A method for preparing a high-fluorine-containing cross-linked polyimide nanofiber membrane and a lithium ion battery separator and lithium ion battery

Abstract

The application discloses a preparation method of a high-fluorine-containing crosslinked polyimide nanofiber membrane, and comprises the following steps: synthesizing a polyamide acid precursor solution by mixing hexafluoro aromatic diamine and aromatic dianhydride in a solvent, preparing the polyamide acid precursor solution into a spinning solution, preparing a polyamide acid nanofiber membrane by a high-pressure electrospinning method, drying the polyamide acid nanofiber membrane in a vacuum environment at 100-200 DEG C for 0.5-1 h, then increasing the temperature to 200-300 DEG C and heating for 2-4 h, and finally increasing the temperature to 300-350 DEG C under nitrogen to perform thermal amidation and thermal crosslinking, and the holding time is 1-2 h. The application further discloses a lithium ion battery separator, which is the high-fluorine-containing crosslinked polyimide nanofiber membrane prepared by the above method. The introduction of dihydroxy and chemical crosslinking solve the problem that too high fluorine group content makes the solubilization ability of the polyimide membrane to the electrolyte too strong, and realize the application of the high-fluorine-containing nanofiber membrane as a high-performance lithium ion battery separator.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion batteries, specifically relating to a method for preparing a high-fluorine-content cross-linked polyimide nanofiber membrane, a lithium-ion battery separator, and a lithium-ion battery. Background Technology

[0002] Lithium-ion batteries, due to their high energy density and long cycle life, are widely used in electric vehicles, energy storage power stations, and other fields. However, these high-energy-density lithium-ion batteries are prone to thermal runaway, and much research has been conducted on battery component materials to improve battery safety. The separator is a crucial component of lithium-ion batteries, acting as an interlayer to isolate the positive and negative electrodes and prevent internal short circuits. However, commercially available polyolefin-based separators have several drawbacks that severely hinder lithium-ion battery performance, such as high thermal shrinkage at high temperatures and low electrolyte wettability. Polyimide materials, due to their high-temperature resistance, excellent mechanical properties, and high affinity for lithium-ion battery electrolytes, are also being used in lithium-ion battery separators.

[0003] To further improve the affinity between polyimide separators and lithium-ion battery electrolytes, increase electrolyte absorption, reduce lithium-ion transport impedance, and enhance the cycle performance of lithium-ion batteries, some researchers have prepared polyimides with certain solubility in polar solvents by selecting monomers containing fluorine groups. The presence of fluorine groups: increases the solubility of polyimide, improves processing performance; increases the surface polarity of the separator, improves affinity with the electrolyte, increases electrolyte absorption of the separator, and reduces electrochemical polarization; increases the dielectric constant of the material, promoting Li-ion transport. + The dissociation of Li; reducing the Guley value and crystallinity of the polymer, which is beneficial to Li + The passage and the reduction of volume resistivity.

[0004] However, if more fluorine-containing groups are introduced to further improve the electrolyte affinity of polyimide materials, excessive fluorine-containing groups will make the polyimide film too solubilizing with the electrolyte, causing it to lose mechanical strength or even dissolve in the electrolyte, making it unsuitable for use as a high-performance lithium-ion battery separator. Summary of the Invention

[0005] In order to overcome the shortcomings of the existing technology, the purpose of this invention is to provide a method for preparing a high-fluorine-content cross-linked polyimide nanofiber membrane. The prepared high-fluorine-content cross-linked polyimide nanofiber membrane solves the problem that high-fluorine-content polyimide membranes and electrolytes cannot be used as high-performance lithium-ion battery separators due to excessive solvation.

[0006] Another object of the present invention is to provide a lithium-ion battery separator.

[0007] Another object of the present invention is to provide a lithium-ion battery.

