A modified polypropylene film and its application in composite current collector

Abstract

The invention discloses a modified polypropylene film and application thereof in a composite current collector. The modified polypropylene film comprises the following raw materials in parts by weight: 80 parts of polypropylene resin, 10-20 parts of linear low-density polyethylene, 10-15 parts of hyperbranched polypropylene, 20-30 parts of polyvinylidene fluoride resin, 1-3 parts of a compatibilizer, 5-8 parts of other auxiliary agents, 3-5 parts of 1,3-bis(oxiranylmethyl)-5-(2-propenyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, 1-3 parts of 1,1'-diaminoferrocene, 2-4 parts of 2,2'-bis(trifluoromethyl)diaminobiphenyl, 3-5 parts of (3,6-diaminoacridine-9-yl)boric acid, 0.8-1.2 parts of quaternary ammonium salt-based calix[3]carbazole and 10-15 parts of fillers. The film has excellent resistance to electrolyte corrosion, good heat resistance, good adhesion to the metal layer and flame retardancy, and sufficient puncture resistance.

Description

Technical Field

[0001] The invention relates to the technical field of current collectors for lithium batteries, and in particular to a modified polypropylene film and application thereof in a composite current collector. Background Art

[0002] The current collector is a key auxiliary material for lithium-ion batteries. Its main function is to conduct electricity. It collects the current generated by the active materials of the battery to form a larger current output, thereby realizing the process of converting chemical energy into electrical energy. The current collector acts as a carrier of the positive and negative active materials, and also acts as a collector and conductor of positive and negative electrons. Its function is to collect the current generated by the active materials of the battery to generate a larger output current. Therefore, an ideal current collector often needs to have comprehensive properties such as high conductivity, good stability, good mechanical strength, and low cost.

[0003] Composite current collector is one of the new lithium battery current collector materials with great potential. From a structural point of view, the structure of the composite current collector is similar to a "sandwich", that is, the middle layer is organic, and the upper and lower layers are metal coatings. At present, the middle organic layer is often made of PP (polypropylene). Polypropylene has good molding and processing performance and excellent mechanical, physical and chemical properties. At the same time, it is light and cheap. It has been widely used in industrial sectors such as chemical fiber, light industry, chemical industry, construction, packaging and home appliances. It is currently the fastest growing general-purpose thermoplastic. However, the polarity of polypropylene is very weak, its surface tension is low, and its affinity with metal is poor. Therefore, the adhesion of the interface between polypropylene and metal is poor, and the bonding force between polypropylene and metal is weak. In the process of preparing the current collector, the metal layer is easy to fall off, resulting in a low yield of the composite current collector. At the same time, the mechanical properties of polypropylene are poor, and there is a risk of film breakage during the preparation process. In addition, when polypropylene on the market is used as a composite current collector base film, its resistance to electrolyte corrosion needs to be further improved, its contact resistance with the metal layer is large, and its heat resistance is poor. When magnetron sputtering or evaporation is used or an electron gun is used for pre-plating, melting may occur, which will greatly affect the production yield and production efficiency.

[0004] Modifying polypropylene is an effective way to solve the above problems. For example, the Chinese invention patent with application publication number CN116922907A discloses a modified polypropylene film and its preparation method, a composite current collector and its preparation method. The film layer structure of the modified polypropylene film includes a first surface layer, an intermediate layer and a second surface layer in sequence; wherein, by weight, the components of the first surface layer and the second surface layer include: 60-70 parts of isotactic polypropylene, 24.5-38.5 parts of random polypropylene, 0.5-3 parts of polar additives, 0.5-1.5 parts of conductive particles, and 0.5-1 parts of dispersants; the components of the intermediate layer include: 85-90 parts of isotactic polypropylene, 5-13.5 parts of random polypropylene, 0.5-3 parts of polar additives, 0.5-1 parts of conductive particles, and 0.5-1 parts of dispersants. The modified polypropylene film provided by the invention has good mechanical properties and excellent electrical conductivity, and has strong bonding strength with metals. As the matrix of the composite current collector, it can improve the yield rate of the composite current collector, reduce the risk of composite current collector film breakage, and meet market demand. However, its resistance to electrolyte corrosion, flame retardancy, and heat resistance still need to be further improved.

