A composite current collector base film based on SiO2 nanocomposite modification and its preparation method

Abstract

This case involves a base film for a composite current collector based on SiO2 nanocomposite modification and its preparation method. The present invention forms modified auxiliary particles by synergistically modifying nano-SiO2 with aluminum hypophosphite, montmorillonite, etc., and extrudes them together with PET masterbatch. At the same time, a modified coating containing nano-SiO2 is coated on the surface of the base film, which significantly improves the mechanical properties, thermal stability and flame retardancy of the base film.

Description

Technical Field

[0001] The present invention relates to the technical field of composite current collector base films, in particular to a composite current collector base film based on SiO2 nanocomposite modification and a preparation method thereof. Background Art

[0002] Traditional current collectors, such as copper and aluminum foil, suffer from mechanical brittleness and high-temperature deformation in flexible batteries and high-voltage systems, limiting their application. Composite current collectors utilize an organic polymer membrane as a base film intermediate layer, with metallic conductive layers formed on either side. Their unique sandwich structure reduces metal usage and weight. More importantly, the organic polymer membrane can incorporate flame-retardant or high-temperature-resistant materials, extending battery life and safety.

[0003] Currently, PET polyester film is widely used in the preparation of composite current collectors. However, pure PET polyester material suffers from insufficient longitudinal tensile strength, poor chemical stability, poor high-temperature resistance, and flame retardancy. Therefore, the modification of PET polyester film is an issue that needs to be overcome and continuously innovated and optimized in this field. Summary of the Invention

[0004] In response to the shortcomings of the existing technology, the present invention is based on SiO2 nanoparticles, which are modified in series and then added to PET masterbatch for co-extrusion and surface coating after film formation to form a modified base film, which effectively solves the problems of insufficient tensile strength, poor stability and non-flame retardancy.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A method for preparing a base film for a composite current collector based on SiO2 nanocomposite modification comprises the following steps:

[0007] 1) Mix the PET masterbatch and the composite modified auxiliary particles, melt and extrude them, and cool them to obtain cast sheets;

[0008] 2) After preheating the casting, first stretch it longitudinally and then stretch it transversely;

[0009] 3) Heat setting the stretched film and cooling it to obtain a crude product;

[0010] 4) Apply modified coating on the upper and lower surfaces of the crude product and dry;

[0011] 5) Pulling and rolling to obtain the base film for the composite current collector;

[0012] Wherein, the composite modified auxiliary particles and the modified coating both contain synergistically modified nano-SiO2, and the preparation method thereof is as follows:

[0013] S1, using isocyanate propyl triethoxysilane to treat nano-SiO2, set aside;

[0014] S2. Ultrasonic dispersion of NCC in DMF was transferred to a three-necked flask, phenylphosphoryl dichloride was slowly added dropwise, and the temperature was raised to 110°C with stirring, and the temperature was kept at 110°C for 3 hours. Hydroxymethyl diethyl phosphate was slowly added dropwise, and the temperature was kept at 110°C for 3 hours. The solvent was removed by rotary evaporation, and the flame retardant modified NCC was obtained by drying.

[0015] S3. Place the flame retardant modified NCC in deionized water, adjust the pH to 3, stir thoroughly, add the nano-SiO2 in step S1, ultrasonicate for 30 minutes, heat to 60°C, add sodium hydroxide to adjust the pH to alkaline, continue heating for 3 hours, cool to room temperature, filter and wash, collect the solid, dry and grind to obtain.

[0016] Furthermore, in the step 1), the composite modified auxiliary particles include synergistically modified nano-SiO2, aluminum hypophosphite, and montmorillonite, and the preparation method is: first, the montmorillonite is acidified, then combined with a vinyltriethoxysilane coupling agent, an aluminum hypophosphite aqueous dispersion is added, and after stirring evenly, a mixture of acrylic acid and an initiator is slowly added dropwise thereto for reaction, and finally, the synergistically modified nano-SiO2 is added and stirred evenly, the solvent is removed, the water is dried, and the composite modified auxiliary particles are obtained by grinding.

