Flame-retardant composite solid electrolyte as well as preparation method and application thereof

Abstract

The invention relates to the technical field of solid-state batteries, in particular to a flame-retardant composite solid-state electrolyte and a preparation method and application thereof.The preparation method of the flame-retardant composite solid-state electrolyte comprises the steps that carbonic ester polymeric monomers, polymeric monomers containing amide groups and lithium salt are mixed, and a monomer solution is obtained; mixing the monomer solution with an inorganic electrolyte and an initiator to obtain a composite electrolyte precursor solution; and loading the composite electrolyte precursor solution on the polyimide porous membrane, and carrying out in-situ curing treatment to obtain the flame-retardant composite solid electrolyte. A polyimide porous membrane is used as a matrix, a carbonate polymeric monomer and an amide group-containing polymeric monomer are copolymerized to form an organic network, and a lithium salt for lithium ion transmission is compounded with an inorganic oxide solid electrolyte to realize organic-inorganic synergistic flame retardance; in addition, the inorganic electrolyte and a polymer chain form a three-dimensional skeleton structure, and a stable composite system is formed through oxygen vacancy anchoring.

Description

Technical Field

[0001] This invention relates to the field of solid-state battery technology, and in particular to a flame-retardant composite solid electrolyte, its preparation method, and its application. Background Technology

[0002] Traditional liquid lithium-ion batteries suffer from frequent safety accidents due to the flammability of the electrolyte and the thermal runaway temperature of less than 100°C. All-solid-state batteries can fundamentally eliminate the risk of combustion by replacing the liquid system with a solid electrolyte. However, their commercialization faces two major challenges: inorganic electrolytes are brittle and have high interfacial impedance, while polymer electrolytes have low room temperature conductivity and are flammable, resulting in insufficient safety. Traditional flame retardants are prone to causing interfacial side reactions and cannot suppress thermal runaway chain reactions, resulting in a lack of flame retardant performance.

[0003] Existing flame-retardant solid electrolyte technology has significant drawbacks: I. Inorganic flame retardant additives (such as silicon dioxide, aluminum oxide, etc.) only physically isolate and inhibit combustion, but cannot block the free radical combustion chain reaction. Their flame retardant effect is generally poor, and they will increase the mass of more inactive substances, thus reducing the energy density of the battery. II. Intrinsically flame-retardant polymers (such as polyphosphazenes) are complex to synthesize and expensive (>$500 / kg), and have insufficient room temperature conductivity (<10). -5 (S / cm), which is limited in practical applications; Third, flame retardant-coated electrolytes have poor coating effects, the coating layer is prone to cracking and failure, and the multi-step process makes large-scale industrial application difficult.

[0004] Therefore, existing technologies still need to be improved and developed. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the purpose of this invention is to provide a flame-retardant composite solid electrolyte, its preparation method and application, in order to solve the problems of insufficient ionic conductivity and defective flame-retardant performance of existing solid electrolytes.

[0006] The technical solution of the present invention is as follows: A method for preparing a flame-retardant composite solid electrolyte includes the following steps: A monomer solution is obtained by mixing carbonate monomers, monomers containing amide groups, and lithium salts. The monomer solution is mixed with an inorganic electrolyte and an initiator to obtain a composite electrolyte precursor solution; The composite electrolyte precursor solution was loaded onto a polyimide porous membrane and then cured in situ to obtain a flame-retardant composite solid electrolyte.

[0007] The method for preparing the flame-retardant composite solid electrolyte, wherein the carbonate polymeric monomer is selected from one or more of vinylene carbonate, vinyl ethylene carbonate, and methyl acrylate; and the polymeric monomer containing an amide group is selected from one or more of N,N'-methylenebisacrylamide, N-vinylformamide, and methacrylamide.

[0008] The method for preparing the flame-retardant composite solid electrolyte, wherein the lithium salt is selected from one or more of lithium hexafluoroarsenate, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(difluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalateborate), and lithium difluorooxalateborate.

