Current collector based on conductive polyimide film and application thereof

Abstract

The invention provides a current collector based on a conductive polyimide film and application thereof, and the current collector is obtained by mixing water-based polyamide acid or water-based polyimide with a conductive filler and then directly coating and curing to form a film or coating two side surfaces of a carrier film and then curing to form a film. According to the current collector based on the conductive polyimide film and the application of the current collector, the conductive polyimide film or the whole carrier film coated with the conductive polyimide film is directly used as the current collector, and the current collector has high heat resistance, low density and high conductivity of polyimide at the same time; and on the premise that the conductive metal film does not need to be deposited through expensive treatment such as evaporation, sputtering and the like, higher cycling stability can be shown.

Description

A current collector based on conductive polyimide film and its application Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a current collector based on a conductive polyimide film and its application. Background Technology

[0002] Current collectors are key auxiliary materials in lithium-ion batteries. Their main function is to conduct electricity, collecting the current generated by the active materials of the lithium-ion battery to form a larger current output, thereby converting chemical energy into electrical energy. In other words, current collectors act as both carriers of the positive and negative electrode active materials and electron collectors and conductors. Therefore, an ideal current collector often needs to possess comprehensive properties such as high conductivity, good stability, good mechanical strength, and low degree of hydrolysis.

[0003] Currently, commercially available lithium-ion batteries typically use aluminum foil as the positive electrode current collector and copper foil as the negative electrode current collector. In a lithium-ion battery system, from a mass breakdown perspective, the current collector accounts for approximately 15% of the mass, with copper foil accounting for about 8% and aluminum foil about 7%. From a cost breakdown perspective, the current collector accounts for approximately 10% of the cost, with copper foil accounting for about 9% and aluminum foil about 1%. Therefore, research on modifying aluminum and copper foil current collectors to achieve thinner and lighter designs can significantly optimize lithium-ion battery technology.

[0004] Composite current collectors are a novel type of current collector material with a "sandwich" structure. The support layer typically uses a polymer insulating resin such as PET (polyethylene terephthalate), PP (polypropylene), or PI (polyimide) as a thin film substrate. Then, a metal layer, such as a copper foil layer, is fabricated on the surface of the thin film substrate using methods such as magnetron sputtering, vacuum evaporation, electroplating, or a combination of these processes, forming the composite current collector's sandwich structure. Compared to traditional all-metal current collectors, composite current collectors offer advantages such as higher energy density and lower metal content. Therefore, composite current collectors replacing traditional metal current collectors has become a current trend in battery development.

[0005] While composite current collectors offer certain advantages over traditional all-metal current collectors, they still have shortcomings. Specifically, in the interaction between the metal layer and the support layer, poor adhesion between the metal layer and the base film support layer often affects the performance and lifespan of the composite current collector. Therefore, improvements are still needed to enhance the adhesion between the support layer and the metal layer. Existing technologies have proposed methods to strengthen the bond between the support layer and the metal layer, such as adding an adhesion-enhancing layer between the base film support layer and the metal layer, by adding copper alloy layers, aluminum alloy layers, or other types of adhesion-enhancing layers to strengthen the adhesion between the base film support layer and the metal layer. However, it is worth noting that the process for realizing this structure is relatively complex, requiring numerous and expensive equipment, which is not conducive to the large-scale production of composite current collectors. Furthermore, the additional adhesion-enhancing layer can easily lead to an increase in the total thickness of the composite copper foil while achieving the same performance, thus weakening the advantages of composite current collectors compared to traditional all-metal current collectors. Summary of the Invention

[0006] Based on the technical problems existing in the background art, the present invention proposes a current collector based on conductive polyimide film and its application. The conductive polyimide film or the entire carrier film coated with conductive polyimide film is directly used as the current collector. Since it has the high heat resistance, low density and high conductivity of polyimide at the same time, it can exhibit higher cycle stability without the need for expensive processes such as evaporation and sputtering to deposit conductive metal film.

[0007] The present invention proposes a current collector based on a conductive polyimide film, which is obtained by mixing aqueous polyamic acid or aqueous polyimide with conductive filler and then directly coating and curing it into a film or coating it onto both sides of a carrier film and then curing it into a film.

[0008] In this invention, waterborne polyamic acid or waterborne polyimide is used as the current collector film substrate. On the one hand, this reduces the use of organic solvents and solves environmental problems. On the other hand, it can exhibit higher cycle stability without the need for expensive processes such as evaporation and sputtering to deposit conductive metal films.

