Silicon-carbon negative electrode material and preparation method thereof

Abstract

The invention relates to the technical field of lithium ion batteries, in particular to a silicon-carbon negative electrode material and a preparation method thereof. The preparation method of the silicon-carbon negative electrode material comprises the following steps: carrying out liquid-phase coating treatment on a porous carbon material and a fast ion conductor precursor to form a porous carbon material coated with a fast ion conductor so as to prepare a modified porous carbon material; carrying out first chemical vapor deposition treatment by taking silane gas as a deposition precursor, and depositing nano silicon on the surface of the modified porous carbon material to prepare a silicon-carbon core; and carrying out secondary chemical vapor deposition treatment by taking a soft carbon gas source as a deposition precursor in an inert gas atmosphere, and depositing nano soft carbon on the surface of the silicon-carbon inner core to prepare the silicon-carbon negative electrode material. The preparation method of the silicon-carbon negative electrode material solves the technical problem that the electrochemical performance of the silicon-carbon material is poor due to the fact that the volume of the existing silicon material is expanded and the ionic conduction performance is reduced by a carbon coating technology.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a silicon-carbon anode material and its preparation method. Background Technology

[0002] With the rapid development of the new energy industry, the demand for performance improvement of lithium-ion batteries, as important energy storage devices, is becoming increasingly urgent. Silicon-based anode materials have attracted much attention due to their theoretical specific capacity being far superior to that of traditional graphite anodes, but they still face many technical bottlenecks in practical applications. Silicon materials undergo significant volume changes during charging and discharging, and this repeated expansion and contraction can easily lead to electrode structure damage and active material shedding. At the same time, silicon itself has poor conductivity and a low ion diffusion rate, which severely restricts the rate performance of the material.

[0003] In existing technologies, carbon coating is a common method to improve the performance of silicon-based materials, but traditional methods have significant shortcomings. While hard carbon or amorphous carbon coating can improve conductivity, their dense structure hinders rapid ion transport. Conventional carbon coating layers are often too thick, increasing the length of ion diffusion paths. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a silicon-carbon anode material and its preparation method, which solves the technical problems of poor electrochemical performance of silicon-carbon materials caused by volume expansion of existing silicon materials and the reduction of ion conduction performance by carbon coating technology.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides a method for preparing a silicon-carbon anode material, comprising the following steps: Porous carbon materials and fast ion conductor precursors are coated in liquid phase to form a porous carbon material coated with fast ion conductors, thus obtaining a modified porous carbon material. Using silane gas as a deposition precursor, a first chemical vapor deposition process is performed to deposit nano-silicon on the surface of the modified porous carbon material, thus obtaining a silicon-carbon core. Under an inert gas atmosphere, using soft carbon gas source as a deposition precursor, a second chemical vapor deposition process is performed to deposit nano-soft carbon on the surface of the silicon-carbon core, thus obtaining a silicon-carbon anode material.

[0006] In one possible implementation, the porous carbon material is at least one of coconut shell carbon, resin carbon, and petroleum coke.

[0007] In one possible implementation, the micropore ratio of the porous carbon material is 80% to 90%.

[0008] In one possible implementation, the fast ion conductor precursor is at least one of phosphate, lithium salt, and aluminum salt, and the fast ion conductor is at least one of lithium phosphate, aluminum phosphate, and aluminum metaphosphate.

[0009] In one possible implementation, the deposition temperature of the first chemical vapor deposition treatment is 500℃~800℃, and the deposition time is 0.5h~24h.

[0010] In one possible implementation, the soft carbon gas source is at least one of ethylene, toluene, and cyclohexane, and the inert gas is at least one of nitrogen and argon.

[0011] In one possible implementation, the deposition temperature of the second chemical vapor deposition process is 700℃~1000℃, and the deposition time is 0.5h~24h.

[0012] In one possible implementation, the liquid phase coating process includes the following steps: In a solvent system, porous carbon material and a fast ion conductor precursor are mixed uniformly, and then filtered to obtain porous carbon powder loaded with the fast ion conductor precursor. Under a low-oxygen atmosphere, the porous carbon powder loaded with the fast ion conductor precursor is calcined at high temperature to form a porous carbon material coated with a fast ion conductor, thus obtaining a modified porous carbon material. The calcination temperature for the high-temperature calcination treatment is 150℃~200℃, and the solvent is water or an alcohol.

