Composite conductive film for current collector and lithium ion battery

Abstract

This invention proposes a composite conductive film for current collectors and a lithium-ion battery. The composite conductive film includes a base film layer and conductive layers attached to both surfaces of the base film layer. The base film layer is a porous polyolefin membrane, and the conductive layers are composed of polyimide resin doped with conductive materials. This invention uses a porous polyolefin membrane as a substrate and then attaches a polyimide resin doped with conductive materials as a conductive layer to both surfaces of the porous polyolefin membrane. The resulting composite conductive film not only has a low density but also exhibits high thermal stability at this low density. Furthermore, it eliminates the need for expensive processes such as evaporation and sputtering to deposit conductive metal films, offering advantages such as low cost and simple process.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a composite conductive film for current collectors and a lithium-ion battery. Background Technology

[0002] Lithium-ion batteries possess a range of advantages, including high specific capacity, high operating voltage, good safety, and no memory effect, making them widely used in 3C products, power devices, and energy storage equipment. In recent years, with the increasing demands for miniaturization, lightweighting, multi-functionality, and long-duration operation in electronic products, automotive, and energy storage devices, the requirements for high energy density, high rate performance, and long cycle life in lithium-ion batteries have also been continuously rising.

[0003] As a crucial component of lithium-ion batteries, current collectors are indispensable electrode materials, playing a vital role in carrying active materials and collecting microcurrents. They can be categorized into traditional current collectors and composite current collectors. Traditional current collectors are simply the copper and aluminum foil used in lithium-ion batteries, often manufactured using calendering. Composite current collectors, on the other hand, have a "sandwich" structure. The inner layer is a polymer layer, such as polyethylene terephthalate (PET), polypropylene (PP), or polyethylene (PE), while the outer sides are metallic conductive layers (such as Al or Cu). Compared to traditional current collectors, composite current collectors based on polymer films offer advantages such as lower cost, lighter weight, and better internal insulation. These characteristics allow composite current collectors to reduce battery costs and improve energy density and safety when used in batteries.

[0004] However, composite current collectors have extremely high requirements for production technology and equipment, requiring a perfect combination of organic polymer materials and metal materials. Because polymer materials such as PET have high crystallinity, low polarity, and low surface energy, they will affect the bonding force between the metal coating and the substrate. Moreover, most polymer materials are non-conductive insulators and cannot be directly electroplated. The polymer materials must first be treated and activated to deposit a conductive metal film on their surface. This coating technology not only has relatively strict process requirements but also has relatively high production costs. Summary of the Invention

[0005] Based on the technical problems existing in the background art, the present invention proposes a composite conductive film for current collectors and a lithium-ion battery. The composite conductive film uses a polyolefin porous film as a substrate, and then attaches a polyimide resin doped with conductive material as a conductive layer to both sides of the polyolefin porous film. The resulting composite conductive film not only has a low density, but also has high thermal stability at a low density. At the same time, it does not require expensive processes such as evaporation and sputtering to deposit conductive metal films, and has the advantages of low cost and simple process.

[0006] The present invention proposes a composite conductive film for current collectors, comprising a base film layer and conductive layers attached to both sides of the base film layer. The base film layer is a polyolefin porous film, and the conductive layers are composed of polyimide resin doped with conductive substances.

[0007] In this invention, a polyolefin porous membrane is selected as the substrate, and a polyimide resin doped with conductive material is attached to the surface of the polyolefin porous membrane. This forms a conductive layer on the surface of the polyolefin porous membrane. The resulting composite conductive membrane not only has a low density, but also has high thermal stability at a low density, and has high application potential in lightweight and flexible electronic products.

[0008] Preferably, the polyolefin porous membrane is a biaxially or uniaxially stretched polyethylene or polypropylene porous membrane with a porosity of 20-60%.

[0009] Preferably, the conductive polymer is at least one of polypyrrole, polythiophene, or polyaniline; Preferably, the doping amount of the conductive polymer is 20-80 wt%.

[0010] Preferably, the polyimide resin is at least one of polyimide, polyamide-imide, or polyamide.

