A flame-retardant composite current collector and its preparation method

Abstract

This application relates to the technical field of current collectors, and specifically relates to a flame-retardant composite current collector and a preparation method thereof. The flame-retardant composite current collector is composed of a base film layer, metal film layers deposited on both sides of the base film layer, and a flame-retardant layer formed by curing a flame-retardant coating applied on the surface of the metal film layers. The preparation steps include: S1. Mix a modified polypropylene resin, a reinforcing component, an antioxidant, a lubricant, a coupling agent, and a compatibilizer to obtain a mixed material; S2. Melt-extrude the mixed material, cast and form it, and then perform stretching through a biaxial stretching process to form the base film layer; S3. Deposit metal film layers on both sides of the base film layer and hot-press and form them; S4. Apply a flame-retardant coating, and after drying and curing, obtain the flame-retardant composite current collector. The flame-retardant composite current collector prepared by this application has excellent flame retardancy, excellent mechanical properties and heat aging resistance, large peel strength, and a firm combination of the metal film layer and the base film layer, effectively improving the quality and safety of the composite current collector.

Description

Technical Field

[0001] The present application relates to the technical field of current collectors, and more specifically, to a flame-retardant composite current collector and a preparation method thereof. Background Art

[0002] With the continuous development and large-scale application of the battery industry, people's requirements for the quality and safety of batteries are also getting higher and higher. As a result, battery manufacturers are required to optimize and improve each component of the battery to enhance its various performance.

[0003] As one of the core components of the battery, the performance of the current collector directly affects the performance of the battery. To achieve the lightweight and safety of the current collector, the concept of composite current collector emerged. The existing composite current collector adopts a "sandwich" structure, that is, a metal film layer + a base film layer + a metal film layer. This structure has attracted wide attention from major battery manufacturers due to its advantages of high safety and high energy density and has broad application prospects. However, the bonding force between the metal film layer and the base film layer of the composite current collector has always been a problem that is difficult to improve in the production technology of the composite current collector and is also a common failure cause of the composite current collector. In addition, the flame-retardant performance is a key safety index of the existing composite current collector. Due to the presence of the middle polymer base film layer, the existing composite current collector can effectively block the short-circuit phenomenon between the two metal layers, providing a certain degree of safety guarantee. However, whether there are holes in the polymer base film layer during the production process or holes or fusing occur due to high temperature during the use of the composite current collector, it will lead to the risk of short circuit between the metal layers, thus seriously affecting the safety performance of the composite current collector. Summary of the Invention

[0004] To solve the technical problems mentioned in the background art, the present application provides a flame-retardant composite current collector and a preparation method thereof.

[0005] In the first aspect, the present application provides a flame-retardant composite current collector, adopting the following technical solution:

[0006] A flame-retardant composite current collector is composed of a base film layer, metal film layers deposited on both sides of the base film layer, and a flame-retardant layer formed by curing a flame-retardant coating applied on the surface of the metal film layer;

[0007] Preferably, the base film layer is made of the following raw materials in parts by weight: 100 - 120 parts of modified polypropylene resin, 10 - 15 parts of reinforcing component, 0.5 - 2 parts of antioxidant, 1 - 3 parts of lubricant, 2 - 3 parts of coupling agent, and 3 - 5 parts of compatibilizer.

[0008] Preferably, the flame-retardant coating is made of the following raw materials in parts by weight: 10 - 12 parts of polymer matrix, 6 - 8 parts of modified nano-silica, 1 - 2 parts of auxiliary agent, and 50 - 60 parts of solvent.

[0009] Preferably, the preparation of the modified polypropylene resin comprises the following steps:

[0010] (1) Place polypropylene and fluorinated ethylene propylene copolymer in a twin-screw extruder, with the working temperature being 180 - 220 °C, and knead for 1.5 - 2 h to obtain Intermediate 1;

[0011] (2) Add liquid crystal polymer to Intermediate 1, with the working temperature being 230 - 250 °C, knead for 2 - 3 h, and after extrusion granulation and cooling, obtain Intermediate 2;

[0012] (3) Disperse Intermediate 2 in toluene, heat to 80 - 100 °C, stir while heating to obtain Solution A, dropwise add 4-trifluoromethylbenzoyl chloride toluene solution to Solution A while continuously stirring, control the temperature at 60 - 80 °C, add pyridine, react for 1 - 2 h, filter, wash, and dry to obtain the modified polypropylene resin.

[0013] Preferably, in step (1), the mass ratio of polypropylene to fluorinated ethylene propylene copolymer is 15 - 20:3 - 6.

[0014] Preferably, in step (2), the mass ratio of Intermediate 1 to liquid crystal polymer is 10 - 12:1 - 2.

[0015] Preferably, in step (3), the mass ratio of Intermediate 2 to toluene is 2 - 3:8 - 10.

[0016] Preferably, in step (3), the mass concentration of 4-trifluoromethylbenzoyl chloride toluene solution is 12 - 15%.

[0017] Preferably, in step (3), the mass ratio of Solution A, 4-trifluoromethylbenzoyl chloride toluene solution, and pyridine is 80 - 100:15 - 20:0.1 - 1.

[0018] Preferably, the reinforcing component consists of nano-montmorillonite and aramid fiber with a mass ratio of 5 - 8:1 - 2.

[0019] Preferably, the antioxidant is one or several of antioxidant 1010, antioxidant 168, and antioxidant 1425WL.

[0020] Preferably, the lubricant is one or several of zinc stearate, calcium stearate, and polyethylene wax.

[0021] Preferably, the coupling agent is a silane coupling agent and / or a titanate coupling agent.

[0022] Preferably, the compatibilizer is maleic anhydride grafted polypropylene and / or ethylene-vinyl acetate copolymer.

[0023] Preferably, the metal film layer is one of a copper film, an aluminum film, and a nickel film, and the thickness of the metal film layer is 1-5 μm.

[0024] Preferably, the deposition method is one of evaporation deposition, sputtering deposition, ion plating, electroplating, and plasma-enhanced chemical vapor deposition.

[0025] Preferably, the preparation method of the flame retardant coating is as follows: dispersing a polymer matrix, modified nano-silica, and an auxiliary agent in a solvent, stirring and mixing, controlling the temperature at 200-230 °C, the stirring speed at 300-400 rpm, and stirring for 1-2 h to obtain the flame retardant coating.

[0026] Preferably, the polymer matrix is polyurethane and / or polyacrylate.

[0027] Preferably, the auxiliary agent is a polycarboxylate dispersant and / or a silicone oil defoamer.

[0028] Preferably, the solvent is one or more of N-methylpyrrolidone, N,N-dimethylformamide, and dimethyl sulfoxide.

[0029] Preferably, the preparation method of the modified nano-silica includes the following steps:

[0030] A1. After ultrasonic mixing of nano-silica, isopropanol, KH-570, and deionized water, heating to 40-60 °C, stirring and reacting for 4-5 h, filtering, washing, and drying to obtain epoxy-group nano-silica;

[0031] A2. Adding epoxy-group nano-silica to an ethanol-phytic acid aqueous solution, ultrasonically dispersing at 50-60 °C for 30-50 min, dropping a surface modification solution, after the dropping is completed, heating to 100-120 °C and stirring for 2-3 h, filtering, washing, and drying to obtain the modified nano-silica.

[0032] Preferably, the mass ratio of nano-silica, isopropanol, KH-570, and deionized water in step A1 is 10-12:30-40:3-4:45-55.

[0033] Preferably, the ethanol-phytic acid aqueous solution in step A2 is composed of phytic acid, absolute ethanol, and deionized water with a mass ratio of 1-2:4-7:10-15.

[0034] Preferably, the surface modification solution in step A2 is composed of tetraethylammonium bromide, 2-hydroxypyridine-3-carboxylic acid, and absolute ethanol with a mass ratio of 0.1-0.2:2-3:15-20.

[0035] Preferably, in step A2, the mass ratio of the ethanol-phytic acid aqueous solution, epoxy group nano-silica, and surface modification liquid is 10-12:3-4:0.5-1.

[0036] Second, the present application also provides a preparation method of a flame-retardant composite current collector, including the following steps:

[0037] S1. Add modified polypropylene resin, reinforcing component, antioxidant, lubricant, coupling agent, and compatibilizer by weight parts to a high-speed mixer, and mix evenly to obtain a mixture.

[0038] S2. Add the mixture to a twin-screw extruder for melt extrusion and casting forming, and then stretch the formed material through a biaxial stretching process to form a base film layer.

[0039] S3. Deposit a metal film layer on both sides of the base film layer and perform hot pressing forming.

