A method for removing and coating the passivation layer on the surface of an LLZO-type solid electrolyte and its application

Abstract

The present invention discloses a method and application for removing and coating the surface passivation layer of an LLZO-type solid electrolyte. The method comprises the following steps: preparing an ammonium formate solution; uniformly dispersing LLZTO@Li2CO3 powder in the ammonium formate solution to obtain a dispersion, and then heat-insulating the dispersion; adjusting the pH of the dispersion using formic acid; adding aluminum sulfate to the pH-adjusted dispersion and stirring at a constant temperature to obtain LLZTO@Al(OH)3 particles; and centrifugally washing, drying, and sintering the LLZTO@Al(OH)3 particles to obtain LLZTO@Al2O3 powder. The present invention utilizes a solution hydrolysis coating method to combine the passivation layer and surface coating steps, simultaneously removing the lithium carbonate passivation layer and forming a surface aluminum oxide coating, thereby ensuring the stability of the LLZTO ceramic filler when stored in air.

Description

Technical Field

[0001] The present invention relates to the field of battery and energy technology, and in particular to a method and application of removing and coating a passivation layer on the surface of an LLZO solid electrolyte. Background Art

[0002] Lithium lanthanum zirconium oxide Li7La3Zr2O 12 (LLZO) type solid electrolyte powders are often used as fillers and composited with polymer electrolytes to prepare composite solid electrolytes (CSEs) materials with good electrochemical and mechanical properties.

[0003] However, years of research have revealed that LLZO-based solid electrolytes (including their various doping systems) exhibit poor stability in aqueous air. They easily react with water and carbon dioxide in the air during transport to form a passivation layer of lithium carbonate and lithium hydroxide. This passivation layer formation reaction is more pronounced in nanopowder materials with high surface area. Furthermore, the presence of ionically insulating and lithiophobic lithium carbonate impurities has been shown to significantly reduce the ionic conductivity of LLZO-based composite electrolytes, while also diminishing interfacial stability in both symmetrical and full cells.

[0004] However, there are currently few methods for addressing the problem of lithium carbonate growth on the surface of LLZO ceramic fillers. Most methods use traditional methods such as acid treatment or high-temperature heat treatment, which are energy-intensive and have limited effectiveness. They cannot permanently solve the problem of lithium carbonate growth on the LLZO surface, thus greatly hindering the actual production and use of LLZO ceramic fillers in composite solid-state electrolytes and the development of high-performance LLZO composite electrolytes. In addition, existing LLZO surface coating technologies often use sol-gel methods, which are relatively complex and cannot simultaneously remove the passivation layer on the surface of LLZO particles unless a surface treatment step is performed in advance.

[0005] Therefore, the existing technology still needs to be improved and developed. Summary of the Invention

[0006] In view of the above-mentioned deficiencies in the prior art, the purpose of the present invention is to provide a method and application for removing and coating the surface passivation layer of an LLZO-type solid electrolyte, aiming to solve the problems in the prior art that the LLZO system electrolyte is unstable in the air, impurities exist on the surface that affect the ionic conductivity, and it is impossible to achieve coating while removing the passivation layer.

[0007] The technical solutions of the present invention are as follows:

[0008] A method for removing and coating a passivation layer on the surface of an LLZO solid electrolyte comprises the following steps:

[0009] Prepare ammonium formate solution;

[0010] LLZTO@Li2CO3 powder is uniformly dispersed in the ammonium formate solution to obtain a dispersion, and then subjected to heat preservation treatment;

[0011] adjusting the pH value of the dispersion using formic acid;

[0012] Aluminum sulfate was added to the pH-adjusted dispersion and stirred at a constant temperature to obtain LLZTO@Al(OH)3 particles;

[0013] The LLZTO@Al(OH)3 particles are centrifugally washed, dried, and sintered to obtain LLZTO@Al2O3 powder.

[0014] The method for removing and coating the surface passivation layer of the LLZO solid electrolyte, wherein the step of preparing the ammonium formate solution specifically comprises:

[0015] Dissolve ammonium formate in deionized water and stir thoroughly to obtain an ammonium formate solution with a concentration of 0.1-0.3 mol / L.

[0016] The method for removing and coating the surface passivation layer of the LLZO-type solid electrolyte, wherein the mass of the LLZTO@Li2CO3 powder in the ammonium formate solution accounts for 1-2 g / L.

[0017] The method for removing and coating the surface passivation layer of the LLZO solid electrolyte, wherein the heat preservation treatment is oil bath heat preservation at 60-80°C.

