A modified polypropylene-based film, a method for preparing the same, and applications thereof

Abstract

This case pertains to the field of composite current collector base film technology, specifically involving a modified polypropylene base film, its preparation method, and its application. The modified polypropylene base film comprises: polypropylene resin, modified silica, modified maleic anhydride-grafted polypropylene, a slip agent, an antioxidant, and a nucleating agent. The modified silica is obtained by treating silica with a silane coupling agent KH560 and then reacting it with compound A (imidazolium diol) via a ring-opening grafting reaction. The modified maleic anhydride-grafted polypropylene is obtained by mixing maleic anhydride with compound B and then melt-extruding it with PP. This invention, by introducing imidazolium-functionalized silica and imidazolium-modified maleic anhydride-grafted polypropylene into the PP matrix, achieves dual enrichment of imidazolium groups in both the base film bulk and surface, improving the adhesion of the metal layer, increasing peel strength, more effectively improving the compatibility between components, avoiding phase separation, achieving a balance between rigidity and toughness, and ensuring the uniformity of film thickness and surface smoothness.

Description

Technical Field

[0001] This invention relates to the field of composite current collector membrane technology, specifically to a modified polypropylene membrane, its preparation method, and its application. Background Technology

[0002] Polypropylene (PP) film is widely used in food packaging, medical packaging, production and transportation pipelines, textiles, electronic components and other fields due to its advantages such as low density, good chemical corrosion resistance and low cost.

[0003] Composite current collectors are a new type of current collector material used in energy storage devices such as lithium-ion batteries. They are typically composed of a metal layer (such as aluminum or copper) and a polymer substrate. PP film, due to its lightweight and chemical inertness, is widely used as the base film material for composite current collectors. When combined with a metal layer, it retains the conductivity of the metal while reducing weight, thus improving battery safety and energy density. However, PP film has relatively poor impact resistance and temperature resistance. During the preparation of composite current collectors, the base film may wrinkle and deform, or lose shape stability under high pressure and high temperature environments, affecting the yield of the finished product. Furthermore, the low surface energy of PP film makes the adhesion between the metal layer and the PP base film insufficient, causing the metal layer to easily detach or peel during subsequent processing (such as winding and bending), seriously affecting battery life and safety.

[0004] To improve the performance of PP films and enable their better application in composite current collectors, current mainstream technologies mainly employ two approaches: adding inorganic fillers (such as talc, calcium carbonate, and silica) and blending with other polymers. However, the direct addition of either inorganic fillers or organic polymers can introduce other defects. While introducing large amounts of inorganic fillers can effectively improve the rigidity and heat resistance of the film, it leads to a significant decrease in film toughness, an increase in density, and a higher susceptibility to brittle fracture. Furthermore, blending with polar polymers often results in phase separation due to insufficient compatibility, forming macroscopic defects that ultimately weaken the overall performance of the material. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention designs an imidazole-functionalized silica and an imidazole-modified polymaleic anhydride-grafted polypropylene, which can effectively improve the overall performance of polypropylene films.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A modified polypropylene-based film, comprising, by weight parts: 100 parts polypropylene resin, 5-12 parts modified silica, 3-8 parts modified maleic anhydride grafted polypropylene, 0.1-0.5 parts slip agent, 0.3-0.8 parts antioxidant, and 0.5-1 part nucleating agent; wherein, The modified silica is obtained by treating nano-silica particles with silane coupling agent KH560 and then reacting them with compound A through a ring-opening grafting reaction. The modified maleic anhydride-grafted polypropylene is obtained by melting and extruding a mixture of maleic anhydride, compound B, initiator and polypropylene. Compound A Compound B .