[0009] The method for preparing the flame-retardant composite solid electrolyte, wherein the inorganic electrolyte includes one of inorganic oxide electrolyte, sulfide electrolyte, and halide electrolyte; Preferably, the inorganic oxide electrolyte is selected from one or more of NASICON type electrolyte, perovskite type electrolyte, garnet type electrolyte, and LISICON type electrolyte; the initiator is selected from one or more of azobisisobutyronitrile, azobisisoheptanenitrile, and benzoyl peroxide.

[0010] The method for preparing the flame-retardant composite solid electrolyte, wherein the molar ratio of the carbonate polymeric monomer to the polymeric monomer containing amide groups is (1-50):1; and the molar fraction of the lithium salt in the monomer solution is 0.1 mol / L-4 mol / L.

[0011] The method for preparing the flame-retardant composite solid electrolyte, wherein the amount of inorganic electrolyte added is 1%-80% of the total mass of the composite electrolyte precursor solution.

[0012] The method for preparing the flame-retardant composite solid electrolyte, wherein the amount of initiator added is 0.01%-1% of the total mass of the composite electrolyte precursor solution.

[0013] The method for preparing the flame-retardant composite solid electrolyte, wherein the temperature of the in-situ curing treatment is 30℃-100℃ and the time of the in-situ curing treatment is 1h-24h.

[0014] A flame-retardant composite solid electrolyte is prepared using the method for preparing the flame-retardant composite solid electrolyte.

[0015] Application of a flame-retardant composite solid electrolyte in all-solid-state lithium metal batteries.

[0016] Beneficial Effects: This invention provides a flame-retardant composite solid electrolyte, its preparation method, and its application. The preparation method of the flame-retardant composite solid electrolyte includes the following steps: mixing carbonate polymeric monomers, amide-containing polymeric monomers, and lithium salts to obtain a monomer solution; mixing the monomer solution with an inorganic electrolyte and an initiator to obtain a composite electrolyte precursor solution; loading the composite electrolyte precursor solution onto a polyimide porous membrane and performing in-situ curing treatment to obtain the flame-retardant composite solid electrolyte. This invention uses a polyimide porous membrane as a matrix, utilizes the copolymerization of carbonate polymeric monomers and amide-containing polymeric monomers to form an organic network, and utilizes lithium salts as lithium-ion transporters to achieve organic-inorganic synergistic flame retardancy through composite with an inorganic oxide solid electrolyte; furthermore, the inorganic electrolyte and polymer chains form a three-dimensional framework structure, and a stable composite system is formed through oxygen vacancy anchoring. Meanwhile, by using polyimide porous membranes to provide an ultrathin flame-retardant substrate, the addition of inorganic electrolytes can comprehensively improve the electrochemical window of the flame-retardant composite solid electrolyte through intrinsic stability, interfacial synergy, crystallization regulation and passivation effect, making it suitable for high-nickel cathodes and lithium metal anodes and improving the theoretical energy density. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the process flow for a flame-retardant composite solid electrolyte preparation method according to the present invention. Figure 2 Optical images of monomer solutions, monomer solutions with added initiators, and precursor solutions after in-situ curing. Figure 3 Infrared spectra of monomeric solution (LE) and electrolyte (CPE) formed by in-situ curing by heating; Figure 4 A cross-sectional view of the flame-retardant composite solid electrolyte membrane obtained by scanning electron microscopy; Figure 5 The AC impedance spectrum of the flame-retardant composite solid electrolyte; Figure 6 A bar chart comparing the ionic conductivity of monomeric solutions (LE) and electrolytes (CPE) formed by in-situ curing by heating; Figure 7 This is a diagram of an ignition and combustion experiment of a monomeric solution (LE); Figure 8 This is a diagram of an ignition and combustion experiment of flame-retardant composite solid electrolyte (CPE). Figure 9 Diagram of a harsh ignition and combustion experiment for monomer solution (LE); Figure 10 Figure 1 shows an experimental diagram of ignition and combustion under harsh conditions for flame-retardant composite solid electrolyte (CPE). Figure 11 Experimental diagram for limiting oxygen index test of flame-retardant solid electrolyte; Figure 12 Half-cell cycle-efficiency and specific capacity test results for coin cells assembled using monomer solution LE and electrolyte CPE. Figure 13 This image shows the result of a soft-pack button cell being properly assembled after being cut using a flame-retardant composite solid electrolyte (CPE). Detailed Implementation

[0018] This invention provides a flame-retardant composite solid electrolyte, its preparation method, and its application. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0019] It will be understood by those skilled in the art that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. It should also be understood that terms such as those defined in general dictionaries should be understood to have the same meaning as in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless specifically defined as herein.

