Base membrane for composite current collector based on SiO2 nano composite modification and preparation method thereof

Abstract

The invention relates to a base membrane for a composite current collector based on SiO2 nano composite modification and a preparation method of the base membrane. Synergistic modified nano SiO2 is compounded with aluminum hypophosphite, montmorillonite and the like to form modified auxiliary particles, the modified auxiliary particles and PET master batches are subjected to blending extrusion, and meanwhile, the surface of the base membrane is coated with a modified coating containing nano SiO2, so that the composite current collector is obtained. The mechanical property, the thermal stability and the flame retardance of the base film are obviously improved.

Description

Technical Field

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

[0002] Traditional current collectors such as copper foils and aluminum foils are affected in applications due to factors such as mechanical brittleness and high-temperature deformation in flexible batteries and high-voltage systems. A composite current collector is a new type of current collector with an organic polymer film as the middle layer of the base film and metal conductive layers formed on both sides thereof. The unique sandwich structure reduces the usage amount of metal and also reduces the weight. More importantly, flame retardant materials or high-temperature resistant materials can be introduced into the organic polymer film to improve the service life and safety of the battery.

[0003] Currently, PET polyester films are widely used in the preparation of composite current collectors. However, pure PET polyester materials have problems such as insufficient longitudinal tensile strength, poor chemical stability, intolerance to high temperatures, and non-flammability. Therefore, the modification of PET polyester films is an issue that needs to be overcome and continuously innovated and optimized in this field. Summary of the Invention

[0004] Aiming at the deficiencies in the prior art, based on SiO2 nanoparticles, after a series of modifications, they are respectively added to PET masterbatch for co-extrusion and surface coating after film formation to form a modified base film, effectively solving the problems of insufficient tensile strength, poor stability, and non-flammability.

[0005] To achieve the above object, the present invention provides the following technical solutions: A preparation method of a base film for a composite current collector based on SiO2 nano-composite modification, comprising the following steps: 1) Mix and melt-extrude PET masterbatch and composite modification auxiliary particles, and cool to obtain a cast sheet; 2) Preheat the cast sheet, first perform longitudinal stretching, and then transverse stretching; 3) Thermally fix the stretched film, and cool to obtain a crude product; 4) Coat a modified coating on the upper and lower surfaces of the crude product, and dry; 5) Traction and winding to obtain the base film for a composite current collector; Wherein, both the composite modification auxiliary particles and the modified coating contain synergistic modified nano-SiO2, and its preparation method is as follows: S1. Treat nano-SiO2 with isocyanatopropyltriethoxysilane, and 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. 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.

[0006] 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.

[0007] 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.

[0008] Furthermore, 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.

[0009] Furthermore, 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 into a reaction flask container. After stirring evenly, heat up to 60 °C and dropwise add 40 - 50 parts of acrylic acid. Keep the temperature at 60 °C for 1 h. After the addition is completed, heat up to 80 °C, 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 into it. Then add 30 parts of an emulsifier aqueous solution, disperse evenly at high speed, and keep the temperature for reaction for 2 - 4 h. Mix 10 - 20 parts of glycerol methacrylate, 15 - 25 parts of butyl acrylate, 5 - 10 parts of vinyltriethoxysilane and 20 - 30 parts of an emulsifier aqueous solution evenly and then dropwise add them into the above reaction system. After the addition is completed, continue to keep the temperature for reaction for 3 h. Cool down to room temperature to remove unreacted monomers, adjust the pH to neutral, slowly add 30 - 50 parts of an aqueous dispersion of 50 wt% synergistic modified nano-SiO₂ while stirring, and finally add 5 - 10 parts of polyamide curing agent, adjust the solid content to 35 - 45%, and then it is obtained.

[0010] Further, the mass ratio of the PET masterbatch to the composite modified auxiliary particles is 100:5 - 20.

[0011] Further, in the step 2), the draw ratio of longitudinal stretching is 2 - 3.5 times, and the draw ratio of transverse stretching is 2.5 - 3.8 times.