[0009] Preferably, the aqueous polyamic acid or aqueous polyimide is obtained by polycondensation reaction of dianhydride or diamine.

[0010] Preferably, the diamine is at least one selected from p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenyl ether, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 2,2'-dichloro-4,4'-diaminobiphenyl, 4,4'-diaminodiphenyl sulfone, 3,4-diaminobenzoic acid, 3,5-diaminobenzoic acid, 3,5-diamino-4-methylbenzoic acid, 2,5-diaminobenzenesulfonic acid, 2,4-diaminobenzenesulfonic acid, 4,4'-diaminodiphenyl ether-2,2'-disulfonic acid, 4,4'-diaminobenzophenone-2,2'-disulfonic acid, or 4,4'-diamino-2,2'-biphenyldisulfonic acid.

[0011] Preferably, the dianhydride is at least one selected from pyromellitic dianhydride, 4,4'-(hexafluoroisopropene) dianhydride, 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, or 3,3',4,4'-biphenyltetracarboxylic dianhydride.

[0012] Preferably, the conductive filler is at least one of carbon black, carbon nanotubes, graphene, or silver nanowires, and more preferably single-walled carbon nanotubes.

[0013] Preferably, the conductive filler is a tertiary amine-modified conductive filler, which is obtained by reacting the conductive filler with a mercaptosilane coupling agent to undergo a mercaptosilane reaction, and then reacting it with a tertiary amine acrylate; preferably, the mercaptosilane coupling agent is at least one of mercaptopropyltrimethoxysilane, mercaptopropyltriethoxysilane, mercaptopropylmethyldimethoxysilane, mercaptopropylmethyldiethoxysilane or mercaptomethylmethyldiethoxysilane, and the tertiary amine acrylate is at least one of dimethylaminoethyl methacrylate, dimethylaminoethyl acrylate or morpholine ethyl methacrylate.

[0014] In this invention, the conductive filler is an inorganic micro / nano filler. To enhance its compatibility with waterborne polyamic acid or waterborne polyimide, the conductive filler is reacted with a mercaptosilane coupling agent to graft mercapto groups onto its surface. Subsequently, it undergoes an addition reaction with tertiary amine acrylate to graft tertiary amine groups onto the surface of the conductive filler. Since the tertiary amine groups can undergo salt formation reactions with the carboxyl and sulfonic acid groups on the waterborne polyamic acid or waterborne polyimide, the dispersibility of the conductive filler in the polyimide resin can be effectively improved, resulting in a current collector with superior heat resistance and conductivity.

[0015] Preferably, the carrier membrane is a porous polyolefin membrane, more preferably a porous polyethylene membrane or a polypropylene membrane.

[0016] Preferably, the curing film-forming temperature is 150-250℃ and the time is 2-5h.

[0017] Preferably, the thickness of the current collector is 1-20 μm.

[0018] The present invention also proposes an application of the above-mentioned composite current collector in electrodes or lithium-ion batteries.

[0019] The beneficial effects of the present invention are as follows: The present invention proposes a current collector based on conductive polyimide film and its application, which replaces the technology of composite metal layers on the upper and lower sides of the base film as the current collector. On the one hand, it avoids the separation and detachment phenomenon between the base film layer and the metal layer due to insufficient bonding strength. On the other hand, the current collector also has good electrical conductivity, which can significantly reduce the mass of the current collector, thereby improving the energy density. Detailed Implementation

[0020] The technical solution of the present invention will be described in detail below through specific embodiments. However, it should be clearly stated that these embodiments are for illustrative purposes only and are not intended to limit the scope of the present invention.

