A polyimide modified nanofiber separator composite gel polymer electrolyte and a preparation method thereof

Abstract

The application provides a preparation method of a polyimide modified nanofiber separator composite gel polymer electrolyte, comprising the following steps: preparing a polyimide surface modified polyolefin nanofiber separator, dissolving polyethylene oxide with an organic solvent to obtain a polyelectrolyte casting solution, immersing the polyimide surface modified polyolefin nanofiber separator into the polyelectrolyte casting solution to obtain a composite membrane, and finally soaking the composite membrane in an electrolyte for activation to obtain the polyimide modified nanofiber separator composite gel polymer electrolyte. The polyimide modified nanofiber separator composite gel polymer electrolyte prepared by the application has excellent ionic conductivity and battery cycle performance, and has the advantages of simple and efficient preparation process, low cost, and significantly improved safety performance, which further promotes the development and application of a new generation of gel electrolyte lithium ion batteries.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion battery gel polymer electrolyte, and particularly relates to a polyimide modified nanofiber separator composite gel polymer electrolyte and a preparation method thereof. BACKGROUND

[0002] Lithium ion batteries are the most popular energy storage systems at present, and are widely used in electric vehicles, electric bicycles and various portable electronic devices due to their high energy density, long cycle life and low self-discharge rate. However, the liquid electrolyte generally uses alkyl carbonate as an organic solution, and such carbonate liquid electrolyte will have excessive parasitic reactions with lithium metal which has strong reactivity, resulting in continuous deterioration of the cycle performance of the battery. At the same time, the low flash point and low boiling point of the organic solvent and uncontrolled lithium dendrite growth can cause combustion and even explosion under certain conditions, and there is a risk of electrolyte leakage, which has certain safety hazards.

[0003] Compared with liquid electrolyte, solid-state polymer electrolyte (SPE) and gel polymer electrolyte (GPE) have great advantages in safety performance. Although the solid-state electrolyte has high energy density and can meet the use requirements of flexible portable devices, its excessively low ionic conductivity limits its application to some extent. The gel polymer electrolyte is a semi-solid electrolyte formed by swelling of the solid-state polymer in the solvent, and under low polymer matrix content, it can make the room temperature conductivity of the lithium ion battery reach 10 -3 S cm -1 , and also has excellent safety performance.

[0004] However, the gel polymer electrolyte still has a series of problems such as low lithium ion transfer number, poor thermal stability and weak mechanical performance, and researchers usually add plasticizers or liquid electrolytes to improve the ionic conductivity of the gel electrolyte, but at the same time, the mechanical performance of the gel electrolyte is reduced. Therefore, in order to ensure the mechanical integrity of the gel electrolyte without adding additional supporting substrate, the gel electrolyte often has a large thickness and a relatively high polymer matrix content, but this will also damage the battery performance and energy density of the gel electrolyte. SUMMARY

[0005] The present application is carried out to solve the above problems, and aims to provide a polyimide modified nanofiber separator composite gel polymer electrolyte and a preparation method thereof.

[0006] This invention provides a method for preparing a polyimide-modified nanofiber membrane composite gel polymer electrolyte, characterized by the following steps: S1, obtaining polyolefin nanofibers through co-extrusion technology, classifying and sieving the polyolefin nanofibers, then dispersing the uniformly sized and appropriately diameterd polyolefin nanofibers in a solvent and filtering them to obtain a polyolefin nanofiber membrane; S2, diluting the polyimide solution, immersing the polyolefin nanofiber membrane in the polyimide solution, removing it after 20-40 minutes, and placing it in a vacuum oven at 60-100℃ to fully dry it to remove excess solvent, obtaining a polymer-modified polyolefin nanofiber membrane. S3. Polyethylene oxide is added to an organic solvent containing a plasticizer and stirred until completely dissolved to prepare a solution. Lithium salt is then added and stirred until fully mixed to obtain a polyelectrolyte casting solution. S4. The polymer-modified polyolefin nanofiber membrane is immersed in the polyelectrolyte casting solution. After 3-5 minutes, it is removed and placed in a vacuum oven to dry thoroughly to remove excess solvent, thus obtaining a composite membrane. S5. The composite membrane is placed in an inert atmosphere glove box and immersed in the electrolyte for full activation. After 1-3 hours, it is removed and the surface electrolyte is completely absorbed with paper to obtain a polyimide-modified nanofiber membrane composite gel polymer electrolyte with a thickness of 20-35 μm.

