Solid-state composite electrolyte for lithium battery, preparation method of solid-state composite electrolyte and lithium battery

Abstract

The invention belongs to the technical field of solid-state electrolytes, and particularly relates to a solid-state composite electrolyte for a lithium battery, a preparation method of the solid-state composite electrolyte and the lithium battery. The solid-state composite electrolyte takes a polymer containing lithium salt as a matrix, and is divided into a positive electrode side functional layer, a negative electrode side functional layer and 0-3 transition layers along the thickness direction of the solid-state composite electrolyte, the transition layers do not exist or are positioned between the positive electrode side functional layer and the negative electrode side functional layer, modified MXene microspheres are dispersed in the positive electrode side functional layer, and the modified MXene microspheres are dispersed in the negative electrode side functional layer. MXene microspheres are dispersed in the negative electrode side functional layer, and secondary modified MXene microspheres are dispersed in the transition layer. The solid-state composite electrolyte provided by the invention has a relatively high lithium ion transference number on the positive electrode side, so that lithium ion concentration polarization on the positive electrode side can be effectively relieved; the solid-state composite electrolyte has a certain electron conductivity on the negative electrode side and can guide lithium to be uniformly deposited, and experiments prove that the lithium metal battery using the solid-state composite electrolyte has long cycle stability and rate capability.

Description

Technical Field

[0001] This invention belongs to the field of solid electrolyte technology, specifically relating to solid composite electrolytes for lithium batteries, their preparation methods, and lithium batteries. Background Technology

[0002] Lithium metal, due to its extremely high theoretical specific capacity and low electrochemical potential, is considered a promising anode material for next-generation high-energy-density batteries. However, lithium metal anodes face severe challenges in practical applications. During charge-discharge cycles, the uneven deposition and stripping of lithium ions on the anode surface can easily lead to the uncontrolled growth of lithium dendrites. Lithium dendrites can puncture the electrolyte / separator, creating an internal short-circuit risk and potentially inducing thermal runaway and other safety hazards.

[0003] Solid electrolytes, especially solid polymer electrolytes, are considered a viable alternative to traditional liquid electrolytes and a way to improve safety due to their excellent flexibility, ease of processing, and good interfacial contact potential with electrodes. However, traditional solid polymer electrolytes generally suffer from two main bottlenecks: low ionic conductivity at normal operating temperatures and low lithium-ion transference number. A low lithium-ion transference number means that under electrochemical polarization, the migration of anions will create a severe concentration gradient near the electrode, thereby introducing a strong local electric field. This is precisely one of the key factors that induces and accelerates lithium dendrite nucleation and growth.

[0004] To improve the overall performance of solid electrolytes, the art often employs a strategy of introducing inorganic active fillers into a polymer matrix to prepare composite solid electrolytes. In recent years, two-dimensional nanomaterials such as MXene have attracted widespread attention as an emerging functional filler due to their excellent conductivity, good lithiophilicity, and unique two-dimensional layered structure. Introducing MXene into polymer electrolytes allows for the use of its lithiophilic surface to regulate interfacial lithium-ion flow and guide uniform lithium deposition. For example, Chinese patent CN 110739489 B discloses an MXene-doped polymer solid electrolyte film.

[0005] However, this strategy of introducing highly conductive fillers such as MXene inherently presents a technical contradiction. On the one hand, the electronic conductivity of the filler helps reduce the charge transfer resistance at the negative electrode / electrolyte interface, promoting rapid lithium-ion reaction; but on the other hand, if the conductive filler forms a through-type conductive network in the electrolyte matrix, it will lead to electron leakage inside the electrolyte, continuously consuming active lithium and reducing the battery's coulombic efficiency and cycle life. Therefore, an ideal solid-state electrolyte needs to simultaneously meet two seemingly conflicting requirements: in the interface region near the negative electrode, a certain level of micro-area electronic conductivity is needed to promote rapid charge transfer; while in the bulk of the electrolyte and the region near the positive electrode, the lithium-ion transference number needs to be increased to alleviate concentration polarization and maintain strict overall electronic insulation.

[0006] Most existing technologies aim to prepare homogeneous composite electrolytes by optimizing the type and amount of fillers or by performing uniform surface modification, attempting to find a balance between ionic conductivity, electronic insulation, and mechanical strength. However, this homogenized design struggles to address the varying electrolyte property requirements of different regions within the battery, often resulting in performance improvements at the expense of other properties. Therefore, how to construct a functional gradient within a single electrolyte membrane through structural design to synergistically optimize interfacial charge transfer, bulk ion transport, and dendrite suppression capabilities remains a pressing and challenging technical problem in the field of high-performance solid-state electrolytes. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a solid electrolyte that can synergistically optimize the interface charge transfer efficiency and bulk ion transport performance, and effectively suppress lithium dendrite growth, and to provide its preparation method and lithium battery.

[0008] To solve the above problems, the technical solution adopted by the present invention is as follows: Technical Topic 1 A solid composite electrolyte for lithium batteries, the key feature of which is that the solid composite electrolyte uses a lithium salt-containing polymer as a matrix, and is divided into a positive electrode side functional layer and a negative electrode side functional layer along the thickness direction of the solid composite electrolyte, and there are 0 to 3 transition layers between the positive electrode side functional layer and the negative electrode side functional layer along the thickness direction of the solid composite electrolyte. Modified MXene microspheres are dispersed in the functional layer on the positive electrode side, and MXene microspheres are dispersed in the functional layer on the negative electrode side; secondary modified MXene microspheres are dispersed in the transition layer. The MXene microspheres are composite microspheres with MXene nanosheets coated on their surface; The modified MXene microspheres and the secondary modified MXene microspheres are obtained by treating MXene microspheres with a surface modifier containing an ortho-biphenol groups, and then mixing and reacting them with a fixed anion precursor to introduce fixed anion sites on their surface. The mass ratio of modified MXene microspheres, lithium salt, and polymer matrix in the positive electrode side functional layer is 3~12 : 15~35 : 100; The mass ratio of MXene microspheres, lithium salt, and polymer matrix in the negative electrode side functional layer is 0.5~10 : 12~30 : 100; The mass ratio of secondary modified MXene microspheres, lithium salt, and polymer matrix in the transition layer is 1~10 : 12~35 : 100.

[0009] As a further improvement of the present invention, when the transition layer is absent, the thickness ratio of the positive electrode side functional layer to the negative electrode side functional layer is 4~10 : 1.

[0010] As a further improvement of the present invention, when the transition layer is 1-3 layers, the thickness ratio between the positive electrode side functional layer, each transition layer, and the negative electrode side functional layer is 4~10 : (1~4) / n : 1, where n=1, 2 or 3, and the thickness of each transition layer in the same composite electrolyte is equal.

[0011] As a further improvement of the present invention, the lithium salt is selected from one or more of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium 2-trifluoromethyl-4,5-dicyanoimidazolium (LiTDI), lithium tetrafluoroborate (LiBF4), lithium difluorooxalate borate (LiDFOB), or lithium borate oxalate (LiBOB).

[0012] As a further improvement of the present invention, the polymer matrix is ​​selected from one or more polymers containing ether oxygen groups, nitrile groups, fluorine atoms or carboxylic acid ester groups; As a further improvement of the present invention, the polymer matrix is ​​one or more of polyethylene oxide (PEO), polyacrylonitrile (PAN), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polymethyl methacrylate (PMMA), and nitrile rubber (NBR).

[0013] As a further improvement of the present invention, the MXene is selected from one or more of transition metal carbides, transition metal nitrides, and transition metal carbonitride ultrathin two-dimensional nanosheets. The microspheres are selected from one or more of polystyrene microspheres, polyvinyl chloride microspheres, silica microspheres, and titanium dioxide microspheres.

[0014] As a further improvement of the present invention, the MXene microspheres are silica microspheres coated with MXene nanosheets.

[0015] As a further improvement of the present invention, the MXene is Ti3C2T x .

[0016] As a further improvement of the present invention, the particle size of the microspheres is 300~1000nm.

[0017] As a further improvement of the present invention, the particle size of the microspheres is preferably 400 nm.

[0018] As a further improvement of the present invention, the method for preparing the MXene microspheres is as follows: Step 1: Disperse the microspheres in water to prepare a solution with a concentration of 1 mg / mL. –1The suspension was prepared by adding polydimethyldiallyl ammonium chloride to the suspension at room temperature, controlling the final concentration of polydimethyldiallyl ammonium chloride to be 0.2 mg / mL. –1 The mixture was magnetically stirred at 500 rpm for 2 hours and then centrifuged at 9000 rpm for 10 minutes to collect the product, resulting in positively charged microspheres. Step 2: Redisperse the microspheres obtained in Step 1 in water to prepare a solution with a concentration of 1 mg / mL. –1 The suspension was ultrasonically dispersed for 10 min, and then a 5 mg / mL solution was added dropwise to the suspension under magnetic stirring at 500 rpm. –1 The volume ratio of MXene nanosheet suspension to microsphere suspension was 40:1. After the addition was complete, the mixture was stirred for 30 min. The product was collected by centrifugation at 6000 rpm for 10 min and then freeze-dried in a freeze dryer for 36 h to obtain MXene microspheres.

