Preparation method of silicon-carbon composite negative electrode material

Abstract

The application discloses a preparation method of a silicon-carbon composite negative electrode material and belongs to the technical field of new energy materials. The preparation method of the silicon-carbon composite negative electrode material comprises the following steps: S1, etching a silicon-based particle to obtain porous silicon; S2, forming porous carbon coating on the surface and inside of the porous silicon; S3, crushing the product obtained in step S2; and S4, pyrolyzing the product obtained in step S3 and a carbon source after mixing. The preparation method of the silicon-carbon composite negative electrode material can improve the overall performance of the obtained silicon-carbon composite negative electrode material through a simple preparation method.

Description

Technical Field

[0001] This invention relates to the field of new energy materials technology, and in particular to a method for preparing a silicon-carbon composite anode material. Background Technology

[0002] Silicon-based materials, due to their extremely high theoretical specific capacity (approximately 4200 mAh / g), are considered core candidates for next-generation high-energy-density lithium-ion battery anode materials. However, the dramatic volume expansion (>300%) of silicon during charge and discharge leads to electrode material pulverization and repeated rupture and regeneration of the solid electrolyte interface film, severely limiting its cycle life. To address these issues, traditional technologies have primarily focused on two directions: One approach is the top-down method, which involves preparing porous silicon using processes such as chemical etching and then coating its surface with carbon materials to form a silicon-carbon composite material with a hierarchical porous structure. The pores within the porous structure provide buffer space for the volume expansion of silicon, alleviating mechanical stress to some extent, while the surface carbon material provides electrical conductivity. However, even with this porous etching method, the silicon substrate remains a single entity, and it still faces the risk of pulverization due to localized stress concentration during cycling.

[0003] Secondly, bottom-up methods, such as chemical vapor deposition and sol-gel, directly prepare nano-silicon or silicon-carbon composite materials. While these methods can control particle size, they are prone to agglomeration due to high particle surface energy, and the resulting silicon particles have a wide particle size distribution and poor processing performance; or the synthesis process is quite difficult. In addition, conventional coating techniques (such as liquid phase coating or dense carbon layer deposition) can provide some protection, but they are difficult to obtain sufficiently small silicon-based particles through simple methods to overcome the performance problems caused by volume expansion.

[0004] In summary, traditional methods for preparing silicon-carbon materials are complex and struggle to effectively overcome the volume expansion problem of silicon-carbon anode materials. Summary of the Invention

[0005] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, this invention proposes a method for preparing silicon-carbon composite anode materials, which can improve the overall performance of the obtained silicon-carbon composite anode materials through a simple preparation method.

[0006] According to an embodiment of the first aspect of the present invention, a method for preparing a silicon-carbon composite anode material is provided, the method comprising the following steps: S1. Etching silicon-based particles to create porous silicon; S2. Form a porous carbon coating on the surface and inside of the porous silicon; S3. The product obtained from crushing step S2; S4. Pyrolyze the product obtained in step S3 and the carbon source.

[0007] The preparation method according to embodiments of the present invention has at least the following beneficial effects: Traditional top-down fabrication methods struggle to produce silicon particles with sufficiently small diameters to accommodate volume changes during charge and discharge. Traditional bottom-up fabrication methods either require expensive equipment and complex processes, or produce silicon-based particles that are prone to agglomeration. Furthermore, traditional fabrication methods, whether top-down or bottom-up, are susceptible to oxidation, leading to a decrease in capacity.

[0008] In the preparation method provided by the present invention, after the coating in step S2, the material is crushed. The porous carbon coating plays a certain role in physical protection and avoiding oxidation. Furthermore, the secondary coating in step S4 protects the new cross-section generated in step S3, significantly preventing oxidation and avoiding side reactions between silicon and electrolyte in the silicon-carbon composite anode material.

[0009] In the preparation method provided by the present invention, the porous carbon coating is crushed after coating. The porous carbon coating plays a certain role in inhibiting agglomeration, avoiding the agglomeration of elemental silicon, improving the dispersion of elemental silicon in the obtained silicon-carbon composite anode material, and thus improving its capacity, cycle performance and rate performance.

