Solid-state battery and composite electrolyte, preparation and application thereof

Abstract

The invention belongs to the field of solid-state batteries, and particularly relates to a solid-state battery and a composite electrolyte, preparation and application thereof, and the preparation method of the composite electrolyte comprises the following steps: dissolving a base membrane polymer with a solvent A to obtain a base membrane solution, and forming the base membrane solution into a wet membrane; pre-forming the wet film in an environment with the humidity of 50-80% RH in advance; soaking the wet film in a solvent B, and forming the wet film into a base film; and compounding the base membrane and a precursor solution for forming the electrolyte, and then carrying out in-situ polymerization to prepare the composite electrolyte, wherein the base membrane polymer comprises at least one of polyether sulfone, sulfonated polyether sulfone and polyetherimide; the solvent B is a mixed solvent of water and C1-C4 alcohol, and the volume ratio of the water to the C1-C4 alcohol is 1: (0.1-10); the precursor solution is a solution containing a monomer, a plasticizer and electrolytic salt. The method provided by the invention can be used for preparing the solid electrolyte with a special structure and excellent performance such as fast charge stability.

Description

Technical Field

[0001] The present invention belongs to the field of battery materials, and particularly relates to the technical field of solid electrolytes. Background Art

[0002] With the rapid development of electronic products, electric vehicles, and intelligent energy storage systems, higher requirements are put forward for energy storage devices with high energy density, high safety, and long life. Traditional liquid lithium-ion batteries have certain risks of thermal runaway and explosion due to the flammability and leakage of their electrolytes, which limits their application in high-safety scenarios. To solve this problem, solid-state batteries, as a new generation of energy storage technology, have gradually become a research hotspot. Solid-state batteries use solid electrolytes to replace liquid electrolytes, which can not only significantly improve the thermal stability and safety of the batteries, but also have a wider working voltage window, which is beneficial to matching high-capacity electrode materials, thereby improving the overall energy density of the batteries. Among many solid electrolyte systems, polymer electrolytes are considered to be an ideal choice for realizing the practical application of solid-state batteries due to their good flexibility, easy processing, and excellent interfacial contact properties. However, pure polymer electrolyte systems still face challenges such as low ionic conductivity, insufficient mechanical strength, and poor interfacial stability, which limit their practical application in high-performance solid-state batteries.

[0003] Adding a base film to the polymer system is a common method to improve the comprehensive performance of polymer electrolytes. For example, the patent document with the publication number CN119725984A discloses a solid electrolyte separator with high ionic conductivity, its preparation method and application, specifically recording a scheme of electrospinning and curing a polyimide precursor to obtain a polyimide base film, and then carrying out polymerization to obtain a solid electrolyte separator.

[0004] The patent document with the publication number CN119560628A discloses an asymmetric solid electrolyte membrane that conducts ions / conducts ions and electrons, its preparation method, and a solid-state lithium metal battery. The asymmetric solid electrolyte membrane disclosed therein includes an electrolyte that conducts ions on the positive electrode side and an electrolyte that conducts ions and electrons while adding an electron-conducting material on the negative electrode side.

[0005] The patent document with the publication number CN118486884A discloses a solid electrolyte membrane, its preparation method, and a secondary battery. Among them, the solid electrolyte membrane includes a base film, a ceramic electrolyte layer on one side of the base film, and a polymer electrolyte layer on the other side of the base film.

[0006] The patent document with the publication number CN118398874A discloses a composite solid electrolyte membrane, a preparation method, and a secondary battery. The composite solid electrolyte membrane includes a halide electrolyte base film and a first electrolyte formed by in-situ reaction on the halide electrolyte base film.

[0007] In summary, the prior art has disclosed some base film-based composite solid electrolyte materials, but the ion and electron conduction capabilities and cyclic interface stability of the existing methods need to be further improved. Summary of the Invention

[0008] Aiming at the problems existing in the existing polymer solid electrolytes, the first object of the present invention is to provide a preparation method of a composite electrolyte, aiming to prepare a composite electrolyte with a special physical and chemical structure and excellent ion and electron conduction capabilities and interface stability.

[0009] The second object of the present invention is to provide the composite electrolyte prepared by the above preparation method and its application in the preparation of solid-state batteries.

[0010] The third object of the present invention is to provide a solid-state battery comprising the composite electrolyte.

