Si@CP powder and stir at 300r / min for 1h. After stirring, freeze dry to obtain a mixed powder.

[0093] S5. The mixed powder obtained in step S4 is heated to 1200℃ at a heating rate of 2℃ / min under a nitrogen atmosphere, and then held at that temperature for 3h to obtain a silicon-carbon composite material.

[0094] S6. The silicon-carbon composite material obtained in step S5 is ball-milled and sieved to obtain a silicon-carbon anode material with a particle size of 10 μm.

[0095] The performance tests were conducted on the negative electrode slurries and silicon-carbon negative electrode materials prepared in Examples 1 to 6, respectively, and their application in lithium-ion batteries. The specific steps are as follows:

[0096] (1) Add 80wt% silicon-carbon anode material, 10wt% conductive carbon (super P) and 10wt% polyacrylic acid (PAA) binder to deionized water, ball mill for 2 hours to form a viscous slurry, and coat it onto copper foil. Place it in a vacuum drying oven and vacuum dry at 80°C for 12 hours.

[0097] (2) The dried electrode sheets were cut into circular pieces with a diameter of 12 μm. In a glove box filled with argon (moisture content < 0.1 ppm, oxygen content < 0.1 ppm), a battery was assembled using lithium sheets as the counter electrode. The assembled battery was then subjected to charge-discharge tests within the range of 0.01-1.5V. The test results are shown in Table 1; the electrochemical performance curves of the silicon-carbon anode material prepared in Example 1 are shown in Table 1. Figure 4 As shown; the electrochemical performance curves of the silicon-carbon anode material prepared in Example 2 are as follows. Figure 5 As shown; the electrochemical performance curves of the silicon-carbon anode material prepared in Example 3 are as follows. Figure 6 As shown; the electrochemical performance curves of the silicon-carbon anode material prepared in Example 4 are as follows. Figure 7 As shown; the electrochemical performance curve of the silicon-carbon anode material prepared in Example 5 is as follows. Figure 8 As shown; the electrochemical performance curves of the silicon-carbon anode material prepared in Example 6 are as follows. Figure 9 As shown.

[0098] Table 1 Electrochemical performance test results

[0099]

[0100] As shown in Table 1, the silicon-carbon anode material with a reverse dual-gradient elemental distribution carbon coating obtained in this application, when used to make lithium-ion batteries, exhibits high initial charge specific capacity, initial coulombic efficiency, and 50-cycle retention rate. This indicates that the preparation method of the silicon-carbon anode material with a reverse dual-gradient elemental distribution carbon coating in this application utilizes inexpensive pitch as a high-carbon source to coat silicon nanoparticles initially, followed by a secondary coating using low-cost gelatin as a high-nitrogen source. This results in a carbon coating layer with a gradient nitrogen distribution from high to low and a gradient carbon distribution from low to high, formed after sintering. The decreasing nitrogen distribution from the coating surface to the silicon particle center ensures a gradually decreasing electronegativity, facilitating rapid lithium-ion migration to the silicon nanoparticles. The increasing carbon distribution ensures high conductivity and structural stability of the coating layer near the silicon surface, effectively suppressing the volume expansion and low conductivity issues of silicon. Therefore, the coating layer with reverse dual gradient element distribution not only increases the diffusion rate of lithium ions to silicon nanoparticles, but also effectively suppresses the volume expansion of silicon and ensures that the silicon-carbon anode material has high electrochemical performance.

[0101] The above embodiments are only used to explain the technical solutions of this application and are not intended to limit it. Although the above embodiments have provided specific descriptions of this application, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation methods of this application. Any modifications and equivalent substitutions that do not depart from the spirit and scope of this application should be covered within the protection scope of this application.

Claims

1. A method for preparing a silicon-carbon anode material with a reverse dual-gradient elemental distribution carbon coating, characterized in that, Includes the following steps: S1. Dissolve coal tar pitch in ethyl acetate and stir until homogeneous to obtain a mixed solution; S2. Centrifuge the mixed solution obtained in step S1 at 200-2000 r / min for 1-5 minutes, filter out the lower layer of insoluble impurities, and reserve the filtrate; S3. Add silicon nanoparticles to the filtrate obtained in step S2, stir until homogeneous, and granulate using a nitrogen-circuit dryer to obtain Si@CP powder coated with a high-carbon carbon precursor; S4. Dissolve gelatin in deionized water and stir until homogeneous, then add... Add Si@CP powder, stir at a stirring speed of 200-300 r / min for 1-3 h, and then freeze-dry to obtain a mixed powder; S5, heat-treat the mixed powder obtained in step S4 under an inert atmosphere. The heat treatment process conditions are: heating to 800-1200℃ at a heating rate of 1-10℃ / min and holding for 1-5 h to obtain a silicon-carbon composite material; S6, ball-mill the silicon-carbon composite material obtained in step S5 and sieve to obtain a silicon-carbon anode material with a particle size <15μm.

2. The method for preparing a silicon-carbon anode material with a reverse dual-gradient elemental distribution carbon coating as described in claim 1, characterized in that, In step S1, the mass-to-volume ratio of the coal tar pitch to the ethyl acetate is (1-3g):(40-120ml).

3. The method for preparing a silicon-carbon anode material with a reverse dual-gradient elemental distribution carbon coating as described in claim 1, characterized in that, In step S1, the process conditions for uniform mixing are: mixing speed 100-500 r / min, mixing time 0.5-5 h.

4. The method for preparing a silicon-carbon anode material with a reverse dual-gradient elemental distribution carbon coating layer according to claim 1, characterized in that, In step S3, the mass ratio of the silicon nanoparticles to the coal tar pitch is (1-3):(1-3), and the particle size of the silicon nanoparticles is 20-150 nm.

5. The method for preparing a silicon-carbon anode material with a reverse dual-gradient elemental distribution carbon coating as described in claim 1, characterized in that, In step S3, the process conditions for achieving uniform mixing are: stirring speed 200-600 r / min, stirring time 1-3 h.

6. The method for preparing a silicon-carbon anode material with a reverse dual-gradient elemental distribution carbon coating layer according to claim 1, characterized in that, In step S4, the mass ratio of the gelatin to the Si@CP powder is (2-4):(1-3); the mass-volume ratio of the gelatin to the deionized water is (2-4g):(40-100ml).

7. The method for preparing a silicon-carbon anode material with a reverse dual-gradient elemental distribution carbon coating as described in claim 1, characterized in that, In step S3, the temperature of the nitrogen circulation closed-loop dryer is 80-150℃.

8. The method for preparing a silicon-carbon anode material with a reverse dual-gradient elemental distribution carbon coating layer according to claim 1, characterized in that, In step S5, the inert atmosphere is either nitrogen or argon.

9. A silicon-carbon anode material with a reverse dual-gradient elemental distribution carbon coating, characterized in that, The silicon-carbon anode material with a reverse dual-gradient elemental distribution carbon coating layer is prepared by the method for preparing the silicon-carbon anode material with a reverse dual-gradient elemental distribution carbon coating layer as described in any one of claims 1-8.

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