Porous composite solid electrolyte membrane and preparation method and application thereof

Abstract

The invention provides a porous composite solid electrolyte membrane as well as a preparation method and application thereof, and belongs to the technical field of solid electrolyte materials. According to the porous composite solid-state electrolyte membrane provided by the invention, the three-dimensional porous fiber membrane constructed by the modified nanofibers is used as a framework of the porous composite solid-state electrolyte membrane, so that the interface bonding capacity of the modified nanofibers, the inorganic solid-state electrolyte powder and the membrane-forming polymer can be improved; further, the porous composite solid electrolyte membrane has excellent mechanical properties such as flexibility; the inorganic solid electrolyte powder is uniformly dispersed in the three-dimensional porous fiber membrane, the porous network structure can provide more lithium ion transmission channels, the ion migration rate is improved, and the conductivity of the porous composite solid electrolyte membrane is improved; the porous composite solid-state electrolyte membrane provided by the invention comprises the flame-retardant plasticizer, and the membrane-forming polymer and the flame-retardant plasticizer are compounded to improve interface contact, so that the mechanical property of the porous composite solid-state electrolyte membrane is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of solid electrolyte materials, and in particular to a porous composite solid electrolyte membrane and a preparation method and application thereof. Background Art

[0002] Inorganic solid electrolytes, a type of solid-state battery electrolyte, suffer from drawbacks such as brittleness and difficulty in processing. To address these issues, research has been conducted on combining inorganic solid electrolytes with polymer matrices to improve their brittleness and make them easier to process.

[0003] However, inorganic solid electrolytes tend to aggregate in polymer matrices. Furthermore, the interfacial bonding between the inorganic solid electrolyte and the polymer matrix is poor, resulting in poor mechanical strength in the resulting composite solid electrolyte membrane. Furthermore, the high interfacial resistance between the inorganic solid electrolyte and the polymer matrix hinders ion transport, resulting in low conductivity in the solid composite electrolyte membrane.

[0004] Therefore, there is an urgent need to provide a porous composite solid electrolyte membrane with good mechanical properties and high electrical conductivity. Summary of the Invention

[0005] The purpose of the present invention is to provide a porous composite solid electrolyte membrane with good mechanical properties and high electrical conductivity, and a preparation method and application thereof.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a porous composite solid electrolyte membrane, comprising a three-dimensional porous fiber membrane and an inorganic solid electrolyte powder, a film-forming polymer, and a flame retardant plasticizer dispersed in the three-dimensional porous fiber membrane; the three-dimensional porous fiber membrane is composed of modified nanofibers; the modified nanofibers are nanofibers grafted with acrylic acid or methacrylic acid;

[0008] In parts by weight, the porous composite solid electrolyte membrane comprises 1 to 3 parts of modified nanofibers, 5 to 7 parts of inorganic solid electrolyte powder, 0.5 to 1 part of film-forming polymer and 2 to 5 parts of flame retardant plasticizer.

[0009] Preferably, the method for preparing the modified nanofiber comprises the following steps:

[0010] (1) mixing the nanofibers with an alkali solution and performing alkali leaching to obtain alkalized nanofibers;

[0011] (2) mixing the alkalized nanofibers obtained in step (1) with a monomer solution and an initiator to carry out a grafting reaction to obtain modified nanofibers; the monomer in the monomer solution is acrylic acid or methacrylic acid.

[0012] Preferably, the diameter of the nanofiber is 4 to 500 nm; the length of the nanofiber is 100 to 20,000 nm.

[0013] Preferably, the inorganic solid electrolyte powder includes one or more of oxide solid electrolyte powder, sulfide solid electrolyte powder and halide solid electrolyte powder.

[0014] Preferably, the particle size of the inorganic solid electrolyte powder is 50 nm to 1 μm.

[0015] Preferably, the film-forming polymer comprises one or more of styrene-butadiene rubber, polyvinylidene fluoride, polyethylene oxide, polyacrylonitrile, polymethyl methacrylate, poly(lithium styrene sulfonate) and poly(lithium methacrylate).

[0016] Preferably, the flame retardant plasticizer includes one or more of silicon-based plasticizers, fluorine-containing plasticizers, phosphorus-based plasticizers, boron-containing compounds and ionic liquids.

[0017] The present invention also provides a method for preparing the porous composite solid electrolyte membrane described in the above technical solution, comprising:

[0018] The modified nanofibers, a film-forming polymer, a flame retardant plasticizer, an inorganic solid electrolyte powder and an organic solvent are mixed to obtain a precursor slurry;

[0019] After the precursor slurry is cast, it is dried to obtain a porous composite solid electrolyte membrane.

[0020] Preferably, the organic solvent includes one or more of N-methylpyrrolidone, dimethyl sulfoxide, acetonitrile, tetrahydrofuran and acetone.

[0021] The present invention also provides the use of the porous composite solid electrolyte membrane described in the above technical solution or the porous composite solid electrolyte membrane prepared by the preparation method described in the above technical solution in a lithium battery.

[0022] The present invention provides a porous composite solid electrolyte membrane, comprising a three-dimensional porous fiber membrane and an inorganic solid electrolyte powder, a film-forming polymer and a flame retardant plasticizer dispersed in the three-dimensional porous fiber membrane; the three-dimensional porous fiber membrane is composed of modified nanofibers; the modified nanofibers are nanofibers grafted with acrylic acid or methacrylic acid; in parts by weight, the porous composite solid electrolyte membrane comprises 1 to 3 parts of modified nanofibers, 5 to 7 parts of inorganic solid electrolyte powder, 0.5 to 1 part of film-forming polymer and 2 to 5 parts of flame retardant plasticizer. The porous composite solid electrolyte membrane provided by the present invention uses modified nanofibers to construct a three-dimensional porous fiber membrane. The three-dimensional network structure serves as the skeleton of the porous composite solid electrolyte membrane, which has good flexibility. In addition, the nanofibers grafted with acrylic acid or methacrylic acid have more active groups, which can undergo further chemical reactions with inorganic solid electrolyte powder, film-forming polymer, and flame retardant plasticizer, thereby improving the interfacial bonding ability of the modified nanofibers, inorganic solid electrolyte powder, and film-forming polymer, thereby giving the porous composite solid electrolyte membrane excellent mechanical properties such as flexibility. The inorganic solid electrolyte powder is dispersed in the three-dimensional porous fiber membrane. The porous network structure can provide more lithium ion transmission channels, thereby increasing the ion migration rate and improving the conductivity of the porous composite solid electrolyte membrane. The porous composite solid electrolyte membrane provided by the present invention includes a flame retardant plasticizer. The film-forming polymer and flame retardant plasticizer are combined to improve the interfacial contact and provide more contact points with the porous structure, thereby improving the mechanical properties and flame retardancy of the porous composite solid electrolyte membrane. The results of the examples show that the porous composite solid electrolyte membrane provided by the present invention has excellent mechanical properties and conductivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a photo of the porous composite solid electrolyte membrane prepared in Example 1 of the present invention;