[0007] Furthermore, the preparation process of the modified silica is as follows: Nano-sized silica particles were ultrasonically dispersed in anhydrous ethanol, and silane coupling agent KH560 was added. The temperature was increased and the mixture was refluxed for 8 hours. After the reaction was completed, the particles were centrifuged, rinsed with anhydrous ethanol, and dried for later use. The dried solid was redispersed in anhydrous ethanol, compound A was added, and the mixture was stirred at 70-90°C for 8-12 hours. After the reaction was completed, the particles were centrifuged, washed with ethanol 3-5 times, and dried under vacuum at 60-80°C to constant weight to obtain imidazole-functionalized modified silica.

[0008] Furthermore, the preparation process of the maleic anhydride-grafted polypropylene is as follows: Polypropylene resin, maleic anhydride, compound B and initiator BPO are mixed evenly and then added to a twin-screw extruder. The mixture undergoes a melt grafting reaction at 180~220℃, followed by extrusion, cooling and pelletizing to obtain modified maleic anhydride grafted polypropylene containing imidazole groups.

[0009] Further, the mass ratio of the polypropylene resin, maleic anhydride, compound B, and initiator BPO is 20~50:0.7~1.2:0.8~1.3:0.01.

[0010] Furthermore, the slip agent is erucamide or oleamide.

[0011] Furthermore, the antioxidant is at least one of antioxidant 1010, antioxidant 1076, and antioxidant 168.

[0012] Furthermore, the nucleating agent is selected from one of calcium carbonate whiskers, alumina, and zeolite.

[0013] A second objective of this invention is to provide a method for preparing the modified polypropylene-based film as described above, comprising the following steps: 1) Weigh out polypropylene resin, modified silica, modified maleic anhydride grafted polypropylene, slip agent, antioxidant and nucleating agent according to the weight parts, put them in a high-speed mixer and mix them evenly to obtain a mixture. 2) Add the mixture obtained in step 1) into a twin-screw extruder, melt-blend and extrude at 190~230℃, and cast it onto a cooling roller through a die to cool and cast the sheet; 3) The casting obtained in step 2) is subjected to biaxial stretching. First, longitudinal stretching is performed at a temperature of 130~150℃ and a stretching ratio of 4~6 times. Then, transverse stretching is performed at a temperature of 150~170℃ and a stretching ratio of 6~10 times. 4) The biaxially stretched film is heat-set at 140~160℃ for 30~60s, cooled, stretched and wound up to obtain a modified polypropylene base film.

[0014] A third objective of this invention is to provide the application of the modified polypropylene-based membrane described above in the preparation of composite current collectors.

[0015] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention achieves dual enrichment of imidazole groups in both the substrate and surface of the PP matrix by introducing imidazole-functionalized silica and imidazole-modified maleic anhydride-grafted polypropylene. The introduction of imidazole groups increases the polarity of the originally non-polar PP surface, significantly improving surface energy and enhancing wettability and chemical bonding with the metal layer. This facilitates the adsorption, nucleation, and growth of metal atoms during the coating process, resulting in a uniform and dense metal layer; it also improves the adhesion of the metal layer and enhances peel strength.

[0016] 2. In modified maleic anhydride-grafted polypropylene, maleic anhydride is polymerized with imidazole monomers containing unsaturated double bonds. The resulting compatibilizer is effective in improving the compatibility between components, such as modified silica, antioxidants, and nucleating agents, preventing phase separation and achieving a balance between rigidity and toughness.

[0017] 3. After organic modification with imidazole compounds, the modified silica, combined with the compatibility of modified maleic anhydride grafted polypropylene, is uniformly dispersed at the nanoscale in the base film without agglomeration, thus ensuring the thickness uniformity and surface smoothness of the film. Detailed Implementation

[0018] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] Furthermore, 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.