[0019] As a further improvement of the present invention, the modified MXene microspheres are obtained by treating MXene microspheres with a surface modifier containing an ortho-biphenol group and mixing them with a fixed anion precursor, thereby introducing fixed anion sites on its surface. The fixed anion sites exist in the form of lithium salts. As a further improvement of the present invention, the surface modifier containing ortho-diphenol groups is selected from one or more of dopamine, catechol, protocatechuic acid, 3,4-dihydroxyphenylacetic acid, gallic acid, or polymers / monomers containing ortho-diphenol groups.

[0020] The fixed anionic precursor is selected from one or more of 2-mercaptoethanesulfonic acid (or its salt), 3-mercaptopropanesulfonic acid (or its salt), mercaptoethylphosphonic acid (or its salt), mercaptophosphonic acid compounds, mercaptoacetic acid, mercaptopropionic acid, and mercapto derivatives of the taurine skeleton.

[0021] As a further improvement of the present invention, the preparation method of the modified MXene microspheres is as follows: Step 1: Disperse MXene microspheres in Tris buffer at pH 8.5 to prepare a solution with a concentration of 1 mg / mL. –1 The suspension was prepared by adding a surface modifier containing an ortho-bisphenol group to the suspension, controlling the final concentration of the surface modifier to be 5 mg / mL. –1 The mixture was stirred at 500 rpm for 12 h at room temperature and then centrifuged to obtain the microsphere intermediate. Step 2: Disperse the microsphere intermediate in water to prepare a concentration of 0.5 mg / mL. –1 The suspension was prepared by adding a fixed anion precursor to the suspension, and controlling the concentration of the fixed anion precursor to be 1 mg / mL. –1A protective gas was introduced and the mixture was stirred at 500 rpm for 24 h at 50 °C. After the reaction was completed, the product was collected by centrifugation. Then, the product was added to a 0.1 M lithium hydroxide solution and stirred for 30 min. The product was collected by centrifugation, washed with deionized water, and freeze-dried in a freeze dryer to obtain modified MXene microspheres.

[0022] As a further improvement of the present invention, the preparation method of the secondary modified MXene microspheres is the same as that of the modified MXene microspheres, except that the final concentration of the surface modifier containing the ortho-bisphenol group is added to the suspension, the stirring time is 500 rpm at room temperature, the final concentration of the fixed anionic precursor is added to the suspension, and argon protective gas is introduced and the stirring time is 500 rpm at 50°C. The preparation method also satisfies conditions I-III. I. In the preparation conditions of the secondary modified MXene microspheres, the final concentration of the surface modifier containing o-diphenol groups added to the suspension and the stirring time at 500 rpm at room temperature are both lower than those in step 1 of the preparation of the modified MXene microspheres. II. In the preparation conditions of the secondary modified MXene microspheres, the final concentration of the fixed anionic precursor added to the suspension and the introduction of argon protective gas and the stirring time at 500 rpm at 50°C are both lower than those in step 2 of the preparation of the modified MXene microspheres. III. Along the thickness direction of the composite electrolyte, from the positive electrode side functional layer through each transition layer to the negative electrode side functional layer, the final concentration of the surface modifier containing o-bisphenol group added to the suspension, the stirring time at 500 rpm at room temperature, the final concentration of the fixed anion precursor added to the suspension, and the introduction of argon protective gas and stirring time at 500 rpm at 50°C are progressively decreased layer by layer in the preparation of secondary modified MXene microspheres.

[0023] When a transition layer is set, the final concentration of the ortho-bisphenol surface modifier, the stirring time at 500 rpm at room temperature, the final concentration of the fixed anionic precursor, and the introduction of argon protective gas and stirring at 500 rpm at 50°C are 50% to 80% of the corresponding conditions for the modified MXene microspheres.

[0024] When two transition layers are set, they are defined as the first transition layer and the second transition layer from the positive electrode side to the negative electrode side, respectively.

[0025] The preparation conditions for secondary modified MXene microspheres in the first transition layer include the final concentration of the ortho-bisphenol surface modifier, the stirring time at 500 rpm at room temperature, the final concentration of the fixed anionic precursor, and the introduction of argon protective gas and stirring at 500 rpm at 50°C, which are 70% to 90% of the corresponding conditions for modified MXene microspheres.

[0026] The preparation conditions for secondary modified MXene microspheres in the second transition layer include a final concentration of the ortho-bisphenol surface modifier, a stirring time of 500 rpm at room temperature, a final concentration of the fixed anionic precursor, and the introduction of argon protective gas with a stirring time of 500 rpm at 50°C, which are 30% to 60% of the corresponding conditions for modified MXene microspheres.

[0027] When three transition layers are set, they are defined as the first transition layer, the second transition layer, and the third transition layer from the positive electrode side to the negative electrode side.

[0028] The preparation conditions for secondary modified MXene microspheres in the first transition layer include the final concentration of the ortho-bisphenol surface modifier, the stirring time at 500 rpm at room temperature, the final concentration of the fixed anionic precursor, and the introduction of argon protective gas and stirring at 500 rpm at 50°C, which are 80% to 95% of the corresponding conditions for modified MXene microspheres.

[0029] The preparation conditions for secondary modified MXene microspheres in the second transition layer include a final concentration of the ortho-bisphenol surface modifier, a stirring time of 500 rpm at room temperature, a final concentration of the fixed anionic precursor, and the introduction of argon protective gas with a stirring time of 500 rpm at 50°C, which are 50% to 70% of the corresponding conditions for modified MXene microspheres.

[0030] The preparation conditions of the secondary modified MXene microspheres in the third transition layer include a final concentration of the ortho-bisphenol surface modifier, a stirring time of 500 rpm at room temperature, a final concentration of the fixed anionic precursor, and the introduction of argon protective gas and stirring at 500 rpm at 50°C, which are 10% to 40% of the corresponding conditions for the modified MXene microspheres.

[0031] Technical Theme Two A method for preparing a solid-state composite electrolyte for a lithium battery as described in Technical Topic 1: When the transition layer is absent, the preparation method of the solid-state composite electrolyte is as shown in Route 1; when the transition layer is present, the preparation method of the solid-state composite electrolyte is as shown in Route 2. Route 1: S1 preparation of MXene microspheres; S2 preparation of modified MXene microspheres; S3 is used to prepare the coating solution; Preparation of S301 positive electrode side coating solution: Modified MXene microspheres, lithium salt, and polymer matrix were dissolved in solvent A at a mass ratio of 3~12 : 15~35 : 100. The polymer matrix content in the prepared mixture was 8-10 wt%, and it was denoted as positive electrode side coating liquid Slurry-C. Preparation of S302 negative electrode side coating solution: MXene microspheres, lithium salt, and polymer matrix were dissolved in solvent A at a mass ratio of 0.5~10 : 12~30 : 100. The polymer matrix content in the prepared mixture was 8-10 wt%, and it was denoted as negative electrode side coating liquid Slurry-A. S4 Coating and Post-treatment: S401 was coated with a layer of Slurry-C on the substrate by a blade coating method using a film maker with a height of 1000-1600μm, and pre-dried at room temperature for 10min. S402 coated a layer of Slurry-A onto a Slurry-C membrane, with the height of the membrane maker increased by 100-400 μm from the height of the already coated Slurry-C wet membrane; then the resulting multilayer structure was dried at room temperature and atmospheric pressure for 4 h and then dried in a vacuum chamber at 60 °C for 12 h; after cooling, it was peeled off to obtain a solid composite electrolyte. Route 2: S1 preparation of MXene microspheres; S2 preparation of modified MXene microspheres; S3 was used to prepare secondary modified MXene microspheres; S4 is used to prepare the coating solution; Preparation of S401 positive electrode side coating solution: Modified MXene microspheres, lithium salt, and polymer matrix were dissolved in solvent A at a mass ratio of 3~12 : 15~35 : 100. The polymer matrix content in the prepared mixture was 8-10 wt%, and it was denoted as positive electrode side coating liquid Slurry-C. Preparation of S402 negative electrode side coating solution: MXene microspheres, lithium salt, and polymer matrix were dissolved in solvent A at a mass ratio of 0.5~10 : 12~30 : 100. The polymer matrix content in the prepared mixture was 8-10 wt%, and it was denoted as negative electrode side coating liquid Slurry-A. Preparation of S403 transition layer coating solution: Secondary modified MXene microspheres, lithium salt, and polymer matrix were dissolved in solvent A at a mass ratio of 1~10: 12~35: 100. The polymer matrix content in the prepared mixture was 10 wt%, and this mixture was denoted as Slurry-T, the transition layer coating solution. The number of types of transition layer coating solutions varied with the number of types of secondary modified MXene microspheres prepared. The resulting transition layer coating solutions were labeled in descending order of the degree of modification of the secondary modified MXene microspheres. S5 Coating and Post-treatment: S501 was coated with a layer of Slurry-C on the substrate by a blade coating method with a film forming device height of 1000 μm and pre-dried at room temperature for 10 min. S502 sequentially coats a transition layer coating solution of secondary modified MXene microspheres with varying degrees of modification onto a Slurry-C membrane to obtain 1-3 transition layers. The height of the membrane builder for each transition layer is increased by 100 μm based on the original wet membrane. After each layer is coated, it is pre-dried at room temperature for 10 min. S503 involves coating a layer of Slurry-A onto the pre-dried transition layer membrane, with the membrane maker height increased by 100 μm from the original wet membrane height. S504 dried the obtained multilayer structure at room temperature and atmospheric pressure for 12 hours, and then dried it in a vacuum chamber at 60°C for 12 hours; after cooling, it was peeled off to obtain a solid composite electrolyte. Solvent A is selected from one or more of N-methylpyrrolidone, dimethylformamide, dimethylacetamide, tetrahydrofuran, acetonitrile, acetone, ethyl acetate, dimethyl carbonate, and ethyl methyl carbonate.

