A hybrid solid electrolyte film with high efficiency flame retardant performance and its preparation method and application

Abstract

The present invention discloses a hybrid solid electrolyte film with efficient flame retardant properties, and a preparation method and application thereof. The hybrid solid electrolyte film is a non-flammable porous polyimide film modified with bromide flame retardant small molecules as a skeleton, and an inorganic oxide precursor solution is coated on the surface of the skeleton to form a modified porous organic-inorganic composite skeleton film; and then a polymer precursor liquid formed by a lightweight flame retardant plasticizer small molecule and an unsaturated monomer is used, and is polymerized by adsorption on the modified porous organic-inorganic composite skeleton film. The present invention achieves high conductivity and non-flammable properties of lithium ions under room temperature conditions through the structural design of polymer molecules, and the resulting hybrid solid electrolyte film has excellent mechanical properties, a stable electrochemical window and great flexibility.

Description

Technical Field

[0001] The present invention relates to the technical field of energy storage and power batteries, and in particular to a hybrid solid electrolyte film with high-efficiency flame retardant performance, and a preparation method and application thereof. Background Art

[0002] Lithium batteries have developed rapidly in recent decades due to their high energy density, long service life, and wide range of applications. They have become one of the main energy storage devices. In order to improve the energy density of lithium-ion batteries, researchers have conducted extensive research on metallic lithium anodes with high-capacity and high-voltage cathodes. However, with the growing demand for lithium battery energy / power density, serious safety issues have arisen. Therefore, it is urgent to develop lithium-ion batteries with both high energy density and high safety performance to meet social requirements.

[0003] Current lithium-ion batteries mostly use liquid organic electrolytes such as esters and ethers as electrolytes. However, liquid organic electrolytes have safety issues such as leakage, volatility, flammability and even explosion. Lithium dendrites generated and accumulated in circulation under high current density can easily pierce the diaphragm and cause battery short circuit.

[0004] Compared with flammable liquid electrolytes, solid electrolytes (SSEs) can ideally suppress the formation of lithium dendrites, thereby ensuring the safe operation of lithium-ion batteries. Generally, research on SSEs can be summarized into three categories: inorganic (ceramic / glass) solid electrolytes, solid polymer electrolytes (SPEs), and their composites.

[0005] Inorganic solid electrolytes have attracted much attention due to their highest ionic conductivity. However, inorganic SSEs are brittle, thick, inflexible, and have large interface impedance with electrodes, which results in lithium still penetrating inorganic SSEs after reaching the critical current density. SPEs are the most widely studied polymer system due to their flexibility, low cost, light weight, and high lithium ion conductivity. However, the inherent flexibility of SPEs makes it impossible to suppress the extension of lithium dendrites, which limits their application in lithium-ion batteries. Although this problem has been avoided by strategies such as using nanoparticle reinforcement, cross-linking, and utilizing stable host bodies, the flammability problem of composite polymer SSEs remains unsolved.

[0006] Therefore, it is urgent to develop solid electrolytes that are flame-retardant or even intrinsically non-flammable, and at the same time have the effect of inhibiting lithium dendrites and high-performance and high-safety electrolytes. Summary of the invention

[0007] The purpose of the present invention is to provide a hybrid solid electrolyte film with high-efficiency flame retardant properties, and a preparation method and application thereof. Through the design of the solid electrolyte skeleton structure and the design and filling of the ion transport polymer main body molecules, the decoupling of the good mechanical properties of the skeleton and the high lithium ion conductivity of the polymer main body is achieved, and at the same time, it has excellent non-flammable properties, so that the obtained hybrid solid electrolyte film has excellent mechanical properties, high ion conductivity and safety, solving the problem of insufficient mechanical properties and difficulty in combining flammability of existing solid electrolytes.

[0008] The present invention achieves the above-mentioned purpose through the following technical solutions:

[0009] First, the present invention provides a method for preparing a hybrid solid electrolyte film with high-efficiency flame retardant performance, comprising the following steps:

[0010] S1, mixing N-methylpyrrolidone and dimethylformamide, then adding diphenylamine, 2,3-pyrazine dianhydride and 1,4-bis(4-aminophenoxy)benzene in sequence to obtain a mixed solution, and then adding a brominated flame retardant small molecule to obtain a precursor liquid solution;

[0011] S2, coating the precursor liquid solution on a glass sheet, washing with a mixed solvent after standing, and drying to obtain a polyamide nanoporous film (PCA);

[0012] S3, subjecting the polyamide nanoporous film to imidization treatment to obtain a modified non-flammable porous polyimide film (PID);

[0013] S4, coating the inorganic oxide precursor solution on the surface of the modified non-combustible porous polyimide film, and drying to obtain a modified porous organic-inorganic composite skeleton film (MLPD);

[0014] S5, immersing the modified porous organic-inorganic composite skeleton film in a polymer precursor liquid, and subjecting the film to ultraviolet curing, to obtain the hybrid solid electrolyte film (HSEF).

[0015] A further improvement is that in step S1, the mass ratio of the N-methylpyrrolidone to the dimethylformamide is 1:(3-5).

[0016] The mass ratio of the diphenylamine to the N-methylpyrrolidone is (0.1-0.12):1.

[0017] The mass ratio of the diphenylamine, the 2,3-pyrazine dianhydride and the 1,4-bis(4-aminophenoxy)benzene is 1:(3-4):(3-5).

[0018] The time interval for adding the diphenylamine, the 2,3-pyrazine dianhydride and the 1,4-bis(4-aminophenoxy)benzene is 10 to 25 minutes.

[0019] Based on the mixed solution, the amount of the brominated flame retardant small molecule is 7-20wt%, preferably 10-15wt%.

[0020] A further improvement is that the mixing conditions of the N-methylpyrrolidone and the dimethylformamide are: a temperature of 55 to 60° C. and a time of 1 to 2 hours;

[0021] The mixing conditions of the mixed solution are: in an inert atmosphere, a temperature of 45 to 60° C., and a time of 1 to 2 hours.

