A high-temperature and high-pressure resistant composite solid-state electrolyte, a preparation method thereof and a high-temperature solid-state lithium battery using the electrolyte

Abstract

A high-temperature and high-pressure resistant composite solid electrolyte, its preparation method, and a high-temperature solid-state lithium battery using the electrolyte are disclosed. The composite solid electrolyte comprises a polymer matrix, a basic lithium salt, a lithium salt additive, and a nanofiber framework. The preparation method of the composite solid electrolyte includes S1: preparing the nanofiber framework; S2: coating the nanofiber framework to prepare a lithium-ion composite solid electrolyte. A high-temperature solid-state lithium battery includes the composite solid electrolyte manufactured using the above-mentioned composite solid electrolyte preparation method. This invention constructs a composite electrolyte system of "three-dimensional network structure nanofiber framework-PEO polymer matrix-interface regulator," introducing a three-dimensional network structure nanofiber framework to form a strong spatial physical confinement of polymer molecular chain segments, thereby improving the mechanical strength of the electrolyte at high temperatures. The addition of a high-pressure lithium salt additive decomposes under high voltage, forming an interfacial protective layer and broadening the electrochemical window of the electrolyte.

Description

Technical Field

[0001] This invention relates to the field of lithium metal battery and solid electrolyte preparation technology, specifically to a high-temperature and high-pressure resistant composite solid electrolyte, its preparation method, and a high-temperature solid lithium battery using the electrolyte. Background Technology

[0002] Against the backdrop of global energy structure transformation and low-carbon transportation development, new energy vehicles, large-scale grid energy storage, and portable electronic devices are experiencing explosive growth, posing unprecedented challenges to the energy density and safety standards of rechargeable batteries. However, traditional lithium-ion batteries rely heavily on flammable, explosive, leak-prone, and gas-generating organic liquid electrolytes, exhibiting significant intrinsic safety defects. Especially in cutting-edge applications such as aerospace, deep-earth exploration, modern defense, and special power systems, lithium-ion batteries are required not only to possess extremely high specific energy but also to maintain stable power output in extreme temperature environments far exceeding ambient temperatures. Under such harsh conditions, the chemical and thermal stability of traditional liquid lithium-ion batteries increasingly reveals insurmountable limitations. Therefore, developing novel composite solid-state electrolyte materials capable of simultaneously withstanding high temperatures and high voltage conditions is of significant scientific and practical value for promoting the engineering application of next-generation high-safety, high-energy-density lithium batteries.

[0003] Solid-state batteries, as a disruptive technology that balances high safety, high energy density, long cycle life, and excellent rate performance, are widely recognized as the most promising technological route for realizing next-generation energy storage systems. Solid-state batteries fundamentally eliminate the safety risk of thermal runaway by using solid electrolytes instead of traditional flammable electrolytes. Solid electrolytes not only possess excellent thermal stability, effectively suppressing the disordered growth of lithium dendrites, but also exhibit good mechanical strength and structural flexibility. More importantly, solid electrolytes can achieve direct series structures within the cell, thereby simplifying battery module assembly processes, reducing system complexity, and significantly increasing the volumetric energy density of the battery pack. This comprehensive innovation, from cell structure to chemical system, provides limitless possibilities for the development of high-performance energy storage devices.

[0004] Solid-state electrolytes, as the core functional unit of solid-state lithium batteries, directly determine the battery's operating temperature range and electrochemical upper limit. Among various solid-state electrolytes, the polyethylene oxide (PEO) system has shown great engineering application potential in the field of polymer all-solid-state batteries due to its good flexibility, excellent film-forming properties, efficient solvation capability for lithium salts, and low economic cost.

[0005] However, the intrinsic performance defects of PEO-based solid electrolytes limit their practical application under the aforementioned special operating conditions. On the one hand, PEO-based electrolytes typically operate at 60-80℃. When the temperature is too high, PEO is prone to shrinkage and liquefaction, leading to a sharp decline in the electrolyte's self-supporting mechanical properties and making the battery highly susceptible to short circuits. On the other hand, the electrochemical window of PEO is generally below 3.8 V (vs. Li+ / Li), making it difficult to match with high-voltage cathode materials (such as high-nickel ternary materials and lithium cobalt oxide materials). This prevents the battery from being used in high-voltage scenarios, resulting in a significant loss of the system's energy density. More seriously, under the coupling effect of high temperature and high voltage, the oxidation side reactions at the cathode interface are catalyzed exponentially, leading to instability of the cathode interface phase structure and a continuous increase in interfacial impedance. This makes the application of PEO-based solid batteries under extreme temperature and pressure conditions face insurmountable technical bottlenecks.

[0006] Chinese patent CN121416596A discloses a lithium metal battery and its high-voltage, wide-temperature-range gel polymer electrolyte, preparation method, and application. It employs a special composite monomer, conductive lithium salt, and ester ether solvent for co-polymerization to improve its high-voltage, wide-temperature-range cycle stability. However, the gel polymer electrolyte system still contains a significant amount of flammable organic liquid, posing a safety hazard. Chinese patent CN113675477A discloses an asymmetric layered polymer-based composite solid electrolyte suitable for 4.5V all-solid-state batteries, its preparation method, and application. The asymmetric multilayer electrolyte structure can simultaneously meet the different requirements of the positive electrode and lithium negative electrode sides for the polymer-based solid electrolyte itself. However, it inevitably leads to increased internal impedance of the battery, a cumbersome preparation process, and application conditions limited to 60℃. Chinese patent CN109672001A discloses a high-temperature lithium battery and its application, achieving stable cycling at 170℃. However, the positive electrode material is still limited to lithium iron phosphate, failing to achieve high-voltage applications and high energy density.

[0007] Therefore, how to construct a high-temperature and high-pressure resistant composite solid electrolyte and a high-temperature solid lithium battery using this electrolyte, which can significantly improve the high-temperature mechanical strength, positive electrode interface oxidation resistance and stability of all-solid batteries under high-temperature, high-pressure and high-voltage conditions, has become an important problem that urgently needs to be solved in this field. Summary of the Invention

[0008] To overcome the shortcomings of the prior art, the present invention aims to provide a high-temperature and high-pressure resistant composite solid electrolyte, its preparation method, and a high-temperature solid-state lithium battery using this electrolyte. By synergistically adding functional components for interfacial chemical regulation and a three-dimensional rigid support framework to the polymer matrix, and utilizing the in-situ evolution of lithium salt additives during electrochemical cycling, an interface protective layer rich in inorganic components is induced on the positive electrode side. Simultaneously, a three-dimensional network framework prepared by electrospinning physically confines the polymer segments, thereby significantly improving the oxidation resistance of the composite solid electrolyte at high cutoff voltages and its mechanical integrity under high-temperature conditions. The high-temperature and high-pressure resistant composite solid electrolyte prepared by the present invention has enhanced high-temperature mechanical strength and positive electrode interface oxidation resistance, and can significantly improve the long-cycle stability of all-solid-state batteries under high-temperature, high-pressure, and high-voltage conditions.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A high-temperature and high-pressure resistant composite solid electrolyte comprises a polymer matrix, a basic lithium salt, a high-pressure lithium salt additive, and a nanofiber skeleton with a three-dimensional network structure; the ratio of polymer matrix: basic lithium salt: high-pressure lithium salt additive is (12-18):1:(0.1-0.9) by molar ratio.