[0032] Technical Theme 3 A lithium battery comprising a solid composite electrolyte as described in Technical Subject 1.

[0033] As a further improvement of the present invention, the lithium battery is a solid-state lithium metal battery.

[0034] The beneficial effects of adopting the above technical solution are as follows: 1. The solid-state composite electrolyte provided in this application constructs a synergistic gradient structure of electronic conductivity and lithium-ion transference number: in the functional layer near the negative electrode, the filler imparts moderate and controllable electronic conductivity to the electrolyte, which can effectively guide uniform lithium deposition; in the functional layer near the positive electrode, a higher lithium-ion transference number can effectively alleviate concentration polarization. Experimental verification shows that the solid-state composite electrolyte provided in this application has good dendrite suppression capability, enabling the battery to cycle stably at a higher critical current density (CCD) while ensuring safety, and exhibiting good long-term cycle stability and rate performance.

[0035] 2. The electrolyte provided in this application has a simple and controllable preparation process and is feasible for industrialization: it adopts mature membrane preparation processes such as stepwise modification and layered coating. By adjusting the degree of modification and amount of fillers in each layer and combining the layer thickness ratio, the physicochemical properties of each functional layer can be precisely controlled, which has good prospects for large-scale production. Attached Figure Description

[0036] Figure 1 Scanning electron microscope images of the silica microspheres prepared in Example 1 of this application, where a) is a morphology image at 30,000x magnification; and b) is a morphology image at 55,000x magnification. Figure 2This is a Zeta potential distribution diagram of the PDDA-modified silica microspheres prepared in Example 1 of this application; Figure 3 The images show the microstructure of the MXene nanosheets used in this application, where a) is a scanning electron microscope image of the stacked state; and b) is a transmission electron microscope image. Figure 4 This is a zeta potential distribution diagram of the MXene nanosheets used in this application; Figure 5 This is a scanning electron microscope image of the Filler-C prepared in Example 1 of this application; Figure 6 The images shown are transmission electron microscope (TEM) images and EDS spectra of Filler-C prepared in Example 1 of this application, where a) is a TEM image and b) is an EDS spectrum. Figure 7 X-ray diffraction patterns of MXene used in this application and modified MXene microspheres prepared in Example 1; Figure 8 The images shown are scanning electron microscope (SEM) images of the positive electrode side surface of the solid composite electrolyte obtained in Example 1, as well as transmission electron microscope (TEM) and energy-dispersive X-ray spectroscopy (EDS) results, where a) is a scanning electron microscope image and b) is an EDS image. Figure 9 The XRD patterns are of the composite electrolyte prepared in Example 1 and the polymer electrolyte prepared in Example 3 of this application. Figure 10 DSC curves of the solid composite electrolyte prepared in Example 1 and the polymer prepared in Example 3 of this application; Figure 11 Figure 1 shows the ion transport number detection curve of the composite electrolyte prepared in Example 1 of this application, where Figure a) is the current-time curve and Figure b) is the electrochemical impedance change curve before and after polarization. Figure 12 Electrochemical window curve of the polymer electrolyte prepared in Example 3 of this application; Figure 13 Electrochemical window curve of the solid composite electrolyte prepared in Example 1 of this application; Figure 14 This is an electrochemical window curve of the solid composite electrolyte prepared in Example 2 of this application; Figure 15 To test the lithium metal symmetric battery assembled with the polymer electrolyte prepared in Example 3 of this application at 30°C with a current of 0.1 mA cm⁻¹ -2 Voltage-time curve of the cycle; Figure 16A lithium metal symmetric battery assembled based on the solid-state composite electrolyte membrane prepared in Example 1 of this application was tested at 30°C with an output of 0.1 mA cm⁻¹. -2 Voltage-time curve of the cycle; Figure 17 The graph shows the cycle performance of a full cell assembled with lithium iron phosphate as the positive electrode and lithium metal as the negative electrode based on the solid composite electrolyte prepared in Example 1 of this application at different rates. Figure 18 The graph shows the long-term cycling performance of a full battery assembled with lithium iron phosphate as the positive electrode and lithium metal as the negative electrode based on the polymer electrolyte prepared in Example 1 of this application at 0.5C. Figure 19 The graph shows the cycle performance of a full cell assembled with the polymer electrolyte prepared in Example 3 of this application as the positive electrode of lithium iron phosphate and the negative electrode of lithium metal at different rates. Figure 20 The graph shows the long-term cycling performance of a full cell assembled with the polymer electrolyte prepared in Example 3 of this application, with lithium iron phosphate as the positive electrode and lithium metal as the negative electrode, at 0.5C. Figure 21 This is a schematic diagram of the structure of the solid composite electrolyte prepared in Example 2 of this application; Figure 22 The lithium metal symmetric battery assembled based on the solid-state composite electrolyte prepared in Example 2 of this application was tested at 30°C with a current of 0.1 mA cm⁻¹. -2 Cyclic voltage-time curve; Figure 23 Example 2 of this application describes a lithium metal symmetric battery assembled based on the prepared solid-state composite electrolyte, operating at 30°C with a current of 0.2 mA cm⁻¹. -2 Cyclic voltage-time curve; Figure 24 These are SEM images of the lithium metal anode surfaces after cycling, based on the solid-state composite electrolyte prepared in Example 1 of this application and the lithium metal symmetric battery assembled based on the polymer electrolyte in Example 2. Wherein, a) shows the surface morphology of the lithium metal anode using the solid-state composite electrolyte, and b) shows the surface morphology of the lithium metal anode using the polymer electrolyte. Figure 25 The cycling performance curves of the full cell assembled based on the prepared polymer electrolyte in Example 2 of this application, with lithium iron phosphate as the positive electrode and lithium metal as the negative electrode, are shown at different rates. Figure 26 This is a long-cycle performance curve at 0.5C for a full battery assembled based on the prepared solid composite electrolyte membrane in Example 2 of this application, with lithium iron phosphate as the positive electrode and lithium metal as the negative electrode. Detailed Implementation

[0037] Preparation Example 1: Preparation of Silica Microspheres The method for preparing the silica microspheres used in this application is as follows: L-Arginine (0.17 g, 1 mmol) was dissolved in deionized water (174 g), and tetraethoxysilane (TEOS, 10.41 g, 50 mmol) was added under magnetic stirring at 1000 rpm. The reaction was carried out at 343 K with magnetic stirring at 1000 rpm for 24 h, yielding a silica dispersion with a diameter of approximately 14 nm, which served as the seed solution. Subsequently, in a newly prepared reaction system, L-Arginine (0.26 g, 1.5 mmol) was dissolved in a mixture of deionized water (41.4 g) and anhydrous ethanol (133.6 g). After stirring at 500 rpm until homogeneous, the aforementioned seed dispersion was added, resulting in a mixture containing 0.0053 mmol of equivalent TEOS. TEOS (10.41 g, 49.99 mmol) was added dropwise with continued stirring, and the reaction was carried out at 343 K with magnetic stirring at 500 rpm for 24 h to promote silica regrowth. After the reaction was complete, the solvent was removed by filtration. The microspheres were then washed with alcohol and water, and dried under vacuum at 80°C for 12 hours before being collected as white silica microspheres. A scanning electron microscope image of the obtained silica microspheres is shown below. Figure 1 As shown, its shape and structure are regular, its size is uniform, its dispersion is good, and its diameter is about 400nm.

[0038] Preparation Example 2: Preparation of MXene The MXene-Ti3C2T used in this application x The preparation method is as follows: Lithium fluoride (LiF, 1.6 g) was dissolved in hydrochloric acid solution (12 M, 20 mL) and stirred at 300 rpm for 10 min in a polytetrafluoroethylene beaker to form an etching solution. Subsequently, Ti3AlC2 powder (1 g) was slowly added under stirring (300 rpm), and the reaction was carried out at 25 °C for 24 h to selectively etch the aluminum layer. After the reaction, the solution was repeatedly washed with deionized water until the pH ≈ 6, and then subjected to ultrasonic exfoliation for 30 min, centrifugation at 3000 rpm, and concentration by centrifugation at 6500 rpm. The resulting lower precipitate was dispersed in argon-protected deionized water to prepare a solution with a concentration of 5 mg / mL. –1 Ti3C2T x Dispersion. This dispersion is used directly for further compounding.

[0039] Preparation Example 3: Preparation of Polymer Electrolytes The preparation method of the polymer electrolyte used in this application is as follows: 1 g of polyethylene oxide (PEO, average molecular weight approximately 600,000) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) were added to 10 mL of anhydrous acetonitrile (ACN) at a mass ratio of 100:30. The mixture was magnetically stirred at 500 rpm for 6 h at room temperature to dissolve and form a homogeneous, transparent solution. The polymer matrix content in the mixture was 11 wt%. The resulting coating solution was uniformly coated onto a polytetrafluoroethylene substrate using a coating tool with a height of 1000 μm. After drying at room temperature and atmospheric pressure for 4 h, the film was dried in a vacuum oven at 60 °C for 12 h. After cooling, the film was peeled off to obtain a polymer electrolyte membrane with a thickness of approximately 110 μm.

