LLZO composite solid electrolyte and preparation method and application thereof

Abstract

The invention discloses an LLZO composite solid electrolyte and a preparation method and application thereof.The LLZO composite solid electrolyte is obtained by mixing lithium hydroxide, lanthanum oxide, zirconium oxychloride and tantalum pentoxide and then sequentially conducting pH adjustment, centrifugal separation, calcination and atom deposition, the LLZO composite solid electrolyte is high in interface chemical stability and ion transmission efficiency, and the performance of the LLZO composite solid electrolyte is improved. When the prepared electrolyte membrane and the prepared negative plate are applied to a lithium battery, the lithium battery can obtain excellent electrochemical performance.

Description

Technical Field

[0001] This invention relates to the field of solid-state battery technology, and in particular to an LLZO composite solid-state electrolyte, its preparation method, and its application. Background Technology

[0002] Solid-state batteries are considered the core of next-generation energy storage technology due to their high safety and energy density, while oxide-based solid electrolytes have become a research hotspot due to their excellent thermal stability and wide electrochemical window. However, existing technologies still face three major challenges: high interfacial impedance, low room temperature ionic conductivity, and difficulties in large-scale preparation, which seriously restrict their commercialization process.

[0003] At the materials level, traditional oxide electrolytes require high-temperature sintering (>1000℃) to achieve densification. However, under high-temperature conditions, lithium volatilization is easily caused, leading to grain boundary defects and reducing ionic conductivity to <10. -4 S / cm. Furthermore, oxides have high rigidity, resulting in poor physical contact with the electrodes, and interfacial impedance often exceeds 100 Ω·cm. 2 This leads to increased battery polarization and decreased cycle life. Meanwhile, at the process level, the film-forming technology for oxide electrolytes is not yet mature. Traditional methods such as tape casting and dry pressing are insufficient to prepare ultra-thin and crack-free electrolyte layers, while advanced pulsed laser deposition or magnetron sputtering are too expensive to meet the demands of large-scale production. Furthermore, oxides are sensitive to moisture, requiring strict environmental control, which further increases manufacturing costs. Therefore, it is necessary to propose a new solution to address these problems. Summary of the Invention

[0004] In view of this, the present invention addresses the deficiencies of the existing technology, and its main objective is to provide an LLZO composite solid electrolyte, its preparation method and application, which effectively solves the problems of low ionic conductivity and high interfacial impedance of existing solid electrolytes.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for preparing an LLZO composite solid electrolyte includes the following steps:

[0007] (1) Lithium hydroxide, lanthanum oxide, zirconium oxychloride and tantalum pentoxide were added to deionized water in a molar ratio of 6.8:1.5:1.4:0.3, and magnetic stirring and ultrasonic treatment were performed simultaneously for 30 min to obtain a mixed solution.

[0008] (2) Adjust the pH of the mixed solution obtained in step (1) to 11-13. After adjustment, heat to 195-205℃ and react for 12-48h. After the reaction is completed, cool naturally to room temperature to obtain the reaction solution.

[0009] (3) Centrifuge the reaction solution obtained in step (2), remove the lower layer solid, wash the obtained solid with deionized water and anhydrous ethanol alternately 3-5 times, and then put it into a constant temperature drying oven to dry for 12 hours at a drying temperature of 80℃ to obtain LLZO precursor powder.

[0010] (4) The LLZO precursor powder obtained in step (3) is calcined at 700-900℃ for 2-4 hours, and then naturally cooled to room temperature. It is then ground with a planetary ball mill for 2 hours to obtain cubic phase LLZO with a particle size of 50-100nm.

[0011] (5) Using lithium tert-butoxide and trimethyl phosphate as precursors, the surface of the cubic phase LLZO obtained in step (4) is coated with a Li3PO4 layer by atomic layer deposition to form a core-shell structure and obtain an LLZO composite solid electrolyte.

[0012] As a preferred embodiment, in step (1), the lithium hydroxide is LiOH·H2O and the zirconium oxychloride is ZrOCl2·8H2O.

