A lithium-stable nanofiber-based composite solid electrolyte, preparation method and application thereof

Abstract

The present invention discloses a lithium-stable nanofiber-based composite solid electrolyte, which uses a conductive polymer nanofiber membrane with a three-dimensional interconnected network structure as a substrate. An electrolyte solution is coated on the surface of the nanofiber membrane and penetrates into the mesopores of the nanofiber membrane with a three-dimensional interconnected network to form a lithium-stable nanofiber-based composite solid electrolyte with a certain thickness. The electrolyte solution is a mixture of succinonitrile, lithium salt and ionic liquid. The problems existing in the existing polymer solid electrolyte are solved, and the polymer solid electrolyte has the advantages of high ionic conductivity, excellent lithium interface stability, a wide operating voltage window, etc. When applied to solid-state batteries, high charge and discharge capacity and long-cycle safe operation of the solid-state battery can be achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a nanofiber-based composite solid electrolyte that is stable to lithium, a preparation method and applications thereof. Background Art

[0002] Solid-state batteries, as the next generation of lithium secondary batteries, have fundamentally solved the safety risks of traditional lithium-ion batteries by using solid-state electrolytes instead of organic electrolytes. They have now become a research hotspot for researchers in high-efficiency, scientific research institutes, and enterprises. Compared with traditional liquid batteries, solid-state batteries have the advantages of high safety and high energy density. However, solid-state electrolytes in solid-state batteries have key technical problems such as high solid-solid interface impedance and weak ability to resist or eliminate lithium dendrite growth. Polymer solid electrolytes among solid electrolytes have attracted widespread attention in scientific research due to their excellent interface compatibility and simple and easy preparation process. However, current polymer solid electrolytes still have disadvantages such as narrow voltage window, instability to lithium, and low ionic conductivity. They cannot meet the current requirements for electrolyte characteristics of solid-state batteries, making it difficult to achieve the high rate and long cycle life requirements of solid-state batteries. Summary of the Invention

[0003] In view of this, the purpose of the present invention is to provide a lithium-stable nanofiber-based composite solid electrolyte, a preparation method and its application, to solve the problems existing in the existing polymer solid electrolytes themselves, so that the polymer solid electrolyte has the advantages of high ionic conductivity, excellent lithium interface stability, wide operating voltage window, etc., and its application in solid-state batteries can achieve high charge and discharge capabilities and long-cycle safe operation of solid-state batteries.

[0004] The lithium-stable nanofiber-based composite solid electrolyte of the present invention uses a conductive polymer nanofiber membrane with a three-dimensional interconnected network structure as a substrate. An electrolyte solution is coated on the surface of the nanofiber membrane and penetrates into the mesopores of the three-dimensional interconnected nanofiber membrane to form a lithium-stable nanofiber-based composite solid electrolyte with a certain thickness. The electrolyte solution is a mixture of succinonitrile, lithium salt and ionic liquid.

[0005] Furthermore, the molar ratio of succinonitrile: lithium salt: ionic liquid in the electrolyte solution is 2-4: 1-2: 0.2-1;

[0006] Further, the ionic liquid is one or more of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide, 1-propyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1-hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1-vinyl-3-ethylimidazolium bis(trifluoromethanesulfonyl)imide, 1-benzyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1-vinyl-3-butylimidazolium bis(trifluoromethanesulfonyl)imide, and 1-benzyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide; the lithium salt is lithium bis(fluorosulfonyl)imide;

[0007] Furthermore, the conductive polymer nanofiber membrane is prepared by electrospinning a spinning solution obtained by dissolving an organic conductive polymer in an organic solvent; the thickness of the conductive polymer nanofiber membrane is 10 μm to 200 μm, and the diameter of the nanofibers in the conductive polymer nanofiber membrane is 5 nm to 500 nm;

[0008] Furthermore, the organic conductive polymer in the conductive polymer nanofiber membrane is one or more of polyvinylidene fluoride, polyethylene oxide, polyvinylidene fluoride-hexafluoropropylene, polyimide, polyacrylonitrile, polytetrafluoroethylene, and polyvinyl chloride;

[0009] Furthermore, the organic solvent is one or more of acetonitrile, anisole, chloroform, dichloroethane, N,N-dimethylformamide, N,N-dimethylformamide, N-methylpyrrolidone, acetone, tetrachloroethane, styrene, benzene, chloroform, xylene, toluene, carbon tetrachloride, methyl ethyl ketone, esters, ethanol, and ether.