[0005] It can be seen that it is particularly important to develop a modified polypropylene film with excellent resistance to electrolyte corrosion, good heat resistance, good adhesion to the metal layer and flame retardancy, sufficient puncture resistance and long service life, and its application in composite current collectors. Summary of the invention

[0006] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a modified polypropylene film with excellent electrolyte corrosion resistance, good heat resistance, good adhesion to the metal layer and flame retardancy, sufficient puncture resistance and long service life, and its application in a composite current collector.

[0007] To achieve the above-mentioned purpose, the technical scheme adopted by the present invention is: a modified polypropylene film, comprising the following raw materials in parts by weight: 80 parts of polypropylene resin, 10-20 parts of linear low-density polyethylene, 10-15 parts of hyperbranched polypropylene, 20-30 parts of polyvinylidene fluoride resin, 1-3 parts of compatibilizer, 5-8 parts of other additives, 3-5 parts of 1,3-bis(oxiranylmethyl)-5-(2-propenyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, 1-3 parts of 1,1'-diaminoferrocene, 2-4 parts of 2,2'-bis(trifluoromethyl)diaminobiphenyl, 3-5 parts of (3,6-diaminoacridine-9-yl)boric acid, 0.8-1.2 parts of quaternary ammonium salt-based cup [3] carbazole, and 10-15 parts of filler.

[0008] Preferably, the polypropylene resin is a mixture of homopolypropylene and copolymer polypropylene in a mass ratio of 1:1; the homopolypropylene is Shanghai Petrochemical brand T30S general-purpose homopolypropylene; the copolymer polypropylene is Dalian Hengli K8003 copolymer polypropylene; the linear low-density polyethylene is selected from linear low-density polyethylene with a brand of DFDA9030.

[0009] Preferably, there is no special requirement for the source of the hyperbranched polypropylene. In one embodiment of the present invention, the hyperbranched polypropylene is prepared according to the method of Example 1 of the Chinese invention patent with authorization announcement number CN107187153B.

[0010] Preferably, the polyvinylidene fluoride resin is selected from polyvinylidene fluoride resin with a brand name of KYNAR FLEX®2501-20.

[0011] Preferably, the compatibilizer is maleic anhydride grafted PP, with a brand name of PO 1020, provided by Exxon in the United States.

[0012] Preferably, the other additives include antioxidants, lubricants, coupling agents, and initiators.

[0013] Preferably, the antioxidant is at least one of antioxidant 1010 and antioxidant 168; the lubricant is at least one of ethylene bisstearamide and butyl stearate; the coupling agent is at least one of silane coupling agent KH550, silane coupling agent KH560, and silane coupling agent KH570; and the initiator is diisopropylbenzene peroxide.

[0014] Preferably, the mass ratio of the antioxidant, lubricant, coupling agent and initiator is 1:(0.8-1.2):(1-2):(0.5-0.8).

[0015] Preferably, there is no special requirement for the source of the quaternary ammonium salt-based calix[3]carbazole. In one embodiment of the present invention, the quaternary ammonium salt-based calix[3]carbazole is prepared according to the method of Example 2 of the Chinese invention patent with authorization publication number CN109836429B.

[0016] Preferably, the filler is glass fiber, and the glass fiber is alkali-free chopped glass fiber, with a single fiber diameter of 3-5 microns and a length of 1-3 mm.

[0017] Another object of the present invention is to provide a method for preparing the modified polypropylene film, comprising the following steps: mixing the raw materials uniformly by weight, extruding through a twin-screw extruder, and then forming a film through a biaxial stretching film-forming machine, then soaking the obtained film in water at 50-60°C for 8-12h, taking it out and drying it at 85-95°C to constant weight to obtain a modified polypropylene film.