[0013] As a preferred embodiment, in step (1), the rotation speed of the magnetic stirring is 500 rpm, and the frequency of the ultrasonic treatment is 40 kHz.

[0014] As a preferred embodiment, in step (3), the centrifugal separation speed is 8000 rpm.

[0015] As a preferred embodiment, in step (5), the thickness of the Li3PO4 layer is 2-5 nm.

[0016] An LLZO composite solid electrolyte is prepared by the aforementioned method for preparing LLZO composite solid electrolyte.

[0017] A composite electrolyte membrane is prepared by the following steps: First, a binder, an ionic liquid, and the aforementioned LLZO composite solid electrolyte are mixed together to obtain a mixture, wherein the weight ratio of the binder, ionic liquid, and LLZO composite solid electrolyte is 1:1:8; then, the temperature is increased to 200°C at a heating rate of 1-5°C / min, and a pressure of 5-10 MPa is applied, and the temperature and pressure are maintained for 10 min; next, the temperature is increased to 400°C at a heating rate of 1-5°C / min, and a pressure of 15-20 MPa is applied, and the temperature and pressure are maintained for 10 min; then, the temperature is increased to 600°C at a heating rate of 1-5°C / min, and a pressure of 5 MPa is applied, and the temperature and pressure are maintained for 10 min; finally, the temperature is decreased to room temperature at a cooling rate of 2-5°C / min to obtain the composite electrolyte membrane; the binder is PDVF.

[0018] A negative electrode includes a lithium foil, a buffer layer, and the aforementioned electrolyte membrane, wherein the buffer layer is stacked on the surface of the lithium foil and the electrolyte membrane is stacked on the buffer layer.

[0019] As a preferred embodiment, the thickness of the buffer layer is 10 nm.

[0020] As a preferred embodiment, the buffer layer is made of alumina and is prepared by the following method: using trimethylaluminum and water as precursors, alumina is deposited on the surface of lithium foil by atomic layer deposition at a deposition temperature of 150°C.

[0021] Compared with the prior art, the present invention has obvious advantages and beneficial effects. Specifically, as can be seen from the above technical solution:

[0022] By coating the surface of cubic LLZO with a Li3PO4 layer to form a core-shell structure, the interfacial chemical stability and ion transport efficiency are simultaneously improved, the interfacial resistance is reduced, and the cycle life of the battery is effectively extended. In addition, the gradient low temperature hot pressing process avoids lithium volatilization, and the nanoparticles are densified without the formation of grain boundary defects, effectively preventing the reduction of ionic conductivity.

[0023] To more clearly illustrate the structural features and effects of the present invention, the present invention will be described in detail below with reference to specific embodiments. Detailed Implementation

[0024] This invention discloses a method for preparing an LLZO composite solid electrolyte, which includes the following steps:

[0025] (1) Lithium hydroxide, lanthanum oxide, zirconium oxychloride and tantalum pentoxide were added to deionized water in a molar ratio of 6.8:1.5:1.4:0.3, and magnetic stirring and ultrasonic treatment were performed simultaneously for 30 min to obtain a mixed solution; wherein, the lithium hydroxide was LiOH·H2O, the zirconium oxychloride was ZrOCl2·8H2O; the magnetic stirring speed was 500 rpm, and the ultrasonic treatment frequency was 40 kHz.

[0026] (2) Adjust the pH of the mixed solution obtained in step (1) to 11-13. After adjustment, heat to 195-205℃ and react for 12-48h. After the reaction is completed, cool naturally to room temperature to obtain the reaction solution.

[0027] (3) Centrifuge the reaction solution obtained in step (2), remove the lower layer of solid, wash the obtained solid with deionized water and anhydrous ethanol alternately 3-5 times, and then put it into a constant temperature drying oven to dry for 12 hours at a drying temperature of 80°C to obtain LLZO precursor powder; the centrifugation speed is 8000 rpm.