[0011] A preparation method of a composite electrolyte, dissolving a base film polymer with solvent A to obtain a base film solution, forming a wet film from the base film solution; pre-forming the wet film at a humidity of 50-80% RH in advance; then soaking it in solvent B to form the wet film into a base film; then compounding the base film with a precursor solution for forming an electrolyte and performing in-situ polymerization to polymerize an electrolyte on the base film to obtain the composite electrolyte;

[0012] Wherein, the base film polymer includes at least one of polyethersulfone, sulfonated polyethersulfone, and polyetherimide; solvent A includes at least one of dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, γ-butyrolactone, dimethylformamide, and tetrahydrofuran;

[0013] The solvent B is a mixed solvent of water and C1-C4 alcohol, wherein the volume ratio of water to C1-C4 alcohol is 1:0.1-10;

[0014] The precursor solution is a solution containing monomers, plasticizers, and electrolytic salts.

[0015] The present invention pre-performs dry pre-forming on the wet film and then performs wet forming. On this basis, further combined with special control of the base film polymer composition, the humidity of pre-forming, and solvent B during the forming process, a base film with a dense surface or sponge structure and asymmetric vertical pores in the bulk phase can be constructed. Further compounding an electrolyte on this base film can achieve synergy, strengthen the ion and electron conduction capabilities, improve the interface stability, mechanical properties, and thermal stability of the material, and effectively improve the electrochemical performance of the solid-state battery, especially excellent fast charging stability can be exhibited under a thin electrolyte film.

[0016] In the present invention, the type of the base film polymer is controlled, in combination with the combined control of the preforming - forming conditions, so as to achieve synergy, which is beneficial to constructing a base film with special asymmetric pores in the bulk phase and a dense surface, thus being beneficial to improving the fast - charging stability of the subsequent obtained composite electrolyte. Preferably, the base film polymer is polyethersulfone. Research shows that the preferred base film polymer and the process of the present invention have better adaptability, which helps to further construct the base film structure and further enhance the fast - charging stability of the prepared solid electrolyte.

[0017] In the present invention, there is no special requirement for the concentration of the base film polymer in the base film solution. For example, it can be 0.05 - 0.5 g / mL, and considering the preparation efficiency, it can further be 0.1 - 0.2 g / mL.

[0018] In the present invention, a regulator is further added to the base film solution, and the regulator includes at least one of polyethylene glycol, polyvinyl alcohol, lithium chloride, calcium chloride, polyvinylpyrrolidone, and glycerol. Research of the present invention shows that, under the combination of the preforming - forming process and parameters, further combined with the use of the regulator, it helps to further synergistically optimize the physical and chemical structure of the base film, helps to further enhance the ionic and electronic conduction capabilities of the prepared composite electrolyte, and helps to further enhance the interfacial stability.

[0019] In the present invention, in the base film solution, the regulator is 1 - 20% by weight of the base film polymer, and further can be 5 - 15%.

[0020] In the present invention, the film - forming methods include coating, spraying, doctor - blading, or printing.

[0021] For example, the base film solution can be formed into a film on a substrate (such as on glass) to form the wet film.

[0022] In the present invention, the wet film can be pre - exposed to an atmosphere such as air and preformed at the humidity.

[0023] In the present invention, innovatively, preforming is carried out under high - humidity conditions in advance, which is beneficial to constructing a sponge - like or dense surface, is beneficial to combining with the subsequent forming, and further improves the fast - charging stability of the prepared solid electrolyte.

[0024] Preferably, the humidity during the preforming process is 55 - 65%RH; further is 58 - 62%RH.

[0025] In the present invention, the preforming temperature during the preforming process is 20 - 35 °C, and further can be 20 - 25 °C.

[0026] In the present invention, the preforming time is 15 - 30 s; further is 15 - 25 s.

[0027] In the present invention, under the preferred preforming conditions, it is helpful for further combination with the process and further improves the performance of the prepared solid electrolyte.

[0028] In the present invention, under the high-humidity preforming treatment, it is further combined with the subsequent phase separation forming treatment of the alcohol-water solvent, which is beneficial for synergy to construct a special asymmetric vertical pore-based membrane and is beneficial for the fast charging stability of the prepared solid electrolyte.

[0029] In the solvent B, the C1-C4 alcohol includes at least one of methanol and ethanol.

[0030] The research of the present invention shows that the forming process includes a first forming process under solvent B1 and a second forming process under solvent B2;

[0031] Among them, solvent B1 is a solvent B with a volume ratio of water to alcohol of 1-5:6-10; solvent B2 is a solvent B with a volume ratio of water to alcohol of 5-10:1-3. The research of the present invention shows that based on the special two-stage forming treatment and the special control of the solvent components for the two-stage forming, the special control of the base membrane can be further strengthened, which is helpful for further constructing the asymmetric vertical pore structure required for fast charging and is helpful for further improving the fast charging stability of the prepared solid electrolyte.