[0040] Example 1: Preparation and Performance Verification of Solid Composite Electrolytes (1) Preparation of MXene microspheres: The silica microspheres obtained in Preparation Example 1 were ultrasonically dispersed in deionized water for 5 min to prepare a solution of 1 mg / mL –1 The dispersion was prepared; polydiallyl ammonium chloride (PDDA) was added to the dispersion at room temperature, controlling the final concentration of PDDA to be 0.2 mg / mL. –1 The mixture was magnetically stirred at 500 rpm for 2 hours. The product was then collected by centrifugation at 9000 rpm for 10 minutes and washed with deionized water to obtain positively charged microspheres. The Zeta potential distribution of the PDDA-modified silica microspheres was measured, and the results are as follows: Figure 2 As shown, its Zeta potential is > +20mV.

[0041] The above-mentioned positively charged silica microspheres were dispensed at a concentration of 1 mg / mL. –1 The concentration was redispersed and ultrasonically dispersed for 10 min; under magnetic stirring at 500 rpm, Ti3C2T prepared in Preparation Example 2 was added dropwise above the dispersion. x Dispersion (5.0 mg / mL) –1 Ti3C2T x Nanosheet microstructures such as Figure 3 As shown, the flake diameter is in the micrometer range; for Ti3C2T x The zeta potential distribution of the dispersion was detected, and the results are as follows: Figure 4 As shown, its Zeta potential is <-40mV. The volume ratio of silica microsphere dispersion to nanosheet suspension (SiO2:Ti3C2T) was controlled. x The volume ratio was 10–80:1, and in this embodiment, a volume ratio of 40:1 was selected. After the addition was complete, the mixture was stirred at 500 rpm for 30 min at room temperature to complete electrostatic self-assembly; the product was collected by centrifugation at 6000 rpm for 10 min, and then freeze-dried in a freeze dryer for 36 h to obtain MXene microspheres, which were designated as the negative electrode side component MXene microspheres Filler-A.

[0042] (2) Preparation of positive electrode side filler modified MXene microspheres: The MXene microspheres obtained in step (1) were sonicated for 5 min and then uniformly dispersed in Tris buffer solution at pH 8.5, with the final concentration adjusted to 1.0 mg / mL. –1 Slowly add dopamine hydrochloride (DA·HCl) to a final volume of 5 mg / mL while magnetically stirring at 500 rpm. –1 The mixture was stirred at 500 rpm for 12 hours, centrifuged, and washed three times with deionized water to obtain PDA@MXene microspheres. The intermediate product was then uniformly dispersed in deionized water to prepare a concentration of 0.5 mg / mL. –1 The suspension was sonicated for 5 minutes, and sodium 3-mercaptopropanesulfonate (MPS, final concentration 1.0 mg / mL) was added. –1 Under argon protection, the mixture was kept at 50°C and magnetically stirred at 500 rpm for 24 h to anchor sulfonic acid sites on the PDA layer via Michael addition. After the reaction was completed, the product was collected by centrifugation and lithiation was performed in 0.1M lithium hydroxide (LiOH) solution for 30 min. After washing three times with deionized water, the product was freeze-dried in a freeze dryer for 36 h to obtain modified MXene microspheres, denoted as Filler-C, the positive electrode filler.

[0043] Scanning electron microscopy characterization of the obtained Filler-C ( Figure 5 The processed microspheres showed a rough surface with visible flaky wrinkles, demonstrating the successful modification of the microspheres. Figure 1 The smooth surfaces of the silica microspheres are significantly different; transmission electron microscopy and energy-dispersive X-ray spectroscopy (EDS) are also used. Figure 6 ) Displays titanium (derived from Ti3C2T) x The uniform distribution of sulfur (derived from -SO3Li) signals on the outer surface of the silicon and oxygen-characterized microspheres indicates that the silica microspheres have been coated with Ti3C2T. x Continuous coating, with sulfonate sites uniformly anchored on the PDA / MXene surface. X-ray diffraction pattern of Filler-C ( Figure 7 The results showed that only a broadened diffraction peak at approximately 22° was observed for silica microspheres, while no obvious characteristic peak was observed for the low-angle (002) peak corresponding to the stacking of MXene nanosheets in this sample. This is attributed to the electrostatic self-assembly of negatively charged MXene nanosheets and positively charged monodisperse silica microspheres, which effectively inhibits the stacking and aggregation of MXene, thus also facilitating the uniform dispersion of modified MXene in polymer solutions.

[0044] (3) Preparation of layered coating solution: Prepare coating solutions for the positive electrode side and negative electrode side respectively.

[0045] Positive electrode side coating solution (Slurry-C): Filler-C, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and polyethylene oxide (PEO, Mw≈600k) are dissolved in anhydrous acetonitrile (ACN) at a mass ratio of 12:30:100 to form a uniform slurry with a polyethylene oxide content of 8–10 wt%. In this application, 9 wt% is used.

[0046] Negative electrode side coating solution (Slurry-A): Filler-A, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and polyethylene oxide (PEO, Mw≈600k) are dissolved in anhydrous acetonitrile (ACN) at a mass ratio of 8:30:100 to form a uniform slurry with a polyethylene oxide content of 8–10 wt%. In this application, 9 wt% is used.

[0047] (4) Solid-state composite electrolyte film formation and post-treatment: A layer of Slurry-C was first coated onto the polytetrafluoroethylene substrate using a film-forming device with a height of 1000 μm, and pre-dried at room temperature for 10 min. Subsequently, a layer of Slurry-A was coated on top, with the film-forming device height increased by 100 μm from the height of the previously coated Slurry-C wet film. After drying at room temperature and atmospheric pressure for 4 h, it was placed in a vacuum oven at 60 °C for 12 h. After peeling off the film, a solid-state composite electrolyte with a total thickness of approximately 100 μm was obtained. The Slurry-A side was marked as the "negative electrode side," and the Slurry-C side was marked as the "positive electrode side." The morphology of the positive electrode side was characterized. Figure 8 The positive electrode side surface is flat, and the corresponding energy dispersive X-ray spectrum shows that carbon, oxygen, sulfur, and titanium elements are uniformly distributed on the surface, proving that lithium salt and modified MXene microspheres are uniformly distributed in the polymer matrix.

[0048] Preparation Example 4 A layer of Slurry-C prepared in Example 1 was coated onto a polytetrafluoroethylene substrate using a film-forming device with a height of 1000 μm. The coating was dried at room temperature and atmospheric pressure for 4 h, and then dried in a vacuum oven at 60 °C for 12 h to obtain a single-layer membrane of the positive electrode side functional layer.

[0049] Preparation Example 5 A layer of Slurry-A prepared in Example 1 was coated onto a polytetrafluoroethylene substrate by a blade coating method with a film forming device height of 500 μm. The film was dried at room temperature and normal pressure for 4 h, and then placed in a vacuum oven at 60 °C for 12 h to obtain a single-layer film of the functional layer on the negative electrode side.

[0050] Example of effect 1 The solid composite electrolyte obtained in Example 1 and the polymer electrolyte prepared in Preparation Example 3 were cut into 2cm × 2cm rectangles and subjected to XRD testing. The results are as follows. Figure 9 As shown, the polymer electrolyte exhibits characteristic diffraction peaks of the PEO crystalline region at 2θ≈19.2° and 2θ≈23.3°. After the introduction of modified MXene microspheres, the interaction between the surface polar sites and PEO segments / Li⁺ restricts the orderly stacking of the segments, resulting in a significant decrease in the crystallinity of PEO. Consequently, the intensity of the aforementioned characteristic peaks is significantly weakened and shows a broadening trend.

[0051] Example 2 Differential scanning calorimetry (DSC) was used to characterize the solid-state composite electrolyte prepared in Example 1 and the polymer electrolyte prepared in Example 3. Test conditions: sample amount approximately 5–10 mg, sealed aluminum crucible; program: “heating to eliminate thermal history (heat to 100 °C, hold for 3 min) → cooling to –20 °C → second heating”, with a temperature change rate of 10 °C / min. –1 The result is as follows Figure 10 As shown, the polymer electrolyte exhibits a distinct melting endothermic peak (T0) around 45–55 °C. m In contrast, the endothermic peak of the composite electrolyte was significantly weakened and shifted towards lower temperatures (approximately 20–30 °C). This indicates that the introduction of modified MXene microspheres effectively reduced crystallinity and suppressed crystal melting behavior, thereby improving the low-temperature mobility of polymer segments, consistent with the XRD results, which is beneficial for improving room-temperature ionic conductivity.

[0052] Example 3 The electronic conductivity of the solid composite electrolyte prepared in Example 1, the positive electrode-side functional monolayer membrane obtained in Example 4, and the negative electrode-side functional monolayer membrane obtained in Example 5 were tested using the four-probe method. The samples were cut into 20mm × 20mm squares with smooth surfaces and no obvious pores or cracks. The four probes were spaced 1.0mm apart, and the constant current source was automatically ranged (10~1000μA). The testing temperature was 25±1℃, and each point was tested 5 times and the average value was taken. The results showed that the electronic conductivity of the solid composite electrolyte membrane of Example 1 and the positive electrode-side functional monolayer membrane of Example 4 were both below the detection limit of the four-probe method, 1×10⁻⁶. -8 S cm -1 This meets the insulation requirements of solid electrolyte membranes; while the electronic conductivity of the single-layer functional layer membrane on the negative electrode side obtained in Example 5 is approximately 4.2 × 10⁻⁶. -4 S cm -1 The results show that it possesses certain electronic conductivity characteristics. These results demonstrate that the composite structure described in this application achieves the characteristics of "moderate electronic conductivity on the negative electrode side and insulation on the positive electrode side and the entire film," which helps promote uniform lithium deposition and ensure battery safety.