[0020] Example: A modified polypropylene-based film, comprising, by weight: 100 parts polypropylene resin, 5-12 parts modified silica, 3-8 parts modified maleic anhydride grafted polypropylene, 0.1-0.5 parts erucamide slip agent, 0.3-0.8 parts antioxidant 1010, and 0.5-1 parts nucleating agent calcium carbonate whiskers; The modified silica is obtained by treating nano-silica particles with silane coupling agent KH560 and then reacting them with compound A via a ring-opening grafting reaction, as follows: Nano-sized silica particles were ultrasonically dispersed in anhydrous ethanol, and an equal mass of silane coupling agent KH560 was added. The temperature was raised and the mixture was refluxed for 8 hours. After the reaction was completed, the particles were centrifuged, rinsed with anhydrous ethanol, and dried for later use. The dried solid was redispersed in anhydrous ethanol, and 20% (by weight) of compound A was added. The mixture was stirred at 70°C for 12 hours. After the reaction was completed, the particles were centrifuged, washed with ethanol 3-5 times, and dried under vacuum at 60-80°C to constant weight to obtain imidazole-functionalized modified silica.

[0021] The preparation process of the modified maleic anhydride-grafted polypropylene is as follows: Polypropylene resin, maleic anhydride, compound B and initiator BPO are mixed evenly and then added to a twin-screw extruder. The mixture undergoes a melt grafting reaction at 180~220℃, followed by extrusion, cooling and pelletizing to obtain modified maleic anhydride grafted polypropylene containing imidazole groups.

[0022] The mass ratio of the polypropylene resin, maleic anhydride, compound B, and initiator BPO is 20~50:0.7~1.2:0.8~1.3:0.01. By changing this ratio, the following series of modified maleic anhydride-grafted polypropylenes are obtained.

[0023]

[0024] In the embodiments of this application, most of the raw materials used are conventional materials in the art, which can be purchased on the market and have little impact on the reaction. The sources and preparation methods of some raw materials are as follows: Polypropylene resin: purchased from Sinopec, model T30S; Nano silica particles: purchased from Lingwei Technology, model CTT300.

[0025] Compound A: Imidazole diol, structural formula: The preparation process is as follows:

[0026] An aldehyde solution was prepared by mixing 5 mmol of phenylglyoxal hydrate (CAS: 78146-52-8) and 5 mmol of formaldehyde in 20 ml of 10% dilute hydrobromic acid aqueous solution in an ice-water bath. Then, 10 mmol of ethanolamine and 20 ml of 10% dilute hydrobromic acid aqueous solution were added to the reaction flask in an ice-water bath and stirred until homogeneous. After purging with nitrogen for 30 min, the mixed aldehyde solution was slowly added dropwise to the reaction flask. Under nitrogen protection, the temperature was raised to 60 °C and stirred continuously for 5 h. After cooling to room temperature, the solvent was removed by vacuum distillation. The obtained product was washed several times with diethyl ether. The reaction yield was 91.1 wt%.

[0027] 1H NMR(300 MHz, DMSO-d6, TMS) δ9.28 (s, 1H, C2-H), 7.85 (s, 1H, C4-H), 7.58-7.42 (m, 5H, ph-H), 4.35 (t, 2H , N+-CH2CH2), 4.25(t, 2H, N+-CH2CH2), 3.98(t, 2H, N-CH2CH2), 3.63(t, 2H, N-CH2CH2), 3.21(br s, 2H, OH)ppm. FT-IR (KBr, cm-1): 3390 (br, OH), 2950, ​​2875 (CH alkyl), 1610 (C=C, imidazole+Ph), 1570 (C=N + , imidazolium), 1485, 1455 (CH2, Ph skeleton), 1390 (CN), 1265, 1135 (CO), 765, 705 (Ph CH out-of-plane bend). Compound B: Structural formula It is obtained by reacting imidazole with methylpropionyl chloride. Weigh 5.2 g of methacryloyl chloride, dissolve it in 50 mL of tetrahydrofuran, and add it dropwise to 100 mL of a THF solution containing 3.4 g of imidazole and 6 g of triethylamine while stirring at 0–10°C. After the addition is complete, continue stirring at room temperature for 24 h. When the reaction is complete, filter the solution and remove the solvent by rotary evaporation to obtain the product.