[0020] Existing solid electrolytes cannot simultaneously achieve high safety (combustion temperature > 300℃) and high conductivity (conductivity > 10 at room temperature). -4 The need for a composite solid electrolyte that combines in-situ curing technology (improving thermal stability), a multi-level flame-retardant synergistic mechanism (physical barrier + chemical flame retardancy + carbonization layer protection), and interface optimization design (oxygen vacancy anchoring of lithium salt) is urgent.

[0021] Based on this, such as Figure 1 As shown, this invention provides a method for preparing a flame-retardant composite solid electrolyte, comprising the following steps: Step S10: Mix carbonate monomers, monomers containing amide groups, and lithium salts to obtain a monomer solution; Step S20: Mix the monomer solution with the inorganic electrolyte and the initiator to obtain a composite electrolyte precursor solution; Step S30: Load the composite electrolyte precursor solution onto a polyimide porous membrane and cure it in situ to obtain a flame-retardant composite solid electrolyte.

[0022] In this embodiment, a polyimide porous membrane is used as the substrate. An organic network is formed by copolymerizing carbonate-based polymeric monomers with polymeric monomers containing amide groups. Lithium salts, acting as lithium-ion transporters, are combined with an inorganic oxide solid electrolyte to achieve organic-inorganic synergistic flame retardancy. Furthermore, the inorganic electrolyte and polymer chains form a three-dimensional framework structure, and a stable composite system is formed through oxygen vacancy anchoring. Simultaneously, the polyimide porous membrane provides an ultrathin flame-retardant substrate. The addition of the inorganic electrolyte, through intrinsic stability, interfacial synergy, crystallization regulation, and passivation effects, can comprehensively improve the electrochemical window of the flame-retardant composite solid electrolyte, making it suitable for high-nickel cathodes and lithium metal anodes, thereby increasing the theoretical energy density.

[0023] In some embodiments, the carbonate-based polymeric monomers are selected from, but are not limited to, one or more of vinylene carbonate (VC), vinyl ethylene carbonate (VEC), and methyl acrylate (MA); the amide-containing polymeric monomers are selected from, but are not limited to, one or more of N,N'-methylenebisacrylamide (MBA), N-vinylformamide (NVF), and methacrylamide (MAM). By using the above-mentioned carbonate-based polymeric monomers containing carbonate groups, double bond groups, etc., as the main polymeric monomers, a polymer network framework is formed through free radical polymerization, imparting flexibility and plasticity to the electrolyte; while the above-mentioned amide-containing polymeric monomers, containing double bond groups and amide groups, can introduce flame-retardant groups, improving the flame retardancy of the system.

[0024] Specifically, this invention uses a polyimide porous membrane as a matrix, copolymerizing monomers containing carbonate groups and monomers containing amide groups, and then curing them in situ with an inorganic electrolyte using an initiator to form a three-dimensional cross-linked network, which can significantly reduce interfacial impedance. In-situ polymerization ensures uniform composite of the organic and inorganic phases, reducing interfacial voids and alleviating electrode / electrolyte interface polarization. Simultaneously, the flame-retardant composite solid electrolyte prepared using this method achieves physical barrier with an oxide ceramic framework, while the amide groups decompose to release N2 / CO2 for chemical flame retardancy, and the carbonized layer provides three-level synergistic protection. At high temperatures, the amide groups release inert gases, including carbon dioxide, while oxygen vacancies on the oxide surface actively capture free radicals, interrupting the combustion chain reaction. Furthermore, the dense carbonized layer of this flame-retardant composite solid electrolyte isolates heat transfer, resulting in a thermal runaway temperature >300℃, overcoming the shortcomings of insufficient thermal stability in traditional electrolytes. Moreover, the soft-pack battery exhibits no liquid leakage or fire after being cut open, achieving a balance between high safety and high energy density.