[0040] S4. Coat a 4-6 μm thick flame-retardant coating on the surface of the metal film layer, and after drying and curing, obtain the flame-retardant composite current collector.

[0041] Preferably, in step S2, the casting forming speed is 1-2 m / min, and the casting forming temperature is 180-200 °C.

[0042] Preferably, in step S2, the biaxial stretching process has a stretching temperature of 120-125 °C, a stretching rate of 8-10 cm / s, a heat setting temperature of 210-230 °C, and a stretching ratio of 4:1.

[0043] Preferably, in step S2, the thickness of the base film layer is 2-5 μm.

[0044] Preferably, in step S3, the hot pressing forming temperature is 120-180 °C, the pressure is 1-2 MPa, and the time is 2-3 min.

[0045] Preferably, in step S4, the curing temperature is 120-150 °C, and the curing time is 0.5-1 h.

[0046] In summary, the present application has the following beneficial effects:

[0047] In the modification process of polypropylene resin, fluorinated ethylene propylene copolymer is introduced first. The fluorine-containing groups in the fluorinated ethylene propylene copolymer improve the thermal stability and flame retardancy of the modified polypropylene resin, enhance the barrier performance of the composite material to liquid electrolyte, and prevent the penetration of liquid electrolyte. Then, liquid crystal polymer and 4-trifluoromethylbenzoyl chloride are introduced to further modify the polyacrylate, which can significantly improve the compatibility of polypropylene resin with liquid crystal polymer and other components, make it disperse more uniformly in the composite material, and enhance the mechanical properties of polypropylene resin, such as tensile strength, fracture toughness and modulus, and significantly improve the heat resistance and chemical resistance. Using nano-montmorillonite and aramid fiber as reinforcing components together, the combination of the lamellar structure of nano-montmorillonite and the anti-melting-dripping property of aramid fiber can not only prevent the transfer of oxygen, combustible gas and heat, but also avoid the danger of secondary combustion and fire spread caused by possible melting drips. In addition, nano-montmorillonite and aramid fiber can significantly improve the tensile strength, modulus and toughness of the base film layer, enhance the mechanical properties of the material, and effectively improve the interfacial compatibility between the base film layer and the metal layer, and improve the adhesion to the metal layer.

[0048] In this application, modified nano-silica is added to the flame retardant coating. On the one hand, the flame retardancy and heat resistance of nano-silica are exerted. On the other hand, phytic acid is introduced into the reaction system first. The phosphate groups in phytic acid molecules can undergo ring-opening reaction with the epoxy groups on the surface of epoxy nano-silica to form stable ester bonds, improve the functional group density on the surface of nano-silica, form a large steric hindrance effect to prevent agglomeration, and the phytic acid molecules carry negative charges and can be electrostatically combined with tetraethylammonium bromide to form a positively charged protective layer, enhancing the interfacial bonding force between nano-silica and the polymer matrix. The hydroxyl and carboxyl groups in 2-hydroxypyridine-3-carboxylic acid molecules can form chelate bonds with the active groups (such as epoxy groups and phosphate ester groups) on the surface of nano-silica, further enhancing the surface modification effect, and introducing the modified nano-silica into polyurethane. The carboxyl group on the surface of 2-hydroxypyridine-3-carboxylic acid crosslinks with the amino group on polyurethane, which not only improves the compatibility of nano-silica and polyurethane, but also can further improve the tensile strength, rigidity and fracture toughness of the composite material. Detailed implementation mode

[0049] The following further elaborates on this application in conjunction with examples.

[0050] The polypropylene (brand name: M02-G) used in the examples and comparative examples of the present invention was purchased from Shanghai Yuanfeng Plastic Technology Co., Ltd.; the fluorinated ethylene propylene copolymer (brand name: L-2213) was purchased from Haozheng New Materials Technology (Dongguan) Co., Ltd.; the liquid crystal polymer (brand name: E5008L BK) was purchased from Dongguan Hongwang Plastic Co., Ltd.; 4-trifluoromethylbenzoyl chloride was purchased from Hubei Xinghengye Technology Co., Ltd.; nano-montmorillonite (model: DK-NF) was purchased from Zhejiang Huate New Materials Co., Ltd.; aramid fiber (model: WAL34) was purchased from Dongguan Yichen Plastic Raw Materials Co., Ltd.; maleic anhydride grafted polypropylene (article number: HH7250BTBMY4) was purchased from Dongguan Zhangmutou Hengtai Plastic Raw Materials Business Department; polyurethane (brand number: A85P4441) was purchased from Dongguan Kaiwan Engineering Plastic Raw Materials Co., Ltd.; dimethyl silicone oil was purchased from Jinan Silicon Port Chemical Co., Ltd.; nano-silica (article number: BTH-5018) was purchased from Lingshou County Ruojia Mineral Products Co., Ltd.; KH-570 was purchased from Dongguan Hongrui Chemical Co., Ltd.; tetraethylammonium bromide was purchased from Shanghai Hongzhuang Chemical Technology Co., Ltd.; 2-hydroxypyridine-3-carboxylic acid was purchased from Hubei Watson Chemical Technology Co., Ltd., and phytic acid (article number: 01-92-5) was purchased from Shaanxi Rankang Biotechnology Co., Ltd.

[0051] Embodiment 1-3 provides a flame retardant composite current collector and a preparation method thereof.

[0052] Example 1

[0053] A flame-retardant composite current collector is composed of a base film layer, a metal film layer deposited on both sides of the base film layer, and a flame-retardant layer formed by curing a flame-retardant coating coated on the surface of the metal film layer; the base film layer is made of the following raw materials in parts by weight: 100 parts of modified polypropylene resin, 10 parts of reinforcing components, 0.5 parts of antioxidants, 1 part of lubricants, 2 parts of coupling agents, and 3 parts of compatibilizers; the flame-retardant coating is made of the following raw materials in parts by weight: 10 parts of polymer matrix, 6 parts of modified nano silicon dioxide, 1 part of auxiliary agent, and 50 parts of solvent; wherein the reinforcing component is composed of nano montmorillonite and aramid fiber in a mass ratio of 5:1, the antioxidant is antioxidant 1010, the lubricant is zinc stearate, the coupling agent is γ-aminopropyl triethoxysilane, the compatibilizer is maleic anhydride grafted polypropylene, the polymer matrix is polyurethane, the auxiliary agent is dimethyl silicone oil, and the solvent is N-methylpyrrolidone.

[0054] Wherein, the preparation of modified polypropylene resin comprises the following steps:

[0055] (1) placing polypropylene and fluorinated ethylene propylene copolymer in a mass ratio of 5:1 in a twin-screw extruder at a working temperature of 180° C. and mixing for 1.5 h to obtain an intermediate 1;

[0056] (2) Add liquid crystal polymer to Intermediate 1, control the mass ratio of Intermediate 1 to liquid crystal polymer to be 10:1, the working temperature to be 230 °C, knead for 2 h, and obtain Intermediate 2 after extrusion granulation and cooling;

[0057] (3) Disperse Intermediate 2 in toluene, heat to 80 °C, stir while heating, the stirring speed is 300 rpm, and the stirring time is 10 min to obtain Solution A; among them, the mass ratio of Intermediate 2 to toluene is 1:4. Dropwise add a toluene solution of 4-trifluoromethylbenzoyl chloride with a mass concentration of 12% to Solution A, control the dropping time to be 15 min, and continuously stir at the same time, control the temperature to be 60 °C, add pyridine, and control the mass ratio of Solution A, the toluene solution of 4-trifluoromethylbenzoyl chloride and pyridine to be 80:15:0.1, react for 1 h, filter, wash, and dry at 60 °C to constant weight to obtain the modified polypropylene resin.

[0058] Among them, the preparation method of the modified nano-silica includes the following steps:

[0059] A1. Mix nano-silica, isopropanol, KH-570 and deionized water, and after ultrasonic treatment at an ultrasonic power of 50 W, an ultrasonic frequency of 40 kHz and room temperature for 30 min, heat up to 40 °C, stir and react for 4 h, the stirring speed is 400 rpm, filter, wash and dry to obtain epoxy nano-silica, among which the mass ratio of nano-silica, isopropanol, KH-570 and deionized water is 10:30:3:45;

[0060] A2. Add epoxy nano-silica to an ethanol-phytic acid aqueous solution, disperse it by ultrasonic treatment at 50 °C for 30 min, the ultrasonic power is 100 W, the ultrasonic frequency is 45 kHz, dropwise add the surface modification liquid, the dropping time is 10 min, after the dropping is completed, heat up to 100 °C, stir for 2 h, filter, wash and dry to obtain the modified nano-silica, among which the ethanol-phytic acid aqueous solution is composed of phytic acid, absolute ethanol and deionized water with a mass ratio of 1:4:10, the surface modification liquid is composed of tetraethylammonium bromide, 2-hydroxypyridine-3-carboxylic acid and absolute ethanol with a mass ratio of 0.1:2:15, and the mass ratio of the ethanol-phytic acid aqueous solution, epoxy nano-silica and the surface modification liquid is 10:3:0.5.