[0024] Figure 2 These are photos of the porous composite solid electrolyte membrane prepared in Example 1 of the present invention before and after thermal shrinkage;

[0025] Figure 3 Pictures of commercially available PE film before and after heat shrinkage;

[0026] Figure 4 This is a picture of the flammability test of the porous composite solid electrolyte membrane prepared in Example 1 of the present invention;

[0027] Figure 5 This is a photo of the flammability test of commercially available PE film;

[0028] Figure 6 SEM image of the porous composite solid electrolyte membrane prepared in Example 1 of the present invention;

[0029] Figure 7This is an SEM image of the raw material LATP used in the examples of the present invention. DETAILED DESCRIPTION

[0030] The present invention provides a porous composite solid electrolyte membrane, comprising a three-dimensional porous fiber membrane and an inorganic solid electrolyte powder, a film-forming polymer, and a flame retardant plasticizer dispersed in the three-dimensional porous fiber membrane; the three-dimensional porous fiber membrane is composed of modified nanofibers; the modified nanofibers are nanofibers grafted with acrylic acid or methacrylic acid;

[0031] In parts by weight, the porous composite solid electrolyte membrane comprises 1 to 3 parts of modified nanofibers, 5 to 7 parts of inorganic solid electrolyte powder, 0.5 to 1 part of film-forming polymer and 2 to 5 parts of flame retardant plasticizer.

[0032] The porous composite solid electrolyte membrane provided by the present invention includes a three-dimensional porous fiber membrane. In the present invention, the three-dimensional porous fiber membrane is composed of modified nanofibers. In the present invention, the nanofibers in the modified nanofibers preferably include one or more of cellulose nanofibers, cellulose nanowhiskers, bacterial nanocellulose and microfibrillated cellulose. The present invention utilizes modified nanofibers to form a three-dimensional porous fiber membrane, which has good flexibility; and the modified nanofibers have rich active groups, which can improve the interfacial bonding ability of the modified nanofibers, inorganic solid electrolyte powder and film-forming polymer, thereby making the porous composite solid electrolyte membrane have excellent mechanical properties such as flexibility.

[0033] The porous composite solid electrolyte membrane provided by the present invention comprises an inorganic solid electrolyte powder, a film-forming polymer, and a flame-retardant plasticizer dispersed in the three-dimensional porous fiber membrane. The present invention uses an inorganic solid electrolyte powder that can be evenly dispersed in the three-dimensional porous fiber membrane. The porous network structure can provide more lithium ion transmission channels, thereby increasing the ion migration rate and improving the conductivity of the porous composite solid electrolyte membrane. The film-forming polymer and the flame-retardant plasticizer are combined to improve the interfacial contact, providing more contact points with the porous structure, thereby improving the mechanical properties of the porous composite solid electrolyte membrane.

[0034] The porous composite solid electrolyte membrane provided by the present invention comprises 1 to 3 parts by weight of modified nanofibers. As one embodiment of the present invention, the modified nanofibers may comprise 1, 2, or 3 parts by weight. The present invention utilizes modified nanofibers to construct a three-dimensional porous fiber membrane, thereby enhancing the interfacial bonding between the modified nanofibers, inorganic solid electrolyte powder, and film-forming polymer.

[0035] In the present invention, the method for preparing the modified nanofiber preferably comprises the following steps:

[0036] (1) mixing the nanofibers with an alkali solution and performing alkali leaching to obtain alkalized nanofibers;

[0037] (2) mixing the alkalized nanofibers obtained in step (1) with a monomer solution and an initiator to carry out a grafting reaction to obtain modified nanofibers; the monomer in the monomer solution is acrylic acid or methacrylic acid.

[0038] In the present invention, the nanofibers are preferably mixed with an alkali solution and alkali-leached to obtain alkalized nanofibers.

[0039] In the present invention, the diameter of the nanofiber is preferably 4 to 500 nm. In the present invention, the length of the nanofiber is preferably 100 to 20,000 nm, more preferably 15,000 to 20,000 nm. In the present invention, the nanofiber preferably includes one or more of cellulose nanofibers, cellulose nanowhiskers, bacterial nanocellulose, microfibrillated cellulose, polyvinyl pyrrolidone nanofibers, polyacrylonitrile-based carbon nanofibers, polystyrene nanofibers, polylactic acid nanofibers, polyvinyl acetate nanofibers, polyvinyl alcohol nanofibers, lignocellulose nanofibers, and carbon nanotube fibers. In the present invention, the length of the cellulose nanofibers is preferably 1000-3000 nm, more preferably 2000-3000 nm; the diameter of the cellulose nanofibers is preferably 4-10 nm, more preferably 5-8 nm; the length of the cellulose nanowhiskers is preferably 100-500 nm, more preferably 200-400 nm; the diameter of the cellulose nanowhiskers is preferably 4-10 nm, more preferably 5-8 nm; the length of the bacterial nanocellulose is preferably 10,000-20,000 nm, more preferably 15,000-18,000 nm; the diameter of the bacterial nanocellulose is preferably 50-100 nm, more preferably 60-80 nm; the length of the microfibrillated cellulose is preferably 1000-20,000 nm, more preferably 1500-20,000 nm; the diameter of the microfibrillated cellulose is preferably 50-500 nm, more preferably 100-300 nm. The use of nanofibers of the above sizes in the present invention makes it easier for the modified nanofibers to form a three-dimensional porous fiber membrane. In an embodiment of the present invention, the source of the nanofibers may be Guilin Qihong Technology Co., Ltd.

[0040] In the present invention, the alkali solution is preferably a sodium hydroxide solution, and the concentration of the sodium hydroxide solution is preferably 0.1 to 0.5 mol / L, more preferably 0.1 mol / L.