[0010] In the preparation method provided by this invention, porous silicon is first obtained, and then it is crushed, which fully enriches the microstructure of elemental silicon and improves its capacity to accommodate volume changes. At the same time, the crushing in step S3 reduces the formation of new fracture surfaces in elemental silicon during the subsequent rolling process of the negative electrode sheet, and further improves the side reactions of the obtained silicon-carbon composite negative electrode material and electrolyte.

[0011] In summary, the preparation method provided by this invention, through reasonable process design, significantly improves the capacity utilization, cycle performance, and rate performance of silicon-carbon composite anode materials. If the order of steps S2 and S3 is reversed, or step S2 is omitted, it will lead to the agglomeration and oxidation of silicon in the silicon-carbon composite anode material. If step S3 is omitted, the porous silicon in the resulting silicon-carbon composite anode material will break during the rolling process of the anode sheet preparation, resulting in new fractures, which will seriously affect the cycle and high-rate performance.

[0012] According to some embodiments of the present invention, in step S1, the mass ratio of the porous silicon to the silicon-based particles is 20~30:100. Specifically, it can be 20:100, 25:100, 30:100; or a range of values ​​consisting of any two of the above points. Thus, the obtained porous silicon has a rich pore structure and sufficiently thin pore walls to facilitate successful crushing in step S3.

[0013] According to some embodiments of the present invention, in step S1, the silicon-based particles include elemental silicon particles or silicon metal alloy particles. Compared with elemental silicon particles, silicon-carbon composite anode materials prepared from silicon metal alloy particles have superior performance. This is because silicon metal alloy particles selectively etch away the metal alloy during etching, and the metal alloy is uniformly distributed within the silicon metal alloy particles. Therefore, the resulting porous silicon has a more uniform pore structure, and the particle size of the product obtained in step S3 is also more uniform.

[0014] According to some embodiments of the present invention, in step S1, the silicon-based particles are silicon-aluminum alloy particles.

[0015] According to some embodiments of the present invention, the mass percentage of aluminum in the silicon-aluminum alloy particles is 70-80%. For example, it can be 70%, 75%, 80%; or a range of values ​​consisting of any two of the above points.

[0016] According to some embodiments of the present invention, in step S1, the particle size of the silicon-based particles is 5~20μm. For example, it can be 5μm, 6μm, 8μm, 10μm, 12μm, 14μm, 15μm, 16μm, 18μm, 20μm; or a range of values ​​composed of any two of the above points.

[0017] In actual production, since step S3 requires crushing, the particle size is not strictly limited here, as long as it is within 100 micrometers and the etching reaction can proceed smoothly.

[0018] According to some embodiments of the present invention, in step S1, the etching method includes at least one of liquid phase method and solid phase method.

[0019] According to some embodiments of the present invention, in step S1, the etchant used for etching includes at least one of an inorganic acid and NaOH. The inorganic acid includes at least one of phosphoric acid, nitric acid, and hydrochloric acid.

[0020] According to some embodiments of the present invention, in step S1, the silicon-based particles are silicon metal alloy particles, and the etching method is as follows: The silicon-based particles and the aqueous solution of the inorganic acid are mixed and reacted. The concentration of the aqueous solution is 1~5 mol / L; for example, it can be 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L, 5 mol / L; or a range of values ​​consisting of any two of the above points. The temperature of the mixing reaction is 50~100℃; for example, it can be 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, 90℃, 95℃, 100℃; or a range of values ​​composed of any two of the above points.

[0021] The amount of the aqueous solution is not strictly limited, as long as it is sufficient to dissolve the metal alloy in the silicon metal alloy particles and to fully submerge the silicon-based particles. For example, it can be 1g:50~100mL. Specifically, it can be 1g:50mL, 1g:50~100mL, 1g:60mL, 1g:70mL, 1g:80mL, 1g:90mL, 1g:100mL; or a range of values ​​consisting of any two of the above points.

[0022] The endpoint of the mixing reaction is when no more bubbles emerge.

[0023] According to some embodiments of the present invention, in step S1, the silicon-based particles are elemental silicon particles, and the etching method is as follows: The silicon-based particles are mixed with sodium hydroxide and then calcined. The proportion of sodium hydroxide used is designed based on the mass ratio of the porous silicon to the silicon-based particles and the stoichiometric ratio of the reaction between sodium hydroxide and silicon.