[0012] Further, in the step 4), the dry coating amount of the modified coating is 0.5 - 1 g / m 2 。

[0013] The present invention further provides a base film for a composite current collector based on SiO₂ nano-composite modification prepared by the preparation method as described above.

[0014] The present invention provides a base film for a composite current collector based on SiO₂ nano-composite modification prepared by the preparation method as described above.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: The synergistic modified nano-SiO₂ forms modified auxiliary particles in combination with aluminum hypophosphite, montmorillonite, etc., and is co-extruded with the PET masterbatch. At the same time, a modified coating containing nano-SiO₂ is coated on the surface of the base film, significantly improving the mechanical properties, thermal stability and flame retardancy of the base film. Specific Embodiments

[0016] The following will clearly and completely describe the technical solutions of the present invention in combination with the embodiments. Obviously, the described embodiments are some embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art without creative efforts based on the embodiments of the present invention belong to the protection scope of the present invention.

[0017] In addition, the technical features involved in different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0018] A preparation method of a base film for a composite current collector based on SiO2 nano-composite modification, comprising the following steps: 1) Mix and melt-extrude PET masterbatch and composite modification auxiliary particles according to a mass ratio of 100:5 to 20, and cool to obtain a cast sheet; 2) After preheating the cast sheet, first perform longitudinal stretching with a stretching ratio of 2 to 3.5 times, and then perform transverse stretching with a stretching ratio of 2.5 to 3.8 times; 3) Perform heat setting on the stretched film, and cool to obtain a crude product; 4) Coating the upper and lower surfaces of the crude product with a modified coating, with a dry coating amount of 0.5 to 1 g / m 2 , and dry; 5) Traction and winding to obtain the base film for the composite current collector; Among them, both the composite modification auxiliary particles and the modified coating contain synergistic modification nano-SiO2, and its preparation method is as follows: S1. Treat nano-SiO2 with isocyanatopropyltriethoxysilane and set aside; S2. Ultrasonically disperse NCC in DMF and transfer it to a three-necked flask. Slowly drop phenylphosphoryl dichloride, stir and heat up. After reaching 110 °C, keep it warm for 3 h. Slowly drop diethyl hydroxymethylphosphate, keep it warm for 3 h, rotate and evaporate to remove the solvent, and dry to obtain flame-retardant modified NCC; S3. Place the flame-retardant modified NCC in deionized water, adjust the pH to 3, fully stir and then add the nano-SiO2 in step S1, ultrasonically for 30 min, heat to 60 °C, add sodium hydroxide to adjust the pH to alkaline, continue to heat for 3 h, cool to room temperature, filter and wash, collect the solid, dry and grind to obtain it.

[0019] In the present invention, the composite modification auxiliary particles include synergistic modification nano-SiO2, aluminum hypophosphite, and montmorillonite, and the dosage ratio is 5 to 8:2 to 3:3 to 6; the preparation method is: first perform acidification treatment on montmorillonite, then combine it with vinyltriethoxysilane coupling agent (A151), add an aluminum hypophosphite aqueous dispersion, stir evenly, and slowly drop a mixed solution of acrylic acid and initiator into it for reaction. Finally, add synergistic modification nano-SiO2 and stir evenly, remove the solvent, dry the moisture, and grind to obtain the composite modification auxiliary particles. Among them, the dosages of vinyltriethoxysilane coupling agent, acrylic acid, and initiator are 2 to 5 times, 0.5 to 1 times, and 0.02 to 0.05 times of montmorillonite respectively.