[0013] like Figure 1 As shown, the present invention also provides a silicon-carbon anode material, which is prepared by the above-mentioned method for preparing silicon-carbon anode materials. The silicon-carbon anode material has a porous core-shell structure and a diameter of 1µm to 20µm.

[0014] In one possible implementation, the mass percentage of Si in the silicon-carbon anode material is 30% to 60%, the mass percentage of C in the silicon-carbon anode material is 30% to 60%, and the mass percentage of the fast ion conductor in the silicon-carbon anode material is 1% to 10%.

[0015] The beneficial effects of this invention are as follows: Compared with the prior art, this invention shortens the lithium-ion diffusion path and improves ion transport efficiency through composite modification of a porous carbon framework and a fast ion conductor; the introduction of nano-silicon ensures high specific capacity while reducing volume effects; the soft carbon coating layer optimizes electron conduction, and its mesoporous structure promotes rapid lithium-ion diffusion. This multi-level structural design achieves the synergistic effect of each component, effectively solving the performance degradation problem of silicon-carbon materials under high-rate charge-discharge. Simultaneously, the introduction of the soft carbon coating layer reduces the direct contact between silicon and the electrolyte, reduces interfacial side reactions, and improves the cycling stability of the material, thereby solving the technical problems of volume expansion of existing silicon materials and the reduced ion conduction performance caused by carbon coating technology, resulting in poor electrochemical performance of silicon-carbon materials. Furthermore, the liquid-phase coating and chemical vapor deposition processes used in this solution are simple and easy to implement, suitable for large-scale industrial production, and have good application prospects. Attached Figure Description

[0016] Figure 1 This is a schematic cross-sectional view of a silicon-carbon anode material provided by the present invention.

[0017] Figure 2 This is a transmission electron microscope (TEM) image of the silicon-carbon anode material prepared in Example 1 of the present invention. Detailed Implementation

[0018] To address the aforementioned technical problems, this invention provides a silicon-carbon anode material and its preparation method. The technical solution and embodiments of this invention will now be described in detail with reference to the accompanying drawings.

[0019] In the description of this application, it should be understood that the terms "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0020] In lithium-ion battery anode material systems, the high specific capacity of silicon-based materials presents a sharp contradiction with their inherently low intrinsic conductivity. Silicon's semiconductor properties result in low electron transport efficiency, and the lithium-ion diffusion coefficient in its crystal structure is around 10⁻⁶. -14 ~10 -13 cm 2 The value is on the order of / s, significantly lower than that of graphite anodes (10). -8 cm 2 The ion transport hysteresis is particularly pronounced under high-rate charge-discharge conditions, manifested as a significant increase in polarization voltage and a sharp decrease in capacity. Simultaneously, irreversible side reactions continuously occur at the silicon-electrolyte interface, generating a low-conductivity solid electrolyte interfacial film, leading to an exponential increase in charge transfer impedance.

[0021] To address the aforementioned issues, this application first analyzes the root causes of the low electron transport efficiency and sluggish lithium-ion diffusion kinetics in silicon-based materials. While existing hard carbon coatings can improve conductivity, their dense structure hinders ion transport and is prone to microcracks due to silicon expansion. An attempt was made to replace traditional hard carbon with porous carbon matrices, but the porous structure resulted in an excessively large specific surface area, exacerbating side reactions. To resolve this contradiction, a composite layer with both ion conduction and interface protection functions was considered for construction on the porous carbon surface. Further research revealed that fast ion conductor materials can optimize the lithium-ion transport path, but direct mechanical mixing makes uniform coating difficult to achieve. Based on this, a liquid-phase coating process was proposed, achieving molecular-level bonding between porous carbon and fast ion conductors through precursor solution wetting. However, simple fast ion conductor modification cannot solve the structural damage problem caused by silicon volume expansion; nano-silicon particles need to be introduced during the active material deposition stage to reduce the volume effect. Finally, regarding the interface stability defects, it was found that soft carbon coatings have better elastic modulus and mesoporous structure than hard carbon, but conventional deposition processes struggle to control the thickness and porosity of the soft carbon layer. This leads to the overall approach of constructing the core-shell structure step by step.