[0024] The calcination temperature is 600~800℃. For example, it can be 600℃, 650℃, 700℃, 750℃, 800℃; or a range of values ​​consisting of any two of the above points.

[0025] The calcination time is 0.5 to 3 hours. For example, it can be 0.5 hours, 1 hour, 1.5 hours, 2 hours, 2.5 hours, or 3 hours; or a range of values ​​consisting of any two of the above points.

[0026] The calcination is carried out in a protective atmosphere.

[0027] According to some embodiments of the present invention, step S1 further includes washing the solid product obtained after etching with water. This removes the reaction products and unreacted etching agent.

[0028] According to some embodiments of the present invention, in step S2, the method for coating the porous carbon includes at least one of a solvothermal method and a chemical vapor deposition method. Due to the permeability of liquids and gases, both methods can ensure that porous carbon coating is also distributed inside the porous silicon.

[0029] According to some embodiments of the present invention, in step S2, the porous carbon coating accounts for 5-15% of the mass percentage of the product obtained in step S2. Specifically, it can be 5%, 8%, 10%, 12%, or 15%; or a range consisting of any two of the above values. As the amount of porous carbon coating increases, its protection of the porous silicon improves, significantly suppressing the oxidation of the porous silicon; however, excessive coating thickness can affect the crushing effect in step S3 to some extent. Within the above range, the resulting silicon-carbon composite anode material exhibits excellent overall performance.

[0030] According to some embodiments of the present invention, in step S2, the porous carbon coating method is a solvothermal method. Specifically, the operation is as follows: The mixture of the porous silicon and glucose aqueous solution is subjected to a solvothermal reaction.

[0031] The temperature of the solvothermal reaction is 160~220℃. For example, it can be 160℃, 180℃, 200℃, 220℃; or a range of any two of the above values.

[0032] The duration of the solvothermal reaction is 1 to 5 hours. For example, it can be 1 hour, 2 hours, 3 hours, 4 hours, or 5 hours; or a range of values ​​consisting of any two of the above points.

[0033] The amount of glucose used is determined by the percentage of the porous carbon coating in the product obtained in step S2. In practice, experiments can be conducted first to determine the conversion efficiency of glucose under specific temperature and time conditions; this can then be used as a reference to add an appropriate amount of glucose in subsequent experiments. For example, within the aforementioned temperature and time range, the conversion rate of glucose to porous carbon is 30-50%. For reference, the mass ratio of porous silicon to glucose is 2-9:1. Specifically, it can be 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, or 9:1; or a range of values ​​consisting of any two of the above points.

[0034] The solid-liquid ratio of the porous silica and the glucose aqueous solution is 1g:30~100mL. For example, it can be 1g:30mL, 1g:40mL, 1g:50mL, 1g:60mL, 1g:70mL, 1g:80mL, 1g:90mL, 1g:100mL; or a range of values ​​consisting of any two of the above points.

[0035] Thus, the porous silicon can be fully submerged, and there is sufficient liquid in the mixed system for flow and mass transfer.

[0036] The solvothermal reaction is followed by sequential water washing and drying. To fully utilize the porous carbon-coated structure, freeze drying is preferably used for the drying process.

[0037] According to some embodiments of the present invention, in step S2, the method for coating porous carbon includes chemical vapor deposition. The carbon source used includes gaseous hydrocarbons, such as at least one of methane, ethane, and ethylene.

[0038] The atmosphere of the chemical vapor deposition method also includes hydrogen, and the flow ratio of the carbon source to hydrogen is 3.5 to 4.5:1. For example, it can be 3.5:1, 4:1, 4.5:1; or a range of values ​​consisting of any two of the above points.

[0039] The temperature for the chemical vapor deposition method is 900~1200℃. For example, it can be 900℃, 950℃, 1000℃, 1050℃, 1100℃, 1150℃, 1200℃; or a range of values ​​consisting of any two of the above points.

[0040] The reaction time of the chemical vapor deposition method is based on the amount of porous carbon coating in the resulting product.

[0041] According to some embodiments of the present invention, in step S3, the crushing method includes at least one of roller pressing, ball milling and air jet milling.

[0042] According to some embodiments of the present invention, in step S3, the crushing method includes ball milling. The ball-to-material ratio of the ball mill is 80 to 150:1. For example, it can be 80:1, 90:1, 100:1, 110:1, 120:1, 130:1, 140:1, 150:1; or a range of values ​​consisting of any two of the above points.