[0018] Preferably, the extrusion temperature of the twin-screw extruder is 210-230°C; the stretching temperature of the biaxial stretching film-forming machine is 110-120°C, the stretching rate is 125-85 mm / s, the heat setting temperature is 215-245°C, and the stretching ratio is 4:1.

[0019] Another object of the present invention is to provide an application of the modified polypropylene film in a composite current collector.

[0020] Due to the application of the above technical solution, the present invention has the following beneficial effects:

[0021] (1) The method for preparing the modified polypropylene film disclosed in the present invention can be realized by using conventional operations and equipment, has low labor intensity, little impact on the environment, low energy consumption and capital investment, high preparation efficiency and yield rate, and is suitable for industrial continuous production.

[0022] (2) The modified polypropylene film disclosed in the present invention is made of the following raw materials in parts by weight: 80 parts of polypropylene resin, 10-20 parts of linear low-density polyethylene, 10-15 parts of hyperbranched polypropylene, 20-30 parts of polyvinylidene fluoride resin, 1-3 parts of compatibilizer, 5-8 parts of other additives, 3-5 parts of 1,3-bis(oxiranylmethyl)-5-(2-propenyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, 1-3 parts of 1,1'-diaminoferrocene, 2-4 parts of 2,2'-bis(trifluoromethyl)diaminobiphenyl, 3-5 parts of (3,6-diaminoacridine-9-yl)boric acid, 0.8-1.2 parts of quaternary ammonium salt-based calix[3]carbazole, and 10-15 parts of filler. Through the mutual cooperation and joint action of various raw materials, the manufactured membrane has excellent resistance to electrolyte corrosion, good heat resistance, good adhesion and flame retardancy with the metal layer, sufficient puncture resistance and long service life.

[0023] (3) The modified polypropylene film disclosed in the present invention uses polypropylene resin, linear low-density polyethylene, hyperbranched polypropylene, and polyvinylidene fluoride resin as substrates, combining their respective advantages to give the product excellent puncture resistance, electrolyte corrosion resistance, and heat resistance; and they have good compatibility with each other, so that the product has good performance stability; at the same time, triazone, ferrocene, fluorinated biphenyl, acridine, boron-containing structure, cup[3]carbazole, and ionic salt structure are introduced into the polymer. Under the multiple effects of electronic effect, steric effect, and conjugation effect, the film has better electrolyte corrosion resistance, better heat resistance, better adhesion to the metal layer and flame retardancy, better puncture resistance, and longer service life. DETAILED DESCRIPTION

[0024] The following description is used to disclose the present invention so that those skilled in the art can implement the present invention. The preferred embodiments described below are only examples, and those skilled in the art may think of other obvious variations.

[0025] Example 1, a modified polypropylene film, comprising the following raw materials in parts by weight: 80 parts of polypropylene resin, 10 parts of linear low-density polyethylene, 10 parts of hyperbranched polypropylene, 20 parts of polyvinylidene fluoride resin, 1 part of compatibilizer, 5 parts of other additives, 3 parts of 1,3-bis(oxiranylmethyl)-5-(2-propenyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, 1 part of 1,1'-diaminoferrocene, 2 parts of 2,2'-bis(trifluoromethyl)diaminobiphenyl, 3 parts of (3,6-diaminoacridine-9-yl)boric acid, 0.8 parts of quaternary ammonium salt-based calix[3]carbazole, and 10 parts of filler.

[0026] The polypropylene resin is a mixture of homopolypropylene and copolymer polypropylene in a mass ratio of 1:1; the homopolypropylene is Shanghai Petrochemical brand T30S general-purpose homopolypropylene; the copolymer polypropylene is Dalian Hengli K8003 copolymer polypropylene; the linear low-density polyethylene is selected from the linear low-density polyethylene with a brand of DFDA9030; the hyperbranched polypropylene is prepared according to the method of Example 1 of the Chinese invention patent with authorization announcement number CN107187153B; the polyvinylidene fluoride resin is selected from the polyvinylidene fluoride resin with a brand of KYNAR FLEX®2501-20; the compatibilizer is maleic anhydride grafted PP with a brand of PO 1020, provided by Exxon in the United States.