[0018] In the method for removing and coating the surface passivation layer of the LLZO solid electrolyte, the pH value of the dispersion is between 4.2 and 4.6.

[0019] The method for removing and coating the surface passivation layer of the LLZO solid electrolyte, wherein the drying condition is at a temperature of 70-90°C for 5-7 hours; the sintering condition is at 300-650°C for 2-4 hours.

[0020] An application of the above-mentioned method for removing and coating the passivation layer on the surface of an LLZO-type solid electrolyte, wherein the method is used for preparing a composite solid electrolyte.

[0021] The application of the method for removing and coating the surface passivation layer of the LLZO-type solid electrolyte, wherein the preparation of the composite solid electrolyte specifically includes the steps of:

[0022] The LLZTO@Al2O3 powder prepared by the above-mentioned method of removing and coating the passivation layer on the surface of the LLZO-type solid electrolyte is ground;

[0023] Then, it is compounded with polymer electrolyte, lithium salt and ionic liquid to obtain a uniform slurry;

[0024] The slurry is prepared by a casting method to obtain the composite solid electrolyte.

[0025] The application of the method for removing and coating the surface passivation layer of the LLZO-type solid electrolyte, wherein the polymer electrolyte is selected from one of PEO, PVDF, PAN, and PPC.

[0026] The application of the method for removing and coating the surface passivation layer of the LLZO-type solid electrolyte, wherein the lithium salt is selected from one of LiClO4, LiTFSI, and LiFSI; and the ionic liquid is selected from one of BMIMTFSI and EMIMTFSI.

[0027] Beneficial Effects: The present invention provides a method and application for removing and coating the surface passivation layer of an LLZO-type solid electrolyte. The method comprises the following steps: preparing an ammonium formate solution; uniformly dispersing LLZTO@Li2CO3 powder in the ammonium formate solution to obtain a dispersion, and then heat-insulating the dispersion; adjusting the pH of the dispersion using formic acid; adding aluminum sulfate to the pH-adjusted dispersion and stirring at a constant temperature to obtain LLZTO@Al(OH)3 particles; and centrifugally washing, drying, and sintering the LLZTO@Al(OH)3 particles to obtain LLZTO@Al2O3 powder. The present invention utilizes a solution hydrolysis coating method to combine the passivation layer and surface coating steps into one, simultaneously removing the lithium carbonate passivation layer and forming a surface aluminum oxide coating, thereby ensuring the stability of the LLZTO ceramic filler when stored in air. Furthermore, the coating improves the stability of the LLZO and its doping system in air, isolating it from water and carbon dioxide, and effectively preventing the re-generation of surface impurities even during high-temperature heat treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a process flow chart of a method for removing and coating a passivation layer on the surface of an LLZO solid electrolyte according to the present invention;

[0029] Figure 2 The XRD patterns and infrared spectrum comparison of the LLZTO particles before and after coating and heat treatment are shown in the figure.

[0030] Figure 3 This is a comparison chart of the impedance of the composite solid electrolyte with LLZTO as filler before and after the LLZTO particles are coated with alumina;

[0031] Figure 4This is a comparison of the XRD patterns of the LLZTO filler before and after the LLZTO particles are coated with alumina and after high-temperature heat treatment. DETAILED DESCRIPTION

[0032] The present invention provides a method and application for removing and coating the surface passivation layer of an LLZO-type solid electrolyte. To clarify the objectives, technical solutions, and effects of the present invention, the present invention is described in further detail below. It should be understood that the specific embodiments described herein are intended only to illustrate the present invention and are not intended to limit the present invention.

[0033] like Figure 1 As shown, the present invention provides a method for removing and coating the passivation layer on the surface of an LLZO-type solid electrolyte, which specifically includes the steps of:

[0034] Step S10: preparing an ammonium formate solution;

[0035] Step S20: uniformly dispersing LLZTO@Li2CO3 powder in the ammonium formate solution to obtain a dispersion, and performing heat preservation treatment;

[0036] Step S30: adjusting the pH value of the dispersion using formic acid;

[0037] Step S40: adding aluminum sulfate to the pH-adjusted dispersion, and stirring at a constant temperature to obtain LLZTO@Al(OH)3 particles;

[0038] Step S50: centrifugally washing, drying, and sintering the LLZTO@Al(OH)3 particles to obtain LLZTO@Al2O3 powder.