[0032] Furthermore, the volume ratio of water to alcohol in solvent B1 is 3-4:6-7. The volume ratio of water to alcohol in solvent B2 is 8-10:1-2.

[0033] In the present invention, under the combined control of the preforming, humidity and temperature, it is further combined with the subsequent combined segmented wet forming process and parameters, so that based on the gradient difference, an asymmetric vertical pore physical and chemical characteristic can be constructed in the base membrane body. The asymmetric vertical pores refer to those with smaller surface pores and larger pores near the substrate side.

[0034] In the present invention, the temperature of the forming process can be 5-35 °C, and further can be 20-30 °C.

[0035] In the present invention, the time of the forming process is 1-25 min. For example, when a two-stage forming process is selected, the time of the first forming process can be 0.1-1 min, and further can be 15-30 s; the second forming time can be 1-20 min, and further can be 15-20 min.

[0036] In the present invention, the process of compounding the electrolyte on the base membrane can be conventional. For example, the precursor solution and the base membrane are compounded by means of coating, spraying, doctor blading or printing. Subsequently, the polymerization of the precursor solution can be realized based on conventional principles and methods.

[0037] For example, in the precursor solution, the monomers include one or more of methoxypolyethylene glycol acrylate, polyethylene glycol diacrylate, polymethyl methacrylate, polyethylene oxide, polyethylene glycol, poly(vinylidene fluoride - co - hexafluoropropylene), polyvinylidene fluoride, polyacrylonitrile, and triethylene glycol dimethacrylate.

[0038] The plasticizer includes one or more of fluoroethylene carbonate, 1,3 - dioxolane, ethylene glycol dimethyl ether, ethylene carbonate, diethyl carbonate, dimethyl carbonate, propylene carbonate, ethyl methyl carbonate, trifluoroacetate, dimethoxyethane, triethylene glycol dimethyl ether, and dimethyl sulfoxide.

[0039] The electrolyte salt is selected from one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium difluoro(oxalato)phosphate, lithium difluorophosphate, sodium bis(trifluoromethanesulfonyl)imide, sodium hexafluorophosphate, sodium perchlorate, sodium tetrafluoroborate, sodium bis(oxalato)borate, sodium difluoro(oxalato)phosphate, sodium difluorophosphate, potassium bis(fluorosulfonyl)imide, potassium fluoroborate, potassium hexafluorophosphate, and potassium perchlorate.

[0040] Among them, in the precursor solution, the content of the monomer is 0.1 - 50 wt.%, and the content of the plasticizer is 1 - 60 wt.%. Further, in the precursor solution, the content of the monomer is 20 - 30 wt.%, and the content of the plasticizer is 40 - 50 wt.%. The electrolyte salt concentration is 0.1 - 5 mol / L, and further can be 0.5 - 1.5 mol / L.

[0041] In the present invention, the precursor solution further contains at least one of a multi - arm cross - linker and an initiator;

[0042] Among them, the multi - arm cross - linker is selected from one or more of ethoxylated glycerol triacrylate, ethoxylated bisphenol A diacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, ethoxylated pentaerythritol tetraacrylate, pentaerythritol tetraacrylate, pentaerythritol glycidyl ether, trimethylolpropane triglycidyl ether, glycerol diglycidyl ether, 1,4 - butanediol diglycidyl ether, and polyethylene glycol diacrylate;

[0043] The initiator can be classified into at least one of a photo - initiator and a thermal initiator according to the initiation conditions, and for example, can be selected from one or more of 2 - hydroxy - 2 - methyl - 1 - phenyl - 1 - propanone, phenylbis(2,4,6 - trimethylbenzoyl)phosphine oxide, azobisisobutyronitrile, 2,2 - dimethoxy - 2 - phenylacetophenone, 1 - hydroxycyclohexyl phenyl ketone, and benzoyl peroxide;

[0044] In the precursor solution described above, the content of the multi-arm crosslinking agent in the precursor solution is 10 wt.% or less, and the content of the initiator is 5 wt.% or less. Further, the content of the multi-arm crosslinking agent in the precursor solution is 1-5 wt.%, and the content of the initiator is 0.1-0.5 wt.%.

[0045] In the present invention, the precursor solution can be compounded on the base film based on conventional processes such as coating and printing.

[0046] In the present invention, the precursor solution can be cured and crosslinked based on a conventional ultraviolet curing process to form a solid electrolyte.