[0061] A preparation method of a flame-retardant composite current collector includes the following steps:

[0062] S1. Add the modified polypropylene resin, reinforcing component, antioxidant, lubricant, coupling agent and compatibilizer by weight to a high-speed mixer, mix at a speed of 600 rpm at room temperature for 45 min to obtain a mixed material;

[0063] S2. Add the mixture into a twin-screw extruder, heat it to 220 °C, after heating for 1 h, melt and extrude it, at a speed of 1 m / min and a temperature of 180 °C, cast and form it, and then stretch the formed material through a biaxial stretching process to form a base film layer with a thickness of 2 μm, where the stretching temperature is 120 °C, the stretching rate is 8 cm / s, the heat setting temperature is 210 °C, and the stretching ratio is 4:1;

[0064] S3. Sputter and deposit a copper film layer with a thickness of 1 μm on both sides of the base film layer, the sputtering power is 480 W, the sputtering voltage is 180 V, the sputtering temperature is 150 °C, the hot pressing forming temperature is 120 °C, the pressure is 1 MPa, and the time is 2 min;

[0065] S4. Coating 4 μm of flame retardant coating on the surface of the copper film layer by using a slot die coater, drying at 50 °C for 2 h and curing at 120 °C for 0.5 h to obtain a flame retardant composite current collector;

[0066] The preparation method of the flame retardant coating is as follows: disperse the polymer matrix, modified nano-silica and additives in a solvent, stir and mix, control the temperature at 200 °C, the stirring speed at 300 rpm, and stir for 1 h to obtain the flame retardant coating.

[0067] Example 2

[0068] A flame retardant composite current collector is composed of a base film layer, a metal film layer deposited on both sides of the base film layer, and a flame retardant layer formed by curing a flame retardant coating coated on the surface of the metal film layer; the base film layer is made of the following raw materials in parts by weight: 110 parts of modified polypropylene resin, 12 parts of reinforcing component, 1 part of antioxidant, 2 parts of lubricant, 2.5 parts of coupling agent, 18 parts of filler and 4 parts of compatibilizer; the flame retardant coating is made of the following raw materials in parts by weight: 11 parts of polymer matrix, 7 parts of modified nano-silica, 1.5 parts of additive and 55 parts of solvent; wherein, the reinforcing component is composed of nano-montmorillonite and aramid fiber with a mass ratio of 6:1.5, the antioxidant is antioxidant 1010, the lubricant is zinc stearate, the coupling agent is γ-aminopropyltriethoxysilane, the compatibilizer is maleic anhydride grafted polypropylene, the polymer matrix is polyurethane, the additive is dimethyl silicone oil, and the solvent is N-methylpyrrolidone.

[0069] Among them, the preparation of the modified polypropylene resin includes the following steps:

[0070] (1) Place polypropylene and fluorinated ethylene propylene copolymer with a mass ratio of 18:5 in a twin-screw extruder, the working temperature is 200 °C, and mix for 1.8 h to obtain intermediate 1;

[0071] (2) Add liquid crystal polymer to intermediate 1, control the mass ratio of intermediate 1 to liquid crystal polymer to be 11:2, the working temperature is 240 °C, mix for 2.5 h, and after extrusion granulation and cooling, obtain intermediate 2;

[0072] (3) Disperse intermediate 2 in toluene, heat to 90 °C, stir while heating, with a stirring speed of 350 rpm and a stirring time of 15 min to obtain solution A; wherein, the mass ratio of intermediate 2 to toluene is 2.5:9. Dropwise add a toluene solution of 4-trifluoromethylbenzoyl chloride with a mass concentration of 14% to solution A over a period of 20 min, while continuously stirring, control the temperature at 70 °C, add pyridine, and control the mass ratio of solution A, the toluene solution of 4-trifluoromethylbenzoyl chloride, and pyridine to be 90:18:0.5. React for 1.5 h, filter, wash, and dry at 70 °C to constant weight to obtain the modified polypropylene resin.

[0073] Among them, the preparation method of the modified nano-silica includes the following steps:

[0074] A1. Mix nano-silica, isopropanol, KH-570, and deionized water, then ultrasonicate at a room temperature for 35 min with an ultrasonic power of 75 W and an ultrasonic frequency of 45 kHz, then raise the temperature to 50 °C, stir and react for 4.5 h with a stirring speed of 500 rpm, filter, wash, and dry to obtain epoxy nano-silica, wherein the mass ratio of nano-silica, isopropanol, KH-570, and deionized water is 11:35:3.5:50;

[0075] A2. Add epoxy nano-silica to an ethanol-phytic acid aqueous solution, ultrasonically disperse at 55 °C for 40 min with an ultrasonic power of 110 W and an ultrasonic frequency of 48 kHz, dropwise add the surface modification solution over a period of 13 min. After the addition is complete, raise the temperature to 110 °C, stir for 2.5 h, filter, wash, and dry to obtain the modified nano-silica. Among them, the ethanol-phytic acid aqueous solution is composed of phytic acid, absolute ethanol, and deionized water with a mass ratio of 1.5:5:12, the surface modification solution is composed of tetraethylammonium bromide, 2-hydroxypyridine-3-carboxylic acid, and absolute ethanol with a mass ratio of 0.15:2.5:18, and the mass ratio of the ethanol-phytic acid aqueous solution, epoxy nano-silica, and the surface modification solution is 11:3.5:0.8.

[0076] A preparation method of a flame-retardant composite current collector includes the following steps:

[0077] S1. Add the modified polypropylene resin, reinforcing component, antioxidant, lubricant, coupling agent, and compatibilizer by weight parts to a high-speed mixer, mix at a speed of 700 rpm at room temperature for 50 min, and mix evenly to obtain a mixture;

[0078] S2. Add the mixture into a twin-screw extruder, heat it to 250 °C, after heating for 1.5 h, melt and extrude it, at a speed of 1.5 m / min and a temperature of 190 °C, cast and form it, and then stretch the formed material through a biaxial stretching process to form a base film layer with a thickness of 3 μm, where the stretching temperature is 123 °C, the stretching rate is 9 cm / s, the heat setting temperature is 220 °C, and the stretching ratio is 4:1;

[0079] S3. Sputter and deposit a copper film layer with a thickness of 3 μm on both sides of the base film layer, the sputtering power is 500 W, the sputtering voltage is 190 V, the sputtering temperature is 160 °C, the hot pressing and forming temperature is 150 °C, the pressure is 1.5 MPa, and the time is 2.5 min;

[0080] S4. Coating 5 μm of flame retardant coating on the surface of the copper film layer by using a slot die coater, drying at 55 °C for 2.5 h and curing at 135 °C for 0.8 h to obtain the flame retardant composite current collector;

[0081] The preparation method of the flame retardant coating is as follows: disperse the polymer matrix, modified nano-silica and additives in a solvent, stir and mix, control the temperature at 220 °C, the stirring speed at 350 rpm, and stir for 1.5 h to obtain the flame retardant coating.

[0082] Example 3

[0083] A flame retardant composite current collector is composed of a base film layer, a metal film layer deposited on both sides of the base film layer, and a flame retardant layer formed by curing a flame retardant coating coated on the surface of the metal film layer; the base film layer is made of the following raw materials in parts by weight: 120 parts of modified polypropylene resin, 15 parts of reinforcing component, 2 parts of antioxidant, 3 parts of lubricant, 3 parts of coupling agent, and 5 parts of compatibilizer; the flame retardant coating is made of the following raw materials in parts by weight: 12 parts of polymer matrix, 8 parts of modified nano-silica, 2 parts of additives, and 60 parts of solvent; among them, the reinforcing component is composed of nano-montmorillonite and aramid fiber with a mass ratio of 4:1, the antioxidant is antioxidant 1010, the lubricant is zinc stearate, the coupling agent is γ-aminopropyltriethoxysilane, the compatibilizer is maleic anhydride grafted polypropylene, the polymer matrix is polyurethane, the additive is dimethyl silicone oil, and the solvent is N-methylpyrrolidone.