[0011] Preferably, the polyimide is obtained by polycondensation of diamine and dianhydride in a solvent; The diamine is at least one of the diamines shown in the following structural formulas: , , , , , , The dianhydride is at least one of the dianhydrides shown in the following structural formulas: , , , , .

[0012] Preferably, the polyamide-imide is obtained by polycondensation of trimellitic anhydride and diisocyanate in a solvent; The diisocyanate is at least one of the diisocyanates shown in the following structural formula: , , , , , .

[0013] Preferably, the polyamide is obtained by polycondensation of diacyl chloride and diamine in a solvent; The diacyl chloride is at least one of the diacyl chlorides shown in the following structural formula: , , , , The diamine is at least one of the diamines shown in the following structural formulas: , , , , , , , , .

[0014] Preferably, the polyimide, polyamide-imide, or polyamide further includes condensation of the polycondensation product with a pyrrole end-capping agent, a thiophene end-capping agent, or an aniline end-capping agent.

[0015] Preferably, the pyrrole end-capping agent is at least one of 1-aminopyrrole, 3-aminopyrrole, or 3-hydroxypyrrole; the thiophene end-capping agent is at least one of 3-aminothiophene, 3-hydroxythiophene, or 4-bromothiophene-3-amine; and the aniline end-capping agent is at least one of o-phenylenediamine, m-phenylenediamine, or p-phenylenediamine.

[0016] In this invention, by condensing the polycondensation product of the corresponding polyimide, polyamide-imide, or polyamide with a pyrrole-capping agent, a thiophene-capping agent, or an aniline-capping agent, a pyrrole-capping agent, a thiophene-capping agent, or an aniline-capping agent can be grafted onto the polyimide, polyamide-imide, or polyamide molecular chain. This enhances the affinity between the polypyrrole, polythiophene, or polyaniline conductive polymer and the polyimide resin, further improving the electrical conductivity and thermal stability of the resulting composite conductive film.

[0017] The present invention also proposes a lithium-ion battery, including an electrode sheet, wherein the electrode sheet includes the above-mentioned composite conductive film and an electrode active material loaded on the surface of the composite conductive film.

[0018] The beneficial effects of the present invention are as follows: The composite conductive film for current collectors described in the present invention has a low density, which can improve the energy density of lithium-ion batteries, reduce the internal resistance of the batteries, and improve the long-term cycle performance of lithium-ion batteries. Detailed Implementation

[0019] 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.

[0020] Example 1

[0021] This embodiment presents a composite conductive film for current collectors, which is specifically manufactured by the following method: (1) Under a nitrogen atmosphere, 4,4'-diaminodiphenyl ether and 4,4'-(hexafluoroisopropene) phthalic anhydride were added to N-methylpyrrolidone in a molar ratio of 1:1 and stirred until completely dissolved. Then, triethylamine was added, the amount of which was 10% of the molar amount of 4,4'-diaminodiphenyl ether. The mixture was heated to 180°C and stirred for 4 hours to obtain a polyimide resin solution with a solid content of 30 wt%. (2) Dissolve pyrrole in hydrochloric acid (concentration of 0.1 mol / L) and stir until completely dissolved in a 0℃ water bath to obtain a pyrrole solution. Dissolve ammonium persulfate in hydrochloric acid (concentration of 0.1 mol / L) and stir until uniformly dissolved in a 0℃ water bath to obtain an ammonium persulfate solution. Mix the pyrrole solution and the ammonium persulfate solution with a mass ratio of 1:3. After stirring and reacting thoroughly at room temperature, wash, filter, and dry to obtain polypyrrole powder. Add the polypyrrole powder to the above polyimide resin solution and stir until completely dispersed. The amount of polypyrrole powder added is 20 wt% of the above polyimide resin solution. Then add N-methylpyrrolidone to obtain a conductive polyimide solution with a solid content of 10 wt%. (3) The polypropylene porous membrane (thickness of 6 μm and porosity of 32%) was fully immersed in N-methylpyrrolidone at 80°C and then fixed on a glass plate. The above-mentioned conductive polyimide solution was scraped onto one side surface of the polypropylene porous membrane and quickly placed in a coagulation bath at room temperature to complete the phase transformation. After drying at 80°C, the membrane was flipped over and the above-mentioned conductive polyimide solution was scraped onto the other side surface of the polypropylene porous membrane again. It was also placed in a coagulation bath at room temperature to complete the phase transformation. After drying at 80°C, it was heated to 180°C for 2 hours to obtain the composite current collector (thickness of 12 μm).

