Polymer solid electrolyte and preparation method thereof, sodium ion battery and electric equipment

Abstract

The invention provides a polymer solid electrolyte and a preparation method thereof, a sodium ion battery and electric equipment, and relates to the field of solid electrolytes. The preparation method comprises the following steps: mixing dimethylacetamide, N-methyl pyrrolidone, a brominated flame retardant, a dianhydride monomer and a diamine monomer to obtain a first mixed solution; coating the surface of a glass plate with the first mixed solution to obtain a film; mixing the thin film, dimethylacetamide and ethanol, and performing first drying to obtain a porous film; carrying out thermosetting on the porous membrane to obtain an imidization porous membrane; polyoxyethylene, bis (trifluoromethylsulfonyl) imide sodium and acetonitrile are mixed, and a second mixed solution is obtained; and mixing the imidization porous membrane with the second mixed solution, heating in a vacuum environment, and carrying out second drying to obtain the polymer solid electrolyte. The flame retardant is added for coating to obtain the film, and then the film is subjected to pore forming and imidization, so that the film has high mechanical strength, and has incombustibility and high safety while potential sodium dendritic crystal permeation can be prevented.

Description

Technical Field

[0001] This application relates to the field of solid electrolytes, and more particularly to a polymer solid electrolyte and its preparation method, a sodium-ion battery, and an electrical device thereof. Background Technology

[0002] The new energy vehicle industry is developing rapidly, but frequent safety accidents and the emergence of energy density bottlenecks are core issues that urgently need to be addressed. Currently, the performance advantage of commercial liquid electrolytes in batteries lies in their high ionic conductivity, but their disadvantages are equally obvious, including lower energy density, susceptibility to leakage, flammability and explosiveness, and the risk of lithium / sodium dendrites penetrating the separator and causing short circuits in the battery system during charging and discharging. Solid-state batteries, by replacing flammable electrolytes with solid electrolytes, can achieve battery safety while being compatible with better-performing positive and negative electrode materials, significantly improving battery energy density. Combining high safety and high energy density, they have become an inevitable choice for comprehensively improving battery performance.

[0003] Solid electrolytes are mainly classified into inorganic (ceramic / glass) solid electrolytes, organic polymer solid electrolytes, and composite solid electrolytes based on their composition. Among them, organic polymer solid electrolytes have been widely studied due to their advantages such as good flexibility, easy processing and molding, and good electrode interface compatibility. In particular, polyethylene oxide (PEO) / lithium (sodium) salt organic polymer solid electrolytes are widely studied because of their flexibility, low cost, lightweight properties, and high sodium ion conductivity.

[0004] However, among the aforementioned solid electrolytes, polymer solid electrolytes and polymer / ceramic composites are typically flammable, yet this safety concern has been largely ignored. Due to the inherent flexibility of these polymer systems, dendrite growth cannot be suppressed. Uncontrolled dendritic sodium dendrites, triggered at high current densities and accumulating with cycling, can penetrate the separator, causing a significant release of heat through an internal short circuit, posing a potential explosion hazard. Therefore, this safety issue severely limits the application of polymer solid electrolytes in batteries.

[0005] Most existing modification strategies employ blending, copolymerization, crosslinking, or the addition of fillers, ionic liquids, and plasticizers to improve performance. While these methods have achieved some improvements in conductivity and mechanical strength and have been effective in suppressing dendrite growth, these composite polymer solid electrolytes remain flammable, posing a risk to the safety performance of the battery cells.

[0006] Therefore, there is an urgent need to provide a polymer solid electrolyte to solve the above problems. Summary of the Invention

[0007] The purpose of this application is to provide a polymer solid electrolyte and its preparation method, a sodium-ion battery, and an electrical device to solve the above-mentioned problems.

[0008] To achieve the above objectives, the first aspect of this application provides a method for preparing a polymer solid electrolyte, comprising: Dimethylacetamide, N-methylpyrrolidone, brominated flame retardant, dianhydride monomer and diamine monomer are first mixed to obtain a first mixed solution; The first mixed solution is coated on the surface of a glass plate to obtain a thin film; the thin film, dimethylacetamide and ethanol are mixed a second time and dried a first time to obtain a porous membrane; the porous membrane is thermoset to obtain an imidized porous membrane; The polymer matrix, sodium electrolyte salt, and solvent are mixed in a third step to obtain a second mixed solution. The imidized porous membrane and the second mixed solution are mixed in a fourth process, and then heated and dried in a vacuum environment to obtain a polymer solid electrolyte.