[0028] (4) The LLZO precursor powder obtained in step (3) is calcined at 700-900℃ for 2-4h, and after naturally cooling to room temperature, it is ground with a planetary ball mill for 2h to obtain cubic phase LLZO with a particle size of 50-100nm; the thickness of the Li3PO4 layer is 2-5nm.

[0029] (5) Using lithium tert-butoxide and trimethyl phosphate as precursors, the surface of the cubic phase LLZO obtained in step (4) is coated with a Li3PO4 layer by atomic layer deposition to form a core-shell structure and obtain an LLZO composite solid electrolyte.

[0030] This invention also discloses a composite electrolyte membrane, prepared by the following steps: First, a binder, an ionic liquid, and the aforementioned LLZO composite solid electrolyte are mixed together to obtain a mixture, wherein the weight ratio of the binder, ionic liquid, and LLZO composite solid electrolyte is 1:1:8; then, the temperature is increased to 200°C at a heating rate of 1-5°C / min, and a pressure of 5-10 MPa is applied, and the temperature and pressure are maintained for 10 min; next, the temperature is increased to 400°C at a heating rate of 1-5°C / min, and a pressure of 15-20 MPa is applied, and the temperature and pressure are maintained for 10 min; then, the temperature is increased to 600°C at a heating rate of 1-5°C / min, and a pressure of 5 MPa is applied, and the temperature and pressure are maintained for 10 min; finally, the temperature is decreased to room temperature at a cooling rate of 2-5°C / min to obtain the composite electrolyte membrane.

[0031] The present invention also discloses a negative electrode sheet comprising a lithium foil, a buffer layer, and the aforementioned electrolyte membrane, wherein the buffer layer is stacked on the surface of the lithium foil and the electrolyte membrane is stacked on the buffer layer; the thickness of the buffer layer is 10 nm and the buffer layer is made of aluminum oxide, and the buffer layer is prepared by means of trimethylaluminum and water as precursors, and aluminum oxide is deposited on the surface of the lithium foil by atomic layer deposition at a deposition temperature of 150°C.

[0032] The following detailed description is based on several embodiments.

[0033] Example 1

[0034] (1) Lithium hydroxide, lanthanum oxide, zirconium oxychloride and tantalum pentoxide were added to deionized water in a molar ratio of 6.8:1.5:1.4:0.3, and magnetic stirring and ultrasonic treatment were performed simultaneously for 30 min to obtain a mixed solution; wherein, the lithium hydroxide was LiOH·H2O, the zirconium oxychloride was ZrOCl2·8H2O; the magnetic stirring speed was 500 rpm, and the ultrasonic treatment frequency was 40 kHz.

[0035] (2) Adjust the pH of the mixed solution obtained in step (1) to 11. After adjustment, heat to 195℃ and react for 36 hours. After the reaction is completed, cool naturally to room temperature to obtain the reaction solution.

[0036] (3) The reaction solution obtained in step (2) is centrifuged to separate the solid layer. The solid is washed three times with deionized water and anhydrous ethanol, and then placed in a constant temperature drying oven to dry for 12 hours at a temperature of 80°C to obtain LLZO precursor powder. The centrifugation speed is 8000 rpm.

[0037] (4) The LLZO precursor powder obtained in step (3) is calcined at 800°C for 3 hours, and after naturally cooling to room temperature, it is ground with a planetary ball mill for 2 hours to obtain cubic phase LLZO with a particle size of 50-100 nm; the thickness of the Li3PO4 layer is 3 nm.

[0038] (5) Using lithium tert-butoxide and trimethyl phosphate as precursors, the surface of the cubic phase LLZO obtained in step (4) is coated with a Li3PO4 layer by atomic layer deposition to form a core-shell structure and obtain an LLZO composite solid electrolyte.