[0027] The other additives include antioxidants, lubricants, coupling agents, and initiators; the antioxidant is antioxidant 1010; the lubricant is ethylene bisstearamide; the coupling agent is silane coupling agent KH550; the initiator is dicumyl peroxide; the mass ratio of the antioxidant, lubricant, coupling agent, and initiator is 1:0.8:1:0.5; the quaternary ammonium salt-based calix [3] carbazole is prepared according to the method of Example 2 of the Chinese invention patent with authorization announcement number CN109836429B; the filler is glass fiber, and the glass fiber is alkali-free chopped glass fiber with a single fiber diameter of 3 microns and a length of 1 mm.

[0028] A method for preparing the modified polypropylene film comprises the following steps: uniformly mixing the raw materials by weight, extruding the raw materials through a twin-screw extruder, and then forming the film through a biaxial stretching film-forming machine, then soaking the obtained film in 50°C water for 8h, taking it out and drying it at 85°C to constant weight to obtain the modified polypropylene film; the extrusion temperature of the twin-screw extruder is 210°C; the stretching temperature of the biaxial stretching film-forming machine is 110°C, the stretching rate is 125mm / s, the heat setting temperature is 215°C, and the stretching ratio is 4:1.

[0029] Example 2, a modified polypropylene film, comprising the following raw materials in parts by weight: 80 parts of polypropylene resin, 13 parts of linear low-density polyethylene, 11 parts of hyperbranched polypropylene, 22 parts of polyvinylidene fluoride resin, 1.5 parts of a compatibilizer, 6 parts of other additives, 3.5 parts of 1,3-bis(oxiranylmethyl)-5-(2-propenyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, 1.5 parts of 1,1'-diaminoferrocene, 2.5 parts of 2,2'-bis(trifluoromethyl)diaminobiphenyl, 3.5 parts of (3,6-diaminoacridine-9-yl)boric acid, 0.9 parts of quaternary ammonium salt-based calix[3]carbazole, and 11 parts of filler.

[0030] The polypropylene resin is a mixture of homopolypropylene and copolymer polypropylene in a mass ratio of 1:1; the homopolypropylene is Shanghai Petrochemical brand T30S general-purpose homopolypropylene; the copolymer polypropylene is Dalian Hengli K8003 copolymer polypropylene; the linear low-density polyethylene is selected from the linear low-density polyethylene with a brand of DFDA9030; the hyperbranched polypropylene is prepared according to the method of Example 1 of the Chinese invention patent with authorization announcement number CN107187153B; the polyvinylidene fluoride resin is selected from the polyvinylidene fluoride resin with a brand of KYNAR FLEX®2501-20; the compatibilizer is maleic anhydride grafted PP with a brand of PO 1020, provided by Exxon in the United States.

[0031] The other additives include antioxidants, lubricants, coupling agents, and initiators; the antioxidant is antioxidant 168; the lubricant is butyl stearate; the coupling agent is silane coupling agent KH560; the initiator is dicumyl peroxide; the mass ratio of the antioxidant, lubricant, coupling agent, and initiator is 1:0.9:1.2:0.6; the quaternary ammonium salt-based calix [3] carbazole is prepared according to the method of Example 2 of the Chinese invention patent with authorization announcement number CN109836429B; the filler is glass fiber, and the glass fiber is alkali-free chopped glass fiber with a single fiber diameter of 3.5 microns and a length of 1.5 mm.

[0032] A method for preparing the modified polypropylene film comprises the following steps: uniformly mixing the raw materials by weight, extruding the raw materials through a twin-screw extruder, and then forming the film through a biaxial stretching film-forming machine, then soaking the obtained film in 53°C water for 9h, taking it out and drying it at 87°C to constant weight to obtain the modified polypropylene film; the extrusion temperature of the twin-screw extruder is 215°C; the stretching temperature of the biaxial stretching film-forming machine is 113°C, the stretching rate is 115mm / s, the heat setting temperature is 225°C, and the stretching ratio is 4:1.

