Surface modification method of silicon-carbon negative electrode material, modified silicon-carbon negative electrode material, negative electrode plate and lithium ion battery
By applying amorphous carbon coating and lithium salt gradient coating to silicon-carbon anode materials, combined with polysuccinimide modification, the problems of poor conductivity and unstable SEI film of silicon-carbon anode materials were solved, thereby improving the kinetic performance and cycle life of lithium-ion batteries.
Patent Information
- Application Number
- CN202610413323.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-03-31
- Publication Date
- 2026-05-12
AI Technical Summary
Silicon-carbon anode materials have poor conductivity, and the solid electrolyte interface film formed during charging and discharging is unstable, which hinders the effective transport of lithium ions, resulting in poor rate performance and short cycle life.
By mixing silicon-carbon composite materials with a carbon source and pyrolyzing them in an inert atmosphere to form an amorphous carbon coating layer, followed by lithium salt gradient coating and polysuccinimide modification, a Li-OC composite conductive network is constructed, and the material surface is optimized to improve conductivity and stabilize the solid electrolyte interface.
This enables rapid lithium-ion passage and improves the electrochemical performance of the solid electrolyte interface, thereby enhancing the kinetic performance and cycle life of silicon-carbon materials.
Smart Images
Figure CN122025523A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a method for surface modification of silicon-carbon anode material, modified silicon-carbon anode material, anode sheet, and lithium-ion battery. Background Technology
[0002] The information disclosed in the background section of this invention is intended only to enhance the understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.
[0003] Silicon-carbon anode materials have become a research hotspot in lithium-ion battery anode materials in recent years due to their extremely high theoretical specific capacity (approximately 10 times that of graphite). However, silicon has poor intrinsic conductivity, and the solid electrolyte interphase (SEI) film formed during charge and discharge is unstable, severely hindering the effective transport of lithium ions, resulting in poor rate performance and short cycle life. Therefore, effectively improving the kinetic performance of silicon-carbon anode materials and constructing a stable SEI film has become a key research direction for enhancing their electrochemical performance. Summary of the Invention
[0004] In view of this, the present invention provides a surface modification method for silicon-carbon anode materials, modified silicon-carbon anode materials, anode sheets, and lithium-ion batteries. By modifying the surface of silicon-carbon anode materials, the present invention improves the kinetic performance of silicon-carbon anode materials, optimizes the surface of silicon-carbon anode materials, thereby enhancing the electrochemical performance of the solid electrolyte interface, promoting lithium-ion insertion / extraction, and resulting in a modified silicon-carbon anode-lithium nickel cobalt manganese oxide full battery exhibiting excellent kinetic performance and long cycle life.
[0005] To achieve the above objectives, the present invention is implemented through the following technical solution: In a first aspect, the present invention provides a method for surface modification of silicon-carbon anode materials, comprising the following steps: Silicon-carbon composite material is mixed with a carbon source and then pyrolyzed and carbonized under an inert atmosphere to obtain amorphous carbon-coated silicon-carbon material. Amorphous carbon-coated silicon-carbon materials are subjected to lithium salt gradient coating; The lithium salt gradient coated silicon-carbon material was dispersed in a polysuccinimide (PSI) N-methylpyrrolidone (NMP) solution, impregnated, filtered, dried, and then heat-treated under an inert atmosphere to obtain the surface-modified silicon-carbon anode material.
[0006] In some embodiments, the method further includes a pretreatment step for the silicon-carbon composite material, specifically drying the silicon-carbon composite material at 100-150 °C for 2-10 h. The purpose of the pretreatment step is to completely remove surface-adsorbed moisture.
[0007] In some implementations, the carbon source is an organic carbon source, preferably glucose, sucrose, or phenolic resin. The organic carbon source, after high-temperature pyrolysis, transforms into amorphous carbon, which can form uniform and dense coating layers, thus improving the conductivity of subsequent silicon-carbon materials.
[0008] In some implementations, the mass ratio of silicon-carbon composite material to carbon source is 1:0.05~0.3.
[0009] In some implementations, the inert atmosphere is argon or nitrogen.
[0010] In some implementations, the pyrolysis carbonization conditions are to heat to 500-700 °C at a rate of 2-5 °C / min and hold at that temperature for 2-5 h.
[0011] In some implementations, the lithium salt gradient coating employs an ethanol-assisted lithium salt gradient coating technique; the solvent is ethanol, and the lithium salts are LiOH and LiCl; preferably, the molar ratio of LiOH to LiCl is 3:1~3. By preparing an ethanol-based lithium salt solution and coating amorphous carbon-coated silicon-carbon materials under negative pressure, a Li-OC composite conductive network can be constructed on the surface and subsurface layers of the inner carbon layers of the silicon-carbon material. This can improve the initial coulombic efficiency, reduce interfacial impedance, and improve the surface conductivity of the silicon-carbon material; preferably, the negative pressure is -0.05~-0.1 MPa. In some implementations, the impregnation conditions are continuous stirring at 50-80 °C for 4-12 h.