[0022] Example 2

[0023] This embodiment presents a composite conductive film for current collectors, which is specifically manufactured by the following method: (1) Under a nitrogen atmosphere, 4,4'-diaminodiphenyl sulfone and 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride were added to N-methylpyrrolidone in a molar ratio of 1:1 and stirred until completely dissolved. Then, triethylamine was added, the amount of which was 10% of the molar amount of 4,4'-diaminodiphenyl sulfone. The mixture was heated to 180°C and stirred for 4 hours to obtain a polyimide resin solution with a solid content of 30 wt%. (2) Dissolve anhydrous ferric chloride in chloroform, add thiophene monomer, the amount of thiophene monomer added is 20 wt% of the mass of anhydrous ferric chloride, stir and react for 12 h in an ice-water bath under a nitrogen atmosphere, add acetone to terminate the reaction and remove acetone, wash with hydrochloric acid, acetone, anhydrous ethanol and deionized water in sequence to remove impurities, and vacuum dry to obtain polythiophene powder; add the polythiophene powder to the above polyimide resin solution and stir to disperse completely, the amount of polythiophene powder added is 20 wt% of the above polyimide resin solution, and then add N-methylpyrrolidone to obtain a conductive polyimide solution with a solid content of 10 wt%; (3) The polypropylene porous membrane (thickness of 6 μm and porosity of 32%) was fully immersed in N-methylpyrrolidone at 80°C and then fixed on a glass plate. The above-mentioned conductive polyimide solution was scraped onto one side surface of the polypropylene porous membrane and quickly placed in a coagulation bath at room temperature to complete the phase transformation. After drying at 80°C, the membrane was flipped over and the above-mentioned conductive polyimide solution was scraped onto the other side surface of the polypropylene porous membrane again. It was also placed in a coagulation bath at room temperature to complete the phase transformation. After drying at 80°C, it was heated to 180°C for 2 hours to obtain the composite current collector (thickness of 12 μm).

[0024] Example 3

[0025] This embodiment presents a composite conductive film for current collectors, which is specifically manufactured by the following method: (1) Under a nitrogen atmosphere, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl and 3,3',4,4'-biphenyltetracarboxylic acid dianhydride were added to N-methylpyrrolidone in a molar ratio of 1:1 and stirred until completely dissolved. Then, triethylamine was added, the amount of which was 10% of the molar amount of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl. The mixture was heated to 180°C and stirred for 4 hours to obtain a polyimide resin solution with a solid content of 30 wt%. (2) Dissolve aniline in hydrochloric acid (concentration of 1 mol / L) and stir until completely dissolved in a 0℃ water bath to obtain an aniline solution. Dissolve ammonium persulfate in hydrochloric acid (concentration of 1 mol / L) and stir until uniformly dissolved in a 0℃ water bath to obtain an ammonium persulfate solution. Mix the aniline solution and the ammonium persulfate solution, with a mass ratio of aniline to ammonium persulfate of 1:2.5. Stir the mixture thoroughly in a 0℃ water bath, then wash, filter, and dry to obtain polyaniline powder. Add the polyaniline powder to the above polyimide resin solution and stir until completely dispersed. The amount of polyaniline powder added is 15 wt% of the above polyimide resin solution. Then add N-methylpyrrolidone to obtain a conductive polyimide solution with a solid content of 10 wt%. (3) The polypropylene porous membrane (thickness of 6 μm and porosity of 32%) was fully immersed in N-methylpyrrolidone at 80°C and then fixed on a glass plate. The aforementioned conductive polyimide solution was scraped onto one side of the polypropylene porous membrane and quickly placed in a coagulation bath at room temperature to complete the phase transformation. After drying at 80°C, the membrane was flipped over and the aforementioned conductive polyimide solution was scraped onto the other side of the polypropylene porous membrane again. The membrane was then placed in a coagulation bath at room temperature to complete the phase transformation. After drying at 80°C, the membrane was heated to 180°C for 2 hours to obtain the composite current collector (thickness of 12 μm).