[0025] In some embodiments, the lithium salt is selected from, but not limited to, one or more of lithium hexafluoroarsenate (LiAsF6), lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bis(difluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(oxalateborate)borate (LiBOB), and lithium difluorooxalateborate (LiDFOB). Utilizing the above lithium salts to provide freely moving lithium ions, it can be composited with inorganic oxide solid electrolytes, and further combined with carbonate polymer monomers and polymer monomers containing amide groups to form an organic network, achieving organic-inorganic synergistic flame retardancy.

[0026] In some embodiments, the inorganic electrolyte includes one of inorganic oxide electrolytes, sulfide electrolytes, and halide electrolytes. By adjusting the morphology of the inorganic electrolyte (e.g., nanowires, porous spheres), ion transport pathways and interactions with polymers can be optimized.

[0027] In a preferred embodiment, the inorganic electrolyte is an inorganic oxide electrolyte; the inorganic oxide electrolyte is selected from, but not limited to, one or more of NASICON-type electrolytes, perovskite-type electrolytes, garnet-type electrolytes, and LISICON-type electrolytes; the initiator is selected from one or more of azobisisobutyronitrile (AlBN), azobisisoheptanenitrile (ABVN), and benzoyl peroxide (BPO). Using the above-mentioned inorganic oxide electrolyte as the inorganic phase provides a rigid framework, inhibits excessive polymer chain movement, improves thermal stability, and synergistically provides flame retardancy. The above-mentioned initiator is a thermal initiator, which can be used to initiate monomer polymerization and achieve in-situ solidification of the electrolyte.

[0028] In a preferred embodiment, the NASICON-type electrolyte includes, but is not limited to, Li. 1.3 Al 0.3 Ti 1.7 (PO4)3, LiZr2(PO4)3, etc.; the perovskite electrolyte includes, but is not limited to, Li 0.33 La 0.56 TiO3, etc.; the garnet-type electrolyte includes, but is not limited to, Li7La3Zr2O 12 Li 6.4 La3Zr 1.4 Ta 0.6 O 12 etc.; the LISICON type electrolyte includes, but is not limited to, Li 3.5 Si 0.5 P 0.5 O4, etc., as inorganic phases, provide a rigid framework, inhibit excessive movement of polymer chain segments, improve thermal stability, and synergistically retardant the flame.

[0029] In some embodiments, the molar ratio of the carbonate polymeric monomer to the polymeric monomer containing the amide group is (1-50):1; by limiting the molar ratio of the reactive monomers, the structure formed by in-situ curing is controlled.

[0030] In some embodiments, the molar fraction of the lithium salt in the monomer solution is 0.1 mol / L to 4 mol / L; by controlling the molar fraction of the lithium salt within the above range, the resulting flame-retardant composite solid electrolyte has a high ionic conductivity.

[0031] In some embodiments, the amount of inorganic electrolyte added is 1%-80% of the total mass of the composite electrolyte precursor solution; by limiting the amount of inorganic electrolyte added to the above mass range, the prepared flame-retardant composite solid electrolyte has good safety performance and electrochemical performance.

[0032] In some embodiments, the amount of the initiator added is 0.01%-1% of the total mass of the composite electrolyte precursor solution; by limiting the amount of the initiator added to the above mass range, the monomer and inorganic electrolyte can be effectively solidified in situ.

[0033] In some embodiments, the temperature of the in-situ curing treatment is 30℃-100℃, and the time of the in-situ curing treatment is 1h-24h. Under this in-situ curing treatment temperature and time, the carbonate polymer monomer and the polymer monomer containing amide groups can copolymerize to form an organic network, and the lithium salt, as a lithium ion transporter, can achieve organic-inorganic synergistic flame retardancy by combining with the inorganic oxide solid electrolyte.