[0012] In some implementations, the heat treatment conditions are 200–350 °C for 1–3 h. The succinimide groups in the polysuccinimide molecule react with or firmly bond with the functional groups on the surface of the gradient-coated silicon-carbon material, thereby completing the surface modification.
[0013] In some embodiments, the heat treatment process further includes washing and drying with an organic solvent; the organic solvent is selected from one or more of DMF, DMSO, and NMP; the drying process is vacuum drying at 80–110 °C for 6–10 h. The purpose of washing is to remove unreacted free polymers.
[0014] Secondly, the present invention provides a modified silicon-carbon anode material prepared by the surface modification method described in the first aspect.
[0015] Thirdly, a negative electrode sheet includes a current collector and an active layer attached to the surface of the current collector, wherein the active material in the active layer is the modified silicon-carbon negative electrode material described in the second aspect of the present invention.
[0016] In some embodiments, the modified silicon-carbon anode material is mixed uniformly with a conductive agent, a binder, and a thickener in a solvent to obtain a slurry. The slurry is then coated onto the surface of a current collector and dried to obtain the final product. Specifically, the conductive agent includes, but is not limited to, graphite and conductive carbon black. Specifically, the binder can be SBR (styrene-butadiene rubber). Specifically, the thickener can be CMC (carboxymethyl cellulose).
[0017] Fourthly, a lithium-ion battery, wherein the negative electrode of the lithium-ion battery is the negative electrode sheet described in the third aspect.
[0018] In some implementations, the active material of the positive electrode is lithium nickel cobalt manganese oxide.
[0019] Compared with the prior art, the present invention has achieved the following beneficial effects: The silicon-carbon anode material provided by this invention forms fast ion channels on the surface of the silicon-carbon material after gradient coating, which enables the rapid passage of lithium ions during the charging and discharging process. At the same time, after surface modification treatment, it can enhance the electrochemical performance of the solid electrolyte interface (SEI), promote the insertion / extraction of lithium ions, reduce its impedance in electrical performance, and improve the kinetic and cycling performance of silicon-carbon materials. Attached Figure Description
[0020] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.
[0021] Figure 1 This is a schematic diagram of the surface-modified silicon-carbon anode material structure in an embodiment of the present invention; Among them, 1. silicon-carbon composite material; 2. amorphous carbon coating layer; 3. lithium salt gradient coating layer; 4. succinimide modified layer. Detailed Implementation
[0022] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.
[0023] The technical solution of the present invention will be further described below with reference to specific embodiments.
[0024] Example 1 A method for surface modification of silicon-carbon anode material includes the following steps: (1) Dry the silicon-carbon composite material in a vacuum oven at 120 °C for 4 hours to completely remove the surface-adsorbed moisture; (2) The pretreated silicon-carbon composite material (1 kg) and glucose (0.05 kg) were placed in a ball mill and thoroughly ground and mixed. The mixture was placed in a tube furnace and heated to 550 °C at a rate of 3 °C / min under an argon atmosphere and held for 3 hours. After the reaction was completed, the mixture was naturally cooled to obtain a silicon-carbon material with an inner amorphous carbon coating.
[0025] (3) Weigh out LiOH (0.3 mol / L) and LiCl (0.1 mol / L) and dissolve them in ethanol (3 L of lithium salt ethanol solution), and stir magnetically until completely dissolved; slowly add the silicon-carbon material with inner amorphous carbon coating obtained in (2) to the lithium salt ethanol solution under gentle stirring until a uniform slurry is formed. Then treat it under a slight negative pressure of -0.05 MPa for 30 minutes to allow the solution to fully penetrate. Finally, dry it at 80 °C for 12 hours to complete the gradient coating of lithium salt.
[0026] (4) The gradient-coated improved silicon-carbon material obtained in (3) was dispersed in 120 g of 3wt% polysuccinimide / N-methylpyrrolidone solution and stirred at 60 °C for 6 hours. The impregnated mixture was filtered and dried, and then heat-treated at 250 °C for 2 hours under an argon atmosphere.
[0027] (5) The product after heat treatment (4) was washed three times with DMF solvent to remove unreacted PSI. Finally, it was vacuum dried at 100 °C for 8 hours to obtain the final modified product.
