Fiber membranes, their preparation methods and applications

Abstract

This invention relates to the field of lithium-ion battery technology, and discloses a fiber membrane, its preparation method, and its application. The fiber membrane comprises a base membrane and a flame retardant, wherein the flame retardant is distributed in the base membrane in the form of particles. The provided fiber membrane has high thermal resistance and the low melting point of the flame retardant, which can rapidly melt and block the pores of the fiber membrane before the battery experiences thermal runaway, thereby hindering ion transport efficiency and delaying thermal runaway. The current collector prepared from the fiber membrane, through targeted structural design and selection of polymer materials, makes the battery lighter and increases the battery's energy density. At the same time, it can also significantly improve the thermal insulation and flame retardant performance of the current collector, ensuring the large-scale production and application of the battery.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a fiber membrane and its preparation method, a current collector, and a battery. Background Technology

[0002] Since 2020, developing efficient, inexpensive, and safe energy storage technologies has become crucial for the new energy industry. Research into lithium batteries has spurred the rapid development of the new energy industry, while also placing higher demands on battery safety and energy density.

[0003] The current collector is an indispensable component of a lithium-ion battery. It not only carries the active material but also collects and outputs the current generated by the electrode active material, which helps reduce the internal resistance of the lithium-ion battery and improve its coulombic efficiency, cycle stability, and rate performance. Its structure is generally a "metal-polymer-metal" sandwich structure. The upper and lower surfaces of the "sandwich layer" are plated with aluminum or copper, typically accounting for 15-50% of the battery's total mass. The middle polymer layer has a lower expansion rate, effectively reducing the shedding of active material caused by metal shrinkage and improving battery cycle life. Simultaneously, the polymer material exhibits a circuit-breaking effect when heated, weakening the factors affecting separator puncture and significantly reducing the risk of battery thermal runaway.

[0004] Current composite current collector fabrication processes are typically divided into two-step and three-step methods, namely "magnetron sputtering + electroplating" and "magnetron sputtering + vacuum plating + electroplating". For example, the two-step method first magnetron sputters a metal layer with a thickness of less than 100 nm onto the surface of the polymer layer to metallize the base film; then, electroplating is used to thicken the metal layer to 1 μm, resulting in an overall composite metal foil thickness of less than 10 μm, thus replacing the traditional electrolytic metal plating method.

[0005] However, existing current collectors do not provide any effective capacity during the charging and discharging process, which seriously affects the energy density of the battery. At the same time, when the battery is subjected to mechanical external forces (especially extrusion, puncture, and impact), thermal stress, and electrical stress, it is easy to cause internal short circuits, resulting in thermal runaway and safety accidents.

[0006] Therefore, it is of great significance to provide a composite current collector with high safety performance. Summary of the Invention

[0007] The purpose of this invention is to overcome the problems of poor flame retardant and heat insulation performance and large battery mass of existing composite current collectors, and to provide a fiber membrane, its preparation method, current collector, and battery.

[0008] To achieve the above objectives, a first aspect of the present invention provides a fiber membrane comprising: a base membrane and a flame retardant, wherein at least a portion of the flame retardant is distributed in the base membrane in the form of particles.

[0009] A second aspect of the present invention provides a method for preparing a fibrous membrane, characterized in that the method comprises:

[0010] (1) In the presence of flame retardant and solvent, the monomer is subjected to polymerization reaction to obtain polymer precursor solution;

[0011] (2) The polymer precursor solution is formed into a film, and then thermal imidization is carried out to obtain a fiber membrane.

[0012] In a third aspect, the present invention provides a fiber membrane prepared by the method described above.

[0013] A fourth aspect of the present invention provides a current collector, characterized in that the current collector comprises: a polymer membrane and metal layers disposed on two surfaces of the polymer membrane, wherein the polymer membrane is the aforementioned fiber membrane.

[0014] In a fifth aspect, the present invention provides a lithium-ion battery, wherein the lithium-ion battery is prepared using the above-described current collector.

[0015] Through the above technical solution, the present invention can achieve at least the following beneficial effects:

[0016] The fiber membrane provided by this invention incorporates flame retardant particles into the base membrane, thereby preventing or delaying the occurrence of battery thermal runaway. Furthermore, the basic performance of the current collector prepared from this fiber membrane remains unaffected; for example, batteries prepared using this current collector exhibit low resistance and high capacity retention after 200 cycles at 1C. In particular, the flame retardant material preferred in this invention is halogen-free and does not produce toxic or harmful substances during thermal decomposition, thus better meeting safety and environmental protection standards. Attached Figure Description

[0017] Figure 1 This is a simplified structural diagram of the composite current collector obtained in Embodiment 1 of the present invention;

[0018] Figure 2 This is a scanning electron microscope image of the fiber membrane obtained in Example 1 of the present invention.