[0017] Furthermore, the usage ratio of the synergistically modified nano-SiO2, aluminum hypophosphite, and montmorillonite is 5~8:2~3:3~6; the usage of the vinyltriethoxysilane coupling agent, acrylic acid, and initiator are 2~5 times, 0.5~1 times, and 0.02~0.05 times that of montmorillonite, respectively.

[0018] Furthermore, the preparation process of the modified coating is as follows:

[0019] Add bisphenol A epoxy resin and tetrabutylammonium bromide to the reaction flask container, stir evenly, heat to 60°C, add acrylic acid dropwise, and keep warm for 1 hour. After the addition is completed, heat to 80°C, add methyl methacrylate, butyl acrylate, methacrylic acid and ammonium polyphosphate, then add emulsifier aqueous solution, disperse evenly at high speed, and keep warm for 2-4 hours; mix methacrylate glycerol ether, butyl acrylate, vinyltriethoxysilane and emulsifier aqueous solution evenly, and add dropwise to the above reaction system. After the addition is completed, continue to keep warm for 3 hours, cool to room temperature to remove unreacted monomers, adjust the pH to neutral, slowly add the synergistic modified nano-SiO2 aqueous dispersion while stirring, and finally add polyamide curing agent, adjust the solid content to 35-45%, and obtain the product.

[0020] Furthermore, the preparation process of the modified coating is as follows:

[0021] Add 1 part of bisphenol A epoxy resin and 0.05-0.1 part of tetrabutylammonium bromide to the reaction bottle container, stir evenly, heat to 60 ° C, add 40-50 parts of acrylic acid, keep warm for 1 hour, heat to 80 ° C after the addition is complete, add 30-35 parts of methyl methacrylate, 25-30 parts of butyl acrylate, 20-30 parts of methacrylic acid and 2-5 parts of ammonium polyphosphate, then add 30 parts of emulsifier aqueous solution, disperse evenly at high speed, keep warm and react for 2-4 hours; add 10-20 parts of methyl Glyceryl acrylate, 15-25 parts of butyl acrylate, 5-10 parts of vinyltriethoxysilane and 20-30 parts of emulsifier aqueous solution are mixed evenly and then added dropwise to the above reaction system. After the addition is completed, the reaction is continued to be kept warm for 3 hours, and the temperature is cooled to room temperature to remove unreacted monomers. The pH is adjusted to neutral, and 30-50 parts of 50wt% synergistic modified nano-SiO2 aqueous dispersion is slowly added while stirring. Finally, 5-10 parts of polyamide curing agent are added and the solid content is adjusted to 35-45%.

[0022] Furthermore, the mass ratio of the PET masterbatch to the composite modified auxiliary particle is 100:5~20.

[0023] Furthermore, in the step 2), the stretching ratio of the longitudinal stretching is 2 to 3.5 times, and the stretching ratio of the transverse stretching is 2.5 to 3.8 times.

[0024] Furthermore, in step 4), the dry coating amount of the modified coating is 0.5-1 g / m 2 .

[0025] The present invention further provides a base film for a composite current collector based on SiO2 nanocomposite modification, which is prepared by the preparation method described above.

[0026] The present invention provides a base film for a composite current collector based on SiO2 nanocomposite modification, which is prepared by the preparation method described above.