[0009] Optionally, the method for preparing the polymer solid electrolyte satisfies at least one of the following conditions: (1) The brominated flame retardant includes one or more of decabromodiphenyl ether, decabromodiphenyl ethane, brominated epoxy resin, brominated polystyrene and tetrabromobisphenol A; (2) The dianhydride monomer includes one or more of biphenyl dianhydride, pyromellitic dianhydride and hexafluorodianhydride; (3) The diamine monomer includes one or more of 4,4'-diaminodiphenyl ether, diphenyl ether diamine and m-phenylenediamine; (4) The polymer matrix includes one or more of polyethylene oxide, polyacrylonitrile, polymethyl methacrylate, polycarbonate-based polymer, monoionic conductor polymer and polyvinylidene fluoride-co-hexafluoropropylene ester; (5) The electrolyte sodium salt includes one or more of sodium bis(trifluoromethanesulfonyl)imide, sodium perchlorate, sodium hexafluorophosphate, sodium bis(fluorosulfonyl)imide and sodium bis(oxalateborate); (6) The solvent includes one or more of acetonitrile, N-methylpyrrolidone, dimethyl sulfoxide, tetrahydrofuran and acetone.

[0010] Optionally, the method for preparing the polymer solid electrolyte satisfies at least one of the following conditions: (1) The molar ratio of the brominated flame retardant, the dianhydride monomer, and the diamine monomer is 1-4:3-5:3-5; (2) The mass ratio of the dimethylacetamide to the N-methylpyrrolidone is 5-9:1-2; (3) The solid-liquid ratio of the first mixed solution is 1g-2g:10mL.

[0011] Optionally, the method for preparing the polymer solid electrolyte satisfies at least one of the following conditions: (1) The volume ratio of the dimethylacetamide to the ethanol is 1:1-4; (2) The mass ratio of the polymer matrix to the electrolyte sodium salt is 2-5:1; (3) The solid-liquid ratio of the second mixed solution is 1g-2g:10mL.

[0012] Optionally, the method for preparing the polymer solid electrolyte satisfies at least one of the following conditions: (1) The thickness of the porous membrane is 10µm-40µm; (2) The coating temperature is room temperature; (3) After the coating is performed, the film is subjected to a first standing period of 60-120 min; (4) The second mixing includes rinsing the film with a mixed solution of dimethylacetamide and ethanol; the rinsing time is 15-60 min and the flow rate of the mixed solution is 300-600 mL / min.

[0013] Optionally, the method for preparing the polymer solid electrolyte satisfies at least one of the following conditions: (1) The first drying time is 60-120 min and the temperature is 80-120℃; (2) The heating temperature is 150℃-200℃, and the heating time is 0.5-2h; (3) The second drying temperature is 60-80℃ and the time is 24-48h; (4) After the second drying, the polymer solid electrolyte is subjected to a second settling under an argon atmosphere; the second settling time is 48-72h and the temperature is 50℃-70℃.

[0014] Optionally, in the method for preparing the polymer solid electrolyte, the thermosetting process includes a first thermosetting, a second thermosetting, and a third thermosetting process performed sequentially. The heating rate of the first thermosetting material is 3-5℃ / min, the final temperature is 90-110℃, and the holding time is 0.5-1h. The heating rate of the second thermosetting process is 3-5℃ / min, the final temperature is 150-250℃, and the holding time is 0.5-1h. The heating rate of the third thermosetting process is 2-5℃ / min, the final temperature is 300-400℃, and the holding time is 0.5-1h.

[0015] The second aspect of this application provides a polymer solid electrolyte, which is prepared by the method described above.

[0016] A third aspect of this application provides a sodium-ion battery, including the aforementioned polymer solid electrolyte.

[0017] A fourth aspect of this application provides an electrical device including the aforementioned sodium-ion battery.

[0018] Compared with the prior art, the beneficial effects of this application include: The method for preparing polymer solid electrolyte provided in this application involves adding a flame retardant to a first mixed solution, coating it to obtain a thin film, and then performing pore formation and imidization on the thin film to give it high mechanical strength, which can prevent potential sodium dendrite penetration while possessing non-flammability and high safety.

[0019] The polymer solid electrolyte provided in this application is composed of a porous mechanical reinforcing agent (polyimide), a flame retardant (bromine-based flame retardant), and an ion-conducting polymer electrolyte (polyethylene oxide) / sodium salt. This polymer solid electrolyte maintains thermal stability and high mechanical strength while preventing spontaneous combustion of sodium-ion solid batteries in accidents, thus meeting the safety performance requirements of solid-state batteries. To ensure that the prepared film possesses both high safety and high performance, the bromine-based flame retardant has advantages such as high flame retardant efficiency, low addition amount, and minimal impact on material properties. Furthermore, its thermal stability (decomposition temperature > 350℃) matches the polyimide skeleton, ensuring that the flame retardant performance does not degrade at high temperatures. In addition, adding the bromine-based flame retardant to the porous matrix can simultaneously improve the tensile strength and elongation of the matrix material. Other halogen-based flame retardants, such as chlorine-based flame retardants, are relatively convenient... While suitable for applications with low thermal stability, this polymer solid electrolyte is only applicable to products processed at temperatures below 200°C. It utilizes a porous polyimide membrane with polyethylene oxide / sodium bis(trifluoromethanesulfonyl)imide as the ion-conductive filler, incorporating a bromine-based flame retardant. This results in a fire-retardant, lightweight solid electrolyte with excellent electrochemical performance. Compared to traditional polyethylene oxide / sodium bis(trifluoromethanesulfonyl)imide-based solid electrolytes, this composite electrolyte exhibits superior flame retardancy. Furthermore, the sodium ion-conductive solid polymer electrolyte filler, also sodium oxide / bis(trifluoromethanesulfonyl)imide, contributes to its high electrical conductivity. The resulting polymer solid electrolyte material not only possesses good flexibility and high electrical conductivity, preventing potential sodium dendrite penetration, but also provides fire resistance.