[0007] The polyimide-modified nanofiber membrane composite gel polymer electrolyte provided by the present invention may also have the following characteristics: wherein the polyolefin nanofiber material in step S1 is one or more of high-density polyethylene, low-density polyethylene, polyethylene, polypropylene, modified polypropylene, and modified polyethylene.

[0008] The polyimide-modified nanofiber membrane composite gel polymer electrolyte provided by the present invention may also have the following feature: wherein the mesh size of the sieve used in step S1 is 100-400 mesh.

[0009] The polyimide-modified nanofiber membrane composite gel polymer electrolyte provided by the present invention may also have the following feature: wherein the solvent used for the polyimide in step S2 is one or more of ethanol, tetrahydrofuran, N-methylpyrrolidone and N,N-dimethylformamide.

[0010] The polyimide-modified nanofiber membrane composite gel polymer electrolyte provided by the present invention may also have the following feature: wherein the mass concentration of the polyimide solution in step S2 is 1-20%.

[0011] The polyimide-modified nanofiber membrane composite gel polymer electrolyte provided by the present invention may also have the following characteristics: wherein the plasticizer selected in step S3 is one or more of propylene carbonate, vinylene carbonate, fluoroethylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl carbonate.

[0012] The polyimide-modified nanofiber membrane composite gel polymer electrolyte provided by the present invention may also have the following characteristics: wherein the organic solvent in step S3 is one or more of diethyl ether, ethyl acetate, n-propanol, acetone and petroleum ether, and the lithium salt is one or more of lithium hexafluorophosphate, lithium perchlorate, lithium trifluoromethanesulfonate, lithium dioxaborate, lithium tetrafluoroborate and lithium hexafluoroarsenate.

[0013] The polyimide-modified nanofiber membrane composite gel polymer electrolyte provided by the present invention may also have the following feature: wherein the drying temperature in step S4, when placed in a vacuum oven, is 60-80°C.

[0014] The polyimide-modified nanofiber membrane composite gel polymer electrolyte provided by the present invention may also have the following characteristics: wherein, in step S5, the electrolyte is ethylene carbonate, dimethyl carbonate, propylene carbonate and lithium hexafluorophosphate, wherein ethylene carbonate: dimethyl carbonate: propylene carbonate = 1:(0.8-1.2):(0.8-1.2) Vol%, and lithium hexafluorophosphate is 0.8-1.2 M.

[0015] The present invention also provides a polyimide-modified nanofiber membrane composite gel polymer electrolyte, characterized in that it is prepared by the above-described method for preparing polyimide-modified nanofiber membrane composite gel polymer electrolyte.

[0016] The role and effect of invention

[0017] This invention relates to a polyimide-modified nanofiber membrane composite gel polymer electrolyte and its preparation method. This invention provides an effective strategy for balancing the mechanical integrity and ionic conductivity of the gel polymer electrolyte. By successfully modifying polyolefin nanofibers with polyimide and then composited with a polyethylene oxide gel electrolyte, the bonding between the modified nanofibers is significantly enhanced, effectively improving the mechanical properties of the membrane. This allows it to serve as a highly porous substrate to support the gel polymer electrolyte, greatly reducing the thickness of the gel polymer electrolyte. Simultaneously, compared to commercially available membranes of the same material, the polyolefin nanofiber membrane exhibits higher porosity and dimensional stability, which is more conducive to the uniform penetration of the polymer matrix, providing a stable channel for lithium-ion transport and effectively inhibiting dendrite growth. Furthermore, this preparation method also provides a novel safety strategy for liquid electrolyte batteries. By composited with the gel polymer electrolyte, excellent ionic conductivity and battery performance are maintained while effectively solving safety issues such as liquid leakage. Attached Figure Description