[0047] In the present invention, the wavelength of the ultraviolet light irradiation is 254-365 nm, and the irradiation time is 0.1-100 min.

[0048] The present invention also provides a composite electrolyte prepared by the preparation method described above.

[0049] The preparation method described in the present invention can endow the prepared material with special physical and chemical characteristics, and can exhibit excellent solid-state battery performance based on these special physical and chemical characteristics. For example, the composite electrolyte described in the present invention includes a base film having asymmetric vertical pores and an electrolyte compounded on the base film. The thickness of the composite electrolyte can be 10-150 μm, wherein the thickness of the base film can be 3-100 μm.

[0050] The present invention also provides an application of the composite electrolyte prepared by the preparation method described above, which is used to prepare a solid-state battery.

[0051] Based on known principles and methods, the present invention can prepare a required solid-state battery from the composite electrolyte described in the present invention. The solid-state battery can be a solid-state lithium battery, a solid-state sodium battery, etc.

[0052] The present invention also provides a solid-state battery, which includes a positive electrode, a solid electrolyte, and a negative electrode that are sequentially compounded, and the solid electrolyte is the composite electrolyte prepared by the preparation method described above.

[0053] For the solid-state battery described in the present invention, except for the composite electrolyte described in the present invention, other components and structural relationships can be well-known.

[0054] The solid-state battery is a full-solid-state or semi-solid-state battery.

[0055] Beneficial effects

[0056] In the present invention, the wet film is preformed by a dry method in advance and then formed by a wet method. On this basis, further combined with the special control of the type of base film polymer, the humidity of preforming, and the solvent during the forming process, a base film with a dense surface or sponge structure and asymmetric vertical pores in the bulk phase can be constructed. Its asymmetric structure is manifested as a top dense layer + a bottom vertical channel layer. The bottom vertical channel layer can guide lithium ions to preferentially migrate along a specific direction, reduce the ion transmembrane migration energy barrier, provide a fast transmission channel, and at the same time has a certain flexibility compared with the dense layer, which can buffer the interfacial stress and adapt to expansion and contraction; the top dense layer has high strength, can resist the growth of lithium dendrites, prevent short circuits, and thus improve the interfacial stability. Based on the porous base film and the adapted polymer system, the effective thickness of the polymer system electrolyte membrane can be significantly reduced, the energy density of the battery can be increased, and the conductivity and ion mobility of the composite solid electrolyte can be synergistically improved.

[0057] In the present invention, by adopting the two-stage forming treatment and combining the joint control of two-stage solvents, further synergy can be realized, which helps to further enhance the fast charging stability of the prepared solid electrolyte. Description of the Drawings

[0058] Figure 1 Optical photograph of the base film obtained in Step 1 of Example 1.

[0059] Figure 2 SEM of the base film obtained in Step 1 of Example 1.

[0060] Figure 3 Impedance diagram of the composite electrolyte membrane obtained in Step 2 of Example 1.

[0061] Figure 4 Linear sweep voltammogram of the composite electrolyte membrane obtained in Step 2 of Example 1.

[0062] Figure 5 Lithium ion transference number results of the composite electrolyte membrane obtained in Step 2 of Example 1, namely the potentiostatic current-time curve and the impedance change before and after.

[0063] Figure 6 Schematic diagram of the long cycle of the Li||LiCoO2 full battery of the composite electrolyte membrane obtained in Step 2 of Example 1 at room temperature and 2 C rate. Detailed Description of the Invention

[0064] The following examples are intended to further illustrate the content of the present invention in detail, rather than limiting the scope of protection of the claims of the present invention.

[0065] In the present invention, an application of the composite electrolyte is provided, which is used as a barrier layer for preparing solid or semi-solid secondary batteries;

[0066] Further, it is disposed between the positive electrode and the negative electrode;

[0067] Further, it is compounded on the positive electrode to form a composite positive electrode, and / or it is compounded on the negative electrode to form a composite negative electrode;

[0068] Further, the solid-state or semi-solid-state secondary battery is a lithium-ion battery and / or a sodium-ion battery.

[0069] The present invention also provides a solid-state or semi-solid-state secondary battery as described above, which contains the composite electrolyte or is prepared by the composite electrolyte.

[0070] For the solid-state or semi-solid-state secondary battery of the present invention, except for containing the composite solid electrolyte of the present invention, other components and structures can be known.

[0071] In the present invention, the application of the asymmetric vertical pore channel-based membrane composite solid electrolyte prepared by any one of the preparation methods described above in a lithium metal, sodium metal or potassium metal battery.