[0022] A further improvement is that the brominated flame retardant small molecule is 3,6-bis(bromomethyl)-1,2,4,5-tetrabromobenzene.

[0023] A further improvement is that in step S2, the mixed solvent is composed of acetone and alcohol in a volume ratio of 1: (1-10); preferably 1:1.5;

[0024] The flushing time is not less than 20 minutes;

[0025] The standing time is 3 to 4 hours;

[0026] The drying conditions are: vacuum drying at 55-60°C for 22-24h;

[0027] A further improvement is that the thickness of the polyamide nanoporous film is 8 to 15 μm, preferably 8 to 10 μm.

[0028] A further improvement is that in step S3, the temperature raising procedure of the imidization treatment is as follows:

[0029] (1) From room temperature to 80°C, the heating rate is 1-5°C / min;

[0030] (2) From 80°C to 100°C, the heating rate is 1-5°C / min;

[0031] (3) Maintain at 100°C for 15 to 20 minutes;

[0032] (4) From 100°C to 200°C, the heating rate is 1-5°C / min;

[0033] (5) Maintain at 200°C for 20 to 40 minutes;

[0034] (6) From 200°C to 300°C, the heating rate is 1-5°C / min;

[0035] (7) Maintain at 300°C for 1 to 5 minutes;

[0036] (8) Cool to 25°C.

[0037] A further improvement is that in step S3, the pore size of the modified non-combustible porous polyimide film (PID) is 5 nm to 5 μm, preferably 1 to 5 μm; the volume percentage of the porosity is 40% to 92%, preferably 17 to 47%; the molecular weight is 1×10 4 ~6×10 7 g / mol, preferably 170000 to 220000 g / mol.

[0038] A further improvement is that in step S4, the inorganic oxide precursor solution is obtained by mixing a solution A containing a soluble polyimide and a solution B containing an inorganic oxide solid electrolyte and then ball milling the mixture.

[0039] The thickness of the single-sided coating is 2 to 10 μm, preferably 5 to 10 μm;

[0040] The drying conditions are: under vacuum conditions, the temperature is 30-80° C., and the time is 1-48 hours.

[0041] A further improvement is that in step S4, the solution A is a solution formed by dissolving the soluble polyimide in a polar aprotic solvent, and its concentration is 1 to 50 mol / L; preferably 10 to 20 mol / L.

[0042] The polar aprotic solvent is dichloromethane.

[0043] The solution B is a suspension formed by dissolving the inorganic oxide in a polar aprotic solvent, and its concentration is 1 to 100 g / L, preferably 30 to 40 g / L.

[0044] The inorganic oxide solid electrolyte is LLZTO.

[0045] The mixing volume ratio of the solution A and the solution B is 1:1.

[0046] A further improvement is that the ball milling conditions are: a rotation speed of 200-300 r / min, such as 250 r / min, and a time of 25-35 min, such as 30 min.

[0047] A further improvement is that in step S5, the polymer precursor liquid is obtained by dissolving lithium salt in small molecules of flame retardant plasticizer to form a eutectic solvent, and then adding unsaturated monomers and initiators to form a copolymerization reaction.

[0048] In the eutectic solvent, the molar concentration of the lithium salt is 0.4-1.2 M; in the polymer precursor liquid, the molar ratio of the active group of the polymer to the lithium salt is (16-32):1.

[0049] Based on the eutectic solvent, the volume fraction of the unsaturated monomer is 2-3 vol%, such as 2.5 vol%, the amount of the initiator is 1-10 wt%, the concentration of the unsaturated monomer in the polymer precursor liquid is 0.2-0.5 mmol / mL, and the molecular weight of the random copolymer is controlled by controlling the amount of the eutectic solvent in the polymer precursor liquid.

[0050] The lithium salt is one or more of LiDFOB (lithium difluorooxalatoborate), LiBOB (lithium bis(oxalate borate), LiTFSI (lithium bis(trifluoromethylsulfonyl)imide), LiFSI (lithium bis(fluorosulfonyl)imide) and LiClO4 (lithium perchlorate); preferably, it is a composite lithium salt with a molar ratio of LiTFSI to LIFSI of 1:(0.5-2).

[0051] The flame retardant plasticizer small molecule is one or more of fluoroethylene carbonate, dimethyl phosphate, triethyl phosphate, N-methylacetamide, methyl trifluoroethyl carbonate and 1,1,2,3,3,3-pentafluoropropyl-2,2,2-trifluoroethyl ether.

[0052] The unsaturated monomer is one or more of polyethylene glycol diacrylate, methyl methacrylate, vinyl acetate, vinylene carbonate, ethyl 2-cyanoacrylate, tripropylene glycol diacrylate, hydroxyethyl acrylate and derivatives thereof.

[0053] The initiator is an acylphosphine oxide.

[0054] A further improvement is that the soaking time is 10 to 48 hours, preferably 24 hours.

[0055] The conditions for the UV curing are: power 1-1000W, time 20-30min, preferably power 1000W, time 20min.

[0056] Second, the present invention provides a hybrid solid electrolyte film prepared by the above preparation method.

[0057] Thirdly, a lithium metal battery of the present invention comprises the following components: a positive electrode, a negative electrode and the hybrid solid electrolyte film.

[0058] A further improvement is that the lithium metal battery is a lithium iron phosphate-graphite battery, a lithium iron phosphate-lithium metal battery or a lithium ternary transition metal oxide-lithium metal battery.

[0059] The beneficial effects of the present invention are:

[0060] 1. The present invention introduces bromine flame retardant small molecules into polyimide through molecular regulation to synthesize a modified non-flammable porous polyimide film (steps S1-S3) with non-flammability, thereby solving the defects of traditional polyimide membranes being extremely flammable and easily causing safety problems as electrolyte skeletons. Bromide preferentially reacts with free radicals such as oxygen and hydroxyl to form inert substances, thereby effectively reducing the violent decomposition of the organic skeleton.