[0010] The present invention also discloses a method for preparing a lithium-stable nanofiber-based composite solid electrolyte, comprising the following steps:

[0011] a. Preparation of a conductive polymer nanofiber membrane: A conductive polymer is dissolved in an organic solvent under rapid stirring conditions to prepare a spinning solution, and then the spinning solution is electrospun to prepare a conductive polymer nanofiber membrane, which is vacuum-dried at 40°C to 100°C for later use;

[0012] b. Preparation of electrolyte solution: Succinonitrile, lithium salt and ionic liquid were stirred at high speed magnetically under heating until uniform to obtain an electrolyte solution;

[0013] c. Preparation of a nanofiber-based composite solid electrolyte: An electrolyte solution is dropped onto the surface of a conductive polymer nanofiber membrane. Using a spatula, the electrolyte solution is evenly coated onto the membrane surface while simultaneously penetrating into the three-dimensional interconnected network of mesopores within the nanofiber membrane to produce a lithium-stable nanofiber-based composite solid electrolyte. The electrolyte is then dried under vacuum at a temperature of 40°C to 60°C to obtain a lithium-stable nanofiber-based composite solid electrolyte of a desired thickness.

[0014] Furthermore, in step b, succinonitrile, lithium salt and ionic liquid are heated to 55° C. to 65° C.; in step c, the viscosity of the spinning solution is 1 mPa.s to 5000 mPa.s.

[0015] The invention also discloses an application of a lithium-stable nanofiber-based composite solid electrolyte, which is applied to solid-state batteries.

[0016] Furthermore, the positive electrode active material of the solid-state battery is one or more of lithium cobalt oxide, lithium iron phosphate, nickel cobalt manganese ternary material, nickel cobalt aluminum ternary material, spinel nickel manganese oxide material and lithium-rich manganese material; the negative electrode active material of the solid-state battery is metallic lithium.

[0017] The beneficial effects of the present invention are as follows: a lithium-stable nanofiber-based composite solid electrolyte, preparation method and application disclosed by the present invention utilizes polymer nanofiber membranes to establish a three-dimensional ion-conducting network structure substrate, and the ion conductivity of the polymer body can be further improved by combining with high-ion-conducting plastic crystal organic matter. The addition of multiple ionic liquid additives can, on the one hand, form a LiF-rich SEI film on the surface of lithium metal, thereby preventing the side reaction between the polymer solid electrolyte and lithium, resisting the growth of lithium dendrites or inducing the uniform deposition of lithium dendrites, and enhancing the lithium ion conductivity of the solid-solid interface. On the other hand, the ionic liquid can be used as a plasticizer to improve the wettability of the interface and enhance the close contact of the solid-solid interface. The present invention provides a method for preparing a lithium-stable nanofiber-based composite solid electrolyte, which has a simple and controllable preparation process and low cost, and the obtained solid electrolyte has excellent performance. The nanofiber-based lithium-stable composite solid electrolyte provided by the present invention has the advantages of high ionic conductivity, excellent lithium interface stability, wide operating voltage window, etc. The lithium-stable nanofiber-based composite solid electrolyte is applied to solid-state batteries, and the solid-state batteries are assembled using a sandwich structure to achieve high charge and discharge capacity and long-cycle safe operation of the solid-state battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The present invention will be further described below in conjunction with the accompanying drawings and embodiments:

[0019] Figure 1 This is the electrochemical window diagram of the polymer composite solid electrolyte of Example 1;

[0020] Figure 2 The AC impedance diagram and ionic conductivity value (25°C) of the polymer composite solid electrolyte in Example 1;