[0041] The present invention has no particular limitation on the ratio of the mass of the nanofibers to the volume of the alkali solution, as long as the nanofibers can be completely immersed in the alkali solution.

[0042] In the present invention, the alkali leaching time is preferably 2 to 4 hours, more preferably 3 to 4 hours. In the present invention, the alkali leaching is preferably performed with stirring at room temperature. Stirring at room temperature facilitates sufficient contact between the alkali solution and the nanofibers. Alkali leaching can enhance the activity of the nanofibers, further facilitating a more complete subsequent grafting reaction.

[0043] In the present invention, after alkali leaching, the mixed system obtained by alkali leaching is preferably washed with water to obtain alkalized nanofibers. The present invention does not specifically limit the number of water washings, as long as the residual alkali solution in the alkalized nanofibers can be fully removed.

[0044] After obtaining the alkalized nanofibers, the present invention preferably mixes the alkalized nanofibers with a monomer solution and an initiator to carry out a grafting reaction to obtain modified nanofibers.

[0045] In the present invention, the monomer in the monomer solution is acrylic acid or methacrylic acid. Using acrylic acid or methacrylic acid as a monomer enables the grafting of polymer segments, such as active groups such as -O-CH2-CH2-COOH, onto the nanofiber molecular chains, thereby improving the reactivity, adsorption properties, and mechanical properties of the modified nanofibers.

[0046] In the present invention, the mass concentration of the monomer solution is preferably 10 to 30%, more preferably 15 to 25%. In an embodiment of the present invention, the solvent of the monomer solution is preferably a polar solvent, more preferably methanol, ethanol or water.

[0047] In the present invention, the ratio of the mass of the alkalized nanofibers to the mass of the monomers is preferably 1:10 to 1:30, more preferably 1:15.

[0048] In the present invention, the initiator is preferably azobisisobutyronitrile (AIBN). The present invention promotes the grafting of monomers onto nanofibers by adding an initiator.

[0049] In the present invention, the mass ratio of the initiator to the total solid content of the alkalized nanofibers, the monomer solution and the initiator is preferably 0.1 to 5%, more preferably 1 to 3%.

[0050] The present invention has no particular limitation on the method of mixing the alkalized nanofibers, the monomer solution and the initiator, as long as the three can be mixed evenly.

[0051] In the present invention, the grafting reaction temperature is preferably 60-80°C, more preferably 70-80°C; the grafting reaction time is preferably 4-10 hours, more preferably 6-8 hours. The above temperature and time are more conducive to a more complete grafting reaction.

[0052] In the present invention, the grafting reaction is preferably carried out under ultrasound, which can increase the reaction rate and promote a more complete grafting reaction.

[0053] In the present invention, the mixed system obtained by the grafting reaction is preferably washed with water to obtain the modified nanofibers. The present invention does not specifically limit the number of washings, as long as the impurities remaining in the modified nanofibers can be sufficiently removed.

[0054] The nanofibers used in the present invention contain a large number of hydroxyl groups, which have certain chemical activity and are the main active sites of the grafting reaction; the alkalized nanofibers are first obtained by alkali leaching, which can further increase the number of active sites of cellulose or improve its activity, enhance the electrostatic interaction with the monomer, and under conditions of heating, light and initiator, the active groups of the monomer (such as double bonds, carbonyl groups, etc.) chemically react with the hydroxyl groups or other active sites of the nanofibers to form covalent bonds.

[0055] The porous composite solid electrolyte membrane provided by the present invention comprises 5 to 7 parts of inorganic solid electrolyte powder, based on 1 to 3 parts by weight of the modified nanofiber. As an embodiment of the present invention, the inorganic solid electrolyte powder may be present in an amount of 5, 6 or 7 parts by weight.

[0056] In the present invention, the inorganic solid electrolyte powder preferably includes one or more of oxide solid electrolyte powder, sulfide solid electrolyte powder and halide solid electrolyte powder.

[0057] In the present invention, the oxide solid electrolyte powder preferably includes one or more of lithium lanthanum titanate, lithium lanthanum zirconium oxide, lithium aluminum titanium phosphate (LATP), and lithium aluminum germanium phosphate, and more preferably lithium lanthanum titanate, lithium lanthanum zirconium oxide, or lithium aluminum titanium phosphate. The use of the above solid electrolyte powders in the present invention is more conducive to improving the ionic conductivity, mechanical strength, and electrochemical stability of the composite solid electrolyte membrane.

[0058] In the present invention, the sulfide solid electrolyte powder is preferably glassy sulfide solid electrolyte powder, glass ceramic sulfide solid electrolyte powder or crystalline sulfide solid electrolyte powder.

[0059] In the present invention, the glassy sulfide solid electrolyte powder is preferably lithium thiophosphate (LPS) or lithium sulfide-germanium sulfide-phosphorus sulfide (Li2S-GeS2-P2S5).

[0060] In the present invention, the glass-ceramic sulfide solid electrolyte powder is preferably lithium sulfide-phosphorus sulfide (Li2S-P2S5) or lithium sulfide-silicon disulfide-phosphorus sulfide (Li2S-SiS2-P2S5).

[0061] In the present invention, the crystalline sulfide solid electrolyte powder is preferably Li6PS5Cl, Li3PS4 or Li 10 GeP2S 12 .

[0062] In the present invention, the halide solid electrolyte powder is preferably Li3YCl6 or Li3ScCl6.

[0063] In the present invention, the particle size of the inorganic solid electrolyte powder is preferably 50 nm to 1 μm, more preferably 50 nm to 100 nm. The present invention controls the particle size of the solid electrolyte powder within the above range, which is more conducive to more uniform dispersion in the three-dimensional porous fiber membrane.

[0064] The porous composite solid electrolyte membrane provided by the present invention includes 0.5 to 1 part of a film-forming polymer, based on 1 to 3 parts by weight of the modified nanofibers. As an embodiment of the present invention, the weight of the film-forming polymer may be 0.5, 0.6, 0.7, 0.8, 0.9, or 1 part. The present invention utilizes the film-forming polymer as a binder.

[0065] In the present invention, the film-forming polymer preferably comprises one or more of styrene-butadiene rubber, polyvinylidene fluoride, polyethylene oxide, polyacrylonitrile, polymethyl methacrylate, poly(lithium styrene sulfonate), and poly(lithium methacrylate). The present invention employs these film-forming polymers, which exhibit good adhesion and are capable of bonding the modified nanofibers and inorganic solid electrolyte powder. The present invention does not particularly limit the source of the film-forming polymer; any conventional commercially available product may be used.

