Preparation method of silicon-based negative electrode material with high specific volume and low expansion

Abstract

The invention discloses a preparation method of a silicon-based negative electrode material with high specific volume and low expansion, and belongs to the technical field of lithium ion battery negative electrode materials. According to the silicon-based negative electrode material prepared by the method, vapor deposition of silicon is carried out in pores of the porous carbon, deposition of silicon is increased on the surface of the porous carbon, the specific capacity of the material is improved, and the pores of the porous carbon effectively absorb expansion of most silicon. The large-length-diameter-ratio carbon nanotubes wound and coated in the middle not only can improve the uniformity of the current density of the material and reduce large expansion caused by excessive lithium intercalation of the local silicon material, but also have a certain effect of constraining the volume expansion of the silicon material. The outermost layer of the material is coated with carbon by adopting a solid phase method, so that a thicker coating layer can be obtained, the expansion of silicon particles is inhibited, and meanwhile, the process is lower in cost, safer and suitable for batch production.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery anode material technology, specifically to a method for preparing a silicon-based anode material with high specific capacity and low expansion. Background Technology

[0002] With the booming development of the new energy industry, higher demands are being placed on the performance of lithium-ion batteries. Currently, most commercially available lithium-ion batteries use graphite as the anode material, but its actual specific capacity is approaching its theoretical limit, leaving very limited room for improvement in energy density. Silicon-based materials, with a theoretical specific capacity as high as 4200 mAh / g, approximately 10 times that of graphite, and abundant silicon reserves in the Earth's crust, have become a highly promising next-generation anode material. However, silicon-based anodes experience a massive volume expansion exceeding 300% during charge and discharge, making the electrode structure extremely vulnerable to damage. This leads to problems such as silicon particle pulverization and electrode coating peeling, while also causing instability in the solid-liquid interface film, severely impacting the battery's cycle life and rate performance.

[0003] Currently, nano-silicon obtained from silane gas decomposition is generally used on porous carbon with small pore sizes to reduce silicon expansion during charge and discharge, thereby improving cycle life. CN118970021A discloses a silicon-based anode composite material, its preparation method, and its application. The silicon-based anode composite material, from the inside out, comprises porous carbon, a porous silicon-carbon material composed of nano-amorphous silicon deposited in the pores of the porous carbon, an amorphous carbon layer, and a composite coating layer composed of metal oxides and a solid electrolyte. Because silicon is deposited only within the pores, the mass proportion of active silicon is small, limiting the specific capacity of the silicon-based anode material, which generally does not exceed 1800 mAh / g. Furthermore, although this patent adds metal oxides and solid electrolytes as coating layers to improve its internal conductivity, when the silicon material expands, the 0-dimensional metal oxides and solid electrolytes easily lose electrical contact and fail to achieve the desired effect. Invention CN118693267A discloses a low-expansion lithium-silver co-doped nano-silicon-carbon composite material. This composite material exhibits a core-shell structure, with a lithium-doped porous nano-silicon core and an outer shell consisting of a first outer shell of metallic silver and a second outer shell of amorphous carbon, arranged from the inside out. The porous nano-silicon obtained through disproportionation reaction and acid washing exhibits low expansion. However, lithium-silver doping involves silver mirror reactions and acid washing, which have stringent requirements, low product yield, and numerous defects, resulting in significant uncertainty regarding its impact on material power performance. Furthermore, this process carries an explosion risk, acid washing introduces numerous environmental problems, and the process is costly and difficult for industrial-scale mass production.

[0004] Despite attempts to improve this through strategies such as nanostructuring and surface coating (e.g., carbon coating), silicon-based anode materials still struggle to achieve a good balance between high specific capacity and low expansion. Furthermore, existing preparation methods suffer from drawbacks such as high energy consumption, complex processes, high costs, and difficulty in process control. Therefore, developing silicon-based anode materials with both high specific capacity and low expansion, along with their efficient preparation methods, is of great significance for driving technological innovation in lithium-ion batteries. Summary of the Invention

[0005] To address the aforementioned shortcomings of existing technologies, the present invention aims to provide a method for preparing silicon-based anode materials with high specific capacity and low expansion, thereby reducing the volume expansion of silicon-based anode materials.