[0028] The preparation methods for negative electrode plates and positive electrode plates, as well as the battery assembly methods, are as follows: The silicon-carbon anode material prepared in this embodiment was dissolved in water with graphite, conductive carbon black, CMC, and SBR to form a negative electrode slurry. The appropriate ratio of silicon-carbon anode material, graphite, conductive carbon black, CMC, and SBR was 5%:91.5%:0.5%:1.2%:1.8%. The stirred negative electrode slurry was coated onto a negative electrode current collector, dried to form a negative electrode sheet, and then rolled, slit, and die-cut. Lithium nickel cobalt manganese oxide, a conductive agent, and PVDF were dissolved in NMP and stirred to form a positive electrode slurry. The appropriate ratio of lithium nickel cobalt manganese oxide (NCM900505, polycrystalline), conductive agent and PVDF is 96%:1.5%:2.5%. The prepared positive electrode slurry is coated on the positive electrode current collector and dried to form a positive electrode sheet. The positive electrode sheet is then rolled, slit and die-cut. The positive electrode sheet, negative electrode sheet, separator and electrolyte (LiPF6: 14.50%, EC: 23%, EMC: 54.50%, FEC: 6%, DTD: 1.50%, TMSP: 0.50%) are assembled into a soft pack battery.
[0029] Example 2 A method for surface modification of silicon-carbon anode material includes the following steps: (1) Dry the silicon-carbon composite material in a vacuum oven at 120 °C for 4 hours to completely remove the surface-adsorbed moisture; (2) The pretreated silicon-carbon composite material (1 kg) and sucrose (0.2 kg) were placed in a ball mill and thoroughly ground and mixed. The mixture was placed in a tube furnace and heated to 650 °C at a rate of 5 °C / min under an argon atmosphere and held for 4 hours. After the reaction was completed, the mixture was naturally cooled to obtain a silicon-carbon material with an inner layer of amorphous carbon coating.
[0030] (3) Weigh out LiOH (0.3 mol / L) and LiCl (0.2 mol / L) and dissolve them in ethanol (3 L of lithium salt ethanol solution), and stir magnetically until completely dissolved; slowly add the silicon-carbon material with inner amorphous carbon coating obtained in (2) to the lithium salt ethanol solution under gentle stirring until a uniform slurry is formed. Then treat it under a slight negative pressure of -0.08 MPa for 45 minutes to allow the solution to fully penetrate. Finally, dry it at 100 °C for 10 hours to complete the gradient coating of lithium salt.
[0031] (4) Disperse the gradient-coated improved silicon-carbon material obtained in (3) in 120 g of 5 wt% polysuccinimide / N-methylpyrrolidone solution and stir at 75 °C for 10 hours. Filter and dry the impregnated mixture and heat treat it at 300 °C for 1.5 hours under an argon atmosphere.
[0032] (5) The product after heat treatment (4) was washed three times with DMF solvent to remove unreacted PSI. Finally, it was vacuum dried at 100 °C for 8 hours to obtain the final modified product.
[0033] The preparation methods for negative electrode plates and positive electrode plates, as well as the battery assembly methods, are as follows: The silicon-carbon anode material prepared in this embodiment was dissolved in water with graphite, conductive carbon black, CMC, and SBR to form a negative electrode slurry. The appropriate ratio of silicon-carbon anode material, graphite, conductive carbon black, CMC, and SBR was 5%:91.5%:0.5%:1.2%:1.8%. The stirred negative electrode slurry was coated onto a negative electrode current collector, dried to form a negative electrode sheet, and then rolled, slit, and die-cut. Lithium nickel cobalt manganese oxide, a conductive agent, and PVDF were dissolved in NMP and stirred to form a positive electrode slurry. The appropriate ratio of lithium nickel cobalt manganese oxide (NCM900505, polycrystalline), conductive agent and PVDF is 96%:1.5%:2.5%. The prepared positive electrode slurry is coated on the positive electrode current collector and dried to form a positive electrode sheet. The positive electrode sheet is then rolled, slit and die-cut. The positive electrode sheet, negative electrode sheet, separator and electrolyte (LiPF6: 14.50%, EC: 23%, EMC: 54.50%, FEC: 6%, DTD: 1.50%, TMSP: 0.50%) are assembled into a soft pack battery.
[0034] Example 3 A method for surface modification of silicon-carbon anode material includes the following steps: (1) Dry the silicon-carbon composite material in a vacuum oven at 120 °C for 4 hours to completely remove the surface-adsorbed moisture; (2) The pretreated silicon-carbon composite material (1 kg) and phenolic resin (0.3 kg) were placed in a ball mill and thoroughly ground and mixed. The mixture was placed in a tube furnace and heated to 700 °C at a rate of 2 °C / min under an argon atmosphere and held at that temperature for 2 hours. After the reaction was completed, the mixture was allowed to cool naturally to obtain a silicon-carbon material with an inner layer of amorphous carbon coating.
[0035] (3) Weigh out LiOH (0.3 mol / L) and LiCl (0.3 mol / L) and dissolve them in ethanol (3 L of lithium salt ethanol solution), and stir magnetically until completely dissolved; slowly add the silicon-carbon material with inner amorphous carbon coating obtained in (2) to the lithium salt ethanol solution under gentle stirring until a uniform slurry is formed. Then treat it under a slight negative pressure of -0.1 MPa for 60 minutes to allow the solution to fully penetrate. Finally, dry it at 90 °C for 15 hours to complete the gradient coating of lithium salt.