[0020] In the present invention, 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 into a reaction flask container. After stirring evenly, heat up to 60 °C and dropwise add 40 - 50 parts of acrylic acid. Keep the temperature at 60 °C for 1 h. After the addition is completed, heat up to 80 °C, and 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 into it. Then add 30 parts of an emulsifier aqueous solution, disperse evenly at high speed, and keep the temperature for reaction for 2 - 4 h. Mix 10 - 20 parts of glycerol methacrylate, 15 - 25 parts of butyl acrylate, 5 - 10 parts of vinyltriethoxysilane, and 20 - 30 parts of an emulsifier aqueous solution evenly and then dropwise add them into the above reaction system. After the addition is completed, continue to keep the temperature for reaction for 3 h. Cool down to room temperature to remove unreacted monomers, adjust the pH to neutral, slowly add 30 - 50 parts of an aqueous dispersion of 50 wt% synergistically modified nano-SiO₂ while stirring, and finally add 5 - 10 parts of a polyamide curing agent, adjust the solid content to 35 - 45%, and then it is obtained.

[0021] The base film for composite current collector prepared by the preparation method provided in the embodiment of the present application, through adding modified auxiliary particles containing synergistically modified nano-SiO₂ into the PET masterbatch, and coating a coating solution containing synergistically modified nano-SiO₂ on the surface of the crude base film product, enables the film to have excellent mechanical strength and flame retardancy.

[0022] In this application, synergistically modified nano-SiO₂ is compounded with aluminum hypophosphite and montmorillonite to form modified auxiliary particles. First, the synergistically modified nano-SiO₂ is silica particles modified with a silane coupling agent, and isocyanate groups are introduced on the surface. Then, flame-retardant modified NCC is prepared by reacting phenylphosphoryl dichloride and diethyl hydroxymethylphosphonate on the surface of NCC. Through hydrogen bond interaction, the flame-retardant modified NCC and the silica particles are combined to form an organic whole. Subsequently, using the intercalation effect of montmorillonite, first acidify it to make its surface have active functional groups, treat it with A151 silane coupling agent and in-situ polymerize with acrylic acid while promoting the intercalation reaction of the flame retardant aluminum hypophosphite. Finally, the modified auxiliary particles formed by mixing with synergistically modified nano-SiO₂ have increased interfacial interaction with the PET polymer film due to the acrylic polymer chains on their surface, effectively improving the compatibility of the modified auxiliary particles in PET. Montmorillonite and cellulose have a good 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 action of the flame retardant greatly improve the flame retardant performance of the base film.

[0023] Furthermore, coat the self-made coating solution on the outer surface of the base film. Carry out aqueous emulsion polymerization with acrylate monomers and epoxy resin. The synergistically modified nano-SiO₂ can be evenly dispersed in this emulsion, and can also be evenly dispersed when coated on the crude base film product. Thus, the flame retardancy and surface strength of the base film can be further increased.

[0024] The following are detailed examples and comparative examples provided on the above basis to further illustrate the present invention. Example 1:

[0025] 1) Mix PET masterbatch and composite modified auxiliary particles in a mass ratio of 100:10, melt and extrude, and cool to obtain a cast sheet; 2) Preheat the cast sheet, first perform longitudinal stretching with a stretching ratio of 2 - 3.5 times, and then perform transverse stretching with a stretching ratio of 2.5 - 3.8 times; 3) Thermally set the stretched film and cool to obtain a rough product; 4) Coat the upper and lower surfaces of the rough product with a modified coating, with a dry coating amount of 0.5 g / m 2 , and dry; 5) Traction and winding to obtain the base film for composite current collectors; Among them, both the composite modified auxiliary particles and the modified coating contain synergistic modified nano - SiO₂, and its preparation method is as follows: S1. Treat nano - SiO₂ with isocyanatopropyltriethoxysilane. Ultrasonically disperse 10 g of nano - SiO₂ in an ethanol - water solution, add 20 g of isocyanatopropyltriethoxysilane and 0.5 g of dibutyltin dilaurate, adjust the pH to alkaline, stir overnight at 60 °C, centrifuge and separate, wash with water and dry to obtain modified SiO₂; S2. Ultrasonically disperse 2 g of NCC in DMF, transfer it to a three - necked flask, slowly dropwise add 10 g of phenylphosphoryl dichloride, stir and heat up. After reaching 110 °C, keep it warm for 3 h, slowly dropwise add 8.6 g of diethyl hydroxymethylphosphonate, keep it warm for 3 h, rotate and evaporate to remove the solvent, and dry to obtain flame - retardant modified NCC; S3. Place 10 g of flame - retardant modified NCC in deionized water, adjust the pH to 3, fully stir, add 10 g of the modified SiO₂ obtained in 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 it.