[0020] The sodium-ion battery and electrical equipment provided in this application have high energy density and good safety performance. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation on the scope of this application.

[0022] Figure 1 EIS diagram of the polymer solid electrolyte provided in Example 1; Figure 2 The graph shows the charge and discharge test results of the battery provided in Example 2. Detailed Implementation

[0023] First, the solution provided in this application will be explained in more detail as follows: The first aspect of this application provides a method for preparing a polymer solid electrolyte, comprising: Dimethylacetamide, N-methylpyrrolidone, brominated flame retardant, dianhydride monomer and diamine monomer are first mixed to obtain a first mixed solution; In some embodiments, the first mixing includes: mixing dimethylacetamide and N-methylpyrrolidone to obtain a mixed solution, sequentially adding dianhydride monomer and diamine monomer, mixing evenly, adding a brominated flame retardant, and stirring under magnetic stirring. It is important to note that solvents such as dimethylacetamide and N-methylpyrrolidone possess high stability, extremely strong dissolving power, and good flowability, providing favorable background conditions for subsequent material dissolution and uniform film coating. The solution form facilitates subsequent blade coating to generate thin, adjustable polymer films.

[0024] In the first mixing process, the anhydride groups in the dianhydride monomer and the amino groups in the diamine monomer undergo a 1:1 polycondensation reaction to form the polyamic acid matrix, a precursor of polyimide. During the mixing polycondensation process, the matrix material and flame retardant components can be mixed evenly so that the continuous film formed by subsequent coating can encapsulate and fix a large number of flame retardant particles together, giving the base material a long-lasting flame retardant function. The first mixed solution is coated on the surface of a glass plate to obtain a thin film; the thin film, dimethylacetamide and ethanol are mixed a second time and dried a first time to obtain a porous membrane. It is important to note that the coating process allows for control of the polymer morphology, resulting in a continuous film that not only encapsulates and fixes a large number of flame retardant particles together to form a flame-retardant functional film, but also allows for thickness control of the organic polymer film through coating. This design enables the prepared polymer solid electrolyte to have the same energy density as traditional membranes / liquid electrolytes. Subsequently, a second mixing and first drying process using dimethylacetamide and ethanol yields a porous membrane. When the dimethylacetamide and ethanol mixture comes into contact with the polymer film, ethanol, as a non-solvent, promotes phase separation in the polymer solution. Dimethylacetamide effluxes from the polymer, while ethanol effluxes, causing the intermediate polyimide polymer to separate and precipitate from the homogeneous solution, simultaneously solidifying to form a fixed porous structure. This porous structure reduces the weight of the film, achieving a thinner solid electrolyte film. Furthermore, the porous structure creates a larger specific surface area, providing more sites for subsequent electrolyte adsorption. The porous membrane is thermoset to obtain an imidized porous membrane; It is important to note that a thermosetting reaction is carried out through low-temperature heating to transform the polyamic acid film into a polyimide film. Before low-temperature heating, the amic acid groups on the polyamic acid are unstable and easily decompose. After low-temperature heating, the amic acid groups undergo dehydration and internal recombination to form an imide film with a rigid three-dimensional network ring structure. Finally, the porous polymer film is completely cured and stabilized. The specific reaction is as follows: -NH-COO→-N=CO-+H2O; The imidized solid electrolyte film exhibits improved high-temperature resistance from 100℃ to 300℃, demonstrating enhanced thermal stability. Furthermore, due to the high thermal stability of brominated flame retardants, this low-temperature curing reaction does not affect their structure or function. The imidization process also allows the flame retardant to be more firmly anchored within the rigid polyimide network, preventing migration and leakage of the brominated flame retardant during long-term use or at high temperatures, thus ensuring the durability of the flame-retardant effect. The polymer matrix, sodium electrolyte salt, and solvent are mixed in a third step to obtain a second mixed solution. It should be noted that the polymer matrix has good solubility, can dissolve various electrolyte sodium salts, has good film-forming properties, and can increase the mechanical strength of subsequent solid electrolytes; The preferred polyethylene oxide polymer matrix is ​​commercially mature, has low cost, and has the potential for mass production. Sodium salts of electrolytes can dissociate into sodium ions in the electrolyte, serving as ion transport carriers for solid electrolytes.