[0010] The polymer matrix comprises polyethylene oxide (PEO); the base lithium salt comprises lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) or lithium bis(fluorosulfonyl)imide (LiFSI); and the lithium salt additive comprises lithium difluorophosphate (LiDFP), lithium difluorooxalate borate (LiDFOB), or lithium bis(oxalate borate) borate (LiBOB).

[0011] The nanofiber framework of the three-dimensional network structure includes polyacrylonitrile (PAN) nanofibers or polyimide (PI) nanofibers.

[0012] A method for preparing a high-temperature and high-pressure resistant composite solid electrolyte includes the following steps: Step S1: Prepare a three-dimensional network structure of nanofiber framework; Step S2: Coat the three-dimensional network structure of the nanofiber skeleton obtained in step S1 to prepare a lithium-ion composite solid electrolyte.

[0013] The specific process for preparing the three-dimensional network structure of the nanofiber framework in step S1 is as follows: Step S1.1: First, add the polymer solute to a polar aprotic solvent at a mass fraction of 10-25 wt%, and stir continuously at 25-60 °C for 12-24 h to obtain a direct-dissolution spinning solution; or dissolve 4,4'-diaminodiphenyl ether (ODA) in a polar aprotic solvent at a mass fraction of 12-22 wt%, and after the 4,4'-diaminodiphenyl ether (ODA) is completely dissolved, add pyromellitic dianhydride (PMDA), wherein the molar ratio of 4,4'-diaminodiphenyl ether (ODA) to pyromellitic dianhydride (PMDA) is 1:0.8-1:1.2, and stir at 25-60 °C for 12-24 h to obtain a precursor conversion spinning solution; The polymer solute includes polyacrylonitrile (PAN); the polar aprotic solvent includes one of N,N-dimethylacetamide (DMAC), N,N-dimethylformamide (DMF), and N-methylpyrrolidone (NMP); the direct-dissolving spinning solution includes polyacrylonitrile (PAN); and the precursor-conversion spinning solution includes polyimide (PI). Step S1.2: Transfer the direct dissolution spinning solution or precursor conversion spinning solution prepared in step S1.1 to an electrospinning spinneret injection pump equipped with a precision needle. The distance between the electrospinning spinneret and the fiber collector is set to 10-25 cm, the propeller speed of the electrospinning spinneret injection pump is 0.5-1.5 mL / h, and a voltage of 10-30 kV is applied to the electrospinning spinneret. During this process, the relative humidity of the environment is adjusted to 20%. After electrospinning for 1-4 h, a preliminary fiber skeleton is obtained on the fiber collector. Step S1.3: Remove residual solvent from the preliminary fiber skeleton obtained in step S1.2; for the preliminary fiber skeleton obtained by direct dissolution, first place it in an 80-100 ℃ forced-air drying oven for 2-4 h, then transfer it to a vacuum drying oven and dry it at 80-100 ℃ for 12-24 h; for the preliminary fiber skeleton obtained by precursor conversion, transfer it to a muffle furnace and heat-treat it step by step at 100 ℃, 200 ℃, and 300 ℃ for 1 h respectively; finally, a nanofiber skeleton with a three-dimensional network structure is obtained; wherein the preliminary fiber skeleton obtained by direct dissolution includes polyacrylonitrile (PAN), and the preliminary fibers obtained by precursor conversion include polyimide (PI). The specific process of step S2 is as follows: Step S2.1: Weigh polyethylene oxide (PEO) and basic lithium salt at a molar ratio of (12-18):1, and mix them to obtain a raw material mixture; then add a high-pressure lithium salt additive to the raw material mixture, the mass of which accounts for 1-15 wt% of the mass of the raw material mixture; then add a dispersant to maintain the total solid content of the electrolyte slurry at 7-20 wt%; stir at 50-60 ℃ and 300-400 r / min for 12-24 h to obtain a lithium-ion composite solid electrolyte slurry; wherein, the average molecular weight of the polyethylene oxide (PEO) is 60 wt% to 200 wt%. w; the base lithium salt includes one or more of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium bis(fluorosulfonyl)imide (LiFSI) in any proportion; the high-voltage lithium salt additive includes one or more of lithium difluorophosphate (LiDFP), lithium difluorooxalate borate (LiDFOB), and lithium bis(oxalate borate) (LiBOB) in any proportion; the dispersant includes anhydrous acetonitrile (ACN) or N,N-dimethylformamide (DMF); Step S2.2: Prepare a composite lithium-ion solid electrolyte membrane. The lithium-ion composite solid electrolyte slurry obtained in step S2.1 is coated onto a polytetrafluoroethylene membrane for the first coating. Then, a three-dimensional network of nanofiber skeletons is covered on the first coated lithium-ion composite solid electrolyte slurry. Then, a second coating of lithium-ion composite solid electrolyte slurry is performed on it. After coating, it is first dried in a forced-air drying oven at 50-70 ℃ for 1-2 h, and then dried in a vacuum drying oven at 50-70 ℃ for 24-48 h. After drying, it is left to stand at room temperature for 12-24 h to obtain the lithium-ion composite solid electrolyte. The thickness of the first electrolyte slurry is 800-1500 μm, and the thickness of the second coating needs to be higher than that of the first coating, with a thickness of 1500-2500 μm.

[0014] A composite solid electrolyte is prepared by the above-described preparation method.

[0015] A high-temperature solid-state lithium battery comprising the above-described composite solid-state electrolyte or a composite solid-state electrolyte manufactured using the above-described composite solid-state electrolyte preparation method.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention achieves in-depth optimization of the intrinsic properties of electrolyte materials by constructing a composite electrolyte system consisting of a three-dimensional network nanofiber skeleton, a PEO polymer matrix, and an interface modifier. The introduction of the three-dimensional network nanofiber skeleton creates a strong spatial physical confinement of the polymer molecular chain segments, thereby enhancing the mechanical strength of the electrolyte at high temperatures. The addition of a high-voltage lithium salt additive, which decomposes under high voltage to form an interfacial protective layer, broadens the electrochemical window of the electrolyte.