[0034] In a preferred embodiment, the in-situ curing temperature is 60°C and the in-situ curing time is 12 hours.

[0035] In some embodiments, in step S10, a copolymer containing amide groups can be synthesized in advance, dissolved in a solvent, blended with an inorganic electrolyte, dried to form a film, and then a flame-retardant composite solid electrolyte can be formed. The copolymer has a uniform molecular weight and the electrochemical window can be broadened.

[0036] In some embodiments, the polymeric monomer containing amide groups can be replaced with a phosphorus-containing (such as TPP) group, which releases phosphoric acid during combustion to capture free radicals and interrupt the combustion chain reaction. Furthermore, phosphorus-based flame retardants are low in cost.

[0037] In addition, the present invention also provides a flame-retardant composite solid electrolyte, which is prepared by the method of preparing the flame-retardant composite solid electrolyte.

[0038] In this embodiment, the flame-retardant composite solid electrolyte prepared by this method uses a polyimide porous membrane as the substrate. An organic network is formed by copolymerizing carbonate monomers with monomers containing amide groups. Lithium salts, acting as lithium-ion transporters, are combined with the inorganic oxide solid electrolyte to achieve organic-inorganic synergistic flame retardancy. Furthermore, the inorganic electrolyte and polymer chains form a three-dimensional framework structure, and a stable composite system is formed through oxygen vacancy anchoring. Simultaneously, the polyimide porous membrane provides an ultra-thin flame-retardant substrate. The addition of the inorganic electrolyte, through intrinsic stability, interfacial synergy, crystallization regulation, and passivation effects, comprehensively enhances the electrochemical window of the flame-retardant composite solid electrolyte, making it suitable for high-nickel cathodes and lithium metal anodes, and improving the theoretical energy density.

[0039] Specifically, this invention achieves the interaction and effective combination of various organic monomers (containing carbonate and amide groups) with inorganic oxide solid electrolytes through in-situ polymerization, forming a three-dimensional cross-linked network. This significantly reduces interfacial impedance, alleviates interfacial polarization, and adds additional lithium-ion transport paths to the inorganic electrolyte, increasing the lithium-ion transference number to over 0.5 and the ionic conductivity to 10. -4 The S / cm value suppresses dendrite penetration, preventing performance degradation caused by increased organic-inorganic interfaces. Simultaneously, this invention achieves a limiting oxygen index (LOI) > 34.5 and a thermal runaway temperature > 300℃ through a three-tiered synergistic effect of physical barrier, chemical flame retardancy, and carbonized layer protection, far exceeding traditional flame-retardant electrolyte materials. Furthermore, the inorganic electrolyte in this invention actively captures free radicals during the combustion reaction to interrupt the combustion chain reaction and continuously forms a dense protective layer with the polymer chains containing amide groups, isolating heat and preventing continued combustion. This makes the flame-retardant composite solid electrolyte difficult to ignite in the outer flame of an alcohol lamp (600℃) and continuously forms a ceramic skeleton and a dense carbonized layer for sustained dynamic flame retardancy at high temperatures.

[0040] In some embodiments, the thickness of the flame-retardant composite solid electrolyte is 0.01cm-0.05cm.

[0041] In a preferred embodiment, the thickness of the flame-retardant composite solid electrolyte is 0.02 cm.

[0042] In addition, the present invention also provides an application of flame-retardant composite solid electrolyte in all-solid-state lithium metal batteries.