[0072] In the following examples, the selected negative electrode is lithium metal, and the specific performance test method includes the following steps:

[0073] (1) Impedance test: In the glove box, the prepared composite solid electrolyte membrane is sandwiched between two steel sheets to assemble a CR2025 type coin cell. The battery is tested by the alternating current impedance technology (EIS) in a Gamry electrochemical workstation.

[0074] (2) Electrochemical stability window test: In the glove box, the prepared composite solid electrolyte membrane is sandwiched between a steel sheet and a commercial lithium sheet to assemble a CR2025 type coin cell. The battery is tested by linear sweep voltammetry (LSV) in a Gamry electrochemical workstation.

[0075] (3) Ion transference number test: In the glove box, the prepared composite solid electrolyte membrane is sandwiched between two commercial lithium sheets to assemble a CR2025 type coin cell. The battery is tested by the alternating current impedance technology (EIS) and direct current polarization (potentiostatic) in a Gamry electrochemical workstation to obtain the change of the constant potential current and the change of the impedance before and after of the battery.

[0076] (4) LiCoO2 battery (Li||LiCoO2 full cell):

[0077] In a glove box, the prepared composite solid electrolyte membrane was sandwiched between a lithium sheet (d = 15.4 mm) and a LiCoO₂ cathode to assemble a CR2025 coin cell. The charge-discharge performance of the battery was tested by a LAND battery test system. The charge-discharge rate was 2C (activated for 5 cycles at 0.2, 0.5, and 1 C initially), and the test voltage range of the LiCoO₂ battery was 3 - 4.3 V; subsequently, it was cycled 400 times at 2 C and 25 °C.

[0078] In the present invention, the ion transference number refers to the ion transference number in a lithium-ion battery.

[0079] In the present invention, the film-forming substrate can be an existing commercial polymer, and its molecular weight can be 20,000 - 80,000; as an alternative, the Mn of polyethersulfone is approximately 60,000. The Mn of sulfonated polyethersulfone is approximately 50,000; the Mn of polyetherimide is approximately 28,000.

[0080] Example 1

[0081] A composite electrolyte based on an asymmetric vertical pore base membrane, with a film-forming substrate of polyethersulfone, a solvent of dimethylacetamide, a regulator of polyvinylpyrrolidone, a polymer monomer of methoxypolyethylene glycol acrylate, a lithium salt of lithium bis(trifluoromethanesulfonyl)imide, a plasticizer of fluoroethylene carbonate, a crosslinking agent of trimethylolpropane triacrylate, and a photoinitiator of 2-hydroxy-2-methyl-1-phenyl-1-propanone.

[0082] Step 1: Preparation of the base membrane:

[0083] (1.1) Take 0.5 g of polyethersulfone and 0.05 g of polyvinylpyrrolidone and dissolve them in 3 ml of dimethylacetamide, stir at 60 °C for 6 h;

[0084] (1.2) Preforming:

[0085] The film-forming solution was blade-coated onto a glass plate with a 50 μm blade, and then preformed in an air atmosphere with a humidity of 60%RH and a temperature of 25 °C (the preforming time was 20 s);

[0086] (1.3) Forming:

[0087] Then it was first immersed in solvent B1 (solvent B1 is a mixture of water and ethanol with a volume ratio of 3:7) for 15 s for the first step of forming; then immersed in solvent B2 (a mixture of water and ethanol with a volume ratio of 10:1) for 20 min for the second step of forming;

[0088] (1.4) Dry at 50 °C for 24 h to obtain the base membrane (also called an asymmetric vertical pore base membrane with a thickness of 20 μm).

[0089] Step 2: The preparation method of the composite solid electrolyte includes the following steps:

[0090] (2.1) Precursor solution: A solution containing polymer monomers (methoxypolyethylene glycol acrylate, the dosage in this case can be 0.5 g), lithium salt (lithium bis(trifluoromethanesulfonyl)imide), plasticizer (fluoroethylene carbonate), crosslinking agent (trimethylolpropane triacrylate), and photoinitiator (2-hydroxy-2-methyl-1-phenyl-1-propanone). Among them, in the precursor solution, the content of polymer monomers is 27.1 wt.%, the content of plasticizer is 43.4 wt.%, the content of crosslinking agent is 2.7 wt.%, and the content of photoinitiator is 0.3 wt.%; the balance is lithium salt.

[0091] (2.2) Scraping and coating the precursor solution on one side of the asymmetric vertical pore base membrane, and transferring it to a 365 nm ultraviolet lamp for ultraviolet photopolymerization for 3 min to obtain the composite electrolyte membrane (total thickness of 26 μm).