[0084] Among them, the preparation of the modified polypropylene resin includes the following steps:

[0085] (1) Place polypropylene and fluorinated ethylene propylene copolymer with a mass ratio of 10:3 in a twin-screw extruder, the working temperature is 220 °C, and knead for 2 h to obtain intermediate 1;

[0086] (2) Add liquid crystal polymer to intermediate 1, control the mass ratio of intermediate 1 to liquid crystal polymer to be 6:1, the working temperature is 250 °C, knead for 3 h, and after extrusion granulation and cooling, obtain intermediate 2;

[0087] (3) Disperse Intermediate 2 in toluene, heat to 100 °C, stir while heating, with a stirring speed of 400 rpm and a stirring time of 20 min to obtain Solution A; wherein, the mass ratio of Intermediate 2 to toluene is 3:10. Dropwise add a toluene solution of 4-trifluoromethylbenzoyl chloride with a mass concentration of 15% to Solution A, control the dropping time to 30 min, and continuously stir while controlling the temperature at 80 °C. Add pyridine, and control the mass ratio of Solution A, the toluene solution of 4-trifluoromethylbenzoyl chloride, and pyridine to be 100:20:1. React for 2 h, filter, wash, and dry at 80 °C to constant weight to obtain the modified polypropylene resin.

[0088] Among them, the preparation method of the modified nano-silica includes the following steps:

[0089] A1. Mix nano-silica, isopropanol, KH-570, and deionized water, and then ultrasonically disperse at an ultrasonic power of 100 W, an ultrasonic frequency of 50 kHz, and room temperature for 40 min. Then raise the temperature to 60 °C, stir and react for 5 h, with a stirring speed of 600 rpm. Filter, wash, and dry to obtain epoxy-group nano-silica, wherein the mass ratio of nano-silica, isopropanol, KH-570, and deionized water is 12:40:4:55;

[0090] A2. Add epoxy-group nano-silica to an ethanol-phytic acid aqueous solution, ultrasonically disperse at 60 °C for 50 min, with an ultrasonic power of 120 W and an ultrasonic frequency of 50 kHz. Dropwise add the surface modification solution, with a dropping time of 15 min. After the dropping is completed, raise the temperature to 120 °C, stir for 3 h, filter, wash, and dry to obtain the modified nano-silica. Among them, the ethanol-phytic acid aqueous solution is composed of phytic acid, absolute ethanol, and deionized water with a mass ratio of 2:7:15, and the surface modification solution is composed of tetraethylammonium bromide, 2-hydroxypyridine-3-carboxylic acid, and absolute ethanol with a mass ratio of 0.2:3:20. The mass ratio of the ethanol-phytic acid aqueous solution, epoxy-group nano-silica, and the surface modification solution is 12:4:1.

[0091] A preparation method of a flame-retardant composite current collector includes the following steps:

[0092] S1. Add the modified polypropylene resin, reinforcing component, antioxidant, lubricant, coupling agent, and compatibilizer by weight parts to a high-speed mixer, and mix at a speed of 800 rpm at room temperature for 60 min to obtain a uniformly mixed material;

[0093] S2. Add the mixture into a twin-screw extruder, heat it to 300 °C, after heating for 2 h, melt and extrude it, at a speed of 2 m / min and a temperature of 200 °C, cast and form it, then stretch the formed material through a biaxial stretching process to form a base film layer with a thickness of 5 μm, where the stretching temperature is 125 °C, the stretching rate is 10 cm / s, the heat setting temperature is 230 °C, and the stretching ratio is 4:1;

[0094] S3. Sputter and deposit a copper film layer with a thickness of 5 μm on both sides of the base film layer, the sputtering power is 550 W, the sputtering voltage is 200 V, the sputtering temperature is 180 °C, the hot pressing forming temperature is 180 °C, the pressure is 2 MPa, and the time is 3 min;

[0095] S4. Coating 6 μm of flame retardant coating on the surface of the copper film layer by using a slot die coater, drying at 60 °C for 3 h and curing at 150 °C for 1 h to obtain a flame retardant composite current collector;

[0096] The preparation method of the flame retardant coating is as follows: Disperse the polymer matrix, modified nano-silica and additives in a solvent, stir and mix, control the temperature at 230 °C, the stirring speed at 400 rpm, and stir for 2 h to obtain the flame retardant coating.

[0097] Comparative Example 1

[0098] A flame retardant composite current collector is composed of a base film layer, a metal film layer deposited on both sides of the base film layer, and a flame retardant layer formed by curing a flame retardant coating coated on the surface of the metal film layer; The base film layer is made of the following raw materials in parts by weight: 100 parts of modified polypropylene resin, 10 parts of reinforcing component, 0.5 part of antioxidant, 1 part of lubricant, 2 parts of coupling agent, and 3 parts of compatibilizer; The flame retardant coating is made of the following raw materials in parts by weight: 10 parts of polymer matrix, 6 parts of modified nano-silica, 1 part of additive, and 50 parts of solvent; Among them, the reinforcing component is composed of nano-montmorillonite and aramid fiber with a mass ratio of 5:1, the antioxidant is antioxidant 1010, the lubricant is zinc stearate, the coupling agent is γ-aminopropyltriethoxysilane, the compatibilizer is maleic anhydride grafted polypropylene, the polymer matrix is polyurethane, the additive is dimethyl silicone oil, and the solvent is N-methylpyrrolidone.

[0099] Among them, the preparation of the modified polypropylene resin includes the following steps:

[0100] (1) Place the polypropylene in a twin-screw extruder, the working temperature is 180 °C, and knead for 1.5 h to obtain Intermediate 1;

[0101] (2) Add liquid crystal polymer to Intermediate 1, control the mass ratio of Intermediate 1 to liquid crystal polymer to be 10:1, the working temperature is 230 °C, knead for 2 h, and after extrusion granulation and cooling, obtain Intermediate 2;

[0102] (3) Disperse Intermediate 2 in toluene, heat to 80 °C, stir while heating, with a stirring speed of 300 rpm and a stirring time of 10 min to obtain Solution A; wherein, the mass ratio of Intermediate 2 to toluene is 1:4. Dropwise add a toluene solution of 4-trifluoromethylbenzoyl chloride with a mass concentration of 12% to Solution A, control the dropping time to 15 min, while continuously stirring, control the temperature at 60 °C, add pyridine, and control the mass ratio of Solution A, the toluene solution of 4-trifluoromethylbenzoyl chloride, and pyridine to be 80:15:0.1. React for 1 h, filter, wash, and dry at 60 °C to constant weight to obtain the modified polypropylene resin.

[0103] Among them, the preparation method of the modified nano-silica includes the following steps:

[0104] A1. Mix nano-silica, isopropanol, KH-570, and deionized water, then ultrasonically disperse at a room temperature for 30 min with an ultrasonic power of 50 W and an ultrasonic frequency of 40 kHz, then heat up to 40 °C and stir and react for 4 h with a stirring speed of 400 rpm. Filter, wash, and dry to obtain epoxy-group nano-silica, wherein the mass ratio of nano-silica, isopropanol, KH-570, and deionized water is 10:30:3:45;

[0105] A2. Add epoxy-group nano-silica to an ethanol-phytic acid aqueous solution, ultrasonically disperse at 50 °C for 30 min with an ultrasonic power of 100 W and an ultrasonic frequency of 45 kHz, dropwise add the surface modification solution with a dropping time of 10 min. After the dropping is completed, heat up to 100 °C and stir for 2 h. Filter, wash, and dry to obtain the modified nano-silica, wherein the ethanol-phytic acid aqueous solution is composed of phytic acid, absolute ethanol, and deionized water with a mass ratio of 1:4:10, the surface modification solution is composed of tetraethylammonium bromide, 2-hydroxypyridine-3-carboxylic acid, and absolute ethanol with a mass ratio of 0.1:2:15, and the mass ratio of the ethanol-phytic acid aqueous solution, epoxy-group nano-silica, and the surface modification solution is 10:3:0.5.

