Preparation method and application of asphalt coated silicon-graphite composite negative electrode material
Through the preparation method of asphalt-covered silicon-graphite composite material, the problem of volume change and poor conductivity of silicon-based materials in lithium-ion batteries during charging and discharging is solved, and the stability and conductivity of the material are improved, while reducing the stability of the material. Production costs and environmental pollution.
Patent Information
- Application Number
- CN202411630911.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-11-15
- Publication Date
- 2025-02-18
AI Technical Summary
The silicon-based materials in lithium-ion batteries have huge volume changes, poor conductivity and repeated formation of solid electrolyte interfaces during charging and discharging, resulting in poor performance under high energy density requirements.
Using the preparation method of asphalt-coated silicon-graphite composite, nano-silicon and natural graphite are uniformly mixed by high-energy ball mill, then dissolved in solvent and carried out preliminary coating, and then processed heating in inert gas to complete the coating, and Multiple coats improve the stability of the material.
Effectively reduce the free silicon distribution in the material, limit the expansion of silicon-based materials, improve the stability and conductivity of the material, and reduce the production cost, simplify the experimental process, reduce the use of harmful reagents and the generation of waste liquids. .
Smart Images
Figure CN119480995A_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of lithium ion battery electrode materials, and relates to a preparation method of an asphalt-coated silicon-graphite composite negative electrode material and an application thereof in lithium ion batteries. Background Art
[0002] In the selection of negative electrodes for lithium-ion batteries, graphite is currently the mainstream negative electrode material. However, as one of the traditional graphite materials, natural graphite still has disadvantages such as low initial coulombic efficiency, poor rate and cycle performance, and with the rapid development of various energy storage fields in recent years, people's requirements for battery energy density have also increased. Traditional graphite negative electrodes are gradually unable to meet people's needs due to their low capacity, so high-energy-density silicon-based materials have attracted people's attention. However, although silicon-based materials have high energy density materials, they still have huge volume changes, poor conductivity, and repeated formation of solid electrolyte interfaces during the charge and discharge process, which need to be solved.
[0003] In order to solve the above-mentioned problems of silicon volume expansion and poor conductivity, scholars have conducted a lot of scientific research. Many carbon materials have shown good ability in limiting silicon volume expansion and conductivity. Therefore, silicon-carbon materials have become the mainstream research content for improving the stability of silicon-based materials. In patent CN118763211A, a preparation method of graphene-doped silicon-carbon material is provided. Graphene is given excellent conductivity and different surface polar groups through bidirectional modification. The modified graphene is then evenly dispersed in the resin solution. After curing, pyrolysis, activation, silane deposition, and carbon coating steps are performed. Although this improves the overall conductivity of the composite material, the experimental steps have high material costs and are relatively cumbersome. In CN118702107A, the researchers used graphite phase carbon nitride formed in situ as both a reducing agent for thermal reduction of nano-silicon to nano-silicon and a pore-forming agent for carrier activated carbon. The g-C3N4-C composite material coated with an indium tin oxide-silicon dioxide composite conductive film was thermally reduced at 560-800°C to form a conductive nano-silicon-carbon negative electrode material, which greatly limited the volume expansion of the silicon-based material and improved the stability of the material. However, a variety of toxic organic raw materials such as formaldehyde, phenol and melamine were used in the experimental steps, and a variety of toxic waste liquids were produced during the experiment, which increased the danger of the experiment and caused great pollution to the environment, which was not conducive to large-scale industrial production. It can be seen from the above patents that the current process still has the disadvantages of complex process, high raw material cost, more toxic waste liquids in the experimental process, and imperfect coating effect. Summary of the invention
[0004] Based on this, the present invention provides a method for preparing an asphalt-coated silicon-graphite composite negative electrode material, which is used to alleviate the problems of volume expansion and poor conductivity of the above-mentioned silicon-based materials.
[0005] To achieve the above objectives, the technical means adopted by the present invention are as follows:
[0006] The present invention provides a preparation method and application of a pitch-coated silicon-graphite composite negative electrode material, comprising the following steps:
[0007] S1. Evenly mix a certain amount of natural graphite and nano-silicon through high-energy ball milling, so that the nano-silicon is fully attached to the natural graphite to obtain product 1.
[0008] S2. Grind the coating material, and then place it in a certain amount of solvent and stir to dissolve it. After the coating material is completely dissolved, a product 2 is obtained.
[0009] S3, adding product 1 to product 2 and continuously stirring and mixing to achieve preliminary coating of the coating material, and removing the solvent by heating to obtain product 3.
[0010] S4. The product 3 is heated under an inert gas in a program-controlled manner to complete the coating, thereby obtaining the product 4.
[0011] S5. Use product 2 to coat product 4 several times to obtain product 5.
[0012] S6. Stir and mix the product 5 with a conductive agent, a binder and a solvent, apply the prepared slurry on a copper foil, and assemble it with a lithium sheet, an electrolyte and a separator into a lithium-ion button battery after drying.
