Asymmetric double-layer flame-retardant solid electrolyte as well as preparation method and application thereof

Abstract

The invention relates to an asymmetric double-layer flame-retardant solid electrolyte as well as a preparation method and application thereof. According to the asymmetric double-layer flame-retardant solid electrolyte as well as the preparation method and the application thereof, the problems that an electrolyte in a liquid lithium ion battery is easy to leak, great potential hazards exist, and the conductivity of a polymer electrolyte membrane is low can be solved. The first layer of the asymmetric double-layer flame-retardant composite solid electrolyte comprises the following main components: a polymer matrix A, a polymer matrix B, zwitterionic liquid SPZ, an inorganic ceramic oxide, a lithium salt, a solvent, a cross-linking agent and a photoinitiator; the first-layer solution and the second-layer solution mainly comprise a polymer base B, zwitterionic liquid SPZ, lithium salt, a solvent, a cross-linking agent and a photoinitiator, the first-layer mixed solution and the second-layer mixed solution are respectively subjected to tape casting onto a polytetrafluoroethylene mold, ultraviolet cross-linking and heating are performed to obtain two-layer ionic liquid composite solid electrolyte, and then the two layers are sequentially stacked together to obtain the composite solid electrolyte. The asymmetric double-layer flame-retardant composite solid electrolyte is obtained.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of composite solid electrolyte materials, in particular to an asymmetric double-layer flame-retardant solid electrolyte and a preparation method and application thereof. BACKGROUND

[0002] The liquid electrolyte used in traditional lithium ion batteries has high flammability and is prone to leakage, and meanwhile, when matched with a high-capacity lithium metal negative electrode, the liquid electrolyte faces technical challenges such as unstable interface and dendrite growth. Moreover, when the liquid electrolyte is in contact with a high-voltage positive electrode (>4.5V vs. Li + / Li), the liquid electrolyte has problems such as oxidative decomposition and intensified interface side reactions, which leads to a decrease in the cycle stability of the battery and seriously restricts the development of a high-energy-density system. The solid electrolyte has the characteristics of non-flammability and can be compatible with a high-voltage positive electrode (>4.5V) and a lithium metal negative electrode at the same time, which can effectively solve the safety and adaptability bottlenecks of the traditional liquid electrolyte and significantly improve the safety performance and energy density of the battery. At present, the solid electrolyte is classified into polymer electrolytes (SPEs), inorganic solid electrolytes (SIEs) and organic-inorganic composite solid electrolytes (CPEs). Among them, the SPEs have excellent electrode interface compatibility, but have the defect of insufficient oxidation resistance; the SIEs exhibit high ionic conductivity, but face the challenge of excessive electrode interface impedance. The CPEs successfully overcome the limitations of single electrolyte systems by combining the advantages of the above two types of electrolytes, and have become one of the key materials in the next generation of solid-state battery systems.

[0003] Although the CPEs have the characteristics of high ionic conductivity, strong interface adaptability and high mechanical performance, the polymer matrix of the CPEs still has the risk of flammability, which limits the safety of the system. In the solid-state battery system, the solid-state electrolyte in contact with the positive electrode side needs to withstand the high-voltage oxidation environment, and on the negative electrode side, it must resist the strong reducing property of lithium metal and effectively inhibit the growth of dendrites. However, the electrochemical stability window of the currently developed CPEs is insufficient, which is difficult to meet the extreme environmental requirements of the high-voltage positive electrode and the lithium metal negative electrode at the same time; and there is still the risk of flammability, which leads to poor cycle performance and safety of the battery. Therefore, in view of the contradictory requirements of the positive and negative electrode interfaces, how to design a flame-retardant CPEs that is compatible with the oxidation resistance of the positive electrode and the reduction resistance of the lithium negative electrode is a difficult problem that needs to be solved in the field. SUMMARY