[0036] (4) Disperse the gradient-coated improved silicon-carbon material obtained in (3) into 120 g of 8wt% polysuccinimide / N-methylpyrrolidone solution and stir at 50 °C for 12 hours. Filter and dry the impregnated mixture and heat treat it at 200 °C for 3 hours under an argon atmosphere.
[0037] (5) The product after heat treatment (4) was washed three times with DMF solvent to remove unreacted PSI. Finally, it was vacuum dried at 100 °C for 8 hours to obtain the final modified product.
[0038] The preparation methods for negative electrode plates and positive electrode plates, as well as the battery assembly methods, are as follows: The silicon-carbon anode material prepared in this embodiment was dissolved in water with graphite, conductive carbon black, CMC, and SBR to form a negative electrode slurry. The appropriate ratio of silicon-carbon anode material, graphite, conductive carbon black, CMC, and SBR was 5%:91.5%:0.5%:1.2%:1.8%. The stirred negative electrode slurry was coated onto a negative electrode current collector, dried to form a negative electrode sheet, and then rolled, slit, and die-cut. Lithium nickel cobalt manganese oxide, a conductive agent, and PVDF were dissolved in NMP and stirred to form a positive electrode slurry. The appropriate ratio of lithium nickel cobalt manganese oxide (NCM900505, polycrystalline), conductive agent and PVDF is 96%:1.5%:2.5%. The prepared positive electrode slurry is coated on the positive electrode current collector and dried to form a positive electrode sheet. The positive electrode sheet is then rolled, slit and die-cut. The positive electrode sheet, negative electrode sheet, separator and electrolyte (LiPF6: 14.50%, EC: 23%, EMC: 54.50%, FEC: 6%, DTD: 1.50%, TMSP: 0.50%) are assembled into a soft pack battery.
[0039] Example 4 A method for surface modification of silicon-carbon anode material includes the following steps: (1) Dry the silicon-carbon composite material in a vacuum oven at 120 °C for 4 hours to completely remove the surface-adsorbed moisture; (2) The pretreated silicon-carbon composite material (1 kg) and glucose (0.1 kg) were placed in a ball mill and thoroughly ground and mixed. The mixture was placed in a tube furnace and heated to 500 °C at a rate of 3 °C / min under an argon atmosphere and held for 5 hours. After the reaction was completed, the mixture was naturally cooled to obtain a silicon-carbon material with an inner layer of amorphous carbon coating.
[0040] (3) Weigh out LiOH (0.3 mol / L) and LiCl (0.1 mol / L) and dissolve them in ethanol (3 L of lithium salt ethanol solution), and stir magnetically until completely dissolved; slowly add the silicon-carbon material with inner amorphous carbon coating obtained in (2) to the lithium salt ethanol solution under gentle stirring until a uniform slurry is formed. Then treat it under a slight negative pressure of -0.05 MPa for 30 minutes to allow the solution to fully penetrate. Finally, dry it at 80 °C for 12 hours to complete the gradient coating of lithium salt.
[0041] (4) The gradient-coated improved silicon-carbon material obtained in (3) was dispersed in 120 g of 3wt% polysuccinimide / N-methylpyrrolidone solution and stirred at 80 °C for 5 hours. The impregnated mixture was filtered and dried, and then heat-treated at 350 °C for 1.5 hours under an argon atmosphere.
[0042] (5) The product after heat treatment (4) was washed three times with DMF solvent to remove unreacted PSI. Finally, it was vacuum dried at 100 °C for 8 hours to obtain the final modified product.
[0043] The preparation methods for negative electrode plates and positive electrode plates, as well as the battery assembly methods, are as follows: The silicon-carbon anode material prepared in this embodiment was dissolved in water with graphite, conductive carbon black, CMC, and SBR to form a negative electrode slurry. The appropriate ratio of silicon-carbon anode material, graphite, conductive carbon black, CMC, and SBR was 5%:91.5%:0.5%:1.2%:1.8%. The stirred negative electrode slurry was coated onto a negative electrode current collector, dried to form a negative electrode sheet, and then rolled, slit, and die-cut. Lithium nickel cobalt manganese oxide, a conductive agent, and PVDF were dissolved in NMP and stirred to form a positive electrode slurry. The appropriate ratio of lithium nickel cobalt manganese oxide (NCM900505, polycrystalline), conductive agent and PVDF is 96%:1.5%:2.5%. The prepared positive electrode slurry is coated on the positive electrode current collector and dried to form a positive electrode sheet. The positive electrode sheet is then rolled, slit and die-cut. The positive electrode sheet, negative electrode sheet, separator and electrolyte (LiPF6: 14.50%, EC: 23%, EMC: 54.50%, FEC: 6%, DTD: 1.50%, TMSP: 0.50%) are assembled into a soft pack battery.