[0021] Example 1

[0022] This embodiment proposes a current collector based on a conductive polyimide film, which is specifically prepared by the following method: (1) p-phenylenediamine is added to N-methylpyrrolidone and stirred until completely dissolved. Then, 3,3',4,4'-biphenyltetracarboxylic acid dianhydride with a molar amount equal to that of p-phenylenediamine is added and stirred until completely dissolved. The mixture is then stirred and reacted at room temperature for 6 hours to obtain a polyamic acid solution. Deionized water is then added to precipitate the solution. The solution is filtered, washed, and dried to obtain an aqueous polyamic acid solid powder. (2) The above aqueous polyamic acid solid powder is added to an ammonia solution (concentration of 2wt%) and dissolved until completely dissolved. Then, single-walled carbon nanotubes (average diameter of 1.5nm and average length of 10μm) are added and stirred until completely dispersed. The amount of single-walled carbon nanotubes added is the same as that added to the above solution. 5 wt% of the aqueous polyamic acid solid powder was used to obtain a conductive polyimide solution with a solid content of 10 wt%; (3) The polyethylene porous membrane (thickness of 6 μm and porosity of 40%) was immersed in N-methylpyrrolidone at 80°C for full wetting, and then fixed on a glass plate. The above conductive polyimide solution was scraped onto one side surface of the polypropylene porous membrane and quickly placed in a coagulation bath of room temperature water to complete the phase transformation. After drying at 80°C, the above conductive polyimide solution was flipped over and scraped onto the other side surface of the polypropylene porous membrane again. It was also placed in a coagulation bath of room temperature water to complete the phase transformation. After drying at 80°C, it was heated to 250°C for heat curing for 4 hours to obtain the current collector (thickness of 12 μm).

[0023] Example 2

[0024] This embodiment proposes a current collector based on a conductive polyimide film, which is specifically prepared by the following method: (1) 4,4'-diaminodiphenyl ether is added to N-methylpyrrolidone and stirred until completely dissolved. Then, 3,3',4,4'-biphenyltetracarboxylic acid dianhydride with a molar amount equal to that of 4,4'-diaminodiphenyl ether is added and stirred until completely dissolved. The mixture is then stirred and reacted at room temperature for 6 hours to obtain a polyamic acid solution. Deionized water is then added to precipitate the solution. The solution is filtered, washed, and dried to obtain an aqueous polyamic acid solid powder. (2) The above aqueous polyamic acid solid powder is added to a triethylamine aqueous solution (concentration of 3wt%) and dissolved until completely dissolved. Then, acetylene black (average particle size of 0.1μm) is added and stirred until completely dispersed. The amount of acetylene black added is the same as that added to the above solution. 25 wt% of the aqueous polyamic acid solid powder was used to obtain a conductive polyimide solution with a solid content of 10 wt%; (3) a polyethylene porous membrane (thickness of 6 μm and porosity of 40%) was immersed in N-methylpyrrolidone at 80°C for full wetting, and then fixed on a glass plate. The above conductive polyimide solution was scraped onto one side surface of the polypropylene porous membrane and quickly placed in a coagulation bath of room temperature water to complete the phase transformation. After drying at 80°C, the above conductive polyimide solution was flipped over and scraped onto the other side surface of the polypropylene porous membrane again. It was also placed in a coagulation bath of room temperature water to complete the phase transformation. After drying at 80°C, it was heated to 250°C for heat curing for 4 hours to obtain the current collector (thickness of 12 μm).

[0025] Example 3 This example proposes a current collector based on a conductive polyimide film, which is specifically prepared by the following method: (1) 4,4'-diaminodiphenyl sulfone is added to N-methylpyrrolidone and stirred until completely dissolved. Then, 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride with a molar amount equal to that of 4,4'-diaminodiphenyl sulfone is added and stirred until completely dissolved. The mixture is stirred and reacted at room temperature for 6 hours to obtain a polyamic acid solution. Then, deionized water is added to precipitate the solution. The solution is filtered, washed, and dried to obtain an aqueous polyamic acid solid powder; (2) The above aqueous polyamic acid solid powder is added to an ammonia solution (concentration of 2wt%) and dissolved until completely dissolved. Then, single-walled carbon nanotubes (average diameter of 1.5 nm and average length of 10 μm) are added and stirred until completely dispersed. The amount of nanotubes added is 5wt% of the above-mentioned aqueous polyamic acid solid powder, and a conductive polyimide solution with a solid content of 10wt% is obtained; (3) The polypropylene porous membrane (thickness of 6μm, porosity of 32%) is immersed in N-methylpyrrolidone at 80°C for full wetting, and then fixed on a glass plate. The above-mentioned conductive polyimide solution is scraped onto one side surface of the polypropylene porous membrane, and quickly placed in a coagulation bath of room temperature water to complete the phase transformation. After drying at 80°C, the above-mentioned conductive polyimide solution is flipped over and scraped onto the other side surface of the polypropylene porous membrane again. It is also placed in a coagulation bath of room temperature water to complete the phase transformation. After drying at 80°C, it is heated to 250°C for heat curing for 4h to obtain the current collector (thickness of 12μm).