[0043] The milling media in the ball mill include large balls and small balls. The large balls are responsible for providing pressure to crush the particles, while the small balls are mainly used for mixing.

[0044] The mass ratio of the large ball to the small ball is 8 to 12:1. For example, it can be 8:1, 9:1, 10:1, 11:1, 12:1; or a range of values ​​consisting of any two of the above points.

[0045] The rotational speed of the ball mill is ≥500 rpm. For example, it can be 500 rpm, 600 rpm, 700 rpm, 800 rpm, 900 rpm, 1000 rpm; or a range of values ​​consisting of any two of the above points.

[0046] The ball milling time is ≥5h. For example, it can be 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h; or a range of values ​​composed of any two of the above points.

[0047] The material obtained after ball milling is sieved. This separates the material from the grinding media and also prevents agglomeration and ensures uniform material distribution.

[0048] According to some embodiments of the present invention, in step S3, the crushing is carried out in a protective atmosphere.

[0049] According to some embodiments of the present invention, in step S4, the carbon source includes at least one of pitch and resin.

[0050] According to some embodiments of the present invention, in step S4, the mass ratio of the product obtained in step S3 to the carbon source is 1:1 to 2. For example, it can be 1:1, 1:1.2, 1:1.5, 1:1.8, 1:2; or a range of values ​​composed of any two of the above points.

[0051] According to some embodiments of the present invention, in step S4, the mixing process also serves as granulation. Compared with crushing after pyrolysis to obtain the corresponding particle size, granulation before pyrolysis avoids the exposure of elemental silicon to subsequent crushing; thus improving the stability of the resulting silicon-carbon composite anode material.

[0052] According to some embodiments of the present invention, in step S4, the pyrolysis temperature is 900~1100℃. For example, it can specifically be 900℃, 1000℃, 1050℃, 1100℃; or a range of values ​​composed of any two of the above points.

[0053] According to some embodiments of the present invention, in step S4, the isothermal duration of the pyrolysis is 2 to 3 hours. For example, it can be 2 hours, 2.5 hours, 3 hours; or a range of values ​​composed of any two of the above points.

[0054] According to some embodiments of the present invention, in step S4, the pyrolysis is carried out in a protective atmosphere.

[0055] According to some embodiments of the present invention, in the preparation method, the protective atmosphere includes at least one of nitrogen and argon.

[0056] According to some embodiments of the present invention, the particle size of the silicon-carbon composite anode material is 11~14μm. For example, it can be 11μm, 12μm, 13μm, 14μm; or a range of values ​​composed of any two of the above points.

[0057] According to some embodiments of the present invention, the carbon content in the silicon-carbon composite anode material is 50-70%. For example, it can be 50%, 55%, 60%, 65%, 70%; or a range of values ​​consisting of any two of the above points.

[0058] According to some embodiments of the present invention, the specific capacity of the silicon-carbon composite anode material at 0.2C is ≥1500mAh / g. Specifically, it can be 1500mAh / g, 1600mAh / g, 1700mAh / g, 1800mAh / g, 1900mAh / g; or a range of values ​​consisting of any two of the above points.

[0059] According to some embodiments of the present invention, the specific capacity of the silicon-carbon composite anode material at 0.5C is ≥1400mAh / g. Specifically, it can be 1400mAh / g, 1500mAh / g, 1600mAh / g, 1700mAh / g; or a range of values ​​consisting of any two of the above points.

[0060] According to some embodiments of the present invention, the specific capacity of the silicon-carbon composite anode material 1C is ≥1200mAh / g. For example, it can be 1200mAh / g, 1300mAh / g, 1400mAh / g, 1500mAh / g; or a range of values ​​consisting of any two of the above points.

[0061] According to some embodiments of the present invention, the specific capacity of the silicon-carbon composite anode material 2C is ≥1000mAh / g. For example, it can be 1000mAh / g, 1100mAh / g, 1200mAh / g; or a range of values ​​composed of any two of the above points.

[0062] According to some embodiments of the present invention, the specific capacity of the silicon-carbon composite anode material 5C is ≥900mAh / g. For example, it can be 900mAh / g, 1000mAh / g, 1100mAh / g; or a range of values ​​composed of any two of the above points.