[0018] Figure 1 These are images showing the mechanical properties of the gel electrolytes in Embodiment 1 and Comparative Examples 1-2 of the present invention;

[0019] Figure 2 The AC impedance spectra of the gel electrolyte assembled into stainless steel-to-stainless steel batteries in Examples 1-5 and Comparative Example 1 of the present invention are shown.

[0020] Figure 3 The rate performance of the gel electrolyte assembled into batteries according to Examples 1-3 and Comparative Example 1 of the present invention; and

[0021] Figure 4 The cycling performance of the gel electrolyte assembled into a battery according to Example 1 and Comparative Example 1 of the present invention is shown. Detailed Implementation

[0022] To make the technical means, creative features, objectives and effects of this invention easy to understand, the following embodiments, in conjunction with the accompanying drawings, specifically illustrate a polyimide-modified nanofiber membrane composite gel polymer electrolyte and its preparation method.

[0023] A method for preparing a polyimide-modified nanofiber membrane composite gel polymer electrolyte specifically includes the following steps:

[0024] S1. Prepare 8192-32768 layer polyolefin nanofibers by co-extrusion technology at a processing temperature of 150-200℃ and an extrusion speed ratio of 1:1 between two extruders. Then, fully disperse the polyolefin nanofibers in anhydrous ethanol and filter them through a 100-500 mesh stainless steel screen to remove coarser fiber-grade excess impurities. Finally, collect the fibers in the filtrate and filter them into diaphragms with a diameter of 4-10 cm in a negative pressure filtration device, controlling the diaphragm thickness to be 15-30 μm.

[0025] S2. Dilute the 5mM polyimide solution with N-methylpyrrolidone solution, immerse the polyolefin nanofiber membrane prepared in S1 in polymer solutions of different concentrations, take it out after 30 minutes, and place it in a vacuum oven at 100℃ to dry it thoroughly to remove excess solvent, thus obtaining nanofiber composite membranes with different polyimide loadings.

[0026] S3. Weigh 0.8-1.0g of polyethylene oxide, then measure 20ml of organic solvent and add it to a round-bottom flask. Mix the polyethylene oxide and organic solvent thoroughly, add 0.05ml of plasticizer and 0.4g of lithium salt, and heat and stir at 50℃ and 150rpm for 30min to obtain the polymer electrolyte casting solution.

[0027] S4. The membrane prepared in S2 and the polymer electrolyte casting solution in S3 are composited by immersion casting. After being thoroughly dried in a vacuum oven at 60°C, a composite membrane of polyimide-modified polyolefin nanofiber membrane and polyethylene oxide gel electrolyte is obtained.

[0028] S5. Place the composite membrane obtained in S4 in a glove box filled with argon atmosphere and immerse it in electrolyte (EC:DMC:PC=1:1:1Vol%,1M LiPF6) for activation. After 2 hours, take it out and use filter paper to absorb the electrolyte on the surface to obtain polyimide modified polyolefin nanofiber composite polyethylene oxide gel electrolyte.

[0029] Example 1

[0030] S1. 16384-layer polyolefin nanofibers were prepared by co-extrusion technology at a processing temperature of 200℃ and an extrusion speed ratio of 1:1 between the two extruders. The polyolefin nanofibers were then fully dispersed in anhydrous ethanol and filtered through 200-mesh and 300-mesh stainless steel screens to remove coarser fiber-grade impurities. Finally, the fibers in the filtrate were collected and filtered into diaphragms with a diameter of 6cm in a negative pressure filtration device, with the diaphragm thickness controlled at 20μm.