[0061] 2. The present invention further coats the surface of the modified non-combustible porous polyimide film with an inorganic oxide precursor solution, and locally undergoes chemical changes to form phase hybridization, thereby forming a modified porous organic-inorganic composite skeleton film with excellent mechanical properties (step S4). At the same time, an ion transmission path is formed inside the solid electrolyte film, thereby promoting the uniform deposition of lithium ions at the negative electrode, and can match with a high-voltage positive electrode of >4.2V without any side reactions.

[0062] 3. The present invention further perfuses an organic polymer by immersing it in the modified porous organic-inorganic composite skeleton film. After the polymer is infiltrated and solidified, it forms a coating and finally forms an integrated electrolyte (step S5). On the one hand, it can promote ion transport, reduce concentration polarization of half-cells and full-cells during the cycle process, and ensure the fast charging performance of the full-cell. On the other hand, through the soft contact between the polymer and the electrode surface, the impedance of the interface is reduced, which further facilitates the transmission of ions between the electrode and the electrolyte.

[0063] In summary, the present invention adopts the above-mentioned design to make the hybrid solid electrolyte film have excellent mechanical properties, high ionic conductivity and safety under the premise of economy and practicality, and can be assembled with different positive and negative electrodes into high-performance and high-safety solid batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Figure 1 This is the XRD pattern of the hybrid solid electrolyte film HSEF prepared in Example 1 of the present invention.

[0065] Figure 2 This is a scanning electron microscope image of the hybrid solid electrolyte film HSEF prepared in Example 1 of the present invention.

[0066] Figure 3 This is a curve diagram showing the change of ionic conductivity of the hybrid solid electrolyte film HSEF prepared in Examples 1-3 of the present invention as a function of temperature.

[0067] Figure 4 This is a comparison diagram of the electrochemical windows of the hybrid solid electrolyte film HSEF prepared in Examples 1-3 of the present invention.

[0068] Figure 5 This is a room temperature cycle performance diagram of the lithium iron phosphate battery prepared by the present invention. DETAILED DESCRIPTION

[0069] The present application is further described in detail below in conjunction with the accompanying drawings. It is necessary to point out here that the following specific implementation methods are only used to further illustrate the present application and cannot be understood as limiting the scope of protection of the present application. Technical personnel in this field can make some non-essential improvements and adjustments to the present application based on the above application content.

[0070] 1. Materials

[0071] The methods used in this example are conventional methods known to those skilled in the art unless otherwise specified, and the reagents and other materials used are commercially available products unless otherwise specified.

[0072] 2. Methods

[0073] 2.1. Preparation of hybrid solid electrolyte films

[0074] 2.1.1 Example 1

[0075] The steps include:

[0076] (1) In a 25 mL three-necked flask equipped with a stirrer, a thermometer, a spherical reflux condenser and a nitrogen protection device, 1.43 g of N-methylpyrrolidone and 6.77 g of dimethylformamide were added, and the mixture was refluxed and stirred at 55° C. for 1 h to form a mixed solution.

[0077] Then, 0.156 g of diphenylamine, 0.476 g of 2,3-pyrazine dianhydride and 0.615 g of 1,4-bis(4-aminophenoxy)benzene were added to the mixed solution in sequence, and stirred for 2 hours under a nitrogen atmosphere at 45°C to form a uniform mixed solution; it should be noted that the time interval for adding the three samples of diphenylamine, 2,3-pyrazine dianhydride and 1,4-bis(4-aminophenoxy)benzene was controlled within 15 minutes.

[0078] (2) The uniform mixed solution was cooled to room temperature and transferred to a glove box. A portion of the mixed solution was placed in a test tube, and 12.5 wt % of 3,6-bis(bromomethyl)-1,2,4,5-tetrabromobenzene was added. The mixture was stirred for 2 h to obtain a precursor liquid solution.

[0079] (3) The obtained precursor liquid solution was applied on the glass with a scraper, and the film thickness was 10 μm by scraping with the scraper. After scraping, the film was left on the glass plate for 4 hours, and then rinsed with a mixture of acetone and alcohol in a volume ratio of 1:15 for 20 minutes to generate pores, and then dried at 60°C under vacuum conditions for 24 hours to completely evaporate the solvent, thereby obtaining a polyamide nanoporous film PCA.

[0080] (4) The dried polyamide nanoporous film PCA is heated from room temperature to 80°C in a box furnace under air atmosphere at a heating rate of 5°C / min; then heated from 80°C to 100°C at a heating rate of 2°C / min; maintained at 100°C for 15 minutes and then heated to 200°C at a heating rate of 4°C / min; maintained at 200°C for 20 minutes and then heated to 300°C at a heating rate of 3°C / min; maintained at 300°C for 30 minutes and then cooled to 25°C to obtain an imidized modified non-flammable porous polyimide film (PID), which is taken out and stored in a glove box for use.

[0081] The pore size of the modified non-combustible porous polyimide film PID is 1 μm, the volume ratio of the porosity is 47%, and the molecular weight is 170000 g / mol.

[0082] (5) A commercial soluble polyimide (molecular weight of 100,000) was dissolved in 15 mL of dichloromethane to form a 15 mol / L uniform solution, labeled as liquid A; the inorganic oxide LLZTO powder was dispersed in dichloromethane to form a 37 g / L suspension, labeled as liquid B.

[0083] Liquid A and liquid B were mixed evenly in a volume ratio of 1:1, and after stirring at room temperature for 4 hours, the mixed solution was ball-milled in a ball mill at a speed of 250 r / min for 30 minutes to prepare an inorganic oxide precursor solution.