[0033] Example 3, a modified polypropylene film, comprising the following raw materials in parts by weight: 80 parts of polypropylene resin, 15 parts of linear low-density polyethylene, 13 parts of hyperbranched polypropylene, 25 parts of polyvinylidene fluoride resin, 2 parts of compatibilizer, 6.5 parts of other additives, 4 parts of 1,3-bis(oxiranylmethyl)-5-(2-propenyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, 2 parts of 1,1'-diaminoferrocene, 3 parts of 2,2'-bis(trifluoromethyl)diaminobiphenyl, 4 parts of (3,6-diaminoacridine-9-yl)boric acid, 1 part of quaternary ammonium salt-based calix[3]carbazole, and 13 parts of filler.

[0034] The polypropylene resin is a mixture of homopolypropylene and copolymer polypropylene in a mass ratio of 1:1; the homopolypropylene is Shanghai Petrochemical brand T30S general-purpose homopolypropylene; the copolymer polypropylene is Dalian Hengli K8003 copolymer polypropylene; the linear low-density polyethylene is selected from the linear low-density polyethylene with a brand of DFDA9030; the hyperbranched polypropylene is prepared according to the method of Example 1 of the Chinese invention patent with authorization announcement number CN107187153B; the polyvinylidene fluoride resin is selected from the polyvinylidene fluoride resin with a brand of KYNAR FLEX®2501-20; the compatibilizer is maleic anhydride grafted PP with a brand of PO 1020, provided by Exxon in the United States.

[0035] The other additives include antioxidants, lubricants, coupling agents, and initiators; the antioxidant is a mixture of antioxidant 1010 and antioxidant 168 in a mass ratio of 3:5; the lubricant is a mixture of ethylene bis stearamide and butyl stearate in a mass ratio of 1:3; the coupling agent is a mixture of silane coupling agent KH550, silane coupling agent KH560, and silane coupling agent KH570 in a mass ratio of 1:1:2; the initiator is dicumyl peroxide; the mass ratio of the antioxidant, lubricant, coupling agent, and initiator is 1:1:1.5:0.65; the quaternary ammonium salt-based calix[3]carbazole is prepared according to the method of Example 2 of the Chinese invention patent with authorization announcement number CN109836429B; the filler is glass fiber, and the glass fiber is alkali-free chopped glass fiber with a single fiber diameter of 4 microns and a length of 2 mm.

[0036] A method for preparing the modified polypropylene film comprises the following steps: uniformly mixing the raw materials by weight, extruding the raw materials through a twin-screw extruder, and then forming the film through a biaxial stretching film-forming machine, then soaking the obtained film in 55°C water for 10 hours, taking it out and drying it at 90°C to constant weight to obtain the modified polypropylene film; the extrusion temperature of the twin-screw extruder is 220°C; the stretching temperature of the biaxial stretching film-forming machine is 115, the stretching rate is 105mm / s, the heat setting temperature is 230°C, and the stretching ratio is 4:1.

[0037] Example 4, a modified polypropylene film, comprising the following raw materials in parts by weight: 80 parts of polypropylene resin, 18 parts of linear low-density polyethylene, 14 parts of hyperbranched polypropylene, 28 parts of polyvinylidene fluoride resin, 2.5 parts of compatibilizer, 7.5 parts of other additives, 4.5 parts of 1,3-bis(oxiranylmethyl)-5-(2-propenyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, 2.5 parts of 1,1'-diaminoferrocene, 3.5 parts of 2,2'-bis(trifluoromethyl)diaminobiphenyl, 4.5 parts of (3,6-diaminoacridine-9-yl)boric acid, 1.1 parts of quaternary ammonium salt-based calix[3]carbazole, and 14 parts of filler.