[0008] The objective of this invention is achieved through the following technical solution:

[0009] A method for preparing a high-fluorine-content cross-linked polyimide nanofiber membrane, the specific steps of which are as follows:

[0010] (1) A polyamic acid precursor solution is synthesized by reacting a hydroxyl-containing hexafluoroaromatic diamine with an aromatic dianhydride in a solvent; the polyamic acid precursor solution is prepared into a spinning solution and polyamic acid nanofiber membrane is prepared by high voltage electrospinning.

[0011] (2) Dry the polyamic acid nanofiber membrane in a vacuum environment at 100-200℃ for 0.5-1h; then heat it to 200-300℃ for 2h-4h.

[0012] (3) The polyamic acid nanofiber membrane is heated to 300-350℃ in a nitrogen atmosphere for thermal amination and thermal crosslinking, and the holding time is 1h-2h to obtain a high-fluorine crosslinked polyimide nanofiber membrane.

[0013] Preferably, the heating in step (3) is carried out at a heating rate of 4-6 / min.

[0014] Preferably, the molar ratio of the hydroxyl-containing hexafluoroaromatic diamine to the aromatic dianhydride is 1:0.9-1.01.

[0015] Preferably, the spinning solution has a solid content of 10-30% by mass.

[0016] Preferably, the structure of the polyamic acid precursor is as follows:

[0017]

[0018] The structural formula of R1 is one of the following:

[0019]

[0020] The structural formula of R2 is one of the following:

[0021]

[0022] Preferably, the solvent is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, or dimethyl sulfoxide.

[0023] Preferably, the specific process conditions for the high-voltage electrospinning method are: ambient temperature of 20-30℃, ambient humidity of 35-50%, feed speed of 0.2-0.4mL / h, and spinning voltage of 11-16kV.

[0024] More preferably, the needle type is 21# and the receiving distance is 20cm.

[0025] Preferably, the fibers in the highly fluorinated cross-linked polyimide nanofiber membrane are bonded together and interwoven to form interconnected micropores.

[0026] Preferably, the thickness of the highly fluorinated cross-linked polyimide nanofiber membrane is 10-100 μm.

[0027] Preferably, the fiber diameter of the highly fluorinated cross-linked polyimide nanofiber membrane is 100-800 nm.

[0028] Preferably, the high-fluorine-content cross-linked polyimide nanofiber membrane is a dense, layered network structure formed by mutually bonded fibers, with a tortuous, interconnected microporous structure, a pore size distribution range of 0.1-1.5 μm, and a porosity of 50-90%.

[0029] A lithium-ion battery separator is a high-fluorine-content cross-linked polyimide nanofiber membrane; the high-fluorine-content cross-linked polyimide nanofiber membrane is prepared by the above-mentioned preparation method of the high-fluorine-content cross-linked polyimide nanofiber membrane.

[0030] A lithium-ion battery comprising the aforementioned lithium-ion battery separator.

[0031] Preferably, the lithium-ion battery is a lithium metal lithium-ion battery, a graphite anode lithium-ion battery, or a silicon-carbon anode lithium-ion battery.

[0032] The present invention has the following advantages and beneficial effects compared with the prior art:

[0033] (1) The present invention introduces dihydroxyl groups and chemical crosslinking, enabling the high-fluorine-containing polyimide separator to maintain its mechanical properties in the electrolyte. The prepared high-fluorine-containing crosslinked polyimide nanofiber membrane solves the problem that excessively high fluorine content would make the polyimide membrane too solubilizing with the electrolyte, thus preventing its application as a high-performance lithium-ion battery separator. This results in batteries equipped with this separator having higher specific capacity, better long-cycle stability, and superior rate performance. The introduction of multiple trifluoromethyl groups endows the polyimide separator with high surface polarity, significantly improving the affinity between the separator and the electrolyte, increasing the electrolyte absorption rate of the separator and reducing electrochemical polarization, increasing the dielectric constant of the material, and promoting the dissociation of lithium ions.