[0106] A preparation method of a flame-retardant composite current collector includes the following steps:

[0107] S1. Add the modified polypropylene resin, reinforcing component, antioxidant, lubricant, coupling agent, and compatibilizer by weight parts to a high-speed mixer, mix at a speed of 600 rpm at room temperature for 45 min to obtain a mixed material;

[0108] S2. Add the mixed material to a twin-screw extruder, heat to 220 °C, after heating for 1 h, melt and extrude, at a speed of 1 m / min and a temperature of 180 °C, cast and form, and then stretch the formed material through a biaxial stretching process to form a base film layer with a thickness of 2 μm, wherein the stretching temperature is 120 °C, the stretching rate is 8 cm / s, the heat setting temperature is 210 °C, and the stretching ratio is 4:1;

[0109] S3. Sputter-deposit a copper film layer with a thickness of 1 μm on both sides of the base film layer, with a sputtering power of 480 W, a sputtering voltage of 180 V, a sputtering temperature of 150 °C, a hot pressing temperature of 120 °C, a pressure of 1 MPa, and a time of 2 min;

[0110] S4. Coating a 4-μm flame retardant coating on the surface of the copper film layer using a slot die coater, drying at 50 °C for 2 h and curing at 120 °C for 0.5 h to obtain a flame retardant composite current collector;

[0111] The preparation method of the flame retardant coating is as follows: Disperse the polymer matrix, modified nano-silica, and additives in a solvent, stir and mix, control the temperature at 200 °C, the stirring speed at 300 rpm, and stir for 1 h to obtain the flame retardant coating.

[0112] Comparative Example 2

[0113] A flame retardant composite current collector is composed of a base film layer, a metal film layer deposited on both sides of the base film layer, and a flame retardant layer formed by curing a flame retardant coating coated on the surface of the metal film layer; the base film layer is made of the following raw materials in parts by weight: 100 parts of modified polypropylene resin, 10 parts of reinforcing component, 0.5 part of antioxidant, 1 part of lubricant, 2 parts of coupling agent, and 3 parts of compatibilizer; the flame retardant coating is made of the following raw materials in parts by weight: 10 parts of polymer matrix, 6 parts of modified nano-silica, 1 part of additive, and 50 parts of solvent; wherein, the reinforcing component is composed of nano-montmorillonite and aramid fiber with a mass ratio of 5:1, the antioxidant is antioxidant 1010, the lubricant is zinc stearate, the coupling agent is γ-aminopropyltriethoxysilane, the compatibilizer is maleic anhydride grafted polypropylene, the polymer matrix is polyurethane, the additive is dimethyl silicone oil, and the solvent is N-methylpyrrolidone.

[0114] Among them, the preparation of the modified polypropylene resin includes the following steps:

[0115] (1) Place polypropylene and fluorinated ethylene propylene copolymer with a mass ratio of 5:1 in a twin-screw extruder, with a working temperature of 180 °C, and mix for 1.5 h to obtain Intermediate 1;

[0116] (2) Disperse Intermediate 1 in toluene, heat to 80 °C, stir while heating, with a stirring speed of 300 rpm and a stirring time of 10 min to obtain Solution A; wherein, the mass ratio of Intermediate 1 to toluene is 1:4. Dropwise add a toluene solution of 4-trifluoromethylbenzoyl chloride with a mass concentration of 12% to Solution A, control the dropping time to 15 min, continuously stir while controlling the temperature at 60 °C, add pyridine, and control the mass ratio of Solution A, the toluene solution of 4-trifluoromethylbenzoyl chloride, and pyridine to be 80:15:0.1, react for 1 h, filter, wash, and dry at 60 °C to constant weight to obtain the modified polypropylene resin.

[0117] Among them, the preparation method of the modified nano-silica includes the following steps:

[0118] A1. After mixing nano-silica, isopropanol, KH-570 and deionized water, ultrasonic treatment is carried out at a ultrasonic power of 50 W, an ultrasonic frequency of 40 kHz and room temperature for 30 min, then the temperature is raised to 40 °C, and stirring reaction is carried out for 4 h at a stirring speed of 400 rpm, followed by filtration, washing and drying to obtain epoxy-group nano-silica. Among them, the mass ratio of nano-silica, isopropanol, KH-570 and deionized water is 10:30:3:45;

[0119] A2. Add epoxy-group nano-silica to an ethanol-phytic acid aqueous solution, carry out ultrasonic dispersion at 50 °C for 30 min with an ultrasonic power of 100 W and an ultrasonic frequency of 45 kHz, dropwise add a surface modification solution with a dropping time of 10 min. After the dropping is completed, the temperature is raised to 100 °C and stirring is carried out for 2 h, followed by filtration, washing and drying to obtain the modified nano-silica. Among them, the ethanol-phytic acid aqueous solution is composed of phytic acid, absolute ethanol and deionized water with a mass ratio of 1:4:10, the surface modification solution is composed of tetraethylammonium bromide, 2-hydroxypyridine-3-carboxylic acid and absolute ethanol with a mass ratio of 0.1:2:15, and the mass ratio of the ethanol-phytic acid aqueous solution, epoxy-group nano-silica and the surface modification solution is 10:3:0.5.

[0120] A preparation method of a flame-retardant composite current collector includes the following steps:

[0121] S1. Add the modified polypropylene resin, reinforcing component, antioxidant, lubricant, coupling agent and compatibilizer by weight to a high-speed mixer, and mix at a speed of 600 rpm at room temperature for 45 min to obtain a mixed material;

[0122] S2. Add the mixed material to a twin-screw extruder, heat to 220 °C, heat for 1 h, then melt and extrude, and cast and form at a speed of 1 m / min and a temperature of 180 °C. Then, the formed material is stretched by a biaxial stretching process to form a base film layer with a thickness of 2 μm, where the stretching temperature is 120 °C, the stretching rate is 8 cm / s, the heat setting temperature is 210 °C, and the stretching ratio is 4:1;

[0123] S3. Sputter and deposit a copper film layer with a thickness of 1 μm on both sides of the base film layer, with a sputtering power of 480 W, a sputtering voltage of 180 V, a sputtering temperature of 150 °C, a hot pressing forming temperature of 120 °C, a pressure of 1 MPa, and a time of 2 min;

[0124] S4. Coating 4 μm of flame-retardant coating on the surface of the copper film layer by using a slot die coater, drying at 50 °C for 2 h and curing at 120 °C for 0.5 h to obtain the flame-retardant composite current collector;

[0125] The preparation method of the flame retardant coating is as follows: disperse the polymer matrix, modified nano-silica and additives in a solvent, stir and mix, control the temperature at 200 °C, the stirring speed at 300 rpm, and stir for 1 h to obtain the flame retardant coating.

[0126] Comparative Example 3

[0127] A flame retardant composite current collector is composed of a base film layer, metal film layers deposited on both sides of the base film layer, and a flame retardant layer formed by curing a flame retardant coating coated on the surface of the metal film layer; the base film layer is made of the following raw materials in parts by weight: 100 parts of modified polypropylene resin, 10 parts of reinforcing component, 0.5 part of antioxidant, 1 part of lubricant, 2 parts of coupling agent, and 3 parts of compatibilizer; the flame retardant coating is made of the following raw materials in parts by weight: 10 parts of polymer matrix, 6 parts of modified nano-silica, 1 part of additive, and 50 parts of solvent; wherein, the reinforcing component is composed of nano-montmorillonite and aramid fiber with a mass ratio of 5:1, the antioxidant is antioxidant 1010, the lubricant is zinc stearate, the coupling agent is γ-aminopropyltriethoxysilane, the compatibilizer is maleic anhydride grafted polypropylene, the polymer matrix is polyurethane, the additive is dimethyl silicone oil, and the solvent is N-methylpyrrolidone.

[0128] Among them, the preparation of the modified polypropylene resin includes the following steps:

[0129] (1) Place polypropylene and ethylene-tetrafluoroethylene copolymer with a mass ratio of 5:1 in a twin-screw extruder, the working temperature is 180 °C, and knead for 1.5 h to obtain Intermediate 1;

[0130] (2) Add liquid crystal polymer to Intermediate 1, control the mass ratio of Intermediate 1 to liquid crystal polymer to be 10:1, the working temperature is 230 °C, knead for 2 h, and after extrusion granulation and cooling, obtain Intermediate 2;

[0131] (3) Disperse Intermediate 2 in toluene, heat to 80 °C, stir while heating, the stirring speed is 300 rpm, and the stirring time is 10 min to obtain Solution A; wherein, the mass ratio of Intermediate 2 to toluene is 1:4, control the temperature at 60 °C, add pyridine, control the mass ratio of Solution A to pyridine to be 80:0.1, react for 1 h, filter, wash, and dry at 60 °C to constant weight to obtain the modified polypropylene resin.

