Fiber membrane as well as preparation method and application thereof

Abstract

The invention relates to the technical field of lithium ion batteries, and discloses a fiber membrane and a preparation method and application thereof, the fiber membrane comprises a base membrane and a flame retardant, and the flame retardant is distributed in the base membrane in the form of particles. The fiber membrane provided by the invention has the characteristics of high heat resistance and low melting point of the flame retardant, and can be quickly melted to block through holes of the fiber membrane before the battery is subjected to thermal runaway, so that the ion transmission efficiency is blocked, and the benefit of delaying the thermal runaway is achieved. According to the current collector prepared from the fiber membrane, through the targeted design of the structure and the screening of a high polymer material, the battery is lighter, the energy density of the battery is improved, meanwhile, the heat insulation and flame retardant properties of the current collector can be greatly improved, and the large-scale production and application of the battery are guaranteed.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a fiber membrane and a preparation method thereof, a current collector and a battery. Background Art

[0002] How to develop efficient, cheap and safe energy storage technology has become the key to the new energy industry since 2020. People's research on lithium batteries has led to the rapid development of the new energy industry, but also put forward higher requirements for the safety performance and energy density of batteries.

[0003] The current collector is one of the indispensable components of lithium-ion batteries. It can not only carry active substances, but also collect and output the current generated by the electrode active substances, which is beneficial to reduce the internal resistance of lithium-ion batteries and improve the coulombic efficiency, cycle stability and rate performance of the battery. Its structure is generally a "metal-polymer-metal" sandwich structure. The upper and lower surfaces of the "sandwich layer" are plated with metal aluminum or metal copper, which usually accounts for 15-50% of the total mass of the battery. The middle polymer layer has a lower expansion rate, which can effectively reduce the shedding of active substances caused by metal shrinkage and improve the battery cycle life. At the same time, the polymer material will have a short-circuit effect when heated, weakening the factors affecting the puncture of the diaphragm, which can greatly reduce the risk of thermal runaway of the battery.

[0004] The current preparation process of composite current collectors is usually divided into "two-step method" and "three-step method" for production, namely "magnetron sputtering + water electroplating" and "magnetron sputtering + vacuum plating + water electroplating" process strategies. For example, the "two-step method" first magnetron sputters a metal layer with a thickness of less than 100nm on the surface of the polymer layer to metallize the base film; then uses water electroplating to thicken the metal layer to 1μm, and the overall thickness of the composite metal foil is within 10μm, thereby replacing the traditional electrolytic metal plating method.

[0005] However, the existing current collector does not provide any effective capacity during the charge and discharge process, which seriously affects the energy density of the battery. At the same time, when the battery is damaged by mechanical external forces (especially extrusion, puncture, impact), thermal stress and electrical stress, internal short circuits are prone to occur, causing thermal runaway of the battery and leading to 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 the present invention is to overcome the problems of poor flame retardancy and heat insulation performance of composite current collectors in the prior art and large battery mass, and to provide a fiber membrane and a preparation method thereof, a current collector and a battery.

[0008] In order to achieve the above objective, a first aspect of the present invention provides a fiber membrane, which includes: 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 fiber membrane, characterized in that the method comprises:

[0010] (1) in the presence of a flame retardant and a solvent, polymerizing the monomer to obtain a polymer precursor solution;

[0011] (2) forming a polymer precursor solution into a film, and then thermally imidizing the film to obtain a fiber membrane.

[0012] A third aspect of the present invention provides a fiber membrane, which is prepared by the above method.

[0013] A fourth aspect of the present invention provides a current collector, characterized in that the current collector comprises: a polymer film and metal layers arranged on two surfaces of the polymer film, wherein the polymer film is the above-mentioned fiber film.

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

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

[0016] The fiber membrane provided by the present invention dopes flame retardant particles into the base membrane, thereby preventing or delaying the occurrence of thermal runaway of the battery, and the basic performance of the current collector prepared by the fiber membrane is not affected, such as the resistance of the battery prepared by the current collector is low, and the capacity retention rate of 200 cycles of 1C is high. In particular, the flame retardant material that is preferably not doped with halogen in the present invention does not produce toxic and harmful substances during the thermal decomposition process, and is more in line with safety and environmental protection standards. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a schematic structural diagram of the composite current collector obtained in Example 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] Description of Reference Numerals

[0020] 1-metal layer; 2-base film; 3-flame retardant. DETAILED DESCRIPTION

[0021] The endpoints and any values ​​of the ranges disclosed in this article 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 each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0022] The specific embodiments of the present invention are described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

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

[0024] In the present invention, the fiber membrane contains through holes for ion transmission, preferably, the average pore size of the through holes is 0.05-1 μm, more preferably 0.2-0.5 μm, and further preferably 0.2-0.3 μm. The average pore size of the through holes falling within the above preferred range can further improve the ion transmission efficiency and the base membrane strength.