[0027] Compared with the existing technology, the beneficial effects of the present invention are: by synergistically modifying nano-SiO2 and compounding it with aluminum hypophosphite, montmorillonite, etc. to form modified auxiliary particles, and blending and extruding it with PET masterbatch, and at the same time coating the surface of the base film with a modified coating containing nano-SiO2, the mechanical properties, thermal stability and flame retardancy of the base film are significantly improved. DETAILED DESCRIPTION

[0028] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0029] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0030] A method for preparing a base film for a composite current collector based on SiO2 nanocomposite modification comprises the following steps:

[0031] 1) PET masterbatch and composite modified auxiliary particles are mixed and melted in a mass ratio of 100:5-20, and cooled to obtain a cast sheet;

[0032] 2) After preheating the cast sheet, first stretch it longitudinally at a stretching ratio of 2 to 3.5 times, and then stretch it transversely at a stretching ratio of 2.5 to 3.8 times;

[0033] 3) Heat setting the stretched film and cooling it to obtain a crude product;

[0034] 4) Apply modified coating on the upper and lower surfaces of the rough product with a dry coating amount of 0.5~1 g / m 2 ,dry;

[0035] 5) Pulling and rolling to obtain the base film for the composite current collector;

[0036] Wherein, the composite modified auxiliary particles and the modified coating both contain synergistically modified nano-SiO2, and the preparation method thereof is as follows:

[0037] S1, using isocyanate propyl triethoxysilane to treat nano-SiO2, set aside;

[0038] S2. Ultrasonic dispersion of NCC in DMF was transferred to a three-necked flask, phenylphosphoryl dichloride was slowly added dropwise, and the temperature was raised to 110°C with stirring, and the temperature was kept at 110°C for 3 hours. Hydroxymethyl diethyl phosphate was slowly added dropwise, and the temperature was kept at 110°C for 3 hours. The solvent was removed by rotary evaporation, and the flame retardant modified NCC was obtained by drying.

[0039] S3. Place the flame retardant modified NCC in deionized water, adjust the pH to 3, stir thoroughly, add the nano-SiO2 in step S1, ultrasonicate for 30 minutes, heat to 60°C, add sodium hydroxide to adjust the pH to alkaline, continue heating for 3 hours, cool to room temperature, filter and wash, collect the solid, dry and grind to obtain.

[0040] In the present invention, the composite modified auxiliary particle comprises synergistically modified nano-SiO2, aluminum hypophosphite, and montmorillonite in a ratio of 5-8:2-3:3-6. The preparation method comprises: first, acidifying the montmorillonite, then combining it with a vinyl triethoxysilane coupling agent (A151), adding an aqueous dispersion of aluminum hypophosphite, stirring uniformly, then slowly adding a mixture of acrylic acid and an initiator dropwise to the mixture for reaction, and finally adding the synergistically modified nano-SiO2, stirring uniformly, removing the solvent, drying the water, and grinding to obtain the composite modified auxiliary particle. The amounts of the vinyl triethoxysilane coupling agent, acrylic acid, and initiator are 2-5 times, 0.5-1 times, and 0.02-0.05 times, respectively, the amounts of the montmorillonite.

[0041] In the present invention, the preparation process of the modified coating is as follows:

[0042] Add 1 part of bisphenol A epoxy resin and 0.05-0.1 part of tetrabutylammonium bromide to the reaction bottle container, stir evenly, heat to 60 ° C, add 40-50 parts of acrylic acid, keep warm for 1 hour, heat to 80 ° C after the addition is complete, add 30-35 parts of methyl methacrylate, 25-30 parts of butyl acrylate, 20-30 parts of methacrylic acid and 2-5 parts of ammonium polyphosphate, then add 30 parts of emulsifier aqueous solution, disperse evenly at high speed, keep warm and react for 2-4 hours; add 10-20 parts of methyl Glyceryl acrylate, 15-25 parts of butyl acrylate, 5-10 parts of vinyltriethoxysilane and 20-30 parts of emulsifier aqueous solution are mixed evenly and added dropwise to the above reaction system. After the addition is completed, the reaction is continued to be kept warm for 3 hours, and the temperature is cooled to room temperature to remove unreacted monomers. The pH is adjusted to neutral, and 30-50 parts of 50wt% synergistic modified nano-SiO2 aqueous dispersion is slowly added while stirring. Finally, 5-10 parts of polyamide curing agent are added and the solid content is adjusted to 35-45%.