[0066] Based on the weight of the modified nanofibers being 1 to 3 parts, the porous composite solid electrolyte membrane provided by the present invention includes 2 to 5 parts of a flame retardant plasticizer. As an embodiment of the present invention, the weight of the flame retardant plasticizer can be 2 parts, 3 parts, 4 parts or 5 parts. The present invention utilizes a composite of a film-forming polymer and a flame retardant plasticizer to improve interfacial contact, thereby providing more contact points with the porous structure, thereby improving the mechanical properties of the porous composite solid electrolyte membrane; and the flame retardant plasticizer can also improve the flame retardancy of the porous composite solid electrolyte membrane.

[0067] In the present invention, the flame retardant plasticizer preferably includes one or more of silicon-based plasticizers, fluorine-containing plasticizers, phosphorus-based plasticizers, boron-containing compounds and ionic liquids.

[0068] In the present invention, the silicon-based plasticizer is preferably polysiloxane (PDMS). PDMS used in the present invention as a plasticizer has a decomposition temperature greater than 300° C. and has excellent thermal stability.

[0069] In the present invention, the fluorine-containing plasticizer preferably includes fluoroethylene carbonate (FEC), methyl-(2,2,2-trifluoroethyl) carbonate (FEMC), or methyl trifluoroethyl carbonate (FEMC). The present invention uses FEC as a plasticizer to form a LiF-rich SEI film that inhibits lithium dendrites and improves the flame retardancy of the porous composite solid electrolyte membrane. The present invention uses FEMC as a plasticizer, which has low viscosity and can improve flame retardancy.

[0070] In the present invention, the phosphorus-based plasticizer is preferably trimethyl phosphate (TMP), tricresyl phosphate (TCP), or triethyl phosphate (TEP).

[0071] In the present invention, the ionic liquid is preferably 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM-TFSI) or 1-butyl-3-methylimidazolium bromide (BMI-Br).

[0072] In the present invention, the boron-containing compound is preferably trimethyl borate (TMB).

[0073] In the present invention, the film-forming polymer is preferably used in combination with a flame-retardant plasticizer. By using the film-forming polymer in combination with a flame-retardant plasticizer, the present invention can utilize the synergistic effects of "condensed phase carbon layer reinforcement" and "gas-phase free radical capture," supplemented by the cross-phase interaction of elements such as lithium salts, silicon, phosphorus, boron, and fluorine, to improve the flame retardancy of the porous composite solid electrolyte membrane.

[0074] In the present invention, when the film-forming polymer is styrene-butadiene rubber, the flame retardant plasticizer is preferably a phosphorus plasticizer or a silicon plasticizer; the phosphorus plasticizer is preferably TCP or TEP. The present invention utilizes the property of TCP having a high phosphorus content, and can improve the flame retardancy through the synergistic effect of gas-phase flame retardancy and condensed-phase flame retardancy; the present invention utilizes the property of TEP having a low viscosity (2.9 mPa·s at 25°C), which has good compatibility with styrene-butadiene rubber, can reduce the glass transition temperature of the membrane, and improve low-temperature ion conductivity. In the present invention, the silicon plasticizer is preferably PDMS, which has a decomposition temperature of >300°C and excellent thermal stability. After blending with styrene-butadiene rubber, it forms a "flexible-rigid" interpenetrating network, and at the same time, the flame retardancy is achieved by forming a SiO2 barrier layer.

[0075] In the present invention, when the film-forming polymer is preferably polyvinylidene fluoride, the flame retardant plasticizer is preferably a fluorine-containing plasticizer, a phosphorus-based plasticizer or an ionic liquid. In the present invention, the fluorine-containing plasticizer is preferably FEC or FEMC. In the present invention, the FEC can inhibit lithium dendrites by forming a LiF-rich SEI film, while improving flame retardancy; FEMC has a low viscosity, and after blending with polyvinylidene fluoride, both the ionic conductivity and the flame retardancy can be improved. In the present invention, the phosphorus-based plasticizer is preferably TMP; TMP matches the polarity of polyvinylidene fluoride, and forms a hydrogen bond with the -CF2- group of polyvinylidene fluoride through the ester group, thereby improving interface stability and flame retardancy. In the present invention, the ionic liquid is preferably EMIM-TFSI. The present invention utilizes EMIM-TFSI to form an ion conductive network with polyvinylidene fluoride, and at the same time improves flame retardancy by decomposing the imidazole ring to form a carbon layer.

[0076] In the present invention, when the film-forming polymer is polyethylene oxide, the flame-retardant plasticizer is preferably a phosphorus-based plasticizer or an ionic liquid. In the present invention, the phosphorus-based plasticizer is preferably TPP; TPP can form hydrogen bonds with polyethylene oxide, reducing crystallinity and improving ionic conductivity. Flame retardancy is achieved by cleaving phosphorus-oxygen bonds and releasing PO radicals. In the present invention, the ionic liquid is preferably BMI-Br; when blended with polyethylene oxide, BMI-Br forms "ion channels," improving ionic conductivity, and flame retardancy is achieved by suppressing flame propagation through the decomposition of bromide.

[0077] In the present invention, when the film-forming polymer is polyacrylonitrile, the flame-retardant plasticizer preferably includes a phosphorus-based plasticizer or a boron-containing compound. In the present invention, the phosphorus-based plasticizer is preferably TCP; TCP can improve tensile strength and ionic conductivity when blended with polyacrylonitrile, and flame retardancy is achieved through phosphorus-nitrogen synergy. In the present invention, the boron-containing compound is preferably TMB; TMB can react with the -CN groups of polyacrylonitrile to form boron-nitrogen bonds, improving thermal stability and ionic conductivity.

[0078] In the present invention, when the film-forming polymer is polymethacrylic acid, the flame-retardant plasticizer is preferably a phosphorus-based plasticizer or a fluorine-containing plasticizer. In the present invention, the phosphorus-based plasticizer is preferably TEP; TEP has good compatibility with polymethacrylic acid and improves ionic conductivity. Its flame retardancy is achieved by cleaving phosphorus-oxygen bonds and releasing PO radicals. In the present invention, the fluorine-containing plasticizer is preferably FEMC; when blended with polymethacrylic acid, FEMC improves ionic conductivity and decomposes fluoride to form LiF, which inhibits lithium dendrites.