[0063] According to some embodiments of the present invention, the first-cycle coulombic efficiency of the silicon-carbon composite anode material at 0.2C is ≥79%. For example, it can be 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%; or a range of values ​​consisting of any two of the above points.

[0064] According to some embodiments of the present invention, the capacity retention rate of the silicon-carbon composite anode material after 500 cycles at 1C is ≥70%. Specifically, it can be 70%, 71%, 72%, or 75%. The capacity after 500 cycles is ≥850 mAh / g; specifically, it can be 850 mAh / g, 900 mAh / g, 950 mAh / g, 1000 mAh / g, or 1050 mAh / g; or a range of values ​​consisting of any two of the above points.

[0065] According to some embodiments of the present invention, the silicon-carbon composite anode material has a capacity retention rate of ≥60% after 1000 cycles at 1C. Specifically, this could be 60%, 61%, 62%, 63%, 64%, 65%, or 70%; or a range of values ​​formed by any two of the above points. The capacity after 1000 cycles is ≥750 mAh / g; specifically, this could be 750 mAh / g, 800 mAh / g, 850 mAh / g, or 900 mAh / g; or a range of values ​​formed by any two of the above points.

[0066] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. Detailed Implementation

[0067] The following will describe the concept and technical effects of the present invention clearly and completely with reference to embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0068] Example 1 This example provides a method for preparing a silicon-carbon composite anode material, the specific steps of which are as follows: S1. Etching silicon-based particles to form porous silicon; wherein... The silicon-based particles are silicon-aluminum alloys, in which aluminum accounts for 75% by mass and the D50 particle size is 12μm.

[0069] The etching solution was a 2.1 mol / L aqueous solution of phosphoric acid; the solid-liquid ratio was 1 g: 70 mL.

[0070] The etching temperature was 80℃, and the etching endpoint was when no obvious bubbles emerged; in this example, it was 30 minutes.

[0071] After etching, the product obtained by water washing is porous silicon.

[0072] S2. Forming a porous carbon coating on and inside the porous silicon; specifically: Porous silica was dispersed in a glucose aqueous solution and subjected to a solvothermal reaction. The solid-liquid ratio of porous silica and glucose aqueous solution was 1 g: 50 mL; the mass ratio of porous silica to glucose was 2.5: 1. The solvothermal reaction was carried out at a temperature of 180℃ for 2 hours.

[0073] After the solvothermal reaction, the sample was washed three times with water and then freeze-dried.

[0074] S3. The product obtained from crushing step S2; The crushing method is ball milling; among which, The grinding beads for the ball mill were a mixture of 3mm and 1mm agate beads in a 10:1 mass ratio; the ball-to-material mass ratio during the ball milling process was 110:1; the ball milling process was carried out in an argon-protected atmosphere. The ball milling speed was 800 rpm, and the milling time was 12 hours.

[0075] After ball milling, the material is sieved through a 400-mesh screen.

[0076] S4. Pyrolyze the product obtained in step S3 and the carbon source.

[0077] The product obtained in step S3 and asphalt are mixed at a mass ratio of 1:1.5 and granulated to form spherical particles with a D50 of approximately 12 μm.

[0078] Then, it is pyrolyzed at 1000℃ for 2.5 hours; the pyrolysis atmosphere is argon.

[0079] Example 2 This example prepares a silicon-carbon composite anode material, which differs from Example 1 in that: In this example, the following steps are used to replace step S1 in Example 1; steps S2 to S4 are the same as in Example 1.

[0080] The silicon-based particles are etched to form porous silicon. The silicon-based particles are elemental silicon. The etching method involves wet mixing the silicon-based particles with sodium hydroxide and then calcining them at 700°C for 1 hour. The calcination atmosphere is argon.

[0081] In this example, by adjusting the amount of sodium hydroxide used, an etching amount (the mass of the etched material) comparable to that in Example 1 was obtained.

[0082] After calcination, wash with pure water and then dry.

[0083] Example 3 This example prepares a silicon-carbon composite anode material, which differs from Example 1 in that: In this example, step S2 of Example 1 is replaced by the following steps; steps S1 and S3~S4 are the same as in Example 1.