[0132] Among them, the preparation method of the modified nano-silica includes the following steps:

[0133] A1. Mix nano-silica, isopropanol, KH-570 and deionized water, then under ultrasonic power of 50 W, ultrasonic frequency of 40 kHz and at room temperature, ultrasonic for 30 min, then heat up to 40 °C, stir and react for 4 h, with stirring speed of 400 rpm, filter, wash and dry to obtain epoxy-group nano-silica, where the mass ratio of nano-silica, isopropanol, KH-570 and deionized water is 10:30:3:45;

[0134] A2. Add epoxy-group nano-silica to ethanol-phytic acid aqueous solution, disperse by ultrasonic at 50 °C for 30 min, with ultrasonic power of 100 W and ultrasonic frequency of 45 kHz, dropwise add the surface modification solution, with dropping time of 10 min. After the dropping is completed, heat up to 100 °C, stir for 2 h, filter, wash and dry to obtain modified nano-silica, where the ethanol-phytic acid aqueous solution consists of phytic acid, absolute ethanol and deionized water with a mass ratio of 1:4:10, the surface modification solution consists of tetraethylammonium bromide, 2-hydroxypyridine-3-carboxylic acid and absolute ethanol with a mass ratio of 0.1:2:15, and the mass ratio of ethanol-phytic acid aqueous solution, epoxy-group nano-silica and surface modification solution is 10:3:0.5.

[0135] A method for preparing a flame-retardant composite current collector, comprising the following steps:

[0136] S1. Add modified polypropylene resin, reinforcing component, antioxidant, lubricant, coupling agent and compatibilizer by weight parts to a high-speed mixer, mix at a speed of 600 rpm at room temperature for 45 min to obtain a mixed material;

[0137] S2. Add the mixed material to a twin-screw extruder, heat to 220 °C, after heating for 1 h, melt and extrude, at a speed of 1 m / min and a temperature of 180 °C, cast and form, and then stretch the formed material through a biaxial stretching process to form a base film layer with a thickness of 2 μm, where the stretching temperature is 120 °C, the stretching rate is 8 cm / s, the heat setting temperature is 210 °C, and the stretching ratio is 4:1;

[0138] S3. Sputter-deposit a copper film layer with a thickness of 1 μm on both sides of the base film layer, with sputtering power of 480 W, sputtering voltage of 180 V, sputtering temperature of 150 °C, hot pressing forming temperature of 120 °C, pressure of 1 MPa and time of 2 min;

[0139] S4. Coating 4 μm of flame-retardant coating on the surface of the copper film layer by using a slot die coater, drying at 50 °C for 2 h and curing at 120 °C for 0.5 h to obtain the flame-retardant composite current collector;

[0140] The preparation method of the flame-retardant coating is as follows: Disperse the polymer matrix, modified nano-silica, and additives in a solvent, stir and mix them, control the temperature at 200 °C, the stirring speed at 300 rpm, and stir for 1 h to obtain the flame-retardant coating.

[0141] Comparative Example 4

[0142] A flame-retardant composite current collector is composed of a base film layer, metal film layers deposited on both sides of the base film layer, and a flame-retardant layer formed by curing a flame-retardant coating coated on the surface of the metal film layer; the base film layer is made of the following raw materials in parts by weight: 100 parts of modified polypropylene resin, 10 parts of reinforcing component, 0.5 part of antioxidant, 1 part of lubricant, 2 parts of coupling agent, and 3 parts of compatibilizer; the flame-retardant coating is made of the following raw materials in parts by weight: 10 parts of polymer matrix, 6 parts of modified nano-silica, 1 part of additive, and 50 parts of solvent; wherein, the reinforcing component is nano-montmorillonite, the antioxidant is antioxidant 1010, the lubricant is zinc stearate, the coupling agent is γ-aminopropyltriethoxysilane, the compatibilizer is maleic anhydride grafted polypropylene, the polymer matrix is polyurethane, the additive is dimethyl silicone oil, and the solvent is N-methylpyrrolidone.

[0143] Among them, the preparation of the modified polypropylene resin includes the following steps:

[0144] (1) Place polypropylene and ethylene-tetrafluoroethylene copolymer with a mass ratio of 5:1 in a twin-screw extruder, with the working temperature at 180 °C, and knead for 1.5 h to obtain Intermediate 1;

[0145] (2) Add liquid crystal polymer to Intermediate 1, control the mass ratio of Intermediate 1 to liquid crystal polymer at 10:1, with the working temperature at 230 °C, knead for 2 h, and then through extrusion granulation and cooling, obtain Intermediate 2;

[0146] (3) Disperse Intermediate 2 in toluene, heat to 80 °C, stir while heating, with the stirring speed at 300 rpm and the stirring time at 10 min to obtain Solution A; wherein, the mass ratio of Intermediate 2 to toluene is 1:4. Dropwise add a toluene solution of 4-trifluoromethylbenzoyl chloride with a mass concentration of 12% to Solution A, control the dropping time at 15 min, while continuously stirring, control the temperature at 60 °C, add pyridine, control the mass ratio of Solution A, the toluene solution of 4-trifluoromethylbenzoyl chloride, and pyridine at 80:15:0.1, react for 1 h, filter, wash, and dry at 60 °C to constant weight to obtain the modified polypropylene resin.

[0147] Among them, the preparation method of the modified nano-silica includes the following steps:

[0148] A1. Mix nano-silica, isopropanol, KH-570 and deionized water, then under an ultrasonic power of 50 W, an ultrasonic frequency of 40 kHz, and at room temperature, ultrasonic for 30 min. Then raise the temperature to 40 °C, stir and react for 4 h with a stirring speed of 400 rpm. Filter, wash, and dry to obtain epoxy-group nano-silica, where the mass ratio of nano-silica, isopropanol, KH-570 and deionized water is 10:30:3:45;

[0149] A2. Add epoxy-group nano-silica to an ethanol-phytic acid aqueous solution, disperse ultrasonically at 50 °C for 30 min with an ultrasonic power of 100 W and an ultrasonic frequency of 45 kHz. Dropwise add the surface modification solution over a period of 10 min. After the addition is complete, raise the temperature to 100 °C and stir for 2 h. Filter, wash, and dry to obtain modified nano-silica. The ethanol-phytic acid aqueous solution consists of phytic acid, absolute ethanol and deionized water with a mass ratio of 1:4:10. The surface modification solution consists of tetraethylammonium bromide, 2-hydroxypyridine-3-carboxylic acid and absolute ethanol with a mass ratio of 0.1:2:15. The mass ratio of the ethanol-phytic acid aqueous solution, epoxy-group nano-silica and the surface modification solution is 10:3:0.5.

[0150] A method for preparing a flame-retardant composite current collector, comprising the following steps:

[0151] S1. Add the modified polypropylene resin, reinforcing component, antioxidant, lubricant, coupling agent and compatibilizer by weight to a high-speed mixer and mix at a speed of 600 rpm at room temperature for 45 min to obtain a mixed material;

[0152] S2. Add the mixed material to a twin-screw extruder, heat to 220 °C, heat for 1 h, then melt and extrude, and cast and form at a speed of 1 m / min and a temperature of 180 °C. Then stretch the formed material through a biaxial stretching process to form a base film layer with a thickness of 2 μm, where the stretching temperature is 120 °C, the stretching rate is 8 cm / s, the heat setting temperature is 210 °C, and the stretching ratio is 4:1;

[0153] S3. Sputter-deposit a copper film layer with a thickness of 1 μm on both sides of the base film layer, with a sputtering power of 480 W, a sputtering voltage of 180 V, a sputtering temperature of 150 °C, a hot pressing forming temperature of 120 °C, a pressure of 1 MPa, and a time of 2 min;

[0154] S4. Coating 4 μm of flame-retardant coating on the surface of the copper film layer by using a slot die coater, drying at 50 °C for 2 h and curing at 120 °C for 0.5 h to obtain the flame-retardant composite current collector;

[0155] The preparation method of the flame retardant coating is as follows: The polymer matrix, modified nano-silica and additives are dispersed in a solvent, stirred and mixed. The temperature is controlled at 200 °C, the stirring speed is 300 rpm, and stirring is carried out for 1 h to obtain the flame retardant coating.

[0156] Comparative Example 5

[0157] A flame retardant composite current collector is composed of a base film layer, metal film layers deposited on both sides of the base film layer, and a flame retardant layer formed by curing a flame retardant coating coated on the surface of the metal film layer; the base film layer is made of the following raw materials in parts by weight: 100 parts of modified polypropylene resin, 10 parts of reinforcing component, 0.5 part of antioxidant, 1 part of lubricant, 2 parts of coupling agent, and 3 parts of compatibilizer; the flame retardant coating is made of the following raw materials in parts by weight: 10 parts of polymer matrix, 6 parts of modified nano-silica, 1 part of additive, and 50 parts of solvent; wherein, the reinforcing component is composed of nano-montmorillonite and aramid fiber with a mass ratio of 5:1, the antioxidant is antioxidant 1010, the lubricant is zinc stearate, the coupling agent is γ-aminopropyltriethoxysilane, the compatibilizer is maleic anhydride grafted polypropylene, the polymer matrix is polyurethane, the additive is dimethyl silicone oil, and the solvent is N-methylpyrrolidone.