[0038] The polypropylene resin is a mixture of homopolypropylene and copolymer polypropylene in a mass ratio of 1:1; the homopolypropylene is Shanghai Petrochemical brand T30S general-purpose homopolypropylene; the copolymer polypropylene is Dalian Hengli K8003 copolymer polypropylene; the linear low-density polyethylene is selected from the linear low-density polyethylene with a brand of DFDA9030; the hyperbranched polypropylene is prepared according to the method of Example 1 of the Chinese invention patent with authorization announcement number CN107187153B; the polyvinylidene fluoride resin is selected from the polyvinylidene fluoride resin with a brand of KYNAR FLEX®2501-20.

[0039] The compatibilizer is maleic anhydride grafted PP with a brand name of PO 1020, provided by Exxon of the United States; the other additives include antioxidants, lubricants, coupling agents, and initiators; the antioxidant is antioxidant 1010; the lubricant is butyl stearate; the coupling agent is silane coupling agent KH570; the initiator is diisopropylbenzene peroxide; the mass ratio of the antioxidant, lubricant, coupling agent, and initiator is 1:1.1:1.9:0.75.

[0040] The quaternary ammonium salt-based calix[3]carbazole is prepared according to the method of Example 2 of the Chinese invention patent with authorization announcement number CN109836429B; the filler is glass fiber, and the glass fiber is alkali-free chopped glass fiber with a single fiber diameter of 4.5 microns and a length of 2.5 mm.

[0041] A method for preparing the modified polypropylene film comprises the following steps: uniformly mixing the raw materials by weight, extruding the raw materials through a twin-screw extruder, and then forming the film through a biaxial stretching film-forming machine, then soaking the obtained film in 58°C water for 11 hours, taking it out and drying it at 93°C to constant weight to obtain the modified polypropylene film; the extrusion temperature of the twin-screw extruder is 225°C; the stretching temperature of the biaxial stretching film-forming machine is 118°C, the stretching rate is 95mm / s, the heat setting temperature is 240°C, and the stretching ratio is 4:1.

[0042] Example 5, a modified polypropylene film, comprising the following raw materials in parts by weight: 80 parts of polypropylene resin, 20 parts of linear low-density polyethylene, 15 parts of hyperbranched polypropylene, 30 parts of polyvinylidene fluoride resin, 3 parts of compatibilizer, 8 parts of other additives, 5 parts of 1,3-bis(oxiranylmethyl)-5-(2-propenyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, 3 parts of 1,1'-diaminoferrocene, 4 parts of 2,2'-bis(trifluoromethyl)diaminobiphenyl, 5 parts of (3,6-diaminoacridine-9-yl)boric acid, 1.2 parts of quaternary ammonium salt-based calix[3]carbazole, and 15 parts of filler.

[0043] The polypropylene resin is a mixture of homopolypropylene and copolymer polypropylene in a mass ratio of 1:1; the homopolypropylene is Shanghai Petrochemical brand T30S general-purpose homopolypropylene; the copolymer polypropylene is Dalian Hengli K8003 copolymer polypropylene; the linear low-density polyethylene is selected from the linear low-density polyethylene with a brand of DFDA9030; the hyperbranched polypropylene is prepared according to the method of Example 1 of the Chinese invention patent with authorization announcement number CN107187153B; the polyvinylidene fluoride resin is selected from the polyvinylidene fluoride resin with a brand of KYNAR FLEX®2501-20; the compatibilizer is maleic anhydride grafted PP with a brand of PO 1020, provided by Exxon in the United States.

[0044] The other additives include antioxidants, lubricants, coupling agents, and initiators; the antioxidant is antioxidant 1010; the lubricant is ethylene bisstearamide; the coupling agent is silane coupling agent KH570; the initiator is diisopropylbenzene peroxide; the mass ratio of the antioxidant, lubricant, coupling agent, and initiator is 1:1.2:2:0.8.

[0045] The quaternary ammonium salt-based calix[3]carbazole is prepared according to the method of Example 2 of the Chinese invention patent with authorization announcement number CN109836429B; the filler is glass fiber, and the glass fiber is alkali-free chopped glass fiber with a single fiber diameter of 5 microns and a length of 3 mm.