[0028] ¹H NMR (300 MHz, CDCl3): δ7.95 (s, 1H, imidazole C2-H), 7.45 (s, 1H, imidazole C4-H), 7.10 (s, 1H, imidazole C5-H), 5.78(s, 1H, =CH2, cis), 5.48(s, 1H, =CH2, trans), 2.01(s, 3H, -C(CH3)=)ppm. Example 1: A modified polypropylene base film 1) Weigh 100 parts by weight of polypropylene resin, 5 parts of modified silica, 3 parts of MAH-g-PP-1, 0.1 parts of erucamide slip agent, 0.3 parts of antioxidant 1010, and 0.5 parts of nucleating agent calcium carbonate whiskers, and mix them evenly in a high-speed mixer to obtain a mixture. 2) Add the mixture obtained in step 1) into a twin-screw extruder, melt-blend and extrude at 210°C, and cast it onto a cooling roller through a die to cool and cast the sheet; 3) The casting obtained in step 2) is subjected to biaxial stretching. First, longitudinal stretching is performed at a temperature of 130℃ and a stretching ratio of 4 times. Then, transverse stretching is performed at a temperature of 150℃ and a stretching ratio of 6 times. 4) The biaxially stretched film is heat-set at 140°C, cooled, stretched, and wound to obtain a modified polypropylene base film.

[0029] Example 2: A modified polypropylene base film 1) Weigh 100 parts polypropylene resin, 8 parts modified silica, 5 parts MAH-g-PP-1, 0.3 parts erucamide slip agent, 0.5 parts antioxidant 1010, and 0.6 parts nucleating agent calcium carbonate whiskers according to the weight ratio, and mix them evenly in a high-speed mixer to obtain a mixture. 2) Add the mixture obtained in step 1) into a twin-screw extruder, melt-blend and extrude at 210±5℃, and cast onto a cooling roller through a die to cool and cast the sheet; 3) The casting obtained in step 2) is subjected to biaxial stretching. First, longitudinal stretching is performed at a temperature of 135℃ and a stretching ratio of 4 times. Then, transverse stretching is performed at a temperature of 155℃ and a stretching ratio of 6 times. 4) The biaxially stretched film is heat-set at 145°C, cooled, stretched, and wound to obtain a modified polypropylene base film.

[0030] Example 3: A modified polypropylene base film 1) Weigh 100 parts polypropylene resin, 12 parts modified silica, 8 parts MAH-g-PP-1, 0.5 parts erucamide slip agent, 0.8 parts antioxidant 1010, and 1 part nucleating agent calcium carbonate whiskers according to the weight ratio, and mix them evenly in a high-speed mixer to obtain a mixture. 2) Add the mixture obtained in step 1) into a twin-screw extruder, melt-blend and extrude at 210±5℃, and cast onto a cooling roller through a die to cool and cast the sheet; 3) The casting obtained in step 2) is subjected to biaxial stretching. First, longitudinal stretching is performed at a temperature of 140℃ and a stretching ratio of 4 times. Then, transverse stretching is performed at a temperature of 160℃ and a stretching ratio of 6 times. 4) The biaxially stretched film is heat-set at 150°C, cooled, stretched, and wound to obtain a modified polypropylene base film.

[0031] Example 4: A modified polypropylene base film 1) Weigh 100 parts polypropylene resin, 12 parts modified silica, 8 parts MAH-g-PP-2, 0.5 parts erucamide slip agent, 0.8 parts antioxidant 1010, and 0.8 parts nucleating agent calcium carbonate whiskers according to the weight ratio, and mix them evenly in a high-speed mixer to obtain a mixture. 2) Add the mixture obtained in step 1) into a twin-screw extruder, melt-blend and extrude at 210±5℃, and cast onto a cooling roller through a die to cool and cast the sheet; 3) The casting obtained in step 2) is subjected to biaxial stretching. First, longitudinal stretching is performed at a temperature of 140℃ and a stretching ratio of 4 times. Then, transverse stretching is performed at a temperature of 160℃ and a stretching ratio of 6 times. 4) The biaxially stretched film is heat-set at 150°C, cooled, stretched, and wound to obtain a modified polypropylene base film.