[0043] The base film for composite current collector based on SiO2 nano-composite modification prepared by the preparation method provided in the embodiment of the present application is obtained by adding modified auxiliary particles containing synergistically modified nano-SiO2 to the PET masterbatch, and coating the surface of the base film rough product with a coating liquid containing synergistically modified nano-SiO2, so that the film has excellent mechanical strength and flame retardancy.

[0044] The present invention prepares a modified auxiliary particle formed by synergistically modifying nano-SiO2 and aluminum hypophosphite and montmorillonite. First, the synergistically modified nano-SiO2 is modified by introducing isocyanate groups on the surface of silica particles modified by silane coupling agent. Then, phenylphosphoryl dichloride and hydroxymethyl diethyl phosphate are reacted on the surface of NCC to prepare flame-retardant modified NCC. Through hydrogen bonding, the flame-retardant modified NCC is combined with silica particles to form an organic whole. Then, the intercalation effect of montmorillonite is used to acidify it to make its surface highly active. Functional groups, treated with A151 silane coupling agent, are in-situ polymerized with acrylic acid while promoting the intercalation reaction of the flame retardant aluminum hypophosphite. Finally, the modified auxiliary particles formed by mixing with synergistic modified nano-SiO2 increase the interfacial force with the PET polymer film due to the acrylic polymer chains on its surface, effectively improving the compatibility of the modified auxiliary particles in PET. Montmorillonite and cellulose have a great improvement effect on the strength and stability of the PET film. At the same time, the introduction of flame retardant functional groups and the dual effects of flame retardants greatly improve the flame retardant properties of the base film.

[0045] A homemade coating liquid is further coated on the outer surface of the base film, and an aqueous emulsion polymerization is carried out with acrylic monomers and epoxy resins. The synergistically modified nano-SiO2 can be evenly dispersed in the emulsion and can also be evenly dispersed when coated on the base film rough product, thereby further increasing the flame retardancy and surface strength of the base film.

[0046] The following are detailed examples and comparative examples based on the above description to further illustrate the present invention. Example 1:

[0047] 1) PET masterbatch and composite modified auxiliary particles are mixed in a mass ratio of 100:10, melt-extruded, and cooled to obtain a cast sheet;

[0048] 2) After preheating the cast sheet, first stretch it longitudinally at a stretching ratio of 2 to 3.5 times, and then stretch it transversely at a stretching ratio of 2.5 to 3.8 times;

[0049] 3) Heat setting the stretched film and cooling it to obtain a crude product;

[0050] 4) Apply modified coating on the upper and lower surfaces of the rough product with a dry coating amount of 0.5 g / m 2 ,dry;

[0051] 5) Pulling and rolling to obtain the base film for the composite current collector;

[0052] Wherein, the composite modified auxiliary particles and the modified coating both contain synergistically modified nano-SiO2, and the preparation method thereof is as follows:

[0053] S1. Treat nano-SiO2 with isocyanatepropyltriethoxysilane. Ultrasonic dispersion of 10 g of nano-SiO2 in an ethanol aqueous solution was performed. 20 g of isocyanatepropyltriethoxysilane and 0.5 g of dibutyltin dilaurate were added. The pH was adjusted to alkaline. The mixture was stirred at 60°C overnight, centrifuged, washed with water, and dried to obtain the modified SiO2.

[0054] S2. Ultrasonic dispersion of 2 g of NCC in DMF was transferred to a three-necked flask, 10 g of phenylphosphoryl dichloride was slowly added dropwise, the temperature was raised with stirring, and after reaching 110°C, the temperature was kept for 3 h, 8.6 g of diethyl hydroxymethyl phosphate was slowly added dropwise, the temperature was kept for 3 h, the solvent was removed by rotary evaporation, and the flame retardant modified NCC was obtained by drying;

[0055] S3. Place 10 g of flame-retardant modified NCC in deionized water, adjust the pH to 3, stir thoroughly, add 10 g of modified SiO2 from step S1, ultrasonicate for 30 min, heat to 60 °C, add sodium hydroxide to adjust the pH to alkaline, continue heating for 3 h, cool to room temperature, filter and wash, collect the solid, dry and grind to obtain.