[0053] Example of effect 4 On the CHI760e electrochemical workstation, the electrochemical impedance spectroscopy (EIS) method was used in combination with... σ= L / ( R b A) The ionic conductivity of the solid composite electrolyte membrane prepared in Example 1 and the polymer electrolyte membrane prepared in Example 3 was measured (wherein... L For film thickness, R b The membrane resistance is obtained using the high-frequency intercept (A represents the effective area). The battery structure is a stainless steel (SS) | electrolyte membrane | stainless steel (SS) symmetrical battery; electrode diameter is 16 mm, frequency range is 1 MHz – 0.01 Hz, AC amplitude is 10 mV, and test temperature is 30 ± 0.5 ℃. The results show that the polymer electrolyte membrane prepared in Example 3 has an ionic conductivity of approximately 4.6 × 10⁻⁶ at 30 °C. –6 S cm –1 The ionic conductivity of the solid composite electrolyte membrane in Example 1 was significantly increased to 3.9 × 10⁻⁶. –4 S cm –1 This improvement is attributed to the modified MXene microspheres creating a continuous, high-speed lithium-ion conduction interface within the polymer matrix, which promotes lithium salt dissociation and enhances interfacial ion migration.

[0054] Example 5 The lithium-ion transport number of the solid composite electrolyte prepared in Example 1 was determined using a CHI760e electrochemical workstation with DC polarization combined with AC impedance spectroscopy. t + The battery structure is a Li|electrolyte membrane|Li symmetric cell; electrode diameter is 16 mm; test temperature is 30 ± 0.5℃. Applied voltage Δ V The initial current was 10mV, and the polarization was continued until the current reached a steady state (3600s); the initial current was recorded. I 0 and steady-state current I ss The AC impedance spectra of the battery (1MHz–0.1Hz, AC amplitude 10mV) were collected before and after polarization to obtain the membrane resistance. R 0 and steady-state resistance R ss Calculated according to the Bruce–Vincent–Evans relationship. t + = I ss (Δ V – I 0 R 0) / [ I 0(Δ V – I ss R ss The experimental results are as follows: Figure 11 As shown, the lithium-ion transference number of the solid composite electrolyte prepared in Example 1 was calculated. t + The value was 0.71. As a control, the polymer electrolyte prepared in Preparation Example 3 was tested using the same method, and its lithium-ion transport number was... t + It is 0.18. t + The significant improvement is attributed to the fixed anion sites such as sulfonic acid groups on the surface of the modified MXene microspheres, which weakens anion migration and promotes lithium salt dissociation and lithium-ion selective conduction.

[0055] Example 6 Electrochemical stability window testing. The electrochemical stability window of the polymer electrolyte membrane prepared in Preparation Example 3 and the solid composite electrolyte membrane prepared in Example 1 were determined using linear sweep voltammetry (LSV) on an electrochemical workstation (CHI760e). The battery structure was stainless steel (SS) | electrolyte membrane | Li, with lithium metal as both the counter and reference electrode; the scan rate was 0.5 mV / s. –1 Voltage range 0–6.0V vs. Li / Li + The test temperature was 30 ± 0.5 ℃. The results are as follows: Figure 12 , Figure 13 As shown, the oxidation initiation potential of the polymer electrolyte is approximately 4.1 V, while that of the solid composite electrolyte is significantly increased to approximately 4.6 V. This indicates that the introduction of modified MXene microspheres effectively improves the interfacial stability and antioxidant capacity of the polymer matrix, broadens the electrochemical stability window of the electrolyte, and is beneficial for its application in high-voltage cathode systems.

[0056] Example 7 (I) Determination of Critical Current Density (CCD). Electrolyte Pretreatment: To avoid poor contact between the positive electrode side of the composite electrolyte and the lithium negative electrode in the lithium metal symmetric battery, and to eliminate interference from interface problems, a thin negative electrode side coating was pre-coated on the "positive electrode side" surface of the solid composite electrolyte membrane obtained in Example 1 (a layer of Slurry-A from Example 1 was first coated on the polytetrafluoroethylene substrate, with a film-forming device height of 100 μm. After coating, it was dried for 10 min, and then the solid composite electrolyte was subsequently coated using the polytetrafluoroethylene substrate coated with Slurry-A as the substrate, according to the preparation method in Example 1). This ensured that both sides of the membrane had "negative electrode side" functional layers at the interface with the lithium metal. A Li|electrolyte|Li coin cell (electrode diameter 16 mm, effective area 2.01 cm²) was assembled in an argon glove box. 2 After encapsulation, the sample was allowed to stand for 12 hours. A constant current stepped lithium deposition / stripping test was performed at 60 °C: initial current density 0.05 mA cm⁻¹. -2Increasing by 0.05 mA cm every 30 minutes -2 The CCD is defined as the highest current density that can be stably maintained for ≥30 minutes without any signs of short circuit during this step sequence. The results show that the CCD of this symmetric cell is 1.10 mA cm⁻¹. –2 (0.55mAh cm –2 This demonstrates that the composite electrolyte supports high current density cycling under the guidance of the functional layer on the negative electrode side. As a control, a lithium metal symmetric battery was assembled based on the polymer electrolyte in Preparation Example 3 using the same assembly method as (I). This electrolyte is a homogeneous monolayer film, and the pre-coating of a thin negative electrode side layer as in (I) was not performed. The same procedure was followed during testing at 60°C; the results showed that the CCD of this symmetric battery was 0.40 mA cm⁻¹. -2 (0.20mAh cm) -2 The current density is significantly lower than that of the solid composite electrolyte of this application, demonstrating the advantages of this invention in interface and transport at high current densities.

[0057] (II) Long-term cycling stability of the polymer electrolyte. A lithium metal symmetric battery was assembled using the same assembly method as in (I) based on the polymer electrolyte from Preparation Example 3. This electrolyte is a homogeneous monolayer film, without the pre-coating of a thin negative electrode side layer as in (I). The battery was cycled at 30°C at 0.1 mA cm⁻¹. –2 (0.1mAh cm) –2 Cyclic testing was performed on the current density of [the sample / unit]. The results are as follows: Figure 15 As shown, the battery's overpotential was approximately 0.74V in the initial stage; after 100 hours of operation, the overpotential fluctuations intensified, and it failed after 125 hours.

[0058] (III) Long-term cycle stability of solid-state composite electrolyte. A lithium metal symmetric battery was assembled using the same solid-state composite electrolyte structure and assembly method as (I), and tested at 30°C with a current of 0.1 mA cm⁻¹. –2 Cyclic testing was performed on the current density. The results are as follows: Figure 16 As shown, the initial overpotential was approximately 0.08V, and it remained stable for 600 hours without any short circuits, demonstrating its good cycle stability.

[0059] Example 8 A coin cell (CR2032) with a LiFePO4|electrolyte membrane|Li configuration was assembled in an argon glove box for performance evaluation. The electrolyte membranes were the solid composite electrolyte of Example 1 and the polymer electrolyte of Preparation Example 3; for the former, the functional layer on the positive electrode side of the electrolyte membrane faced LiFePO4, and the functional layer on the negative electrode side faced Li. The test temperature was 30 ± 0.5 °C, and the voltage range was 2.5–4.0 V vs. Li / Li. +The charging and discharging programs were all constant current, with a 30-second rest period before and after each charge / discharge cycle. The rate test used a stepwise method: 10 cycles each of 0.2C → 0.5C → 1C → 1.5C → 2C → 2.5C, followed by 10 cycles at 0.2C for capacity recovery; the long-term cycle test was performed with 200 constant current charge and discharge cycles at 0.5C.

[0060] The results show that the rate performance of the full cell using the composite electrolyte of Example 1 is as follows: Figure 17 The discharge capacity at 0.2C is approximately 138 mAh g. –1 It can still maintain approximately 104 mAh g at 2.5C. –1 The capacity retention rate is not less than 75%; it can be cycled for 200 times at 0.5C. Figure 18 The initial capacity is 135mAh g. –1 After long cycling, the capacity retention rate was higher than 93%, demonstrating good rate performance and cycle stability. As a control, the rate performance of the full cell prepared using the polymer electrolyte of Example 3 under the same conditions is shown in [reference needed]. Figure 19 The discharge capacity at 0.2C is approximately 126 mAh g. –1 It drops to about 50mAh g at 2.5C. –1 The capacity retention rate is less than 40%; its long-term cycling results at 0.5C are shown in [reference needed]. Figure 20 The capacity retention rate is approximately 28%. The above comparison further demonstrates that the solid-state composite electrolyte of this application can effectively improve the rate output and significantly enhance the cycle stability of the full cell near room temperature.

[0061] Comparative Example 1 The preparation method of this comparative example is the same as that of Example 1, except that only the positive electrode component (Filler-C) from Example 1 is used, and a homogeneous slurry with a polyethylene oxide content of 8–10 wt% is prepared by mixing it with LiTFSI and PEO at a mass ratio of 12:30:100. In this application, 9 wt% is used, and the slurry is coated to form an electrolyte membrane with a total thickness equivalent to that of Example 1. This comparative example is a homogeneous monolayer membrane, and the pre-coating of a thin negative electrode coating layer as in Effect Example 7 (I) is not performed.

[0062] The electrolyte prepared in Comparative Example 1 was tested using the detection conditions (I) and (III) in Effect Example 7.