[0046] A method for preparing the modified polypropylene film comprises the following steps: uniformly mixing the raw materials by weight, extruding the raw materials through a twin-screw extruder, and then forming the film through a biaxial stretching film-forming machine, then soaking the obtained film in 60°C water for 12 hours, taking it out and drying it at 95°C to constant weight to obtain the modified polypropylene film; the extrusion temperature of the twin-screw extruder is 230°C; the stretching temperature of the biaxial stretching film-forming machine is 120°C, the stretching rate is 85mm / s, the heat setting temperature is 245°C, and the stretching ratio is 4:1.

[0047] Comparative Example 1, a modified polypropylene film and its application in a composite current collector, is basically the same as Example 1, except that an equal amount of polypropylene resin is used instead of linear low-density polyethylene, and 2,2'-bis(trifluoromethyl)diaminobiphenyl and quaternary ammonium salt-based calix[3]carbazole are not added.

[0048] Comparative Example 2, a modified polypropylene film and its application in a composite current collector, is basically the same as Example 1, except that an equal amount of polypropylene resin is used instead of polyvinylidene fluoride resin, and 1,1'-diaminoferrocene and (3,6-diaminoacridine-9-yl)boric acid are not added.

[0049] Comparative Example 3, a modified polypropylene film and its application in a composite current collector, is basically the same as Example 1, except that an equal amount of p-phenylenediamine is used to replace 1,1'-diaminoferrocene and (3,6-diaminoacridine-9-yl)boric acid.

[0050] Comparative Example 4, a modified polypropylene film and its application in a composite current collector, is basically the same as Example 1, except that an equal amount of p-phenylenediamine is used to replace 2,2'-bis(trifluoromethyl)diaminobiphenyl and quaternary ammonium salt-based calix[3]carbazole.

[0051] In order to further illustrate the beneficial technical effects of the modified polypropylene films involved in each embodiment of the present invention, relevant performance tests were performed on the modified polypropylene films involved in Examples 1-5 and Comparative Examples 1-4; the test methods are as follows:

[0052] Puncture resistance: Puncture resistance strength test is carried out according to GB / T 37841-2019.

[0053] (2) Heat resistance: Refer to ASTM D1204-2008 for heat shrinkage test, the test conditions are 150℃, 30min.

[0054] (3) Resistance to electrolyte corrosion: The modified polypropylene film resistant to electrolyte corrosion in each example was immersed in an electrolyte whose weight was 40 times that of the modified polypropylene film for 24 hours; then the modified polypropylene film was taken out, and the electrolyte on the surface of the film was absorbed with absorbent paper, and the film was dried at 90°C to constant weight. After cooling to room temperature, the puncture resistance strength was measured again, and the retention rate of the puncture resistance strength was used as the measure. The larger the value, the better the resistance to electrolyte corrosion. The electrolyte was a mixture of ethylene carbonate, diethyl carbonate and methyl ethyl carbonate in a mass ratio of 1:2:1.

[0055] (4) Adhesion between the film and the metal conductive layer: The base films of each example were placed in a magnetron sputtering chamber, and aluminum metal with a purity of 99.99% was used as the target material and argon gas was used as the gas source. A 1200 nm thick aluminum metal layer was plated on both sides of the modified polypropylene film in the thickness direction by magnetron sputtering in the magnetron sputtering chamber to obtain a composite current collector; a layer of Permacel P-94 double-sided tape was adhered to a 1 mm thick aluminum foil, and the composite current collector was adhered on the double-sided tape. A layer of ethylene acrylic acid copolymer film (DuPont Nurcel0903, 50 μm thick) was covered on the composite current collector, and then a 1.3×10 5 N / m 2 , hot pressing at 120°C for 10s, cooling to room temperature, and cutting into small strips of 150mm×15mm; finally, the ethylene acrylic acid copolymer film of the small sample strip is fixed on the upper clamp of the tensile machine, and the rest is fixed on the lower clamp. After fixation, the two are peeled off at an angle of 180° and a speed of 100mm / min to test the peeling force, which is the adhesion between the film and the metal conductive layer.