[0039] (6) First, the binder, ionic liquid and the aforementioned LLZO composite solid electrolyte are mixed together to obtain a mixture, wherein the weight ratio of the binder, ionic liquid and LLZO composite solid electrolyte is 1:1:8; then the temperature is increased to 200°C at a heating rate of 1°C / min and a pressure of 8MPa is applied, and the temperature and pressure are maintained for 10min; then the temperature is increased to 400°C at a heating rate of 5°C / min and a pressure of 15MPa is applied, and the temperature and pressure are maintained for 10min; then the temperature is increased to 600°C at a heating rate of 2°C / min and a pressure of 5MPa is applied, and the temperature and pressure are maintained for 10min; finally, the temperature is decreased to room temperature at a cooling rate of 4°C / min to obtain the composite electrolyte membrane.

[0040] (7) The composite electrolyte membrane obtained in step (6) is stacked on the lithium foil, and then a buffer layer is inserted between the lithium foil and the composite electrolyte membrane by atomic layer deposition using trimethylaluminum and water as precursors. The buffer layer is made of aluminum oxide and has a thickness of 10 nm to obtain the negative electrode.

[0041] Example 2

[0042] (1) Lithium hydroxide, lanthanum oxide, zirconium oxychloride and tantalum pentoxide were added to deionized water in a molar ratio of 6.8:1.5:1.4:0.3, and magnetic stirring and ultrasonic treatment were performed simultaneously for 30 min to obtain a mixed solution; wherein, the lithium hydroxide was LiOH·H2O, the zirconium oxychloride was ZrOCl2·8H2O; the magnetic stirring speed was 500 rpm, and the ultrasonic treatment frequency was 40 kHz.

[0043] (2) Adjust the pH of the mixed solution obtained in step (1) to 13. After adjustment, heat to 205℃ and react for 40h. After the reaction is completed, cool naturally to room temperature to obtain the reaction solution.

[0044] (3) The reaction solution obtained in step (2) is centrifuged to separate the solid layer. The solid is washed 5 times with deionized water and anhydrous ethanol, and then placed in a constant temperature drying oven to dry for 12 hours at a temperature of 80°C to obtain LLZO precursor powder. The centrifugation speed is 8000 rpm.

[0045] (4) The LLZO precursor powder obtained in step (3) is calcined at 700-900℃ for 4h, and after naturally cooling to room temperature, it is ground with a planetary ball mill for 2h to obtain cubic phase LLZO with a particle size of 50-100nm; the thickness of the Li3PO4 layer is 2nm.

[0046] (5) Using lithium tert-butoxide and trimethyl phosphate as precursors, the surface of the cubic phase LLZO obtained in step (4) is coated with a Li3PO4 layer by atomic layer deposition to form a core-shell structure and obtain an LLZO composite solid electrolyte.

[0047] (6) First, the binder, ionic liquid and the aforementioned LLZO composite solid electrolyte are mixed together to obtain a mixture, wherein the weight ratio of the binder, ionic liquid and LLZO composite solid electrolyte is 1:1:8; then the temperature is increased to 200°C at a heating rate of 5°C / min and a pressure of 5MPa is applied, and the temperature and pressure are maintained for 10min; then the temperature is increased to 400°C at a heating rate of 1°C / min and a pressure of 18MPa is applied, and the temperature and pressure are maintained for 10min; then the temperature is increased to 600°C at a heating rate of 4°C / min and a pressure of 5MPa is applied, and the temperature and pressure are maintained for 10min; finally, the temperature is decreased to room temperature at a cooling rate of 2°C / min to obtain the composite electrolyte membrane.

[0048] (7) The composite electrolyte membrane obtained in step (6) is stacked on the lithium foil, and then a buffer layer is inserted between the lithium foil and the composite electrolyte membrane by atomic layer deposition using trimethylaluminum and water as precursors. The buffer layer is made of aluminum oxide and has a thickness of 10 nm to obtain the negative electrode.