[0063] The results show that its critical current density is 0.75 mA cm⁻¹. –2 (0.375mAh cm) –2 (60℃); the initial overpotential of the battery was about 0.35V. After stabilizing for 350 hours, the curve fluctuations intensified, and its critical current density and long-term cycle stability were inferior to those of Example 1.

[0064] Comparative Example 2: Composite electrolyte with reversed gradient direction The composite electrolyte membrane used in this comparative example was prepared in exactly the same way as in Example 1, except that the assembly orientation was reversed: Slurry-C was oriented toward the lithium metal anode, and Slurry-A was oriented toward the cathode.

[0065] The cyclic performance of the composite electrolyte prepared in Comparative Example 2 was tested according to the experimental steps of Effect Example 8.

[0066] The results showed that its initial capacity at 0.5C was 112 mAh g. –1 The capacity retention rate after 200 cycles is approximately 58%. The composite electrolyte with the gradient direction reversed exhibits inferior cycling performance in full cells compared to Example 1.

[0067] Example 2 This embodiment adds two transitional functional layers between the two functional layers, based on embodiment 1.

[0068] (1) Preparation of the transition component (Filler-T1): The MXene microspheres prepared in step (1) of Example 1 were sonicated for 5 min and then uniformly dispersed in Tris buffer at pH 8.5, with the final concentration adjusted to 1.0 mg / mL. –1 Slowly add dopamine hydrochloride (DA·HCl) to a final volume of 4 mg / mL while stirring magnetically at 500 rpm. –1 The mixture was stirred for another 10 hours, centrifuged, and the product was washed three times with deionized water to obtain PDA@MXene microspheres. The intermediate product was then uniformly dispersed in deionized water to prepare a concentration of 0.5 mg / mL. –1 The suspension was sonicated for 5 minutes, and sodium 3-mercaptopropanesulfonate (MPS, final concentration 0.7 mg / mL) was added. –1 Under argon protection, the mixture was kept at 50°C and magnetically stirred at 500 rpm for 18 h to anchor sulfonic acid sites on the PDA layer via Michael addition. After the reaction was completed, lithiation was carried out in 0.1M lithium hydroxide (LiOH) solution for 30 min; after washing three times with deionized water, the mixture was freeze-dried in a freeze dryer for 36 h to obtain secondary modified MXene microspheres Filler-T1.

[0069] (2) Preparation of the transition component (Filler-T2): The MXene microspheres prepared in step (1) of Example 1 were sonicated for 5 min and then uniformly dispersed in Tris buffer at pH 8.5, with the final concentration adjusted to 1.0 mg / mL. –1 Dopamine hydrochloride (DA·HCl) was slowly added to a final volume of 2.5 mg / mL while the mixture was magnetically stirred at 500 rpm. –1The mixture was stirred for another 7 hours, centrifuged, and the product was washed three times with deionized water to obtain PDA@MXene microspheres. The intermediate product was then uniformly dispersed in deionized water to prepare a concentration of 0.5 mg / mL. –1 The suspension was sonicated for 5 minutes, and sodium 3-mercaptopropanesulfonate (MPS, final concentration 0.4 mg / mL) was added. –1 Under argon protection, the mixture was kept at 50°C and magnetically stirred at 500 rpm for 12 h to anchor sulfonic acid sites on the PDA layer via Michael addition. After the reaction was completed, lithiation was carried out in 0.1M lithium hydroxide (LiOH) solution for 30 min. After washing three times with deionized water, the mixture was freeze-dried in a freeze dryer for 36 h to obtain secondary modified MXene microspheres Filler-T2.

[0070] (3) Layered coating: Preparation of transition layer coating liquid Slurry-T1 The secondary modified MXene microspheres Filler-T1, lithium salt, and polymer matrix were dissolved in anhydrous acetonitrile at a mass ratio of 10:30:100. The polymer matrix content in the prepared mixture was 10 wt%, and it was denoted as the transition layer coating liquid Slurry-T1.

[0071] Preparation of transition layer coating liquid Slurry-T2 The secondary modified MXene microspheres Filler-T2, lithium salt, and polymer matrix were dissolved in anhydrous acetonitrile at a mass ratio of 8:30:100. The polymer matrix content in the prepared mixture was 10 wt%, and it was denoted as the transition layer coating liquid Slurry-T2.

[0072] (4) Coating and post-treatment A layer of Slurry-C prepared by the method described in Example 1 was coated onto the substrate by a blade coating method. The height of the film builder was 1000 μm, and the film was pre-dried at room temperature for 10 min. Slurry-T1 and Slurry-T2 were sequentially coated onto the Slurry-C membrane. The height of the membrane casting device for each transition layer was increased by 100 μm from the original wet membrane. After each layer was coated, it was pre-dried at room temperature for 10 min. A layer of Slurry-A prepared by the method described in Example 1 was coated onto the Slurry-T2 membrane, and the height of the membrane maker was increased by 100 μm based on the height of the already coated multilayer wet membrane; The obtained multilayer structure was dried at room temperature and atmospheric pressure for 12 hours, and then dried in a vacuum chamber at 60°C for 12 hours. After cooling, it was peeled off to obtain a solid composite electrolyte. A schematic diagram of the cross-sectional structure of this solid composite electrolyte membrane containing the transition layer is shown below. Figure 21As shown, the insulating positive electrode side functional layer and transition layer account for the majority of the film thickness, while the negative electrode side functional layer, which has a certain conductivity, accounts for less than one-tenth of the film thickness.

[0073] verify: The electrochemical window curve of the composite electrolyte prepared in Example 2 was detected using the method described in Example 6, and the results are as follows: Figure 14 As shown, the oxidation initiation potential is approximately 4.75V.

[0074] The electrolyte was assembled into a lithium metal symmetric battery using the method described in Example 7 (III) and tested at 30°C with a current of 0.1 mA / cm². -2 (0.1mAh cm) -2 It operates under the following conditions, such as Figure 22 As shown, the overpotential in the initial stage is about 0.05V; it runs stably for 2000 hours.

[0075] The electrolyte was assembled into a lithium metal symmetric battery using the method described in Example 7 (III) and tested at 30°C with a current of 0.2 mA / cm². -2 Under the conditions of operation, the results are as follows Figure 23 As shown, the initial overpotential was approximately 0.2V; after 700 hours of stable operation, the operation ended. The battery was disassembled, and the lithium anode corresponding to the composite electrolyte was removed for SEM surface morphology inspection. The surface morphology was compared with that of the lithium anode corresponding to the polymer electrolyte in Example 1, Detection 7 (II). The results are as follows. Figure 24 As shown, the former has a smooth and flat surface without dendrite protrusions, while the latter has a rough surface with obvious protrusions and uneven deposition traces. This indicates that the negative electrode side functional layer rich in MXene microspheres can effectively promote uniform lithium deposition and stripping, and significantly inhibit dendrite formation; in contrast, the homogeneous polymer electrolyte without MXene microspheres is prone to local current density concentration, thereby inducing dendrite growth and interface instability.

[0076] The electrolyte prepared in this embodiment was assembled into a LiFePO4|solid-state composite electrolyte|Li full cell using the detection method of Example 8, and the results were obtained under the same detection conditions. Figure 25 As shown, the discharge capacities at 0.2C, 0.5C, 1C, 1.5C, 2C, and 2.5C are approximately 152, 147, 138, 132, 126, and 118 mAh g, respectively. –1 At 2.5C, the battery retains approximately 78% of its initial capacity, and upon returning to 0.2C, the capacity is almost fully recovered, indicating good rate reversibility. Long-cycle testing at 0.5C yielded the following results: Figure 26 As shown, the capacity retention rate is approximately 95%.

[0077] Example 3 Different polymer matrices To verify the universality of this invention for polymer matrices, this embodiment uses a PVDF-HFP matrix.

[0078] The preparation of Filler-A and Filler-C is the same as that in Example 1.

[0079] Preparation of layered coating solutions: Two coating solutions were prepared separately.

[0080] Positive electrode side coating solution (Slurry-C2): PVDF-HFP was dissolved in DMF / acetone (1:1, v:v), LiTFSI (salt / polymer mass ratio 30:100) was added, and Filler-C (mass ratio of Filler-C, LiTFSI and PVDF-HFP was 10:30:100) was dispersed to obtain Slurry-C2, with the polymer matrix content controlled at 9 wt%.

[0081] Negative electrode side coating solution (Slurry-A2): PVDF-HFP was dissolved in DMF / acetone (1:1, v:v), LiTFSI (salt / polymer mass ratio 30 / 100) was added, and Filler-A (mass ratio of Filler-A, LiTFSI and PVDF-HFP was 8:30:100) was dispersed to obtain Slurry-A2, with the polymer matrix content controlled at 9 wt%.

[0082] Film Formation and Assembly: A layer of Slurry-C2 was first coated onto the polytetrafluoroethylene substrate using a film-forming device with a height of 1200 μm, and pre-dried at room temperature for 10 min. Subsequently, a layer of Slurry-A2 was coated on top, with the film-forming device height increased by 150 μm from the height of the previously coated Slurry-C2 wet film. After drying at room temperature for 30 min, the film was placed in a vacuum oven at 80 °C for 12 h. After peeling off the film, a solid composite electrolyte with a total thickness of approximately 125 μm was obtained. The Slurry-A2 side was marked as the "negative electrode side," and the Slurry-C2 side was marked as the "positive electrode side."

[0083] The solid composite electrolyte prepared in this embodiment was tested using the methods described in Effect Example 7 (I) and Effect Example 8.