[0026] Example 4

[0027] This embodiment proposes a composite conductive film for current collectors, which is specifically made by the method described in Example 1. The difference is that in step (1), 4,4'-diaminodiphenyl ether and 4,4'-(hexafluoroisopropene) phthalic anhydride are added to N-methylpyrrolidone in a molar ratio of 1:1 and stirred until completely dissolved. Then, triethylamine is added, and the amount of triethylamine added is 10% of the molar amount of 4,4'-diaminodiphenyl ether. After heating to 180°C, the mixture is stirred and reacted for 2 hours. Then, 3-aminopyrrole is added, and the amount of 3-aminopyrrole added is 40% of the molar amount of 4,4'-diaminodiphenyl ether. After heating to 180°C, the mixture is stirred and reacted for 2 hours to obtain a polyimide resin solution with a solid content of 30 wt%.

[0028] Example 5

[0029] This embodiment proposes a composite conductive film for current collectors, which is specifically made by the method described in Example 2. The difference is that in step (1), 4,4'-diaminodiphenyl sulfone and 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride are added to N-methylpyrrolidone in a molar ratio of 1:1 and stirred until completely dissolved. Then, triethylamine is added, and the amount of triethylamine added is 10% of the molar amount of 4,4'-diaminodiphenyl sulfone. After heating to 180°C, the mixture is stirred and reacted for 2 hours. Then, 3-aminothiophene is added, and the amount of 3-aminothiophene added is 40% of the molar amount of 4,4'-diaminodiphenyl sulfone. After heating to 180°C, the mixture is stirred and reacted for 2 hours to obtain a polyimide resin solution with a solid content of 30 wt%.

[0030] Example 6

[0031] This embodiment proposes a composite conductive film for current collectors, which is specifically made by the method described in Example 3. The difference is that in step (1), 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl and 3,3',4,4'-biphenyltetracarboxylic acid dianhydride are added to N-methylpyrrolidone in a molar ratio of 1:1 and stirred until completely dissolved. Then, triethylamine is added, and the amount of triethylamine added is 10% of the molar amount of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl. The mixture is heated to 180°C and stirred for 2 hours. Then, o-phenylenediamine is added, and the amount of o-phenylenediamine added is 40% of the molar amount of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl. The mixture is heated to 180°C and stirred for 2 hours to obtain a polyimide resin solution with a solid content of 30 wt%.

[0032] Example 7

[0033] This embodiment proposes a composite conductive film for current collectors, which is specifically made by the method described in Example 1. The difference is that in step (2), the polypyrrole powder and single-walled carbon nanotubes (average diameter of 1.5 nm and average length of 10 μm) are added to the above polyimide resin solution and stirred until completely dispersed. The amount of polypyrrole powder added is 20 wt% of the above polyimide resin solution, and the amount of single-walled carbon nanotubes added is 1 wt% of the above polyimide resin solution. Then, N-methylpyrrolidone is added to obtain a conductive polyimide solution with a solid content of 10 wt%.

[0034] Example 8

[0035] This embodiment proposes a composite conductive film for current collectors, which is specifically made by the method described in Example 2. The difference is that in step (2), the polythiophene powder and single-walled carbon nanotubes (average diameter of 1.5 nm and average length of 10 μm) are added to the above polyimide resin solution and stirred until completely dispersed. The amount of polythiophene powder added is 20 wt% of the above polyimide resin solution, and the amount of single-walled carbon nanotubes added is 1 wt% of the above polyimide resin solution. Then, N-methylpyrrolidone is added to obtain a conductive polyimide solution with a solid content of 10 wt%.