[0158] Among them, the preparation of the modified polypropylene resin includes the following steps:

[0159] (1) Polypropylene and ethylene-tetrafluoroethylene copolymer with a mass ratio of 5:1 are placed in a twin-screw extruder, the working temperature is 180 °C, and mixing is carried out for 1.5 h to obtain Intermediate 1;

[0160] (2) Liquid crystal polymer is added to Intermediate 1, and the mass ratio of Intermediate 1 to the liquid crystal polymer is controlled at 10:1. The working temperature is 230 °C, and mixing is carried out for 2 h. After extrusion granulation and cooling, Intermediate 2 is obtained;

[0161] (3) Intermediate 2 is dispersed in toluene, heated to 80 °C, stirred while heating, the stirring speed is 300 rpm, and the stirring time is 10 min to obtain Solution A; wherein, the mass ratio of Intermediate 2 to toluene is 1:4. A toluene solution of 4-trifluoromethylbenzoyl chloride with a mass concentration of 12% is added dropwise to Solution A, the dropping time is controlled at 15 min, and stirring is continuously carried out while controlling the temperature at 60 °C. Pyridine is added, and the mass ratio of Solution A, the toluene solution of 4-trifluoromethylbenzoyl chloride, and pyridine is controlled at 80:15:0.1. The reaction is carried out for 1 h, filtered, washed, and dried at 60 °C to constant weight to obtain the modified polypropylene resin.

[0162] Among them, the preparation method of the modified nano-silica includes the following steps:

[0163] A1. Mix nano-silica, isopropanol, KH-570 and deionized water, and then ultrasonicate at a power of 50 W, a frequency of 40 kHz and room temperature for 30 min. Then raise the temperature to 40 °C and stir for 4 h at a stirring speed of 400 rpm. Filter, wash and dry to obtain epoxy-functionalized nano-silica. The mass ratio of nano-silica, isopropanol, KH-570 and deionized water is 10:30:3:45;

[0164] A2. Add epoxy-functionalized nano-silica to an ethanol aqueous solution, ultrasonically disperse at 50 °C for 30 min with a power of 100 W and a frequency of 45 kHz, and dropwise add the surface modification solution over 10 min. After the addition, raise the temperature to 100 °C and stir for 2 h. Filter, wash and dry to obtain modified nano-silica. The ethanol aqueous solution consists of absolute ethanol and deionized water with a mass ratio of 2:5, and the surface modification solution consists of tetraethylammonium bromide, 2-hydroxypyridine-3-carboxylic acid and absolute ethanol with a mass ratio of 0.1:2:15. The mass ratio of the ethanol aqueous solution, epoxy-functionalized nano-silica and the surface modification solution is 10:3:0.5.

[0165] A method for preparing a flame-retardant composite current collector, comprising the following steps:

[0166] S1. Add the modified polypropylene resin, reinforcing component, antioxidant, lubricant, coupling agent and compatibilizer by weight to a high-speed mixer and mix at a speed of 600 rpm at room temperature for 45 min to obtain a mixed material;

[0167] S2. Add the mixed material to a twin-screw extruder, heat to 220 °C, heat for 1 h, then melt and extrude, and cast into a film at a speed of 1 m / min and a temperature of 180 °C. Then stretch the formed material by a biaxial stretching process to form a base film layer with a thickness of 2 μm, where the stretching temperature is 120 °C, the stretching rate is 8 cm / s, the heat setting temperature is 210 °C, and the stretching ratio is 4:1;

[0168] S3. Sputter-deposit a copper film layer with a thickness of 1 μm on both sides of the base film layer, with a sputtering power of 480 W, a sputtering voltage of 180 V, a sputtering temperature of 150 °C, a hot pressing temperature of 120 °C, a pressure of 1 MPa and a time of 2 min;

[0169] S4. Coating 4 μm of flame-retardant coating on the surface of the copper film layer by a slot die coater, drying at 50 °C for 2 h and curing at 120 °C for 0.5 h to obtain the flame-retardant composite current collector;

[0170] The preparation method of the flame-retardant coating is: disperse the polymer matrix, modified nano-silica and additives in a solvent, stir and mix, control the temperature at 200 °C, the stirring speed at 300 rpm, and stir for 1 h to obtain the flame-retardant coating.

[0171] Comparative Example 6

[0172] A flame-retardant composite current collector is composed of a base film layer, metal film layers deposited on both sides of the base film layer, and a flame-retardant layer formed by curing a flame-retardant coating applied on the surface of the metal film layer; the base film layer is made of the following raw materials in parts by weight: 100 parts of modified polypropylene resin, 10 parts of reinforcing component, 0.5 part of antioxidant, 1 part of lubricant, 2 parts of coupling agent, and 3 parts of compatibilizer; the flame-retardant coating is made of the following raw materials in parts by weight: 10 parts of polymer matrix, 6 parts of modified nano-silica, 1 part of auxiliary agent, and 50 parts of solvent; wherein, the reinforcing component is composed of nano-montmorillonite and aramid fiber with a mass ratio of 5:1, the antioxidant is antioxidant 1010, the lubricant is zinc stearate, the coupling agent is γ-aminopropyltriethoxysilane, the compatibilizer is maleic anhydride grafted polypropylene, the polymer matrix is polyurethane, the auxiliary agent is dimethyl silicone oil, and the solvent is N-methylpyrrolidone.

[0173] Among them, the preparation of the modified polypropylene resin includes the following steps:

[0174] (1) Polypropylene and ethylene-tetrafluoroethylene copolymer with a mass ratio of 5:1 are placed in a twin-screw extruder, the working temperature is 180 °C, and they are kneaded for 1.5 h to obtain Intermediate 1;

[0175] (2) Liquid crystal polymer is added to Intermediate 1, and the mass ratio of Intermediate 1 to the liquid crystal polymer is controlled to be 10:1. The working temperature is 230 °C, and they are kneaded for 2 h. After extrusion granulation and cooling, Intermediate 2 is obtained;

[0176] (3) Intermediate 2 is dispersed in toluene, heated to 80 °C, stirred while heating, the stirring speed is 300 rpm, and the stirring time is 10 min to obtain Solution A; wherein, the mass ratio of Intermediate 2 to toluene is 1:4. A toluene solution of 4-trifluoromethylbenzoyl chloride with a mass concentration of 12% is added dropwise to Solution A, the dropping time is controlled for 15 min, and stirring is continued while controlling the temperature at 60 °C. Pyridine is added, and the mass ratio of Solution A, the toluene solution of 4-trifluoromethylbenzoyl chloride, and pyridine is controlled to be 80:15:0.1. The reaction is carried out for 1 h, filtered, washed, and dried at 60 °C to constant weight to obtain the modified polypropylene resin.

[0177] Among them, the preparation method of the modified nano-silica includes the following steps:

[0178] A1. Mix nano-silica, isopropanol, KH-570 and deionized water, and then under an ultrasonic power of 50 W, an ultrasonic frequency of 40 kHz, and at room temperature, ultrasonic for 30 min. Then, heat up to 40 °C and stir for reaction for 4 h at a stirring speed of 400 rpm. Filter, wash, and dry to obtain epoxy-functionalized nano-silica, where the mass ratio of nano-silica, isopropanol, KH-570 and deionized water is 10:30:3:45;

[0179] A2. Add epoxy-functionalized nano-silica to an ethanol-phytic acid aqueous solution, disperse ultrasonically at 50 °C for 30 min with an ultrasonic power of 100 W and an ultrasonic frequency of 45 kHz, filter, wash, and dry to obtain modified nano-silica, where the ethanol-phytic acid aqueous solution is composed of phytic acid, absolute ethanol and deionized water with a mass ratio of 1:4:10, and the mass ratio of the ethanol-phytic acid aqueous solution to epoxy-functionalized nano-silica is 3:10.