[0079] In the present invention, when the film-forming polymer is poly(lithium styrene sulfonate), the flame retardant plasticizer is preferably a phosphorus-based plasticizer. This invention utilizes the sulfonic acid groups (S) of poly(lithium styrene sulfonate) to form POS covalent bonds with phosphorus (P), creating a "phosphorus-sulfur" synergistic network in the carbon layer, improving the high-temperature resistance and barrier properties of the carbon layer.

[0080] In the present invention, when the film-forming polymer is poly(lithium methacrylate), the flame retardant plasticizer is preferably a boron-containing compound. The present invention utilizes the lithium carboxylate in poly(lithium methacrylate) to form a Li-OB coordination bond with the borate ester, promoting the bonding of B2O3 with the carbon layer to form a "lithium-boron-carbon" composite protective layer.

[0081] The porous composite solid electrolyte membrane provided by the present invention comprises a three-dimensional porous fiber membrane and an inorganic solid electrolyte powder, a film-forming polymer and a flame retardant plasticizer dispersed in the three-dimensional porous fiber membrane. The active groups of the nanofibers grafted with acrylic acid or methacrylic acid can react with the monomers of the film-forming polymer, so that the grafted chains are continuously extended to form longer polymer chains. At the same time, cross-linking reactions may also occur between different grafted chains to form a three-dimensional network structure, thereby improving the mechanical properties and stability of the film-forming polymer. This cross-linked structure can prevent the grafted chains from falling off the cellulose main chain during the film-forming process, so that the grafted modified cellulose has better compatibility and bonding strength with the film-forming polymer. Hydrogen bonds can be formed between the hydroxyl groups of the nanofibers grafted with acrylic acid or methacrylic acid and the polar groups (such as hydroxyl groups, carboxyl groups, amide groups, etc.) in the film-forming polymer monomers, which can increase the interaction force between cellulose and the film-forming polymer and improve the uniformity and stability of the film-forming polymer. The surface of the nanofiber grafted with acrylic acid or methacrylic acid has a certain roughness and pore structure. During the film formation process, the monomers of the film-forming polymer and the inorganic solid electrolyte powder can enter these pores and be embedded in them during the curing process, thereby improving the mechanical properties of the porous composite solid electrolyte membrane.

[0082] The present invention also provides a method for preparing the porous composite solid electrolyte membrane described in the above technical solution, comprising:

[0083] The modified nanofibers, a film-forming polymer, a flame retardant plasticizer, an inorganic solid electrolyte powder and an organic solvent are mixed to obtain a precursor slurry;

[0084] After the precursor slurry is poured, it is dried to obtain a porous composite solid electrolyte membrane.

[0085] The invention mixes modified nanofibers, film-forming polymers, flame retardant plasticizers, inorganic solid electrolyte powders and organic solvents to obtain precursor slurry.

[0086] In the present invention, the method for mixing the modified nanofibers, film-forming polymers, flame retardant plasticizers, inorganic solid electrolyte powders and organic solvents is preferably: dispersing the modified nanofibers in a portion of the organic solvent to obtain a modified nanofiber dispersion; dissolving the film-forming polymer in the remaining portion of the organic solvent to obtain a film-forming polymer solution; mixing the modified nanofiber dispersion with the film-forming polymer solution to obtain a mixed dispersion; mixing the mixed dispersion with the flame retardant plasticizer to obtain a mixed slurry; and mixing the mixed slurry with the inorganic solid electrolyte powder to obtain a precursor slurry.

[0087] In the present invention, the modified nanofibers are preferably dispersed in a portion of the organic solvent by solution replacement or mixing the modified nanofiber powder with the organic solvent by stirring or sand milling. The present invention is not particularly limited to the specific method of solution replacement, stirring, or sand milling, as long as the modified nanofibers are fully dispersed in the organic solvent.

[0088] The present invention has no particular limitation on the specific value of the portion of organic solvent, as long as the modified nanofibers can be fully dispersed and the remaining portion of organic solvent can dissolve the film-forming polymer.

[0089] In the present invention, the method for dissolving the film-forming polymer in the remaining organic solvent is preferably heating and stirring. In an embodiment of the present invention, the heating temperature can be 60° C. The present invention promotes rapid dissolution of the film-forming polymer in the remaining organic solvent by heating and stirring.

[0090] In the present invention, the modified nanofiber dispersion and the film-forming polymer solution are preferably mixed by stirring, preferably for 0.5 to 2 hours, more preferably 1 to 1.5 hours. The stirring speed is not particularly limited and can be adjusted based on the mixing conditions. Stirring promotes uniform mixing of the modified nanofiber dispersion and the film-forming polymer solution.

[0091] In the present invention, the mixed dispersion and the flame retardant plasticizer are preferably mixed by stirring, and the stirring time is preferably 10 to 60 minutes, more preferably 20 to 30 minutes. The stirring speed is not particularly limited in the present invention and can be adjusted according to the mixing conditions. Stirring can promote uniform mixing of the mixed dispersion and the flame retardant plasticizer.

[0092] In the present invention, the method for mixing the mixed slurry with the inorganic solid electrolyte powder is preferably stirring and ball milling in sequence. In the present invention, the stirring time is preferably 0.5 to 2 hours, more preferably 1 to 2 hours. In the present invention, the rotation speed of the ball mill is preferably 400 to 800 rpm, more preferably 500 to 600 rpm; the ball milling time is preferably 0.5 to 2 hours, more preferably 1 to 1.5 hours. The present invention can fully disperse the inorganic solid electrolyte powder in the mixed slurry through the sequential stirring and ball milling.

[0093] After the precursor slurry is obtained, the present invention casts the precursor slurry and then dries it to obtain a porous composite solid electrolyte membrane.

[0094] The present invention has no particular limitation on the casting method, and conventional casting methods can be used to cast the precursor slurry into the mold. The present invention has no particular limitation on the specific model of the mold, and the mold can be selected according to the thickness and size of the porous composite solid electrolyte membrane required.

[0095] In the present invention, the drying temperature is preferably 60 to 105°C, more preferably 80 to 100°C. The present invention does not specifically limit the drying time, and it is adjusted according to the amount of the precursor slurry used, so that the precursor slurry can be fully dried to form a dry porous composite solid electrolyte membrane. The present invention does not specifically limit the drying method, and a conventional drying method can be used. In an embodiment of the present invention, the drying method can be drying in an oven.