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

[0026] In the present 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 preferred range, the energy density of the ion transport channel and the current collector is further increased, and the occurrence of thermal runaway can be more effectively controlled.

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

[0028] In the present invention, the flame retardant can be various flame retardants commonly used in the art. In some embodiments of the present invention, the flame retardant is made of a phosphorus-based flame retardant; further 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%; preferably 15-25%.

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

[0030] In the present invention, the flame retardant is preferably a flame retardant material not doped with halogen, so no toxic or harmful substances are generated during the thermal decomposition process of the 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 fiber membrane, characterized in that the method comprises:

[0032] (1) in the presence of a flame retardant and a solvent, polymerizing the monomer to obtain a polymer precursor solution;

[0033] (2) forming a polymer precursor solution into a film, and then thermally imidizing the film to obtain a fiber membrane.

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

[0035] In the present invention, the monomers may be substances commonly used in the art for synthesizing current collector separators, preferably organic anhydrides and organic amines. In some embodiments of the present invention, preferably, the molar ratio of the organic anhydride:organic amine is 1:0.9-1.1.

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

[0037] More preferably, the organic amine is an organic diamine, preferably at least one selected from 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 present 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 the present invention, there is no special requirement for the polymerization reaction conditions, as long as the monomer can be polymerized. Preferably, the polymerization reaction conditions include: a temperature of -20°C to 0°C and a time of 4-6 hours.

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

[0040] In the present invention, the film can be formed by common methods in the art, such as coating. However, in order to obtain a fiber membrane whose pore size and porosity meet the aforementioned ranges, in some embodiments of the present invention, the film forming treatment is preferably electrospinning. The electrospinning method can prepare a membrane with lower thickness, more uniform pore size distribution and higher porosity, which can further improve the transmission efficiency of ions in the fiber membrane, thereby increasing the energy density of the current collector, so that the battery has better charge and discharge performance.

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

[0042] In some embodiments of the present invention, preferably, the spinning temperature used is 30-60°C, 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, and 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 thinner the fiber, the lower the base film strength, and the higher the porosity, and vice versa.

[0044] In some embodiments of the present invention, preferably, the rotation speed of the substrate used is 20-200 rpm, and more preferably 50-100 rpm. When the substrate rotation speed falls within the preferred range, the fibers are evenly distributed and the base film thickness 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 metal foil, non-woven fabric, and felt paper with a smooth and neat surface.

[0046] In some embodiments of the present invention, the thermal imidization method adopts a segmented heating method, which is: first keep warm at 70-120°C for 20-60 minutes, then heat to 180-240°C for 30-60 minutes, and then heat to 250-350°C 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] A third aspect of the present invention provides a fiber membrane, which is prepared by the above method.

[0049] A fourth aspect of the present invention, as Figure 1 As shown, a current collector is provided, characterized in that the current collector comprises: a polymer film and a metal layer 1 arranged on two surfaces of the polymer film, wherein the polymer film is the above-mentioned fiber film.

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

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

[0052] The lithium-ion battery provided by the present invention has high energy density and light weight, and the special film structure of 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 examples, room temperature refers to 25°C, normal pressure refers to 101 kPa, and the experimental consumables and reagents used, unless otherwise specified, can be obtained from commercial sources.

[0054] The average pore size and porosity were obtained by mercury intrusion testing;

[0055] The fiber film thickness was measured by a film thickness gauge.

[0056] Example 1

[0057] (1) Preparation of precursor solution: Dissolve dianhydride monomer BPDA (biphenyltetracarboxylic acid dianhydride), diamine monomer DABA (3,5-diaminobenzoic acid), diamine monomer ODA (4,4'-diaminodiphenyl ether) and flame retardant triphenyl phosphate 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, mass of solution monomers accounted for 20 g / 100 mL of solvent volume, reaction temperature -10°C, normal pressure, reaction time 5 h);

[0058] (2) Preparation of fiber membrane: The polyimide precursor solution prepared in (1) was subjected to electrospinning (voltage 55 kV, temperature 40°C, receiving distance 20 cm, substrate speed 80 rpm) to obtain a polyimide precursor fiber membrane; the polyimide precursor fiber membrane was then thermally imidized in a high-temperature oven (100°C constant temperature for 1 h, 200°C constant temperature for 1 h, 300°C constant temperature for 1 h, N2 atmosphere) to obtain a fiber membrane (through-hole average pore size 0.25 μm, porosity 48%, thickness 7 μm); the sample fiber membrane was observed by scanning electron microscopy, as shown in FIG. 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: A 500 nm thick copper foil was plated on both sides of the fiber membrane in the thickness direction by vacuum sputtering to obtain a flame retardant composite current collector.