[0025] The preferred sodium bis(trifluoromethanesulfonyl)imide exhibits excellent thermal and chemical stability, making it more suitable for high-safety flame-retardant solid electrolytes. Furthermore, its bis(trifluoromethanesulfonyl)imide anions are large in size and have dispersed charges, resulting in weak interaction with cations. This facilitates the dissociation of sodium bis(trifluoromethanesulfonyl)imide in the polymer matrix, providing more free sodium ions and thus achieving higher ionic conductivity. The solvent is used in the preparation process to fully dissolve and mix the polymer matrix and sodium salt to form a homogeneous solution, so that it can be uniformly impregnated and mixed with the polymer / flame retardant solid electrolyte film in the subsequent process. The preferred acetonitrile not only has excellent solubility, but also has a low boiling point, which can be completely removed in subsequent steps to avoid residues that may affect the long-term performance and safety of the battery. The imidized porous membrane and the second mixed solution are mixed in a fourth process, and then heated and dried in a vacuum environment to obtain a polymer solid electrolyte.

[0026] It is important to note that the solid electrolyte solution is mixed with the polymer / flame retardant matrix film and then baked and heated under vacuum to ensure that the solid electrolyte is completely permeated into the nanopores, thus guaranteeing the high ionic conductivity and high stability of the polymer solid electrolyte.

[0027] The dried polymer solid electrolyte achieves excellent flexibility, low electrolyte resistance, and a potentially high energy density for the entire battery. When this solid electrolyte battery experiences thermal runaway, the brominated flame retardant in the non-flammable imidized porous membrane (polyimide film matrix) effectively inhibits the combustion of flammable polyethylene oxide / bis(trifluoromethanesulfonyl)imide sodium. Upon heating, the brominated flame retardant degrades to generate bromine radicals (Br•); the highly reactive free radicals H• and OH• released from the burning electrolyte can be captured by Br•, thereby weakening or terminating the combustion chain branching reaction. Furthermore, gaseous products released during the free radical scavenging reaction, such as HBr, H2O, and Br2, limit heat and mass transfer, diluting the oxygen concentration between the heat source and the electrolyte, thus delaying self-sustaining combustion.

[0028] Furthermore, a fire-retardant, lightweight solid-state electrolyte with excellent electrochemical performance can be achieved using a porous polyimide membrane with a brominated flame retardant as the main component and a polymer matrix and sodium electrolyte salt as the ion-conducting filler. Compared with traditional solid-state electrolytes, this composite electrolyte exhibits superior flame retardancy. In addition, the composite electrolyte demonstrates excellent cycle stability in sodium-ion solid-state batteries. Therefore, the polymer solid-state electrolyte configuration provided in this application represents a general and promising approach for manufacturing high-energy-density and safe sodium batteries.

[0029] In some embodiments, the method for preparing the polymer solid electrolyte satisfies at least one of the following conditions: (1) The brominated flame retardant includes one or more of decabromodiphenyl ether, decabromodiphenyl ethane, brominated epoxy resin, brominated polystyrene and tetrabromobisphenol A; It is important to note that the selected bromine-based flame retardants are all high molecular weight or reactive flame retardants, exhibiting higher flame retardant efficiency compared to other small molecule flame retardants. Furthermore, they possess higher thermal stability, enabling them to maintain excellent flame retardant properties during the preparation of solid electrolytes. (2) The dianhydride monomer includes one or more of biphenyl dianhydride, pyromellitic dianhydride and hexafluorodianhydride; It is important to note that the choice of dianhydride monomer directly determines the performance of polyimide films during the preparation process. Biphenyltetracarboxylic dianhydride, pyromellitic dianhydride, and hexafluorodianhydride possess structural characteristics of rigid structure, symmetrical linear structure, and special functional group structure, respectively. A mixture of one or more of these monomers can yield high-performance films with high mechanical strength, high heat resistance, and high ionic conductivity. (3) The diamine monomer includes one or more of 4,4'-diaminodiphenyl ether, diphenyl ether diamine and m-phenylenediamine.

[0030] It is worth noting that both possess rigid benzene ring structures and flexible ether functional groups, balancing the flexibility and mechanical strength of the thin-film solid electrolyte and improving its processing and assembly performance. Furthermore, they exhibit relatively better thermal stability, enhancing the flame-retardant properties of the solid electrolyte. (4) The polymer matrix includes one or more of polyethylene oxide, polyacrylonitrile, polymethyl methacrylate, polycarbonate-based polymer, monoionic conductor polymer and polyvinylidene fluoride-co-hexafluoropropylene ester; (5) The electrolyte sodium salt includes one or more of sodium bis(trifluoromethanesulfonyl)imide, sodium perchlorate, sodium hexafluorophosphate, sodium bis(fluorosulfonyl)imide and sodium bis(oxalateborate); (6) The solvent includes one or more of acetonitrile, N-methylpyrrolidone, dimethyl sulfoxide, tetrahydrofuran and acetone.