[0017] 2. This invention innovatively combines a three-dimensional network nanofiber framework with multi-component interface protection, significantly improving the cycle performance of polyethylene oxide (PEO)-based solid-state batteries under extreme conditions. The three-dimensional network nanofiber framework promotes rapid lithium-ion transport and maintains the electrolyte morphology at high temperatures to prevent internal short circuits. High-voltage lithium salt additives establish a stable, oxidation-resistant interface with ion conductivity, effectively reducing interfacial impedance and promoting the formation of a good cathode / electrolyte interface. This strategy simultaneously overcomes three major technical challenges: electrolyte mechanical instability at high temperatures, interfacial oxidative decomposition under high voltage, and the surge in interfacial impedance during cycling.

[0018] 3. The addition of high-voltage lithium salt additives can construct a dense protective phase (CEI) rich in highly stable inorganic components in situ on the cathode surface, which cuts off the catalytic decomposition path of ether bonds in PEO-based polymers by the dual coupling effect of ultra-high temperature and high voltage, and inhibits the continuous malignant side reactions at the interface. This results in a breakthrough improvement in the long-cycle stability and capacity retention of all-solid-state batteries under extreme temperature and voltage conditions.

[0019] 4. The present invention adopts a preparation process of direct addition of multiple components and one-step coating of slurry, which eliminates the need for cumbersome processes such as in-situ crosslinking or multi-layer composite, greatly simplifies the production process, has strong compatibility with existing battery production lines, and has outstanding industrial mass production value and economic benefits.

[0020] In summary, this invention achieves multi-dimensional breakthroughs in high-temperature physical strength, high-pressure oxidation resistance, and electrochemical kinetic stability through interfacial chemical regulation and a three-dimensional framework confinement strategy, providing a novel solution for overcoming the performance failure of solid-state batteries under the dual harsh conditions of "extreme over-temperature and high operating voltage". Attached Figure Description

[0021] Figure 1 Electrochemical impedance spectroscopy (EIS) diagrams of the composite solid electrolytes prepared in all examples and comparative examples at 100 °C and 120 °C; wherein, Figure (a) is the EIS diagram at 100 °C and Figure (b) is the EIS diagram at 120 °C.

[0022] Figure 2 Electrochemical window diagrams of the composite solid electrolytes prepared in all examples and comparative examples at 100 °C and 120 °C; wherein, Figure 2 (a) is an electrochemical window diagram at 100℃. Figure 2 (b) is an electrochemical window diagram at 120 °C.

[0023] Figure 3 These are optical images of the composite solid electrolyte films of Example 1 and Comparative Example 1 after heat treatment at different temperatures for 1 hour. Figure 3 (a) is Example 1. Figure 3 (b) is Comparative Example 1.

[0024] Figure 4 The diagram shows the full-cell cycle diagrams of the high-temperature solid-state batteries prepared in Example 1 and Comparative Example 1.

[0025] Figure 5 The diagram shows the full-cell cycle diagrams of the high-temperature solid-state batteries prepared in Example 4 and Comparative Example 4.

[0026] Figure 6 This is a schematic diagram of the structure of the soft-pack battery of the present invention.

[0027] Figure 7 This is a schematic diagram of the coin cell of the present invention.

[0028] Figure 8 This is a schematic diagram of the electrospinning apparatus of the present invention. Detailed Implementation

[0029] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0030] A high-temperature solid-state lithium battery using the above-mentioned electrolyte, such as Figure 6 As shown, the soft-pack battery, from bottom to top, consists of a negative electrode shell, a negative electrode sheet, a composite solid electrolyte film, a positive electrode sheet, a gasket, a spring sheet, and a positive electrode shell; Figure 7 As shown, the button cell is arranged from bottom to top as follows: aluminum-plastic film, negative electrode, composite solid electrolyte film, positive electrode, and aluminum-plastic film.

[0031] Example 1 Step S1: Prepare a three-dimensional polyimide (PI) network framework; Step S1.1: Preparation of precursor conversion spinning solution: Dissolve 4,4'-diaminodiphenyl ether (ODA) in N,N-dimethylacetamide (DMAC) at a mass fraction of 12 wt%. After the 4,4'-diaminodiphenyl ether (ODA) is completely dissolved, add pyromellitic dianhydride (PMDA). The molar ratio of 4,4'-diaminodiphenyl ether (ODA) to pyromellitic dianhydride (PMDA) is 1:1.2. Stir at 25 °C for 18 h to obtain the precursor conversion spinning solution. Step S1.2: Refer to Figure 8The precursor conversion spinning solution prepared in step S1.1 is transferred to an electrospinning spinneret injection pump equipped with a precision needle. The distance between the electrospinning spinneret and the fiber collector is set to 15 cm. The propulsion speed of the electrospinning spinneret injection pump is 0.8 mL / h. An 18 kV voltage is applied to the spinning solution spinneret. During this process, the relative humidity of the environment is adjusted to 20%. After 3 h of electrospinning, a preliminary fiber skeleton can be obtained on the fiber collector. Step S1.3: Remove the residual solvent from the preliminary fiber skeleton obtained in step S1.2; transfer it to a muffle furnace and heat-treat it step by step at temperature gradients of 100℃, 200℃ and 300℃ for 1 hour each, and finally obtain a polyimide (PI) nanofiber skeleton with a three-dimensional network structure. Step S2: Coating the three-dimensional network structure of polyimide (PI) nanofiber skeleton obtained in step S1 to prepare a lithium-ion composite solid electrolyte. Step S2.1: Weigh polyethylene oxide (PEO) and base lithium salt at a molar ratio of 18:1, mix them to obtain a raw material mixture; then add a high-pressure lithium salt additive, which accounts for 5 wt% of the mass of the raw material mixture; then add an appropriate amount of dispersant to maintain the total solid content of the electrolyte slurry at 7 wt%; stir at 60℃ and 350 r / min for 18 h to obtain a lithium-ion composite solid electrolyte slurry; wherein, the polyethylene oxide has an average molecular weight of 200 wt%; the base lithium salt is lithium bis(trifluoromethanesulfonyl)imide (LiTFSI); the high-pressure lithium salt additive is lithium difluorophosphate (LiDFP); and the dispersant is anhydrous acetonitrile (ACN). Step S2.2: Prepare a composite lithium-ion solid electrolyte membrane. Using a fully automated coating machine, coat the slurry obtained in step S2.1 onto a polytetrafluoroethylene membrane for the first coating. Then, cover the first-coated electrolyte slurry with a three-dimensional network of nanofibers. Next, coat the membrane with a second lithium-ion composite solid electrolyte slurry. After coating, dry the membrane in a forced-air drying oven at 60 ℃ for 1 h, then in a vacuum drying oven at 60 ℃ for 24 h, and then let it stand at room temperature in the drying chamber for 24 h to obtain the lithium-ion composite solid electrolyte thin film material. The thickness of the first electrolyte slurry is 1000 μm, and the thickness of the second coating is 1600 μm.