[0031] S2. Dilute the 5mM polyimide solution with N-methylpyrrolidone solution at a 3% dilution ratio. Immerse the polyolefin nanofiber membrane prepared in S1 in polymer solutions of different concentrations. After 30 minutes, remove the membrane and place it in a vacuum oven at 100°C to dry it thoroughly to remove excess solvent, thus obtaining nanofiber composite membranes with different polyimide loadings.

[0032] S3. Weigh 0.9g of polyethylene oxide, then measure 20ml of acetone and add it to a round-bottom flask. Mix the polyethylene oxide and acetone thoroughly, then add 0.05ml of propylene carbonate and 0.4g of lithium bis(trifluoromethanesulfonyl)imide. Heat and stir at 50℃ and 150rpm for 30min to obtain the polymer electrolyte casting solution.

[0033] S4. The membrane prepared in S2 and the polymer electrolyte casting solution in S3 are composited by immersion casting. After being thoroughly dried in a vacuum oven at 60°C, a composite membrane of polyimide-modified polyolefin nanofiber membrane and polyethylene oxide gel electrolyte is obtained.

[0034] S5. Place the composite membrane obtained in S4 in a glove box filled with argon atmosphere and immerse it in electrolyte (EC:DMC:PC=1:1:1Vol%,1M LiPF6) for activation. After 2 hours, take it out and use filter paper to absorb the electrolyte on the surface to obtain polyimide modified polyolefin nanofiber composite polyethylene oxide gel electrolyte.

[0035] Example 2

[0036] In this embodiment, based on the preparation conditions of Example 1, the 16384 layers of alternating polypropylene fibers were replaced with 16384 layers of alternating high-density polyethylene fibers, the processing temperature was replaced with 160℃, and the membrane with a diameter of 6cm and a thickness of 20μm was replaced with a membrane with a diameter of 8cm and a thickness of 22μm. In step S2, the immersion in a 3% diluted polyimide solution was replaced with immersion in a 5% diluted polyimide solution. In step S3, the weighing of 0.9g of polyethylene oxide was replaced with the weighing of 1.0g of polyethylene oxide, acetone was replaced with n-propanol, and propylene carbonate was replaced with ethylene carbonate.

[0037] Example 3

[0038] In this embodiment, based on the preparation conditions of Example 1, the membrane with a diameter of 6 cm and a thickness of 20 μm was replaced with a membrane with a diameter of 8 cm and a thickness of 22 μm; in step S3, 0.9 g of polyethylene oxide was replaced with 1.0 g of polyethylene oxide, acetone was replaced with diethyl ether, propylene carbonate was replaced with ethylene carbonate, and lithium bis(trifluoromethanesulfonylimide) was replaced with lithium hexafluorophosphate.

[0039] Example 4

[0040] In this embodiment, based on the preparation conditions of Example 1, the membrane with a diameter of 6 cm and a thickness of 20 μm was replaced with a membrane with a diameter of 6 cm and a thickness of 15 μm; the immersion in a 3% diluted polyimide solution in step S2 was replaced with immersion in a 5% diluted polyimide solution; in step S3, acetone was replaced with diethyl ether, propylene carbonate was replaced with ethylene carbonate, and lithium bis(trifluoromethanesulfonyl)imide was replaced with lithium hexafluorophosphate.

[0041] Example 5

[0042] In this embodiment, based on the preparation conditions of Example 1, the membrane with a diameter of 6 cm and a thickness of 20 μm was replaced with a membrane with a diameter of 6 cm and a thickness of 15 μm; in step S3, 0.9 g of polyethylene oxide was replaced with 1.0 g of polyethylene oxide, acetone was replaced with diethyl ether, propylene carbonate was replaced with ethylene carbonate, and lithium bis(trifluoromethanesulfonylimide) was replaced with lithium hexafluorophosphate.