[0056] In this embodiment, the composite modified auxiliary particle comprises synergistically modified nano-SiO2, aluminum hypophosphite, and montmorillonite in a ratio of 6:3:5. The preparation method is as follows: first, the montmorillonite is acidified, then combined with a vinyl triethoxysilane coupling agent (A151), an aqueous dispersion of aluminum hypophosphite is added, and after stirring, a mixture of acrylic acid and an initiator is slowly added dropwise to the mixture for reaction. Finally, the synergistically modified nano-SiO2 is added, stirred evenly, the solvent is removed, the water is dried, and the composite modified auxiliary particle is ground. The amounts of the vinyl triethoxysilane coupling agent, acrylic acid, and initiator are 2 times, 0.5 times, and 0.02 times the amounts of the montmorillonite, respectively.

[0057] In this embodiment, the preparation process of the modified coating is as follows:

[0058] Add 1 part of bisphenol A epoxy resin and 0.1 part of tetrabutylammonium bromide to the reaction bottle container, stir evenly, heat to 60°C, add 40 parts of acrylic acid, keep warm for 1 hour, heat to 80°C after the addition is completed, add 30 parts of methyl methacrylate, 25 parts of butyl acrylate, 20 parts of methacrylic acid and 3 parts of ammonium polyphosphate, then add 30 parts of emulsifier aqueous solution, disperse evenly at high speed, and keep warm for 2-4 hours; mix 10 parts of methacrylate glycerol ether, 20 parts of butyl acrylate, 8 parts of vinyltriethoxysilane and 20-30 parts of emulsifier aqueous solution evenly, and add dropwise to the above reaction system, continue to keep warm for 3 hours after the addition is completed, cool to room temperature to remove unreacted monomers, adjust the pH to neutral, slowly add 30 parts of 50wt% synergistic modified nano-SiO2 aqueous dispersion while stirring, and finally add 5 parts of polyamide curing agent, and adjust the solid content to 40%. Example 2:

[0059] 1) PET masterbatch and composite modified auxiliary particles are mixed in a mass ratio of 100:15, melt-extruded, and cooled to obtain a cast sheet;

[0060] 2) After preheating the cast sheet, first stretch it longitudinally at a stretching ratio of 2 to 3.5 times, and then stretch it transversely at a stretching ratio of 2.5 to 3.8 times;

[0061] 3) Heat setting the stretched film and cooling it to obtain a crude product;

[0062] 4) Apply modified coating on the upper and lower surfaces of the rough product with a dry coating amount of 0.8 g / m 2 ,dry;

[0063] 5) Pulling and rolling to obtain the base film for the composite current collector;

[0064] The composite modified auxiliary particles and modified coating are the same as those in Example 1. Example 3:

[0065] 1) PET masterbatch and composite modified auxiliary particles are mixed in a mass ratio of 100:5, melt-extruded, and cooled to obtain a cast sheet;

[0066] 2) After preheating the cast sheet, first stretch it longitudinally at a stretching ratio of 2 to 3.5 times, and then stretch it transversely at a stretching ratio of 2.5 to 3.8 times;

[0067] 3) Heat setting the stretched film and cooling it to obtain a crude product;

[0068] 4) Apply modified coating on the upper and lower surfaces of the rough product with a dry coating amount of 0.5 g / m 2 ,dry;

[0069] 5) Pulling and rolling to obtain the base film for the composite current collector;

[0070] The composite modified auxiliary particles and modified coating are the same as those in Example 1.

[0071] Comparative Example 1:

[0072] This example is basically the same as Example 1, except that the composite modified auxiliary particles and the synergistic modified nano-SiO2 in the modified coating are replaced by ordinary nano-SiO2.