[0084] The inorganic oxide precursor solution is coated on the modified non-combustible porous polyimide film (PID) with a scraper, double-sided coating, and the single-sided coating thickness is controlled at 5 μm. The coated PID film is vacuum dried at 60°C for 24 hours to obtain a modified porous organic-inorganic composite skeleton film MLPD.

[0085] (6) The composite lithium salt (with a molar ratio of LiTFSI:LIFSI = 1:1.5) was dissolved in the triethyl phosphate small molecule monomer to form a eutectic solvent with a molar concentration of 0.4 M, and then 2.5 vol% of polyethylene glycol diacrylate monomer was added and stirred for 4 h to form a mixed solution. At the same time, 5 wt% of the initiator acylphosphine oxide was added and stirred for 2 h in a light-proof condition to obtain a polymer precursor liquid.

[0086] (7) Soaking MLPD in the above polymer precursor solution for 24 hours to fully absorb and infiltrate to obtain a composite film MLPD. It is worth noting that this step is carried out under light-proof conditions.

[0087] (8) Finally, the excess liquid on the surface of the composite film MLPD was scraped off with a scraper and cured under 1000W ultraviolet light for 20 minutes to obtain a solid electrolyte thin film HSEF.

[0088] The XRD pattern of the obtained hybrid solid electrolyte film HSEF is shown in Figure 1 As shown in the figure, there is a characteristic peak of the polymer; the characteristic peak appears at the peak position of ~21°, which is a typical amorphous flexible chain segment characteristic peak of the polymer amorphous region, indicating that the crystallinity of the polymer electrolyte prepared by us is greatly reduced, which is conducive to the transmission of ions. Figure 2 As shown, the surface is smooth and flat, indicating that the polymer electrolyte has excellent interface contact and can ensure the transport of lithium ions between the electrode and the electrolyte.

[0089] 2.1.2 Example 2

[0090] The steps include:

[0091] (1) In a 25 mL three-necked flask equipped with a stirrer, a thermometer, a spherical reflux condenser and a nitrogen protection device, 1.43 g of N-methylpyrrolidone and 4.29 g of dimethylformamide were added, and the mixture was refluxed and stirred at 60° C. for 2 h to form a mixed solution.

[0092] Then, 0.156 g of diphenylamine, 0.542 g of 2,3-pyrazine dianhydride and 0.615 g of 1,4-bis(4-aminophenoxy)benzene were added to the mixed solution in sequence, and stirred for 2 h under a nitrogen atmosphere at 50 °C to form a uniform mixed solution. It should be noted that the time interval for adding the three samples of diphenylamine, 2,3-pyrazine dianhydride and 1,4-bis(4-aminophenoxy)benzene was controlled within 20 minutes.

[0093] (2) The uniform mixed solution was cooled to room temperature and transferred into a glove box. A portion of the mixed solution was placed in a test tube and 10 wt % of 3,6-bis(bromomethyl)-1,2,4,5-tetrabromobenzene was added. The mixture was stirred for 2 h and uniformly mixed to obtain a precursor liquid solution.

[0094] (3) The obtained precursor liquid solution was coated on the glass with a scraper, and the film thickness was 8 μm. After the coating, the film was left on the glass plate for 4 h, and then rinsed with a mixture of acetone and alcohol in a volume ratio of 1:15 for 20 minutes to generate pores, and then dried at 60°C under vacuum conditions for 24 h to completely evaporate the solvent, thereby obtaining a polyamide nanoporous film PCA.

[0095] (4) The dried polyamide nanoporous film PCA was heated from room temperature to 80°C at a rate of 5°C / min in a box furnace under air atmosphere; from 80°C to 100°C at a rate of 2°C / min; kept at 100°C for 15 minutes and then heated to 200°C at a rate of 4°C / min; kept at 200°C for 20 minutes and then heated to 300°C at a rate of 3°C / min; kept at 300°C for 30 minutes and finally cooled to 25°C to obtain an imidized modified non-flammable porous polyimide film (PID), which was taken out and stored in a glove box for use.

[0096] The pore size of the modified non-combustible porous polyimide film PID is 5 μm, the volume ratio of the porosity is 44%, and the molecular weight is 178000 g / mol.

[0097] (5) A commercial soluble polyimide (molecular weight of 80,000) was dissolved in 15 mL of dichloromethane to form a 15 mol / L uniform solution, which was labeled as liquid A; the inorganic oxide LLZTO powder was dispersed in dichloromethane to form a 37 g / L suspension, which was labeled as liquid B. Liquid A and liquid B were mixed evenly at a volume ratio of 1:1, stirred at room temperature for 4 h, and then the mixed solution was ball milled in a ball mill at a speed of 250 r / min for 30 min to prepare an inorganic oxide precursor solution.

[0098] The inorganic oxide precursor solution is coated on the modified non-combustible porous polyimide film (PID) with a scraper, double-sided coating, and the single-sided coating thickness is controlled at 4 μm. The coated PID film is vacuum dried at 60°C for 24 hours to obtain the modified porous organic-inorganic composite skeleton film MLPD.

[0099] (6) The composite lithium salt (with a molar ratio of LiTFSI:LIFSI = 1:2) was dissolved in the triethyl phosphate small molecule monomer to form a eutectic solvent with a molar concentration of 0.6 M, and then 2.5 vol% of polyethylene glycol diacrylate monomer was added and stirred for 4 h to form a mixed solution. At the same time, 1 wt% of the initiator acylphosphine oxide was added and stirred for 2 h in a light-proof condition to obtain a polymer precursor liquid.

[0100] (7) Soaking MLPD in the above polymer precursor solution for 24 hours to fully absorb and infiltrate to obtain a composite film MLPD. It is worth noting that this step is carried out under light-proof conditions.