[0043] Comparative Example 1

[0044] 16384-layer polypropylene nanofibers were prepared using nanolayer co-extrusion technology at a processing temperature of 200℃ and an extrusion speed ratio of 1:1 between two extruders. The pulverized fibers were then soaked in anhydrous ethanol and filtered through a 300-mesh stainless steel screen to remove coarser fiber impurities. Finally, the fibers in the filtrate were collected and filtered into diaphragms with a diameter of 6 cm in a negative pressure filtration device, with the diaphragm thickness controlled at 25 μm.

[0045] S2. Weigh 0.9g of polyethylene oxide, then measure 20ml of acetone and add it to a round-bottom flask. Mix the polyethylene oxide and organic solvent thoroughly, then add 0.05ml of propylene carbonate and 0.4g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). Heat and stir at 50℃ and 150rpm for 30min to obtain the polymer electrolyte casting solution.

[0046] S3. The membrane prepared in S1 and the polymer electrolyte casting solution in S2 are composited by immersion casting. After being thoroughly dried in a vacuum oven at 60°C, a composite membrane of polypropylene nanofiber membrane and polyethylene oxide gel electrolyte is obtained.

[0047] S4. Place the composite membrane obtained in S3 in a glove box filled with argon atmosphere and immerse it in an electrolyte (EC:DMC:PC=1:1:1Vol%, 1M LiPF6) for activation. After 2 hours, take it out and use filter paper to absorb the electrolyte on the surface to obtain polypropylene nanofiber composite polyethylene oxide gel electrolyte.

[0048] Comparative Example 2

[0049] Weigh 0.9g of polyethylene oxide, then measure 20ml of acetone and add it to a round-bottom flask. Mix the polyethylene oxide and organic solvent thoroughly, then add 0.05ml of propylene carbonate and 0.4g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). Heat and stir at 50℃ and 150rpm for 30min to obtain the polymer electrolyte casting solution.

[0050] S2. After pouring the casting solution into the mold and letting it stand for 10 minutes, place it in a 60℃ vacuum oven to dry it thoroughly, and then obtain a polyethylene oxide gel film.

[0051] S3. Place the composite membrane obtained in S2 in a glove box filled with argon atmosphere and immerse it in electrolyte (EC:DMC:PC=1:1:1Vol%,1M LiPF6) for activation. After 2 hours, take it out and use filter paper to absorb the electrolyte on the surface to obtain polyoxyethylene gel electrolyte.

[0052] Figure 1 These are images showing the mechanical properties of the gel electrolytes in Examples 1 and 1-2 of the present invention. Figure 2 Examples 1-5 and Comparative Example 1 are AC impedance spectra of stainless steel to stainless steel batteries.

[0053] like Figure 1 As shown, the gel electrolytes prepared in Example 1 and Comparative Examples 1-2 all exhibit good flexibility. However, the gel electrolyte prepared in Comparative Example 2 exhibits poor mechanical properties due to the lack of strong porous substrate support. In contrast, the maximum tensile stress of the strong porous modified nanofiber membrane-supported gel electrolyte prepared in Example 1 is 18.12 MPa, and the gel thickness is greatly improved (reduced from 150 μm to 25 μm).

[0054] like Figure 2 As shown, the polyimide-modified nanofiber diaphragm prepared by the present invention exhibits high ionic conductivity as a gel polymer electrolyte. Examples 1-5 and Comparative Example 1 all show good ionic conductivity. However, compared to Comparative Example 2 with the same thickness, it exhibits short circuit phenomenon. This is attributed to the diaphragm acting as a supporting structure inside, while the pure polyethylene oxide gel electrolyte has insufficient mechanical strength due to its thinness, resulting in short circuit.

[0055] Examples 1-3 and Comparative Example 1 were assembled into lithium-ion batteries and their performance was tested. LiNi was selected as the lithium-ion battery. 0.8 Co 0.1 Mn 0.1O2 (NCM811) was used as the positive electrode material, graphite as the negative electrode material, and the electrolyte was a 1M lithium hexafluorophosphate (LiPF6) solution, in which the solvent was a mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) in a volume ratio of 1:1:1. Electrochemical tests were performed on the Xinwei Battery Testing System.