[0032] The preparation method of high-temperature solid-state lithium battery using this electrolyte is as follows: Step T1: Prepare the positive electrode material; Step T1.1: The positive electrode active material, binder, conductive additive, and dispersing solvent are weighed and mixed according to a mass ratio of 8:1:1:30. The mixture is then ball-milled in a micro-ball mill at room temperature at a stirring speed of 300 r / min for 6 hours to obtain a uniform positive electrode slurry. The positive electrode active material is a ternary material (LiNi). 0.8 Co 0.1 Mn 0.1 O2); the dispersing solvent is N-methylpyrrolidone (NMP), the binder is polyvinylidene fluoride (PVDF), and the conductive additive is superconducting carbon black. Step T1.2: Coat the positive electrode slurry prepared in step S1.1 onto the current collector by scraping with a scraper; first dry in a forced-air drying oven at 80 ℃ for 1 h, then dry in a vacuum drying oven at 80 ℃ for 24 h to obtain the positive electrode material; wherein the current collector is carbon-coated aluminum foil, and the thickness of the positive electrode slurry is 100 μm.

[0033] Step T2: Encapsulate the battery using the positive electrode material prepared in step T1; Step T2.1: In an argon-filled glove box, the obtained positive electrode material and composite electrolyte film are cut to appropriate sizes, and then placed into a mold in the following order: negative electrode, electrolyte, positive electrode, stainless steel sheet, and spring sheet. The mold is then sealed using a sealing machine and stored in a glove box. The button cell specification is CR2025; the soft-pack battery is encapsulated with an aluminum-plastic film; the positive electrode is a ternary material (LiNi). 0.8 Co 0.1 Mn 0.1 O2); the negative electrode is metallic lithium.

[0034] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that LiDFP, as a high-voltage lithium salt additive, was not added in step S2.

[0035] See Figure 2 , Figure 4 Testing revealed that at high temperatures of 100°C and 120°C, the electrochemical window of Example 1 was significantly wider than that of Comparative Example 1. Regarding full-cell cycle performance, at 100°C with a charging cutoff voltage of 4.3 V, Example 1 maintained a capacity retention of 59.9% after 150 cycles, while Comparative Example 1's capacity retention decreased to 46.2% after only 50 cycles. This clearly demonstrates the improvement in high-voltage resistance of the high-voltage lithium salt additive LiDFP to the PEO-based solid electrolyte at high temperatures.

[0036] Example 2 Step S1: Prepare a three-dimensional polyimide (PI) network framework; Step S1.1: Preparation of precursor conversion spinning solution: Dissolve 4,4'-diaminodiphenyl ether (ODA) in N,N-dimethylacetamide (DMAC) at a mass fraction of 22 wt%. After the 4,4'-diaminodiphenyl ether (ODA) is completely dissolved, add pyromellitic dianhydride (PMDA). The molar ratio of 4,4'-diaminodiphenyl ether (ODA) to pyromellitic dianhydride (PMDA) is 1:0.8. Stir at 25 °C for 18 h to obtain the precursor conversion spinning solution. Step S1.2: Refer to Figure 8 The precursor conversion spinning solution prepared in step S1.1 was transferred to an electrospinning spinneret injection pump equipped with a precision needle. The distance between the electrospinning spinneret and the fiber collector was set to 20 cm, the propeller speed of the electrospinning spinneret injection pump was 0.4 mL / h, and a voltage of 22 kV was applied to the spinning solution spinneret. During this process, the relative humidity of the environment was adjusted to 20%. After 3 hours of electrospinning, a preliminary fiber skeleton could be obtained on the fiber collector. Step S1.3: Remove the residual solvent from the preliminary fiber skeleton obtained in step S1.2; transfer it to a muffle furnace and heat-treat it step by step at temperature gradients of 100℃, 200℃ and 300℃ for 1 hour each; finally obtain a polyimide (PI) nanofiber skeleton with a three-dimensional network structure. Step S2: Coating the three-dimensional network structure of polyimide (PI) nanofiber skeleton obtained in step S1 to prepare a lithium-ion composite solid electrolyte. Step S2.1: Weigh polyethylene oxide (PEO) and base lithium salt at a molar ratio of 16:1, mix them to obtain a raw material mixture; then add a high-pressure lithium salt additive, with a mass of 10 wt% of the raw material mixture; then add an appropriate amount of dispersant to maintain the total solid content of the electrolyte slurry at 14 wt%; stir at 60℃ and 350 r / min for 18 h to obtain a lithium-ion composite solid electrolyte slurry; wherein, the polyethylene oxide has an average molecular weight of 100 wt%; the base lithium salt is lithium bis(trifluoromethanesulfonyl)imide (LiTFSI); the high-pressure lithium salt additive is lithium difluorooxalate borate (LiDFOB); and the dispersant is anhydrous acetonitrile (ACN). Step S2.2: Prepare a composite lithium-ion solid electrolyte membrane. Using a fully automated coating machine, coat the slurry obtained in step S2.1 onto a polytetrafluoroethylene membrane for the first coating. Then, cover the first-coated electrolyte slurry with a three-dimensional network of nanofibers. Next, coat the membrane with a second lithium-ion composite solid electrolyte slurry. After coating, dry the membrane in a forced-air drying oven at 60 ℃ for 1 h, then in a vacuum drying oven at 60 ℃ for 24 h, and then let it stand at room temperature in the drying chamber for 24 h to obtain the lithium-ion composite solid electrolyte thin film material. The thickness of the first electrolyte slurry is 800 μm, and the thickness of the second coating is 1000 μm.

[0037] The preparation method of high-temperature solid-state lithium battery using this electrolyte is as follows: Step T1: Prepare the positive electrode material; Step T1.1: Weigh and mix the positive electrode active material, binder, conductive additive, and dispersing solvent according to a mass ratio of 8:1:1:35. Then, use a micro-ball mill to mix the materials at room temperature and a stirring speed of 350 r / min for 5 hours to obtain a uniform positive electrode slurry. The positive electrode active material is lithium cobalt oxide (LiCoO2); the dispersing solvent is N-methylpyrrolidone (NMP); the binder is polyvinylidene fluoride (PVDF); and the conductive additive is superconducting carbon black. Step T1.2: Coat the positive electrode slurry prepared in step T1.1 onto the current collector using a scraper; first dry it in a forced-air drying oven at 80 ℃ for 1 h, then dry it in a vacuum drying oven at 80 ℃ for 24 h to obtain the positive electrode material; wherein the current collector is a carbon-coated aluminum foil and the thickness of the positive electrode slurry is 200 μm; Step T2: Encapsulate the battery using the positive electrode material prepared in step S1; Step T2.1: In an argon-filled glove box, the obtained positive electrode material and composite electrolyte film are cut to appropriate sizes, and then placed into a mold in the following order: negative electrode, electrolyte, positive electrode, stainless steel sheet, and spring sheet. The mold is then sealed with a sealing machine and stored in a glove box for testing. The button cell specification is CR2025; the soft-pack battery is encapsulated with an aluminum-plastic film; the positive electrode is lithium cobalt oxide (LiCoO2); and the negative electrode is lithium metal.