[0043] In this embodiment, the flame-retardant composite solid electrolyte is applied in an all-solid-state lithium metal battery. Oxygen vacancies on the surface of the inorganic electrolyte capture free radicals during the combustion chain reaction, blocking the continued combustion reaction. During combustion, the amide groups release non-flammable gases N2 / CO2, diluting the oxygen concentration and forming a dense carbonized layer. This effectively blocks heat transfer and the escape of combustible gases, delaying the combustion process. This synergistic flame-retardant mechanism results in a limiting oxygen index (LOI) > 34.5 and a thermal runaway temperature > 300°C, achieving high safety. Simultaneously, in-situ solidification reduces interfacial impedance, alleviates interfacial polarization, and achieves a room-temperature ionic conductivity > 10. -4 S / cm. Furthermore, in the flame-retardant composite solid electrolyte, the polyimide porous membrane provides an ultra-thin flame-retardant substrate. The addition of the inorganic electrolyte, through intrinsic stability, interfacial synergy, crystallization regulation, and passivation effects, comprehensively enhances the electrochemical window of the polymer electrolyte, making it suitable for high-nickel cathodes (NCM811) and lithium metal anodes, with a theoretical energy density >300Wh / kg. In other words, the flame-retardant composite solid electrolyte of this invention improves the battery interface and achieves multi-level flame-retardant synergy through in-situ curing technology, breaking through the safety and performance bottlenecks of traditional solid electrolytes and realizing a high-safety, high-energy-density all-solid-state battery.

[0044] The following examples further illustrate the present invention in detail. It should also be understood that the following examples are only for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention.

[0045] Example 1 This embodiment provides a flame-retardant composite solid electrolyte, the preparation method of which is as follows: In a glove box, weigh 1g of carbonate monomer VEC, 0.1g of amide-containing monomer MBA, and 0.287g of lithium salt LiTFSI, and stir until homogeneous to obtain a monomer solution; after the monomer solution has been purified from turbid to clear and transparent, 10wt% of the oxide electrolyte LLZTO (Li 6.4 La3Zr 1.4 Ta 0.6 O 12 0.14 g and 0.5 wt% of initiator AlBN (0.0076 g) were further stirred and mixed to form a composite electrolyte precursor solution. The composite electrolyte precursor solution was loaded onto a polyimide porous membrane (PI membrane) and heated at 60°C for 12 h to obtain a flame-retardant composite solid electrolyte membrane cured outside the battery. Further, the composite electrolyte precursor solution was injected into the dry cell and heated at 60°C for 12 h to obtain a flame-retardant all-solid-state battery.

[0046] Optical images of monomer solution (left), monomer solution with initiator added (middle), and precursor solution after in-situ curing (right) are shown below. Figure 2 As shown, the monomer solution without initiator and oxide is in a fluid dynamic state; the electrolyte formed by heating and solidifying the monomer solution with initiator is non-fluid dynamic; similarly, the flame-retardant electrolyte formed by heating and solidifying the monomer solution with LLZTO and initiator is also non-fluid dynamic; this indicates that the precursor solution can be successfully solidified in situ.

[0047] The infrared spectra of the monomer solution (LE) prepared in this embodiment and the electrolyte (CPE) formed by in-situ curing by heating are shown below. Figure 3 As shown, the electrolyte CPE formed by in-situ solidification is at 1640 cm⁻¹. -1 The carbon-carbon double bond peaks have largely disappeared, indicating that the polymerization reaction was relatively complete and the monomers were basically converted into polymer electrolytes.

[0048] The cross-sectional image of the flame-retardant composite solid electrolyte membrane obtained in this embodiment using a scanning electron microscope is shown below. Figure 4 As shown, the oxide particles are uniformly distributed inside.

[0049] The flame-retardant composite solid electrolyte prepared in this embodiment was subjected to impedance testing, and its AC impedance spectrum is shown below. Figure 5 As shown, the impedance of the flame-retardant solid electrolyte cured outside the battery is 13.1 ohms, and the contact area is 1.77 cm². 2 The electrolyte thickness is approximately 0.02 cm. Calculated using the formula σ = L / SR, the ionic conductivity of the flame-retardant composite solid electrolyte is σ = 8.3 × 10⁻⁶. -4 The ionic conductivity of the liquid monomer solution, measured by a conductivity meter, is 1.08 × 10⁻⁶ S / cm. -3 The bar chart comparing the ionic conductivity (S / cm) is shown below. Figure 6 As shown.