[0022] In response, this application proposes a method for preparing silicon-carbon anode materials, comprising the following steps: Porous carbon materials and fast ion conductor precursors are coated in liquid phase to form a porous carbon material coated with fast ion conductors, thus obtaining a modified porous carbon material. Using silane gas as a deposition precursor, a first chemical vapor deposition process is performed to deposit nano-silicon on the surface of the modified porous carbon material, thus obtaining a silicon-carbon core. Under an inert gas atmosphere, using soft carbon gas source as a deposition precursor, a second chemical vapor deposition process is performed to deposit nano-soft carbon on the surface of the silicon-carbon core, thus obtaining a silicon-carbon anode material.

[0023] The composite modification of a porous carbon framework with a fast ion conductor shortens the lithium-ion diffusion path and improves ion transport efficiency. The introduction of nano-silicon ensures high specific capacity while reducing volume effects. A soft carbon coating optimizes electron conduction, and its mesoporous structure promotes rapid lithium-ion diffusion. This multi-layered structural design achieves synergistic effects among the components, effectively solving the performance degradation problem of silicon-carbon materials under high-rate charge-discharge conditions. Simultaneously, the introduction of the soft carbon coating reduces direct contact between silicon and the electrolyte, lowers interfacial side reactions, and improves the material's cycle stability. Furthermore, the liquid-phase coating and chemical vapor deposition processes used in this scheme are simple and easy to implement, suitable for large-scale industrial production, and have promising application prospects.

[0024] Specifically, the liquid-phase coating process includes the following steps: In a solvent system, porous carbon material and a fast-ion conductor precursor are mixed uniformly, and then filtered to obtain porous carbon powder loaded with the fast-ion conductor precursor; under a protective atmosphere, the porous carbon powder loaded with the fast-ion conductor precursor is calcined at high temperature to form a porous carbon material coated with a fast-ion conductor, thus obtaining a modified porous carbon material. The calcination temperature for the high-temperature calcination is 150℃~200℃, and the solvent is water or an alcohol.

[0025] The alcohol solution can be at least one of ethanol, isopropanol, or butanol, whose polar properties promote the uniform adsorption of precursor molecules onto the porous carbon surface. Vacuum filtration allows for solid-liquid separation and precise adjustment of the precursor loading by controlling the filter membrane pore size. The high-temperature calcination temperature range promotes the conversion of phosphate or lithium salt precursors into fast ion conductors while avoiding exceeding the thermal decomposition critical temperature of the porous carbon material. A protective atmosphere of nitrogen or argon can be used, primarily to prevent oxidation of the carbon framework of the porous carbon material during high-temperature calcination.

[0026] Specifically, the porous carbon material is at least one of coconut shell carbon, resin carbon, and petroleum coke.

[0027] Specifically, the micropore ratio of porous carbon materials is 80% to 90%.

[0028] When the micropore ratio is below 80%, a bottleneck structure forms between the pores, hindering ion transport. When the micropore ratio is above 90%, the mechanical strength of the carbon skeleton decreases significantly.

[0029] When the micropore ratio is limited to 80%–90%, the carbon framework of the porous carbon material forms dense and isolated nanoscale cavities. The curvature effect of the micropore walls causes silicon particles to be distributed discretely in each independent cavity. Each micropore can independently bear the volume expansion of the silicon particles, avoiding stress superposition that could lead to the collapse of the overall framework structure. At the same time, it further maximizes the contact area between the inner wall of the micropore and silicon, forming a nanoscale lithium-ion diffusion interface, shortening the ion transport path to the atomic scale.

[0030] Therefore, the aforementioned ratio range balances the porosity and mechanical strength of the porous carbon material, ensuring sufficient space to accommodate silicon deposition while maintaining the supporting rigidity of the carbon framework, thus reducing the risk of pore collapse during charge-discharge cycles. Simultaneously, it ensures the continuity of the microporous structure of the porous carbon material, optimizing the electron conduction network, while the dense, independent cavities formed by the porous carbon material reduce side reactions caused by electrolyte penetration. Therefore, this application uses porous carbon material with a micropore ratio of 80%–90%, improving the structural stability and ion transport efficiency of the silicon-carbon anode material, thereby improving the cycle performance and rate performance of the battery.