[0004] In view of the above problems existing in the prior art, the purpose of the present application is to develop an asymmetric double-layer flame-retardant composite solid electrolyte and a preparation method and application thereof. The composite solid electrolyte prepared by the method has an asymmetric structure and a flame-retardant property, and can be applied in high-temperature batteries. The inorganic ceramic layer facing the positive electrode has excellent oxidation resistance and mechanical strength, can prevent electrolyte decomposition and maintain high pressure stability; the polymer layer close to the lithium metal negative electrode closely adheres to the electrode surface by using the flexibility of the molecular chain, and inhibits lithium dendrite penetration through adaptive deformation. The asymmetric double-layer flame-retardant composite solid electrolyte solves the bottleneck problem of the oxidation-reduction property of the positive and negative electrodes, has good flame-retardant properties, and the assembled battery has a high capacity retention rate and a discharge specific capacity after 150 cycles at 60 DEG C. This new electrolyte can not only significantly improve the safety performance of the battery, but also provide strong support for the development of high-energy density, long-life, portable renewable green energy storage devices.

[0005] To achieve the purpose of the present application, the following technical solutions are provided:

[0006] The present application provides a preparation method of an asymmetric double-layer flame-retardant composite solid electrolyte and a preparation method and application thereof, comprising the following steps:

[0007] 1) Mix polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP), polyethylene glycol diacrylate (PEGDA), zwitterionic liquid SPZ, lithium salt, inorganic ceramic oxide, solvent, crosslinking agent and photoinitiator to obtain solution A;

[0008] 2) Mix polyethylene glycol diacrylate (PEGDA), zwitterionic liquid SPZ, lithium salt, solvent, crosslinking agent and photoinitiator to obtain solution B;

[0009] Further, the mixing speed in step 1) 2) is 500-600 r / min, and the mixing time is 5-10 h.

[0010] 3) Drop the obtained solution A into a polytetrafluoroethylene film, and use ultraviolet curing. After the curing is completed, heat for a period of time to completely cure. Then, drop solution B on the composite solid electrolyte film formed by solution A in situ, and cure it in the same way to obtain an asymmetric double-layer flame-retardant composite solid electrolyte.

[0011] Further, the wavelength of ultraviolet curing in step 3) is 330-450 nm, the ultraviolet curing time is 5-30 min, the heating temperature is 40-70 DEG C, and the heating time is 6-9 h.

[0012] Further, in step 1) 2), the mass-volume ratio of vinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) and the solvent is 1 g: 20-50 mL, and the molar ratio of lithium salt to zwitterionic liquid SPZ is 1:1-6;

[0013] The mass of the zwitterionic liquid SPZ is 10-60% of the sum of the masses of polyethylene glycol diacrylate (PEGDA) or vinylidene fluoride-co-hexafluoropropylene (PVDF-HFP), zwitterionic liquid SPZ, lithium salt, solvent, crosslinking agent, and photoinitiator;

[0014] The mass of the crosslinking agent is 1-10% of the sum of the masses of the zwitterionic liquid SPZ and lithium salt, and the mass of the photoinitiator is 0.5-10% of the sum of the masses of the zwitterionic liquid SPZ and lithium salt.

[0015] The inorganic ceramic oxide is alumina, silica, barium titanate, cerium oxide, lithium lanthanum zirconium oxide, lithium lanthanum titanium oxide, lithium lanthanum zirconium oxide doped with tantalum, or lithium titanium aluminum phosphate;

[0016] The lithium salt is one or more of lithium perchlorate, lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium tetrafluoroborate, lithium dihydroxyborate, lithium difluoroxyborate, lithium trifluoromethylsulfonate, and lithium bistrifluoromethylsulfonimide;

[0017] The crosslinking agent is ethoxylated trimethylolpropane triacrylate, N,N-methylenebisacrylamide, or 2-phenoxyethyl acrylate;

[0018] The photoinitiator is 2-hydroxy-2-methylpropiophenone, methyl benzoylformate, or 2,4,6-trimethylbenzoyl-diphenylphosphine oxide;

[0019] The solvent is dimethyl sulfoxide, tetrahydrofuran, N-methylpyrrolidone, N,N-dimethylformamide, or acetonitrile.

[0020] The mixing speed is 500-600 r / min, and the mixing time is 5-10 h.