[0060] Example 2

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

[0062] The fiber membrane thus obtained had an average pore diameter 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 the electrospinning was 18 cm;

[0065] The fiber membrane thus obtained has an average pore diameter of 0.36 μm, a 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 in step (2), the thermal imidization temperature was 80° C. for 1 h, 180° C. for 1 h, and 250° C. for 1 h.

[0068] The fiber membrane thus obtained has an average pore size of 0.48 μm, a 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 prepared polyimide precursor solution monomer accounted for 17 g / 100 mL of the solvent volume;

[0071] The fiber membrane thus obtained has an average pore diameter of 0.1 μm, a 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 65 kV;

[0074] The fiber membrane thus obtained has an average pore diameter of 0.05 μm, a porosity of 55% and a thickness of 6.5 μm.

[0075] Example 7

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

[0077] The fiber membrane thus obtained has an average pore diameter of 0.19 μm, a 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 fiber membrane thus obtained has the same average pore diameter, porosity and thickness as those in Example 1.

[0081] Example 9

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

[0083] The fiber membrane thus obtained had an average pore diameter of 0.23 μm, a porosity of 46%, and a thickness of 6.8 μm.

[0084] Example 10

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

[0086] The fiber membrane thus obtained had an average pore diameter of 0.23 μm, a porosity of 46%, and a thickness of 6.8 μm.

[0087] Embodiment 11

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

[0089] The fiber membrane thus obtained has the same average pore diameter, porosity and thickness as those in Example 1.

[0090] Comparative Example 1

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

[0092] The fiber membrane thus obtained has the same average pore diameter, porosity and thickness as those in Example 1.

[0093] Comparative Example 2

[0094] A current collector is prepared according to the method of Example 1, except that the flame retardant is not doped in the base film, but is coated on the surface of the fiber membrane by coating.

[0095] The fiber membrane thus obtained has the same average pore diameter, porosity and thickness as those in Example 1.

[0096] Test Case

[0097] Soft-pack battery assembly: The positive and negative electrode slurries are coated on the current collectors of the above-mentioned Examples 1-8 and Comparative Examples 1-2, and the positive and negative electrode sheets are obtained by drying and welding. The positive and negative electrode sheets are cut to obtain 16 mm sheets, and the positive and negative electrode sheets are isolated by winding and wound into a battery cell; then the battery shell is loaded, the battery cover is covered, and the seal is welded; then the electrolyte is injected into the battery shell, and then the shell is sealed for a second time. The fixture is baked at 80°C and then the capacity is divided to obtain a finished soft-pack battery. Each group of 5 is connected in series to form a soft-pack battery, and the obtained soft-pack batteries are experimentally tested.

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

[0099] The composition of the negative electrode slurry is: graphite, sodium carboxymethyl cellulose CMC, water, binder LA133 and conductive agent SP

[0100] Hot box test conditions: After the battery is fully charged, put it into the temperature box. When the temperature starts to rise, start timing. Raise the temperature from room temperature to 150±2℃ at a rate of 5℃ / min, and keep this temperature for 30 minutes, then stop heating and observe for 1 hour.

[0101] Needle puncture test conditions: After the battery is fully charged, use a 4mm diameter steel needle to completely penetrate the center of the battery at a speed of 10mm / s. Keep the needle penetrated and observe for 1h or when thermal runaway occurs, the battery surface temperature drops to 50℃ and the test is terminated.

[0102] Electrical performance test conditions: The battery was cycled for 200 cycles at a charge and discharge rate of 1C at room 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 at 0.5C constant current to 4.2V, charge at 4.2V constant voltage to 0.02C cutoff, and then 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 Acupuncture test results

[0108] Serial number Acupuncture test Fire time Example 1 No fire, no explosion No fire Example 2 No fire, no explosion No fire Example 3 No fire, no explosion No fire Example 4 No fire, no explosion No fire Example 5 No fire, no explosion No fire Example 6 No fire, no explosion No fire Example 7 Fire 22min Example 8 Fire 48min Example 9 No fire, no explosion No fire Example 10 No fire, no explosion No fire Embodiment 11 Fire 32min Comparative Example 1 Fire 1min Comparative Example 2 Fire 120min

[0109] Conclusion: The hot box and needle puncture tests showed that the batteries prepared without adding the flame retardant of the corresponding content and type as in Example 1 all caught fire, and the fiber membrane obtained by using only one diamine monomer as the polymerization monomer had no obvious defects in safety performance, indicating that the addition of flame retardants has excellent effects on safety performance.