[0032] Example 5: A modified polypropylene-based film 1) Weigh 100 parts polypropylene resin, 12 parts modified silica, 8 parts MAH-g-PP-3, 0.5 parts erucamide slip agent, 0.8 parts antioxidant 1010, and 0.8 parts nucleating agent calcium carbonate whiskers according to the weight ratio, and mix them evenly in a high-speed mixer to obtain a mixture. 2) Add the mixture obtained in step 1) into a twin-screw extruder, melt-blend and extrude at 210±5℃, and cast onto a cooling roller through a die to cool and cast the sheet; 3) The casting obtained in step 2) is subjected to biaxial stretching. First, longitudinal stretching is performed at a temperature of 140℃ and a stretching ratio of 4 times. Then, transverse stretching is performed at a temperature of 160℃ and a stretching ratio of 6 times. 4) The biaxially stretched film is heat-set at 150°C, cooled, stretched, and wound to obtain a modified polypropylene base film.

[0033] Example 6: A modified polypropylene base film 1) Weigh 100 parts polypropylene resin, 12 parts modified silica, 8 parts MAH-g-PP-4, 0.5 parts erucamide slip agent, 0.8 parts antioxidant 1010, and 0.8 parts nucleating agent calcium carbonate whiskers according to the weight ratio, and mix them evenly in a high-speed mixer to obtain a mixture. 2) Add the mixture obtained in step 1) into a twin-screw extruder, melt-blend and extrude at 210±5℃, and cast onto a cooling roller through a die to cool and cast the sheet; 3) The casting obtained in step 2) is subjected to biaxial stretching. First, longitudinal stretching is performed at a temperature of 140℃ and a stretching ratio of 4 times. Then, transverse stretching is performed at a temperature of 160℃ and a stretching ratio of 6 times. 4) The biaxially stretched film is heat-set at 150°C, cooled, stretched, and wound to obtain a modified polypropylene base film.

[0034] Example 7: A modified polypropylene base film 1) Weigh 100 parts polypropylene resin, 12 parts modified silica, 8 parts MAH-g-PP-5, 0.5 parts erucamide slip agent, 0.8 parts antioxidant 1010, and 0.8 parts nucleating agent calcium carbonate whiskers according to the weight ratio, and mix them evenly in a high-speed mixer to obtain a mixture. 2) Add the mixture obtained in step 1) into a twin-screw extruder, melt-blend and extrude at 210±5℃, and cast onto a cooling roller through a die to cool and cast the sheet; 3) The casting obtained in step 2) is subjected to biaxial stretching. First, longitudinal stretching is performed at a temperature of 140℃ and a stretching ratio of 4 times. Then, transverse stretching is performed at a temperature of 160℃ and a stretching ratio of 6 times. 4) The biaxially stretched film is heat-set at 150°C, cooled, stretched, and wound to obtain a modified polypropylene base film.

[0035] Comparative Example 1: A modified polypropylene-based film 1) Weigh 100 parts polypropylene resin, 8 parts MAH-g-PP-3, 0.5 parts erucamide slip agent, 0.8 parts antioxidant 1010, and 0.8 parts nucleating agent calcium carbonate whiskers according to the weight ratio, and mix them evenly in a high-speed mixer to obtain a mixture. 2) Add the mixture obtained in step 1) into a twin-screw extruder, melt-blend and extrude at 210±5℃, and cast onto a cooling roller through a die to cool and cast the sheet; 3) The casting obtained in step 2) is subjected to biaxial stretching. First, longitudinal stretching is performed at a temperature of 140℃ and a stretching ratio of 4 times. Then, transverse stretching is performed at a temperature of 160℃ and a stretching ratio of 6 times. 4) The biaxially stretched film is heat-set at 150°C, cooled, stretched, and wound to obtain a modified polypropylene base film.