[0031] Specifically, the fast ion conductor precursor is at least one of phosphate, lithium salt and aluminum salt, and the fast ion conductor is at least one of lithium phosphate, aluminum phosphate and aluminum metaphosphate.

[0032] Specifically, the deposition temperature for the first chemical vapor deposition (CVD) treatment is 500℃–800℃, and the deposition time is 0.5h–24h. The deposition temperature for the second CVD treatment is 700℃–1000℃, and the deposition time is 0.5h–24h.

[0033] In the first chemical vapor deposition process, excessively low temperatures can lead to incomplete decomposition of silane gases, resulting in a slow deposition rate and insufficient silicon layer density. Excessively high temperatures may damage the microporous structure of the porous carbon framework and cause excessive agglomeration of silicon particles. Furthermore, excessively short deposition times can result in insufficient silicon layer thickness, failing to form an effective conductive network; excessively long times may cause excessively thick silicon layers or carbon framework collapse, leading to accelerated volume expansion.

[0034] Therefore, by controlling the deposition temperature within the range of 500℃ to 800℃, it is possible to ensure that the silane gas is fully pyrolyzed to generate nano-silicon particles, while avoiding the damage to the microporous structure of the porous carbon framework caused by high temperatures. Controlling the deposition time within the range of 0.5h to 24h allows for precise control of the thickness and density of the silicon layer, ensuring that the silicon-carbon core has a high specific surface area and a uniform distribution of nano-silicon.

[0035] In the second chemical vapor deposition process, when the temperature is below 700℃, the soft carbon gas source such as ethylene, toluene, or cyclohexane may not be completely decomposed, which may lead to an excessively high proportion of disordered structures in the deposited carbon layer and a decrease in electron mobility. When the temperature exceeds 1000℃, the deposited carbon layer tends to become long-range ordered graphitization, which may result in a loss of the ability to buffer the volume expansion of silicon due to an excessively high elastic modulus.

[0036] Therefore, the above-mentioned temperature and time range parameters can enable the deposited nano-soft carbon coating layer to have an appropriate thickness and mesoporous structure, thereby effectively buffering the volume expansion of the silicon core and maintaining the rapid transport of lithium ions, thus improving the cycle stability and rate performance of the silicon-carbon anode material.

[0037] Specifically, the soft carbon gas source is at least one of ethylene, toluene, and cyclohexane, and the inert gas is at least one of nitrogen and argon.

[0038] The present invention will now be described in detail through specific embodiments. These embodiments are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0039] In the following embodiments, unless otherwise specified, the methods described are conventional methods; and unless otherwise specified, the reagents and materials described are commercially available.

[0040] Example 1 This embodiment provides a method for preparing a silicon-carbon anode material, including the following steps: Step 1: Prepare modified porous carbon materials.

[0041] One kilogram of coconut shell porous carbon material was prepared into a 20% (w / w) aqueous solution. Then, 50g of lithium dihydrogen phosphate was added, and the mixture was stirred for 30 minutes to ensure homogeneity. Next, 30g of lithium hydroxide was prepared into a 20% (w / w) aqueous solution. This solution was then slowly added to the porous carbon material solution, allowing the lithium dihydrogen phosphate and lithium hydroxide to react and form lithium phosphate. The solution was stirred for 30 minutes to ensure homogeneity. The resulting mixed solution was then filtered, and the resulting powder was dried in a vacuum drying oven at 200°C for 2 hours to obtain a modified porous carbon material coated with fast ion conductors.

[0042] Step 2: Prepare the silicon-carbon core.

[0043] Take 1 kg of the modified porous carbon material obtained in step 1 and put it into a fluidized bed device. Silane gas at a rate of 3 L / min is introduced into the device. Silane is decomposed at a high temperature of 500℃ to form elemental silicon, which is attached to the porous carbon channels and surface. The silane deposition time is 5 h. After the silane deposition is completed, the silicon-carbon core is obtained.

[0044] Step 3: Prepare silicon-carbon anode material.

[0045] After the silane deposition in step 2 is completed, the temperature is raised to 800°C, and ethylene gas at a rate of 3 L / min is continuously introduced into the fluidized bed equipment for soft carbon deposition and coating. At the same time, nitrogen gas at a rate of 20 L / min is introduced for atmosphere protection. The deposition time is 2 hours, and then the temperature is lowered to obtain silicon-carbon anode material.