[0019] Explanation of reference numerals in the attached figures

[0020] 1-Metal layer; 2-Base film; 3-Flame retardant. Detailed Implementation

[0021] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0022] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0023] like Figure 1 As shown, in a first aspect, the present invention provides a fiber membrane comprising: a base membrane 2 and a flame retardant 3, wherein at least a portion of the flame retardant is distributed in the base membrane in the form of particles.

[0024] In this invention, the fiber membrane contains through-pores for ion transport. Preferably, the average pore diameter is 0.05-1 μm, more preferably 0.2-0.5 μm, and even more preferably 0.2-0.3 μm. An average pore diameter falling within the above-mentioned preferred range can further improve ion transport efficiency and base membrane strength.

[0025] In this invention, the thickness of the base film is preferably 6-10 μm. A base film thickness falling within the above-mentioned preferred range can improve mechanical strength, increase ion transport rate and current collector energy density, and avoid or delay the occurrence of thermal runaway.

[0026] In this invention, the porosity of the fiber membrane is preferably 30-80%, more preferably 40-60%. When the porosity of the fiber membrane falls within the above-mentioned preferred range, it can further increase the energy density of the ion transport channels and current collectors, while also more effectively controlling the occurrence of thermal runaway.

[0027] In this invention, the base film can be a polymer film commonly used in current collectors in the art. In some embodiments of this invention, the base film is polyimide.

[0028] In this invention, the flame retardant can be any of the flame retardants commonly found in the art. In some embodiments of this invention, the flame retardant is a phosphorus-based flame retardant; more preferably, it is selected from at least one of diphenyl phosphate, triphenyl phosphate, triethyl phosphate, trimethyl phosphate, and diethyl ethyl phosphate. Preferably, based on the total molar number of dianhydride and diamine monomers, the molar fraction of the flame retardant is preferably 5-30%; more preferably 15-25%.

[0029] In this invention, the flame retardant is distributed in the form of particles within the base film, and there is also a possibility that the flame retardant is distributed on the surface of the base film. Preferably, the average particle size of the flame retardant particles is 0.5-2 μm. Preferably, at least 90% of the flame retardant is distributed in the form of particles within the base film.

[0030] In this invention, the preferred flame retardant is a flame retardant material that is not doped with halogens. Therefore, no toxic or harmful substances are produced during the thermal decomposition process of the preferred flame retardant, which is more in line with safety and environmental protection standards.

[0031] A second aspect of the present invention provides a method for preparing a fibrous membrane, characterized in that the method comprises:

[0032] (1) In the presence of flame retardant and solvent, the monomer is subjected to polymerization reaction to obtain polymer precursor solution;

[0033] (2) The polymer precursor solution is formed into a film, and then thermal imidization is carried out to obtain a fiber membrane.

[0034] In a preferred embodiment of the present invention, the amount of flame retardant used is 15-25% of the total amount of monomers. The types of flame retardants are as described above and will not be repeated here. In some embodiments of the present invention, there are no particular requirements for the type of solvent, as long as it can dissolve the monomers and allow them to undergo a polymerization reaction. Preferably, the solvent is selected from at least one of N,N-dimethylformamide or N,N-dimethylacetamide; more preferably, the solvent is N,N-dimethylacetamide.

[0035] In this invention, the monomer can be a substance commonly used in the art for synthesizing current collector membranes, preferably an organic acid anhydride and an organic amine. In some embodiments of this invention, preferably, the molar ratio of the organic acid anhydride to the organic amine is 1:0.9-1.1.

[0036] More preferably, the organic anhydride is an organic dicarboxylic acid anhydride; preferably selected from at least one of pyromellitic dianhydride, 1,2',3,3'-benzophenone tetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 2,2',3,3'-biphenyltetracarboxylic dianhydride, and 3,3',4,4'-biphenyltetracarboxylic dianhydride.

[0037] More preferably, the organic amine is an organic diamine; preferably selected from at least one of 4,4'-diaminodiphenyl ether, 4,4'-diaminobenzophenone, 4,4'-diaminobiphenyl, 2,4-diaminotoluene, 2,5-diaminotoluene, 3,3'-dimethoxybenzidine, m-phenylenediamine, and p-phenylenediamine. According to a particularly preferred embodiment of the invention, the organic amine is 3,5-diaminobenzoic acid and 4,4'-diaminodiphenyl ether, and the molar ratio of the two is 1:1-9.