[0036] Comparative Example 2: A modified polypropylene-based film 1) Weigh 100 parts polypropylene resin, 12 parts modified silica, 0.5 parts erucamide slip agent, 0.8 parts antioxidant 1010, and 0.8 parts nucleating agent calcium carbonate whiskers according to the weight ratio, and mix them evenly in a high-speed mixer to obtain a mixture. 2) Add the mixture obtained in step 1) into a twin-screw extruder, melt-blend and extrude at 210±5℃, and cast onto a cooling roller through a die to cool and cast the sheet; 3) The casting obtained in step 2) is subjected to biaxial stretching. First, longitudinal stretching is performed at a temperature of 140℃ and a stretching ratio of 4 times. Then, transverse stretching is performed at a temperature of 160℃ and a stretching ratio of 6 times. 4) The biaxially stretched film is heat-set at 150°C, cooled, stretched, and wound to obtain a modified polypropylene base film.

[0037] The base films prepared in the above embodiments and comparative examples were subjected to performance tests. All tests followed national or international standards, and the test items included: Tensile strength and elongation at break: Refer to GB / T1040.3-2006; Heat shrinkage rate (150℃, 30min): Refer to GB / T12027-2004; Wetting tension: Refer to GB / T14216-2008; Peel strength: The composite current collector is obtained by electroplating a copper layer onto the surface of the base film. The composite current collector is subjected to a 180° peel test (T-type peel) with a sample width of 15 mm.

[0038] Table 1

[0039] As the amount of additives such as modified silica in the formulation increases, the mechanical strength and heat resistance of the resulting PP-based film are also improved. This is because the modified silica is obtained by modifying imidazole salt ionic liquid, and the modified maleic anhydride-grafted polypropylene also contains abundant imidazole groups. On the one hand, it enhances the coordination with the metal layer, and on the other hand, it improves the compatibility between the polar additives and the PP matrix, making the filler more uniformly dispersed, thereby improving the overall performance. The performance of Example 4 is further improved compared to Example 3. This is because the example uses MAH-g-PP-2 (MAH to imidazole monomer mass ratio 1:1). Under the same content, the imidazole group content is higher than that of Example 3 (MAH:imidazole = 1.2:0.8). Appropriately increasing the imidazole ratio can enhance the coordination ability and improve the interfacial bonding effect. However, observing Example 5, the amount of imidazole monomer added should not be too much. When the amount is excessive, the tendency of imidazole monomer to self-polymerize is enhanced, which will lead to a decrease in grafting efficiency. Unreacted imidazole monomer may form homopolymers, which will disrupt the interfacial continuity and even be lower than that of Example 2 with less addition. This shows that excessive imidazole will actually damage the performance.

[0040] Observing Examples 6 and 7, MAH-g-PP-4 and MAH-g-PP-5 were used respectively. The difference lies in the proportion of PP in the samples. When the PP proportion is low, it means that the monomer concentration of the polymer is too high, which easily leads to chain entanglement or local cross-linking during the grafting process, resulting in stress concentration in the base film, which manifests as a significant decrease in mechanical properties. When the PP proportion is too high, it means that the monomer concentration of the polymer is low, there are fewer grafting points, and insufficient effective imidazole groups, resulting in a decrease in various properties, close to the level of Example 2.

[0041] Comparative Example 1, lacking modified silica, showed a significant decrease in mechanical strength. Due to the presence of MAH-g-PP-3, surface wetting tension and peel strength were slightly reduced. Comparative Example 2, lacking modified maleic anhydride-grafted polypropylene, although the modified silica itself could be well dispersed in the base film, still contained other additives in large quantities, leading to agglomeration in the base film and a significant decrease in peel strength.

[0042] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details.