[0038] Comparative Example 2 The difference between Comparative Example 2 and Example 2 is that the three-dimensional network skeleton polyimide (PI) obtained in step S1 was not added.

[0039] See Figure 1Tests showed that at 100 °C, the ionic conductivity of Example 2 was significantly improved compared to Comparative Example 2. However, at 120 °C, Comparative Example 2 experienced a short circuit due to the lack of support from the nanofiber framework. This demonstrates that nanofiber polyimide (PI) can both promote lithium-ion transport and maintain the mechanical integrity of the PEO-based solid electrolyte at high temperatures.

[0040] Example 3 Step S1: Prepare a three-dimensional polyimide (PI) network framework; Step S1.1: Preparation of precursor conversion spinning solution: Dissolve 4,4'-diaminodiphenyl ether (ODA) in N,N-dimethylacetamide (DMAC) at a mass fraction of 15 wt%. After the 4,4'-diaminodiphenyl ether (ODA) is completely dissolved, add pyromellitic dianhydride (PMDA). The molar ratio of 4,4'-diaminodiphenyl ether (ODA) to pyromellitic dianhydride (PMDA) is 1:1. Stir at 25 °C for 18 h to obtain the precursor conversion spinning solution. Step S1.2: Refer to Figure 8 The precursor conversion spinning solution prepared in step S1.1 is transferred to an electrospinning spinneret injection pump equipped with a precision needle. The distance between the electrospinning spinneret and the fiber collector is set to 28 cm, the propulsion speed of the electrospinning spinneret injection pump is 0.9 mL / h, and an 18 kV voltage is applied to the spinning solution spinneret. During this process, the relative humidity of the environment is adjusted to 20%. After 3 h of electrospinning, a preliminary fiber skeleton can be obtained on the fiber collector. Step S1.3: Remove the residual solvent from the preliminary fiber skeleton obtained in step S1.2; transfer it to a muffle furnace and heat-treat it step by step at temperature gradients of 100℃, 200℃ and 300℃ for 1 hour each; finally obtain a polyimide (PI) nanofiber skeleton with a three-dimensional network structure. Step S2: Coating the three-dimensional network structure of polyimide (PI) nanofiber skeleton obtained in step S1 to prepare a lithium-ion composite solid electrolyte. Step S2.1: Weigh polyethylene oxide (PEO) and base lithium salt at a molar ratio of 12:1, mix them to obtain a raw material mixture; then add a high-pressure lithium salt additive, which accounts for 15 wt% of the mass of the raw material mixture; then add an appropriate amount of dispersant to maintain the total solid content of the electrolyte slurry at 16 wt%; stir at 60℃ and 350 r / min for 18 h to obtain a lithium-ion composite solid electrolyte slurry; wherein, the polyethylene oxide has an average molecular weight of 60 wt%; the base lithium salt is lithium bis(trifluoromethanesulfonyl)imide (LiTFSI); the high-pressure lithium salt additive is lithium bis(oxalato)borate (LiBOB); and the dispersant is N,N-dimethylformamide (DMF). Step S2.2: Prepare a composite lithium-ion solid electrolyte membrane. Using a fully automated coating machine, coat the lithium-ion composite solid electrolyte slurry obtained in step S2.1 onto a polytetrafluoroethylene membrane for the first coating. Then, cover the three-dimensional network skeleton obtained in step 1 onto the first-coated electrolyte slurry. Then, coat the membrane with lithium-ion composite solid electrolyte slurry a second time. After coating, dry the membrane in a forced-air drying oven at 60 ℃ for 1 h, then in a vacuum drying oven at 60 ℃ for 24 h, and then let it stand at room temperature in the drying chamber for 24 h to obtain the lithium-ion composite solid electrolyte thin film material. The thickness of the first electrolyte slurry is 900 μm, and the thickness of the second coating is 1500 μm.

[0041] The preparation method of high-temperature solid-state lithium battery using this electrolyte is as follows: Step T1: Prepare the positive electrode material; Step T1.1: The positive electrode active material, binder, conductive additive, and dispersing solvent are weighed and mixed according to a mass ratio of 8:1:1:32. The mixture is then ball-milled in a micro-ball mill at room temperature at a stirring speed of 300 r / min for 6 hours to obtain a uniform positive electrode slurry. The positive electrode active material is a ternary material (LiNi). 0.6 Co 0.2 Mn 0.2 O2); the dispersing solvent is N-methylpyrrolidone (NMP), the binder is polyvinylidene fluoride (PVDF), and the conductive additive is superconducting carbon black. Step T1.2: Coat the positive electrode slurry prepared in step T1.1 onto the current collector using a scraper; first dry it in a forced-air drying oven at 80 ℃ for 1 h, then dry it in a vacuum drying oven at 80 ℃ for 24 h to obtain the positive electrode material; wherein the current collector is a carbon-coated aluminum foil and the thickness of the positive electrode slurry is 150 μm; Step T2: Encapsulate the battery using the positive electrode material prepared in step T1; Step T2.1: In an argon-filled glove box, the obtained positive electrode material and composite electrolyte film are cut to appropriate sizes, and then placed into a mold in the following order: negative electrode, electrolyte, positive electrode, stainless steel sheet, and spring sheet. The mold is then sealed using a sealing machine and stored in a glove box for testing. The button cell specification is CR2025; the soft-pack battery is encapsulated with an aluminum-plastic film; the positive electrode is a ternary material (LiNi). 0.6 Co 0.2 Mn 0.2 O2); the negative electrode is graphite.

[0042] Comparative Example 3 The difference between Comparative Example 3 and Example 3 is that the three-dimensional network skeleton PI obtained in step S1 was not added, and LiBOB as a high-voltage lithium salt additive was not added in step S2.

[0043] See Figure 2 , Figure 4 Testing revealed that at high temperatures of 100°C and 120°C, the electrochemical window of Example 3 was significantly wider than that of Comparative Example 3. Regarding full-cell cycle performance, at 120°C with a charging cutoff voltage of 4.2 V, Example 1 retained 58.46% of its capacity after 50 cycles, while Comparative Example 1's capacity almost decreased to zero after only 40 cycles. This clearly demonstrates the improvement in high-voltage resistance of the high-voltage lithium salt additive LiBOB to PEO-based solid electrolytes at high temperatures.