[0039] In the present invention, the solution hydrolysis coating method is used to remove the passivation layer on the surface of the LLZO type solid electrolyte and generate an alumina coating layer to ensure the stability of the solid electrolyte when stored in air. The ammonium formate solution is mixed with the LLZTO@Li2CO3 powder and then heat-treated. The pH value of the dispersion is adjusted by formic acid to achieve LLZTO (Li 6.4 La3Zr 1.4 Ta 0.6 O 12) particles; then, aluminum sulfate was added to the pH-adjusted dispersion to obtain LLZTO@Al(OH)3 particles with varying coating thicknesses; the LLZTO@Al(OH)3 particles were centrifugally washed and dried to obtain LLZTO@Al(OH)3 powders; and finally, sintering was performed to thermally decompose the aluminum hydroxide on the surface of the LLZTO particles, producing LLZTO@Al2O3 powders coated with an aluminum oxide coating. This coating significantly improved the ionic conductivity of the electrolyte containing LLZTO, from 0.49×10 -4 S cm -1 Increased to 1.24×10 -4 S cm- 1 ; It can also play the role of isolating air, so it can completely solve the problem of LLZO phase instability when stored in air. Even after another high-temperature (300°C) heat treatment, the phase remains stable and no lithium carbonate impurities are produced. However, the fresh LLZTO sample that has not been coated shows an obvious peak of lithium carbonate impurities after high-temperature treatment at 300°C.

[0040] In some embodiments, the step S10 of preparing the ammonium formate solution specifically includes: dissolving ammonium formate in deionized water and stirring thoroughly to obtain an ammonium formate solution with a concentration of 0.1-0.3 mol / L. Preferably, in this embodiment, the concentration of the ammonium formate solution is 0.2 mol / L.

[0041] In some embodiments, the mass of the LLZTO@Li2CO3 powder added to the ammonium formate solution in step S20 is 1-2 g / L. The solution is then treated in an oil bath at 60-80°C. This oil bath maintains a more uniform temperature in the dispersion, making it less likely that the center temperature will be lower than the edge temperature, thus facilitating the removal of the passivation layer.

[0042] In some embodiments, formic acid is used as an acid-base regulator to adjust the pH value of the dispersion to between 4.2 and 4.6 and maintain stability. During this process, the lithium carbonate passivation layer on the surface of the LLZTO particles can be effectively removed, thereby improving the ionic conductivity of the electrolyte with LLZTO as a filler, while improving the interface stability in symmetric cells and full cells.

[0043] Specifically, when the pH value of the dispersion is adjusted to 4.4 using the formic acid and kept stable, the removal efficiency of the passivation layer reaches the highest, thus saving process time to a great extent.

[0044] In some embodiments, after aluminum sulfate is added to the dispersion in step S40, constant temperature stirring is performed for 0.5-2 hours, so that the surface of the LLZTO particles after the passivation layer is removed is coated with aluminum hydroxide, resulting in LLZTO@Al(OH)3 particles with varying coating thicknesses. Finally, under the action of sintering, the aluminum hydroxide coated on the surface of the LLZTO particles undergoes thermal decomposition to obtain LLZTO particles coated with aluminum oxide. At this time, the aluminum oxide on the surface of the LLZTO particles forms a coating layer that acts as an air barrier, solving the problem of LLZO phase instability when stored in air. The mass of the aluminum sulfate added is 1.2-1.6 times the mass of the LLZTO@Li2CO3 powder; preferably, the mass of the aluminum sulfate added is 1.5 times the mass of the LLZTO@Li2CO3 powder.

[0045] In some embodiments, the drying condition of the LLZTO@Al(OH)3 particles in step S50 is 70-90°C for 5-7 hours; and the sintering condition is 300-650°C for 2-4 hours.

[0046] Specifically, the coated LLZTO@Al(OH)3 particles were centrifugally washed and dried at 80°C for 6 hours to finally obtain LLZTO@Al(OH)3 powder. The powder was then sintered at 400°C for 2 hours. The aluminum hydroxide was thermally decomposed, leaving a layer of aluminum oxide on the surface of the LLZTO particles to form an aluminum oxide coating layer, that is, LLZTO@Al2O3 powder was obtained after sintering.