[0026] In this example, the composite modified auxiliary particles include synergistic modified nano - SiO₂, aluminum hypophosphite, and montmorillonite, and the dosage ratio is 6:3:5; the preparation method is: first, acidify montmorillonite, then combine it with vinyltriethoxysilane coupling agent (A151), add an aluminum hypophosphite aqueous dispersion, stir evenly, and then slowly dropwise add a mixed solution of acrylic acid and initiator to react. Finally, add synergistic modified nano - SiO₂ and stir evenly, remove the solvent, dry the moisture, and grind to obtain the composite modified auxiliary particles. Among them, the dosages of vinyltriethoxysilane coupling agent, acrylic acid, and initiator are 2 times, 0.5 times, and 0.02 times that of montmorillonite respectively.

[0027] In this embodiment, the preparation process of the modified coating is as follows: Add 1 part of bisphenol A epoxy resin and 0.1 part of tetrabutylammonium bromide into a reaction flask container. After stirring evenly, heat up to 60°C and dropwise add 40 parts of acrylic acid. Keep the temperature at 60°C for 1 hour. After the dropping is completed, heat up to 80°C, add 30 parts of methyl methacrylate, 25 parts of butyl acrylate, 20 parts of methacrylic acid, and 3 parts of ammonium polyphosphate into it. Then add 30 parts of an emulsifier aqueous solution, disperse evenly at high speed, and keep the temperature for reaction for 2 - 4 hours; Mix 10 parts of glycerol methacrylate, 20 parts of butyl acrylate, 8 parts of vinyltriethoxysilane, and 20 - 30 parts of an emulsifier aqueous solution evenly and dropwise add them into the above reaction system. After the dropping is completed, continue to keep the temperature for reaction for 3 hours. Cool to room temperature to remove unreacted monomers, adjust the pH to neutral, slowly add 30 parts of an aqueous dispersion of synergistic modified nano-SiO2 with a solid content of 50% while stirring, and finally add 5 parts of a polyamide curing agent to adjust the solid content to 40% to obtain the product. Example 2:

[0028] 1) Mix and melt-extrude PET masterbatch and composite modified auxiliary particles according to a mass ratio of 100:15, and cool to obtain a cast sheet; 2) Preheat the cast sheet and first perform longitudinal stretching with a stretching ratio of 2 - 3.5 times, and then perform transverse stretching with a stretching ratio of 2.5 - 3.8 times; 3) Perform heat setting on the stretched film, and cool to obtain a crude product; 4) Coat the modified coating on the upper and lower surfaces of the crude product, with a dry coating amount of 0.8 g / m 2 , and dry; 5) Traction and winding to obtain the base film for composite current collectors; The composite modified auxiliary particles and the modified coating are the same as those in Example 1. Example 3:

[0029] 1) Mix and melt-extrude PET masterbatch and composite modified auxiliary particles according to a mass ratio of 100:5, and cool to obtain a cast sheet; 2) Preheat the cast sheet and first perform longitudinal stretching with a stretching ratio of 2 - 3.5 times, and then perform transverse stretching with a stretching ratio of 2.5 - 3.8 times; 3) Perform heat setting on the stretched film, and cool to obtain a crude product; 4) Coat the modified coating on the upper and lower surfaces of the crude product, with a dry coating amount of 0.5 g / m 2 , and dry; 5) Traction and winding to obtain the base film for composite current collectors; The composite modified auxiliary particles and the modified coating are the same as those in Example 1.