[0046] Example 2 This embodiment provides a method for preparing a silicon-carbon anode material, including the following steps: Step 1: Prepare modified porous carbon materials.

[0047] One kilogram of coconut shell porous carbon material was prepared into a 20% (w / w) aqueous solution. Then, 50 g of lithium dihydrogen phosphate was added, and the mixture was stirred for 30 minutes to ensure homogeneity. Next, 30 g of lithium hydroxide was prepared into a 20% (w / w) aqueous solution. This solution was then slowly added to the porous carbon material solution, allowing the lithium dihydrogen phosphate and lithium hydroxide to react and form lithium phosphate. The solution was stirred for 30 minutes to ensure homogeneity. The resulting mixed solution was then filtered, and the resulting powder was dried in a vacuum drying oven at 150°C for 2 hours to obtain a modified porous carbon material coated with fast ion conductors.

[0048] Step 2: Prepare the silicon-carbon core.

[0049] Take 1 kg of the modified porous carbon material obtained in step 1 and put it into a fluidized bed device. Silane gas at a rate of 3 L / min is introduced into the device. Silane is decomposed at a high temperature of 500℃ to form elemental silicon, which is attached to the porous carbon channels and surface. The silane deposition time is 5 h. After the silane deposition is completed, the silicon-carbon core is obtained.

[0050] Step 3: Prepare silicon-carbon anode material.

[0051] After the silane deposition in step 2 is completed, the temperature is raised to 800°C, and ethylene gas at a rate of 3 L / min is continuously introduced into the fluidized bed equipment for soft carbon deposition and coating. At the same time, nitrogen gas at a rate of 20 L / min is introduced for atmosphere protection. The deposition time is 2 hours, and then the temperature is lowered to obtain silicon-carbon anode material.

[0052] Example 3 This embodiment provides a method for preparing a silicon-carbon anode material, including the following steps: Step 1: Prepare modified porous carbon materials.

[0053] 1 kg of petroleum coke porous carbon material was prepared into a 20% (w / w) aqueous solution. Then, 50 g of lithium dihydrogen phosphate was added, and the mixture was stirred for 30 min to ensure homogeneity. Next, 30 g of lithium hydroxide was prepared into a 20% (w / w) aqueous solution. This solution was then slowly added to the porous carbon material solution, allowing the lithium dihydrogen phosphate and lithium hydroxide to react and form lithium phosphate. The solution was stirred for 30 min to ensure homogeneity. The resulting mixed solution was then filtered, and the resulting powder was dried in a vacuum drying oven at 200°C for 2 h to obtain a modified porous carbon material coated with fast ion conductors.

[0054] Step 2: Prepare the silicon-carbon core.

[0055] Take 1 kg of the modified porous carbon material obtained in step 1 and put it into a fluidized bed device. Silane gas at a rate of 3 L / min is introduced into the device. Silane is decomposed at a high temperature of 500℃ to form elemental silicon, which is attached to the porous carbon channels and surface. The silane deposition time is 5 h. After the silane deposition is completed, the silicon-carbon core is obtained.

[0056] Step 3: Prepare silicon-carbon anode material.

[0057] After the silane deposition in step 2 is completed, the temperature is raised to 800°C, and ethylene gas at a rate of 3 L / min is continuously introduced into the fluidized bed equipment for soft carbon deposition and coating. At the same time, nitrogen gas at a rate of 20 L / min is introduced for atmosphere protection. The deposition time is 2 hours, and then the temperature is lowered to obtain silicon-carbon anode material.

[0058] Example 4 The only difference from Example 1 is that the porous carbon material is resin carbon.

[0059] Example 5 The only difference from Example 1 is that the temperature of the silane deposition process in step 2 is 800°C.

[0060] Example 6 The only difference from Example 1 is that the temperature of the silane deposition process in step 2 is 650°C.

[0061] Example 7 The only difference from Example 1 is that the temperature of the soft carbon deposition process in step 2 is 700°C.

[0062] Example 8 The only difference from Example 1 is that the temperature of the soft carbon deposition process in step 2 is 1000°C.