[0026] Example 4 This example proposes a current collector based on a conductive polyimide film, specifically prepared by the following method: (1) 3,5-diaminobenzoic acid and p-phenylenediamine are added to N-methylpyrrolidone at a molar ratio of 1:3 and stirred until completely dissolved. Then, pyromellitic dianhydride equal to the total molar amount of 3,5-diaminobenzoic acid and p-phenylenediamine is added. Next, triethylamine equal to 20% of the total molar amount of 3,5-diaminobenzoic acid and p-phenylenediamine is added. After stirring until completely dissolved, the mixture is stirred and reacted at room temperature for 6 hours, and then heated to 180°C and stirred and reacted for 2 hours to obtain an aqueous polyimide solution with a solid content of 30 wt%; (2) Acetylene black (average particle size of 0.1 μm) is added to the above aqueous polyimide solution and stirred until completely dispersed. The addition of acetylene black... The amount is 10wt% of the above aqueous polyimide solution, and then pure water is added to obtain a conductive polyimide solution with a solid content of 10wt%; (3) The polyethylene porous membrane (thickness of 6μm, porosity of 40%) is immersed in N-methylpyrrolidone at 80℃ for full wetting, and then placed on a glass plate for fixation. The above conductive polyimide solution is scraped onto one side surface of the polypropylene porous membrane, and then quickly placed in a coagulation bath of room temperature water to complete the phase transformation. After drying at 80℃, the above conductive polyimide solution is flipped over and scraped onto the other side surface of the polypropylene porous membrane again. It is also placed in a coagulation bath of room temperature water to complete the phase transformation. After drying at 80℃, it is heated to 180℃ for heat curing for 2h to obtain the current collector (thickness of 12μm).

[0027] Example 5 This example proposes a current collector based on a conductive polyimide film, which is specifically prepared by the following method: (1) 4,4'-diaminobiphenyl-2,2'-dicarboxylic acid and 4,4'-diaminodiphenyl ether are added to N-methylpyrrolidone at a molar ratio of 1:3 and stirred until completely dissolved. Then, 4,4'-(hexafluoroisopropene) phthalic anhydride is added in a molar amount equal to the total molar amount of 4,4'-diaminobiphenyl-2,2'-dicarboxylic acid and 4,4'-diaminodiphenyl ether. Next, triethylamine is added in a molar amount equal to 20% of the total molar amount of 4,4'-diaminobiphenyl-2,2'-dicarboxylic acid and 4,4'-diaminodiphenyl ether. After stirring until completely dissolved, the mixture is stirred at room temperature for 6 hours and then heated to 180°C and stirred for 2 hours to obtain an aqueous polyimide solution with a solid content of 30wt%; (2) Single-walled carbon nanotubes (with an average diameter of 1.5 nm and an average length of 1.5 nm) are used to dissolve the current collector. Add the 10μm thick carbon nanotubes to the above aqueous polyimide solution and stir until completely dispersed. The amount of single-walled carbon nanotubes added is 3wt% of the above aqueous polyimide solution. Then add pure water to obtain a conductive polyimide solution with a solid content of 10wt%. (3) Immerse the polyethylene porous membrane (thickness of 6μm and porosity of 40%) in N-methylpyrrolidone at 80°C until fully wetted. Then place it on a glass plate for fixation. Scrape the above conductive polyimide solution onto one side surface of the polypropylene porous membrane. Quickly place it in a coagulation bath at room temperature to complete the phase transformation. After drying at 80°C, turn it over and scrape the above conductive polyimide solution onto the other side surface of the polypropylene porous membrane again. Similarly, place it in a coagulation bath at room temperature to complete the phase transformation. After drying at 80°C, heat it to 180°C for 2 hours to obtain the current collector (thickness of 12μm).