[0084] A porous carbon coating is formed on the surface and inside of the porous silicon; specifically, the coating method is chemical vapor deposition, and the deposited carbon accounts for 14% of the mass of the porous silicon obtained in step S1. In chemical vapor deposition, the temperature is 1050℃, the carbon source is methane, the reducing gas is hydrogen, and the flow ratio of methane to hydrogen is 80:20.

[0085] Example 4 This example prepares a silicon-carbon composite anode material, which differs from Example 3 in that: Some parameters in steps S2 and S3 have been adjusted, as follows: In step S2, the deposited carbon accounts for 5% of the mass of porous silicon obtained in step S1.

[0086] In step S3, the amount of asphalt is adjusted so that the carbon content in the resulting product is comparable to that in Example 3.

[0087] The remaining steps not mentioned are the same as those in Example 3.

[0088] Comparative Example 1 This example prepares a silicon-carbon composite anode material, which differs from Example 1 in that: The order of steps S2 and S3 is reversed, that is, crushing is performed first, followed by carbon coating treatment.

[0089] Comparative Example 2 This example prepares a silicon-carbon composite anode material, which differs from Example 1 in that: Step S3 is not performed.

[0090] Test case In this example, the C content in the products obtained in steps S2 (and step S3 in Comparative Example 1) and S4 was tested using thermogravimetric analysis (TGA). During the process, the sample and the porous silicon obtained in step S1 were tested under the same conditions; the sum of the weight loss of the sample and the weight gain of the porous silicon was the C mass. The thermogravimetric analysis was conducted in air at temperatures ranging from room temperature to 800°C. The test results are shown in Table 1.

[0091] In the second aspect of this example, a laser particle size analyzer was used to test the D50 particle size of the products obtained in the examples and comparative examples. The specific results are shown in Table 1.

[0092] The third aspect of this example tests the electrochemical performance of the silicon-carbon composite anode materials obtained in the embodiments and comparative examples.

[0093] The active material of the working electrode of the coin cell used in the test was the silicon-carbon composite anode material obtained in the examples and comparative examples, and the counter electrode was a lithium sheet. The voltage range during the test was 0.01~2.5V; the nominal specific capacity was 1500mAh / g. Capacities at 0.2C, 0.5C, 1C, 2C, and 5C were tested, as well as the first-cycle coulombic efficiency at 0.2C.

[0094] The negative electrode active material of the full cell used in the test was the silicon-carbon composite negative electrode material prepared in the examples and comparative examples, and the positive electrode active material was lithium iron phosphate. The test voltage was 2~3.7V; after 3 cycles at 0.2C, a 1C cycle test was performed, and the capacity retention rate at 500 cycles and 1000 cycles was recorded.

[0095] For the above test items, four parallel tests were conducted in each group. After removing obviously abnormal results, the average of the remaining results was calculated, and the corresponding significant figures were retained. The statistical results are shown in Table 1.

[0096] Table 1. Performance of silicon-carbon composite anode materials obtained in the examples and comparative examples. The particle size results show that the silicon-carbon composite anode material basically inherits the particle size of the precursor (granulated spheroids in step S4), and only undergoes a small amount of shrinkage during subsequent sintering. Due to the influence of the amount of carbon source used in step S4 and the morphology of the product obtained in step S3, the amount of shrinkage will vary slightly in different specific embodiments. In Comparative Example 2, the crushing in step S3 was not performed, and the resulting silicon-carbon composite anode material will, in principle, inherit the particle size of the silicon-based particles obtained in step S1. However, due to the irregular crushing and agglomeration of the intermediate product during the processing in steps S2 and S4, the particle size deviates significantly from the particle size of the silicon-based particles, and the results differ from those of other specific embodiments.

[0097] Based on the above results, it can be seen that within the scope of the technical solution provided by this invention, silicon-carbon composite anode materials with excellent capacity, rate capability, first-cycle efficiency, and cycle performance can be obtained. Specifically, the capacity at 0.2C rate is ≥1500mAh / g, the first-cycle coulombic efficiency is ≥75%, the capacity retention rate at 1C 500 cycles is ≥70%, and the capacity retention rate at 1C 1000 cycles is ≥60%.