[0049] Example 3

[0050] (1) Lithium hydroxide, lanthanum oxide, zirconium oxychloride and tantalum pentoxide were added to deionized water in a molar ratio of 6.8:1.5:1.4:0.3, and magnetic stirring and ultrasonic treatment were performed simultaneously for 30 min to obtain a mixed solution; wherein, the lithium hydroxide was LiOH·H2O, the zirconium oxychloride was ZrOCl2·8H2O; the magnetic stirring speed was 500 rpm, and the ultrasonic treatment frequency was 40 kHz.

[0051] (2) Adjust the pH of the mixed solution obtained in step (1) to 12. After adjustment, heat to 200℃ and react for 12 hours. After the reaction is completed, cool naturally to room temperature to obtain the reaction solution.

[0052] (3) The reaction solution obtained in step (2) is centrifuged to separate the solid layer. The solid is washed three times with deionized water and anhydrous ethanol, and then placed in a constant temperature drying oven to dry for 12 hours at a temperature of 80°C to obtain LLZO precursor powder. The centrifugation speed is 8000 rpm.

[0053] (4) The LLZO precursor powder obtained in step (3) is calcined at 700°C for 2.5 h, naturally cooled to room temperature, and then ground with a planetary ball mill for 2 h to obtain cubic phase LLZO with a particle size of 50-100 nm; the thickness of the Li3PO4 layer is 5 nm.

[0054] (5) Using lithium tert-butoxide and trimethyl phosphate as precursors, the surface of the cubic phase LLZO obtained in step (4) is coated with a Li3PO4 layer by atomic layer deposition to form a core-shell structure and obtain an LLZO composite solid electrolyte.

[0055] (6) First, the binder, ionic liquid and the aforementioned LLZO composite solid electrolyte are mixed together to obtain a mixture, wherein the weight ratio of the binder, ionic liquid and LLZO composite solid electrolyte is 1:1:8; then the temperature is increased to 200°C at a heating rate of 3°C / min and a pressure of 10MPa is applied, and the temperature and pressure are maintained for 10min; then the temperature is increased to 400°C at a heating rate of 2°C / min and a pressure of 16MPa is applied, and the temperature and pressure are maintained for 10min; then the temperature is increased to 600°C at a heating rate of 4°C / min and a pressure of 5MPa is applied, and the temperature and pressure are maintained for 10min; finally, the temperature is decreased to room temperature at a cooling rate of 5°C / min to obtain the composite electrolyte membrane.

[0056] (7) The composite electrolyte membrane obtained in step (6) is stacked on the lithium foil, and then a buffer layer is inserted between the lithium foil and the composite electrolyte membrane by atomic layer deposition using trimethylaluminum and water as precursors. The buffer layer is made of aluminum oxide and has a thickness of 10 nm to obtain the negative electrode.

[0057] Example 4

[0058] (1) Lithium hydroxide, lanthanum oxide, zirconium oxychloride and tantalum pentoxide were added to deionized water in a molar ratio of 6.8:1.5:1.4:0.3, and magnetic stirring and ultrasonic treatment were performed simultaneously for 30 min to obtain a mixed solution; wherein, the lithium hydroxide was LiOH·H2O, the zirconium oxychloride was ZrOCl2·8H2O; the magnetic stirring speed was 500 rpm, and the ultrasonic treatment frequency was 40 kHz.

[0059] (2) Adjust the pH of the mixed solution obtained in step (1) to 12. After adjustment, heat to 200℃ and react for 48 hours. After the reaction is completed, cool naturally to room temperature to obtain the reaction solution.

[0060] (3) The reaction solution obtained in step (2) is centrifuged to separate the solid layer. The solid is washed 5 times with deionized water and anhydrous ethanol, and then placed in a constant temperature drying oven to dry for 12 hours at a temperature of 80°C to obtain LLZO precursor powder. The centrifugation speed is 8000 rpm.

[0061] (4) The LLZO precursor powder obtained in step (3) is calcined at 850°C for 4 hours, naturally cooled to room temperature, and then ground with a planetary ball mill for 2 hours to obtain cubic phase LLZO with a particle size of 50-100 nm; the thickness of the Li3PO4 layer is 5 nm.