[0028] Example 6 This example proposes a current collector based on a conductive polyimide film, which is specifically prepared by the following method: (1) 2,5-diaminobenzenesulfonic acid and 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl are added to N-methylpyrrolidone at a molar ratio of 1:3 and stirred until completely dissolved. Then, 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride with a molar amount equal to the total molar amount of 2,5-diaminobenzenesulfonic acid and 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl is added. Then, 20% of the total molar amount of 2,5-diaminobenzenesulfonic acid and 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl is added. After stirring until completely dissolved, the mixture is stirred at room temperature for 6 hours and then heated to 180°C and stirred for 2 hours to obtain an aqueous polyimide solution with a solid content of 30wt%; (2) Single-walled carbon nanotubes (with an average diameter of 1. 5nm, average length of 10μm) is added to the above aqueous polyimide solution and stirred until completely dispersed. The amount of acetylene black added is 3wt% of the above aqueous polyimide solution. Then pure water is added to obtain a conductive polyimide solution with a solid content of 10wt%. (3) The polyethylene porous membrane (thickness of 6μm, porosity of 40%) is immersed in N-methylpyrrolidone at 80℃ for full wetting, and then placed on a glass plate for fixation. The above conductive polyimide solution is scraped onto one side surface of the polypropylene porous membrane and quickly placed in a coagulation bath of room temperature water to complete the phase transformation. After drying at 80℃, the above conductive polyimide solution is flipped over and scraped onto the other side surface of the polypropylene porous membrane again. It is also placed in a coagulation bath of room temperature water to complete the phase transformation. After drying at 80℃, it is heated to 180℃ for 2h for heat curing to obtain the current collector (thickness of 12μm).

[0029] Example 7 This example proposes a current collector based on a conductive polyimide film, which is specifically prepared by the following method: (1) 4,4'-diaminodiphenyl ether is added to N-methylpyrrolidone and stirred until completely dissolved. Then, 3,3',4,4'-biphenyltetracarboxylic acid dianhydride with a molar amount equal to that of 4,4'-diaminodiphenyl ether is added and stirred until completely dissolved. The mixture is then stirred and reacted at room temperature for 6 hours to obtain a polyamic acid solution. Deionized water is then added to precipitate the solution. The solution is filtered, washed, and dried to obtain an aqueous polyamic acid solid powder. Finally; (2) Dissolve the above-mentioned aqueous polyamic acid solid powder completely in triethylamine aqueous solution (concentration of 3wt%), then add tertiary amine-modified acetylene black and stir to disperse completely. The amount of tertiary amine-modified acetylene black added is 25wt% of the above-mentioned aqueous polyamic acid solid powder, to obtain a conductive polyimide solution with a solid content of 10wt%; add acetylene black (average particle size of 0.1μm) to ethanol and disperse evenly, then add mercaptopropyltriethoxysilane and ammonia. The amount of mercaptopropyltriethoxysilane added is 25wt% of the acetylene black. 20 wt% of black, the amount of ammonia added is 40 wt% of acetylene black, ultrasonically dispersed for 1 h, heated to 80 ℃ and stirred for 6 h, after distillation to remove ethanol, washed, dried, and then added back into ethanol and dispersed evenly, then added dimethylaminoethyl methacrylate, the amount of dimethylaminoethyl methacrylate added is 5 wt% of acetylene black, heated to 50 ℃ and stirred for 2 h to obtain tertiary amino-modified acetylene black; (3) the polyethylene porous membrane (thickness is 6 μm, porosity is 40%) was immersed in 80 ℃ The membrane is fully impregnated with N-methylpyrrolidone and then fixed on a glass plate. The conductive polyimide solution is then scraped onto one side of the polypropylene porous membrane and quickly placed in a coagulation bath at room temperature to complete the phase inversion. After drying at 80°C, the membrane is flipped over and the conductive polyimide solution is scraped onto the other side of the polypropylene porous membrane again. It is then placed in a coagulation bath at room temperature to complete the phase inversion. After drying at 80°C, it is heated to 250°C for heat curing for 4 hours to obtain the current collector (thickness of 12 μm).