[0050] The prepared flame-retardant composite solid electrolyte and monomer solution were used in combustion test experiments. Figure 7 This demonstrates that the monomer solution will burn after being continuously ignited for 6 seconds, and Figure 8 The flame-retardant composite solid electrolyte demonstrated remained non-flammable after 6 seconds of continuous ignition, indicating that the solid electrolyte of this invention possesses intrinsically excellent flame-retardant properties. Further testing of the flame-retardant effect on the base film was conducted by performing a combustion test on a PI film immersed in the monomer solution. Figure 9 As shown, the sample ignites when a flame approaches, and after burning for 3.9 seconds, the sample is almost completely burned. The flame-retardant composite solid electrolyte, however, does not ignite. Figure 10 As shown, only a black carbonized layer appears, with no obvious flame. This indicates that the flame-retardant composite solid electrolyte of the present invention has excellent flame-retardant properties, significantly improving the safety of solid-state batteries.

[0051] like Figure 11 The limiting oxygen index of the flame-retardant solid electrolyte solidified in situ on the base film was tested and reached 34.5%, meeting the national standard for non-combustible materials.

[0052] like Figure 12 The prepared flame-retardant solid electrolyte was used to assemble coin cells for testing. The positive electrode material was NCM613, the negative electrode material was lithium metal, and the intermediate layer was a flame-retardant composite solid electrolyte (CPE). It was found that at a rate of 0.5C, the CPE could stably cycle for over 1000 cycles, retaining 80% of its capacity after 783 charge-discharge cycles, while the liquid monomer solution failed after less than 200 cycles. This demonstrates that the in-situ solid-state constructed organic-inorganic composite electrolyte maintains high safety performance while also forming a stable electrode / electrolyte interface with the positive and negative electrodes, ensuring good cycle performance of the solid-state battery.

[0053] like Figure 13 The prepared flame-retardant composite solid electrolyte was used to assemble soft-pack button batteries for testing. It was found that no liquid flowed out of the battery after it was cut open, it did not catch fire, and it could still work normally, achieving a balance between high safety and high energy density in an all-solid-state battery.

[0054] Example 2 This embodiment provides a flame-retardant composite solid electrolyte, the preparation method of which is as follows: In a glove box, weigh 1.5g of carbonate monomer VC, 0.1g of amide-containing monomer NVF, and 0.35g of lithium salt LiBF4, and stir until homogeneous to obtain a monomer solution. After the monomer solution is turbid to clear and transparent, add 10wt% of the oxide electrolyte Li. 1.3 Al 0.3 Ti 1.7 30.14 g of (PO4) and 0.5 wt% of initiator AlBN (0.0076 g) were further stirred and mixed to form a composite electrolyte precursor solution. The composite electrolyte precursor solution was loaded onto a polyimide porous membrane (PI membrane) and heated at 80°C for 12 h to obtain a flame-retardant composite solid electrolyte membrane cured outside the battery. Further, the composite electrolyte precursor solution was injected into the dry cell and heated at 80°C for 12 h to obtain a flame-retardant all-solid-state battery.

[0055] Example 3 This embodiment provides a flame-retardant composite solid electrolyte, the preparation method of which is as follows: In a glove box, weigh 2g of carbonate monomer MA, 0.3g of amide-containing monomer MAM, and 0.3g of lithium salt LiBOB, and stir until homogeneous to obtain a monomer solution. After the monomer solution changes from turbid to clear and transparent, add 10wt% of the oxide electrolyte Li. 3.5 Si 0.5 P 0.5 0.14 g of O4 and 0.009 g of 0.5 wt% initiator BPO were further stirred and mixed to form a composite electrolyte precursor solution. The composite electrolyte precursor solution was loaded onto a polyimide porous membrane (PI membrane) and heated at 90°C for 12 h to obtain a flame-retardant composite solid electrolyte membrane cured outside the battery. Further, the composite electrolyte precursor solution was injected into the dry cell and heated at 90°C for 12 h to obtain a flame-retardant all-solid-state battery.