[0180] A method for preparing a flame-retardant composite current collector, comprising the following steps:

[0181] S1. Add the modified polypropylene resin, reinforcing component, antioxidant, lubricant, coupling agent and compatibilizer by weight to a high-speed mixer and mix at a speed of 600 rpm at room temperature for 45 min to obtain a mixed material;

[0182] S2. Add the mixed material to a twin-screw extruder, heat to 220 °C, after heating for 1 h, melt and extrude, at a speed of 1 m / min and a temperature of 180 °C, cast and form, and then stretch the formed material through a biaxial stretching process to form a base film layer with a thickness of 2 μm, where the stretching temperature is 120 °C, the stretching rate is 8 cm / s, the heat setting temperature is 210 °C, and the stretching ratio is 4:1;

[0183] S3. Sputter-deposit a copper film layer with a thickness of 1 μm on both sides of the base film layer, with a sputtering power of 480 W, a sputtering voltage of 180 V, a sputtering temperature of 150 °C, a hot pressing forming temperature of 120 °C, a pressure of 1 MPa, and a time of 2 min;

[0184] S4. Coating 4 μm of flame-retardant coating on the surface of the copper film layer by using a slot die coater, drying at 50 °C for 2 h and curing at 120 °C for 0.5 h to obtain the flame-retardant composite current collector;

[0185] The preparation method of the flame-retardant coating is: disperse the polymer matrix, modified nano-silica and additives in a solvent, stir and mix, control the temperature at 200 °C, the stirring speed at 300 rpm, and stir for 1 h to obtain the flame-retardant coating.

[0186] Performance testing

[0187] The comprehensive properties of the flame-retardant composite current collectors prepared in Examples 1-3 and Comparative Examples 1-6 of the present application are as follows:

[0188] Tensile strength and elongation at break: Referring to the standard ASTM D882-12 "Standard Test Method for Tensile Properties of Thin Films and Sheets", a universal tensile testing machine was used to test the tensile strength and elongation at break of the current collector;

[0189] Heat aging performance test: The flame-retardant composite current collector was placed in hot air at 80 °C and a relative humidity of 50% for artificial accelerated aging for 168 h. After cooling to room temperature, the longitudinal tensile strength was measured, and the heat aging performance was evaluated by the retention rate of the longitudinal tensile strength. The larger the value, the better the heat aging performance;

[0190] Flame retardancy test: Test was carried out according to the national standard GB / T 2406.2-2009 "Plastics - Determination of burning behavior by the oxygen index method - Part 2: Ambient temperature test". The larger the limiting oxygen index, the better the flame retardancy;

[0191] Peel strength test: The tape was evenly attached to the steel plate, the sample (i.e., the flame-retardant composite current collector) was fixed to the tape, an auxiliary tape was attached to the surface of the sample, and the steel plate and the auxiliary tape were fixed to a constant-speed tensile machine to start the test, and the peel strength of each sample was recorded;

[0192] The specific test results are shown in Table 1 below.

[0193] Table 1 Performance parameters of the flame-retardant composite current collectors in Examples 1-3 and Comparative Examples 1-6

[0194]

[0195]

[0196] As can be seen from Table 1, the flame-retardant composite current collector prepared in the present application has excellent flame retardancy, excellent mechanical properties and heat aging performance, large peel strength, and a firm bonding force between the metal film layer and the base film layer, effectively improving the quality and safety of the composite current collector.

[0197] This specific embodiment is only an explanation of the present application and does not limit the present application. Those skilled in the art can make modifications without creative contributions to this embodiment according to needs after reading this specification, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A flame-retardant composite current collector, characterized in that, The flame-retardant composite current collector is composed of a base film layer, metal film layers deposited on both sides of the base film layer, and a flame-retardant layer formed by curing a flame-retardant coating applied on the surface of the metal film layers; the base film layer is made of the following raw materials in parts by weight: 100-120 parts of modified polypropylene resin, 10-15 parts of reinforcing component, 0.5-2 parts of antioxidant, 1-3 parts of lubricant, 2-3 parts of coupling agent, and 3-5 parts of compatibilizer; the flame-retardant coating is made of the following raw materials in parts by weight: 10-12 parts of polymer matrix, 6-8 parts of modified nano-silica, 1-2 parts of auxiliary agent, and 50-60 parts of solvent; Among them, the preparation of the modified polypropylene resin includes the following steps: (1) Place polypropylene and fluorinated ethylene propylene copolymer in a twin-screw extruder, with the working temperature of 180-220 °C, and knead for 1.5-2 h to obtain intermediate 1; (2) Add liquid crystal polymer to intermediate 1, with the working temperature of 230-250 °C, knead for 2-3 h, and after extrusion granulation and cooling, obtain intermediate 2; (3) Disperse intermediate 2 in toluene, heat to 80-100 °C, stir while heating to obtain solution A, dropwise add 4-trifluoromethylbenzoyl chloride toluene solution to solution A, continuously stir while controlling the temperature at 60-80 °C, add pyridine, react for 1-2 h, filter, wash, and dry to obtain modified polypropylene resin; The reinforcing component is composed of nano-montmorillonite and aramid fiber with a mass ratio of 5-8:1-2; The preparation method of the modified nano-silica includes the following steps: A1. Ultrasonically mix nano-silica, isopropanol, KH-570, and deionized water, heat up to 40-60 °C, stir and react for 4-5 h, filter, wash, and dry to obtain epoxy-group nano-silica; A2. Add epoxy-group nano-silica to ethanol-phytic acid aqueous solution, ultrasonically disperse at 50-60 °C for 30-50 min, dropwise add the surface modification solution, after the dropping is completed, heat up to 100-120 °C, stir for 2-3 h, filter, wash, and dry to obtain modified nano-silica.

2. The flame-retardant composite current collector according to claim 1, wherein In the step (1), the mass ratio of polypropylene to fluorinated ethylene propylene copolymer is 15-20:3-6; in the step (2), the mass ratio of intermediate 1 to liquid crystal polymer is 10-12:1-2; in the step (3), the mass ratio of intermediate 2 to toluene is 2-3:8-10; in the step (3), the mass concentration of 4-trifluoromethylbenzoyl chloride toluene solution is 12-15%; in the step (3), the mass ratio of solution A, 4-trifluoromethylbenzoyl chloride toluene solution, and pyridine is 80-100:15-20:0.1-1.

3. The flame-retardant composite current collector according to claim 1, wherein The preparation method of the flame-retardant coating is: disperse the polymer matrix, modified nano-silica, and auxiliary agent in the solvent, stir and mix, control the temperature at 200-230 °C, the stirring speed at 300-400 rpm, and stir for 1-2 h to obtain the flame-retardant coating.

4. The flame-retardant composite current collector according to claim 1, characterized in that, In the step A1, the mass ratio of nano-silica, isopropanol, KH-570 and deionized water is 10-12:30-40:3-4:45-55; in the step A2, the ethanol-phytic acid aqueous solution is composed of phytic acid, absolute ethanol and deionized water with a mass ratio of 1-2:4-7:10-15; in the step A2, the surface modification liquid is composed of tetraethylammonium bromide, 2-hydroxypyridine-3-carboxylic acid and absolute ethanol with a mass ratio of 0.1-0.2:2-3:15-20, and in the step A2, the mass ratio of the ethanol-phytic acid aqueous solution, epoxy nano-silica and the surface modification liquid is 10-12:3-4:0.5-1.

5. The preparation method of the flame-retardant composite current collector according to any one of claims 1-4, characterized in that, It includes the following preparation steps: S1. Add the modified polypropylene resin, reinforcing component, antioxidant, lubricant, coupling agent and compatibilizer by weight parts into a high-speed mixer, and mix evenly to obtain a mixed material; S2. Add the mixed material into a twin-screw extruder for melt extrusion and cast molding, and then stretch the molded material through a biaxial stretching process to form a base film layer; S3. Deposit metal film layers on both sides of the base film layer and perform hot pressing molding; S4. Coating a 4-6 μm flame retardant coating on the surface of the metal film layer, and after drying and curing, obtain a flame retardant composite current collector.

6. The preparation method of the flame-retardant composite current collector according to claim 5, wherein, In the step S2, the casting molding speed is 1-2 m / min, and the casting molding temperature is 180-200 °C; in the step S2, the biaxial stretching process is that the stretching temperature is 120-125 °C, the stretching rate is 8-10 cm / s, the heat setting temperature is 210-230 °C, and the stretching ratio is 4:

1.

7. The preparation method of the flame-retardant composite current collector according to claim 5, characterized in that, In the step S2, the thickness of the base film layer is 2-5 μm; in the step S3, the hot pressing molding temperature is 120-180 °C, the pressure is 1-2 MPa, and the time is 2-3 min; in the step S4, the curing temperature is 120-150 °C, and the curing time is 0.5-1 h.

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