[0021] Figure 3 The charge-discharge cycle curve of the lithium symmetric solid-state battery with the polymer composite solid electrolyte in Example 1 (25°C);

[0022] Figure 4 This is a charge and discharge curve diagram of the solid-state battery in Example 1 at 25°C and a rate of 1C. DETAILED DESCRIPTION

[0023] Example 1

[0024] The preparation method of the lithium-stable nanofiber-based composite solid electrolyte of this embodiment includes the following steps:

[0025] (1) Preparation of conductive polymer nanofiber membrane: According to the weight ratio of polyethylene oxide (PEO) to acetonitrile (AN) of 1:7, 10g of PEO was weighed and placed in a beaker, 70g of AN organic solvent was added thereto and dissolved under conditions of rapid magnetic stirring to prepare a spinning solution. The viscosity of the spinning solution was 3500mPa.s. The ambient humidity was controlled to be ≤50%. A certain amount of spinning solution was taken with a syringe. The electrospinning conditions were: voltage: 15kV, the receiving distance of the receiver was 13cm, and the injection rate was 1mL / min. Three-dimensional mesh-shaped ion-conducting network structure polymer nanofibers were prepared by electrospinning technology and vacuum dried at 60°C for use.

[0026] (2) Preparation of electrolyte solution: According to the weight ratio of succinonitrile: lithium bis(fluorosulfonyl)imide: ionic liquid (1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt: 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt) of 3:2.2:1.8 (7:1), samples were taken and placed in a beaker, and stirred at 60°C with high-speed magnetic stirring until uniform electrolyte solution was obtained for use.

[0027] (3) Nanofiber-based composite solid electrolyte: Cut a 20 μm thick dried PEO nanofiber membrane into a certain size of 10 cm × 10 cm and place it in a polytetrafluoroethylene mold. Take 40 g of electrolyte solution and drop it on its surface. Use a scraper to evenly coat the electrolyte solution on the surface of the nanofiber membrane and simultaneously penetrate into the mesopores of the three-dimensional interconnected network of the nanofiber membrane to obtain a lithium-stable nanofiber-based composite solid electrolyte. Then transfer it to a vacuum drying oven and dry it under vacuum conditions at 60 ° C to obtain a 25 μm thick lithium-stable nanofiber-based composite solid electrolyte.

[0028] (4) Preparation of solid-state battery: The positive electrode sheet is prepared using nickel-cobalt-manganese (811) active material and cut into a diameter of 16 mm using a slicer. A 16 mm lithium metal sheet is selected as the negative electrode sheet. The prepared nanofiber-based composite solid electrolyte membrane is cut into a circular sheet with a diameter of 18 mm using a slicer. The positive electrode sheet, nanofiber-based composite solid electrolyte and lithium metal sheet are assembled into a sandwich structure solid-state button battery.

[0029] A sandwich-structured solid-state battery with a diameter of 12 mm was assembled using stainless steel sheets to test the AC impedance of the composite solid-state electrolyte. A symmetrical sandwich-structured solid-state battery with a diameter of 12 mm using lithium metal sheets was assembled to test the electrochemical window and charge-discharge cycle curve of the composite solid-state electrolyte.

[0030] Figure 1 This is the electrochemical window diagram of the polymer composite solid electrolyte of Example 1. It can be seen from the figure that the operating voltage window is 5.1V;

[0031] Figure 2 The AC impedance diagram and ionic conductivity of the polymer solid electrolyte in Example 1 are shown in FIG. 1 . The internal resistance is 4.6 Ω, and the ionic conductivity of the polymer composite solid electrolyte at room temperature is calculated to be 4.81×10 -4 S / cm;

[0032] Figure 3 This is the charge and discharge cycle curve of the lithium symmetric solid-state battery with the polymer composite solid electrolyte in Example 1. From the figure, it can be seen that under the charge and discharge conditions of 1 mA constant current, the polarization voltage is 30.7 mV and the cycle life is 1000 h.