[0021] Further, in step 1) 2), the preparation method of the zwitterionic liquid SPZ includes the following steps:

[0022] (1) A toluene solution of 1,3-propyl-2-R2 alkylsulton is added dropwise to a tetrahydrofuran solution containing N ring derivative NCC and stirred to obtain a white precipitate;

[0023] (2) The white precipitate is sequentially washed, filtered, and dried to obtain the zwitterionic liquid SPZ;

[0024] The N-containing ring derivative NCC is a 1-R1 alkenyl imidazole ring, a 1-R1 alkenyl 1,2,4-triazole ring, a 1-R1 alkenyl tetrahydropyrrole or a 1-R1 alkenyl morpholine, and the structural formula of the derivative is:

[0025]

[0026] The structural formula of the 1,3-propyl-2-R2 alkyl sultone is:

[0027]

[0028] The structure of the zwitterionic liquid SPZ is:

[0029]

[0030] (3) In the N-containing ring derivative NCC, the derivative is an imidazole derivative, a 1,2,4-triazole ring derivative, a tetrahydropyrrole derivative or a morpholine derivative.

[0031] (4) In the N-containing ring derivative NCC, R1 is a carbon chain with 1-7 carbon atoms, and R2 is a carbon chain or hydrogen; when R2 is a carbon chain, the number of carbon atoms in R2 is 1-10.

[0032] The application provides an asymmetric double-layer flame-retardant composite solid-state electrolyte prepared by the preparation method.

[0033] The application also provides application of the asymmetric double-layer flame-retardant composite solid-state electrolyte in a lithium ion battery.

[0034] The application has the following beneficial effects:

[0035] The application has the advantages that the zwitterionic liquid containing a lithiumophilic group can be used as a polymer matrix of a polymer solid-state electrolyte, which not only strengthens the mechanical strength of the electrolyte, but also is conducive to forming a high-efficiency and stable Li + channel for transporting lithium ions. The inorganic ceramic oxide further improves the ionic conductivity, and the double-layer asymmetric structure ensures that the electrolyte can solve the contradictory requirements of two poles, that is, the positive pole requires resistance to oxidation, and the negative pole requires resistance to reduction, and the double-layer structure exactly meets this condition, so that the asymmetric double-layer flame-retardant composite solid-state electrolyte has good high-voltage resistance and also has relatively high ionic conductivity at room temperature. The ion liquid double-layer polymer composite solid-state electrolyte prepared by the application has excellent ion transmission capacity, and the ionic conductivity thereof can reach 6.69×10 -3 S / cm at 30 DEG C, and also has a relatively wide electrochemical stability window. The assembled Li|asymmetric double-layer flame-retardant composite solid-state electrolyte|NCM811 lithium battery can still provide excellent cycle performance at a high temperature of 60 DEG C, can have excellent interface compatibility with lithium metal, and can also have excellent cycle stability in a room temperature environment or an extremely high-temperature environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a cycling performance diagram of a Li|asymmetric double-layer flame-retardant composite solid electrolyte|LFP battery assembled with the asymmetric double-layer flame-retardant composite solid electrolyte prepared in Example 1 at 25°C and 1C;

[0037] Figure 2 This is a cycling performance diagram of a Li|asymmetric double-layer flame-retardant composite solid electrolyte|LFP battery assembled with the asymmetric double-layer flame-retardant composite solid electrolyte prepared in Example 1 at 60°C and 0.5C;

[0038] Figure 3 This is the electrochemical window diagram of the asymmetric double-layer flame-retardant composite solid electrolyte prepared in Example 1;

[0039] Figure 4 This is a scatter plot of the dependence of the electrical conductivity of the asymmetric double-layer flame-retardant composite solid electrolyte prepared in Example 1 on temperature. DETAILED DESCRIPTION

[0040] The present invention provides a method for preparing a zwitterionic liquid double-layer polymer composite solid electrolyte, comprising the following steps:

[0041] 1) mixing poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), zwitterionic liquid SPZ, lithium salt, non-electrode ceramic oxide, solvent, cross-linking agent and photoinitiator to obtain solution A;

[0042] 2) mixing polyethylene glycol diacrylate (PEGDA), zwitterionic liquid SPZ, lithium salt, solvent, crosslinker, and photoinitiator to obtain solution B;

[0043] 3) The resulting solution A is added dropwise to a polytetrafluoroethylene mold and cured using ultraviolet light. After curing, it is heated for a period of time to completely cure. Solution B is then added dropwise in situ onto the composite solid electrolyte membrane formed by solution A and cured in the same manner to obtain an asymmetric double-layer flame-retardant composite solid electrolyte.