[0044] Example 4 Step S1: Prepare a three-dimensional polyacrylonitrile (PAN) network framework; Step S1.1: Preparation of polyacrylonitrile (PAN) spinning solution: Add polyacrylonitrile (PAN) to N,N-dimethylformamide (DMF) at a mass fraction of 24 wt%, and stir continuously at 25°C for 12 h to obtain polyacrylonitrile (PAN) spinning solution; Step S1.2: Refer to Figure 8 The direct-dissolving spinning solution prepared in step S1.1 is transferred to an electrospinning spinneret injection pump equipped with a precision needle. The distance between the electrospinning spinneret and the fiber collector is set to 18 cm, the propeller speed of the electrospinning spinneret pump is 1.0 mL / h, and a voltage of 24 kV is applied to the spinning solution spinneret. During this process, the relative humidity of the environment is adjusted to 20%. After 4 hours of electrospinning, a preliminary fiber skeleton can be obtained on the fiber collector. Step S1.3: Remove the residual solvent from the preliminary fiber skeleton obtained in step S1.2; first place it in an 80°C forced-air drying oven to dry for 4 h, and then transfer it to a vacuum drying oven to dry at 80°C for 24 h; Step S2: Coating the three-dimensional network structure of polyacrylonitrile (PAN) nanofiber skeleton obtained in step S1 to prepare a lithium-ion composite solid electrolyte. Step S2.1: Weigh polyethylene oxide (PEO) and base lithium salt at a molar ratio of 18:1, mix them to obtain a raw material mixture; then add a high-pressure lithium salt additive, which accounts for 3 wt% of the mass of the raw material mixture; then add an appropriate amount of dispersant to maintain the total solid content of the electrolyte slurry at 12 wt%; stir at 60℃ and 350 r / min for 18 h to obtain a lithium-ion composite solid electrolyte slurry; wherein, the polyethylene oxide has an average molecular weight of 100 wt%; the base lithium salt is lithium bis(trifluoromethanesulfonyl)imide (LiTFSI); the high-pressure lithium salt additive is lithium difluorophosphate (LiDFP); and the dispersant is anhydrous acetonitrile (ACN). Step S2.2: Prepare a composite lithium-ion solid electrolyte membrane. Using a fully automated coating machine, coat the lithium-ion composite solid electrolyte slurry obtained in step S2.1 onto a polytetrafluoroethylene membrane for the first coating. Then, cover the three-dimensional network skeleton obtained in step S1 onto the first-coated electrolyte slurry. Then, coat the membrane with lithium-ion composite solid electrolyte slurry a second time. After coating, dry the membrane first in a forced-air drying oven at 60 ℃ for 1 h, then in a vacuum drying oven at 60 ℃ for 24 h, and then let it stand at room temperature in the drying chamber for 24 h to obtain the lithium-ion composite solid electrolyte thin film material. The thickness of the first electrolyte slurry is 800 μm, and the thickness of the second coating is 1000 μm.

[0045] The preparation method of high-temperature solid-state lithium battery using this electrolyte is as follows: Step T1: Prepare the positive electrode material; Step T1.1: Weigh and mix the positive electrode active material, binder, conductive additive, and dispersing solvent according to a mass ratio of 8:1:1:32. Then, use a micro-ball mill to mix the materials at room temperature and a stirring speed of 400 r / min for 4 hours to obtain a uniform positive electrode slurry. The positive electrode active material is lithium cobalt oxide (LiCoO2); the dispersing solvent is N-methylpyrrolidone (NMP); the binder is polyvinylidene fluoride (PVDF); and the conductive additive is superconducting carbon black. Step T1.2: Coat the positive electrode slurry prepared in step T1.1 onto the current collector using a scraper; first dry it in a forced-air drying oven at 80 ℃ for 1 h, then dry it in a vacuum drying oven at 80 ℃ for 24 h to obtain the positive electrode material; wherein the current collector is a carbon-coated aluminum foil and the thickness of the positive electrode slurry is 200 μm; Step T2: Encapsulate the battery using the positive electrode material prepared in step T1; Step T2.1: In an argon-filled glove box, the obtained positive electrode material and composite electrolyte film are cut to appropriate sizes, and then placed into a mold in the following order: negative electrode, electrolyte, positive electrode, stainless steel sheet, and spring sheet. The mold is then sealed with a sealing machine and stored in a glove box for testing. The button cell specification is CR2025; the soft-pack battery is encapsulated with an aluminum-plastic film; the positive electrode is lithium cobalt oxide (LiCoO2); and the negative electrode is graphite.

[0046] Comparative Example 4 The difference between Comparative Example 4 and Example 4 is that LiDFP, as a high-voltage lithium salt additive, was not added in step S2.

[0047] See Figure 1 , Figure 2 Tests showed that at high temperatures of 100°C and 120°C, the ionic conductivity of Example 4 was higher than that of Comparative Example 4, and the electrochemical window of Example 4 was significantly wider.

[0048] Example 5 Step S1: Prepare a three-dimensional polyacrylonitrile (PAN) network framework; Step S1.1: Prepare a polyacrylonitrile (PAN) spinning solution. Add polyacrylonitrile (PAN) to N,N-dimethylformamide (DMF) at a mass fraction of 12 wt%, and stir continuously at 25°C for 12 h to obtain a polyacrylonitrile (PAN) spinning solution. Step S1.2: Transfer the direct-dissolving spinning solution prepared in step S1.1 to an electrospinning spinneret injection pump equipped with a precision needle. The distance between the electrospinning spinneret and the fiber collector is set to 25 cm. The propeller speed of the electrospinning solution spinneret pump is 0.6 mL / h. A voltage of 20 kV is applied to the spinning solution spinneret. During this process, the relative humidity of the environment is adjusted to 20%. After 4 hours of electrospinning, a preliminary fiber skeleton can be obtained on the fiber collector. Step S1.3: Remove the residual solvent from the preliminary fiber skeleton obtained in step S1.2; first place it in an 80°C forced-air drying oven to dry for 4 h, and then transfer it to a vacuum drying oven to dry at 80°C for 24 h; Step S2: Coating the three-dimensional network structure of the nanofiber skeleton obtained in step S1 to prepare a lithium-ion composite solid electrolyte. Step S2.1: Weigh polyethylene oxide (PEO) and base lithium salt at a molar ratio of 18:1, mix them to obtain a raw material mixture; then add a high-pressure lithium salt additive, which accounts for 10 wt% of the mass of the raw material mixture; then add an appropriate amount of dispersant to maintain the total solid content of the electrolyte slurry at 12 wt%; stir at 60℃ and 350 r / min for 18 h to obtain a lithium-ion composite solid electrolyte slurry; wherein, the polyethylene oxide has an average molecular weight of 100 wt%; the base lithium salt is lithium bis(fluorosulfonyl)imide (LiFSI); the high-pressure lithium salt additive is a mixture of lithium difluorophosphate (LiDFP) and lithium bis(oxalate borate) (LiBOB) at a molar ratio of 1:1; the dispersant is N,N-dimethylformamide (DMF). Step S2.2: Prepare a composite lithium-ion solid electrolyte membrane. Using a fully automated coating machine, coat the lithium-ion composite solid electrolyte slurry obtained in step S2.1 onto a polytetrafluoroethylene membrane for the first coating. Then, cover the three-dimensional network skeleton obtained in step 1 onto the first-coated electrolyte slurry. Then, coat the membrane with lithium-ion composite solid electrolyte slurry a second time. After coating, dry the membrane in a forced-air drying oven at 60 ℃ for 1 h, then in a vacuum drying oven at 60 ℃ for 24 h, and then let it stand at room temperature in the drying chamber for 24 h to obtain the lithium-ion composite solid electrolyte thin film material. The thickness of the first electrolyte slurry is 800 μm, and the thickness of the second coating is 1000 μm.