[0063] Example 9 The difference from Example 1 is that in step 1, aluminum phosphate is generated by reacting aluminum sulfate and sodium phosphate, that is, the fast ion conductor in the modified porous carbon material is aluminum phosphate.

[0064] Example 10 The difference from Example 1 is that in step 1, aluminum metaphosphate is generated by reacting aluminum sulfate and sodium hexametaphosphate, that is, the fast ion conductor in the modified porous carbon material is aluminum metaphosphate.

[0065] Example 11 The difference from Example 1 is that the solvents for both the porous carbon material solution and the lithium hydroxide solution in step 1 are alcohols.

[0066] It should be noted that the performance of the silicon-carbon anode materials prepared in Examples 4 to 11 is not significantly different from that in Examples 1 to 3.

[0067] Comparative Example 1 This embodiment provides a method for preparing a silicon-carbon anode material, including the following steps: 1 kg of coconut shell porous carbon material was placed in a fluidized bed apparatus, and silane gas at a rate of 3 L / min was introduced into the apparatus. Under high temperature conditions of 500℃, silane was decomposed to form elemental silicon, which adhered to the porous carbon channels and surface. The silane deposition time was 5 h. After the silane deposition was completed, acetylene gas at a rate of 3 L / min was introduced into the apparatus to perform carbon coating at 500℃ for 2 h. After cooling, silicon-carbon anode material was obtained.

[0068] Test and statistical results of coin cell performance of silicon-carbon anode materials: Button cell testing method: The silicon-carbon anode materials prepared in Examples 1-3 and Comparative Example 1 were thoroughly ground into a slurry with conductive agent SP and binder CMC at a mass ratio of 8:1:1. The mixed electrode material was then coated onto copper foil to form an electrode sheet. The electrode sheet was dried in a vacuum drying oven at 80°C for 12 hours and then punched into Ø16mm circular electrode sheets. Using the punched Ø16mm electrode sheet as the positive electrode and lithium metal sheet as the negative electrode, a CR2032 type button cell was assembled. The charge and discharge cutoff voltages were 1.5V and 0.005V, respectively. After activating the battery by three charge-discharge cycles at a current density of 0.1C, its rate performance was tested at current densities of 1C / 2C / 5C / 10C, ​​followed by cycle stability testing at a current density of 0.5C. The specific capacity, initial efficiency, rate capability, and cycle retention rate results are shown in Table 1.

[0069] Table 1. Statistical Chart of Button Circuit Test Results As shown in Table 1, compared with Comparative Example 1, the silicon-carbon anode materials prepared in Examples 1 to 3 have higher reversible capacity. This indicates that compared with the amorphous carbon layer formed in Comparative Example 1, the nano-soft carbon layer formed in Examples 1 to 3 has a short-range ordered graphite microcrystalline structure. This structure has the characteristics of high electron mobility and reduced interfacial charge transfer impedance, which is beneficial to lithium ion transport and migration, thereby giving the silicon-carbon anode materials prepared in Examples 1 to 3 higher reversible capacity.

[0070] Furthermore, as shown in Table 1, compared with Comparative Example 1, the silicon-carbon anode materials prepared in Examples 1 to 3 have better first-cycle efficiency, charging DC internal resistance, capacity retention rate at 2C / 5C discharge rate, and 100-cycle retention rate. This indicates that the electrochemical performance of the silicon-carbon anode materials has been improved to a certain extent under the synergistic effect of the short-range ordered graphite microcrystalline structure of the nano-soft carbon layer and the fast ion conductor.

[0071] In summary, the preparation method of silicon-carbon anode material provided by this invention can effectively improve the electrochemical performance of silicon-carbon anode material, especially the rate performance of silicon-carbon anode material, which is particularly suitable for application environments that require high rate performance.

[0072] Particle size testing and statistical results of silicon-carbon anode materials: Appropriate amounts of silicon-carbon anode materials prepared in Examples 1 to 3 and Comparative Example 1 were taken and tested using a particle size analyzer. The specific particle size test results are shown in Table 2.