[0031] In some embodiments, the method for preparing the polymer solid electrolyte satisfies at least one of the following conditions: (1) The molar ratio of the brominated flame retardant, the dianhydride monomer, and the diamine monomer is 1-4:3-5:3-5; Optionally, the molar ratio of brominated flame retardant, dianhydride monomer and diamine monomer can be any value between 1:3:3, 2:3:3, 3:3:3, 4:3:3, 4:4:5, 2:5:5 or 1-4:3-5:3-5; (2) The mass ratio of the dimethylacetamide to the N-methylpyrrolidone is 5-9:1-2; Optionally, the mass ratio of dimethylacetamide to N-methylpyrrolidone can be any value between 5:1, 6:1, 7:1, 8:1, 9:1, 5:2, 6:2, 8:2, 9:2 or 5-9:1-2; (3) The solid-liquid ratio of the first mixed solution is 1g-2g:10mL.

[0032] Optionally, the solid-liquid ratio of the first mixed solution can be any value between 1g:10mL, 1.5g:10mL, 2g:10mL, or 1g-2g:10mL.

[0033] In some embodiments, the method for preparing the polymer solid electrolyte satisfies at least one of the following conditions: (1) The volume ratio of the dimethylacetamide to the ethanol is 1:1-4; Optionally, the volume ratio of dimethylacetamide to ethanol can be any value between 1:1, 1:2, 1:3, 1:4 or 1:1-4; (2) The mass ratio of the polymer matrix to the electrolyte sodium salt is 2-5:1; Optionally, the mass ratio of the polymer matrix to the electrolyte sodium salt can be any value between 2:1, 3:1, 4:1, 5:1, or 2-5:1; Preferably, the polymer matrix is ​​polyethylene oxide; Preferably, the electrolyte sodium salt is sodium bis(trifluoromethanesulfonyl)imide, and the mass ratio can be any value between 5:1, 6:1, 7:1, 8:1, 9:1, 10:1 or 5-10:1; (3) The solid-liquid ratio of the second mixed solution is 1g-2g:10mL.

[0034] Optionally, the solid-liquid ratio of the second mixed solution can be any value between 1g:10mL, 1.5g:10mL, 2g:20mL, or 1g-2g:10mL.

[0035] In some embodiments, the method for preparing the polymer solid electrolyte satisfies at least one of the following conditions: (1) The thickness of the porous membrane is 10µm-40µm; Optionally, the thickness of the porous membrane can be any value between 10µm, 15µm, 20µm, 25µm, 30µm, 35µm, 40µm or 10µm-40µm; (2) The coating temperature is room temperature; (3) After the coating is performed, the film is subjected to a first standing period of 60-120 min; (4) The second mixing includes rinsing the film with a mixed solution of dimethylacetamide and ethanol; the rinsing time is 15-60 min and the flow rate of the mixed solution is 300-600 mL / min.

[0036] Optionally, the rinsing time can be any value between 15 min, 30 min, 45 min, 60 min, or 15-60 min, and the flow rate of the mixed solution can be any value between 300 mL / min, 400 mL / min, 500 mL / min, 600 mL / min, or 300-600 mL / min.

[0037] In some embodiments, the method for preparing the polymer solid electrolyte satisfies at least one of the following conditions: (1) The first drying time is 60-120 min and the temperature is 80-120℃; Optionally, the first drying time can be any value between 60 min, 90 min, 120 min or 60-120 min, and the temperature can be any value between 80℃, 90℃, 100℃, 110℃, 120℃ or 80-120℃. (2) The heating temperature is 150℃-200℃, and the heating time is 0.5-2h; Optionally, the heating temperature can be any value between 150℃, 160℃, 170℃, 180℃, 190℃, 200℃ or 150-200℃, and the time can be any value between 0.5h, 1h, 1.5h, 2h or 0.5-2h. (3) The second drying temperature is 60-80℃ and the time is 24-48h; Optionally, the temperature for the second drying can be any value between 60°C, 70°C, 80°C or 60-80°C, and the time can be any value between 24h, 30h, 36h, 42h or 24-48h. (4) After the second drying, the polymer solid electrolyte is subjected to a second settling under an argon atmosphere; the second settling time is 48-72h and the temperature is 50℃-70℃.

[0038] Optionally, the second settling time can be any value between 48h, 54h, 60h, 66h, 72h or 48-72h, and the temperature can be any value between 50℃, 60℃, 70℃ or 50-70℃.