[0034] (2) The preparation process of the high-fluorine-content cross-linked polyimide nanofiber membrane in this invention is simple and easy to mass-produce. Attached Figure Description

[0035] Figure 1 This is a SEM image of the polyamic acid nanofiber membrane in Example 1 of the present invention.

[0036] Figure 2 This is a SEM image of the surface of the C-12FPI nanofiber membrane in Example 1 of the present invention.

[0037] Figure 3 This is a structural diagram of the hydroxyl-crosslinked polyimide prepared according to the present invention.

[0038] Figure 4 The graph shows the battery cycle performance at 0.5C for lithium-ion batteries assembled with the C-12FPI nanofiber membrane in Example 1 of the present invention and the commercial PE separator in Comparative Example 3.

[0039] Figure 5 The graph shows the battery cycle performance at 1C for lithium-ion batteries assembled with the C-12FPI nanofiber membrane in Example 1 of the present invention and the commercial PE separator in Comparative Example 3.

[0040] Figure 6 The rate performance curves of lithium-ion batteries assembled with the C-12FPI nanofiber membrane in Example 1 of the present invention and the commercial PE separator in Comparative Example 3 are shown.

[0041] Figure 7 The graph shows the battery cycle performance at 0.5C for lithium-ion batteries assembled with the C1-12FPI nanofiber membrane in Example 2 of the present invention and the commercial PE separator in Comparative Example 3.

[0042] Figure 8 The graph shows the battery cycle performance at 0.5C for lithium-ion batteries assembled with the C2-12FPI nanofiber membrane in Example 3 of the present invention and the commercial PE separator in Comparative Example 3.

[0043] Figure 9 The thermal stability test results are shown for the C-12FPI nanofiber membrane in Example 1 of the present invention and the commercial PE membrane in Comparative Example 3.

[0044] Figure 10 The charge-discharge voltage curves of lithium-ion batteries assembled with the C-12FPI nanofiber membrane in Example 1 and the NC-12FPI nanofiber membrane in Comparative Example 1 are shown.

[0045] Figure 11 The graphs show the solvent resistance test results of the C-12FPI nanofiber membrane in Example 1 and the NC-12FPI nanofiber membrane in Comparative Example 1 in the electrolyte. Detailed Implementation

[0046] The invention's objective will be further described in detail below with reference to the accompanying drawings and specific embodiments. The embodiments cannot be described in detail here, but the implementation of the invention is not limited to the following embodiments.

[0047] Example 1

[0048] 1.1072 g of dianhydride containing R1 and 0.9038 g of diamine containing R2 (molar ratio 1.01:1) were dissolved in 5 mL of N,N-dimethylacetamide. The mixture was stirred at 0 °C for 6 h under a nitrogen atmosphere, resulting in a condensation reaction. The viscosity of the solution in the container increased, eventually forming a polyamic acid precursor (OH-12FPAA) of a certain molecular weight, with the following structure:

[0049]

[0050] R1 is R2 is

[0051] The prepared polyamic acid precursor was mixed with N,N-dimethylacetamide to prepare a spinning solution with a mass content of 20%. High-voltage electrospinning was then performed under the following conditions: ambient temperature 25℃, ambient humidity 45%, needle type 21#, feed speed 0.3 mL / h, spinning voltage 14.8 kV, and receiving distance 20 cm. This resulted in a polyamic acid nanofiber membrane with a thickness of 35 μm. Figure 1 The image shows a SEM image of a polyamic acid nanofiber membrane. As can be seen from the image, the overall characteristic of its fiber arrangement is random orientation, with the fibers stacked loosely or even scattered. Such fiber arrangement cannot form uniform pores, and the pore distribution is wide and the pore size is large, which has a negative impact on the isolation between positive and negative electrodes, ion transport, and current stability.