[0006] The technical solution of this invention to solve the above-mentioned technical problems is as follows: A method for preparing a silicon-based anode material with high specific capacitance and low expansion is provided, comprising the following steps: (1) Porous carbon is introduced into the reaction equipment, and then inert gas is introduced; (2) Heat the reaction equipment from step (1) to the first temperature, and then introduce silicon source gas; (3) After heating the reaction equipment in step (2) to the second temperature, continue to introduce silicon source gas; (4) After the reaction is complete, stop the flow of silicon source gas and use high-pressure gas to spray carbon nanotube material into the reaction equipment; (5) Cool the product obtained in step (4) under an inert atmosphere, and then add solid carbon source material; (6) The product obtained in step (5) is heated to a third temperature for sintering and then cooled to obtain the final product.

[0007] Furthermore, in step (1), the porous carbon has a pore size of 1-20 nm and a D50 of 4-12 μm.

[0008] Furthermore, the first temperature in step (2) is 450-700℃.

[0009] Furthermore, the second temperature in step (3) is 500-900℃.

[0010] Furthermore, in steps (2) and (3), the silicon source gas is either silane, hexachlorosilane, disilane, or tetrasilane.

[0011] Furthermore, in step (4), the carbon nanotube material is at least one of single-walled carbon nanotubes and multi-walled carbon nanotubes, and its solid content is 0.1-5.0 wt%.

[0012] Furthermore, the solvent system for carbon nanotube materials includes N-methylpyrrolidone, isopropanol, ethylene glycol, or ethanol.

[0013] Furthermore, in step (5), the solid carbon source material is at least one of modified asphalt, resin, sucrose, tannic acid, and polyacrylonitrile.

[0014] Furthermore, the mass of the solid carbon source material in step (5) is 5 to 60% of the mass of the product obtained in step (4).

[0015] Furthermore, in step (6), the third temperature is 800-1200℃; the sintering time is 3-20h.

[0016] The present invention has the following beneficial effects: The silicon-based anode material prepared by the present invention not only achieves vapor-phase deposition of silicon within the pores of porous carbon, but also increases silicon deposition on the surface of the porous carbon, thereby improving the specific capacity of the material. Simultaneously, the pores of the porous carbon effectively absorb most of the silicon expansion. The large aspect ratio carbon nanotubes wrapped around the core not only improve the uniformity of the material's current density and reduce the large expansion caused by excessive lithium intercalation in local silicon materials, but also have a certain effect on confining the volume expansion of the silicon material. The outermost layer of the material is coated with carbon using a solid-phase method, which not only achieves a thicker coating layer and suppresses the expansion of silicon particles, but also has lower cost, is safer, and is suitable for mass production. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the process for preparing silicon-based anode materials according to the present invention; Figure 2 This is a SEM image of the silicon-based anode material prepared in Example 1 of the present invention; Figure 3 This is a schematic diagram of the silicon-based anode material prepared in Example 1 of the present invention; wherein 1 is porous carbon; 2 is vapor-deposited silicon; 3 is carbon nanotubes; and 4 is a carbon coating layer. Figure 4 The first charge-discharge curve of the silicon-based anode material prepared in Example 1 of this invention; Figure 5 The first charge-discharge curves are for the silicon-based anode materials prepared in Example 1 and Comparative Examples 1-3 of this invention. Detailed Implementation