[0110] Table 3 Electrical performance test results

[0111]

[0112]

[0113] Conclusion: The electrochemical performance test shows that the formula and process parameters used in Example 1 have the best cycle performance, can maintain the battery capacity to the greatest extent, and have a slow decay; compared with the method of coating the flame retardant on the surface of the fiber membrane, the internal resistance is lower, so the loss during the charge and discharge process is smaller. Although the fiber membrane obtained by polymerizing only one diamine monomer passed the safety performance test, its electrical performance was poor and the synergistic effect of the two diamine monomers was not brought into play.

[0114] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A fiber membrane, characterized in that: The fiber membrane comprises: a base membrane and a flame retardant; Wherein, at least part of the flame retardant is distributed in the base film in the form of particles.

2. The fiber membrane according to claim 1, wherein: The fiber membrane has through holes; Preferably, the average pore size of the through hole is 0.05-1 μm; more preferably 0.2-0.5 μm; Preferably, the porosity of the fiber membrane is 30-80%, and more preferably 40-60%.

3. The fiber membrane according to claim 1 or 2, characterized in that: The base film is polyimide; Preferably, the flame retardant is a phosphorus-based flame retardant; further preferably, it is at least one selected from 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 5-30%; preferably 15-25%; Preferably, the flame retardant has an average particle size of 0.5-2 μm; Preferably, at least 90% of the flame retardant is distributed in the base film in the form of particles; Preferably, the fiber membrane has a thickness of 6-10 μm.

4. A method for preparing a fiber membrane, characterized in that: The method includes: (1) in the presence of a flame retardant and a solvent, polymerizing the monomer to obtain a polymer precursor solution; (2) forming a polymer precursor solution into a film, and then thermally imidizing the film to obtain a fiber membrane.

5. The preparation method according to claim 4, wherein In step (1), the flame retardant is a phosphorus-based flame retardant; preferably at least one selected from diphenyl phosphate, triphenyl phosphate, triethyl phosphate, trimethyl phosphate, and diethyl ethyl phosphate; and / or, the solvent is selected from at least one of N,N-dimethylformamide and N,N-dimethylacetamide; And / or, based on the total molar number of monomers, the molar fraction of the flame retardant is 5-30%, preferably 15-25%.

6. The preparation method according to claim 4 or 5, wherein: In step (1), the conditions of the polymerization reaction include: reaction temperature of -20°C to 0°C, reaction time of 4-6h; And / or, the mass of the monomer in the polymer precursor solution accounts for 12-25 g / 100 mL of the solvent volume; preferably 20-22 g / 100 mL; and / or, the monomers include organic anhydrides and organic amines; Preferably, the molar ratio of the organic anhydride to the organic amine is 1:0.9-1.1; Preferably, the organic acid anhydride is an organic dibasic acid anhydride; preferably at least one selected from pyromellitic dianhydride, 1,2',3,3'-benzophenonetetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 2,2',3,3'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride; Preferably, the organic amine is an organic diamine; preferably at least one selected from 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; More preferably, the organic amine is 3,5-diaminobenzoic acid and 4,4'-diaminodiphenyl ether, and the molar ratio of the two is 1:1-9.

7. The method for preparing a fiber membrane according to any one of claims 4 to 6, wherein: The film is formed by an electrostatic spinning method; Preferably, the electrospinning allows the fiber membrane to have through pores with an average pore size of 0.05-1 μm, more preferably 0.2-0.5 μm; Preferably, the electrospinning makes the porosity of the fiber membrane 30-80%, more preferably 40-60%; Preferably, the electrospinning makes the thickness of the fiber membrane 6-10 μm; Further preferably, the electrospinning conditions are: voltage of 40-60 kV; distance between electrode wire and substrate of 15-25 cm; substrate rotation speed of 20-200 rpm; spinning temperature of 30-60° C.; Further preferably, the electrospinning conditions are: voltage 50-60 kV; distance between electrode wire and substrate 18-23 cm; substrate rotation speed 50-100 rpm; spinning temperature 35-45°C.

8. The method for preparing a fiber membrane according to any one of claims 4 to 7, wherein: The thermal imidization method is to first keep the temperature at 70-120° C. for 20-60 minutes, then heat it to 180-240° C. for 30-60 minutes, and then heat it to 250-350° C. for 30-60 minutes.

9. The fiber membrane obtained by the preparation method according to any one of claims 4 to 8.

10. A current collector, characterized in that: The current collector comprises: a fiber membrane and a metal layer attached to two surfaces of the fiber membrane; wherein the fiber membrane is the fiber membrane described in any one of claims 1-3 and 8.

11. The current collector according to claim 10, wherein: The thickness of the metal layer is 200-700nm; preferably 400-600nm; The material of the metal layer is a conductive metal; preferably at least one of copper, aluminum, gold, silver, iron or zinc.

12. A lithium ion battery, characterized in that: The lithium ion battery comprises the current collector according to claim 10 or 11.

Images