[0052] The prepared polyamic acid nanofiber membrane was subjected to heat treatment: the solvent was evaporated by drying in a vacuum oven at 150℃ for 1 hour, and the vacuum oven was heated to 200℃ and 250℃ for 1 hour each to thermally ammoniate the polyamic acid nanofiber membrane. Then, part of the thermally ammoniated fiber membrane was placed in a tube furnace under a nitrogen atmosphere and held at 300℃ for 2 hours to ensure complete thermal ammoniation and the occurrence of hydroxyl crosslinking reaction, finally obtaining the finished crosslinked polyimide nanofiber membrane (C-12FPI). Figure 2 The image shows a SEM image of the surface of a cross-linked polyimide nanofiber membrane (C-12FPI). As can be seen from the image, compared with the untreated polyamic acid nanofiber membrane, the main change is that after heat treatment, the fibers begin to show slight adhesion, the local fibers are tightly stacked, and the overall diameter of the fibers becomes thicker due to adhesion. The arrangement direction is still random, but the direction is no longer straight but curved, which reduces the pore size to some extent.

[0053] Example 2

[0054] 0.9026 g of dianhydride containing R1 and 1.1064 g of diamine containing R2 (molar ratio 1.01:1) were dissolved in 5 mL of N,N-dimethylformamide. The mixture was stirred at 0 °C for 6 h under a nitrogen atmosphere, resulting in a condensation reaction. The viscosity of the solution in the container increased, eventually forming a polyamic acid precursor with a certain molecular weight, the structure of which is as follows:

[0055] R1 is R2 is

[0056] The obtained polyamic acid precursor was mixed with N,N-dimethylacetamide to prepare a spinning solution with a mass content of 20% for high-voltage electrospinning. Spinning was carried out under the conditions of ambient temperature of 25℃, ambient humidity of 45%, needle type 21#, feed speed of 0.3mL / h, spinning voltage of 15.4kV, and receiving distance of 20cm to prepare a polyamic acid nanofiber membrane with a thickness of 45μm.

[0057] The prepared polyamic acid nanofiber membrane was subjected to heat treatment: the solvent was evaporated by drying in a vacuum oven at 150℃ for 1 hour, and the vacuum oven was heated to 200℃ and 250℃ for 1 hour each to thermally ammoniate the polyamic acid nanofiber membrane. Then, part of the thermally ammoniated fiber membrane was placed in a tube furnace under a nitrogen atmosphere and held at 300℃ for 2 hours to ensure complete thermal ammoniation and the occurrence of hydroxyl crosslinking reaction, finally obtaining the finished crosslinked polyimide nanofiber membrane (C1-12FPI).

[0058] Example 3

[0059] 1.0967 g of dianhydride containing R1 and 0.9141 g of diamine containing R2 (molar ratio 1.01:1) were dissolved in 5 mL of N-methylpyrrolidone. The mixture was stirred at 0 °C for 6 h under a nitrogen atmosphere, resulting in a condensation reaction. The viscosity of the solution in the container increased, eventually forming a polyamic acid precursor with a certain molecular weight, the structure of which is as follows:

[0060]

[0061] R1 is R2 is

[0062] The obtained polyamic acid precursor was mixed with N,N-dimethylacetamide to prepare a spinning solution with a mass content of 20% for high-voltage electrospinning. Spinning was carried out under the conditions of ambient temperature of 25℃, ambient humidity of 45%, needle type 21#, feed speed of 0.3mL / h, spinning voltage of 15.4kV, and receiving distance of 20cm to prepare a polyamic acid nanofiber membrane with a thickness of 40μm.

[0063] The prepared polyamic acid nanofiber membrane was subjected to heat treatment: the solvent was evaporated by drying in a vacuum oven at 150℃ for 1 hour, and the vacuum oven was heated to 200℃ and 250℃ for 1 hour each to thermally ammoniate the polyamic acid nanofiber membrane. Then, part of the thermally ammoniated fiber membrane was placed in a tube furnace under a nitrogen atmosphere and held at 300℃ for 2 hours to ensure complete thermal ammoniation and the occurrence of hydroxyl crosslinking reaction, finally obtaining the finished crosslinked polyimide nanofiber membrane (C2-12FPI).