[0044] In the present invention, in steps 1) and 2), the mass volume ratio of vinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) to the solvent is 1g:10-50ml, preferably 1g:20-40ml, more preferably 1g:30ml, the mass volume ratio of polyethylene oxide to the solvent is 1g:20-100ml, preferably 1g:30-80ml, more preferably 1g:50ml, and the molar ratio of lithium salt to ionic liquid A is 1:1-6, preferably 1:2-4, more preferably 1:3;

[0045] In the present application, the mass of the zwitterionic liquid SPZ in step 1) is 10-60%, preferably 20-50%, further preferably 20-30% of the sum of the mass of vinylidene fluoride-co-hexafluoropropylene (PVDF-HFP), the zwitterionic liquid SPZ, the lithium salt, the solvent, the crosslinking agent and the photoinitiator;

[0046] In the present application, the mass of the zwitterionic liquid SPZ in step 2) is 10-60%, preferably 20-50%, further preferably 30-40% of the sum of the mass of polyethylene glycol diacrylate (PEGDA), the zwitterionic liquid SPZ, the lithium salt, the solvent, the crosslinking agent and the photoinitiator;

[0047] The mass of the crosslinking agent is 1-10%, preferably 3-7%, further preferably 5% of the sum of the mass of the zwitterionic liquid SPZ and the lithium salt, and the mass of the photoinitiator is 0.5-10%, preferably 1-6%, further preferably 4% of the sum of the mass of the zwitterionic liquid SPZ and the lithium salt.

[0048] In the present application, the solvent in step 1) is dimethyl sulfoxide, tetrahydrofuran, N-methyl pyrrolidone, N,N-dimethylformamide or acetonitrile, preferably N-methyl pyrrolidone.

[0049] In the present application, the solvent in step 2) is dimethyl sulfoxide, tetrahydrofuran, N-methyl pyrrolidone, N,N-dimethylformamide or acetonitrile, preferably acetonitrile.

[0050] The inorganic ceramic oxide is alumina, silica, barium titanate, ceria, lithium lanthanum zirconium oxide, lithium lanthanum titanium oxide, tantalum-doped lithium lanthanum zirconium oxide or titanium aluminum lithium phosphate, preferably one of lithium lanthanum zirconium oxide, lithium lanthanum titanium oxide, tantalum-doped lithium lanthanum zirconium oxide and titanium aluminum lithium phosphate, further preferably titanium aluminum lithium phosphate;

[0051] In the present application, the lithium salt is one or more of lithium perchlorate, lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium tetrafluoroborate, lithium bisoxalate borate, lithium difluorooxalate borate, lithium trifluoromethylsulfonate and lithium bistrifluoromethylsulfonimide, preferably one or more of lithium perchlorate, lithium hexafluorophosphate, lithium hexafluoroarsenate and lithium tetrafluoroborate, further preferably lithium tetrafluoroborate;

[0052] The crosslinking agent is ethoxylated trimethylolpropane triacrylate, N,N-methylenebisacrylamide or 2-phenoxyethyl acrylate, preferably ethoxylated trimethylolpropane triacrylate;

[0053] The photoinitiator is 2-hydroxy-2-methylpropiophenone, methyl benzoylformate or 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, preferably 2-hydroxy-2-methylpropiophenone;

[0054] In the present application, the rotation speed of the mixing in step 3) is 500-600 r / min, preferably 550 r / min, and the mixing time is 5-10 h, preferably 5 h.

[0055] In the present application, in step 3), the wavelength of the ultraviolet curing is 330-450 nm, preferably 340-370 nm, further preferably 365 nm, the ultraviolet curing time is 5-30 min, preferably 10 min, the heating temperature is 40-70℃, preferably 45℃, and the heating time is 6-9 h, preferably 6.5 h.