[0098] Comparing the results of Example 1 and Example 2, it can be seen that silicon-based particles using silicon metal alloy particles have better performance. This is because, compared with using elemental silicon particles, the porous silicon obtained after etching with silicon metal alloy particles has a richer and more regular pore structure. Therefore, the particle size of the product obtained from subsequent crushing is smaller, and the crushed product may still contain microscopic pore structures, which is more conducive to the utilization of capacity and the release of stress during charging and discharging.

[0099] Comparing the results of Examples 1 and 3, it can be seen that the silicon-carbon composite anode material obtained by chemical vapor deposition (CVD) coating porous silicon exhibits slightly better performance. This is because, compared to liquid-phase coating, the carbon coating layer obtained by vapor-phase coating is more uniform, and the coating method used in Example 3 can form upright graphene on the surface and within the pore structure of the porous silicon. This upright structure further prevents the re-agglomeration of the fragmentation products during subsequent crushing, and Example 3 also fully utilizes the electrical conductivity of graphene.

[0100] Comparing the results of Example 1 and Example 4, it can be seen that if the amount of carbon coating on the porous silicon surface decreases, the hindering effect of the carbon coating layer on the agglomeration of porous silicon will decrease to a certain extent, and the protection of the new cross-section of the broken product will also decrease to a certain extent. Therefore, the overall performance of the obtained silicon-carbon composite anode material is slightly reduced.

[0101] Comparing the results of Example 1 and Comparative Example 1, it can be seen that if the product is crushed before coating, it will be rapidly oxidized and agglomerated. Therefore, the structure of the resulting silicon-carbon composite anode material is insufficient to accommodate the huge volume change, and its composition is also insufficient to utilize the capacity of elemental silicon to accommodate lithium. As a result, the overall performance is significantly reduced.

[0102] Comparing the results of Example 1 and Comparative Example 2, it can be seen that if the porous silicon is not broken, it remains a whole and may break during the rolling process of electrode preparation, generating new cross-sections and increasing its side reactions. If it is not broken, the whole still cannot accommodate volume changes and will suffer from problems such as pulverization during long cycles, resulting in a significant decrease in cycle performance and high-rate performance.

[0103] In summary, the preparation method provided by this invention fully utilizes the suggestive nature of a top-down approach while combining the precision of a bottom-up synthesis method, resulting in a silicon-carbon composite anode material with excellent overall electrochemical performance. Due to the superior performance of this silicon-carbon composite anode material, it is expected to find wide application in energy storage, power, and other battery fields.

[0104] The embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof can be combined with each other unless otherwise specified.

Claims

1. A method for preparing a silicon-carbon composite anode material, characterized in that, The preparation method includes the following steps: S1. Etching silicon-based particles to create porous silicon; S2. Form a porous carbon coating on the surface and inside of the porous silicon; S3. The product obtained from crushing step S2; S4. Pyrolyze the product obtained in step S3 and the carbon source.

2. The preparation method according to claim 1, characterized in that, In step S1, the etching method includes at least one of liquid phase method and solid phase method; and / or, in step S1, the etchant used for etching includes at least one of inorganic acid and NaOH.

3. The preparation method according to claim 1, characterized in that, In step S1, the mass ratio of the porous silicon to the silicon-based particles is 20~30:100; and / or, in step S1, the silicon-based particles include elemental silicon particles or silicon metal alloy particles.

4. The preparation method according to claim 1, characterized in that, In step S2, the porous carbon coating method includes at least one of solvothermal method and chemical vapor phase method.

5. The preparation method according to claim 1, characterized in that, In step S2, the porous carbon coating accounts for 5-15% of the mass percentage of the product obtained in step S2.

6. The preparation method according to claim 1, characterized in that, In step S3, the crushing method includes at least one of roller pressing, ball milling and air jet milling.

7. The preparation method according to claim 1, characterized in that, In step S4, the mass ratio of the product obtained in step S3 to the carbon source is 1:1~2.

8. The preparation method according to claim 1, characterized in that, In step S4, the pyrolysis temperature is 900~1100℃; and / or, in step S4, the isothermal duration of the pyrolysis is 2~3h.

9. The preparation method according to any one of claims 1 to 8, characterized in that, The particle size of the silicon-carbon composite anode material is 11~14μm.

10. The preparation method according to any one of claims 1 to 8, characterized in that, The specific capacity of the silicon-carbon composite anode material is ≥1500mAh / g.

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