[0038] In this invention, there are no special requirements for the conditions of the polymerization reaction, as long as the monomer can be polymerized. Preferably, the conditions of the polymerization reaction include: a temperature of -20°C to 0°C and a time of 4-6 hours.

[0039] In this invention, the monomer in the polymer precursor solution accounts for 12-25 g / 100 mL of the solvent volume; preferably 20-22 g / 100 mL.

[0040] In this invention, film formation can be performed using methods commonly found in the art, such as coating. However, in order to obtain a fiber membrane with pore size and porosity that meet the aforementioned range, in some embodiments of this invention, the film formation process is preferably electrospinning. Electrospinning can prepare membranes with lower thickness, more uniform pore size distribution, and higher porosity, which can further improve the ion transport efficiency in the fiber membrane, thereby increasing the energy density of the current collector and enabling the battery to have better charge and discharge performance.

[0041] In some embodiments of the present invention, preferably, the spinning voltage used is 40-70kV, more preferably 40-60kV. The higher the spinning voltage of the electrospinning method, the finer the fiber, the lower the base film strength, and the higher the porosity, and vice versa.

[0042] In some embodiments of the present invention, preferably, the spinning temperature is 30-60°C, and more preferably 35-45°C.

[0043] In some embodiments of the present invention, preferably, the distance between the electrode wire and the substrate is 15-25 cm, more preferably 18-23 cm. When the distance between the electrode wire and the substrate falls within the preferred range, the greater the distance between the electrode wire and the substrate in the electrospinning method, the faster the solvent evaporates, the finer the fiber, the lower the strength of the base film, and the higher the porosity, and vice versa.

[0044] In some embodiments of the present invention, preferably, the rotation speed of the substrate is 20-200 rpm, more preferably 50-100 rpm. When the substrate rotation speed falls within the preferred range, the fiber distribution is uniform and the thickness of the base film per unit time is small.

[0045] In some embodiments of the present invention, the substrate used in the electrospinning method is preferably at least one of the following: smooth and clean metal foil, non-woven fabric, and felt paper.

[0046] In some embodiments of the present invention, the thermal imidization method adopts a segmented heating method, which is as follows: first, hold at 70-120℃ for 20-60 minutes, then raise the temperature to 180-240℃ and hold for 30-60 minutes, and then raise the temperature to 250-350℃ and hold for 30-60 minutes.

[0047] In some embodiments of the present invention, the thermal imidization process is carried out in an inert atmosphere, and the gas providing the inert atmosphere may be nitrogen and / or a rare gas, preferably at least one of nitrogen, argon and neon.

[0048] In a third aspect, the present invention provides a fiber membrane prepared by the method described above.

[0049] The fourth aspect of the invention, as follows Figure 1 As shown, a current collector is provided, characterized in that the current collector comprises: a polymer membrane and a metal layer 1 disposed on two surfaces of the polymer membrane, wherein the polymer membrane is the aforementioned fiber membrane.

[0050] In some embodiments of the present invention, the metal layer in the thickness direction is uniformly attached to the surface of the base film by one or more processes such as vacuum evaporation, magnetron sputtering, or electroplating, and the thickness of the metal layer is 200-700 nm, preferably 400-600 nm.

[0051] In a fifth aspect, the present invention provides a lithium-ion battery, wherein the lithium-ion battery is prepared using the above-described current collector.

[0052] The lithium-ion battery provided by this invention has high energy density, light weight, and a special membrane structure for the current collector in the battery can effectively delay or prevent thermal runaway.

[0053] The present invention will be described in detail below through examples. In the following examples, comparative examples and test cases, room temperature refers to 25°C, atmospheric pressure refers to 101 kPa, and the experimental consumables and reagents used are commercially available unless otherwise specified.

[0054] The average pore size and porosity were obtained by mercury porosimetry.

[0055] The thickness of the fiber membrane was obtained by measuring the thickness of a thin film using a film thickness gauge.