[0044] Comparative Example 1 Perform all the steps of Example 1, but omit step (4), that is, directly wash and dry after lithium salt gradient coating and drying to obtain the product. The specific steps are as follows: (1) Dry the silicon-carbon composite material in a vacuum oven at 120 °C for 4 hours to completely remove the surface-adsorbed moisture; (2) The pretreated silicon-carbon composite material (1 kg) and glucose (0.05 kg) were placed in a ball mill and thoroughly ground and mixed. The mixture was placed in a tube furnace and heated to 550°C at a rate of 3°C / min under an argon atmosphere and held for 3 hours. After the reaction was completed, the mixture was naturally cooled to obtain a silicon-carbon material with an inner amorphous carbon coating.
[0045] (3) Weigh out LiOH (0.3 mol / L) and LiCl (0.1 mol / L) and dissolve them in ethanol (3 L of lithium salt ethanol solution), and stir magnetically until completely dissolved; slowly add the silicon-carbon material with inner amorphous carbon coating obtained in (2) to the lithium salt ethanol solution under gentle stirring until a uniform slurry is formed. Then treat it under a slight negative pressure of -0.05 MPa for 30 minutes to allow the solution to fully penetrate. Finally, dry it at 80 °C for 12 hours to complete the gradient coating of lithium salt.
[0046] (4) The product from (3) was washed three times with DMF solvent and then vacuum dried at 100 °C for 8 hours to obtain the final product.
[0047] The preparation methods for negative electrode plates and positive electrode plates, as well as the battery assembly methods, are as follows: The silicon-carbon anode material prepared in this comparative example was dissolved in water with graphite, conductive carbon black, CMC, and SBR to form a negative electrode slurry. The appropriate ratio of silicon-carbon anode material, graphite, conductive carbon black, CMC, and SBR was 5%:91.5%:0.5%:1.2%:1.8%. The stirred negative electrode slurry was coated onto a negative electrode current collector, dried to form a negative electrode sheet, and then rolled, slit, and die-cut. Lithium nickel cobalt manganese oxide, a conductive agent, and PVDF were dissolved in NMP and stirred to form a positive electrode slurry. The appropriate ratio of lithium nickel cobalt manganese oxide (NCM900505, polycrystalline), conductive agent and PVDF is 96%:1.5%:2.5%. The prepared positive electrode slurry is coated on the positive electrode current collector and dried to form a positive electrode sheet. The positive electrode sheet is then rolled, slit and die-cut. The positive electrode sheet, negative electrode sheet, separator and electrolyte (LiPF6: 14.50%, EC: 23%, EMC: 54.50%, FEC: 6%, DTD: 1.50%, TMSP: 0.50%) are assembled into a soft pack battery.
[0048] Comparative Example 2 Perform all the steps of Example 1, but omit step (3), that is, after obtaining the amorphous carbon-coated silicon-carbon material, directly perform succinimide surface modification to obtain the product. The specific steps are as follows: (1) Dry the silicon-carbon composite material in a vacuum oven at 120 °C for 4 hours to completely remove the surface-adsorbed moisture; (2) The pretreated silicon-carbon composite material (1 kg) and glucose (0.05 kg) were placed in a ball mill and thoroughly ground and mixed. The mixture was placed in a tube furnace and heated to 550 °C at a rate of 3 °C / min under an argon atmosphere and held for 3 hours. After the reaction was completed, the mixture was naturally cooled to obtain a silicon-carbon material with an inner amorphous carbon coating.
[0049] (3) The silicon-carbon material with an inner amorphous carbon coating obtained in (2) was dispersed in 120 g of 3wt% polysuccinimide / N-methylpyrrolidone solution and stirred at 60 °C for 6 hours. The impregnated mixture was filtered and dried, and then heat-treated at 250 °C for 2 hours under an argon atmosphere.
[0050] (4) The product after heat treatment in (3) was washed three times with DMF solvent to remove unreacted PSI. Finally, it was vacuum dried at 100 °C for 8 hours to obtain the final modified product.
[0051] The preparation methods for negative electrode plates and positive electrode plates, as well as the battery assembly methods, are as follows: The silicon-carbon anode material prepared in this comparative example was dissolved in water with graphite, conductive carbon black, CMC, and SBR to form a negative electrode slurry. The appropriate ratio of silicon-carbon anode material, graphite, conductive carbon black, CMC, and SBR was 5%:91.5%:0.5%:1.2%:1.8%. The stirred negative electrode slurry was coated onto a negative electrode current collector, dried to form a negative electrode sheet, and then rolled, slit, and die-cut. Lithium nickel cobalt manganese oxide, a conductive agent, and PVDF were dissolved in NMP and stirred to form a positive electrode slurry. The appropriate ratio of lithium nickel cobalt manganese oxide (NCM900505, polycrystalline), conductive agent and PVDF is 96%:1.5%:2.5%. The prepared positive electrode slurry is coated on the positive electrode current collector and dried to form a positive electrode sheet. The positive electrode sheet is then rolled, slit and die-cut. The positive electrode sheet, negative electrode sheet, separator and electrolyte (LiPF6: 14.50%, EC: 23%, EMC: 54.50%, FEC: 6%, DTD: 1.50%, TMSP: 0.50%) are assembled into a soft pack battery.