[0047] In this embodiment, aluminum sulfate is in situ hydrolyzed in a formic acid / ammonium formate buffer solution to hydrolyze and coat the surface of LLZO nanoparticles stored in the air. During the process of uniformly dispersing the LLZTO particles in the acidic solution and stirring, the lithium carbonate / aluminum hydroxide impurities on the LLZTO surface react with the formic acid, thereby effectively removing the passivation layer on the surface of the LLZTO particles. The chemical reaction equation is as follows:

[0048] HCOOH+Li2CO3→2LiCOOH+CO2+H2O

[0049] Subsequently, aluminum sulfate is added to the LLZTO dispersion, where aluminum ions hydrolyze in situ on the LLZTO surface to form an amphoteric hydroxide coating. The thickness of the coating can be controlled by controlling the in-situ hydrolysis time. After heat treatment, the aluminum hydroxide decomposes to form a stable aluminum oxide layer, which comes into direct contact with the LLZTO. During heating and subsequent electrochemical cycling, lithium volatilizes and diffuses into the aluminum oxide, converting it into the fast-conducting LiAlO2.

[0050] The present invention replaces the original ion-insulating lithium carbonate and lithium hydroxide passivation layer with a lithium ion conductor coating layer after a simple in-situ hydrolysis coating step. After the modification and coating, the ionic conductivity of the electrolyte with LLZTO as the filler can be significantly improved from 0.49×10-4S cm before modification. -1 Increased to 1.24×10-4S cm -1 Furthermore, the coating layer can also act as an air barrier, thus completely resolving the problem of LLZO phase instability when stored in air. Even after heat treatment at 300°C, the phase remains stable and no lithium carbonate impurities are generated. Compared with the uncoated fresh LLZTO sample, a clear peak of lithium carbonate impurities appears after high-temperature treatment at 300°C.

[0051] In some embodiments, the method for removing and coating the surface passivation layer of the LLZO solid electrolyte described in the present invention is not only applicable to tantalum-doped LLZO electrolyte materials, but is also applicable to LLZO electrolyte materials doped with other doping elements, and the doping elements include but are not limited to Ca, Ga, Ta, Fe, Nb, Ti, Sb, Mg, Zn and other elements at different doping sites.

[0052] In some embodiments, in addition to in-situ coating of a synthetic alumina coating layer, the coating layer can also be formed using the same in-situ hydrolysis method with various metal oxide materials such as Ca, Mg, Zn, Fe and Cu. It is only necessary to adjust the pH value of the buffer solution to the value at which the corresponding different metal elements undergo hydrolysis after removing the passivation layer, so as to achieve the same lithium carbonate removal and oxide coating effects.

[0053] The present invention combines two surface modification methods, namely, removal of the passivation layer and surface coating, to achieve the removal of the passivation layer on the surface of LLZTO particles and the conversion of the lithium conductive layer into a lithium conductive layer in a one-step in-situ coating process. This simplifies the process of preparing LLZTO@Al2O3 powder, reduces operating costs, and ultimately improves the ionic conductivity of the composite electrolyte filled with LLZTO and its stability during storage or transportation in air.

[0054] Compared to the traditional method of removing lithium carbonate from the surface of LLZO and its doping system by acid treatment, the present invention uses a hydrolysis in-situ coating method, which effectively utilizes the reaction between the impurities on the surface of the LLZTO particles and the formic acid buffer in the early stage of coating to remove the surface lithium hydroxide and lithium carbonate passivation layer, and then coats the surface of the treated LLZTO particles to obtain aluminum oxide, which not only eliminates its contact with air. In addition, aluminum oxide is easily lithiated by the lithium element volatilized from LLZTO during the heat treatment process and converted into a lithium-containing oxide. The lithium-containing oxide often has a high lithium ion conductivity. Therefore, the removal and coating method of the LLZO-type solid electrolyte surface passivation layer used in the present invention can ultimately realize the conversion of lithium ion insulating layers such as lithium carbonate into a fast lithium conductive intermediate layer, thereby improving the lithium conductivity at the organic-inorganic interface in the composite electrolyte and between LLZTO particles. In addition, the coating layer can also improve the stability of LLZO and its doping system in the air, isolate water and carbon dioxide in the air, and effectively prevent the re-generation of surface impurities even during high-temperature heat treatment.

[0055] In addition, the present invention also provides an application of the method for removing and coating the surface passivation layer of the LLZO-type solid electrolyte, and the method for removing and coating the surface passivation layer of the LLZO-type solid electrolyte is used to prepare a composite solid electrolyte.