[0084] The results show that its critical current density is 1.2 mA cm⁻¹. –2 (0.6mAh cm) –2 The 0.5C long-cycle stability test results are as follows: initial capacity approximately 155mAh g. –1 After 200 cycles, the capacity retention rate was 96%, which is slightly improved compared to Example 1 and far superior to the performance of the polymeric electrolyte obtained in Example 3.

[0085] Example 4: Different lithium salts and types of fixed anions (1) Lithium salt replacement: In the formulation of Example 1, the lithium salt LiTFSI was replaced with an equal mass of LiFSI.

[0086] (2) Replacement of fixed anions: In the preparation of Filler-C, MPS is replaced by an equal mass of mercaptoethylphosphonic acid.

[0087] The remaining preparation conditions were the same as in Example 1, and a solid composite electrolyte was prepared.

[0088] Cross-sectional SEM measurements (supplemented by EDS to confirm layer distribution) showed that the dry film thickness ratio of the positive electrode functional layer to the negative electrode functional layer was approximately 7:1.

[0089] The solid composite electrolyte prepared in this embodiment was tested using the methods described in Effect Example 7 (I) and Effect Example 8.

[0090] The results show that its critical current density is 1.0 mA cm⁻¹. –2 (0.5mAh cm) –2 The 0.5C long-cycle stability test result was 130mAh g. –1 After 200 cycles, the capacity retention rate was 93%, which is comparable to that of Example 1.

[0091] Example 5: Variation in layer thickness ratio Based on Example 1, the coating thickness was adjusted. The coating thickness of the functional layer on the positive electrode side was 1600 μm, and the coating thickness of the functional layer on the negative electrode side was 400 μm. The remaining preparation steps were the same as in Example 1. The total thickness of the solid composite electrolyte membrane obtained was approximately 210 μm.

[0092] The prepared solid composite electrolyte was tested using the methods in Example 7 (I) and (III).

[0093] The results show that its critical current density is 0.90 mA cm⁻¹. –2 (0.45mAh cm) –2 The long-cycle stability test results showed that after 500 cycles at 0.5C, the capacity retention rate was 90%. Its critical current density was slightly lower than that of Example 1, but its long-cycle life was longer than that of Example 1.

[0094] The material was tested using the method described in Example 3. The results showed that the σ of the entire membrane was... e Still ≤1×10 -8 S·cm -1 .

[0095] Example 6 The MXene microspheres prepared in step (1) of Example 1 were sonicated for 5 min and then uniformly dispersed in Tris buffer at pH 8.5, with the final concentration adjusted to 1.0 mg / mL. –1 Dopamine hydrochloride (DA·HCl) was slowly added to a final volume of 2.5 mg / mL while the mixture was magnetically stirred at 500 rpm. –1 The mixture was stirred for another 6 hours, centrifuged, and the product was washed three times with deionized water to obtain PDA@MXene microspheres. The intermediate product was then uniformly dispersed in deionized water to prepare a concentration of 0.5 mg / mL. –1 The suspension was sonicated for 5 minutes, and sodium 3-mercaptopropanesulfonate (MPS, final concentration 0.5 mg / mL) was added. –1 Under argon protection, the mixture was kept at 50°C and magnetically stirred at 500 rpm for 12 h to anchor sulfonic acid sites on the PDA layer via Michael addition. After the reaction was completed, lithiation was carried out in 0.1M lithium hydroxide (LiOH) solution for 30 min; after washing three times with deionized water, the mixture was freeze-dried in a freeze dryer for 36 h to obtain secondary modified MXene microspheres Filler-T3.

[0096] The secondary modified MXene microspheres Filler-T3, lithium salt, and polymer matrix were dissolved in anhydrous acetonitrile at a mass ratio of 1:12:100. The polymer matrix content in the prepared mixture was 10 wt%, and it was denoted as the transition layer coating liquid Slurry-T3.

[0097] Filler-C, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and polyethylene oxide (PEO, Mw≈600k) prepared in Example 1 were dissolved in anhydrous acetonitrile (ACN) at a mass ratio of 3:15:100 to form a homogeneous slurry Slurry-C3 with a polyethylene oxide content of 10 wt%.

[0098] Filler-A, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and polyethylene oxide (PEO, Mw≈600k) prepared in Example 1 were dissolved in anhydrous acetonitrile (ACN) at a mass ratio of 0.5:12:100 to form a homogeneous slurry Slurry-A3 with a polyethylene oxide content of 10 wt%.

[0099] First, a layer of Slurry-C3 was coated onto the polytetrafluoroethylene substrate using a film maker with a height of 1000 μm, and pre-dried at room temperature for 10 min. Then, a layer of Slurry-T3 was coated onto the Slurry-C3 film, with the height of the film maker increased by 100 μm from the original wet film. After coating, the film was pre-dried for 10 min. A layer of Slurry-A3 was coated onto the Slurry-T3 membrane, and the height of the membrane maker was increased by 100 μm based on the height of the already coated multilayer wet membrane. The obtained multilayer structure was dried at room temperature and atmospheric pressure for 12 hours, and then placed in a vacuum chamber at 60°C for 12 hours. After cooling, it was peeled off to obtain a solid composite electrolyte. The solid composite electrolyte prepared in this example was tested using the methods in Effect Example 7 (I) and Effect Example 8 (long-term cycle test).

[0100] The results show that its critical current density is 0.90 mA cm⁻¹. -2 (0.45 mAh cm) -2 The 0.5C long-cycle stability test results are as follows: initial capacity approximately 112 mAh g⁻¹. -1 After 200 cycles, the capacity retention rate was 92%, which was slightly lower than that of Example 1, but better than the performance of the polymer electrolyte obtained in Preparation Example 3.

[0101] The secondary modified MXene microspheres Filler-T1, lithium salt, and polymer matrix were dissolved in anhydrous acetonitrile at a mass ratio of 10:35:100. The polymer matrix content in the prepared mixture was 10 wt%, and it was designated as the transition layer coating solution Slurry-T4.

[0102] Filler-C, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and polyethylene oxide (PEO, Mw≈600k) prepared in Example 1 were dissolved in anhydrous acetonitrile (ACN) at a mass ratio of 12:35:100 to form a homogeneous slurry Slurry-C4 with a polyethylene oxide content of 10 wt%.

[0103] Filler-A, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and polyethylene oxide (PEO, Mw≈600k) prepared in Example 1 were dissolved in anhydrous acetonitrile (ACN) at a mass ratio of 10:30:100 to form a homogeneous slurry Slurry-A4 with a polyethylene oxide content of 10 wt%.

[0104] First, a layer of Slurry-C4 was coated onto the polytetrafluoroethylene substrate using a film maker with a height of 1000 μm, and pre-dried at room temperature for 10 min. Then, a layer of Slurry-T4 was coated onto the Slurry-C4 film, with the height of the film maker increased by 100 μm from the original wet film. After coating, the film was pre-dried for 10 min. A layer of Slurry-A4 was coated onto the Slurry-T4 membrane, and the height of the membrane maker was increased by 100 μm based on the height of the already coated multilayer wet membrane. The obtained multilayer structure was dried at room temperature and atmospheric pressure for 12 hours, and then placed in a vacuum chamber at 60°C for 12 hours. After cooling, it was peeled off to obtain a solid composite electrolyte. The solid composite electrolyte prepared in this example was tested using the methods in Effect Example 7 (I) and Effect Example 8 (long-term cycle test).

[0105] The results show that its critical current density is 1.2 mA cm⁻¹. -2 (0.6 mAh cm) -2 The 0.5C long-cycle stability test results are as follows: initial capacity approximately 145 mAh g. -1 After 200 cycles, the capacity retention rate was 95%, which is slightly improved compared to Example 1.

[0106] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A solid composite electrolyte for lithium batteries, characterized in that: The solid composite electrolyte uses a lithium salt-containing polymer as a matrix and is divided into a positive electrode side functional layer and a negative electrode side functional layer along the thickness direction of the solid composite electrolyte. There are also 0 to 3 transition layers between the positive electrode side functional layer and the negative electrode side functional layer along the thickness direction of the solid composite electrolyte. Modified MXene microspheres are dispersed in the functional layer on the positive electrode side, and MXene microspheres are dispersed in the functional layer on the negative electrode side; secondary modified MXene microspheres are dispersed in the transition layer. The MXene microspheres are composite microspheres with MXene nanosheets coated on their surface; The modified MXene microspheres and the secondary modified MXene microspheres are obtained by treating MXene microspheres with a surface modifier containing an ortho-biphenol groups, and then mixing and reacting them with a fixed anion precursor to introduce fixed anion sites on their surface. The mass ratio of modified MXene microspheres, lithium salt, and polymer matrix in the positive electrode side functional layer is 3~12 : 15~35 : 100; The mass ratio of MXene microspheres, lithium salt, and polymer matrix in the negative electrode side functional layer is 0.5~10 : 12~30 : 100; The mass ratio of secondary modified MXene microspheres, lithium salt, and polymer matrix in the transition layer is 1~10 : 12~35 :

100.

2. The solid composite electrolyte according to claim 1, characterized in that: When the transition layer is absent, the thickness ratio of the positive electrode side functional layer to the negative electrode side functional layer is 4~10 :

1.