[0013] In an embodiment of the present invention, the graphite in S1 is natural spherical graphite with a diameter of 5 to 15 um, and the mass ratio of nano-silicon to natural graphite is 1:4 to 1:20.
[0014] In an embodiment of the present invention, the ball milling in S1 is dry milling, the ball milling speed is 300-600 rpm, and the ball milling time is 2-10 h.
[0015] In an embodiment of the present invention, the coating material in S2 is asphalt, and the softening point ranges from 220 to 280°C.
[0016] In an embodiment of the present invention, the mass of the coating material in S2 accounts for 5-30% of the silicon-carbon composite material.
[0017] In an embodiment of the present invention, the solvent in S2 is one of tetrahydrofuran, toluene, dichloromethane and chloroform. In an embodiment of the present invention, the stirring time in S3 is 0.5 to 2 hours, and the heating method is any one of water bath, drying and rotary evaporation.
[0018] In an embodiment of the present invention, the inert gas in S4 is argon or nitrogen, the heating rate is 1 to 5°C / min, the heating temperature is 250 to 350°C, and the heating time is 2 to 4h.
[0019] In an embodiment of the present invention, the mass of the coating material in S5 accounts for 5% of the silicon-carbon composite material. The re-coating temperature is 900-1000°C.
[0020] In an embodiment of the present invention, the conductive agent in S6 is one of carbon black or carbon nanotubes, and the binder is one of sodium alginate, polyvinylidene fluoride, carboxymethyl cellulose or polyacrylic acid. The drying temperature is 60-100° C. and the drying time is 8-12 hours.
[0021] According to the specific implementation scheme, compared with the prior art, the beneficial effects of the present invention are as follows:
[0022] The present invention greatly reduces the use of harmful reagents and the generation of waste liquid, reduces pollution during the experiment, selects lower-priced experimental materials, reduces the cost of the entire production process, and the experimental operation process is relatively simple and convenient, which is more conducive to the commercial development of the material. At the same time, the two-layer asphalt coating reduces the distribution of free silicon in the material, more effectively limits the expansion of the silicon-based material, increases the stability of the material, and avoids the performance degradation caused by the excessive thickness of the coating layer. BRIEF DESCRIPTION OF THE DRAWINGS
[0023] Figure 1 This is a SEM image of the silicon-carbon material prepared in Example 2 of the present invention;
[0024] Figure 2 is the X-ray diffraction pattern of the silicon-carbon material in Example 2 of the present invention;
[0025] Figure 3 is the cyclic voltammetry curve of the silicon-carbon material in Example 1 of the present invention;
[0026] Figure 4 This is the AC impedance curve of the silicon-carbon material in Example 3 of the present invention. DETAILED DESCRIPTION
[0027] The present invention is further illustrated by the following specific examples.
[0028] Example 1
[0029] Take 80mg of nano-silicon and 820mg and place them in a ball mill, then add zirconium oxide ball milling beads and ball mill at a speed of 600rpm for 6h, and take out the silicon-graphite precursor for use. Put the asphalt into a mortar and grind it for 15min, weigh 50mg of the ground asphalt and place it in 20ml of tetrahydrofuran and stir for 30min to form a mixed solution. Then weigh 400mg of silicon-graphite precursor and add it to the tetrahydrofuran mixed solution and stir in a 60℃ water bath until the tetrahydrofuran is completely volatilized. Take out the mixture and grind it for 15min, then put the mixture in the center of the tube furnace and pass argon gas, keep it at 305℃ for 3h, and then heat it to 950℃ and keep it for 2h to get the final product. The final product is mixed with carbon black and carboxymethyl cellulose and coated on copper foil, and finally assembled into a battery for electrochemical testing at different current densities.
[0030] Example 2
[0031] Take 80mg of nano-silicon and 820mg and place them in a ball mill, then add zirconium oxide ball milling beads and ball mill at a speed of 600rpm for 6h. Put the asphalt in a mortar and grind for 15min, weigh 50mg of the ground asphalt and place it in 20ml of tetrahydrofuran and stir for 30min. Then weigh 400mg of silicon-graphite precursor and add it to the tetrahydrofuran mixed solution and stir it in a 60℃ water bath until the tetrahydrofuran is completely volatilized, take out the mixture and grind it for 15min, then put the mixture in the center of the tube furnace and pass argon, keep it at 305℃ for 3h, and take out the product for use. Weigh 15mg of asphalt and place it in 20ml of tetrahydrofuran and stir it for 30min to form a mixed solution, put the previously reserved product into the mixed solution and stir it in a 60℃ water bath until the tetrahydrofuran is completely volatilized, then take out the mixture and grind it for 15min, then put it in a tube furnace and keep it at 305℃ for 3h, then heat it to 950℃ and keep it for 2h to get the final product. The final product was mixed with carbon black and carboxymethyl cellulose and coated on copper foil, and finally assembled into a battery for electrochemical testing at different current densities.