[0056] Example 1

[0057] (1) Preparation of precursor solution: Dihydric anhydride monomer BPDA (biphenyltetracarboxylic dianhydride), diamine monomer DABA (3,5-diaminobenzoic acid), diamine monomer ODA (4,4'-diaminodiphenyl ether), and flame retardant triphenyl phosphate were dissolved in DMAc (N,N-dimethylacetamide) at a molar ratio of 1:0.2:0.8:0.5 to prepare a polyimide precursor solution (stirring speed 300 rpm, monomer mass of solution is 20 g / 100 mL, reaction temperature -10℃, atmospheric pressure, reaction time 5 h).

[0058] (2) Preparation of fiber membrane: The polyimide precursor solution prepared in (1) was electrospun (voltage 55kV, temperature 40℃, receiving distance 20cm, substrate rotation speed 80rpm) to obtain a polyimide precursor fiber membrane; then the polyimide precursor fiber membrane was thermally imidized in a high-temperature oven (100℃ for 1h, 200℃ for 1h, 300℃ for 1h, N2 atmosphere) to obtain a fiber membrane (average pore size 0.25μm, porosity 48%, thickness 7μm); the sample fiber membrane was observed by scanning electron microscopy, such as Figure 2 As shown, from Figure 2 It can be seen that the fiber size is relatively uniform and has a high porosity;

[0059] (3) Preparation of composite current collector: 500 nm copper foil is deposited on both sides of the fiber membrane in the thickness direction by vacuum sputtering to obtain flame retardant composite current collector.

[0060] Example 2

[0061] The composite current collector was prepared according to the method of Example 1, except that in step (1), the molar ratio of dianhydride monomer BPDA (biphenyl tetracarboxylic dianhydride), diamine monomer DABA (3,5-diaminobenzoic acid), diamine monomer ODA (4,4'-diaminodiphenyl ether) and flame retardant triphenyl phosphate was 1:0.3:0.7:0.5, and the mass of the monomer in the obtained polyimide precursor solution accounted for 20 g / 100 mL of the solvent volume;

[0062] The resulting fiber membrane has an average pore size of 0.28 μm, a porosity of 46%, and a thickness of 6.3 μm.

[0063] Example 3

[0064] The composite current collector was prepared according to the method of Example 1, except that in step (2), the receiving distance of electrospinning was 18 cm;

[0065] The resulting fiber membrane has an average pore size of 0.36 μm, a flame-retardant fiber membrane porosity of 43%, and a thickness of 6 μm.

[0066] Example 4

[0067] The composite current collector was prepared according to the method of Example 1, except that the thermal imidization temperature in step (2) was 80℃ for 1 hour, 180℃ for 1 hour, and 250℃ for 1 hour.

[0068] The resulting fiber membrane has an average pore size of 0.48 μm, a flame-retardant fiber membrane porosity of 41%, and a thickness of 8 μm.

[0069] Example 5

[0070] The composite current collector was prepared according to the method of Example 1, except that in step (1), the mass of the monomer of the polyimide precursor solution obtained was 17 g / 100 mL of the solvent volume.

[0071] The resulting fiber membrane has an average pore size of 0.1 μm, a flame-retardant fiber membrane porosity of 52%, and a thickness of 8 μm.

[0072] Example 6

[0073] The composite current collector was prepared according to the method of Example 1, except that in step (2), the voltage of electrospinning was 65kV;

[0074] The resulting fiber membrane has an average pore size of 0.05 μm, a flame-retardant fiber membrane porosity of 55%, and a thickness of 6.5 μm.

[0075] Example 7

[0076] The composite current collector was prepared according to the method of Example 1, except that in step (1), the molar ratio of dianhydride monomer BPDA (biphenyl tetracarboxylic dianhydride), diamine monomer DABA (3,5-diaminobenzoic acid), diamine monomer ODA (4,4'-diaminodiphenyl ether) and flame retardant triphenyl phosphate was 1:0.2:0.8:0.2, and the mass of the monomer in the obtained polyimide precursor solution accounted for 18 g / 100 mL of the solvent volume;

[0077] The resulting fiber membrane has an average pore size of 0.19 μm, a flame-retardant fiber membrane porosity of 47%, and a thickness of 6.9 μm.

[0078] Example 8

[0079] The composite current collector was prepared according to the method of Example 1, except that in step (1), after the monomer polymerization was completed, the flame retardant was mixed with the polymerization solution;

[0080] The resulting fiber membrane has the same average pore size, flame-retardant fiber membrane porosity, and thickness as in Example 1.

[0081] Example 9

[0082] The composite current collector was prepared according to the method of Example 1, except that the molar ratio of dianhydride monomer BPDA (biphenyl dianhydride), diamine monomer DABA (3,5-diaminobenzoic acid) and flame retardant triphenyl phosphate in step (1) was 1:1:0.5.