[0064] Comparative Example 1

[0065] 1.1531 g of dianhydride containing R1 and 0.8583 g of diamine containing R2 (molar ratio 1.01:1) were dissolved in 5 mL of N,N-dimethylacetamide. The mixture was stirred at 0 °C for 6 h under a nitrogen atmosphere, resulting in a condensation reaction. The viscosity of the solution in the container increased, eventually forming a polyamic acid precursor with a certain molecular weight, the structure of which is as follows:

[0066]

[0067] R1 is R2 is

[0068] The prepared polyamic acid precursor was mixed with N,N-dimethylacetamide to prepare a spinning solution with a mass content of 20% for high-voltage electrospinning. Spinning was carried out under the following conditions: ambient temperature of 25℃, ambient humidity of 45%, needle type 21#, feed speed of 0.3mL / h, spinning voltage of 14.6kV, and receiving distance of 20cm. A polyamic acid nanofiber membrane with a thickness of 38μm was prepared.

[0069] The prepared polyamic acid nanofiber membrane was subjected to heat treatment: the solvent was evaporated by drying in a vacuum oven at 150℃ for 1 hour, and the vacuum oven was heated to 200℃ and 250℃ for 1 hour each to thermally ammoniate the polyamic acid nanofiber membrane. Then, part of the thermally ammoniated fiber membrane was placed in a tube furnace under a nitrogen atmosphere and held at 300℃ for 2 hours to ensure complete thermal ammoniation, and finally the finished non-crosslinked polyimide nanofiber membrane (NC-12FPI) was obtained.

[0070] Comparative Example 2

[0071] 1.3929 g of dianhydride containing R1 and 0.6209 g of diamine containing R2 (molar ratio 1.01:1) were dissolved in 5 mL of N,N-dimethylacetamide. The mixture was stirred at 0 °C for 6 h under a nitrogen atmosphere, resulting in a condensation reaction. The viscosity of the solution in the container increased, eventually forming a polyamic acid precursor with a certain molecular weight, the structure of which is as follows:

[0072]

[0073] R1 is R2 is

[0074] The prepared polyamic acid precursor was mixed with N,N-dimethylacetamide to prepare a spinning solution with a mass content of 20% for high-voltage electrospinning. Spinning was carried out under the conditions of ambient temperature of 25℃, ambient humidity of 45%, needle type 21#, feed speed of 0.3mL / h, spinning voltage of 13.8kV, and receiving distance of 20cm to prepare a polyamic acid nanofiber membrane with a thickness of 50μm.

[0075] The prepared polyamic acid nanofiber membrane was subjected to heat treatment: the solvent was evaporated by drying in a vacuum oven at 150℃ for 1 hour, and the vacuum oven was heated to 200℃ and 250℃ for 1 hour each to thermally ammoniate the polyamic acid nanofiber membrane. Then, part of the thermally ammoniated fiber membrane was placed in a tube furnace under a nitrogen atmosphere and held at 300℃ for 2 hours to ensure complete thermal ammoniation, and finally the finished non-crosslinked polyimide nanofiber membrane (NC-6FPI) was obtained.

[0076] Comparative Example 3

[0077] Commercial Celgard 2325 membrane separator.

[0078] Table 1 shows the test data of electrolyte absorption rate and electrolyte contact angle of the fiber membranes prepared in Example 1 and Comparative Examples 2 and 3.

[0079] Table 1

[0080] Electrolyte absorption rate Electrolyte contact angle Example 1 (C-12FPI) 591％ 6.5° Comparative Example 2 (NC-6FPI) 485％ 13.5° Comparative Example 3 98％ 53.6°

[0081] As shown in Table 1, the electrolyte absorption rate and contact angle test data of the fiber membrane indicate that Example 1 (C-12FPI) has a higher electrolyte absorption rate and a smaller contact angle than Comparative Examples 2 and 3. Higher absorption rate and smaller contact angle indicate better affinity and better battery performance. Therefore, the separator prepared in this invention exhibits significant advantages in electrolyte affinity and wettability for lithium-ion batteries.