[0030] Example 8 This example proposes a current collector based on a conductive polyimide film, specifically prepared by the following method: (1) 3,5-diaminobenzoic acid and p-phenylenediamine are added to N-methylpyrrolidone at a molar ratio of 1:3 and stirred until completely dissolved. Then, pyromellitic dianhydride equal to the total molar amount of 3,5-diaminobenzoic acid and p-phenylenediamine is added. Next, triethylamine equal to 20% of the total molar amount of 3,5-diaminobenzoic acid and p-phenylenediamine is added. After stirring until completely dissolved, the mixture is stirred and reacted at room temperature for 6 hours, and then heated to 180°C and stirred and reacted for 2 hours to obtain an aqueous polyimide solution with a solid content of 30 wt%; (2) The tertiary amine-modified acetylene black described in Example 7 is added to the above aqueous polyimide solution and stirred until completely dispersed. The addition of tertiary amine-modified acetylene black... The amount of water added is 10 wt% of the above aqueous polyimide solution, and then pure water is added to obtain a conductive polyimide solution with a solid content of 10 wt%; (3) The polyethylene porous membrane (thickness of 6 μm, porosity of 40%) is immersed in N-methylpyrrolidone at 80°C for full wetting, and then placed on a glass plate for fixation. The above conductive polyimide solution is scraped onto one side surface of the polypropylene porous membrane, and then quickly placed in a coagulation bath of room temperature water to complete the phase transformation. After drying at 80°C, the membrane is flipped over and the above conductive polyimide solution is scraped onto the other side surface of the polypropylene porous membrane again. It is also placed in a coagulation bath of room temperature water to complete the phase transformation. After drying at 80°C, it is heated to 180°C for heat curing for 2 hours to obtain the current collector (thickness of 12 μm).

[0031] Example 9 This example proposes a current collector based on a conductive polyimide film, specifically prepared by the following method: (1) 4,4'-diaminodiphenyl sulfone is added to N-methylpyrrolidone and stirred until completely dissolved. Then, 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride with a molar amount equal to that of 4,4'-diaminodiphenyl sulfone is added and stirred until completely dissolved. The mixture is then stirred at room temperature for 6 hours to obtain a polyamic acid solution. Deionized water is then added to precipitate the solution. The solution is filtered, washed, and dried to obtain an aqueous polyamic acid solid powder; (2) The above-mentioned aqueous polyamic acid solid powder was completely dissolved in an ammonia solution (concentration of 2 wt%), and then tertiary amine-modified single-walled carbon nanotubes were added and stirred until completely dispersed. The amount of tertiary amine-modified single-walled carbon nanotubes added was 5 wt% of the above-mentioned aqueous polyamic acid solid powder, resulting in a conductive polyimide solution with a solid content of 10 wt%. Single-walled carbon nanotubes (average diameter 1.5 nm, average length 10 μm) were added to ethanol and dispersed evenly, and then mercaptopropyltriethoxysilane and ammonia were added. The amount of mercaptopropyltriethoxysilane added was... 20 wt% of single-walled carbon nanotubes and 40 wt% of ammonia were added. After ultrasonic dispersion for 1 h, the temperature was raised to 80 °C and stirred for 6 h. After distillation to remove ethanol, the mixture was washed, dried, and then added back into ethanol and dispersed evenly. Dimethylaminoethyl methacrylate was added, with the amount of dimethylaminoethyl methacrylate being 5 wt% of the single-walled carbon nanotubes. The temperature was raised to 50 °C and stirred for 2 h to obtain tertiary amine-modified single-walled carbon nanotubes. (3) A polyethylene porous membrane (thickness 6 μm, porosity 40%) was soaked in water. The membrane is fully impregnated in N-methylpyrrolidone at 80°C, then fixed on a glass plate. The conductive polyimide solution is scraped onto one side of the porous polypropylene membrane and quickly placed in a coagulation bath at room temperature to complete the phase inversion. After drying at 80°C, the membrane is flipped over and the conductive polyimide solution is scraped onto the other side of the porous polypropylene membrane again. It is then placed in a coagulation bath at room temperature to complete the phase inversion. After drying at 80°C, it is heated to 250°C for 4 hours to heat-cur it, thus obtaining the current collector (12 μm thick).