[0032] Example 3
[0033] Take 80mg of nano-silicon and 820mg and place them in a ball mill, then add zirconium oxide ball milling beads and ball mill at a speed of 600rpm for 6h. Put the asphalt in a mortar and grind for 15min, weigh 50mg of the ground asphalt and place it in 20ml of tetrahydrofuran and stir for 30min. Then weigh 400mg of silicon-graphite precursor and add it to the tetrahydrofuran mixed solution and stir it in a 60℃ water bath until the tetrahydrofuran is completely volatilized, take out the mixture and grind it for 15min, then put the mixture in the center of the tube furnace and pass argon, keep it warm at 305℃ for 3h, and take out the product for use. Weigh 15mg of asphalt and place it in 20ml of tetrahydrofuran and stir it for 30min to form a mixed solution, put the previously reserved product into the mixed solution and stir it in a 60℃ water bath until the tetrahydrofuran is completely volatilized, then take out the mixture and grind it for 15min, then put it in a tube furnace and keep it warm at 305℃ for 3h, and then use the previous steps to coat it again to obtain the final product. The final product was mixed with carbon black and carboxymethyl cellulose and coated on copper foil, and finally assembled into a battery for electrochemical testing at different current densities.
[0034] Table 1 Electrochemical performance data of different embodiments
[0035]
[0036] Different embodiments can successfully obtain asphalt-coated silicon-graphite composite materials. Figure 1 This is a SEM image of the silicon-carbon composite material in Example 2. It can be seen from the image that the asphalt coating layer is relatively complete and can completely coat the graphite and silicon particles. Figure 2 The X-ray diffraction spectrum of Example 2 shows that no impurities are generated or doped during the material preparation process. By comparing the examples in Table 1, it can be concluded that mixing nano-silicon with natural graphite and coating with asphalt can improve the discharge capacity and cycle life. Figure 3 This is the cyclic voltammetry curve of Example 1. It can be seen from the figure that the capacity comes from the redox peaks of silicon and carbon, and there is no redox peak of other elements incorporated. Figure 4 The AC impedance spectrum of the battery assembled in Example 3 shows that the high-frequency region has a smaller semicircle, indicating that its charge transfer impedance is low, which also proves that the material prepared in Example 3 has higher electrochemical kinetics.
Claims
1. A preparation method and application of asphalt-coated silicon-graphite composite negative electrode material, characterized in that The following steps are involved: S1. Evenly mix a certain amount of natural graphite and nano-silicon through high-energy ball milling, so that the nano-silicon is fully attached to the natural graphite to obtain product 1. S2. Grind the coating material, and then place it in a certain amount of solvent and stir to dissolve it. After the coating material is completely dissolved, a product 2 is obtained. S3, adding product 1 to product 2 and continuously stirring and mixing to achieve preliminary coating of the coating material, and removing the solvent by heating to obtain product 3. S4. The product 3 is heated under an inert gas in a program-controlled manner to complete the coating, thereby obtaining the product 4. S5. Use product 2 to coat product 4 several times to obtain product 5. S6. Stir and mix the product 5 with a conductive agent, a binder and a solvent, apply the prepared slurry on a copper foil, and assemble it with a lithium sheet, an electrolyte and a separator into a lithium-ion button battery after drying.
2. The method for preparing a silicon-carbon negative electrode material according to claim 1, characterized in that the graphite in S1 is natural spherical graphite with a diameter of 5 to 15 um, and the mass ratio of nano-silicon to natural graphite is 1:4 to 1:
20.
3. The method for preparing a silicon-carbon negative electrode material according to claim 1 is characterized in that the ball milling in S1 is dry milling, the ball milling speed is 300 to 600 rpm, and the ball milling time is 2 to 10 hours.
4. The method for preparing a silicon-carbon negative electrode material according to claim 1, wherein the coating material in S2 is asphalt having a softening point of 220 to 280°C.
5. The method for preparing a silicon-carbon negative electrode material according to claim 1, wherein the mass of the coating material in S2 accounts for 5 to 30% of the silicon-carbon composite material.
6. The method for preparing a silicon-carbon negative electrode material according to claim 1, wherein the solvent in S2 is one of tetrahydrofuran, toluene, dichloromethane and chloroform.
7. The method for preparing a silicon-carbon negative electrode material according to claim 1, characterized in that the stirring time in S3 is 0.5 to 2 hours, and the heating method is any one of water bath, drying, and rotary evaporation.
8. The method for preparing a silicon-carbon negative electrode material according to claim 1 is characterized in that the inert gas in S4 is argon or nitrogen, the heating rate is 1 to 5°C / min, the heating temperature is 250 to 350°C, and the heating time is 2 to 4h.
9. The method for preparing silicon-carbon negative electrode material according to claim 1, characterized in that the mass of the coating material in S5 accounts for 5% of the silicon-carbon composite material, and the secondary coating temperature is 900-1000°C.
10. The method for preparing a silicon-carbon negative electrode material according to claim 1, wherein the conductive agent in S6 is one of carbon black or carbon nanotubes, and the binder is one of sodium alginate, polyvinylidene fluoride, carboxymethyl cellulose or polyacrylic acid. The drying temperature is 60-100°C and the drying time is 8-12 hours.