[0049] The preparation method of high-temperature solid-state lithium battery using this electrolyte is as follows: Step T1: Prepare the positive electrode material; Step T1.1: Weigh and mix the positive electrode active material, binder, conductive additive, and dispersing solvent according to a mass ratio of 8:1:1:32. Then, use a micro-ball mill to mix the materials at room temperature and a stirring speed of 350 r / min for 5 hours to obtain a uniform positive electrode slurry. The positive electrode active material is lithium cobalt oxide (LiCoO2); the dispersing solvent is N-methylpyrrolidone (NMP); the binder is polyvinylidene fluoride (PVDF); and the conductive additive is superconducting carbon black. Step T1.2: Coat the positive electrode slurry prepared in step T1.1 onto the current collector using a scraper; first dry it in a forced-air drying oven at 80 ℃ for 1 h, then dry it in a vacuum drying oven at 80 ℃ for 24 h to obtain the positive electrode material; wherein the current collector is a carbon-coated aluminum foil and the thickness of the positive electrode slurry is 200 μm; Step T2: Encapsulate the battery using the positive electrode material prepared in step T1; Step T2.1: In an argon-filled glove box, the obtained positive electrode material and composite electrolyte film are cut to appropriate sizes, and then placed into a mold in the following order: negative electrode, electrolyte, positive electrode, stainless steel sheet, and spring sheet. The mold is then sealed with a sealing machine and stored in a glove box for testing. The button cell specification is CR2025; the soft-pack battery is encapsulated with an aluminum-plastic film; the positive electrode is lithium cobalt oxide (LiCoO2); and the negative electrode is graphite.

[0050] Comparative Example 5 The difference between Comparative Example 5 and Example 5 is that the nanofiber skeleton PAN of the three-dimensional network obtained in step S1 was not added.

[0051] See Figure 1 , Figure 3 Testing revealed that, at 100 °C, the ionic conductivity of Example 5 was significantly improved compared to Comparative Example 5. However, at 120 °C, Comparative Example 5 experienced a short circuit due to the lack of support from the nanofiber framework. This demonstrates that nanofiber polyacrylonitrile (PAN) can both promote lithium-ion transport and inhibit the shrinkage and liquefaction of PEO-based solid electrolytes at high temperatures, thereby improving their self-supporting mechanical properties.

[0052] Table 1. Comparison of ionic conductivity of composite solid electrolytes prepared in the examples and comparative examples. From Table 1 and Figure 1 It is evident that the physical channel construction of the three-dimensional network nanofiber framework and the chemical kinetic optimization of the additives create a synergistic effect, enabling the composite electrolyte to significantly improve ionic conductivity while ensuring mechanical integrity and thermal safety under high-temperature conditions. On one hand, the three-dimensional network nanofiber framework, by constructing a continuous and interconnected network structure, provides high-speed cross-interface transport channels for lithium ions, significantly reducing their migration activation energy. On the other hand, the high-voltage lithium salt additive enhances the ion conduction kinetics within the electrolyte from a chemical perspective by increasing the concentration of free carriers in the system and promoting the full dissociation of lithium salts.

[0053] Table 2. Comparison of electrochemical windows of the composite solid electrolytes prepared in Examples 1, 3, and 4 and Comparative Examples 1, 3, and 4. From Table 2 and Figure 2 The linear sweep voltammetry curves show that the introduction of high-voltage lithium salt additives significantly broadens the electrochemical window of the composite solid electrolyte. Comparative Examples 1, 3, and 4 exhibit obvious oxidation current fluctuations at lower voltages, and the peak point of the oxidation current shifts earlier, indicating that the electrolyte itself begins to oxidize. In contrast, the initial oxidation potential of Examples 1, 3, and 4 is increased after the addition of high-voltage lithium salt additives. Figure 2(a) is 100℃, Figure 2 (b) is 120℃.

[0054] like Figure 3 As shown, Figure 3 (a) Example 5 and Figure 3 (b) Comparative Example 5 was heat-treated at 80 °C, 100 °C, 120 °C, and 150 °C for 1 hour. Example 1 showed no significant change in dimensional morphology at 100-150 °C, exhibiting excellent high-temperature dimensional thermal shrinkage. In contrast, Comparative Example 1 began to shrink at 100 °C and completely liquefied at 150 °C. This indicates that the introduction of the three-dimensional network nanofiber framework significantly improves the thermal stability of the PEO-based composite solid electrolyte film, ensuring its thermal stability and mechanical integrity for high-temperature applications.

[0055] like Figure 4 As shown, Example 1 exhibits significantly better cycle stability than Comparative Example 1 under both high temperature and high voltage conditions. The added high-voltage lithium salt additive constructs a stable and effective cathode interface protective layer (CEI) in situ on the cathode surface during the initial cycling phase. This layer possesses excellent thermodynamic stability and ionic conductivity. It significantly inhibits the continuous oxidative decomposition of the polymer matrix under high voltage and also blocks the direct contact between the electrolyte and the cathode active material, thereby cutting off the kinetic pathway of interfacial side reactions at high temperatures. Therefore, Example 1 can maintain a low interfacial impedance increment during long-term cycling, demonstrating excellent coulombic efficiency and capacity retention.