[0073] Comparative Example 2:

[0074] This example is basically the same as Example 1, except that the composite modified auxiliary particles are obtained by directly mixing the synergistically modified nano-SiO2, aluminum hypophosphite, and montmorillonite and then melt-extruding and granulating them.

[0075] Comparative Example 3:

[0076] This example is basically the same as Example 1, except that no composite modified auxiliary particles are added.

[0077] Performance testing:

[0078] 1. Flame retardant performance: The limiting oxygen index of the base film is tested using the standard JIS-K7201-3-2008. The larger the value, the better the flame retardant performance.

[0079] 2. Tensile strength: Tested in accordance with GB / T1040.1-2018.

[0080] 3. Heat deformation temperature: tested using ASTM D648 method.

[0081] Table 1

[0082]

[0083] As can be seen from the test results in Table 1, the base films prepared in Examples 1-3 have flame retardancy, and their tensile strength and heat distortion temperature are significantly improved compared to pure PET film. In Comparative Example 1, the limiting oxygen index decreases significantly, the tensile strength is relatively well maintained, and the heat distortion temperature is lower than that of Examples 1-3, but higher in the comparative example. This is because the synergistically modified nano-SiO2 in the composite modified auxiliary particles and the modified coating are all replaced by ordinary nano-SiO2. Ordinary nano-SiO2 has no flame retardancy and is not compounded with cellulose, has poor thermal stability, and is not as dispersible as the synergistically modified nano-SiO2. The composite modified auxiliary particles in Comparative Example 2 are obtained by directly mixing synergistically modified nano-SiO2, aluminum hypophosphite, and montmorillonite and then melt-extruding and granulating them. The effect of the direct miscibility of the three is not as good as the effect of the in-situ polymerization intercalation reaction on the montmorillonite surface, resulting in a decrease in various properties, especially the greatest impact on tensile strength and heat distortion temperature. Comparative Example 3 does not add composite modified auxiliary particles, and only relies on the coating liquid containing synergistic modified nano-SiO2 to coat and modify the base film crude product. Although it can make the base film have a certain flame retardancy, the effect is very small, and other properties have not been significantly improved.

[0084] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the description and implementation methods. They can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to specific details.

Claims

1. A method for preparing a base film for a composite current collector based on SiO2 nanocomposite modification, characterized in that: The steps include: 1) Mix the PET masterbatch and the composite modified auxiliary particles, melt and extrude them, and cool them to obtain cast sheets; 2) After preheating the casting, first stretch it longitudinally and then stretch it transversely; 3) Heat setting the stretched film and cooling it to obtain a crude product; 4) Apply modified coating on the upper and lower surfaces of the crude product and dry; 5) Pulling and rolling to obtain the base film for the composite current collector; Wherein, the composite modified auxiliary particles and the modified coating both contain synergistically modified nano-SiO2, and the preparation method thereof is as follows: S1, using isocyanate propyl triethoxysilane to treat nano-SiO2, set aside; S2. Ultrasonic dispersion of NCC in DMF was transferred to a three-necked flask, phenylphosphoryl dichloride was slowly added dropwise, and the temperature was raised to 110°C with stirring, and the temperature was kept at 110°C for 3 hours. Hydroxymethyl diethyl phosphate was slowly added dropwise, and the temperature was kept at 110°C for 3 hours. The solvent was removed by rotary evaporation, and the flame retardant modified NCC was obtained by drying. S3, placing the flame retardant modified NCC in deionized water, adjusting the pH to 3, adding the nano-SiO2 in step S1 after thorough stirring, ultrasonicating for 30 minutes, heating to 60°C, adding sodium hydroxide to adjust the pH to alkaline, continuing heating for 3 hours, cooling to room temperature, filtering and washing, collecting the solid, drying and grinding, to obtain; The composite modified auxiliary particles include synergistically modified nano-SiO2, aluminum hypophosphite, and montmorillonite. The preparation method is as follows: first, the montmorillonite is acidified, then combined with a vinyl triethoxysilane coupling agent, an aluminum hypophosphite aqueous dispersion is added, and after stirring evenly, a mixture of acrylic acid and an initiator is slowly added dropwise to the mixture for reaction, and finally, the synergistically modified nano-SiO2 is added and stirred evenly, the solvent is removed, the water is dried, and the composite modified auxiliary particles are prepared by grinding. The preparation process of the modified coating is as follows: Add bisphenol A epoxy resin and tetrabutylammonium bromide to the reaction flask container, stir evenly, heat to 60°C, add acrylic acid dropwise, and keep warm for 1 hour. After the addition is completed, heat to 80°C, add methyl methacrylate, butyl acrylate, methacrylic acid and ammonium polyphosphate, then add emulsifier aqueous solution, disperse evenly at high speed, and keep warm for 2-4 hours; mix methacrylate glycerol ether, butyl acrylate, vinyltriethoxysilane and emulsifier aqueous solution evenly, and add dropwise to the above reaction system. After the addition is completed, continue to keep warm for 3 hours, cool to room temperature to remove unreacted monomers, adjust the pH to neutral, slowly add the synergistic modified nano-SiO2 aqueous dispersion while stirring, and finally add polyamide curing agent, adjust the solid content to 35-45%, and obtain the product.