[0062] (5) Using lithium tert-butoxide and trimethyl phosphate as precursors, the surface of the cubic phase LLZO obtained in step (4) is coated with a Li3PO4 layer by atomic layer deposition to form a core-shell structure and obtain an LLZO composite solid electrolyte.

[0063] (6) First, the binder, ionic liquid and the aforementioned LLZO composite solid electrolyte are mixed together to obtain a mixture, wherein the weight ratio of the binder, ionic liquid and LLZO composite solid electrolyte is 1:1:8; then the temperature is increased to 200°C at a heating rate of 3°C / min and a pressure of 9MPa is applied, and the temperature and pressure are maintained for 10min; then the temperature is increased to 400°C at a heating rate of 2°C / min and a pressure of 20MPa is applied, and the temperature and pressure are maintained for 10min; then the temperature is increased to 600°C at a heating rate of 1°C / min and a pressure of 5MPa is applied, and the temperature and pressure are maintained for 10min; finally, the temperature is decreased to room temperature at a cooling rate of 5°C / min to obtain the composite electrolyte membrane.

[0064] (7) The composite electrolyte membrane obtained in step (6) is stacked on the lithium foil, and then a buffer layer is inserted between the lithium foil and the composite electrolyte membrane by atomic layer deposition using trimethylaluminum and water as precursors. The buffer layer is made of aluminum oxide and has a thickness of 10 nm to obtain the negative electrode.

[0065] Example 5

[0066] (1) Lithium hydroxide, lanthanum oxide, zirconium oxychloride and tantalum pentoxide were added to deionized water in a molar ratio of 6.8:1.5:1.4:0.3, and magnetic stirring and ultrasonic treatment were performed simultaneously for 30 min to obtain a mixed solution; wherein, the lithium hydroxide was LiOH·H2O, the zirconium oxychloride was ZrOCl2·8H2O; the magnetic stirring speed was 500 rpm, and the ultrasonic treatment frequency was 40 kHz.

[0067] (2) Adjust the pH of the mixed solution obtained in step (1) to 11. After adjustment, heat to 195℃ and react for 36 hours. After the reaction is completed, cool naturally to room temperature to obtain the reaction solution.

[0068] (3) The reaction solution obtained in step (2) is centrifuged to separate the solid layer. The solid is washed three times with deionized water and anhydrous ethanol, and then placed in a constant temperature drying oven to dry for 12 hours at a temperature of 80°C to obtain LLZO precursor powder. The centrifugation speed is 8000 rpm.

[0069] (4) The LLZO precursor powder obtained in step (3) is calcined at 00℃ for 2h, naturally cooled to room temperature, and then ground with a planetary ball mill for 2h to obtain cubic phase LLZO with a particle size of 50-100nm; the thickness of the Li3PO4 layer is 4nm.

[0070] (5) Using lithium tert-butoxide and trimethyl phosphate as precursors, the surface of the cubic phase LLZO obtained in step (4) is coated with a Li3PO4 layer by atomic layer deposition to form a core-shell structure and obtain an LLZO composite solid electrolyte.

[0071] (6) First, the binder, ionic liquid and the aforementioned LLZO composite solid electrolyte are mixed together to obtain a mixture, wherein the weight ratio of the binder, ionic liquid and LLZO composite solid electrolyte is 1:1:8; then the temperature is increased to 200°C at a heating rate of 3°C / min and a pressure of 7MPa is applied, and the temperature and pressure are maintained for 10min; then the temperature is increased to 400°C at a heating rate of 3°C / min and a pressure of 17MPa is applied, and the temperature and pressure are maintained for 10min; then the temperature is increased to 600°C at a heating rate of 3°C / min and a pressure of 5MPa is applied, and the temperature and pressure are maintained for 10min; finally, the temperature is decreased to room temperature at a cooling rate of 3°C / min to obtain the composite electrolyte membrane.