[0036] Example 9

[0037] This embodiment presents a composite conductive film for current collectors, which is specifically manufactured by the following method: (1) Under a nitrogen atmosphere, trimellitic anhydride and 4,4'-diphenylmethane diisocyanate were added to N-methylpyrrolidone in a molar ratio of 1:1 and stirred until completely dissolved. Then, triethylamine was added, with the amount of triethylamine being 5% of the molar amount of trimellitic anhydride. The mixture was heated to 120°C and stirred for 6 hours to obtain a polyimide resin solution with a solid content of 30 wt%. (2) The polypyrrole powder described in Example 1 was added to the above polyimide resin solution and stirred until completely dispersed. The amount of polypyrrole powder added was 20 wt% of the above polyimide resin solution. Then N-methylpyrrolidone was added to obtain a conductive polyimide solution with a solid content of 10 wt%. (3) The polypropylene porous membrane (thickness of 6 μm and porosity of 32%) was fully immersed in N-methylpyrrolidone at 80°C and then fixed on a glass plate. The above-mentioned conductive polyimide solution was scraped onto one side surface of the polypropylene porous membrane and quickly placed in a coagulation bath at room temperature to complete the phase transformation. After drying at 80°C, the membrane was flipped over and the above-mentioned conductive polyimide solution was scraped onto the other side surface of the polypropylene porous membrane again. It was also placed in a coagulation bath at room temperature to complete the phase transformation. After drying at 80°C, it was heated to 180°C for 2 hours to obtain the composite current collector (thickness of 12 μm).

[0038] Example 10

[0039] This embodiment presents a composite conductive film for current collectors, which is specifically manufactured by the following method: (1) Under a nitrogen atmosphere, trimellitic anhydride and 4,4'-diphenylmethane diisocyanate were added to N-methylpyrrolidone in a molar ratio of 1:1 and stirred until completely dissolved. Then, triethylamine was added, the amount of which was 5% of the molar amount of trimellitic anhydride. The mixture was heated to 120°C and stirred for 3 hours. Then, 3-aminopyrrole was added, the amount of which was 40% of the molar amount of trimellitic anhydride. The mixture was heated to 120°C and stirred for 3 hours to obtain a polyimide resin solution with a solid content of 30 wt%. (2) The polypyrrole powder described in Example 1 was added to the above polyimide resin solution and stirred until completely dispersed. The amount of polypyrrole powder added was 20 wt% of the above polyimide resin solution. Then N-methylpyrrolidone was added to obtain a conductive polyimide solution with a solid content of 10 wt%. (3) The polypropylene porous membrane (thickness of 6 μm and porosity of 32%) was fully immersed in N-methylpyrrolidone at 80°C and then fixed on a glass plate. The above-mentioned conductive polyimide solution was scraped onto one side surface of the polypropylene porous membrane and quickly placed in a coagulation bath at room temperature to complete the phase transformation. After drying at 80°C, the membrane was flipped over and the above-mentioned conductive polyimide solution was scraped onto the other side surface of the polypropylene porous membrane again. It was also placed in a coagulation bath at room temperature to complete the phase transformation. After drying at 80°C, it was heated to 180°C for 2 hours to obtain the composite current collector (thickness of 12 μm).

[0040] Example 11

[0041] This embodiment presents a composite conductive film for current collectors, which is specifically manufactured by the following method: (1) Under a nitrogen atmosphere, 4,4'-diaminodiphenyl ether and terephthaloyl chloride were added to N-methylpyrrolidone in a molar ratio of 1:1 and stirred until completely dissolved. Then, triethylamine was added, the amount of which was 5% of the molar amount of 4,4'-diaminodiphenyl ether. The mixture was heated to 120°C and stirred for 6 hours to obtain a polyimide resin solution with a solid content of 30 wt%. (2) The polythiophene powder described in Example 2 was added to the above polyimide resin solution and stirred until completely dispersed. The amount of polythiophene powder added was 20 wt% of the above polyimide resin solution. Then N-methylpyrrolidone was added to obtain a conductive polyimide solution with a solid content of 10 wt%. (3) The polypropylene porous membrane (thickness of 6 μm and porosity of 32%) was fully immersed in N-methylpyrrolidone at 80°C and then fixed on a glass plate. The above-mentioned conductive polyimide solution was scraped onto one side surface of the polypropylene porous membrane and quickly placed in a coagulation bath at room temperature to complete the phase transformation. After drying at 80°C, the membrane was flipped over and the above-mentioned conductive polyimide solution was scraped onto the other side surface of the polypropylene porous membrane again. It was also placed in a coagulation bath at room temperature to complete the phase transformation. After drying at 80°C, it was heated to 180°C for 2 hours to obtain the composite current collector (thickness of 12 μm).