[0039] In some embodiments, the method for preparing the polymer solid electrolyte includes a thermosetting process comprising a first thermosetting process, a second thermosetting process, and a third thermosetting process performed sequentially. The heating rate of the first thermosetting material is 3-5℃ / min, the final temperature is 90-110℃, and the holding time is 0.5-1h. Optionally, the heating rate of the first thermosetting process can be any value between 3℃ / min, 4℃ / min, 5℃ / min or 3-5℃ / min, the endpoint temperature can be any value between 90℃, 100℃, 110℃ or 90-110℃, and the isothermal temperature can be any value between 0.5h, 0.7h, 1h or 0.5-1h. The heating rate of the second thermosetting process is 3-5℃ / min, the final temperature is 150-250℃, and the holding time is 0.5-1h. Optionally, the heating rate of the second thermosetting process can be any value between 3℃ / min, 4℃ / min, 5℃ / min or 3-5℃ / min, the endpoint temperature can be any value between 150℃, 200℃, 250℃ or 150-250℃, and the isothermal temperature can be any value between 0.5h, 0.7h, 1h or 0.5-1h. The heating rate of the third thermosetting process is 2-5℃ / min, the final temperature is 300-400℃, and the holding time is 0.5-1h.

[0040] Optionally, the heating rate of the third thermosetting material can be any value between 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min or 2-5℃ / min, the endpoint temperature can be any value between 300℃, 350℃, 400℃ or 300-400℃, and the isothermal temperature can be any value between 0.5h, 0.7h, 1h or 0.5-1h.

[0041] It should be noted that the main benefits of the first thermosetting process are the removal of most of the solvent, preventing bubbles and pinholes caused by solvent boiling after rapid heating, and initially triggering the film to begin a slow imidization reaction, which helps to form a uniform and ordered chain structure.

[0042] The beneficial effect of the second thermosetting process is to complete the main imidization reaction, ensuring that most of the polyamic acid is completely dehydrated and forms a stable imide ring.

[0043] The beneficial effects of the third thermosetting process are the complete removal of residual solvents and water produced by the reaction, and high-temperature curing helps to improve the thermal stability of the film.

[0044] Compared with the one-step method, the three-step curing method produces films with higher consistency, smoother surfaces, higher imide content, and fewer impurities.

[0045] The second aspect of this application provides a polymer solid electrolyte, which is prepared by the method described above.

[0046] A third aspect of this application provides a sodium-ion battery, including the aforementioned polymer solid electrolyte.

[0047] A fourth aspect of this application provides an electrical device including the aforementioned sodium-ion battery.

[0048] The implementation schemes of this application will be described in detail below with reference to specific embodiments. However, those skilled in the art will understand that the following embodiments are only for illustrating this application and should not be regarded as limiting the scope of this application. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments used without specified manufacturers are all conventional products that can be purchased commercially.

[0049] Example 1 This embodiment provides a polymer solid electrolyte and its preparation method, the specific preparation process of which is as follows: S1: Mix 9g of dimethylacetamide and 1g of N-methylpyrrolidone evenly to obtain a mixed solution. Then, add 0.16g of 4,4'-diaminodiphenyl ether, 0.36g of pyromellitic dianhydride and 0.60g of diphenyl ether diamine monomer to the mixed solution in sequence. After mixing evenly, add 0.48g of decabromodiphenyl ethane flame retardant and stir under magnetic stirring for 12 h to obtain the first mixed solution. S2: Then, the first mixed solution is coated onto a glass plate with a thickness of 15 μm using a doctor blade, and left to stand on the glass plate for 60 min to obtain a thin film; S3: Rinse the membrane with a dimethylacetamide / ethanol solution (v:v=1:1) for 15 min, and then dry it in an oven for 120 min to obtain a porous membrane; S4: The porous membrane was thermoset at low temperature. The thermosetting heating program was as follows: first, the temperature was increased to 100℃ at a heating rate of 5℃ / min and held for 0.5h; then, the temperature was increased to 200℃ at a heating rate of 3℃ / min and held for 0.5h; then, the temperature was increased to 300℃ at a heating rate of 2℃ / min and held for 0.5h; finally, the temperature was allowed to cool naturally to room temperature to obtain the imidized porous membrane. S5: Polyoxyethylene, sodium bis(trifluoromethanesulfonyl)imide and acetonitrile are mixed and stirred at high speed in a mixer to obtain a second mixed solution. The mass ratio of polyoxyethylene to sodium bis(trifluoromethanesulfonyl)imide is 3:1, and the solid-liquid ratio of the second mixed solution is 1.5g:10mL. S6: Immerse the imidized porous membrane in the second mixed solution above, heat it under vacuum at 180°C, then bake it under vacuum at 60°C for 24 hours, and then transfer it to an argon glove box and let it stand at 80°C for 48 hours to obtain the polymer solid electrolyte.

[0050] The second aspect of this application provides a battery, the specific preparation method of which is as follows: S7: Using layered oxide as the positive electrode, hard carbon as the negative electrode, and copper foil and aluminum foil as the current collectors for the negative and positive electrodes respectively, and using the above-mentioned polymer solid electrolyte as the solid electrolyte, the cells are assembled into a soft-pack battery in a stacked manner, with a designed capacity of 1.2Ah.

[0051] Batteries fabricated using the above basic conditions were tested using a computer-controlled testing instrument. The charging current was 0.2C, the discharging current was 0.2C, and the charging / discharging voltage range was 1.5-3.8 V. The EIS of the polymer solid electrolyte was as follows: Figure 1 As shown, the battery charge / discharge test results are as follows: Figure 2 As shown.