2. The method for preparing a composite current collector base film based on SiO2 nanocomposite modification according to claim 1, characterized in that: The dosage ratio of the synergistically modified nano-SiO2, aluminum hypophosphite, and montmorillonite is 5-8:2-3:3-6; the dosage of the vinyl triethoxysilane coupling agent, acrylic acid, and initiator are 2-5 times, 0.5-1 times, and 0.02-0.05 times that of montmorillonite, respectively.

3. The method for preparing a composite current collector base film based on SiO2 nanocomposite modification according to claim 1, characterized in that: The preparation process of the modified coating is as follows: Add 1 part of bisphenol A epoxy resin and 0.05-0.1 part of tetrabutylammonium bromide to the reaction bottle container, stir evenly, heat to 60 ° C, add 40-50 parts of acrylic acid, keep warm for 1 hour, heat to 80 ° C after the addition is complete, add 30-35 parts of methyl methacrylate, 25-30 parts of butyl acrylate, 20-30 parts of methacrylic acid and 2-5 parts of ammonium polyphosphate, then add 30 parts of emulsifier aqueous solution, disperse evenly at high speed, keep warm and react for 2-4 hours; add 10-20 parts of methyl Glyceryl acrylate, 15-25 parts of butyl acrylate, 5-10 parts of vinyltriethoxysilane and 20-30 parts of emulsifier aqueous solution are mixed evenly and added dropwise to the above reaction system. After the addition is completed, the reaction is continued to be kept warm for 3 hours, and the temperature is cooled to room temperature to remove unreacted monomers. The pH is adjusted to neutral, and 30-50 parts of 50wt% synergistic modified nano-SiO2 aqueous dispersion is slowly added while stirring. Finally, 5-10 parts of polyamide curing agent are added and the solid content is adjusted to 35-45%.

4. The method for preparing a composite current collector base film based on SiO2 nanocomposite modification according to claim 1, characterized in that: The mass ratio of the PET masterbatch to the composite modified auxiliary particle is 100:5~20.

5. The method for preparing a composite current collector base film based on SiO2 nanocomposite modification according to claim 1, characterized in that: In the step 2), the stretching ratio of the longitudinal stretching is 2 to 3.5 times, and the stretching ratio of the transverse stretching is 2.5 to 3.8 times.

6. The method for preparing a composite current collector base film based on SiO2 nanocomposite modification according to claim 1, characterized in that: In step 4), the dry coating amount of the modified coating is 0.5-1 g / m 2 .

7. A base film for a composite current collector based on SiO2 nanocomposite modification, prepared by the preparation method according to any one of claims 1 to 6.

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