[0033] Figure 4 This is a charge and discharge curve of the solid-state battery in Example 1 at 25°C and a rate of 1C. From the data in the figure, it can be seen that the discharge capacity is 119 mAh / g.

[0034] Example 2

[0035] The preparation method of the lithium-stable nanofiber-based composite solid electrolyte of this embodiment includes the following steps:

[0036] (1) Preparation of conductive polymer nanofiber membrane: According to the weight ratio of polyvinylidene fluoride to N-methylpyrrolidone of 1:10, 10g of polyvinylidene fluoride was weighed and placed in a beaker. 100g of N-methylpyrrolidone organic solvent was added thereto and dissolved under conditions of rapid magnetic stirring to prepare a spinning solution. The viscosity of the spinning solution was 3600mPa.s. The ambient humidity was controlled to be ≤50%. A certain amount of spinning solution was taken with a syringe. The electrospinning conditions were: voltage: 15kV, the receiving distance of the receiver was 13cm, and the injection rate was 1mL / min. Three-dimensional mesh-shaped ion-conducting network structure polymer nanofibers were prepared by electrospinning technology and vacuum dried at 60°C for use.

[0037] (2) Preparation of electrolyte solution: Samples were taken from the mixture in a weight ratio of 5:3:2 between succinonitrile, lithium bis(fluorosulfonyl)imide and ionic liquid, and placed in a beaker. The mixture was stirred at 60°C with a high-speed magnetic stirrer until uniform electrolyte solution was obtained for use. The ionic liquid was 1-propyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt.

[0038] (3) Nanofiber-based composite solid electrolyte: Cut a 50 μm thick dried nanofiber membrane of a certain size of 10 cm × 10 cm and place it in a polytetrafluoroethylene mold. Take 45 g of electrolyte solution and drop it on its surface. Use a scraper to evenly coat the electrolyte solution on the surface of the nanofiber membrane and simultaneously penetrate into the mesopores of the three-dimensional interconnected network of the nanofiber membrane to obtain a lithium-stable nanofiber-based composite solid electrolyte. Then transfer it to a vacuum drying oven and dry it under vacuum conditions at 60 ° C to obtain a lithium-stable nanofiber-based composite solid electrolyte.

[0039] (4) Preparation of solid-state battery: The positive electrode sheet is prepared using nickel-cobalt-manganese (811) active material and cut into a diameter of 16 mm using a slicer. A 16 mm lithium metal sheet is selected as the negative electrode sheet. The prepared nanofiber-based composite solid electrolyte membrane is cut into a circular sheet with a diameter of 18 mm using a slicer. The positive electrode sheet, nanofiber-based composite solid electrolyte and lithium metal sheet are assembled into a sandwich structure solid-state button battery.

[0040] Example 3

[0041] The preparation method of the lithium-stable nanofiber-based composite solid electrolyte of this embodiment includes the following steps:

[0042] (1) Preparation of conductive polymer nanofiber membrane: According to the weight ratio of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) to N,N-dimethylformamide of 1:9, 10g of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) was weighed and placed in a beaker, 90g of N,N-dimethylformamide organic solvent was added thereto and dissolved under the condition of rapid magnetic stirring to prepare a spinning solution. The viscosity of the spinning solution was 3500mPa.s. The ambient humidity was controlled to be ≤50%. A certain amount of spinning solution was taken with a syringe. The electrospinning conditions were: voltage: 15kV, the receiving distance of the receiver was 11cm, and the injection rate was 1.5mL / min. Three-dimensional mesh-shaped ion-conducting network structure polymer nanofibers were prepared by electrospinning technology and vacuum dried at 60℃ for use.

[0043] (2) Preparation of electrolyte solution: According to the weight ratio of succinonitrile: lithium bis(fluorosulfonyl)imide: ionic liquid of 2:0.5:0.5, samples were taken and placed in beakers, and stirred at 58°C with high-speed magnetic stirring until uniform electrolyte solution was obtained for use. The ionic liquids were 1-benzyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt and 1-vinyl-3-butylimidazolium bis(trifluoromethanesulfonyl)imide salt.