[0056] In the present application, solution A and solution B are drop-casted onto a polytetrafluoroethylene mold in an in-situ polymerization manner, and are irradiated to form a film by ultraviolet curing to form an asymmetric double-layer flame-retardant composite solid-state electrolyte.

[0057] In the present application, the drop-casting drop-adding rate is 0.1-1 drop / s, preferably 0.7 drop / s.

[0058] In the present application, the thickness of each film is 100-400 μm, preferably 150-300 μm, further preferably 200 μm.

[0059] The present application provides an asymmetric double-layer flame-retardant composite solid-state electrolyte prepared by the preparation method.

[0060] The present application also provides application of the asymmetric double-layer flame-retardant composite solid-state electrolyte in lithium ion batteries.

[0061] The technical solutions provided by the present application will be described in detail below in combination with examples, but they should not be understood as limiting the scope of protection of the present application.

[0062] Example 1

[0063] 8 g of 1-vinylimidazole was dissolved in 37 mL of acetonitrile, and stirred at a speed of 550 r / min for 40 min to obtain a 1-vinylimidazole acetonitrile solution; 12 g of 1,3-propyl-2-R2 alkyl sultone (R2 is a carbon chain with 5 carbon atoms) was dissolved in 7 mL of toluene, and stirred at a speed of 550 r / min for 30 min to obtain a 1,3-propyl-2-R2 alkyl sultone toluene solution; the 1,3-propyl-2-R2 alkyl sultone toluene solution was added dropwise to the 1-vinylimidazole acetonitrile solution at a speed of 0.5 drops / s under ice-bath conditions and stirring at a speed of 550 r / min, and after the dropwise addition was completed, stirring was continued at 60°C and a speed of 550 r / min for 3 h to produce a white precipitate; after natural cooling to room temperature, the white precipitate was filtered 6 times, washed with ether 6 times, and then dried in a vacuum drying oven at 60°C and a vacuum degree of 1 bar for 18 h to obtain the zwitterionic liquid SPZ;

[0064] 0.05 g of lithium aluminum titanium phosphate and 0.2 g of vinylidene fluoride-co-hexafluoropropylene (PVDF-HFP), 0.4 g of zwitterionic liquid SPZ, 0.4 g of lithium bis-trifluoromethylsulfonylimide, and 2 mL of N-methylpyrrolidone were mixed, and the obtained mixture was mixed with 0.02 g of ethoxylated trimethylolpropane triacrylate and 0.02 g of methyl benzoylformate under light shielding at a speed of 550 r / min for 5 h to obtain solution A; solution A (200 μL was removed) was drop-casted on the surface of a polytetrafluoroethylene film at a rate of 0.8 drops / 10 s, and a UV curing lamp (wavelength: 365 nm) was used for irradiation for 10 min to form a film, and then the film was baked on a hot plate at 43°C for 5 h to sufficiently volatilize the solvent, thereby obtaining a layer of composite solid electrolyte with a film thickness of 230 μm.

[0065] 0.1 g of polyethylene glycol diacrylate (PEGDA) was placed in a vacuum drying oven with a vacuum degree of 1 bar, and dried at 60°C for 12 h, and then mixed with 0.5 g of zwitterionic liquid SPZ, 0.5 g of lithium bis-trifluoromethylsulfonylimide, and 3 mL of N-methylpyrrolidone, and the obtained mixture was mixed with 0.02 g of ethoxylated trimethylolpropane triacrylate and 0.02 g of methyl benzoylformate under light shielding at a speed of 550 r / min for 10 min to obtain solution B; solution B (200 μL was removed) was drop-casted on the layer of composite solid electrolyte at a rate of 1 drop / 10 s, and a UV curing lamp (wavelength: 365 nm) was used for irradiation for 8 min to form a film, and then the film was baked on a hot plate at 40°C for 5 h to sufficiently volatilize the solvent, thereby obtaining an asymmetric double-layer flame-retardant composite solid electrolyte with a film thickness of 410 μm.