[0101] (8) Finally, the excess liquid on the surface of the composite film MLPD was scraped off with a scraper, and the film was cured under 1000W ultraviolet light for 20 minutes to obtain a solid electrolyte film HSEF. Its XRD characterization diagram and electron microscope scanning diagram are similar to those of Example 1, indicating that the crystallinity of the polymer electrolyte prepared in Example 2 is greatly reduced, which is conducive to the transmission of ions. The surface is smooth and flat, indicating that the polymer electrolyte prepared in Example 2 has excellent interface contact and can ensure the transportation of lithium ions between the electrode and the electrolyte.

[0102] 2.1.3 Example 3

[0103] The steps include:

[0104] (1) In a 25 mL three-necked flask equipped with a stirrer, a thermometer, a spherical reflux condenser and a nitrogen protection device, 1.43 g of N-methylpyrrolidone and 5.72 g of dimethylformamide were added, and the mixture was refluxed and stirred at 55° C. for 1 h to form a mixed solution;

[0105] Then, 0.156 g of diphenylamine, 0.476 g of 2,3-pyrazine dianhydride and 0.715 g of 1,4-bis(4-aminophenoxy)benzene were added to the mixed solution in sequence, and stirred and mixed for 2 h at 60° C. under a nitrogen atmosphere to form a uniform mixed solution. It should be noted that the time interval between adding three samples was controlled within 15 minutes.

[0106] (2) The uniform mixed solution is then cooled to room temperature and transferred to a glove box. A portion of the mixed solution is taken and placed in a test tube and 15 wt % of 3,6-bis(bromomethyl)-1,2,4,5-tetrabromobenzene is added. The mixture is stirred for 2 h and uniformly mixed to obtain a precursor liquid solution.

[0107] (3) The obtained solution was applied on glass using a scraper, and the film thickness was 15 μm. After scraping, the film was left on the glass plate for 4 h, then rinsed with a mixture of acetone and alcohol in a volume ratio of 1:2 for 30 minutes to generate pores, and then dried at 60°C under vacuum conditions for 24 h to completely evaporate the solvent, thereby obtaining a polyamide nanoporous film PCA.

[0108] (4) The dried polyamide nanoporous film PCA was heated from room temperature to 80°C at a rate of 5°C / min in a box furnace under air atmosphere; from 80°C to 100°C at a rate of 2°C / min; kept at 100°C for 15 minutes and then heated to 200°C at a rate of 4°C / min; kept at 200°C for 20 minutes and then heated to 300°C at a rate of 3°C / min; kept at 300°C for 30 minutes and finally cooled to 25°C to obtain an imidized modified non-flammable porous polyimide film (PID), which was taken out and stored in a glove box for use.

[0109] The pore size of the modified non-combustible porous polyimide film PID is 2 μm, the volume ratio of the porosity is 17%, and the molecular weight is 190000 g / mol.

[0110] (5) A commercial soluble polyimide (molecular weight of 100,000) was dissolved in 15 mL of dichloromethane to form a 15 mol / L uniform solution, labeled as liquid A, and the inorganic oxide LLZTO powder was dispersed in dichloromethane to form a 37 g / L suspension, labeled as liquid B. Liquid A and liquid B were mixed uniformly at a volume ratio of 1:1, stirred at room temperature for 4 h, and then the mixed solution was ball milled in a ball mill at a speed of 250 r / min for 30 min to prepare an inorganic oxide precursor solution.

[0111] The inorganic oxide precursor solution is coated on the modified non-combustible porous polyimide film (PID) with a scraper, double-sided coating, and the single-sided coating thickness is controlled at 6 μm. The coated PID film is vacuum dried at 60°C for 24 hours to obtain the modified porous organic-inorganic composite skeleton film MLPD.

[0112] (6) Based on the above steps (1)-(5), LiDFOB, LiBOB, LiTFSI, LiFSI and a composite lithium salt (with a molar ratio of LiTFSI:LiFSI=1:1) were dissolved in triethyl phosphate small molecule monomer to form a eutectic solvent with a molar concentration of 1M, and then 2.5 vol% of polyethylene glycol diacrylate monomer was added and stirred for 4 hours to form a mixed solution, and 5 wt% of acylphosphine oxide was added at the same time, and stirred and mixed for 2 hours under light-proof conditions to obtain a polymer precursor solution. Then, the five groups of polymer precursor solutions were subjected to operations (7)-(8) respectively.

[0113] (7) Soaking MLPD in the above polymer precursor solution for 24 hours to fully absorb and infiltrate to obtain a composite film MLPD. It is worth noting that this step is carried out under light-proof conditions.

[0114] (8) Finally, scrape off the excess liquid on the surface of the composite film MLPD with a scraper, and cure it under 1000w ultraviolet light for 20 minutes to obtain a solid electrolyte film HSEF. Among them, LiDFOB (Example 3-1), LiBOB (Example 3-2), LiTFSI (Example 3-3), LIFSI (Example 3-4) and compound lithium salt (Example 3-5); and the XRD characterization diagrams and electron microscope scanning diagrams of the above five groups of solid electrolyte films HSEF are similar to those of Example 1, indicating that the crystallinity of the polymer electrolyte prepared in Example 3 is greatly reduced, which is conducive to the transmission of ions, and has excellent interface contact, which can ensure the transportation of lithium ions between the electrode and the electrolyte.

[0115] 2.1.4 Example 4

[0116] The steps include:

[0117] (1) In a 25 mL three-necked flask equipped with a stirrer, a thermometer, a spherical reflux condenser and a nitrogen protection device, 1.43 g of N-methylpyrrolidone and 7.15 g of dimethylformamide were added, and the mixture was refluxed and stirred at 60° C. for 1 h to form a mixed solution.

[0118] Then, 0.156 g of diphenylamine, 0.476 g of 2,3-pyrazine dianhydride and 0.615 g of 1,4-bis(4-aminophenoxy)benzene were added to the mixed solution in sequence, and stirred and mixed for 2 h at 45° C. in a nitrogen atmosphere to form a uniform mixed solution. It should be noted that the time interval between adding three samples was controlled within 15 minutes.