[0052] Comparative Example 3 The silicon-carbon composite material was pretreated and dried without any coating or modification treatment, and used as a benchmark for performance comparison. The specific steps were as follows: The silicon-carbon composite material was dried in a vacuum oven at 120 °C for 4 hours to completely remove the surface-adsorbed moisture.
[0053] The preparation methods for negative electrode plates and positive electrode plates, as well as the battery assembly methods, are as follows: The pretreated and dried silicon-carbon anode material of this comparative example was dissolved in water with graphite, conductive carbon black, CMC, and SBR to form a negative electrode slurry. The appropriate ratio of silicon-carbon anode material, graphite, conductive carbon black, CMC, and SBR was 5%:91.5%:0.5%:1.2%:1.8%. The stirred negative electrode slurry was coated onto a negative electrode current collector, dried to form a negative electrode sheet, and then rolled, slit, and die-cut. Lithium nickel cobalt manganese oxide, conductive agent, and PVDF were dissolved in NMP and stirred to form a positive electrode slurry. The appropriate ratio of lithium nickel cobalt manganese oxide (NCM900505, polycrystalline), conductive agent and PVDF is 96%:1.5%:2.5%. The prepared positive electrode slurry is coated on the positive electrode current collector and dried to form a positive electrode sheet. The positive electrode sheet is then rolled, slit and die-cut. The positive electrode sheet, negative electrode sheet, separator and electrolyte (LiPF6: 14.50%, EC: 23%, EMC: 54.50%, FEC: 6%, DTD: 1.50%, TMSP: 0.50%) are assembled into a soft pack battery.
[0054] Comparative Example 4 Perform steps (1), (2), and (5) of Example 1, omitting steps (3) and (4). That is, after obtaining the amorphous carbon-coated silicon-carbon material, the product is obtained. The specific steps are as follows: (1) Dry the silicon-carbon composite material in a vacuum oven at 120 °C for 4 hours to completely remove the surface adsorbed moisture.
[0055] (2) The pretreated silicon-carbon composite material (1 kg) and glucose (0.05 kg) were placed in a ball mill and thoroughly ground and mixed. The mixture was placed in a tube furnace and heated to 550°C at a rate of 3°C / min under an argon atmosphere and held for 3 hours. After the reaction was completed, the mixture was naturally cooled to obtain a silicon-carbon material with an inner amorphous carbon coating.
[0056] (3) The product after heat treatment (2) is washed three times with DMF solvent and then vacuum dried at 100 °C for 8 hours to obtain the final product.
[0057] The preparation methods for negative electrode plates and positive electrode plates, as well as the battery assembly methods, are as follows: The pretreated and dried silicon-carbon anode material of this comparative example was dissolved in water with graphite, conductive carbon black, CMC, and SBR to form a negative electrode slurry. The appropriate ratio of silicon-carbon anode material, graphite, conductive carbon black, CMC, and SBR was 5%:91.5%:0.5%:1.2%:1.8%. The stirred negative electrode slurry was coated onto a negative electrode current collector, dried to form a negative electrode sheet, and then rolled, slit, and die-cut. Lithium nickel cobalt manganese oxide, conductive agent, and PVDF were dissolved in NMP and stirred to form a positive electrode slurry. The appropriate ratio of lithium nickel cobalt manganese oxide (NCM900505, polycrystalline), conductive agent and PVDF is 96%:1.5%:2.5%. The prepared positive electrode slurry is coated on the positive electrode current collector and dried to form a positive electrode sheet. The positive electrode sheet is then rolled, slit and die-cut. The positive electrode sheet, negative electrode sheet, separator and electrolyte (LiPF6: 14.50%, EC: 23%, EMC: 54.50%, FEC: 6%, DTD: 1.50%, TMSP: 0.50%) are assembled into a soft pack battery.
[0058] Comparative Example 5 A method for surface modification of silicon-carbon anode material includes the following steps: (1) Dry the silicon-carbon composite material in a vacuum oven at 120 °C for 4 hours to completely remove the surface-adsorbed moisture; (2) The pretreated silicon-carbon composite material (1 kg) and glucose (0.05 kg) were placed in a ball mill and thoroughly ground and mixed. The mixture was placed in a tube furnace and heated to 550 °C at a rate of 3 °C / min under an argon atmosphere and held for 3 hours. After the reaction was completed, the mixture was naturally cooled to obtain a silicon-carbon material with an inner amorphous carbon coating.