[0044] (3) Nanofiber-based composite solid electrolyte: Cut a certain size of 10cm×10cm and place a dried 35um thick nanofiber membrane in a polytetrafluoroethylene mold. Take 30g of electrolyte solution and drop it on its surface. Use a scraper to evenly coat the electrolyte solution on the surface of the nanofiber membrane and simultaneously penetrate into the mesopores of the three-dimensional interconnected network of the nanofiber membrane to obtain a lithium-stable nanofiber-based composite solid electrolyte. Then transfer it to a vacuum drying oven and dry it under vacuum conditions at 40℃ to obtain a lithium-stable nanofiber-based composite solid electrolyte.

[0045] (4) Preparation of solid-state battery: The positive electrode sheet is prepared using nickel-cobalt-manganese (811) active material and cut into a diameter of 16 mm using a slicer. A 16 mm lithium metal sheet is selected as the negative electrode sheet. The prepared nanofiber-based composite solid electrolyte membrane is cut into a circular sheet with a diameter of 18 mm using a slicer. The positive electrode sheet, nanofiber-based composite solid electrolyte and lithium metal sheet are assembled into a sandwich structure solid-state button battery.

[0046] Example 4

[0047] The preparation method of the lithium-stable nanofiber-based composite solid electrolyte of this embodiment includes the following steps:

[0048] (1) Preparation of conductive polymer nanofiber membrane: According to the weight ratio of polyvinyl chloride (PVC) to ethanol of 1:6, 10g of polyvinyl chloride (PVC) was weighed and placed in a beaker. 60% ethanol organic solvent was added to the PVC and dissolved under rapid magnetic stirring to prepare a spinning solution. The viscosity of the spinning solution was 4000mPa.s. The ambient humidity was controlled to be ≤50%. A certain amount of spinning solution was taken with a syringe. The electrospinning conditions were: voltage: 15kV, the receiving distance of the receiver was 13cm, and the injection rate was 1mL / min. Three-dimensional mesh-shaped ion-conducting network structure polymer nanofibers were prepared by electrospinning technology and vacuum dried at 100℃ for use.

[0049] (2) Preparation of electrolyte solution: Samples were taken from the mixture in a weight ratio of succinonitrile: lithium bis(fluorosulfonyl)imide: ionic liquid of 10:5:3 and placed in a beaker. The mixture was stirred at 62°C with a high-speed magnetic stirrer until uniform electrolyte solution was obtained for use. The ionic liquid was 1-hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt.

[0050] (3) Nanofiber-based composite solid electrolyte: Cut a 100 μm thick dried PEO nanofiber membrane into a certain size of 10 cm × 10 cm and place it in a polytetrafluoroethylene mold. Take 65 g of electrolyte solution and drop it on its surface. Use a scraper to evenly coat the electrolyte solution on the surface of the nanofiber membrane and simultaneously penetrate into the mesopores of the three-dimensional interconnected network of the nanofiber membrane to obtain a lithium-stable nanofiber-based composite solid electrolyte. Then transfer it to a vacuum drying oven and dry it under vacuum conditions at 55°C to obtain a lithium-stable nanofiber-based composite solid electrolyte.

[0051] (4) Preparation of solid-state battery: The positive electrode sheet is prepared using nickel-cobalt-manganese (811) active material and cut into a diameter of 16 mm using a slicer. A 16 mm lithium metal sheet is selected as the negative electrode sheet. The prepared nanofiber-based composite solid electrolyte membrane is cut into a circular sheet with a diameter of 18 mm using a slicer. The positive electrode sheet, nanofiber-based composite solid electrolyte and lithium metal sheet are assembled into a sandwich structure solid-state button battery.