[0072] (7) The composite electrolyte membrane obtained in step (6) is stacked on the lithium foil, and then a buffer layer is inserted between the lithium foil and the composite electrolyte membrane by atomic layer deposition using trimethylaluminum and water as precursors. The buffer layer is made of aluminum oxide and has a thickness of 10 nm to obtain the negative electrode.

[0073] Example 6

[0074] (1) Lithium hydroxide, lanthanum oxide, zirconium oxychloride and tantalum pentoxide were added to deionized water in a molar ratio of 6.8:1.5:1.4:0.3, and magnetic stirring and ultrasonic treatment were performed simultaneously for 30 min to obtain a mixed solution; wherein, the lithium hydroxide was LiOH·H2O, the zirconium oxychloride was ZrOCl2·8H2O; the magnetic stirring speed was 500 rpm, and the ultrasonic treatment frequency was 40 kHz.

[0075] (2) Adjust the pH of the mixed solution obtained in step (1) to 11-13. After adjustment, heat to 205℃ and react for 24 hours. After the reaction is completed, cool naturally to room temperature to obtain the reaction solution.

[0076] (3) The reaction solution obtained in step (2) is centrifuged to separate the solid layer. The solid is washed 5 times with deionized water and anhydrous ethanol, and then placed in a constant temperature drying oven to dry for 12 hours at a temperature of 80°C to obtain LLZO precursor powder. The centrifugation speed is 8000 rpm.

[0077] (4) The LLZO precursor powder obtained in step (3) is calcined at 900°C for 2 hours, and after naturally cooling to room temperature, it is ground with a planetary ball mill for 2 hours to obtain cubic phase LLZO with a particle size of 50-100 nm; the thickness of the Li3PO4 layer is 2-5 nm.

[0078] (5) Using lithium tert-butoxide and trimethyl phosphate as precursors, the surface of the cubic phase LLZO obtained in step (4) is coated with a Li3PO4 layer by atomic layer deposition to form a core-shell structure and obtain an LLZO composite solid electrolyte.

[0079] (6) First, the binder, ionic liquid and the aforementioned LLZO composite solid electrolyte are mixed together to obtain a mixture, wherein the weight ratio of the binder, ionic liquid and LLZO composite solid electrolyte is 1:1:8; then the temperature is increased to 200°C at a heating rate of 4°C / min and a pressure of 10 MPa is applied, and the temperature and pressure are maintained for 10 min; then the temperature is increased to 400°C at a heating rate of 5°C / min and a pressure of 20 MPa is applied, and the temperature and pressure are maintained for 10 min; then the temperature is increased to 600°C at a heating rate of 5°C / min and a pressure of 5 MPa is applied, and the temperature and pressure are maintained for 10 min; finally, the temperature is decreased to room temperature at a cooling rate of 5°C / min to obtain the composite electrolyte membrane.

[0080] (7) The composite electrolyte membrane obtained in step (6) is stacked on the lithium foil, and then a buffer layer is inserted between the lithium foil and the composite electrolyte membrane by atomic layer deposition using trimethylaluminum and water as precursors. The buffer layer is made of aluminum oxide and has a thickness of 10 nm to obtain the negative electrode.

[0081] The composite electrolyte membranes prepared in the above embodiments were tested for interfacial resistance, relative density and conductivity. The negative electrode sheets prepared in the above embodiments were tested for cycle performance. The test results are shown in Table 1.

[0082]

[0083] Table 1

[0084] The data above clearly demonstrate that the electrolyte membrane prepared by the method of this invention has a much lower interfacial resistance than traditional electrolyte membranes, a higher relative density (up to 96.3%), and a higher conductivity (up to 1.20 × 10⁻⁶). -3 S / cm 3 It is ten times that of traditional electrolyte membranes, and the negative electrode sheet made from it has excellent cycle performance.