[0059] (3) Weigh out LiOH (0.4 mol / L) and dissolve it in ethanol (3 L of lithium salt ethanol solution), and stir magnetically until completely dissolved; slowly add the silicon-carbon material with inner amorphous carbon coating obtained in (2) to the lithium salt ethanol solution under gentle stirring until a uniform slurry is formed. Then treat it under a slight negative pressure of -0.05 MPa for 30 minutes to allow the solution to fully penetrate. Finally, dry it at 80 °C for 12 hours to complete the lithium salt coating.
[0060] (4) The gradient-coated improved silicon-carbon material obtained in (3) was dispersed in 120 g of 3wt% polysuccinimide / N-methylpyrrolidone solution and stirred at 60 °C for 6 hours. The impregnated mixture was filtered and dried, and then heat-treated at 250 °C for 2 hours under an argon atmosphere.
[0061] (5) The product after heat treatment (4) was washed three times with DMF solvent to remove unreacted PSI. Finally, it was vacuum dried at 100 °C for 8 hours to obtain the final modified product.
[0062] The preparation methods for negative electrode plates and positive electrode plates, as well as the battery assembly methods, are as follows: The silicon-carbon anode material prepared in this embodiment was dissolved in water with graphite, conductive carbon black, CMC, and SBR to form a negative electrode slurry. The appropriate ratio of silicon-carbon anode material, graphite, conductive carbon black, CMC, and SBR was 5%:91.5%:0.5%:1.2%:1.8%. The stirred negative electrode slurry was coated onto a negative electrode current collector, dried to form a negative electrode sheet, and then rolled, slit, and die-cut. Lithium nickel cobalt manganese oxide, a conductive agent, and PVDF were dissolved in NMP and stirred to form a positive electrode slurry. The appropriate ratio of lithium nickel cobalt manganese oxide (NCM900505, polycrystalline), conductive agent and PVDF is 96%:1.5%:2.5%. The prepared positive electrode slurry is coated on the positive electrode current collector and dried to form a positive electrode sheet. The positive electrode sheet is then rolled, slit and die-cut. The positive electrode sheet, negative electrode sheet, separator and electrolyte (LiPF6: 14.50%, EC: 23%, EMC: 54.50%, FEC: 6%, DTD: 1.50%, TMSP: 0.50%) are assembled into a soft pack battery.
[0063] Comparative Example 6 A method for surface modification of silicon-carbon anode material includes the following steps: (1) Dry the silicon-carbon composite material in a vacuum oven at 120 °C for 4 hours to completely remove the surface-adsorbed moisture; (2) The pretreated silicon-carbon composite material (1 kg) and glucose (0.05 kg) were placed in a ball mill and thoroughly ground and mixed. The mixture was placed in a tube furnace and heated to 550 °C at a rate of 3 °C / min under an argon atmosphere and held for 3 hours. After the reaction was completed, the mixture was naturally cooled to obtain a silicon-carbon material with an inner amorphous carbon coating.
[0064] (3) Weigh out LiCl (0.4 mol / L) and dissolve it in ethanol (3 L of lithium salt ethanol solution), and stir magnetically until completely dissolved; slowly add the silicon-carbon material with inner amorphous carbon coating obtained in (2) to the lithium salt ethanol solution under gentle stirring until a uniform slurry is formed. Then treat it under a slight negative pressure of -0.05 MPa for 30 minutes to allow the solution to fully penetrate. Finally, dry it at 80 °C for 12 hours to complete the lithium salt coating.
[0065] (4) Disperse the gradient-coated improved silicon-carbon material obtained in (3) into 120 g of a 3wt% polysuccinimide / N-methylpyrrolidone solution and stir at 60 °C for 6 hours. Filter and dry the impregnated mixture and heat treat it at 250 °C for 2 hours under an argon atmosphere.
[0066] (5) The product after heat treatment (4) was washed three times with DMF solvent to remove unreacted PSI. Finally, it was vacuum dried at 100 °C for 8 hours to obtain the final modified product.
[0067] The preparation methods for negative electrode plates and positive electrode plates, as well as the battery assembly methods, are as follows: The silicon-carbon anode material prepared in this embodiment was dissolved in water with graphite, conductive carbon black, CMC, and SBR to form a negative electrode slurry. The appropriate ratio of silicon-carbon anode material, graphite, conductive carbon black, CMC, and SBR was 5%:91.5%:0.5%:1.2%:1.8%. The stirred negative electrode slurry was coated onto a negative electrode current collector, dried to form a negative electrode sheet, and then rolled, slit, and die-cut. Lithium nickel cobalt manganese oxide, a conductive agent, and PVDF were dissolved in NMP and stirred to form a positive electrode slurry. The appropriate ratio of lithium nickel cobalt manganese oxide (NCM900505, polycrystalline), conductive agent and PVDF is 96%:1.5%:2.5%. The prepared positive electrode slurry is coated on the positive electrode current collector and dried to form a positive electrode sheet. The positive electrode sheet is then rolled, slit and die-cut. The positive electrode sheet, negative electrode sheet, separator and electrolyte (LiPF6: 14.50%, EC: 23%, EMC: 54.50%, FEC: 6%, DTD: 1.50%, TMSP: 0.50%) are assembled into a soft pack battery.