[0032] Example 10 This example proposes a current collector based on a conductive polyimide film, which is specifically prepared by the following method: (1) 4,4'-diaminobiphenyl-2,2'-dicarboxylic acid and 4,4'-diaminodiphenyl ether are added to N-methylpyrrolidone at a molar ratio of 1:3 and stirred until completely dissolved. Then, 4,4'-(hexafluoroisopropene) phthalic anhydride is added in a molar amount equal to the total molar amount of 4,4'-diaminobiphenyl-2,2'-dicarboxylic acid and 4,4'-diaminodiphenyl ether. Next, 20% of the total molar amount of 4,4'-diaminobiphenyl-2,2'-dicarboxylic acid and 4,4'-diaminodiphenyl ether is added. After stirring until completely dissolved, the mixture is stirred at room temperature for 6 hours and then heated to 180°C and stirred for 2 hours to obtain an aqueous polyimide solution with a solid content of 30 wt%; (2) The tertiary amine-modified single-walled carbon nanotubes described in Example 9 are used. Add the above aqueous polyimide solution and stir until completely dispersed. The amount of tertiary amine-modified single-walled carbon nanotubes added is 3wt% of the above aqueous polyimide solution. Then add pure water to obtain a conductive polyimide solution with a solid content of 10wt%. (3) Immerse the polyethylene porous membrane (thickness of 6μm, porosity of 40%) in N-methylpyrrolidone at 80°C until fully wetted. Then place it on a glass plate for fixation. Scrape the above conductive polyimide solution onto one side surface of the polypropylene porous membrane. Quickly place it in a coagulation bath at room temperature to complete the phase transformation. After drying at 80°C, turn it over and scrape the above conductive polyimide solution onto the other side surface of the polypropylene porous membrane again. Similarly, place it in a coagulation bath at room temperature to complete the phase transformation. After drying at 80°C, heat it to 180°C for 2 hours to obtain the current collector (thickness of 12μm).

[0033] Example 11 This example proposes a current collector based on a conductive polyimide film, which is specifically prepared by the following method: (1) p-phenylenediamine is added to N-methylpyrrolidone and stirred until completely dissolved. Then, 3,3',4,4'-biphenyltetracarboxylic acid dianhydride with a molar amount equal to that of p-phenylenediamine is added and stirred until completely dissolved. The mixture is stirred and reacted at room temperature for 6 hours to obtain a polyamic acid solution. Then, deionized water is added to precipitate the solution. The solution is filtered, washed, and dried to obtain an aqueous polyamic acid solid powder; (2) The above aqueous polyimide film is used to precipitate the polyamic acid solution. The acid solid powder was dissolved completely in an ammonia solution (concentration of 2wt%), and then single-walled carbon nanotubes (average diameter of 1.5nm and average length of 10μm) were added and stirred to disperse completely. The amount of single-walled carbon nanotubes added was 5wt% of the above-mentioned aqueous polyamic acid solid powder, and a conductive polyimide solution with a solid content of 10wt% was obtained; (3) After casting the above-mentioned conductive polyimide solution into a film, it was dried at 80°C and then heated to 250°C for 4h to obtain the current collector (thickness of 12μm).

[0034] Example 12 This example proposes a current collector based on a conductive polyimide film, which is specifically prepared by the following method: (1) 3,5-diaminobenzoic acid and p-phenylenediamine are added to N-methylpyrrolidone at a molar ratio of 1:3 and stirred until completely dissolved. Then, pyromellitic dianhydride equal to the total molar amount of 3,5-diaminobenzoic acid and p-phenylenediamine is added. Next, triethylamine equal to 20% of the total molar amount of 3,5-diaminobenzoic acid and p-phenylenediamine is added. After stirring until completely dissolved, the mixture is stirred at room temperature for 6 hours and then heated to 180°C and stirred for 2 hours. (1) Aqueous polyimide with a solid content of 30wt% was obtained; (2) Single-walled carbon nanotubes (average diameter of 1.5nm and average length of 10μm) were added to the above polyimide resin solution and stirred until completely dispersed. The amount of single-walled carbon nanotubes added was 3wt% of the above polyimide resin solution. Pure water was then added to obtain a conductive polyimide solution with a solid content of 10wt%; (3) The above conductive polyimide solution was cast into a film, dried at 80°C, and then heated to 180°C for 2h for thermal curing to obtain the current collector (thickness of 12μm).

[0035] A negative electrode active material (graphite), conductive agent (Super P), thickener (sodium carboxymethyl cellulose), and binder (styrene-butadiene rubber) are mixed in a mass ratio of 95:2:1:2. Deionized water is added and stirred until homogeneous and stable to obtain a negative electrode slurry. The obtained negative electrode slurry is uniformly coated onto the current collector described in the example, air-dried at room temperature, dried at 120°C for 1 hour, cold-pressed, and slit to obtain a negative electrode sheet. A positive electrode active material (lithium cobalt oxide), binder (polyvinylidene fluoride PVDF), and conductive agent (acetylene black) are mixed in a mass ratio of 94:3:3. N-methylpyrrolidone (NMP) is added and stirred until homogeneous and stable to obtain a positive electrode slurry. The obtained positive electrode slurry is coated onto the surface of aluminum foil, dried, cold-pressed, and slit to obtain a positive electrode sheet. The negative electrode sheet and the separator (Celgard) are then combined. 2400), positive electrode sheets are stacked to obtain a cell. After the cell is placed in the packaging shell, an electrolyte (ethylene carbonate EC / dimethyl carbonate DMC / diethyl carbonate DEC = 1:1:1 of 1 mol / L LiPF6) is injected and sealed. After processes such as standing, compaction, formation, degassing and sealing, a lithium-ion battery is obtained.