[0119] (2) The uniform mixed solution is then cooled to room temperature and transferred to a glove box. A portion of the mixed solution is taken out and placed in a test tube. 12.5 wt % of 3,6-bis(bromomethyl)-1,2,4,5-tetrabromobenzene is added. The mixture is stirred for 2 h and uniformly mixed to obtain a precursor liquid solution.

[0120] (3) The obtained solution was applied on glass using a scraper, and the film thickness was 10 μm. After scraping, the film was left on the glass plate for 4 h, then rinsed with a mixture of acetone and alcohol in a volume ratio of 1:1.5 for 20 minutes to generate pores, and then dried at 60°C under vacuum conditions for 24 h to completely evaporate the solvent, thereby obtaining a polyamide nanoporous film PCA.

[0121] (4) The dried polyamide nanoporous film PCA was heated from room temperature to 80°C at a rate of 5°C / min in a box furnace under air atmosphere; from 80°C to 100°C at a rate of 2°C / min; kept at 100°C for 15 minutes and then heated to 200°C at a rate of 4°C / min; kept at 200°C for 20 minutes and then heated to 300°C at a rate of 3°C / min; kept at 300°C for 30 minutes and finally cooled to 25°C to obtain an imidized modified non-flammable porous polyimide film (PID), which was taken out and stored in a glove box for use.

[0122] The pore size of the modified non-combustible porous polyimide film PID is 1 μm, the volume ratio of the porosity is 37%, and the molecular weight is 200000 g / mol.

[0123] (5) The commercial soluble polyimide (molecular weight of 100000) was dissolved in 15mL of dichloromethane to form a 15mol / L uniform solution, marked as A, and the inorganic oxide LLZTO powder was dispersed in dichloromethane to form a 37g / L suspension, marked as B. Liquid A and liquid B were mixed evenly at a volume ratio of 1:1, stirred at room temperature for 4h, and then the mixed solution was ball milled in a ball mill at a speed of 250r / min for 30min to prepare an inorganic oxide precursor solution. The inorganic oxide precursor solution was coated on a modified non-flammable porous polyimide film (PID) with a doctor blade, double-sided coating, and the single-sided coating thickness was controlled to be 10μm. The coated PID film was vacuum dried at 60℃ for 24h to obtain a modified porous organic-inorganic composite skeleton film MLPD.

[0124] (6) The composite lithium salt (with a molar ratio of LiTFSI:LIFSI=1:1.5) was dissolved in the triethyl phosphate small molecule monomer to form a eutectic solvent with a molar concentration of 0.4 M, and then 2.5 vol% of hydroxyethyl acrylate was added and stirred for 4 h to form a mixed solution. At the same time, 5 wt% of acylphosphine oxide was added and stirred for 2 h in a light-proof condition to obtain a polymer precursor liquid.

[0125] (7) Soak the MLPD in the above polymer precursor solution for 24 hours to fully absorb and infiltrate. It is worth noting that this step is carried out under light-proof conditions.

[0126] (8) Finally, the excess liquid on the surface of the composite film MLPD was scraped off with a scraper, and the film was cured under 1000W ultraviolet light for 20 minutes to obtain a solid electrolyte film. However, the conductivity could not be detected because a complete electrolyte film could not be formed. This was because the reaction time of hydroxyethyl acrylate was too long, and the high degree of polymerization caused the polymer to agglomerate, resulting in reduced mechanical properties. When assembling button cells, cracks appeared in the polymer film, resulting in the inability to form a complete electrolyte film.

[0127] 2.1.5 Example 5

[0128] The steps include:

[0129] (1) In a 25 mL three-necked flask equipped with a stirrer, a thermometer, a spherical reflux condenser and a nitrogen protection device, 1.43 g of N-methylpyrrolidone and 6.77 g of dimethylformamide were added, and the mixture was refluxed and stirred at 55° C. for 1 h to form a mixed solution.

[0130] Then, 0.156 g of diphenylamine, 0.476 g of 2,3-pyrazine dianhydride and 0.615 g of 1,4-bis(4-aminophenoxy)benzene were added to the mixed solution in sequence, and stirred and mixed for 2 h at 45° C. in a nitrogen atmosphere to form a uniform mixed solution. It should be noted that the time interval between adding three samples was controlled within 15 minutes.

[0131] (2) The uniform mixed solution is then cooled to room temperature and transferred to a glove box. A portion of the mixed solution is taken out and placed in a test tube. 12.5 wt % of 3,6-bis(bromomethyl)-1,2,4,5-tetrabromobenzene is added. The mixture is stirred for 2 h and uniformly mixed to obtain a precursor liquid solution.

[0132] (3) The obtained solution was applied on glass using a scraper, and the film thickness was 10 μm. After scraping, the film was left on the glass plate for 4 h, then rinsed with a mixture of acetone and alcohol in a volume ratio of 1:1.5 for 20 minutes to generate pores, and then dried at 60°C under vacuum conditions for 24 h to completely evaporate the solvent, thereby obtaining a polyamide nanoporous film PCA.

[0133] (4) The dried polyamide nanoporous film PCA was heated from room temperature to 80°C at a rate of 5°C / min in a box furnace under air atmosphere; from 80°C to 100°C at a rate of 2°C / min; kept at 100°C for 15 minutes and then heated to 200°C at a rate of 4°C / min; kept at 200°C for 20 minutes and then heated to 300°C at a rate of 3°C / min; kept at 300°C for 30 minutes and finally cooled to 25°C to obtain an imidized modified non-flammable porous polyimide film (PID), which was taken out and stored in a glove box for use.

[0134] The pore size of the modified non-combustible porous polyimide film PID is 4 μm, the volume ratio of the porosity is 41%, and the molecular weight is 2,200,000 g / mol.