[0056] (5) Flame retardancy: tested in accordance with UL94 standard.

[0057]

[0058] As can be seen from Table 1, the modified polypropylene films involved in the embodiments of the present invention have better puncture resistance, heat resistance, electrolyte corrosion resistance and adhesion to the metal conductive layer than the comparative example products. The combined use of linear low-density polyethylene, 2,2'-bis(trifluoromethyl)diaminobiphenyl, quaternary ammonium salt-based calix[3]carbazole, polyvinylidene fluoride resin, 1,1'-diaminoferrocene and (3,6-diaminoacridine-9-yl)boric acid is beneficial to improving the above properties.

[0059] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with this technology to understand the contents of the present invention and implement them accordingly. They cannot be used to limit the protection scope of the present invention. All equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A modified polypropylene film, characterized in that: The invention comprises the following raw materials in parts by weight: 80 parts of polypropylene resin, 10-20 parts of linear low-density polyethylene, 10-15 parts of hyperbranched polypropylene, 20-30 parts of polyvinylidene fluoride resin, 1-3 parts of compatibilizer, 5-8 parts of other additives, 3-5 parts of 1,3-bis(oxiranylmethyl)-5-(2-propenyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, 1-3 parts of 1,1'-diaminoferrocene, 2-4 parts of 2,2'-bis(trifluoromethyl)diaminobiphenyl, 3-5 parts of (3,6-diaminoacridine-9-yl)boric acid, 0.8-1.2 parts of quaternary ammonium salt-based calix[3]carbazole, and 10-15 parts of filler; The polypropylene resin is a mixture of homopolypropylene and copolymer polypropylene in a mass ratio of 1:1; the homopolypropylene is a general-purpose homopolypropylene with a grade of T30S; the copolymer polypropylene is a copolymer polypropylene with a grade of K8003; the linear low-density polyethylene is selected from a linear low-density polyethylene with a grade of DFDA9030; and the polyvinylidene fluoride resin is selected from a polyvinylidene fluoride resin with a grade of KYNAR FLEX®2501-20.

2. The modified polypropylene film according to claim 1, characterized in that The compatibilizer is maleic anhydride grafted PP, with the brand name PO 1020; the other additives include antioxidants, lubricants, coupling agents, and initiators.

3. The modified polypropylene film according to claim 2, characterized in that: The antioxidant is at least one of antioxidant 1010 and antioxidant 168; the lubricant is at least one of ethylene bis stearamide and butyl stearate; the coupling agent is at least one of silane coupling agent KH550, silane coupling agent KH560, and silane coupling agent KH570; and the initiator is diisopropylbenzene peroxide.

4. The modified polypropylene film according to claim 2, characterized in that: The mass ratio of the antioxidant, lubricant, coupling agent and initiator is 1:(0.8-1.2):(1-2):(0.5-0.8).

5. The modified polypropylene film according to claim 1, characterized in that: The filler is glass fiber, and the glass fiber is alkali-free chopped glass fiber, with a single fiber diameter of 3-5 microns and a length of 1-3 millimeters.

6. A method for preparing a modified polypropylene film according to any one of claims 1 to 5, characterized in that: The method comprises the following steps: uniformly mixing the raw materials by weight, extruding the raw materials through a twin-screw extruder, and then forming a film through a biaxial stretching film-forming machine; then soaking the obtained film in water at 50-60°C for 8-12 hours, taking it out, and drying it at 85-95°C to constant weight to obtain a modified polypropylene film.

7. The method for preparing a modified polypropylene film according to claim 6, characterized in that: The extrusion temperature of the twin-screw extruder is 210-230°C; the stretching temperature of the biaxial stretching film-forming machine is 110-120°C, the stretching rate is 125-85 mm / s, the heat setting temperature is 215-245°C, and the stretching ratio is 4:

1.

8. Use of the modified polypropylene film according to any one of claims 1 to 5 in a composite current collector.

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