[0036] Lithium-ion battery performance testing: At 25℃, the lithium-ion battery was first discharged at 1C to the lower limit of the charge / discharge cutoff voltage, then charged at 1C constant current to the upper limit of the charge / discharge cutoff voltage, and then charged at constant voltage to 0.05C; discharged at 1C constant current to the lower limit of the charge / discharge cutoff voltage, which constitutes one charge / discharge cycle. 500 cycles were performed using the above method. The discharge capacity of the lithium-ion battery at 25℃ for the 500th cycle was recorded, and the capacity retention rate (%) after 500 cycles at 25℃ was recorded as: discharge capacity of the 500th cycle / discharge capacity of the first cycle * 100%. The results are shown in Table 1 below. In addition, the electronic conductivity of the composite conductive film was measured using the four-probe method; the thermal stability of the current collector was tested by heating it from 25℃ to 800℃ at a rate of 10℃ / min.

[0037] Table 1 shows the performance of the current collectors described in the embodiments.

[0038] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A current collector based on a conductive polyimide film, characterized in that, It is obtained by mixing water-based polyamic acid or water-based polyimide with conductive filler, and then directly coating and curing it into a film or coating it onto both sides of a carrier film and then curing it into a film.

2. The current collector based on a conductive polyimide film according to claim 1, characterized in that, The aqueous polyamic acid or aqueous polyimide is obtained by polycondensation reaction of dianhydride or diamine.

3. The current collector based on a conductive polyimide film according to claim 2, characterized in that, The diamine is at least one of p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenyl ether, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 2,2'-dichloro-4,4'-diaminobiphenyl, 4,4'-diaminodiphenyl sulfone, 3,4-diaminobenzoic acid, 3,5-diaminobenzoic acid, 3,5-diamino-4-methylbenzoic acid, 2,5-diaminobenzenesulfonic acid, 2,4-diaminobenzenesulfonic acid, 4,4'-diaminodiphenyl ether-2,2'-disulfonic acid, 4,4'-diaminodibenzophenone-2,2'-disulfonic acid, or 4,4'-diamino-2,2'-biphenyldisulfonic acid.

4. The current collector based on a conductive polyimide film according to claim 2, characterized in that, The dianhydride is at least one of pyromellitic dianhydride, 4,4'-(hexafluoroisopropene) dianhydride, 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, or 3,3',4,4'-biphenyltetracarboxylic dianhydride.

5. The current collector based on a conductive polyimide film according to any one of claims 1-4, characterized in that, The conductive filler is at least one of carbon black, carbon nanotubes, graphene, or silver nanowires, preferably single-walled carbon nanotubes.

6. The current collector based on a conductive polyimide film according to any one of claims 1-5, characterized in that, The conductive filler is a tertiary amine-modified conductive filler, which is obtained by reacting the conductive filler with a mercaptosilane coupling agent to undergo a mercaptosilane reaction, and then reacting it with a tertiary amine acrylate. Preferably, the mercaptosilane coupling agent is at least one of mercaptopropyltrimethoxysilane, mercaptopropyltriethoxysilane, mercaptopropylmethyldimethoxysilane, mercaptopropylmethyldiethoxysilane, or mercaptomethylmethyldiethoxysilane, and the tertiary amine acrylate is at least one of dimethylaminoethyl methacrylate, dimethylaminoethyl acrylate, or morpholine ethyl methacrylate.

7. The current collector based on a conductive polyimide film according to any one of claims 1-6, characterized in that, The carrier membrane is a porous polyolefin membrane, preferably a porous polyethylene membrane or a polypropylene membrane.

8. The current collector based on a conductive polyimide film according to any one of claims 1-7, characterized in that, The curing temperature is 150-250℃, and the time is 2-5 hours.

9. The current collector based on a conductive polyimide film according to any one of claims 1-8, characterized in that, The thickness of the current collector is 1-20 μm.

10. The use of the current collector according to any one of claims 1-9 in an electrode or lithium-ion battery.

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