[0030] Comparative Example 1: This example is basically the same as Example 1, except that the synergistic modified nano-SiO2 in the composite modified auxiliary particles and the modified coating is replaced with ordinary nano-SiO2.

[0031] Comparative Example 2: This example is basically the same as Example 1, except that the composite modified auxiliary particles are obtained by directly mixing synergistic modified nano-SiO2, aluminum hypophosphite, and montmorillonite and then melt-extruding and pelletizing.

[0032] Comparative Example 3: This example is basically the same as Example 1, except that the composite modified auxiliary particles are not added.

[0033] Performance test: 1. Flame retardancy: The limiting oxygen index of the base film was tested according to the standard JIS-K7201-3-2008. The larger the value, the better the flame retardancy.

[0034] 2. Tensile strength: Tested with reference to GB / T1040.1-2018.

[0035] 3. Heat distortion temperature: Tested by the ASTM D648 method.

[0036] Table 1

[0037] It can be seen from the test results in Table 1 that the base films prepared in Examples 1-3 have flame retardancy, and the tensile strength and heat distortion temperature have been greatly improved compared with the pure PET film. In Comparative Example 1, the limiting oxygen index decreased significantly, the tensile strength was relatively well maintained, and the heat distortion temperature was lower than that in Examples 1-3 but higher among the comparative examples. This is because the synergistic modified nano-SiO2 in the composite modified auxiliary particles and the modified coating was replaced with ordinary nano-SiO2. Ordinary nano-SiO2 has no flame retardancy, is not compounded with cellulose, has poor thermal stability, and has worse dispersibility than the synergistic modified nano-SiO2. In Comparative Example 2, the composite modified auxiliary particles were obtained by directly mixing synergistic modified nano-SiO2, aluminum hypophosphite, and montmorillonite and then melt-extruding and pelletizing. The effect of direct miscibility of the three is not as good as that of the in-situ polymerization intercalation reaction on the surface of montmorillonite, resulting in a decrease in various properties, especially the tensile strength and heat distortion temperature are most affected. In Comparative Example 3, the composite modified auxiliary particles were not added. Although coating the crude base film with the coating solution containing synergistic modified nano-SiO2 can endow the base film with a certain flame retardancy, the effect is very small, and other properties have not been significantly improved.

[0038] Although the embodiments of the present invention have been disclosed as above, they are not limited to the applications listed in the specification and embodiments. It can be fully applied to various fields suitable for the present invention. For those skilled in the art, additional modifications can be easily made. Therefore, without departing from the general concept defined by the claims and the equivalent scope, the present invention is not limited to specific details.

Claims

1. A preparation method of a base film for a composite current collector based on SiO2 nano-composite modification, characterized in that, It includes the following steps: 1) Mix and melt-extrude PET masterbatch and composite modification auxiliary particles, and cool to obtain a cast sheet; 2) Preheat the cast sheet, first perform longitudinal stretching, and then transverse stretching; 3) Thermally set the stretched film, and cool to obtain a crude product; 4) Coat the upper and lower surfaces of the crude product with a modified coating and dry; 5) Traction and winding to obtain the base film for composite current collector; Among them, both the composite modification auxiliary particles and the modified coating contain synergistic modification nano-SiO₂, and its preparation method is as follows: S1. Treat nano-SiO₂ with isocyanatopropyltriethoxysilane and set aside; S2. Ultrasonically disperse NCC in DMF and transfer it to a three-necked flask. Slowly drop phenylphosphoryl dichloride, stir and heat up. After reaching 110 °C, keep it warm for 3 h. Slowly drop diethyl hydroxymethylphosphate, keep it warm for 3 h, rotate and evaporate to remove the solvent, and dry to obtain flame-retardant modified NCC; S3. Place the flame-retardant modified NCC in deionized water, adjust the pH to 3, fully stir and then add the nano-SiO₂ in step S1, ultrasonically for 30 min, heat to 60 °C, add sodium hydroxide to adjust the pH to alkaline, continue to heat for 3 h, cool to room temperature, filter and wash, collect the solid, dry and grind to obtain it.