[0018] The examples given below are for illustrative purposes only and are not intended to limit the scope of the invention. Unless otherwise specified, conditions in the examples are performed under standard conditions or as recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0019] Example 1: A method for preparing a silicon-based anode material with high specific capacitance and low expansion (preparation process is described in [link]). Figure 1 ), including the following steps: (1) Add 7 kg of porous carbon to the fluidized bed equipment and purge the air in the equipment with nitrogen; (2) Heat the fluidized bed equipment to 500℃, then introduce silane gas for 7 hours at a flow rate of 12L / min to carry out adsorption, pyrolysis and deposition; (3) Heat the fluidized bed equipment to 650°C and continue to introduce silane gas for 2 hours at a gas flow rate of 12 L / min to carry out silicon pyrolysis deposition on the porous carbon surface; (4) After the reaction is complete, stop the silane gas flow and keep the powder in the equipment in a fluidized state. Use high-pressure gas to spray a single-walled carbon nanotube slurry (solvent is ethylene glycol) with a solid content of 0.4 wt% into the furnace to coat the surface of the product obtained in step (3). The amount of single-walled carbon nanotubes used is 0.06% of the mass of deposited silicon (the mass of deposited silicon can be calculated by multiplying the flow rate of silane gas by the time to obtain the mass of silane gas. The mass of silicon element accounts for 87.5%. Multiplying the two can give the theoretical mass, and then make corrections based on the gas flow meter and the mass weighing value of silane). (5) The product obtained in step (4) is transferred to a transfer kettle for cooling under nitrogen atmosphere, and then transported to a mixing kettle. Modified asphalt (30% of the mass of the product obtained in step (4), purchased from Hubei Guochuang High-tech Materials Co., Ltd.) is added, and after high-speed mixing, it is transported to a sintering furnace. (6) The product obtained in step (5) is sintered in a sintering furnace at 950°C for 5 hours and then cooled to obtain the final product.

[0020] A schematic diagram of the high specific capacitance and low expansion silicon-based anode material of the present invention is shown below. Figure 3 ,Depend on Figure 3 As can be seen, the high specific capacitance and low expansion silicon-based anode material of the present invention comprises porous carbon, vapor-deposited silicon, carbon nanotubes, and a carbon coating layer; wherein, 1 is porous carbon; 2 is vapor-deposited silicon; 3 is carbon nanotubes; and 4 is a carbon coating layer. The SEM image of the high specific capacitance and low expansion silicon-based anode material prepared in this embodiment is shown below. Figure 2 .Depend on Figure 2 It can be seen that the silicon-based anode material prepared in this embodiment has a uniform outer coating, with no exposed carbon nanotubes, and the coating effect is good.

[0021] Example 2: A method for preparing a silicon-based anode material with high specific capacitance and low expansion includes the following steps: (1) Add 6 kg of porous carbon to the fluidized bed equipment and introduce inert gas to replace the air in the equipment; (2) Heat the fluidized bed equipment to 450°C, then introduce silane gas for 6 hours at a flow rate of 13 L / min to carry out adsorption, pyrolysis and deposition; (3) Heat the fluidized bed equipment to 500°C and continue to introduce silane gas for 3 hours at a gas flow rate of 13 L / min to carry out silicon pyrolysis deposition on the porous carbon surface; (4) After the reaction is completed, stop the silane gas supply and keep the powder in the equipment in a fluidized state. Use high pressure gas to spray a single-walled carbon nanotube slurry with a solid content of 0.1 wt% (solvent is isopropanol) into the furnace so that it coats the surface of the product obtained in step (3). The amount of single-walled carbon nanotubes used is 0.06% of the mass of deposited silicon (the calculation method of the mass of deposited silicon is the same as in Example 1). (5) The product obtained in step (4) is transferred to a transfer vessel for cooling under an inert atmosphere, then transported to a mixing vessel, and then resin (60% of the mass of the product obtained in step (4)) is added. After high-speed mixing, the mixture is transported to a sintering furnace. (6) The product obtained in step (5) is sintered in a sintering furnace at 800°C for 5 hours and then cooled to obtain the final product.

[0022] Example 3: A method for preparing a silicon-based anode material with high specific capacitance and low expansion includes the following steps: (1) Add 8 kg of porous carbon to the fluidized bed equipment and introduce inert gas to replace the air in the equipment; (2) Heat the fluidized bed equipment to 700℃, then introduce silane gas for 9 hours at a flow rate of 14 L / min to carry out adsorption, pyrolysis and deposition; (3) Heat the fluidized bed equipment to 900°C and continue to introduce silane gas for 4 hours at a gas flow rate of 14 L / min to carry out silicon pyrolysis deposition on the porous carbon surface; (4) After the reaction is completed, stop the silane gas supply and keep the powder in the equipment in a fluidized state. Use high pressure gas to spray a single-walled carbon nanotube slurry with a solid content of 5.0 wt% (solvent is ethanol) into the furnace so that it coats the surface of the product obtained in step (3). The amount of single-walled carbon nanotubes used is 0.06% of the mass of deposited silicon (the calculation method of the mass of deposited silicon is the same as in Example 1). (5) The product obtained in step (4) is transferred to a transfer vessel for cooling under an inert atmosphere, then transported to a mixing vessel, and then polyacrylonitrile (5% of the mass of the product obtained in step (4)) is added. After high-speed mixing, it is transported to a sintering furnace. (6) The product obtained in step (5) is sintered in a sintering furnace at 1100℃ for 5 hours and then cooled to obtain the final product.