[0082] Figure 3 This is a structural diagram of the hydroxyl-crosslinked polyimide prepared in this invention. Figure 3 It is known that the cross-linking reaction between hydroxyl groups transforms linear C-12FPI into three-dimensional C-12FPI, enabling the cross-linked polyimide fiber membrane of this structure to maintain shape stability and mechanical properties in the electrolyte, thus enabling its application in high-performance lithium-ion battery separators.

[0083] The lithium-ion batteries assembled with the C-12FPI nanofiber membrane in Example 1, the C1-12FPI nanofiber membrane in Example 2, and the C2-12FPI nanofiber membrane in Example 3, and the commercial PE separator in Comparative Example 3, are shown in the following graphs at 0.5C: Figure 4 , Figure 7 , Figure 8 As shown, by Figure 4 , Figure 7 , Figure 8 It is evident that the cross-linked polyimide nanofiber membrane prepared by this invention exhibits superior battery performance when applied to lithium-ion battery separators.

[0084] The battery cycle performance of lithium-ion batteries assembled with C-12FPI nanofiber membrane in Example 1 and commercial PE separator in Comparative Example 3 at 1C is shown in the graph. Figure 5 As shown, by Figure 5 It is known that, at 1C, lithium-ion batteries using the cross-linked polyimide nanofiber membrane prepared in this invention as the separator exhibit better battery performance than batteries using commercial PE separators.

[0085] The rate performance curves of lithium-ion batteries assembled with the C-12FPI nanofiber membrane prepared in this invention and the commercial PE separator in Comparative Example 3 are as follows: Figure 6 As shown, by Figure 6 It can be seen that the discharge specific capacity of the C-12FPI separator battery at current densities of 0.2C, 0.5C, 1C, 2C, and 4C is higher than that of the PE commercial separator battery. Moreover, the capacity loss after increasing the current density is much lower than that of the PE commercial separator battery. After 50 charge-discharge cycles, the reversible capacity retention rates of the C-12FPI separator battery and the PE separator battery are 97.5% and 92.3%, respectively. In terms of battery rate performance, the former has an absolute advantage.

[0086] Figure 9 The figures show the thermal stability test results of the C-12FPI nanofiber membrane in Example 1 and the commercial PE separator in Comparative Example 3 of this invention. Figure 9 It can be seen that the commercial Celgard 2325 membrane in Comparative Example 3 underwent significant thermal deformation at a temperature of 100°C, while the fiber membrane (C-12FPI) in Example 1 did not deform even when placed in an environment of 300°C. This demonstrates that the polyimide fiber membrane prepared by this invention has a much greater ability to resist thermal deformation than commercial olefin membranes.

[0087] Figure 10 The charging and discharging voltage curves of lithium-ion batteries assembled with the C-12FPI nanofiber membrane in Example 1 and the NC-12FPI nanofiber membrane in Comparative Example 1 of the present invention are shown below. Figure 10It can be seen that the battery assembled with the fiber membrane of Comparative Example 1 (NC-12FPI) that has not undergone high-temperature heat treatment and crosslinking has abnormal charge and discharge voltage and cannot perform normal charge and discharge cycles. However, the fiber membrane of Example 1 (C-12FPI) after heat crosslinking has good charge and discharge voltage cycle stability, which proves that the crosslinked polyimide fiber membrane prepared by the present invention can be used as a lithium-ion battery separator.