[0052] Example 2 The difference from Example 1 is that in step S2, the coating thickness is 40 μm.

[0053] Example 3 The difference from Example 1 is that in step S1, the brominated flame retardant is a brominated epoxy resin.

[0054] Example 4 The difference from Example 1 is that in step S5, the polymer matrix, electrolyte sodium salt and solvent combination is polyvinylidene fluoride-co-hexafluoropropylene ester, sodium bis(trifluoromethanesulfonyl)imide and acetone.

[0055] Comparative Example 1 The difference from Example 1 is that only the film of step S2 is prepared, and the decabromodiphenyl ethane flame retardant is not added in step S1.

[0056] Comparative Example 2 The difference from Example 1 is that only the solid electrolyte of step S5 is prepared, specifically: Polyethylene oxide, sodium bis(trifluoromethanesulfonyl)imide, and acetonitrile were mixed and stirred at high speed in a mixer to obtain a homogeneous mixed solution. The mass ratio of polyethylene oxide to sodium bis(trifluoromethanesulfonyl)imide was 3:1, and the solid-liquid ratio of the second mixed solution was 1.5 g: 10 mL. The mixed solution was coated onto a glass plate to a thickness of 15 μm and allowed to stand on the glass plate for 60 min to obtain a thin film.

[0057] Comparative Example 3 The difference from Example 1 is that no decabromodiphenyl ethane flame retardant is added.

[0058] Comparative Example 4 The difference from Example 1 is that only the imidized porous membrane of step S4 is prepared.

[0059] Comparative Example 5 The difference from Example 1 is that in step S3, the film rinsing time is 10 min.

[0060] Comparative Example 6 The difference from Example 1 is that in step S2, the coating thickness is 50 μm.

[0061] Comparative Example 7 The difference from Example 1 is that step S3 is not performed, i.e., an imidized film is prepared, and the imidized film is immersed in the second mixed solution and heated under vacuum at 180°C, then baked under vacuum at 60°C for 24 hours, and then transferred to an argon glove box and left to stand at 80°C for 48 hours to obtain a polymer solid electrolyte.

[0062] The electrochemical performance tests of the batteries prepared in the above embodiments and comparative examples are shown in Table 1. Specifically, the flammability was tested by ignition test, and the membrane conductivity was tested by conductivity test.

[0063] Table 1 Electrochemical performance

[0064] analyze: As can be seen from the above tests, Examples 1 and 2 demonstrate that solid electrolyte films with a thickness in the range of 10-40 μm can have high ionic conductivity and tensile strength, and are also non-flammable, that is, solid electrolyte films have high safety and high performance characteristics.

[0065] Examples 1, 3, and 4 illustrate the universality of flame retardant and electrolyte types. Within a certain range, solid electrolyte films are adjustable, and flame retardants and electrolytes can be replaced according to the cell type to meet specific requirements such as high voltage and high rate.

[0066] Example 1 and Comparative Example 1 demonstrate that the substrate film is non-flammable without flame retardants. Furthermore, the absence of a pore-forming process negatively impacts the porosity and ionic conductivity of the substrate film.

[0067] Example 1 and Comparative Example 2 demonstrate that solid electrolytes are inherently flammable.

[0068] Examples 1 and 3 demonstrate that even without flame retardants, the solid electrolyte combined with the polyimide film remains flammable.

[0069] Example 1 and Comparative Example 4 demonstrate that the substrate film is non-flammable under conditions without flame retardants.

[0070] Examples 1 and Comparative Examples 5 and 7 demonstrate that reduced porosity of the polyimide-based film negatively impacts the wetting of the solid electrolyte, thereby reducing ionic conductivity.

[0071] Examples 1 and 6 illustrate that when the thickness exceeds a certain limit, the ionic conductivity and tensile strength of the solid electrolyte film will decrease significantly.

[0072] In summary, this composite solid-state electrolyte is made of a porous bifunctional polyimide matrix with a sodium-ion-conducting polymer electrolyte filler. The bifunctional matrix consists of a non-flammable and robust (10-40 μm) porous polyimide film and a lightweight brominated flame-retardant material. This matrix not only possesses sufficient mechanical strength to prevent potential sodium dendrite penetration but also imparts fire resistance to the solid-state electrolyte. The sodium-ion-conducting polymer electrolyte filler is composed of a polymer / sodium electrolyte salt, thereby improving the ionic conductivity of the solid-state electrolyte. The polymeric properties of the composite electrolyte give it good flexibility, low electrolyte resistance, and a potentially high energy density for the entire battery. When a battery using the solid-state electrolyte experiences thermal runaway, the flame retardant in the non-flammable polyimide matrix effectively inhibits the combustion of the flammable solid-state electrolyte.