[0066] Example 2

[0067] A solution A was prepared by mixing 0.08 g of lithium lanthanum titanium oxide with 0.15 g of vinylidene fluoride-co-hexafluoropropylene (PVDF-HFP), 0.35 g of zwitterionic liquid SPZ, 0.35 g of lithium difluoro(oxalato)borate, and 1.8 mL of acetonitrile, and then mixing the resulting mixture with 0.015 g of N,N-methylenebisacrylamide and 0.015 g of methyl benzoylformate or 2,4,6-trimethylbenzoyl-diphenylphosphine oxide at a rotation speed of 600 r / min in the dark for 4 h. The solution A (200 μL removed) was drop-cast on the surface of a polytetrafluoroethylene film at a rate of 1 drop per 10 s, and a film was formed by irradiation with a UV curing lamp (wavelength of 365 nm) for 12 min, followed by baking on a hot plate at 43 °C for 6 h. After the solvent was sufficiently volatilized, a one-layer composite solid-state electrolyte with a thickness of 236 μm was obtained.

[0068] A solution B was prepared by drying 0.15 g of polyethylene glycol diacrylate (PEGDA) in a vacuum drying oven at a vacuum degree of 1 bar for 18 h at 60 °C, and then mixing the dried PEGDA with 0.35 g of zwitterionic liquid SPZ, 0.35 g of lithium perchlorate, and 3 mL of N-methylpyrrolidone, and then ultrasonically stirring the mixture at a frequency of 30 kHz for 3.5 h. The resulting mixture was mixed with 0.015 g of ethoxylated trimethylolpropane triacrylate and 0.015 g of 2-hydroxy-2-methylpropiophenone at a rotation speed of 570 r / min in the dark for 10 min. The solution B (200 μL removed) was drop-cast on a one-layer composite solid-state electrolyte at a rate of 0.8 drop per 10 s, and a film was formed by irradiation with a UV curing lamp (wavelength of 365 nm) for 10 min, followed by baking on a hot plate at 42 °C for 5 h. After the solvent was sufficiently volatilized, an asymmetric double-layer flame-retardant composite solid-state electrolyte with a thickness of 513 μm was obtained.

[0069] Example 3

[0070] A solution Q was prepared by mixing 0.1 g of tantalum-doped lithium lanthanum zirconium oxide with 0.25 g of vinylidene fluoride-co-hexafluoropropylene (PVDF-HFP), 0.47 g of zwitterionic liquid SPZ, 0.47 g of lithium trifluoromethylsulfonylimide, and 2.6 mL of lithium trifluoromethylsulfonylimide, and then mixing the resulting mixture with 0.023 g of 2-phenoxyethyl acrylate and 0.023 g of 2-phenoxyethyl acrylate at a rotation speed of 580 r / min in the dark for 5.5 h. The solution A (200 μL removed) was drop-cast on the surface of a polytetrafluoroethylene film at a rate of 1.2 drop per 10 s, and a film was formed by irradiation with a UV curing lamp (wavelength of 365 nm) for 10 min, followed by baking on a hot plate at 45 °C for 5 h. After the solvent was sufficiently volatilized, a one-layer composite solid-state electrolyte with a thickness of 217 μm was obtained.

[0071] 0.2 g of polyethylene glycol diacrylate (PEGDA) was placed in a vacuum drying oven with a vacuum degree of 1 bar, dried at 60 DEG C for 15 h, mixed with 0.47 g of zwitterionic liquid SPZ, 0.47 g of lithium hexafluoroarsenate and 3.8 mL of N,N-dimethylformamide, ultrasonic stirring at a frequency of 30 kHz for 3.5 h, the obtained mixed solution was mixed with 0.23 g of 2-phenoxyethyl acrylate and 0.023 g of 2-hydroxy-2-methylpropiophenone at a rotation speed of 580 r / min for 15 min in the dark to obtain solution B; solution B (200 μL was removed) was drop-casted on the surface of a layer of composite solid electrolyte at a rate of 1.2 drops per 10 s, irradiated for 10 min to form a film using a UV curing lamp (wavelength 365 nm), and then baked on a hot plate at 45 DEG C for 5 h to fully volatilize the solvent to obtain an asymmetric double-layer flame-retardant composite solid electrolyte with a film thickness of 407 μm