[0056] Figure 3 The rate performance of the gel electrolyte assembled into batteries according to Examples 1-3 and Comparative Example 1 of the present invention is shown. Figure 4 The cycling performance of the gel electrolyte assembled into a battery according to Example 1 and Comparative Example 1 of the present invention is shown.

[0057] like Figure 3 , 4 As shown, the polyimide-modified nanofiber membrane composite gel polymer electrolyte prepared by this invention exhibits excellent electrochemical performance. For example, when the current density reaches 5C, Example 1 still has a high specific capacity (80 mAh / g), while in Examples 2 and 3, the increased membrane thickness and concentration of the polyimide solution both negatively impact battery performance. Compared to Comparative Example 1, the presence of a membrane as a supporting structure significantly improves the high-rate performance of the battery. Furthermore, the battery prepared in Example 1 exhibits a higher capacitance retention rate (91.3%) after 150 charge-discharge cycles than Comparative Example 1 (79.2%), demonstrating excellent cycle stability.

[0058] In summary, the polyimide-modified nanofiber membrane composite gel electrolyte prepared by this invention has excellent performance, low cost, and significantly improved safety performance, which is conducive to further promoting the development and application of next-generation gel electrolyte lithium-ion batteries.

[0059] The role and effect of the embodiments

[0060] This invention relates to a polyimide-modified nanofiber membrane composite gel polymer electrolyte and its preparation method. This invention provides an effective strategy for balancing the mechanical integrity and ionic conductivity of the gel polymer electrolyte. By successfully modifying polyolefin nanofibers with polyimide and then composited with a polyethylene oxide gel electrolyte, the bonding between the modified nanofibers is significantly enhanced, effectively improving the mechanical properties of the membrane. This allows it to serve as a highly porous substrate to support the gel polymer electrolyte, greatly reducing the thickness of the gel polymer electrolyte. Simultaneously, compared to commercially available membranes of the same material, the polyolefin nanofiber membrane exhibits higher porosity and dimensional stability, which is more conducive to the uniform penetration of the polymer matrix, providing a stable channel for lithium-ion transport and effectively inhibiting dendrite growth. Furthermore, this preparation method also provides a novel safety strategy for liquid electrolyte batteries. By composited with the gel polymer electrolyte, excellent ionic conductivity and battery performance are maintained while effectively solving safety issues such as liquid leakage.

[0061] This invention uses nanolayer co-extrusion technology to prepare polyolefin nanofibers with uniform size, excellent porosity, and strong electrolyte affinity, and then filters them into a membrane. The polyolefin nanofibers are immersed in polyimide solutions of different concentrations through a solution wetting method. After a certain period of wetting, the excess solvent is removed by vacuum drying, which completes the surface modification of the polyolefin nanofibers. This allows the membrane to maintain excellent porosity and wettability while greatly improving its mechanical strength.

[0062] This invention provides an effective strategy for balancing the mechanical integrity and ionic conductivity of gel polymer electrolytes by incorporating an additional high-strength porous membrane into the gel polymer electrolyte. The polyolefin nanofiber membrane exhibits higher porosity and electrolyte permeability compared to commercial membranes, which is more conducive to the uniform permeation of the polymer matrix and provides a stable medium for lithium-ion transport. Simultaneously, the polyimide-modified polyolefin nanofiber membrane demonstrates excellent mechanical properties, effectively reducing the thickness of the gel polymer electrolyte to a much lower level than the widely used 120–200 μm, enabling the prepared gel polymer electrolyte to achieve room-temperature conductivity comparable to that of traditional liquid electrolytes.