[0073] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

[0074] Furthermore, those skilled in the art will understand that although some embodiments herein include certain features included in other embodiments but not others, combinations of features from different embodiments are intended to be within the scope of this application and form different embodiments. For example, any of the claimed embodiments can be used in any combination. The information disclosed in this background section is intended only to enhance the understanding of the general background of this application and should not be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

Claims

1. A method for preparing a polymer solid electrolyte, characterized in that, include: Dimethylacetamide, N-methylpyrrolidone, brominated flame retardant, dianhydride monomer and diamine monomer are first mixed to obtain a first mixed solution; The first mixed solution is coated on the surface of a glass plate to obtain a thin film; the thin film, dimethylacetamide and ethanol are mixed a second time and dried a first time to obtain a porous membrane; the porous membrane is thermoset to obtain an imidized porous membrane; The polymer matrix, sodium electrolyte salt, and solvent are mixed in a third step to obtain a second mixed solution. The imidized porous membrane and the second mixed solution are mixed in a fourth process, and then heated and dried in a vacuum environment to obtain a polymer solid electrolyte.

2. The method for preparing the polymer solid electrolyte according to claim 1, characterized in that, At least one of the following conditions must be met: (1) The brominated flame retardant includes one or more of decabromodiphenyl ether, decabromodiphenyl ethane, brominated epoxy resin, brominated polystyrene and tetrabromobisphenol A; (2) The dianhydride monomer includes one or more of biphenyl dianhydride, pyromellitic dianhydride and hexafluorodianhydride; (3) The diamine monomer includes one or more of 4,4'-diaminodiphenyl ether, diphenyl ether diamine and m-phenylenediamine; (4) The polymer matrix includes one or more of polyethylene oxide, polyacrylonitrile, polymethyl methacrylate, polycarbonate-based polymer, monoionic conductor polymer and polyvinylidene fluoride-co-hexafluoropropylene ester; (5) The electrolyte sodium salt includes one or more of sodium bis(trifluoromethanesulfonyl)imide, sodium perchlorate, sodium hexafluorophosphate, sodium bis(fluorosulfonyl)imide and sodium bis(oxalateborate); (6) The solvent includes one or more of acetonitrile, N-methylpyrrolidone, dimethyl sulfoxide, tetrahydrofuran and acetone.

3. The method for preparing the polymer solid electrolyte according to claim 1, characterized in that, At least one of the following conditions must be met: (1) The molar ratio of the brominated flame retardant, the dianhydride monomer, and the diamine monomer is 1-4:3-5:3-5; (2) The mass ratio of the dimethylacetamide to the N-methylpyrrolidone is 5-9:1-2; (3) The solid-liquid ratio of the first mixed solution is 1g-2g:10mL.

4. The method for preparing the polymer solid electrolyte according to claim 1, characterized in that, At least one of the following conditions must be met: (1) The volume ratio of the dimethylacetamide to the ethanol is 1:1-4; (2) The mass ratio of the polymer matrix to the electrolyte sodium salt is 2-5:1; (3) The solid-liquid ratio of the second mixed solution is 1g-2g:10mL.

5. The method for preparing the polymer solid electrolyte according to claim 1, characterized in that, At least one of the following conditions must be met: (1) The thickness of the porous membrane is 10µm-40µm; (2) The coating temperature is room temperature; (3) After the coating is performed, the film is subjected to a first standing period of 60-120 min; (4) The second mixing includes rinsing the film with a mixed solution of dimethylacetamide and ethanol; the rinsing time is 15-60 min and the flow rate of the mixed solution is 300-600 mL / min.

6. The method for preparing the polymer solid electrolyte according to claim 1, characterized in that, At least one of the following conditions must be met: (1) The first drying time is 60-120 min and the temperature is 80-120℃; (2) The heating temperature is 150℃-200℃, and the heating time is 0.5-2h; (3) The second drying temperature is 60-80℃ and the time is 24-48h; (4) After the second drying, the polymer solid electrolyte is subjected to a second settling under an argon atmosphere; the second settling time is 48-72h and the temperature is 50℃-70℃.

7. The method for preparing the polymer solid electrolyte according to any one of claims 1-6, characterized in that, The thermosetting process includes a first thermosetting, a second thermosetting, and a third thermosetting performed sequentially. The heating rate of the first thermosetting material is 3-5℃ / min, the final temperature is 90-110℃, and the holding time is 0.5-1h. The heating rate of the second thermosetting process is 3-5℃ / min, the final temperature is 150-250℃, and the holding time is 0.5-1h. The heating rate of the third thermosetting process is 2-5℃ / min, the final temperature is 300-400℃, and the holding time is 0.5-1h.

8. A polymer solid electrolyte, characterized in that, It is prepared by the method for preparing polymer solid electrolyte according to any one of claims 1-7.

9. A sodium-ion battery, characterized in that, Includes the polymer solid electrolyte as described in claim 8.

10. An electrical appliance, characterized in that, Including the sodium-ion battery as described in claim 9.

Images