[0056] like Figure 5 As shown, the high-temperature and high-voltage cycling stability of Example 3 is significantly better than that of Comparative Example 3. The interfacial chemical regulation of the high-voltage lithium salt additive and the confinement of the three-dimensional network structure nanofiber skeleton have a synergistic effect. On the one hand, the high-voltage lithium salt additive establishes an antioxidant barrier on the positive electrode side through in-situ interfacial modification; on the other hand, the three-dimensional network structure nanofiber skeleton prepared by electrospinning plays a key role in spatial support and mechanical reinforcement under high-temperature conditions.

Claims

1. A high-temperature and high-pressure resistant composite solid electrolyte, characterized in that, It includes a polymer matrix, a basic lithium salt, a high-pressure lithium salt additive, and a nanofiber skeleton with a three-dimensional network structure; the molar ratio is polymer matrix: basic lithium salt: high-pressure lithium salt additive = (12-18):1:(0.1-0.9).

2. The high-temperature and high-pressure resistant composite solid electrolyte according to claim 1, characterized in that, The polymer matrix comprises polyethylene oxide (PEO); the base lithium salt comprises lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) or lithium bis(fluorosulfonyl)imide (LiFSI); and the lithium salt additive comprises lithium difluorophosphate (LiDFP), lithium difluorooxalate borate (LiDFOB), or lithium bis(oxalate borate) borate (LiBOB).

3. The high-temperature and high-pressure resistant composite solid electrolyte according to claim 1, characterized in that, The nanofiber framework of the three-dimensional network structure includes polyacrylonitrile (PAN) nanofibers or polyimide (PI) nanofibers.

4. A method for preparing a high-temperature and high-pressure resistant composite solid electrolyte, characterized in that, Includes the following steps: Step S1: Prepare a three-dimensional network structure of nanofiber framework; Step S2: Coat the three-dimensional network structure of the nanofiber skeleton obtained in step S1 to prepare a lithium-ion composite solid electrolyte.

5. The method for preparing a high-temperature and high-pressure resistant composite solid electrolyte according to claim 4, characterized in that, The specific process for preparing the three-dimensional network structure of the nanofiber framework in step S1 is as follows: Step S1.1: First, add the polymer solute to a polar aprotic solvent at a mass fraction of 10-25 wt%, and stir continuously at 25-60 °C for 12-24 h to obtain a direct-dissolution spinning solution; or dissolve 4,4'-diaminodiphenyl ether (ODA) in a polar aprotic solvent at a mass fraction of 12-22 wt%, and after the 4,4'-diaminodiphenyl ether (ODA) is completely dissolved, add pyromellitic dianhydride (PMDA), wherein the molar ratio of 4,4'-diaminodiphenyl ether (ODA) to pyromellitic dianhydride (PMDA) is 1:0.8-1:1.2 to obtain a precursor conversion spinning solution; The polymer solute includes polyacrylonitrile (PAN); the polar aprotic solvent includes one of N,N-dimethylacetamide (DMAC), N,N-dimethylformamide (DMF), and N-methylpyrrolidone (NMP); the direct-dissolving spinning solution includes polyacrylonitrile (PAN); and the precursor-conversion spinning solution includes polyimide (PI). Step S1.2: Transfer the direct-dissolution spinning solution or precursor-conversion spinning solution prepared in step S1.1 to an electrospinning spinneret injection pump equipped with a precision needle. The distance between the electrospinning spinneret and the fiber collector is set to 10-25 cm, the propeller speed of the electrospinning spinneret injection pump is 0.5-1.5 mL / h, and a voltage of 10-30 kV is applied to the electrospinning spinneret. During this process, the relative humidity of the environment is adjusted to 20%. After electrospinning for 1-4 h, a preliminary fiber skeleton is obtained on the fiber collector. Step S1.3: Remove the residual solvent from the preliminary fiber skeleton obtained in step S1.2; for the preliminary fiber skeleton obtained by direct dissolution, first place it in an 80-100 ℃ forced-air oven to dry for 2-4 h, then transfer it to a vacuum drying oven and dry it at 80-100 ℃ for 12-24 h; for the preliminary fiber skeleton obtained by precursor conversion, transfer it to a muffle furnace and heat treat it step by step at temperature gradients of 100 ℃, 200 ℃, and 300 ℃ for 1 h; finally, a nanofiber skeleton with a three-dimensional network structure is obtained; wherein the preliminary fiber skeleton obtained by direct dissolution includes polyacrylonitrile (PAN), and the preliminary fiber obtained by precursor conversion includes polyimide (PI).

6. The method for preparing a high-temperature and high-pressure resistant composite solid electrolyte according to claim 4, characterized in that, The specific process of step S2 is as follows: Step S2.1: Weigh polyethylene oxide (PEO) and basic lithium salt at a molar ratio of (12-18):1, and mix them to obtain a raw material mixture; then add a high-pressure lithium salt additive to the raw material mixture, the mass of which accounts for 1-15 wt% of the mass of the raw material mixture; then add a dispersant to maintain the total solid content of the electrolyte slurry at 7-20 wt%; stir at 50-60 ℃ and 300-400 r / min for 12-24 h to obtain a lithium-ion composite solid electrolyte slurry; wherein, the average molecular weight of the polyethylene oxide (PEO) is 60 wt% to 200 wt%. w; the base lithium salt includes one or more of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium bis(fluorosulfonyl)imide (LiFSI) in any proportion; the high-voltage lithium salt additive includes one or more of lithium difluorophosphate (LiDFP), lithium difluorooxalate borate (LiDFOB), and lithium bis(oxalate borate) (LiBOB) in any proportion; the dispersant includes anhydrous acetonitrile (ACN) or N,N-dimethylformamide (DMF); Step S2.2: Prepare a composite lithium-ion solid electrolyte membrane. The lithium-ion composite solid electrolyte slurry obtained in step S2.1 is coated onto a polytetrafluoroethylene membrane for the first coating. Then, a three-dimensional network of nanofiber skeletons is covered on the first coated electrolyte slurry. Then, a second coating of lithium-ion composite solid electrolyte slurry is performed on it. After coating, it is first dried in a forced-air drying oven at 50-70 ℃ for 1-2 h, and then dried in a vacuum drying oven at 50-70 ℃ for 24-48 h. After drying, it is left to stand at room temperature for 12-24 h to obtain the lithium-ion composite solid electrolyte. The thickness of the first electrolyte slurry is 800-1500 μm, and the thickness of the second coating needs to be higher than that of the first coating, with a thickness of 1500-2500 μm.

7. A composite solid electrolyte, characterized in that, The composite solid electrolyte is prepared by any one of the composite solid electrolyte preparation methods according to claims 1-6.

8. A high-temperature solid-state lithium battery, characterized in that, The high-temperature solid-state lithium battery includes the above-mentioned composite solid-state electrolyte or a composite solid-state electrolyte manufactured using the above-mentioned composite solid-state electrolyte preparation method.

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