[0052] Example 5

[0053] The preparation method of the lithium-stable nanofiber-based composite solid electrolyte of this embodiment includes the following steps:

[0054] (1) Preparation of conductive polymer nanofiber membrane: According to the weight ratio of polyimide to N-N-dimethylacetamide of 2:10, 20g of polyimide was weighed and placed in a beaker. 100g of N-N-dimethylacetamide organic solvent was added thereto and dissolved under conditions of rapid magnetic stirring to prepare a spinning solution. The viscosity of the spinning solution was 4000mPa.s. The ambient humidity was controlled to be ≤50%. A certain amount of spinning solution was taken with a syringe. The electrospinning conditions were: voltage: 15kV, the receiving distance of the receiver was 13cm, and the injection rate was 1mL / min. Three-dimensional mesh-shaped ion-conducting network structure polymer nanofibers were prepared by electrospinning technology and vacuum dried at 80℃ for use.

[0055] (2) Preparation of electrolyte solution: Samples were taken from the mixture in a weight ratio of 8:4:1 between succinonitrile, lithium bis(fluorosulfonyl)imide and ionic liquid, and placed in a beaker. The mixture was stirred at 65°C with a high-speed magnetic stirrer until uniform electrolyte solution was obtained for use. The ionic liquid was 1-benzyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide salt.

[0056] (3) Nanofiber-based composite solid electrolyte: Cut a 50 μm thick dried nanofiber membrane of a certain size of 10 cm × 10 cm and place it in a polytetrafluoroethylene mold. Take 45 g of electrolyte solution and drop it on its surface. Use a scraper to evenly coat the electrolyte solution on the surface of the nanofiber membrane and simultaneously penetrate into the mesopores of the three-dimensional interconnected network of the nanofiber membrane to obtain a lithium-stable nanofiber-based composite solid electrolyte. Then transfer it to a vacuum drying oven and dry it under vacuum conditions at 60 ° C to obtain a lithium-stable nanofiber-based composite solid electrolyte.

[0057] (4) Preparation of solid-state battery: The positive electrode sheet is prepared using nickel-cobalt-manganese (811) active material and cut into a diameter of 16 mm using a slicer. A 16 mm lithium metal sheet is selected as the negative electrode sheet. The prepared nanofiber-based composite solid electrolyte membrane is cut into a circular sheet with a diameter of 18 mm using a slicer. The positive electrode sheet, nanofiber-based composite solid electrolyte and lithium metal sheet are assembled into a sandwich structure solid-state button battery.

[0058] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A lithium-stable nanofiber-based composite solid electrolyte, characterized by: The conductive polymer nanofiber membrane with a three-dimensional interconnected network structure is used as the substrate, and the electrolyte solution is coated on the surface of the nanofiber membrane and penetrates into the mesopores of the nanofiber membrane with a three-dimensional interconnected network to form a nanofiber-based composite solid electrolyte that is stable to lithium, and a LiF-containing SEI film is formed on the surface of the lithium metal. The electrolyte solution is a mixture of succinonitrile, lithium salt and ionic liquid, and the ionic liquid is 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide salt, 1-propanediol One or more of 1-benzyl-3-methylimidazolium bis(trifluoromethanesulfonyl imide), 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl imide), 1-hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl imide), 1-vinyl-3-ethylimidazolium bis(trifluoromethanesulfonyl imide), 1-benzyl-3-methylimidazolium bis(trifluoromethanesulfonyl imide), 1-vinyl-3-butylimidazolium bis(trifluoromethanesulfonyl imide), and 1-benzyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl imide); the preparation method of the composite solid electrolyte comprises the following steps: a. Preparation of a conductive polymer nanofiber membrane: A conductive polymer is dissolved in an organic solvent under rapid stirring conditions to prepare a spinning solution, and then the spinning solution is electrospun to prepare a conductive polymer nanofiber membrane, which is vacuum-dried at 40°C to 100°C for later use; b. Preparation of electrolyte solution: Succinonitrile, lithium salt and ionic liquid were stirred at high speed magnetically under heating until uniform to obtain an electrolyte solution; c. Preparation of nanofiber-based composite solid electrolyte: Drop the electrolyte solution on the surface of the conductive polymer nanofiber membrane, use a scraper to evenly coat the electrolyte solution on the surface of the nanofiber membrane and simultaneously penetrate into the mesopores of the three-dimensional interconnected network of the nanofiber membrane to obtain a lithium-stable nanofiber-based composite solid electrolyte, and then dry it under vacuum conditions at a temperature of 40°C to 60°C to obtain a lithium-stable nanofiber-based composite solid electrolyte.