[0085] The above description is merely a preferred embodiment of the present invention and does not constitute any limitation on the technical scope of the present invention. Therefore, any minor modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A method for preparing an LLZO composite solid electrolyte, characterized in that: It includes the following steps: (1) Lithium hydroxide, lanthanum oxide, zirconium oxychloride and tantalum pentoxide were added to deionized water in a molar ratio of 6.8:1.5:1.4:0.3, and magnetic stirring and ultrasonic treatment were performed simultaneously for 30 min to obtain a mixed solution. (2) Adjust the pH of the mixed solution obtained in step (1) to 11-13. After adjustment, heat to 195-205℃ and react for 12-48h. After the reaction is completed, cool naturally to room temperature to obtain the reaction solution. (3) Centrifuge the reaction solution obtained in step (2), remove the lower layer solid, wash the obtained solid with deionized water and anhydrous ethanol alternately 3-5 times, and then put it into a constant temperature drying oven to dry for 12 hours at a drying temperature of 80℃ to obtain LLZO precursor powder. (4) The LLZO precursor powder obtained in step (3) is calcined at 700-900℃ for 2-4 hours, and then naturally cooled to room temperature. It is then ground with a planetary ball mill for 2 hours to obtain cubic phase LLZO with a particle size of 50-100nm. (5) Using lithium tert-butoxide and trimethyl phosphate as precursors, the surface of the cubic phase LLZO obtained in step (4) is coated with a Li3PO4 layer by atomic layer deposition to form a core-shell structure and obtain an LLZO composite solid electrolyte.

2. The method for preparing the LLZO composite solid electrolyte according to claim 1, characterized in that: In step (1), the lithium hydroxide is LiOH·H2O and the zirconium oxychloride is ZrOCl2·8H2O.

3. The method for preparing the LLZO composite solid electrolyte according to claim 1, characterized in that: In step (1), the magnetic stirring speed is 500 rpm and the ultrasonic treatment frequency is 40 kHz.

4. The method for preparing the LLZO composite solid electrolyte according to claim 1, characterized in that: In step (3), the centrifugal separation speed is 8000 rpm.

5. The method for preparing the LLZO composite solid electrolyte according to claim 1, characterized in that: In step (5), the thickness of the Li3PO4 layer is 2-5 nm.

6. An LLZO composite solid electrolyte, characterized in that: It is prepared by the method of any one of claims 1-5 for preparing LLZO composite solid electrolyte.

7. A composite electrolyte membrane, characterized in that: The composite electrolyte membrane is prepared by the following steps: First, a binder, an ionic liquid, and the LLZO composite solid electrolyte as described in claim 6 are mixed together to obtain a mixture, wherein the weight ratio of the binder, the ionic liquid, and the LLZO composite solid electrolyte is 1:1:8; then, the temperature is increased to 200°C at a heating rate of 1-5°C / min, and a pressure of 5-10 MPa is applied, and the temperature and pressure are maintained for 10 min; next, the temperature is increased to 400°C at a heating rate of 1-5°C / min, and a pressure of 15-20 MPa is applied, and the temperature and pressure are maintained for 10 min; then, the temperature is increased to 600°C at a heating rate of 1-5°C / min, and a pressure of 5 MPa is applied, and the temperature and pressure are maintained for 10 min; finally, the temperature is decreased to room temperature at a cooling rate of 2-5°C / min to obtain the composite electrolyte membrane.

8. A negative electrode sheet, characterized in that: It includes a lithium foil, a buffer layer, and the electrolyte membrane as described in claim 6, wherein the buffer layer is stacked on the surface of the lithium foil and the electrolyte membrane is stacked on the buffer layer.

9. The negative electrode sheet according to claim 8, characterized in that: The thickness of the buffer layer is 10 nm.

10. The negative electrode sheet according to claim 8, characterized in that: The buffer layer is made of aluminum oxide and is prepared by the following method: using trimethylaluminum and water as precursors, aluminum oxide is deposited on the surface of lithium foil by atomic layer deposition at a deposition temperature of 150°C.

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