[0063] Those skilled in the art should understand that this invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to this invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a polyimide-modified nanofiber membrane composite gel polymer electrolyte, characterized in that, Specifically, the steps include the following: S1. Polyolefin nanofibers are obtained by co-extrusion technology, and the polyolefin nanofibers are graded and sieved. Then, the polyolefin nanofibers with uniform size and appropriate diameter are dispersed in a solvent and filtered to obtain a polyolefin nanofiber membrane. S2. Dilute the polyimide solution, immerse the polyolefin nanofiber membrane in the polyimide solution, remove it after 20-40 minutes, and place it in a vacuum oven at 60-100℃ to dry it thoroughly to remove excess solvent, thereby obtaining a polymer-modified polyolefin nanofiber membrane. S3. Add polyethylene oxide to an organic solvent containing plasticizer and stir until completely dissolved to prepare a solution. Then add lithium salt and continue stirring until fully mixed to obtain a polyelectrolyte casting solution. S4. The polymer-modified polyolefin nanofiber membrane is immersed in the polyelectrolyte casting solution. After 3-5 minutes, it is taken out and placed in a vacuum oven to dry thoroughly to remove excess solvent, thus obtaining a composite membrane. S5. Place the composite membrane in an inert atmosphere glove box and immerse it in the electrolyte for full activation. After 1-3 hours, take it out and use paper to completely absorb the surface electrolyte to obtain a polyimide modified nanofiber membrane composite gel polymer electrolyte with a thickness of 20-35 μm.

2. The method for preparing the polyimide-modified nanofiber membrane composite gel polymer electrolyte according to claim 1, characterized in that: in, The polyolefin nanofiber material in step S1 is one or more of polyethylene and polypropylene, wherein the polyethylene includes high-density polyethylene and low-density polyethylene.

3. The method for preparing the polyimide-modified nanofiber membrane composite gel polymer electrolyte according to claim 1, characterized in that: in, In step S1, the sieve mesh size for grading and sieving is 100-400 mesh.

4. The method for preparing the polyimide-modified nanofiber membrane composite gel polymer electrolyte according to claim 1, characterized in that: in, The solvent used for the polyimide in step S2 is one or more of ethanol, tetrahydrofuran, N-methylpyrrolidone, and N,N-dimethylformamide.

5. The method for preparing the polyimide-modified nanofiber membrane composite gel polymer electrolyte according to claim 1, characterized in that: in, The mass concentration of the polyimide solution in step S2 is 1-20%.

6. The method for preparing the polyimide-modified nanofiber membrane composite gel polymer electrolyte according to claim 1, characterized in that: in, The plasticizer selected in step S3 is one or more of propylene carbonate, vinylene carbonate, fluoroethylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate.

7. The method for preparing the polyimide-modified nanofiber membrane composite gel polymer electrolyte according to claim 1, characterized in that: in, The organic solvent in step S3 is one or more of diethyl ether, ethyl acetate, n-propanol, acetone and petroleum ether, and the lithium salt is one or more of lithium hexafluorophosphate, lithium perchlorate, lithium trifluoromethanesulfonate, lithium dioxalate borate, lithium tetrafluoroborate and lithium hexafluoroarsenate.

8. The method for preparing the polyimide-modified nanofiber membrane composite gel polymer electrolyte according to claim 1, characterized in that: in, In step S4, the drying temperature in the vacuum oven is 60-80℃.

9. The method for preparing the polyimide-modified nanofiber membrane composite gel polymer electrolyte according to claim 1, characterized in that: in, In step S5, the electrolyte is ethylene carbonate, dimethyl carbonate, propylene carbonate, and lithium hexafluorophosphate, wherein the ratio of ethylene carbonate:dimethyl carbonate:propylene carbonate is 1:(0.8-1.2):(0.8-1.2) Vol%, and the lithium hexafluorophosphate is 0.8-1.2 M.

10. A polyimide-modified nanofiber membrane composite gel polymer electrolyte, characterized in that, The polyimide-modified nanofiber membrane composite gel polymer electrolyte was prepared by the method described in any one of claims 1-9.

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