[0092] The room temperature ionic conductivity of the composite solid electrolyte (M-CPE) prepared in Example 1 is 2.8×10 -4 Scm -1 , the electrochemical window is 4.86 V, the transference number is 0.24, and the assembled LiCoO2 battery can be stably cycled 400 times at a high rate of 2 C, with a capacity retention rate of 90%.

[0093] Example 2

[0094] Compared with Example 1, the difference is only that the composition of the film-forming substrate is changed, and other operations and parameters are the same as those in Example 1. The experimental results are as follows:

[0095] Group A: The film-forming substrate is sulfonated polyethersulfone. Other operations and parameters are the same as those in Example 1. The results are as follows: the ionic conductivity is 2.5×10 -4 S cm -1 , the electrochemical window is 4.76 V, the transference number is 0.19, and the assembled LiCoO2 battery is cycled 400 times at 2 C, with a capacity retention rate of 74%.

[0096] Group B: The film-forming substrate is polyetherimide. Other operations and parameters are the same as those in Example 1. The results are as follows: the ionic conductivity is 2.3×10 -4 S cm -1 , the electrochemical window is 4.80 V, the transference number is 0.20, and the assembled LiCoO2 battery is cycled 400 times at 2 C, with a capacity retention rate of 72%.

[0097] As can be seen from Examples 1 and 2, when sulfonated polyethersulfone, polyetherimide, and polyethersulfone are used as the base film polymers, especially when polyethersulfone is used as the base film polymer, the process of the present invention can be adapted to obtain better fast charging stability.

[0098] Example 3

[0099] Compared with Example 1, the only difference is that the preforming conditions in Step 1.2 are changed. The experimental groups are as follows:

[0100] Group A: The humidity of preforming is 65%RH;

[0101] Group B: The humidity of preforming is 55%RH;

[0102] Group C: The temperature of preforming is 30 °C and the time of preforming is 10 s;

[0103] Other operations, parameters, and tests are the same as those in Example 1. The results are as follows:

[0104] Group A: The ionic conductivity is 2.5×10 -4 S cm -1 , the electrochemical window is 4.87 V, the transference number is 0.23. The assembled LiCoO2 battery is cycled 400 times at 2 C, and the capacity retention rate is 91%;

[0105] Group B: The ionic conductivity is 3.0×10 -4 S cm -1 , the electrochemical window is 4.78 V, the transference number is 0.20. The assembled LiCoO2 battery is cycled 400 times at 2 C, and the capacity retention rate is 86%;

[0106] Group C: The ionic conductivity is 2.1×10 -4 S cm -1 , the electrochemical window is 4.75 V, the transference number is 0.21. The assembled LiCoO2 battery is cycled 400 times at 2 C, and the capacity retention rate is 88%.

[0107] Example 4

[0108] Compared with Example 1, the only difference is that the forming conditions in Step 1.3 are changed. The experimental groups are as follows:

[0109] Group A: The preformed film is only formed in Solvent B1 in the first stage, and the time of the first stage forming is 20 min + 15 s; other operations and parameters are the same as those in Example 1;

[0110] Group B: The preformed film is not subjected to the first-stage forming and directly continues the second-stage forming in solvent B2, and the time for the second-stage forming is 20 min + 15 s; other operations and parameters are the same as in Example 1;

[0111] Group C: Two-stage forming process, wherein solvent B1 is a water-ethanol mixture with a volume ratio of 4:6, and the time for the first-stage forming is 30 s; solvent B2 is a water-ethanol mixture with a volume ratio of 8:2, and the time for the second-stage forming is 15 min; other operations and parameters are the same as in Example 1.

[0112] The results are as follows:

[0113] Group A: The ionic conductivity is 2.1×10 -4 S cm -1 , the electrochemical window is 4.67 V, the transference number is 0.21, the assembled LiCoO2 battery is cycled 400 times at 2 C, and the capacity retention rate is 81%;

[0114] Group B: The ionic conductivity is 2.3×10 -4 S cm -1 , the electrochemical window is 4.58 V, the transference number is 0.21, the assembled LiCoO2 battery is cycled 400 times at 2 C, and the capacity retention rate is 76%;

[0115] Group C: The ionic conductivity is 2.6×10 -4 S cm -1 , the electrochemical window is 4.79 V, the transference number is 0.23, the assembled LiCoO2 battery is cycled 400 times at 2 C, and the capacity retention rate is 89%.