[0056] In summary, this invention provides a flame-retardant composite solid electrolyte, its preparation method, and its application. The preparation method of the flame-retardant composite solid electrolyte includes the following steps: mixing carbonate polymeric monomers, amide-containing polymeric monomers, and lithium salts to obtain a monomer solution; mixing the monomer solution with an inorganic electrolyte and an initiator to obtain a composite electrolyte precursor solution; loading the composite electrolyte precursor solution onto a polyimide porous membrane and performing in-situ curing treatment to obtain the flame-retardant composite solid electrolyte. This invention uses a polyimide porous membrane as a matrix, utilizes the copolymerization of carbonate polymeric monomers and amide-containing polymeric monomers to form an organic network, and utilizes lithium salts as lithium-ion transporters to achieve organic-inorganic synergistic flame retardancy through composite with an inorganic oxide solid electrolyte; furthermore, the inorganic electrolyte and polymer chains form a three-dimensional framework structure, and a stable composite system is formed through oxygen vacancy anchoring. Meanwhile, by using polyimide porous membranes to provide an ultrathin flame-retardant substrate, the addition of inorganic electrolytes can comprehensively improve the electrochemical window of the flame-retardant composite solid electrolyte through intrinsic stability, interfacial synergy, crystallization regulation and passivation effect, making it suitable for high-nickel cathodes and lithium metal anodes and improving the theoretical energy density.

[0057] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A method for preparing a flame-retardant composite solid electrolyte, characterized in that, Including the following steps: A monomer solution is obtained by mixing carbonate monomers, monomers containing amide groups, and lithium salts. The monomer solution is mixed with an inorganic electrolyte and an initiator to obtain a composite electrolyte precursor solution; The composite electrolyte precursor solution was loaded onto a polyimide porous membrane and then cured in situ to obtain a flame-retardant composite solid electrolyte.

2. The preparation method of the flame-retardant composite solid electrolyte according to claim 1, characterized in that, The carbonate polymer monomer is selected from one or more of vinylene carbonate, vinyl ethylene carbonate, and methyl acrylate; the polymer monomer containing amide groups is selected from one or more of N,N'-methylenebisacrylamide, N-vinylformamide, and methacrylamide.

3. The preparation method of the flame-retardant composite solid electrolyte according to claim 1, characterized in that, The lithium salt is selected from one or more of lithium hexafluoroarsenate, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(difluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(oxalate-borate), and lithium difluorooxalate-borate.

4. The preparation method of the flame-retardant composite solid electrolyte according to claim 1, characterized in that, The inorganic electrolyte includes one of inorganic oxide electrolytes, sulfide electrolytes, and halide electrolytes; Preferably, the inorganic oxide electrolyte is selected from one or more of NASICON type electrolyte, perovskite type electrolyte, garnet type electrolyte, and LISICON type electrolyte; the initiator is selected from one or more of azobisisobutyronitrile, azobisisoheptanenitrile, and benzoyl peroxide.

5. The preparation method of the flame-retardant composite solid electrolyte according to claim 1, characterized in that, The molar ratio of the carbonate polymer monomer to the polymer monomer containing the amide group is (1-50):1; the molar fraction of the lithium salt in the monomer solution is 0.1 mol / L-4 mol / L.

6. The preparation method of the flame-retardant composite solid electrolyte according to claim 1, characterized in that, The amount of inorganic electrolyte added is 1%-80% of the total mass of the composite electrolyte precursor solution.

7. The preparation method of the flame-retardant composite solid electrolyte according to claim 1, characterized in that, The amount of the initiator added is 0.01%-1% of the total mass of the composite electrolyte precursor solution.

8. The preparation method of the flame-retardant composite solid electrolyte according to claim 1, characterized in that, The temperature of the in-situ curing treatment is 30℃-100℃, and the time of the in-situ curing treatment is 1h-24h.

9. A flame-retardant composite solid electrolyte, characterized in that, It is prepared using the method for preparing flame-retardant composite solid electrolyte as described in any one of claims 1-8.

10. The application of the flame-retardant composite solid electrolyte as described in claim 9 in an all-solid-state lithium metal battery.

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