[0072] As can be seen from the above examples, the present application provides an asymmetric double-layer flame-retardant composite solid electrolyte and a preparation method and application thereof. Figure 1 When the asymmetric double-layer flame-retardant composite solid electrolyte prepared in Example 1 is applied to a lithium battery, the cycle performance diagram of the Li|asymmetric double-layer flame-retardant composite solid electrolyte|LFP battery obtained by assembly at 25 DEG C and 0.2 C is as follows: Figure 1 As can be seen from the above examples, the present application provides an asymmetric double-layer flame-retardant composite solid electrolyte and a preparation method and application thereof. Figure 2 When the asymmetric double-layer flame-retardant composite solid electrolyte prepared in Example 1 is applied to a lithium battery, the cycle performance diagram of the Li|asymmetric double-layer flame-retardant composite solid electrolyte|LFP battery obtained by assembly at 60 DEG C and 0.5 C is as follows: Figure 2 As can be seen from the above examples, the present application provides an asymmetric double-layer flame-retardant composite solid electrolyte and a preparation method and application thereof. Figure 3 The electrochemical window diagram of the asymmetric double-layer flame-retardant composite solid electrolyte prepared in Example 1. Figure 4 The dependence relationship scatter diagram of the conductivity and temperature of the asymmetric double-layer flame-retardant composite solid electrolyte prepared in Example 1. As can be seen from the above examples, the present application provides an asymmetric double-layer flame-retardant composite solid electrolyte and a preparation method and application thereof. -3 The electrochemical window of the asymmetric double-layer flame-retardant composite solid electrolyte prepared by the method is 5.4 V, the ionic conductivity at 30 DEG C is 6.69 x 10

[0073] While embodiments of the application have been shown and described, it is to be understood that the embodiments described are merely exemplary of the principles and application of the present application. Numerous modifications and adaptions can be effected without departing from the spirit and scope of the present application, which is not limited to the exact construction and arrangement described. It is intended, therefore, to cover all modifications and adaptions that fall within the scope of the claims and their equivalents.

Claims

1. An asymmetric double-layer flame-retardant solid electrolyte and its preparation method and application, characterized by: It includes an anti-oxidation layer A close to the positive electrode side and a reduction-resistant layer B close to the lithium metal negative electrode side; The anti-oxidation layer A and the reduction-resistant layer B are formed into an asymmetric double-layer flame-retardant composite solid electrolyte through layer-by-layer in-situ polymerization.

2. The asymmetric double-layer flame-retardant solid electrolyte and its preparation method and application according to claim 1, characterized in that: The antioxidant layer A comprises vinylidene fluoride-co-hexafluoropropylene (PVDF-HFP), zwitterionic liquid SPZ, lithium salt, inorganic ceramic oxide, solvent, crosslinker, and photoinitiator. The reduction-resistant layer B comprises polyethylene glycol diacrylate (PEGDA), zwitterionic liquid SPZ, lithium salt, inorganic ceramic oxide, solvent, crosslinker, and photoinitiator.

3. An asymmetric double-layer flame-retardant composite solid electrolyte according to claims 1 and 2, characterized in that: The average molecular weight of the vinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) is 45,500.

4. The asymmetric double-layer flame-retardant composite solid electrolyte according to claim 1 or 2, characterized in that: The average molecular weight of the poly(ethylene glycol) diacrylate (PEGDA) is 600.

5. The method for preparing an asymmetric double-layer flame-retardant composite solid electrolyte according to claim 1 or 2, characterized in that: The preparation method of the zwitterionic liquid SPZ comprises the following steps: (1) A toluene solution of 1,3-propyl-2-R2 alkyl sultone was added dropwise to a tetrahydrofuran solution containing an N-ring derivative NCC and stirred to obtain a white precipitate; (2) washing, filtering, and drying the white precipitate in sequence to obtain the zwitterionic liquid SPZ; The N-ring derivative NCC is 1-R1 alkenyl imidazole, 1-R1 alkenyl 1,2,4-triazole ring, 1-R1 alkenyl tetrahydropyrrole or 1-R1 alkenyl morpholine, and the structural formula of the derivative is: The structural formula of 1,3-propyl-2-R2 alkyl sultone is: The structure of the zwitterionic liquid SPZ is: (3) In item 2, the N-ring-containing derivative NCC is an imidazole derivative, a 1,2,4-triazole ring derivative, a tetrahydropyrrole derivative or a morpholine derivative. (4) In 2, R1 is a carbon chain having 1 to 7 carbon atoms, and R2 is a carbon chain or hydrogen; when R2 is a carbon chain, the number of carbon atoms in R2 is 1 to 10.