[0042] Example 12

[0043] This embodiment presents a composite conductive film for current collectors, which is specifically manufactured by the following method: (1) Under a nitrogen atmosphere, 4,4'-diaminodiphenyl ether and terephthaloyl chloride were added to N-methylpyrrolidone in a molar ratio of 1:1 and stirred until completely dissolved. Then, triethylamine was added, with the amount of triethylamine being 5% of the molar amount of 4,4'-diaminodiphenyl ether. The mixture was heated to 120°C and stirred for 3 hours. Then, 3-aminothiophene was added, with the amount of 3-aminothiophene being 40% of the molar amount of 4,4'-diaminodiphenyl ether. The mixture was heated to 120°C and stirred for 3 hours to obtain a polyimide resin solution with a solid content of 30 wt%. (2) The polythiophene powder described in Example 2 was added to the above polyimide resin solution and stirred until completely dispersed. The amount of polythiophene powder added was 20 wt% of the above polyimide resin solution. Then N-methylpyrrolidone was added to obtain a conductive polyimide solution with a solid content of 10 wt%. (3) The polypropylene porous membrane (thickness of 6 μm and porosity of 32%) was fully immersed in N-methylpyrrolidone at 80°C and then fixed on a glass plate. The above-mentioned conductive polyimide solution was scraped onto one side surface of the polypropylene porous membrane and quickly placed in a coagulation bath at room temperature to complete the phase transformation. After drying at 80°C, the membrane was flipped over and the above-mentioned conductive polyimide solution was scraped onto the other side surface of the polypropylene porous membrane again. It was also placed in a coagulation bath at room temperature to complete the phase transformation. After drying at 80°C, it was heated to 180°C for 2 hours to obtain the composite current collector (thickness of 12 μm).

[0044] Comparative Example 1 This comparative example presents a composite conductive film for current collectors, which is specifically manufactured by the following method: (1) Under a nitrogen atmosphere, 4,4'-diaminodiphenyl ether and 4,4'-(hexafluoroisopropene) phthalic anhydride were added to N-methylpyrrolidone in a molar ratio of 1:1 and stirred until completely dissolved. Then, triethylamine was added, the amount of which was 10% of the molar amount of 4,4'-diaminodiphenyl ether. The mixture was heated to 180°C and stirred for 4 hours to obtain a polyimide resin solution with a solid content of 30 wt%. (2) Add acetylene carbon black (average particle size of 0.1 μm) to the above polyimide resin solution and stir until completely dispersed. The amount of acetylene carbon black added is 10 wt% of the above polyimide resin solution. Then add N-methylpyrrolidone to obtain a conductive polyimide solution with a solid content of 10 wt%. (3) The polypropylene porous membrane (thickness of 6 μm and porosity of 32%) was fully immersed in N-methylpyrrolidone at 80°C and then fixed on a glass plate. The above-mentioned conductive polyimide solution was scraped onto one side surface of the polypropylene porous membrane and quickly placed in a coagulation bath at room temperature to complete the phase transformation. After drying at 80°C, the membrane was flipped over and the above-mentioned conductive polyimide solution was scraped onto the other side surface of the polypropylene porous membrane again. It was also placed in a coagulation bath at room temperature to complete the phase transformation. After drying at 80°C, it was heated to 180°C for 2 hours to obtain the composite current collector (thickness of 12 μm).