[0023] Comparative Example 1: A method for preparing a silicon-based anode material includes the following steps: (1) Add 7 kg of porous carbon to the fluidized bed equipment and introduce inert gas to replace the air in the equipment; (2) Heat the fluidized bed equipment to 500℃, then introduce silane gas for 7 hours at a flow rate of 12L / min to carry out adsorption, pyrolysis and deposition; (3) Heat the fluidized bed equipment to 650°C and continue to introduce silane gas for 2 hours at a gas flow rate of 12 L / min to carry out silicon pyrolysis deposition on the porous carbon surface; (4) After the reaction is complete, stop the silane gas supply and keep the powder in the equipment in a fluidized state. Use high-pressure gas to spray an alcohol-based single-walled carbon nanotube slurry with a solid content of 0.4 wt% into the furnace to coat the surface of the material. The amount of single-walled carbon nanotubes used is 0.06% of the mass of the deposited silicon (the calculation method for the mass of deposited silicon is the same as in Example 1); (5) The powder is transferred to a transfer kettle for cooling under an inert atmosphere, and then transported to a mixing kettle. Modified asphalt (purchased from Hubei Guochuang High-tech Materials Co., Ltd.) is added at a ratio of 10% of the powder mass. After thorough high-speed mixing, it is transported to the sintering furnace. (6) Heat the sintering furnace to 950°C for sintering for 5 hours, and collect the powder after cooling.

[0024] Comparative Example 2: A method for preparing a silicon-based anode material includes the following steps: (1) Porous carbon is introduced into the fluidized bed equipment and the air inside the equipment is replaced with inert gas; (2) Heat the fluidized bed equipment to 500°C, and then introduce silane gas for adsorption, pyrolysis and deposition; (3) Heat the fluidized bed equipment to 650°C and continue to introduce silane gas to carry out silicon pyrolysis deposition on the porous carbon surface; (4) The powder is transferred to a transfer kettle for cooling under an inert atmosphere, and then transported to a mixing kettle. Modified asphalt is added at a ratio of 30% of the powder mass. After thorough high-speed mixing, it is transported to a sintering furnace. (5) Heat the sintering furnace to 950°C for sintering for 5 hours, and collect the powder after cooling.

[0025] The various properties of the silicon-based anode material prepared in this comparative example were tested. The sample preparation and testing methods were the same as in Example 1.

[0026] Comparative Example 3: A method for preparing a silicon-based anode material includes the following steps: (1) Porous carbon is introduced into the fluidized bed equipment and the air inside the equipment is replaced with inert gas; (2) Heat the fluidized bed equipment to 500°C, and then introduce silane gas for adsorption, pyrolysis and deposition; (3) Stop the introduction of silane gas and keep the powder in the equipment in a fluidized state. After heating the fluidized bed equipment to 620°C, introduce acetylene gas to carry out gas phase pyrolysis deposition pre-carbon coating; (4) Under an inert atmosphere, the powder is transferred into a rotary kiln and acetylene gas is introduced to further perform gas phase pyrolysis deposition pre-carbon coating. The amount of carbon coating in the two processes is 6% of the relative silicon mass. The powder is collected after coating is completed.