6. The method for preparing an asymmetric double-layer flame-retardant composite solid electrolyte according to claim 1, characterized in that: The lithium salt is one or more of lithium perchlorate, lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium tetrafluoroborate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium trifluoromethanesulfonate and lithium bis(trifluoromethanesulfonyl imide); The inorganic ceramic oxide is aluminum oxide, silicon dioxide, barium titanate, cerium oxide, lithium lanthanum zirconium oxide, lithium lanthanum titanium oxide, tantalum-doped lithium lanthanum zirconium oxide or lithium aluminum titanium phosphate; The solvent is acetonitrile, N-methylpyrrolidone, tetrahydrofuran, N,N-dimethylformamide or dimethyl sulfoxide. The cross-linking agent is ethoxylated trimethylolpropane triacrylate, N,N-methylenebisacrylamide or 2-phenoxyethyl acrylate; The photoinitiator is 2-hydroxy-2-methylpropiophenone, methyl benzoylformate or 2,4,6-trimethylbenzoyl-diphenylphosphine oxide.

7. The asymmetric double-layer flame-retardant composite solid electrolyte according to any one of claims 1 to 6, characterized in that: The following steps are involved: 1) mixing vinylidene fluoride-co-hexafluoropropylene (PVDF-HFP), zwitterionic liquid SPZ, lithium salt, inorganic ceramic oxide, solvent, crosslinking agent and photoinitiator, and stirring to obtain solution A; 2) Polyethylene glycol diacrylate (PEGDA), zwitterionic liquid SPZ, lithium salt, solvent, crosslinking agent and photoinitiator are mixed and stirred to obtain solution B.

8. The asymmetric double-layer flame-retardant composite solid electrolyte according to claim 6, characterized in that: The following steps are involved: 1) The mixing speed is 500-600 r / min, and the mixing time is 5-10 h. 2) The resulting solution A is added dropwise to a polytetrafluoroethylene mold and cured using ultraviolet light. After curing, it is heated for a period of time to completely cure. Solution B is then added dropwise in situ onto the composite solid electrolyte membrane formed by solution A and cured in the same manner to obtain an asymmetric double-layer flame-retardant composite solid electrolyte.

9. The method for preparing an asymmetric double-layer flame-retardant composite solid electrolyte according to claim 8, characterized in that: In step 2), the wavelength of the UV curing is 330-450 nm, the UV curing time is 5-30 min, the heating temperature is 40-70° C., and the heating time is 6-9 h.

10. The method for preparing an asymmetric double-layer flame-retardant composite solid electrolyte according to claim 7 or 8, characterized in that: In steps 1) and 2), the mass volume ratio of vinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) to the solvent is 1 g:10-50 ml, the mass volume ratio of polyethylene glycol diacrylate (PEGDA) to the solvent is 1 g:20-100 ml, and the molar ratio of the lithium salt to the zwitterionic liquid SPZ is 1:1-6.

11. The method for preparing an asymmetric double-layer flame-retardant composite solid electrolyte according to claim 7 or 8, characterized in that: In steps 1) and 2), the mass of the zwitterionic liquid SPZ is 10 to 60% of the sum of the mass of polyethylene glycol diacrylate (PEGDA) or vinylidene fluoride-co-hexafluoropropylene (PVDF-HFP), the zwitterionic liquid SPZ, the lithium salt, the non-polar ceramic oxide, the solvent, the crosslinker and the photoinitiator.

12. The method for preparing an asymmetric double-layer flame-retardant composite solid electrolyte according to claim 7 or 8, characterized in that: In steps 1) and 2), the mass of the crosslinking agent is 1-10% of the sum of the mass of the zwitterionic liquid SPZ and the lithium salt, and the mass of the photoinitiator is 0.5-10% of the sum of the mass of the zwitterionic liquid SPZ and the lithium salt.

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