[0116] It can be seen from Examples 1 and 4 that using the forming alcohol-water combined process described in the present invention for forming treatment is beneficial to the fast charging stability of the solid electrolyte.

[0117] Example 5

[0118] Compared with Example 1, the difference is only that the composition of the precursor solution in Step 2 is changed, specifically:

[0119] In the precursor solution, the polymer monomer is triethylene glycol dimethacrylate (the content in the precursor solution is 25 wt.%), the lithium salt is lithium hexafluorophosphate, the plasticizer is ethylene glycol dimethyl ether (the content in the precursor solution is 50 wt.%), the crosslinking agent is trimethylolpropane triacrylate (the content in the precursor solution is 2 wt.%), the photoinitiator is phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (the content in the precursor solution is 0.2 wt.%), and the balance is lithium salt. The time for photocuring is 2 min.

[0120] All other operations, parameters, and tests are the same as in Example 1.

[0121] The room-temperature ionic conductivity of the composite solid electrolyte (M-CPE) prepared in Example 5 is 2.6×10 -4 Scm -1 , the electrochemical window is 4.82 V, the transference number is 0.23, and the assembled LiCoO2 battery can be stably cycled 400 times at a high rate of 2 C, with a capacity retention rate of 87%.

[0122] Comparative Example 1

[0123] Compared with Example 1, the only difference is that the film-forming substrate is polysulfone. All other operations and parameters are the same as in Example 1, and the results are as follows: the ionic conductivity is 1.1×10 -4 S cm -1 , the electrochemical window is 4.77 V, the transference number is 0.20, and the assembled LiCoO2 battery is cycled 400 times at 2 C, with a capacity retention rate of 51%.

[0124] Comparative Example 2

[0125] Compared with Example 1, the only difference is that the preforming conditions in Step 1.2 are changed. The experimental groups are as follows:

[0126] Control Group A: The humidity for preforming is 20%RH;

[0127] Control Group B: The humidity for preforming is 40%RH;

[0128] The results are as follows:

[0129] Control Group A: The ionic conductivity is 9.8×10 -5 S cm -1 , the electrochemical window is 4.59 V, the transference number is 0.20, and the assembled LiCoO2 battery is cycled 400 times at 2 C, with a capacity retention rate of 55%;

[0130] Control Group B: The ionic conductivity is 6.3×10 -5 S cm -1 , the electrochemical window is 4.55 V, the transference number is 0.18, and the assembled LiCoO2 battery is cycled 400 times at 2 C, with a capacity retention rate of 67%.

[0131] Comparative Example 3

[0132] Compared with Example 1, the only difference is that in Step 1.3, both Solvent B1 and Solvent B2 are water, and all other operations and parameters are the same as in Example 1.

[0133] The result is: the ionic conductivity is 1.1×10 -4 S cm-1 The electrochemical window is 4.64 V and the transference number is 0.16. The assembled LiCoO2 battery is cycled 400 times at 2 C, and the capacity retention rate is 57%.

[0134] Comparative Example 4

[0135] Compared with Example 1, the difference is only that in Step 1.3, both Solvent B1 and Solvent B2 are ethanol, and other operations and parameters are the same as those in Example 1.

[0136] The result is: the ionic conductivity is 2.2×10 -5 S cm -1 , the electrochemical window is 4.76 V and the transference number is 0.21. The assembled LiCoO2 battery is cycled 400 times at 2 C, and the capacity retention rate is 71%.

[0137] It can be seen from Example 1 and Comparative Examples 1 to 4 that the wet film is preformed by dry method first, and then formed by wet method. On this basis, further combined with the special control of the type of base film polymer, the humidity of preforming, and the solvent during the forming process, a base film with a dense surface or sponge structure and asymmetric vertical pores in the bulk phase can be constructed, which is beneficial to improving the performance of the solid electrolyte such as fast charging stability.

[0138] In addition, it can be seen from Example 1 and Example 4 that by adopting the two-stage forming treatment and combining the joint control of the two-stage solvents, synergism can be further achieved, which is helpful to further strengthen the fast charging stability of the prepared solid electrolyte.

Claims

1. A method for preparing a composite electrolyte, characterized in that, Dissolve the base film polymer in solvent A to obtain a base film solution, and form a wet film by forming the base film solution into a film; pre-form the wet film at a humidity of 50-80% RH; then soak it in solvent B to form the wet film into a base film; then composite the base film with the precursor solution for forming an electrolyte and carry out in-situ polymerization to polymerize and form an electrolyte on the base film, thereby obtaining the composite electrolyte described; Among them, the base film polymer includes at least one of polyethersulfone, sulfonated polyethersulfone, and polyetherimide; solvent A includes at least one of dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, γ-butyrolactone, dimethylformamide, and tetrahydrofuran; The solvent B is a mixed solvent of water and C1-C4 alcohol, wherein the volume ratio of water to C1-C4 alcohol is 1:0.1-10; The precursor solution is a solution containing monomers, plasticizers, and electrolyte salts.