[0083] The resulting fiber membrane has an average pore size of 0.23 μm, a porosity of 46%, and a thickness of 6.8 μm.

[0084] Example 10

[0085] The composite current collector was prepared according to the method of Example 1, except that the molar ratio of dianhydride monomer BPDA (biphenyl dianhydride), diamine monomer ODA (4,4'-diaminodiphenyl ether), and flame retardant triphenyl phosphate in step (1) was 1:1:0.5.

[0086] The resulting fiber membrane has an average pore size of 0.23 μm, a porosity of 46%, and a thickness of 6.8 μm.

[0087] Example 11

[0088] The composite current collector was prepared according to the method of Example 1, except that in step (1), ammonium polyphosphate was selected as the flame retardant.

[0089] The resulting fiber membrane has the same average pore size, flame-retardant fiber membrane porosity, and thickness as in Example 1.

[0090] Comparative Example 1

[0091] The composite current collector was prepared according to the method of Example 1, except that no flame retardant was added in step (1);

[0092] The resulting fiber membrane has the same average pore size, flame-retardant fiber membrane porosity, and thickness as in Example 1.

[0093] Comparative Example 2

[0094] The current collector was prepared according to the method of Example 1, except that the flame retardant used was not incorporated into the base film, but was coated onto the surface of the fiber film.

[0095] The resulting fiber membrane has the same average pore size, flame-retardant fiber membrane porosity, and thickness as in Example 1.

[0096] Test case

[0097] Soft-pack battery assembly: Positive and negative electrode slurries are coated onto the current collectors of Examples 1-8 and Comparative Examples 1-2, dried, and welded to obtain positive and negative electrode sheets. The positive and negative electrode sheets are cut to 16mm diameter, separated by winding, and wound into a cell body. Then, the cell is installed in the battery case, the battery cover is closed, and the opening is welded. Next, electrolyte is injected into the battery case, and then the opening is sealed again. The clamps are baked at 80°C and then capacity tested to obtain the finished soft-pack battery. Five cells are connected in series in each group to form a soft-pack battery, and the obtained soft-pack batteries are tested experimentally.

[0098] The positive electrode slurry consists of: lithium iron phosphate, NMP, PVDF binder, and SP conductive agent.

[0099] The negative electrode slurry consists of: graphite, sodium carboxymethyl cellulose (CMC), water, binder LA133, and conductive agent SP.

[0100] Hot chamber test conditions: After the battery is fully charged, it is placed in the temperature chamber. When the temperature starts to rise, the timer is started. The temperature is raised from room temperature to 150±2℃ at a rate of 5℃ / min, and this temperature is maintained for 30 minutes before heating is stopped. The temperature is then observed for 1 hour.

[0101] Needle penetration test conditions: After the battery is fully charged, use a steel needle with a diameter of 4mm to completely penetrate the center of the battery at a speed of 10mm / s, keep it in the penetrated state, and observe for 1 hour or until the battery surface temperature drops to 50℃ after thermal runaway occurs, then terminate the test.

[0102] Electrical performance testing conditions: The battery was subjected to 200 cycles of charge and discharge at a rate of 1C under normal temperature and pressure, with a charging voltage of 4.2V, and the battery capacity retention rate was recorded.

[0103] AC internal resistance test conditions: Charge the battery to 4.2V at a constant current of 0.5C, and then charge it to 0.02C at a constant voltage of 4.2V. After that, use an internal resistance tester to test the battery internal resistance at 1kHz.

[0104] Table 1. Hot Box Test Results

[0105]

[0106]

[0107] Table 2 Results of acupuncture test

[0108] Serial Number Needle prick test Time of fire Example 1 No fire or explosion No fire Example 2 No fire or explosion No fire Example 3 No fire or explosion No fire Example 4 No fire or explosion No fire Example 5 No fire or explosion No fire Example 6 No fire or explosion No fire Example 7 fire 22min Example 8 fire 48min Example 9 No fire or explosion No fire Example 10 No fire or explosion No fire Example 11 fire 32min Comparative Example 1 fire 1min Comparative Example 2 fire 120min

[0109] Conclusion: The hot box and needle penetration tests showed that the batteries prepared without the same amount and type of flame retardant as in Example 1 all caught fire, and the fiber membrane obtained by using only one diamine monomer as the polymerization monomer did not show any obvious defects in safety performance, indicating that the addition of flame retardant has excellent safety performance.