[0056] The preparation of the composite solid electrolyte specifically includes the following steps:

[0057] Step S1: grinding the LLZTO@Al2O3 powder prepared by the method for removing and coating the surface passivation layer of the LLZO-type solid electrolyte;

[0058] Step S2: then compounding with polymer electrolyte, lithium salt and ionic liquid to obtain a uniform slurry;

[0059] Step S3: The slurry is prepared by a casting method to obtain the composite solid electrolyte.

[0060] In some embodiments: the polymer electrolyte is selected from one of PEO (Polyethylene oxide), PVDF (Poly (vinylidene fluoride), polyvinylidene fluoride), PAN (Polyacrylonitrile), and PPC (Polypropylene carbonate); the lithium salt is selected from one of LiClO4, LiTFSI (Lithium Bis (trifluoromethanesulphonyl) imide, and LiFSI (Lithium Bis (fluorosulfonyl) imide). The ionic liquid is selected from one of BMIMTFSI (1-butyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide) and EMIMTFSI (1-ethyl-3-methylimidazoline bis (trifluoromethylsulfonyl) imide).

[0061] Specifically, taking the preparation of a PEO-based composite solid electrolyte as an example, the steps include:

[0062] 10% of the PEO weight ratio of the coated modified LLZTO powder and 0.24g LiTFSI, 440μL ionic liquid (BMIMTFSI) were added to 25g anhydrous acetonitrile (ACN) and ultrasonically dispersed;

[0063] After ultrasonic dispersion, 1 g of PEO (Mw = 600,000) was added and magnetic stirring was performed for 6-8 h to obtain a uniform slurry;

[0064] The slurry was poured into a circular polytetrafluoroethylene mold and then dried in a vacuum oven at 60° C. to remove the residual solvent, thereby obtaining a uniform composite electrolyte film.

[0065] The present invention is further described below with reference to the following examples. It should also be understood that the following examples are only used to further illustrate the present invention and are not to be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above contents of the present invention fall within the scope of protection of the present invention.

[0066] Example 1

[0067] Preparation of LLZTO@Al2O3 powder specifically includes the following steps:

[0068] Dissolve 5.045 g of ammonium formate in 400 ml of deionized water to prepare a 0.2 mol / L ammonium formate solution.

[0069] 0.44g of LLZTO@Li2CO3 powder was added to an ammonium formate solution and ultrasonically dispersed to obtain a uniform dispersion. The dispersion was then kept in an oil bath at 70°C. Formic acid was used as an acid-base regulator to adjust the pH of the dispersion to 4.4 and maintain a stable pH. During this process, the lithium carbonate passivation layer on the surface of the LLZTO particles was effectively removed.

[0070] Weigh 0.6 g of aluminum sulfate and add it to the dispersion, and stir it at a constant temperature for 0.5-2 h to obtain LLZTO@Al(OH)3 particles with different coating thicknesses;

[0071] After coating, LLZTO@Al(OH)3 powder was obtained by centrifugation, washing and drying at 80 °C for 6 h;

[0072] LLZTO@Al(OH)3 powder was sintered at 400℃ for 2h to obtain LLZTO@Al2O3 powder.

[0073] In this embodiment, aluminum sulfate is added to the LLZTO dispersion, and aluminum ions are in situ hydrolyzed on the LLZTO surface to form an amphoteric hydroxide coating layer. The thickness of the coating layer can be controlled by controlling the in situ hydrolysis time.

[0074] Powder XRD and infrared spectra before and after coating and heat treatment Figure 2 As shown in the figure, the infrared and XRD peak intensities of lithium carbonate on the surface of LLZO powder after in situ coating are significantly weakened, and no impurity peaks are generated, indicating that the formic acid solution can fully remove lithium carbonate impurities.

[0075] After heat treatment, Figure 2 Mid-infrared spectroscopy shows that aluminum hydroxide decomposes to form stable aluminum oxide (1100 cm -1 and 1575cm -1 This layer of aluminum oxide is in direct contact with LLZTO. During heating and subsequent electrochemical cycles, the lithium element will first enter the aluminum oxide and be converted into the fast conductor LiAlO2 due to volatilization and diffusion.

[0076] In this embodiment, the original ion-insulating lithium carbonate and lithium hydroxide passivation layers are replaced with lithium ion conductor coating layers after a simple in-situ hydrolysis coating step. After modification and coating, the ionic conductivity of the electrolyte filled with LLZTO can be significantly improved from 0.49×10 -4 S cm -1 Increased to 1.24×10 -4 S cm -1 (like Figure 3 shown).