[0027] Experimental example: (1) Using a CR2032 coin cell as a model, the electrochemical performance of the silicon-based anode materials prepared in Example 1 and Comparative Examples 1-3 was tested. The specific operation steps are as follows: Silicon-based anode material, modified polyacrylic acid, and conductive carbon black were mixed in a mass ratio of 8:1:1 to prepare a slurry. The slurry was coated onto a copper foil surface to form an electrode sheet, which was then dried in an 80°C oven for 2 hours. A battery was assembled using a lithium foil as the counter electrode, a polyethylene porous membrane as the separator, and 1M LiPF6 with a mass ratio of EC:EMC:FEC of 7:2:1 as the electrolyte. The battery charge / discharge current density was 100 mA / g. The electrochemical performance test results are shown in […]. Figure 4-5 .Depend on Figure 4-5 It can be seen that the silicon-carbon anode material prepared by the preparation method provided by the present invention has a significantly higher specific capacity than that of comparative examples 1-3.

[0028] (2) The silicon-based anode materials prepared in Example 1 and Comparative Examples 1-3 were compounded with graphite to a strength of 600 mAh / g and assembled with an NCM811 cathode to form a 5Ah pouch cell. The cell was charged at 23±2℃ with a constant current and constant voltage of 4.20V at 1C until the current was less than 0.02C, and then left to stand for 10 minutes. It was then discharged at a constant current of 1C to a termination voltage of 2.75V and left to stand for 10 minutes, constituting one cycle. This cycle was repeated for 500 cycles. The full-charge expansion of the cell was recorded at cycles 100, 200, 300, 400, and 500. The test results are shown in Table 1.

[0029] As shown in Table 1, compared to Example 1, Comparative Example 1, which reduced the amount of outer solid-phase carbon coating, and Comparative Example 2, which omitted the use of carbon nanotubes, both exhibited greater cell expansion with cycling. Comparative Example 3, a silicon-carbon anode prepared by the conventional vapor-phase method, showed the greatest expansion. This invention addresses this by spraying carbon nanotubes onto the surface of a porous carbon material with vapor-phase deposited silicon. This improves conductivity, prevents excessive local current density that could lead to excessive silicon expansion, and also somewhat restricts the volume expansion of the silicon material. The outermost layer of the material is coated with carbon using a solid-phase method; the thicker carbon coating layer also effectively suppresses silicon expansion.

[0030] Table 1 Comparison of Cyclic Expansion Test Results of Silicon-Based Anode Materials (%) The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a silicon-based anode material with high specific capacitance and low expansion, characterized in that, Includes the following steps: (1) Porous carbon is introduced into the reaction equipment, and then inert gas is introduced; (2) Heat the reaction equipment from step (1) to the first temperature, and then introduce silicon source gas; (3) After heating the reaction equipment in step (2) to the second temperature, continue to introduce silicon source gas; (4) After the reaction is complete, stop the flow of silicon source gas and use high-pressure gas to spray carbon nanotube material into the reaction equipment; (5) Cool the product obtained in step (4) under an inert atmosphere, and then add solid carbon source material; (6) The product obtained in step (5) is heated to a third temperature for sintering and then cooled to obtain the final product.

2. The preparation method according to claim 1, characterized in that, The porous carbon described in step (1) has a pore size of 1-20 nm and a D50 of 4-12 μm.

3. The preparation method according to claim 1, characterized in that, In step (2), the first temperature is 450-700℃.

4. The preparation method according to claim 1, characterized in that, In step (3), the second temperature is 500-900℃.

5. The preparation method according to claim 1, characterized in that, The silicon source gas mentioned in steps (2) and (3) is silane gas, hexachlorosilane, disilane or tetrasilane.

6. The preparation method according to claim 1, characterized in that The carbon nanotube material mentioned in step (4) is at least one of single-walled carbon nanotubes and multi-walled carbon nanotubes, and its solid content is 0.1-5.0 wt%.

7. The preparation method according to claim 6, characterized in that, The solvent system for the carbon nanotube material includes N-methylpyrrolidone, isopropanol, ethylene glycol, or ethanol.

8. The preparation method according to claim 1, characterized in that, The solid carbon source material mentioned in step (5) is at least one of modified asphalt, resin, sucrose, tannic acid and polyacrylonitrile.

9. The preparation method according to claim 1, characterized in that, The mass of the solid carbon source material mentioned in step (5) is 5 to 60% of the mass of the product obtained in step (4).

10. The preparation method according to claim 1, characterized in that, The third temperature in step (6) is 800-1200℃; the sintering time is 3-20h.

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