[0135] (5) The commercial soluble polyimide (molecular weight of 100000) was dissolved in 15 mL of dichloromethane to form a 15 mol / L uniform solution, marked as A, and the inorganic oxide LLZTO powder was dispersed in dichloromethane to form a 37 g / L suspension, marked as B. Liquid A and liquid B were mixed evenly in a volume ratio of 1:1, stirred at room temperature for 4 hours, and then the mixed solution was ball milled in a ball mill at a speed of 250 r / min for 30 minutes to prepare an inorganic oxide precursor solution. The inorganic oxide precursor solution was coated on a modified non-flammable porous polyimide film (PID) with a doctor blade, double-sided coating, and the single-sided coating thickness was controlled to be 5 μm. The coated PID film was vacuum dried at 60°C for 24 hours to obtain a modified porous organic-inorganic composite skeleton film MLPD.

[0136] (6) The composite lithium salt (with a molar ratio of LiTFSI:LIFSI = 1:0.75) was dissolved in the triethyl phosphate small molecule monomer to form a eutectic solvent with a molar concentration of 0.4 M, and then 2.5 vol% of tripropylene glycol diacrylate monomer was added and stirred for 4 hours to form a mixed solution. At the same time, 5 wt% of acylphosphine oxide was added and stirred for 2 hours in a light-proof condition to obtain a polymer precursor liquid.

[0137] (7) Soak the MLPD in the above polymer precursor solution for 24 hours to fully absorb and infiltrate. It is worth noting that this step is carried out under light-proof conditions.

[0138] (8) Finally, the excess liquid on the surface of the composite film MLPD was scraped off with a scraper, and the film was cured under 1000W ultraviolet light for 20 minutes to obtain the final solid electrolyte film. However, the film-forming effect was poor and the conductivity could not be detected. This is because the tripropylene glycol diacrylate monomer cannot be polymerized to form an electrolyte membrane with mechanical strength. After polymerization, it still has a certain fluidity and cannot form a complete composite electrolyte membrane.

[0139] 2.2 Effect Verification

[0140] 2.2.1 Ionic conductivity test

[0141] The test method of solid electrolyte ion conductivity is: the ionic conductivity of solid electrolyte is tested by AC impedance method, and the instrument used is Shanghai Chenhua Instrument Co., Ltd. CHI660E electrochemical workstation. In an argon glove box, button cells are assembled in the order of positive electrode shell, stainless steel gasket, solid electrolyte, stainless steel gasket, spring, and negative electrode shell. The AC impedance test frequency is 100mHz to 1000KHz, the amplitude voltage is 5mV, and the test temperature is room temperature. The ionic conductivity of Examples 1-3 at room temperature is shown in Table 1:

[0142] Table 1 Conductivity of product ions at room temperature

[0143]

[0144] It can be seen from the above table that the solid electrolyte thin films HSEF prepared in Examples 1-3 all have high ionic conductivity at room temperature. The ionic conductivity of the HSEF obtained in Examples 1-3 at different temperatures is tested. The test results of Examples 1, 2, 3-5 are as follows: Figure 3 As shown: As the temperature increases, the ionic conductivity increases gradually.

[0145] 2.2.2LSV curve

[0146] Using Li|solid electrolyte|stainless steel gasket, at a scan rate of 1 mV / s, the electrochemical stability window of the solid electrolyte film HSEF obtained in Examples 1-3 between 3 and 7 V was determined by linear sweep voltammogram (LSV). The test results are shown in Table 2:

[0147] Table 2 Electrochemical stability window of each product

[0148]

[0149]

[0150] Among them, the test results of Examples 1, 2, 3-5 are as follows Figure 4 As shown, Examples 3-5 have better electrochemical stability.

[0151] 2.2.3 Stress-strain test

[0152] The tensile tester was used to obtain a tensile speed of 0.2 cm min -1 The stress-strain curve and tensile strength of the polymer electrolyte at the time of , the mechanical properties of Examples 1-3 were obtained. The test results are shown in Table 3:

[0153] Table 3 Mechanical properties of each product

[0154]

[0155] 2.2.4 Flame retardancy test

[0156] The solid electrolyte film HSEF prepared in Examples 1-3 was subjected to thermogravimetric testing using a SDTQ600 synchronous thermal analyzer. The LOI value of the material was used to indicate the applicability of the HSEF in flame retardant applications, and the Van Krevelen and Hoftyzer equations were used to calculate the LOI values ​​of different HSEFs. The test results are shown in Table 4:

[0157] Table 4 Thermal characteristic parameters of each product

[0158]

[0159] It can be seen from the above table that the solid electrolyte film HSEF prepared in Examples 1-3 has excellent flame retardant properties. The introduction of bromine flame retardant small molecules into polyimide through molecular regulation greatly improves the flame retardant properties of the material, and synthesizes a modified non-flammable porous polyimide film with non-flammability, which solves the defects of traditional polyimide membranes that are extremely easy to burn and prone to safety problems as electrolyte skeletons. Bromide preferentially reacts with free radicals such as oxygen and hydroxyl to form inert substances, thereby effectively reducing the violent decomposition of the organic skeleton.

[0160] 2.3 Preparation of lithium iron phosphate battery

[0161] The HSEF obtained in Examples 3-5 is combined with a positive electrode material to construct a high energy density lithium metal battery, wherein a solid electrolyte membrane HSEF is used instead of a separator, metallic lithium is used as a negative electrode, and lithium iron phosphate is used as a positive electrode to assemble a lithium battery.

[0162] The electrochemical performance was tested and the results were as follows Figure 5 As shown in the figure, after 300 cycles at 30°C and 1C, the discharge capacity is still 127 mAh g -1 , the capacity retention efficiency is greater than 90%.

[0163] The above embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present invention. It should be pointed out that, for those of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention.