[0088] Figure 11 These are solvent resistance (electrolyte) test results for the C-12FPI nanofiber membrane in Example 1 and the NC-12FPI nanofiber membrane in Comparative Example 1 of the present invention. Figure 11 It can be seen that after immersing the fiber membrane of Example 1 (C-12FPI) in the electrode solution for 24 hours, the fiber membrane of Example 1 (C-12FPI) still maintains its shape stability, with minimal volume expansion, and possesses certain mechanical properties and excellent solvent resistance. In contrast, the fiber membrane of Comparative Example 1 (NC-12FPI) dissolves rapidly in the electrode solution upon immersion. The fiber membrane of Comparative Example 1 (NC-12FPI) without high-temperature heat treatment, due to its high fluorine content, strong polarity, and large steric hindrance, dissolves instantly upon immersion in the electrolyte. In contrast, the thermally cross-linked fiber membrane of Example 1 (C-12FPI), despite its high fluorine content, remains stable in the electrolyte and maintains its shape stability. This demonstrates that high-temperature thermal cross-linking of hydroxyl groups can endow highly fluorinated polyimide with solvent (electrolyte) resistance, thus enabling its application as a high-performance lithium-ion battery separator.

[0089] The above-described specific embodiments are preferred embodiments of the present invention and are not intended to limit the present invention. Any other changes or equivalent substitutions made without departing from the technical solution of the present invention are included within the protection scope of the present invention.

Claims

1. A method for preparing a high-fluorine-content cross-linked polyimide nanofiber membrane, characterized in that, The specific steps are as follows: (1) A polyamic acid precursor solution is synthesized by reacting a hydroxyl-containing hexafluoroaromatic diamine with an aromatic dianhydride in a solvent; the polyamic acid precursor solution is prepared into a spinning solution and polyamic acid nanofiber membrane is prepared by high voltage electrospinning. The structure of the polyamic acid precursor is as follows: ； Among them, the structural formula of R1 is one of the following structural formulas: ； The structural formula of R2 is one of the following: ； (2) Dry the polyamic acid nanofiber membrane in a vacuum environment at 100-200℃ for 0.5-1h; then heat it to 200-300℃ for 2h-4h. (3) The polyamic acid nanofiber membrane is heated to 300-350°C under a nitrogen atmosphere to perform thermal amination and thermal crosslinking. The holding time is 1h-2h to obtain a high-fluorine crosslinked polyimide nanofiber membrane.

2. The method for preparing a high-fluorine-content cross-linked polyimide nanofiber membrane according to claim 1, characterized in that, The molar ratio of the hydroxyl-containing hexafluoroaromatic diamine to the aromatic dianhydride is 1:0.9-1.

01.

3. The method for preparing a high-fluorine-content cross-linked polyimide nanofiber membrane according to claim 1, characterized in that, The spinning solution has a solid content of 10-30% by mass.

4. The method for preparing a high-fluorine-content cross-linked polyimide nanofiber membrane according to claim 1, characterized in that, The solvent is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, or dimethyl sulfoxide.

5. The method for preparing a high-fluorine-content cross-linked polyimide nanofiber membrane according to claim 1, characterized in that, The specific process conditions for the high-voltage electrospinning method are as follows: ambient temperature 20-30 ℃, ambient humidity 35-50%, feed speed 0.2-0.4 mL / h, and spinning voltage 11-16 kV.

6. The method for preparing a high-fluorine-content cross-linked polyimide nanofiber membrane according to claim 1, characterized in that, The heating described in step (3) is specifically a heating rate of 4-6℃ / min.

7. A lithium-ion battery separator, characterized in that, It is a high-fluorine-content cross-linked polyimide nanofiber membrane; the high-fluorine-content cross-linked polyimide nanofiber membrane is prepared by the preparation method of the high-fluorine-content cross-linked polyimide nanofiber membrane according to any one of claims 1 to 6.

8. A lithium-ion battery, characterized in that, It includes a lithium-ion battery separator as described in claim 7.

9. A lithium-ion battery according to claim 8, characterized in that, The lithium-ion battery is a lithium metal lithium-ion battery, a graphite anode lithium-ion battery, or a silicon-carbon anode lithium-ion battery.

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