[0096] The preparation method provided by the present invention is simple to operate, easy to control, suitable for large-scale production, and can obtain a porous composite solid electrolyte membrane with excellent mechanical properties and electrical conductivity.

[0097] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0098] The method for preparing modified nanofibers in the embodiment of the present invention comprises the following steps:

[0099] (1) immersing nanofibers (bacterial nanocellulose with a diameter of 60 to 80 nm and a length of 10,000 to 20,000 nm) in a 0.1 mol / L sodium hydroxide solution, stirring at room temperature for 3 h for alkali leaching, and washing with water to remove residual alkali solution to obtain alkalized nanofibers;

[0100] (2) 10 g of the alkalized nanofibers obtained in step (1) were mixed and dissolved with a 10% mass concentration of acrylic acid monomer solution and initiator AIBN (the mass ratio of the initiator to the total solid content of the alkalized nanofibers, acrylic acid monomer solution and AIBN was 1%), and the grafting reaction was carried out at 60° C. for 10 h. The modified nanofibers were washed with water to remove impurities.

[0101] Example 1

[0102] A porous composite solid electrolyte membrane, comprising a three-dimensional porous fiber membrane and inorganic solid electrolyte powder, a film-forming polymer, and a flame retardant plasticizer dispersed in the three-dimensional porous fiber membrane; the three-dimensional porous fiber membrane is composed of modified nanofibers;

[0103] The components of the porous composite solid electrolyte membrane are as follows: 1 part of modified nanofiber, 6 parts of inorganic solid electrolyte powder LATP powder, 0.5 parts of film-forming polymer styrene-butadiene rubber (SBR), and 2 parts of flame retardant plasticizer TCP.

[0104] The preparation method of the porous composite solid electrolyte membrane is:

[0105] The modified nanofibers were dispersed in 50 parts of N-methylpyrrolidone under stirring at 600 rpm and 60°C for 1 hour to obtain a modified nanofiber dispersion; the film-forming polymer was dissolved in 50 parts of N-methylpyrrolidone in a 60°C water bath to obtain a film-forming polymer solution; the modified nanofiber dispersion and the film-forming polymer solution were stirred at 600 rpm for 1 hour to obtain a mixed dispersion; the mixed dispersion and the flame retardant plasticizer were stirred at 600 rpm for 30 minutes to obtain a mixed slurry; the mixed slurry was stirred with inorganic solid electrolyte powder at 800 rpm for 2 hours, and then ball-milled at 500 rpm for 1 hour to obtain a precursor slurry; the precursor slurry was poured into a mold, and after drying at 100°C for 24 hours, a porous composite solid electrolyte membrane with a thickness of 0.02 cm was obtained.

[0106] Example 2

[0107] A porous composite solid electrolyte membrane, comprising a three-dimensional porous fiber membrane and inorganic solid electrolyte powder, a film-forming polymer, and a flame retardant plasticizer dispersed in the three-dimensional porous fiber membrane; the three-dimensional porous fiber membrane is composed of modified nanofibers;

[0108] The difference from Example 1 is that the components of the porous composite solid electrolyte membrane are adjusted to: 2 parts of modified nanofibers, 5 parts of inorganic solid electrolyte powder LATP powder, 0.6 parts of film-forming polymer SBR and 3 parts of flame retardant plasticizer TEP;

[0109] The preparation method of the porous composite solid electrolyte membrane is the same as that of Example 1.

[0110] Example 3

[0111] A porous composite solid electrolyte membrane, comprising a three-dimensional porous fiber membrane and inorganic solid electrolyte powder, a film-forming polymer, and a flame retardant plasticizer dispersed in the three-dimensional porous fiber membrane; the three-dimensional porous fiber membrane is composed of modified nanofibers;

[0112] The difference from Example 1 is that the components of the porous composite solid electrolyte membrane are adjusted to: 3 parts of modified nanofibers, 6 parts of inorganic solid electrolyte powder LATP powder, 0.6 parts of film-forming polymer SBR and 3 parts of PDMS;

[0113] The preparation method of the porous composite solid electrolyte membrane is the same as that of Example 1.

[0114] Example 4

[0115] A porous composite solid electrolyte membrane, comprising a three-dimensional porous fiber membrane and inorganic solid electrolyte powder, a film-forming polymer, and a flame retardant plasticizer dispersed in the three-dimensional porous fiber membrane; the three-dimensional porous fiber membrane is composed of modified nanofibers;

[0116] The difference from Example 1 is that the components of the porous composite solid electrolyte membrane are adjusted to: 3 parts of modified nanofibers, 6 parts of inorganic solid electrolyte powder LATP powder, 0.8 parts of film-forming polymer polyvinylidene fluoride (PVDF) and 4 parts of flame retardant plasticizer FEC;

[0117] The preparation method of the porous composite solid electrolyte membrane is the same as that of Example 1.

[0118] Example 5

[0119] A porous composite solid electrolyte membrane, comprising a three-dimensional porous fiber membrane and inorganic solid electrolyte powder, a film-forming polymer, and a flame retardant plasticizer dispersed in the three-dimensional porous fiber membrane; the three-dimensional porous fiber membrane is composed of modified nanofibers;

[0120] The difference from Example 1 is that the components of the porous composite solid electrolyte membrane are adjusted to: 3 parts of modified nanofibers, 6 parts of inorganic solid electrolyte powder LATP powder, 0.9 parts of film-forming polymer PVDF and 4 parts of FEMC;

[0121] The preparation method of the porous composite solid electrolyte membrane is the same as that of Example 1.

[0122] Example 6

[0123] A porous composite solid electrolyte membrane, comprising a three-dimensional porous fiber membrane and inorganic solid electrolyte powder, a film-forming polymer, and a flame retardant plasticizer dispersed in the three-dimensional porous fiber membrane; the three-dimensional porous fiber membrane is composed of modified nanofibers;

[0124] The difference from Example 1 is that the components of the porous composite solid electrolyte membrane are adjusted to: 2 parts of modified nanofibers, 5 parts of inorganic solid electrolyte powder LATP powder, 0.9 parts of film-forming polymer PVDF and 4 parts of TMP;

[0125] The preparation method of the porous composite solid electrolyte membrane is the same as that of Example 1.