[0068] Performance testing: (I) DCR Test: ① Room temperature DCR test: Test conditions (25 ± 2 ℃, 15~90% RH), fully charge the soft pack battery, then discharge it to 50% SOC using 1.0 C, and record the process data using 2 C pulse discharge for 30 s (sampling frequency 0.1 s).
[0069] ② Low temperature DCR test: Test conditions (-20 ± 2 ℃, 15~90% RH), the soft pack battery is fully charged, then discharged to 50% SOC at 1.0 C, and the process data is recorded by pulse discharge at 0.36 C for 30 s (sampling frequency 0.1 s).
[0070] The test results are shown in Table 1.
[0071] Table 1 DCR Test Results
[0072] By measuring the DCR data of the pouch cells prepared in Examples 1-4 and Comparative Examples 1-6 under the same test conditions, it can be seen that the kinetics of silicon-carbon materials after gradient coating and surface modification are significantly improved.
[0073] (II) Cyclic Performance Test: Cyclic performance tests were conducted on the soft-pack cells corresponding to the groups of each embodiment and comparative example. The test conditions were: charge / discharge voltage range of 2.75~4.25 V, temperature of 25 ± 2.0 ℃, and charge / discharge rate of 1.0 C / 1.0 C. The test results are shown in Table 2.
[0074] Table 2 Cyclic performance test results
[0075] By measuring the capacity retention rate of the pouch cells prepared in the examples and comparative examples under the same test conditions after a certain number of cycles, it can be seen that the application of gradient-coated and surface-modified silicon-carbon anode materials in pouch cells can improve the cycle retention rate of pouch cells. In other words, surface modification treatment can enhance the stability of the solid electrolyte interface (SEI).
[0076] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.
Claims
1. A method for surface modification of silicon-carbon anode materials, characterized in that, Includes the following steps: Silicon-carbon composite material is mixed with a carbon source and then pyrolyzed and carbonized under an inert atmosphere to obtain amorphous carbon-coated silicon-carbon material. Amorphous carbon-coated silicon-carbon materials are coated with lithium salt gradients; The lithium salt gradient coated silicon-carbon material was dispersed in the NMP solution of PSI, impregnated, filtered, dried, and then heat-treated under an inert atmosphere to obtain the modified silicon-carbon anode material.
2. The method as described in claim 1, characterized in that, The method also includes a pretreatment step for the silicon-carbon composite material, specifically: drying the silicon-carbon composite material at 100~150 ℃ for 2~10 h.
3. The method as described in claim 1, characterized in that, The carbon source is an organic carbon source, preferably glucose, sucrose or phenolic resin.
4. The method as described in claim 3, characterized in that, The mass ratio of silicon-carbon composite material to carbon source is 1:0.05~0.3; or, the inert atmosphere is argon or nitrogen.
5. The method as described in claim 1, characterized in that, The pyrolysis carbonization conditions are to heat to 500-700 °C at a rate of 2-5 °C / min and hold for 2-5 h; or, the lithium salt is LiOH and LiCl; preferably, the molar ratio of LiOH to LiCl is 3:1-3.
6. The method as described in claim 1, characterized in that, The impregnation conditions are continuous stirring at 50~80 ℃ for 4~12 h; or, the heat treatment conditions are heat treatment at 200~350 ℃ for 1~3 h; or, after heat treatment, the process includes washing and drying with an organic solvent, preferably, the organic solvent is selected from one or more of DMF, DMSO, and NMP; the drying operation is vacuum drying at 80~110 ℃ for 6~10 h.
7. The modified silicon-carbon anode material prepared by the surface modification method according to any one of claims 1 to 6.
8. A negative electrode sheet, characterized in that, It includes a current collector and an active layer attached to the surface of the current collector, wherein the active material in the active layer is the modified silicon-carbon anode material as described in claim 7.
9. The method for preparing the negative electrode sheet as described in claim 8, characterized in that, The modified silicon-carbon anode material is mixed with a conductive agent, a binder, and a thickener in a solvent to obtain a slurry. The slurry is then coated onto the surface of a current collector and dried to obtain the final product.
10. A lithium-ion battery, characterized in that, The negative electrode of the lithium-ion battery is the negative electrode sheet as described in claim 8.