[0110] Table 3 Electrical performance test results

[0111]

[0112]

[0113] Conclusion: Electrochemical performance tests show that the formulation and process parameters used in Example 1 have optimal cycle performance, maximizing battery capacity retention and exhibiting slower degradation. Compared to coating the flame retardant onto the fiber membrane surface, it has lower internal resistance, resulting in less loss during charge and discharge. While the fiber membrane obtained using only one diamine monomer passed the safety performance test, its electrical performance was poor, failing to leverage the synergistic effect of the two diamine monomers.

[0114] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing a fibrous membrane, characterized in that, The method includes: (1) In the presence of flame retardant and solvent, the monomer is subjected to polymerization reaction to obtain polymer precursor solution; (2) The polymer precursor solution is formed into a film, and then thermal imidization is performed to obtain a fiber membrane; In the polymer precursor solution, the mass of the monomer accounts for 20-22 g / 100 mL of the solvent volume; The monomers include organic acid anhydrides and organic amines; The flame retardant is selected from diphenyl phosphate and / or triphenyl phosphate; The film is formed using an electrospinning method; The electrospinning process results in a fiber membrane with through-pores having an average pore size of 0.2-0.5 μm.

2. The method according to claim 1, wherein, The solvent is selected from at least one of N,N-dimethylformamide or N,N-dimethylacetamide; And / or, based on the total molar number of monomers, the molar fraction of the flame retardant is 5-30%.

3. The method according to claim 2, wherein, Based on the total molar number of monomers, the molar fraction of the flame retardant is 15-25%.

4. The method according to claim 1, wherein, In step (1), the conditions for the polymerization reaction include: a reaction temperature of -20°C to 0°C and a reaction time of 4-6 hours.

5. The method according to claim 4, wherein, The molar ratio of the organic acid anhydride to the organic amine is 1:0.9-1.1; And / or, the organic acid anhydride is an organic dicarboxylic acid anhydride; And / or, the organic amine is an organic diamine.

6. The method according to claim 4, wherein, The organic acid anhydride is selected from at least one of pyromellitic dianhydride, 1,2',3,3'-benzophenone tetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 2,2',3,3'-biphenyltetracarboxylic dianhydride, and 3,3',4,4'-biphenyltetracarboxylic dianhydride. And / or, the organic amine is selected from at least one of 3,5-diaminobenzoic acid, 4,4'-diaminodiphenyl ether, 4,4'-diaminobenzophenone, 4,4'-diaminobiphenyl, 2,4-diaminotoluene, 2,5-diaminotoluene, 3,3'-dimethoxybenzidine, m-phenylenediamine, and p-phenylenediamine.

7. The method according to claim 6, wherein, The organic amine is 3,5-diaminobenzoic acid and 4,4'-diaminodiphenyl ether, and the molar ratio of the two is 1:1-9.

8. The method according to claim 1, wherein, The electrospinning process results in a fiber membrane with a porosity of 30-80%. And / or, the electrospinning results in a fiber membrane thickness of 6-10 μm; And / or, the conditions for electrospinning are: voltage of 40-60kV; distance between electrode wire and substrate of 15-25cm; rotation speed of substrate of 20-200rpm; and spinning temperature of 30-60℃.

9. The method according to claim 8, wherein, The electrospinning process results in a fiber membrane with a porosity of 40-60%. And / or, the conditions for electrospinning are: voltage 50-60kV; distance between electrode wire and substrate 18-23cm; rotation speed of substrate 50-100rpm; spinning temperature 35-45℃.

10. The method according to any one of claims 1-7, wherein, The thermal imidization process involves first holding the temperature at 70-120℃ for 20-60 minutes, then raising the temperature to 180-240℃ and holding it for 30-60 minutes, and finally raising the temperature to 250-350℃ and holding it for 30-60 minutes.

11. The fiber membrane prepared by the method according to any one of claims 1-10.

12. A current collector, characterized in that, The current collector includes: a fiber membrane and a metal layer attached to two surfaces of the fiber membrane; wherein the fiber membrane is the fiber membrane according to claim 11.

13. The current collector according to claim 12, wherein, The thickness of the metal layer is 200-700 nm; The metal layer is made of conductive metal.

14. The current collector according to claim 13, wherein, The thickness of the metal layer is 400-600 nm; And / or, the metal layer is made of at least one of copper, aluminum, gold, silver, iron, or zinc.

15. A lithium-ion battery, characterized in that, The lithium-ion battery contains the current collector as described in any one of claims 12-14.

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