Claims

1. A modified polypropylene-based film, characterized by, Included by weight parts: 100 parts polypropylene resin, 5-12 parts modified silica, 3-8 parts modified maleic anhydride grafted polypropylene, 0.1-0.5 parts slip agent, 0.3-0.8 parts antioxidant, and 0.5-1 part nucleating agent; wherein, The modified silica is obtained by treating nano-silica particles with silane coupling agent KH560 and then reacting them with compound A through a ring-opening grafting reaction. The modified maleic anhydride-grafted polypropylene is obtained by melting and extruding a mixture of maleic anhydride, compound B, initiator and polypropylene resin. Compound A Compound B is obtained by reacting imidazole with methylpropionyl chloride. Weigh 5.2 g of methacryloyl chloride, dissolve it in 50 mL of tetrahydrofuran, and add it dropwise to 100 mL of a THF solution containing 3.4 g of imidazole and 6 g of triethylamine while stirring at 0–10°C. After the addition is complete, continue stirring at room temperature for 24 h. When the reaction is complete, filter the solution and remove the solvent by rotary evaporation to obtain the product.

2. The modified polypropylene-based film according to claim 1, characterized in that, The preparation process of the modified silica is as follows: Nano-sized silica particles were ultrasonically dispersed in anhydrous ethanol, and silane coupling agent KH560 was added. The temperature was increased and the mixture was refluxed for 8 hours. After the reaction was completed, the particles were centrifuged, rinsed with anhydrous ethanol, and dried for later use. The dried solid was redispersed in anhydrous ethanol, compound A was added, and the mixture was stirred at 70-90°C for 8-12 hours. After the reaction was completed, the particles were centrifuged, washed with ethanol 3-5 times, and dried under vacuum at 60-80°C to constant weight to obtain imidazole-functionalized modified silica.

3. The modified polypropylene-based film according to claim 1, characterized in that, The preparation process of the modified maleic anhydride-grafted polypropylene is as follows: Polypropylene resin, maleic anhydride, compound B and initiator BPO are mixed evenly and then added to a twin-screw extruder. The mixture undergoes a melt grafting reaction at 180~220℃, followed by extrusion, cooling and pelletizing to obtain modified maleic anhydride grafted polypropylene containing imidazole groups.

4. The modified polypropylene-based film according to claim 3, characterized in that, The mass ratio of the polypropylene resin, maleic anhydride, compound B, and initiator BPO is 20~50:0.7~1.2:0.8~1.3:0.

01.

5. The modified polypropylene-based film according to claim 1, characterized in that, The slip agent is erucamide or oleamide.

6. The modified polypropylene-based film according to claim 1, characterized in that, The antioxidant is at least one of antioxidant 1010, antioxidant 1076, and antioxidant 168.

7. The modified polypropylene-based film according to claim 1, characterized in that, The nucleating agent is selected from one of calcium carbonate whiskers, alumina, and zeolite.

8. The method for preparing the modified polypropylene-based film according to any one of claims 1-7, characterized in that, Includes the following steps: 1) Weigh out polypropylene resin, modified silica, modified maleic anhydride grafted polypropylene, slip agent, antioxidant and nucleating agent according to the weight parts, put them in a high-speed mixer and mix them evenly to obtain a mixture. 2) Add the mixture obtained in step 1) into a twin-screw extruder, melt-blend and extrude at 190~230℃, and cast it onto a cooling roller through a die to cool and cast the sheet; 3) The casting obtained in step 2) is subjected to biaxial stretching. First, longitudinal stretching is performed at a temperature of 130~150℃ and a stretching ratio of 4~6 times. Then, transverse stretching is performed at a temperature of 150~170℃ and a stretching ratio of 6~10 times. 4) The biaxially stretched film is heat-set at 140~160℃ for 30~60s, cooled, stretched and wound up to obtain a modified polypropylene base film.

9. The application of the modified polypropylene base film as described in any one of claims 1-7 in the preparation of composite current collectors.

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