3. The solid composite electrolyte according to claim 1, characterized in that: When there are 1-3 transition layers, the thickness ratio between the positive electrode side functional layer, each transition layer, and the negative electrode side functional layer is 4~10 : (1~4) / n : 1, where n=1, 2 or 3, and the thickness of each transition layer in the same composite electrolyte is equal.

4. The solid composite electrolyte according to claim 1, characterized in that: The lithium salt is selected from one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium 2-trifluoromethyl-4,5-dicyanoimidazolium, lithium tetrafluoroborate, lithium difluorooxalate borate, or lithium borate oxalate. The polymer is one or more of the following: polyethylene oxide, polyacrylonitrile, polyvinylidene fluoride-hexafluoropropylene copolymer, polymethyl methacrylate, and nitrile rubber.

5. The solid composite electrolyte according to claim 1, characterized in that, The MXene is selected from one or more of transition metal carbides, transition metal nitrides, and transition metal carbonitride ultrathin two-dimensional nanosheets; The microspheres are selected from one or more of polystyrene microspheres, polyvinyl chloride microspheres, silica microspheres, and titanium dioxide microspheres; The microspheres have a particle size of 400 nm; The preparation method of the MXene microspheres is as follows: Step 1: Disperse the microspheres in water to prepare a solution with a concentration of 1 mg / mL. –1 The suspension was prepared by adding polydimethyldiallyl ammonium chloride to the suspension at room temperature, controlling the final concentration of polydimethyldiallyl ammonium chloride to be 0.2 mg / mL. –1 The mixture was magnetically stirred at 500 rpm for 2 hours and then centrifuged at 9000 rpm for 10 minutes to collect the product, resulting in positively charged microspheres. Step 2: Redisperse the microspheres obtained in Step 1 in water to prepare a solution with a concentration of 1 mg / mL. –1 The suspension was ultrasonically dispersed for 10 min, and then a 5 mg / mL solution was added dropwise to the suspension under magnetic stirring at 500 rpm. –1 The volume ratio of MXene nanosheet suspension to microsphere suspension was 40:

1. After the addition was complete, the mixture was stirred for 30 min. The product was collected by centrifugation at 6000 rpm for 10 min and then freeze-dried in a freeze dryer for 36 h to obtain MXene microspheres.

6. The solid composite electrolyte according to claim 1, characterized in that: The modified MXene microspheres are obtained by treating MXene microspheres with a surface modifier containing o-biphenol groups and mixing them with a fixed anion precursor to introduce fixed anion sites on the surface of the microspheres. The fixed anion sites exist in the form of lithium salts. The surface modifier containing ortho-diphenol group is selected from one or more of dopamine, catechol, protocatechuic acid, 3,4-dihydroxyphenylacetic acid, and gallic acid; The fixed anion precursor is selected from one or more of 2-mercaptoethanesulfonic acid, 3-mercaptopropanesulfonic acid, mercaptoethylphosphonic acid, mercaptoacetic acid, and mercaptopropionic acid.

7. The solid composite electrolyte according to claim 1, characterized in that: The specific method for preparing the modified MXene microspheres is as follows: Step 1: Disperse MXene microspheres in Tris buffer at pH 8.5 to prepare a solution with a concentration of 1 mg / mL. –1 The suspension was prepared by adding a surface modifier containing an ortho-bisphenol group to the suspension, controlling the final concentration of the surface modifier to be 5 mg / mL. –1 The mixture was stirred at 500 rpm for 12 h at room temperature and then centrifuged to obtain the microsphere intermediate. Step 2: Disperse the microsphere intermediate in water to prepare a concentration of 0.5 mg / mL. –1 The suspension was prepared by adding a fixed anion precursor to the suspension, and controlling the concentration of the fixed anion precursor to be 1 mg / mL. –1 A protective gas was introduced and the mixture was stirred at 500 rpm for 24 hours at 50°C. After the reaction was completed, the product was collected by centrifugation. The product was then added to a 0.1 M lithium hydroxide solution and stirred for 30 min. The product was collected by centrifugation, washed with deionized water, and freeze-dried in a freeze dryer to obtain modified MXene microspheres.

8. The solid composite electrolyte according to claim 7, characterized in that, The preparation method of the secondary modified MXene microspheres is the same as that of the modified MXene microspheres, except that the final concentration of the surface modifier containing the ortho-diphenol group is added to the suspension, the stirring time is 500 rpm at room temperature, the final concentration of the fixed anionic precursor is added to the suspension, and argon protective gas is introduced and the stirring time is 500 rpm at 50°C. The preparation method also satisfies conditions I-III. I. In the preparation conditions of the secondary modified MXene microspheres, the final concentration of the surface modifier containing o-diphenol groups added to the suspension and the stirring time at 500 rpm at room temperature are both lower than those in step 1 of the preparation of the modified MXene microspheres. II. In the preparation conditions of the secondary modified MXene microspheres, the final concentration of the fixed anionic precursor added to the suspension and the introduction of argon protective gas and the stirring time at 500 rpm at 50°C are both lower than those in step 2 of the preparation of the modified MXene microspheres. III. Along the thickness direction of the composite electrolyte, from the positive electrode side functional layer through each transition layer to the negative electrode side functional layer, the final concentration of the surface modifier containing o-bisphenol group added to the suspension, the stirring time at 500 rpm at room temperature, the final concentration of the fixed anion precursor added to the suspension, and the introduction of argon protective gas and stirring time at 500 rpm at 50°C are progressively decreased layer by layer in the preparation of secondary modified MXene microspheres.

9. A method for preparing a solid composite electrolyte as described in any one of claims 1 to 8, characterized in that, When the transition layer is absent, the preparation method of the solid composite electrolyte is as shown in Route 1; when the transition layer is present, the preparation method of the solid composite electrolyte is as shown in Route 2. Route 1: S1 preparation of MXene microspheres; S2 preparation of modified MXene microspheres; S3 is used to prepare the coating solution; Preparation of S301 positive electrode side coating solution: Modified MXene microspheres, lithium salt, and polymer matrix were dissolved in solvent A at a mass ratio of 3~12 : 15~35 :

100. The polymer matrix content in the prepared mixture was 8-10 wt%, and it was denoted as positive electrode side coating liquid Slurry-C. Preparation of S302 negative electrode side coating solution: MXene microspheres, lithium salt, and polymer matrix were dissolved in solvent A at a mass ratio of 0.5~10 : 12~30 :

100. The polymer matrix content in the prepared mixture was 8-10 wt%, and it was denoted as negative electrode side coating liquid Slurry-A. S4 Coating and Post-treatment: S401 was coated with a layer of Slurry-C on the substrate by a blade coating method using a film maker with a height of 1000-1600μm, and pre-dried at room temperature for 10min. S402 coated a layer of Slurry-A onto a Slurry-C membrane, with the height of the membrane maker increased by 100-400 μm from the height of the already coated Slurry-C wet membrane; then the resulting multilayer structure was dried at room temperature and atmospheric pressure for 4 h and then dried in a vacuum chamber at 60 °C for 12 h; after cooling, it was peeled off to obtain a solid composite electrolyte. Route 2: S1 preparation of MXene microspheres; S2 preparation of modified MXene microspheres; S3 was used to prepare secondary modified MXene microspheres; S4 is used to prepare the coating solution; Preparation of S401 positive electrode side coating solution: Modified MXene microspheres, lithium salt, and polymer matrix were dissolved in solvent A at a mass ratio of 3~12 : 15~35 :

100. The polymer matrix content in the prepared mixture was 8-10 wt%, and it was denoted as positive electrode side coating liquid Slurry-C. Preparation of S402 negative electrode side coating solution: MXene microspheres, lithium salt, and polymer matrix were dissolved in solvent A at a mass ratio of 0.5~10 : 12~30 :

100. The polymer matrix content in the prepared mixture was 8-10 wt%, and it was denoted as negative electrode side coating liquid Slurry-A. Preparation of S403 transition layer coating solution: Secondary modified MXene microspheres, lithium salt, and polymer matrix were dissolved in solvent A at a mass ratio of 1~10 : 12~35 :

100. The polymer matrix content in the prepared mixture was 10 wt%, and this mixture was denoted as Slurry-T, the transition layer coating solution. The number of types of transition layer coating solutions varied with the number of types of secondary modified MXene microspheres prepared. The resulting transition layer coating solutions were labeled in descending order of the degree of modification of the secondary modified MXene microspheres. S5 Coating and Post-treatment: S501 was coated with a layer of Slurry-C on the substrate by a blade coating method with a film forming device height of 1000 μm and pre-dried at room temperature for 10 min. S502 sequentially coats a transition layer coating solution of secondary modified MXene microspheres with varying degrees of modification onto a Slurry-C membrane to obtain 1-3 transition layers. The height of the membrane builder for each transition layer is increased by 100 μm based on the original wet membrane. After each layer is coated, it is pre-dried at room temperature for 10 min. S503 involves coating a layer of Slurry-A onto the pre-dried transition layer membrane, with the membrane maker height increased by 100 μm from the original wet membrane height. S504 dried the obtained multilayer structure at room temperature and atmospheric pressure for 12 hours, and then dried it in a vacuum chamber at 60°C for 12 hours; after cooling, it was peeled off to obtain a solid composite electrolyte. Solvent A is selected from one or more of N-methylpyrrolidone, dimethylformamide, dimethylacetamide, tetrahydrofuran, acetonitrile, acetone, ethyl acetate, dimethyl carbonate, and ethyl methyl carbonate.

10. A lithium battery, characterized in that, It includes the solid composite electrolyte as described in any one of claims 1 to 8.

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