[0073] Table 2 Statistical chart of particle size test results As shown in Table 2, compared to Comparative Example 1, the D of the silicon-carbon anode materials prepared in Examples 1 to 3 is significantly higher. 50 Larger particle size, D min Larger particle size, D max The smaller particle size results in better particle size uniformity. Due to the modification of porous carbon, a fast ion conductor layer is pre-deposited in the porous carbon, so the median particle size of the silicon-carbon anode materials prepared in Examples 1 to 3 is slightly higher than that of Comparative Example 1; at the same time, due to the modification, the uniformity of the silicon-carbon anode materials prepared in Examples 1 to 3 is better than that of Comparative Example 1, thus exhibiting the characteristics of a narrow particle size range and a smaller maximum particle size.

[0074] The transmission electron microscopy (TEM) results of the silicon-carbon anode material prepared in Example 1 are as follows: Figure 2 As shown in the figure, a soft carbon coating layer with a thickness of about 4 nm is formed on the surface of the silicon-carbon core, indicating that the technical solution of depositing nano-soft carbon on the surface of the silicon-carbon core using chemical vapor deposition is feasible.

[0075] The above description is merely a preferred embodiment of the present invention, and the specific embodiments described above are not intended to limit the present invention. Various modifications and variations can be made within the scope of the technical concept of the present invention. All refinements, modifications, or equivalent substitutions made by those skilled in the art based on the above description are within the scope of protection of the present invention.

Claims

1. A method for preparing a silicon-carbon anode material, characterized in that, Includes the following steps: Porous carbon materials and fast ion conductor precursors are coated with liquid phase to form porous carbon materials coated with fast ion conductors, thus obtaining modified porous carbon materials. Using silane gas as a deposition precursor, a first chemical vapor deposition process was performed to deposit nano-silicon on the surface of modified porous carbon material, thus obtaining a silicon-carbon core. In an inert gas atmosphere, using soft carbon gas as a deposition precursor, a second chemical vapor deposition process is performed to deposit nano-soft carbon on the surface of the silicon-carbon core, thus obtaining silicon-carbon anode material.

2. The method for preparing the silicon-carbon anode material according to claim 1, characterized in that, The porous carbon material is at least one of coconut shell carbon, resin carbon, and petroleum coke.

3. The method for preparing the silicon-carbon anode material according to claim 2, characterized in that, The porous carbon material has a micropore ratio of 80% to 90%.

4. The method for preparing the silicon-carbon anode material according to claim 1, characterized in that, The fast ion conductor precursor is at least one of phosphate, lithium salt and aluminum salt, and the fast ion conductor is at least one of lithium phosphate, aluminum phosphate and aluminum metaphosphate.

5. The method for preparing the silicon-carbon anode material according to claim 1, characterized in that, The deposition temperature for the first chemical vapor deposition treatment is 500℃~800℃, and the deposition time is 0.5h~24h.

6. The method for preparing the silicon-carbon anode material according to claim 1, characterized in that, The soft carbon gas source is at least one of ethylene, toluene, and cyclohexane, and the inert gas is at least one of nitrogen and argon.

7. The method for preparing the silicon-carbon anode material according to claim 6, characterized in that, The deposition temperature for the second chemical vapor deposition process is 700℃~1000℃, and the deposition time is 0.5h~24h.

8. The method for preparing the silicon-carbon anode material according to any one of claims 1 to 7, characterized in that, The liquid phase coating process includes the following steps: In a solvent system, porous carbon material and fast ion conductor precursor are mixed evenly and then filtered to obtain porous carbon powder loaded with fast ion conductor precursor. In a low-oxygen atmosphere, porous carbon powder loaded with fast ion conductor precursors is calcined at high temperature to form a porous carbon material coated with fast ion conductors, thus obtaining a modified porous carbon material. The calcination temperature of the high-temperature calcination treatment is 150℃~200℃, and the solvent is water or alcohol.

9. A silicon-carbon anode material, characterized in that, The silicon-carbon anode material is prepared by the preparation method according to any one of claims 1 to 8, wherein the silicon-carbon anode material has a porous core-shell structure and the diameter of the silicon-carbon anode material is 1µm to 20µm.

10. The silicon-carbon anode material according to claim 9, characterized in that, The silicon-carbon anode material contains 30% to 60% Si by mass, 30% to 60% C by mass, and the fast ion conductor by mass is 1% to 10% of the silicon-carbon anode material.

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