2. The preparation method of the base film for a composite current collector based on SiO2 nano-composite modification according to claim 1, characterized in that, In the said step 1), the composite modification auxiliary particles include synergistic modification nano-SiO₂, aluminum hypophosphite, and montmorillonite. The preparation method is: first acidify montmorillonite, then combine it with vinyltriethoxysilane coupling agent, add an aluminum hypophosphite aqueous dispersion, stir evenly, and then slowly drop a mixed solution of acrylic acid and initiator into it for reaction. Finally, add synergistic modification nano-SiO₂, stir evenly, remove the solvent, dry the moisture, and grind to obtain the composite modification auxiliary particles.

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

4. The preparation method of the base film for a composite current collector based on SiO2 nano-composite modification according to claim 1, characterized in that, The preparation process of the said modified coating is as follows: Add bisphenol A epoxy resin and tetrabutylammonium bromide to a reaction flask container, stir evenly and heat up to 60 °C to drop acrylic acid, keep it warm for 1 h. After dropping, heat up to 80 °C, add methyl methacrylate, butyl acrylate, methacrylic acid, and ammonium polyphosphate into it. Then add an aqueous solution of emulsifier, disperse evenly at high speed, and keep it warm for reaction for 2-4 h; Mix methylglyceryl methacrylate, butyl acrylate, vinyltriethoxysilane, and an aqueous solution of emulsifier evenly and dropwise add them to the above reaction system one by one. After dropping, continue to keep it warm for reaction for 3 h, cool to room temperature, remove the unreacted monomers, adjust the pH to neutral, slowly add an aqueous dispersion of synergistic modification nano-SiO₂ while stirring, and finally add a polyamide curing agent to adjust the solid content to 35-45% to obtain it.

5. The preparation method of the base film for a composite current collector based on SiO2 nano-composite modification according to claim 4, characterized in that, The preparation process of the said modified coating is as follows: Add 1 part of bisphenol A epoxy resin and 0.05 - 0.1 part of tetrabutylammonium bromide into a reaction flask container. After stirring evenly, heat up to 60 °C and dropwise add 40 - 50 parts of acrylic acid. Keep the temperature at 60 °C for 1 h. After the addition is completed, heat up to 80 °C, and add 30 - 35 parts of methyl methacrylate, 25 - 30 parts of butyl acrylate, from 20 to 30 parts of methacrylic acid and 2 - 5 parts of ammonium polyphosphate into it. Then add 30 parts of an emulsifier aqueous solution, disperse evenly at high speed, and keep the temperature for reaction for 2 - 4 h; Mix 10 - 20 parts of glycerol methacrylate, 15 - 25 parts of butyl acrylate, 5 - 10 parts of vinyltriethoxysilane and 20 - 30 parts of an emulsifier aqueous solution evenly and then dropwise add them into the above reaction system. After the addition is completed, continue to keep the temperature for reaction for 3 h. Cool down to room temperature to remove unreacted monomers, adjust the pH to neutral, slowly add 30 - 50 parts of an aqueous dispersion of 50 wt% synergistic modified nano-SiO₂ while stirring, and finally add 5 - 10 parts of a polyamide curing agent, and adjust the solid content to 35 - 45% to obtain the product.

6. The preparation method of the base film for a composite current collector based on SiO2 nano-composite modification according to claim 1, characterized in that, The mass ratio of the PET masterbatch to the composite modified auxiliary particles is 100:5 - 20.

7. The preparation method of the base film for a composite current collector based on SiO2 nano-composite modification according to claim 1, characterized in that, In the step 2), the draw ratio for longitudinal drawing is 2 - 3.5 times, and the draw ratio for transverse drawing is 2.5 - 3.8 times.

8. The preparation method of the base film for a composite current collector based on SiO2 nano-composite 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 .

9. A base film for a composite current collector based on SiO₂ nano-composite modification prepared by the preparation method according to any one of claims 1 - 8.

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