Claims

1. A method for preparing a hybrid solid electrolyte film with high efficiency flame retardancy, characterized in that: The following steps are involved: S1, mixing N-methylpyrrolidone and dimethylformamide, then adding diphenylamine, 2,3-pyrazine dianhydride and 1,4-bis(4-aminophenoxy)benzene in sequence to obtain a mixed solution, and then adding a brominated flame retardant small molecule to obtain a precursor liquid solution; S2, coating the precursor liquid solution on a glass sheet, washing it with a mixed solvent after standing, and drying it to obtain a polyamide nanoporous film; S3, performing imidization treatment on the polyamide nanoporous film to obtain a modified non-flammable porous polyimide film; S4, coating the inorganic oxide precursor solution on the surface of the modified non-combustible porous polyimide film, and drying to obtain a modified porous organic-inorganic composite skeleton film; The inorganic oxide precursor solution is obtained by mixing equal volumes of solution A containing soluble polyimide and solution B containing inorganic oxide solid electrolyte and then ball milling; The solution A is a solution formed by dissolving the soluble polyimide in a polar aprotic solvent, and the polar aprotic solvent is dichloromethane; The solution B is a suspension formed by dissolving the inorganic oxide in a polar aprotic solvent, and the inorganic oxide solid electrolyte is LLZTO; S5, immersing the modified porous organic-inorganic composite skeleton film in a polymer precursor liquid, and subjecting the film to ultraviolet curing to obtain the hybrid solid electrolyte film; The polymer precursor liquid is obtained by dissolving lithium salt in small molecules of flame retardant plasticizer to form a eutectic solvent, and then adding unsaturated monomers and initiators to undergo copolymerization reaction; The lithium salt is one or more of LiDFOB, LiBOB, LiTFSI, LiFSI and LiClO4; The flame retardant plasticizer small molecule is one or more of fluoroethylene carbonate, dimethyl phosphate, triethyl phosphate, N-methylacetamide, methyl trifluoroethyl carbonate and 1,1,2,3,3,3-pentafluoropropyl-2,2,2-trifluoroethyl ether; The unsaturated monomer is one or more of polyethylene glycol diacrylate, methyl methacrylate, vinyl acetate, vinylene carbonate, ethyl 2-cyanoacrylate, tripropylene glycol diacrylate, hydroxyethyl acrylate and derivatives thereof; The initiator is an acylphosphine oxide.

2. The method for preparing a hybrid solid electrolyte film according to claim 1, characterized in that: In step S1, the mass ratio of the N-methylpyrrolidone to the dimethylformamide is 1:(3-5); The mass ratio of the diphenylamine to the N-methylpyrrolidone is (0.1-0.12):1; The mass ratio of the diphenylamine, the 2,3-pyrazine dianhydride and the 1,4-bis(4-aminophenoxy)benzene is 1:(3-4):(3-5); The time interval for adding the diphenylamine, the 2,3-pyrazine dianhydride and the 1,4-bis(4-aminophenoxy)benzene is 10 to 25 minutes; Based on the mixed solution, the dosage of the brominated flame retardant small molecules is 10-15 wt %.

3. The method for preparing a hybrid solid electrolyte film according to claim 1, characterized in that: In step S1, the mixing conditions of the N-methylpyrrolidone and the dimethylformamide are: temperature of 55-60° C. and time of 1-2 h; The mixing conditions of the mixed solution are: in an inert atmosphere, the temperature is 45-60° C., and the reaction time is 1-2 hours.

4. The method for preparing a hybrid solid electrolyte film according to claim 1, characterized in that: The brominated flame retardant small molecule is 3,6-bis(bromomethyl)-1,2,4,5-tetrabromobenzene.

5. The method for preparing a hybrid solid electrolyte film according to claim 1, characterized in that: In step S2, the mixed solvent is composed of acetone and alcohol in a volume ratio of 1: (1-10).

6. The method for preparing a hybrid solid electrolyte film according to claim 1, characterized in that: The thickness of the polyamide nanoporous film is 8 to 15 μm.

7. The method for preparing a hybrid solid electrolyte film according to claim 1, characterized in that: In step S3, the heating steps of the imidization treatment are as follows: (1) From room temperature to 80°C, the heating rate is 1-5°C / min; (2) From 80°C to 100°C, the heating rate is 1-5°C / min; (3) Maintain at 100°C for 15 to 20 minutes; (4) From 100°C to 200°C, the heating rate is 1-5°C / min; (5) Maintain at 200°C for 20 to 40 minutes; (6) From 200°C to 300°C, the heating rate is 1-5°C / min; (7) Maintain at 300°C for 1 to 5 minutes; (8) Cool to 25°C.

8. The method for preparing a hybrid solid electrolyte film according to claim 1, characterized in that: In step S4, the thickness of the applied single-sided coating is 2-10 μm.

9. The method for preparing a hybrid solid electrolyte film according to claim 1, characterized in that: In step S5, based on the eutectic solvent, the volume fraction of the unsaturated monomer is 2-3 vol%; the amount of the initiator is 1-10 wt%.

10. The method for preparing a hybrid solid electrolyte film according to claim 1, characterized in that: The lithium salt is a composite lithium salt composed of LiTFSI and LIFSI in a molar ratio of 1:(0.5-2).

11. The method for preparing a hybrid solid electrolyte film according to claim 1, characterized in that: In step S5, the soaking time is 10 to 48 hours; The conditions of the ultraviolet curing are: power 1-1000w, time 20-30min.

12. A hybrid solid electrolyte film obtained by the preparation method according to any one of claims 1 to 11.

13. A lithium metal battery, characterized in that: The invention comprises the following components: a positive electrode, a negative electrode and the hybrid solid electrolyte film according to claim 12.

14. The lithium metal battery according to claim 13, characterized in that: The lithium metal battery is a lithium iron phosphate-lithium metal battery.

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