[0126] Example 7

[0127] A porous composite solid electrolyte membrane, comprising a three-dimensional porous fiber membrane and inorganic solid electrolyte powder, a film-forming polymer, and a flame retardant plasticizer dispersed in the three-dimensional porous fiber membrane; the three-dimensional porous fiber membrane is composed of modified nanofibers;

[0128] The difference from Example 1 is that the components of the porous composite solid electrolyte membrane are adjusted to: 3 parts of modified nanofibers, 6 parts of inorganic solid electrolyte powder LATP powder, 0.8 parts of film-forming polymer PVDF and 4 parts of EMIM-TFSI;

[0129] The preparation method of the porous composite solid electrolyte membrane is the same as that of Example 1.

[0130] Example 8

[0131] A porous composite solid electrolyte membrane, comprising a three-dimensional porous fiber membrane and inorganic solid electrolyte powder, a film-forming polymer, and a flame retardant plasticizer dispersed in the three-dimensional porous fiber membrane; the three-dimensional porous fiber membrane is composed of modified nanofibers;

[0132] The difference from Example 1 is that the composition of the porous composite solid electrolyte membrane is adjusted to: 3 parts of modified nanofibers, 7 parts of inorganic solid electrolyte powder LATP powder, 1 part of film-forming polymer polyethylene oxide (PEO) and 5 parts of TPP;

[0133] The preparation method of the porous composite solid electrolyte membrane is the same as that of Example 1.

[0134] Example 9

[0135] A porous composite solid electrolyte membrane, comprising a three-dimensional porous fiber membrane and inorganic solid electrolyte powder, a film-forming polymer, and a flame retardant plasticizer dispersed in the three-dimensional porous fiber membrane; the three-dimensional porous fiber membrane is composed of modified nanofibers;

[0136] The difference from Example 1 is that the components of the porous composite solid electrolyte membrane are adjusted to: 3 parts of modified nanofibers, 6 parts of inorganic solid electrolyte powder LATP powder, 1 part of film-forming polymer PEO and 3 parts of BMI-Br;

[0137] The preparation method of the porous composite solid electrolyte membrane is the same as that of Example 1.

[0138] Example 10

[0139] A porous composite solid electrolyte membrane, comprising a three-dimensional porous fiber membrane and inorganic solid electrolyte powder, a film-forming polymer, and a flame retardant plasticizer dispersed in the three-dimensional porous fiber membrane; the three-dimensional porous fiber membrane is composed of modified nanofibers;

[0140] The difference from Example 1 is that the composition of the porous composite solid electrolyte membrane is adjusted to: 3 parts of modified nanofibers, 7 parts of inorganic solid electrolyte powder LATP powder, 1 part of film-forming polymer polyacrylonitrile (PAN), and 5 parts of TCP;

[0141] The preparation method of the porous composite solid electrolyte membrane is the same as that of Example 1.

[0142] Example 11

[0143] A porous composite solid electrolyte membrane, comprising a three-dimensional porous fiber membrane and inorganic solid electrolyte powder, a film-forming polymer, and a flame retardant plasticizer dispersed in the three-dimensional porous fiber membrane; the three-dimensional porous fiber membrane is composed of modified nanofibers;

[0144] The difference from Example 1 is that the components of the porous composite solid electrolyte membrane are adjusted to: 3 parts of modified nanofibers, 7 parts of inorganic solid electrolyte powder LATP powder, 1 part of film-forming polymer PAN and 5 parts of TMB;

[0145] The preparation method of the porous composite solid electrolyte membrane is the same as that of Example 1.

[0146] Example 12

[0147] A porous composite solid electrolyte membrane, comprising a three-dimensional porous fiber membrane and inorganic solid electrolyte powder, a film-forming polymer, and a flame retardant plasticizer dispersed in the three-dimensional porous fiber membrane; the three-dimensional porous fiber membrane is composed of modified nanofibers;

[0148] The difference from Example 1 is that the components of the porous composite solid electrolyte membrane are adjusted to: 2 parts of modified nanofibers, 6 parts of inorganic solid electrolyte powder LATP powder, 0.6 parts of polymethyl methacrylate (PMMA) and 3 parts of TEP;

[0149] The preparation method of the porous composite solid electrolyte membrane is the same as that of Example 1.

[0150] Example 13

[0151] A porous composite solid electrolyte membrane, comprising a three-dimensional porous fiber membrane and inorganic solid electrolyte powder, a film-forming polymer, and a flame retardant plasticizer dispersed in the three-dimensional porous fiber membrane; the three-dimensional porous fiber membrane is composed of modified nanofibers;

[0152] The difference from Example 1 is that the components of the porous composite solid electrolyte membrane are adjusted to: 3 parts of modified nanofibers, 6 parts of inorganic solid electrolyte powder LATP powder, 0.6 parts of film-forming polymer PMMA and 3 parts of FEMC;

[0153] The preparation method of the porous composite solid electrolyte membrane is the same as that of Example 1.

[0154] Comparative Example 1

[0155] A solid electrolyte membrane, which differs from Example 1 in that the components of the composite solid electrolyte membrane are: 6 parts of inorganic solid electrolyte powder LATP powder, 0.5 parts of film-forming polymer SBR, and 1 part of plasticizer sulfolane and 1 part of ethylene carbonate;

[0156] The preparation method of the solid electrolyte membrane is the same as that of Example 1.

[0157] Comparative Example 2

[0158] A porous composite solid electrolyte membrane, comprising a three-dimensional porous fiber membrane and inorganic solid electrolyte powder and a film-forming polymer dispersed in the three-dimensional porous fiber membrane; the three-dimensional porous fiber membrane is composed of nanofibers;

[0159] The difference from Example 1 is that the composition of the porous composite solid electrolyte membrane is adjusted to: 1 part of modified nanofiber, 6 parts of inorganic solid electrolyte powder LATP powder and 0.5 parts of film-forming polymer SBR;

[0160] The preparation method of the porous composite solid electrolyte membrane is the same as that of Example 1.

[0161] Test Case

[0162] The photo of the porous composite solid electrolyte membrane prepared in Example 1 is as follows Figure 1 As shown. Figure 1 In the figure, a is a side view, b and c are folded views at different angles, and d is the unfolded view after folding. Figure 1It can be seen that the porous composite solid electrolyte membrane prepared in Example 1 is a membrane with uniform thickness. After testing, the porous composite solid electrolyte membrane prepared in Example 1 is a square with a length and width of 5 cm and a thickness of 0.08 mm. It has excellent flexibility, can be bent and folded 180°, and no cracks appear after unfolding.