2. The lithium-stable nanofiber-based composite solid electrolyte according to claim 1, characterized in that: The molar ratio of succinonitrile: lithium salt: ionic liquid in the electrolyte solution is 2-4: 1-2: 0.2-1.

3. The lithium-stable nanofiber-based composite solid electrolyte according to claim 2, characterized in that: The lithium salt is lithium bis(fluorosulfonyl)imide.

4. The lithium-stable nanofiber-based composite solid electrolyte according to claim 3, characterized in that: The conductive polymer nanofiber membrane is prepared by electrostatic spinning of a spinning solution obtained by dissolving an organic conductive polymer in an organic solvent; the thickness of the conductive polymer nanofiber membrane is 10um to 200um, and the diameter of the nanofibers in the conductive polymer nanofiber membrane is 5nm to 500nm.

5. The lithium-stable nanofiber-based composite solid electrolyte according to claim 4, characterized in that: The organic conductive polymer in the conductive polymer nanofiber membrane is one or more of polyvinylidene fluoride, polyethylene oxide, polyvinylidene fluoride-hexafluoropropylene, polyimide, polyacrylonitrile, polytetrafluoroethylene, and polyvinyl chloride.

6. The lithium-stable nanofiber-based composite solid electrolyte according to claim 5, characterized in that: The organic solvent is one or more of acetonitrile, anisole, chloroform, dichloroethane, N,N-dimethylformamide, N-methylpyrrolidone, acetone, tetrachloroethane, styrene, benzene, chloroform, xylene, toluene, carbon tetrachloride, methyl ethyl ketone, esters, ethanol, and ether.

7. The method for preparing a lithium-stable nanofiber-based composite solid electrolyte according to claim 1, wherein: The following steps are involved: a. Preparation of a conductive polymer nanofiber membrane: A conductive polymer is dissolved in an organic solvent under rapid stirring conditions to prepare a spinning solution, and then the spinning solution is electrospun to prepare a conductive polymer nanofiber membrane, which is vacuum-dried at 40°C to 100°C for later use; b. Preparation of electrolyte solution: Succinonitrile, lithium salt and ionic liquid were stirred at high speed magnetically under heating until uniform to obtain an electrolyte solution; c. Preparation of nanofiber-based composite solid electrolyte: Drop the electrolyte solution on the surface of the conductive polymer nanofiber membrane, use a scraper to evenly coat the electrolyte solution on the surface of the nanofiber membrane and simultaneously penetrate into the mesopores of the three-dimensional interconnected network of the nanofiber membrane to obtain a lithium-stable nanofiber-based composite solid electrolyte, and then dry it under vacuum conditions at a temperature of 40°C to 60°C to obtain a lithium-stable nanofiber-based composite solid electrolyte.

8. The method for preparing a lithium-stable nanofiber-based composite solid electrolyte according to claim 7, wherein: In step b, succinonitrile, lithium salt and ionic liquid are heated to 55° C. to 65° C.; in step c, the viscosity of the spinning solution is 1 mPa.s to 5000 mPa.s.

9. The use of the lithium-stable nanofiber-based composite solid electrolyte according to claim 1, characterized in that: The lithium-stable nanofiber-based composite solid electrolyte is applied to solid-state batteries.

10. The use of the lithium-stable nanofiber-based composite solid electrolyte according to claim 9, characterized in that: The positive electrode active material of the solid-state battery is one or more of lithium cobalt oxide, lithium iron phosphate, nickel-cobalt-manganese ternary material, nickel-cobalt-aluminum ternary material, spinel nickel-manganese oxide material and lithium-rich manganese material; the negative electrode active material of the solid-state battery is metallic lithium.

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