[0045] The performance of the composite conductive films for current collectors obtained in the examples and comparative examples was tested. The mechanical properties were tested, including tensile strength (refer to GB / T1040.3-2006) and elongation at break (refer to GB / T 1040.3-2006). The heat resistance was measured by the area change rate as a standard for stability. The films were placed in a forced-air drying oven at 150°C for 1 hour to test the thermal shrinkage. The performance of the composite conductive films for current collectors obtained in the examples and comparative examples was tested in lithium-ion batteries: A negative electrode active material (graphite), conductive agent (acetylene black), thickener (CMC-Na), and binder (SBR) are mixed in a mass ratio of 95.5:2:1:1.5. 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 composite current collector obtained in the examples or comparative examples. After drying, cold pressing, and slitting, a negative electrode sheet is obtained. A positive electrode active material (lithium iron phosphate), conductive agent (acetylene black), and positive electrode binder (polyvinylidene fluoride PVDF) are mixed in a mass ratio of 90:5:5. N-methylpyrrolidone is added and stirred until homogeneous and stable to obtain a positive electrode slurry. The obtained positive electrode slurry is uniformly coated onto aluminum foil. After drying, cold pressing, and slitting, a positive electrode sheet is obtained. The negative electrode sheet and the separator (Celgard) are then combined. 2400), positive electrode sheets are stacked to obtain a cell. The cell is placed in a packaging shell, injected with electrolyte (1M lithium hexafluorophosphate LiPF6, ethylene carbonate EC, diethyl carbonate DEC = 1:1) and sealed. After processes such as settling, compaction, formation, venting, and sealing, a lithium-ion battery is obtained. At 25℃, the lithium-ion battery is 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. This constitutes one charge / discharge cycle. 500 cycles are performed according to the above method. The discharge capacity of the lithium battery in the 500th cycle at 25℃ is recorded, and the capacity retention rate (%) of the lithium-ion battery after 500 cycles at 25℃ is recorded as: discharge capacity in the 500th cycle / discharge capacity in the first cycle × 100%.

[0046] Table 1. Performance characteristics of the composite conductive films for current collectors obtained in the examples and comparative examples.

[0047] As shown in Table 1 above, the composite conductive film for current collectors obtained in the examples has good tensile strength and toughness, and its electrochemical performance is relatively better than that of the composite current collector described in Comparative Example 1.

[0048] 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 composite conductive film for current collectors, characterized in that, It includes a base film layer and conductive layers attached to both sides of the base film layer. The base film layer is a polyolefin porous membrane, and the conductive layers are composed of polyimide resin doped with conductive polymers.

2. The composite conductive film for current collectors according to claim 1, characterized in that, The polyolefin porous membrane is a biaxially or uniaxially stretched polyethylene or polypropylene porous membrane with a porosity of 20-60%.

3. The composite conductive film for current collectors according to claim 1 or 2, characterized in that, The conductive polymer is at least one of polypyrrole, polythiophene, or polyaniline; Preferably, the doping amount of the conductive polymer is 20-80 wt%.

4. The composite conductive film for current collectors according to any one of claims 1-3, characterized in that, The polyimide resin is at least one of polyimide, polyamide-imide, or polyamide.

5. The composite conductive film for current collectors according to claim 4, characterized in that, The polyimide is obtained by polycondensation of diamine and dianhydride in a solvent; The diamine is at least one of the diamines shown in the following structural formulas: , , , , , , The dianhydride is at least one of the dianhydrides shown in the following structural formulas: 、 、 、 、 。 6. The composite conductive film for current collectors according to claim 4, characterized in that, The polyamide-imide is obtained by polycondensation of trimellitic anhydride and diisocyanate in a solvent; The diisocyanate is at least one of the diisocyanates shown in the following structural formula: 、 、 、 、 、 。 7. The composite conductive film for current collectors according to claim 4, characterized in that, The polyamide is obtained by polycondensation of diacyl chloride and diamine in a solvent; The diacyl chloride is at least one of the diacyl chlorides shown in the following structural formula: , , , , The diamine is at least one of the diamines shown in the following structural formulas: 、 、 、 、 、 、 、 、 。 8. The composite conductive film for current collectors according to any one of claims 1-7, characterized in that, The polyimide, polyamide-imide, or polyamide further includes the condensation of the polycondensation product with a pyrrole-capping agent, a thiophene-capping agent, or an aniline-capping agent.

9. The composite conductive film for current collectors according to claim 8, characterized in that, The pyrrole end-capping agent is at least one of 1-aminopyrrole, 3-aminopyrrole, or 3-hydroxypyrrole; the thiophene end-capping agent is at least one of 3-aminothiophene, 3-hydroxythiophene, or 4-bromothiophene-3-amine; and the aniline end-capping agent is at least one of o-phenylenediamine, m-phenylenediamine, or p-phenylenediamine.

10. A lithium-ion battery, characterized in that, It includes an electrode sheet, wherein the electrode sheet comprises the composite conductive film according to any one of claims 1-9 and an electrode active material loaded on the surface of the composite conductive film.

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