[0163] The photos of the porous composite solid electrolyte membrane prepared in Example 1 before and after thermal shrinkage are as follows: Figure 2 As shown. Figure 2 The left picture is the porous composite solid electrolyte membrane prepared in Example 1, and the right picture is the photo of the porous composite solid electrolyte membrane prepared in Example 1 after heat treatment at 250°C for 30 minutes. Figure 2 It can be seen that the porous composite solid electrolyte membrane prepared in the present invention has excellent thermal stability and does not shrink after high-temperature treatment.

[0164] Figure 3 The following are pictures of the commonly used commercially available diaphragm PE film before and after heat shrinkage. Figure 3 The left picture is a PE film, and the right picture is a photo of the PE film after being heat treated at 250℃ for 10 minutes. Figure 3 It can be seen that the PE film has shrunk significantly after 10 minutes of high temperature treatment. Figure 2 and Figure 3 It can be seen that the porous composite solid electrolyte membrane provided by the present invention has excellent thermal stability, which is much higher than that of commercially available PE membranes.

[0165] The flammability test photo of the porous composite solid electrolyte membrane prepared in Example 1 is as follows: Figure 4 As shown. Figure 4 From left to right, the pictures are before burning, when burning, burning for 5 seconds, burning for 10 seconds and after burning. Figure 4 It can be seen that the porous composite solid electrolyte membrane prepared by the present invention is not easy to ignite, and after ignition, the flame goes out after burning for 10 seconds. This shows that the flame retardant performance of the porous composite solid electrolyte membrane prepared by the present invention is significantly improved. When the same method is used to ignite the currently available PE membrane, such as Figure 5 As shown. Figure 5 From left to right are the pictures before combustion, during ignition, 1 second after combustion, and after combustion. Figure 5 It can be seen that the PE film currently available on the market will obviously agglomerate and burn after being in contact with the flame for 1 second.

[0166] The SEM image of the porous composite solid electrolyte prepared in Example 1 is as follows: Figure 6 As shown; the SEM image of LATP is shown Figure 7 As shown. Figure 6It can be seen that in the porous composite solid electrolyte membrane prepared in the embodiment of the present invention, the inorganic solid electrolyte powder is uniformly embedded in the network structure of the modified nanofiber. Figure 7 It can be seen that LATP is in the form of agglomerated particles.

[0167] From the above results, it can be seen that the inorganic solid electrolyte powder of the porous composite solid electrolyte membrane provided by the present invention is uniformly embedded in the network structure of the modified nanofiber. This is because the nanofiber grafted with acrylic acid or methacrylic acid has more active groups, which can further react with the inorganic solid electrolyte powder, film-forming polymer and flame retardant plasticizer, thereby improving the interface bonding ability of the modified nanofiber, inorganic solid electrolyte powder and film-forming polymer, thereby making the porous composite solid electrolyte membrane have excellent flexibility; the inorganic solid electrolyte powder is dispersed in the three-dimensional porous fiber membrane, and the porous network structure can provide more lithium ion transmission channels, thereby increasing the ion migration rate and improving the conductivity of the porous composite solid electrolyte membrane; the porous composite solid electrolyte membrane provided by the present invention includes a flame retardant plasticizer, and the film-forming polymer and the flame retardant plasticizer are combined to improve the interface contact, and can provide more contact points with the porous structure, thereby improving the mechanical properties and flame retardancy of the porous composite solid electrolyte membrane.

[0168] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A porous composite solid electrolyte membrane, characterized in that: The invention comprises a three-dimensional porous fiber membrane and an inorganic solid electrolyte powder, a film-forming polymer and a flame retardant plasticizer dispersed in the three-dimensional porous fiber membrane; the three-dimensional porous fiber membrane is composed of modified nanofibers; the modified nanofibers are nanofibers grafted with acrylic acid or methacrylic acid; In parts by weight, the porous composite solid electrolyte membrane comprises 1 to 3 parts of modified nanofibers, 5 to 7 parts of inorganic solid electrolyte powder, 0.5 to 1 part of film-forming polymer and 2 to 5 parts of flame retardant plasticizer.

2. The porous composite solid electrolyte membrane according to claim 1, characterized in that The preparation method of the modified nanofiber comprises the following steps: (1) mixing the nanofibers with an alkali solution and performing alkali leaching to obtain alkalized nanofibers; (2) The alkalized nanofibers obtained in step (1) are mixed with a monomer solution and an initiator to carry out a grafting reaction to obtain modified nanofibers; the monomer in the monomer solution is acrylic acid or methacrylic acid.

3. The porous composite solid electrolyte membrane according to claim 2, characterized in that The diameter of the nanofiber is 4 to 500 nm; the length of the nanofiber is 100 to 20000 nm.

4. The porous composite solid electrolyte membrane according to claim 1, characterized in that The inorganic solid electrolyte powder includes one or more of oxide solid electrolyte powder, sulfide solid electrolyte powder and halide solid electrolyte powder.

5. The porous composite solid electrolyte membrane according to claim 1 or 4, characterized in that: The particle size of the inorganic solid electrolyte powder is 50 nm to 1 μm.

6. The porous composite solid electrolyte membrane according to claim 1, characterized in that The film-forming polymer includes one or more of styrene-butadiene rubber, polyvinylidene fluoride, polyethylene oxide, polyacrylonitrile, polymethyl methacrylate, poly(lithium styrene sulfonate) and poly(lithium methacrylate).

7. The porous composite solid electrolyte membrane according to claim 1, characterized in that: The flame retardant plasticizer includes one or more of silicon-based plasticizers, fluorine-containing plasticizers, phosphorus-based plasticizers, boron-containing compounds and ionic liquids.

8. The method for preparing the porous composite solid electrolyte membrane according to any one of claims 1 to 7, comprising: The modified nanofibers, a film-forming polymer, a flame retardant plasticizer, an inorganic solid electrolyte powder and an organic solvent are mixed to obtain a precursor slurry; After the precursor slurry is cast, it is dried to obtain a porous composite solid electrolyte membrane.

9. The preparation method according to claim 8, characterized in that The organic solvent includes one or more of N-methylpyrrolidone, dimethyl sulfoxide, acetonitrile, tetrahydrofuran and acetone.

10. Use of the porous composite solid electrolyte membrane according to any one of claims 1 to 7 or the porous composite solid electrolyte membrane prepared by the preparation method according to any one of claims 8 to 9 in lithium batteries.

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