[0077] In addition, Figure 4As shown in the figure, the coating layer can also play the role of isolating the air, so it can completely solve the problem of unstable LLZO phase in air storage. Even after another high-temperature heat treatment at 300°C, the phase remains stable and no lithium carbonate impurities are produced. Compared with the uncoated fresh LLZTO sample, an obvious peak of lithium carbonate impurities appears after high-temperature treatment at 300°C.

[0078] In summary, the present invention provides a method and application for removing and coating the surface passivation layer of an LLZO-type solid electrolyte. The method comprises the following steps: preparing an ammonium formate solution; uniformly dispersing LLZTO@Li2CO3 powder in the ammonium formate solution to obtain a dispersion, which is then insulated; adjusting the pH of the dispersion using formic acid; adding aluminum sulfate to the pH-adjusted dispersion and stirring at a constant temperature to obtain LLZTO@Al(OH)3 particles; and centrifugally washing, drying, and sintering the LLZTO@Al(OH)3 particles to obtain LLZTO@Al2O3 powder. The present invention utilizes a solution hydrolysis coating method to combine the passivation layer and surface coating steps, simultaneously removing the lithium carbonate passivation layer and forming a surface aluminum oxide coating, thereby ensuring the stability of the LLZTO ceramic filler when stored in air. Furthermore, the coating improves the stability of the LLZO and its doping system in air, isolating it from water and carbon dioxide, and effectively preventing the re-generation of surface impurities even during high-temperature heat treatment.

[0079] It should be understood that the application of the present invention is not limited to the above examples. For those skilled in the art, improvements or changes can be made based on the above description. All these improvements and changes should fall within the scope of protection of the claims attached to the present invention.

Claims

1. A method for removing and coating the surface passivation layer of an LLZO solid electrolyte, characterized in that: Including steps: Prepare an ammonium formate solution; the concentration of the ammonium formate solution is 0.1-0.3 mol / L; LLZTO@Li2CO3 powder is uniformly dispersed in the ammonium formate solution to obtain a dispersion, and then subjected to heat preservation treatment; Adjusting the pH value of the dispersion to between 4.2 and 4.6 using formic acid; Aluminum sulfate was added to the pH-adjusted dispersion and stirred at a constant temperature for 0.5-2 h to obtain LLZTO@Al(OH)3 particles; The LLZTO@Al(OH)3 particles are centrifugally washed, dried, and sintered to obtain LLZTO@Al2O3 powder; The mass of the LLZTO@Li2CO3 powder in the ammonium formate solution is 1-2 g / L; the drying conditions are 70-90°C for 5-7 hours; the sintering conditions are 300-650°C for 2-4 hours; and the amount of aluminum sulfate added is 1.2-1.6 times the mass of the LLZTO@Li2CO3 powder.

2. The method for removing and coating the surface passivation layer of the LLZO type solid electrolyte according to claim 1, characterized in that: The steps of configuring the ammonium formate solution specifically include: Dissolve ammonium formate in deionized water and stir thoroughly to obtain an ammonium formate solution with a concentration of 0.1-0.3 mol / L.

3. The method for removing and coating the surface passivation layer of the LLZO type solid electrolyte according to claim 1, characterized in that: The heat preservation treatment is carried out in an oil bath at 60-80°C.

4. An application of the method for removing and coating the surface passivation layer of the LLZO solid electrolyte according to any one of claims 1 to 3, characterized in that: The method for removing and coating the surface passivation layer of the LLZO-type solid electrolyte is used to prepare a composite solid electrolyte.

5. Application of the method for removing and coating the surface passivation layer of the LLZO type solid electrolyte according to claim 4, characterized in that: The preparation of the composite solid electrolyte specifically includes the following steps: Grinding the LLZTO@Al2O3 powder prepared by the method for removing and coating the surface passivation layer of the LLZO-type solid electrolyte according to any one of claims 1 to 3; Then, it is compounded with polymer electrolyte, lithium salt and ionic liquid to obtain a uniform slurry; The slurry is prepared by a casting method to obtain the composite solid electrolyte.

6. Application of the method for removing and coating the surface passivation layer of the LLZO type solid electrolyte according to claim 5, characterized in that: The polymer electrolyte is selected from one of PEO, PVDF, PAN and PPC.

7. Application of the method for removing and coating the surface passivation layer of the LLZO solid electrolyte according to claim 5, characterized in that: The lithium salt is selected from one of LiClO4, LiTFSI, and LiFSI; and the ionic liquid is selected from one of BMIMTFSI and EMIMTFSI.

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