2. The preparation method of the composite electrolyte according to claim 1, characterized in that, The concentration of the base film polymer in the base film solution is 0.05-0.5 g / mL; The base film solution is further added with a regulator, and the regulator includes at least one of polyethylene glycol, polyvinyl alcohol, lithium chloride, calcium chloride, polyvinylpyrrolidone, and glycerol; In the base film solution, the regulator is 1-20% by weight of the base film polymer.

3. The preparation method of the composite electrolyte according to claim 1, characterized in that, The film-forming methods include coating, spraying, knife coating, or printing; The pre-forming temperature is 20-35 °C; The pre-forming time is 15-30 s.

4. The preparation method of the composite electrolyte according to claim 1, characterized in that, In the solvent B, the C1-C4 alcohol includes at least one of methanol and ethanol.

5. The preparation method of the composite electrolyte according to claim 1 or 4, characterized in that, The forming process includes a first-stage forming process under solvent B1 and a second-stage forming process under solvent B2; Among them, solvent B1 is a solvent B with a volume ratio of water to alcohol of 1-5:6-10; solvent B2 is a solvent B with a volume ratio of water to alcohol of 5-10:1-3.

6. The preparation method of the composite electrolyte according to claim 1, characterized in that, In the precursor solution, the monomers include one or more of methoxypolyethylene glycol acrylate, polyethylene glycol diacrylate, polymethyl methacrylate, polyethylene oxide, polyethylene glycol, poly(vinylidene fluoride-co-hexafluoropropylene), polyvinylidene fluoride, polyacrylonitrile, and triethylene glycol dimethacrylate; The plasticizers include one or more of fluorinated ethylene carbonate, 1,3-dioxolane, ethylene glycol dimethyl ether, ethylene carbonate, diethyl carbonate, dimethyl carbonate, propylene carbonate, methyl ethyl carbonate, trifluoroacetate, dimethoxyethane, triethylene glycol dimethyl ether, and dimethyl sulfoxide; The electrolyte salts are selected from one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium difluoro(oxalato)phosphate, lithium difluorophosphate, sodium bis(trifluoromethanesulfonyl)imide, sodium hexafluorophosphate, sodium perchlorate, sodium tetrafluoroborate, sodium bis(oxalato)borate, sodium difluoro(oxalato)phosphate, sodium difluorophosphate, potassium bis(fluorosulfonyl)imide, potassium fluoroborate, potassium hexafluorophosphate, and potassium perchlorate; Among them, in the precursor solution, the content of the monomers is 0.1-50 wt.%, the content of the plasticizers is 1-60 wt.%, and the electrolyte salt concentration is 0.1-5 mol / L.

7. The preparation method of the composite electrolyte according to claim 1 or 6, characterized in that, The precursor solution further contains at least one of multi-arm crosslinking agents and initiators; Among them, the multi-arm crosslinking agent is selected from one or more of ethoxylated glycerol triacrylate, ethoxylated bisphenol A diacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, ethoxylated pentaerythritol tetraacrylate, pentaerythritol tetraacrylate, pentaerythritol glycidyl ether, trimethylolpropane triglycidyl ether, glycerol diglycidyl ether, 1,4-butanediol diglycidyl ether, and polyethylene glycol diacrylate; The initiator is selected from one or more of 2-hydroxy-2-methyl-1-phenyl-1-propanone, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, azobisisobutyronitrile, 2,2-dimethoxy-2-phenylethanone, 1-hydroxycyclohexyl phenyl ketone, and benzoyl peroxide; In the precursor solution, the content of the multi-arm crosslinking agent in the precursor solution is 10 wt.% or less, and the initiator content is 5 wt.% or less.

8. A composite electrolyte prepared by the preparation method according to any one of claims 1 to 7.

9. Use of a composite electrolyte prepared by the preparation method according to any one of claims 1 to 7, characterized in that, It is used to prepare a solid-state battery.

10. A solid-state battery, comprising a positive electrode, a solid electrolyte, and a negative electrode that are sequentially compounded, characterized in that, The solid electrolyte is the composite electrolyte prepared by the preparation method according to any one of claims 1 to 7.

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