Composite solid-state electrolyte, method for preparing the same, and solid-state lithium metal battery

Abstract

The application provides a composite solid electrolyte, a preparation method thereof and a solid lithium metal battery, and the composite solid electrolyte and the preparation method thereof comprise the following steps: grinding a pore-forming agent and then tabletting to obtain a mixed electrolyte wafer; placing the mixed electrolyte wafer into a tube furnace for pre-sintering; placing the obtained electrolyte after pre-sintering into deionized water and then placing the electrolyte into the tube furnace again for sintering to obtain a porous inorganic ceramic; placing a polyionic liquid without exchanged anions and a lithium salt into water for continuous stirring for ion exchange to obtain a polyionic liquid solution; placing the polyionic liquid solution and the porous inorganic ceramic in an argon environment glove box, dropping the polyionic liquid solution on the surface of the porous inorganic ceramic, and heating and drying in a heating bin in the argon environment to obtain an organic-inorganic composite solid electrolyte. The application has high lithium ion conductivity, can reduce the crystallinity of a polymer, and thus achieves the purpose of improving the room temperature ion conductivity of the polymer.

Description

Technical Field

[0001] This invention relates to a composite solid electrolyte, its preparation method, and a solid lithium metal battery, belonging to the technical fields of electrolyte preparation and lithium metal battery. Background Technology

[0002] Research on solid-state electrolytes can generally be divided into three types: inorganic solid-state electrolytes, polymer solid-state electrolytes, and composite solid-state electrolytes. Inorganic solid-state electrolytes, with their ideal mechanical strength, wide electrochemical window, and high ionic conductivity, have the potential to overcome the lithium dendrite problem that is a pressing issue in traditional lithium-ion batteries.

[0003] A commonly used preparation method involves adding zero-dimensional inorganic particles or one-dimensional inorganic fibers to the polymer. Adding inorganic fillers can reduce the crystallinity of the polymer to some extent, thereby improving the conductivity of the polymer matrix. However, the contribution of zero-dimensional or one-dimensional inorganic fillers to improving the conductivity of the composite electrolyte is limited. Further increasing the content of inorganic fillers will lead to the aggregation of particles or fibers, making it difficult to further improve the conductivity of the composite electrolyte, and it may even decrease it. Simultaneously, the inorganic fillers are separated by the polymer, preventing the formation of continuous and rapid ion transport channels, further limiting the improvement of the composite electrolyte's conductivity.

[0004] In view of this, it is indeed necessary to propose a composite solid electrolyte and its preparation method, as well as a solid lithium metal battery, to solve the above problems. Summary of the Invention

[0005] The purpose of this invention is to provide a composite solid electrolyte, its preparation method, and a solid lithium metal battery. The solid electrolyte preparation method is simple, has high room temperature ionic conductivity, and the assembled solid lithium metal battery has excellent performance.

[0006] To achieve the above objectives, the present invention provides a method for preparing a composite solid electrolyte, which mainly includes the following steps:

[0007] Step 1: Grind the pore-forming agent and compress it into tablets to obtain mixed electrolyte discs;

[0008] Step 2: Place the mixed electrolyte discs into a tube furnace for pre-sintering. After placing the pre-sintered electrolyte into deionized water, place it into the tube furnace again for sintering to obtain porous inorganic ceramics.

[0009] Step 3: Mix the unexchanged anion polyionic liquid with lithium salt and place it in water for continuous stirring to carry out ion exchange, thereby obtaining a polyionic liquid solution.

[0010] Step 4: Place the polyionic liquid solution and porous inorganic ceramic in a glove box under an argon atmosphere. Drop the polyionic liquid solution onto the surface of the porous inorganic ceramic and heat and dry it in a heating chamber under an argon atmosphere to obtain an organic-inorganic composite solid electrolyte.

[0011] As a further improvement of the present invention, in step 1, the pore-forming agent is a mixture of inorganic ceramic powder and sodium chloride, wherein the ratio of inorganic ceramic powder to NaCl is any one of 2:3, 1:1 or 3:2.

[0012] As a further improvement of the present invention, the template method is adopted in step 1: after mixing and grinding the inorganic ceramic powder with the sodium chloride, 0.24-0.26g of the mixed powder is poured into a metal mold and pressed at 16-18MP for 3-5min by a powder press to obtain mixed electrolyte discs.

[0013] As a further improvement of the present invention, in step 2, the mixed electrolyte disc is pre-sintered at 250-350°C, in a deionized water bath at 30-50°C for 3-5 hours, and then sintered again at 700-800°C.

[0014] As a further improvement of the present invention, in step 2, the porous inorganic ceramic is Li. 1.3 Al 0.3 Ti 1.7 P3O 12 Or Li 1.5 Al 0.5 Ge 1.5 P3O 12 Any one of them.

[0015] As a further improvement of the present invention, in step 3, the polyionic liquid is any one of poly(1-ethyl-3-acrylate) imidazole bis(trifluoromethanesulfonyl)imide salt, PEO, PVDF, or PVDF-HFP.

[0016] As a further improvement of the present invention, in step 3, the lithium salt is lithium bis(trifluoromethanesulfonyl)imide.

[0017] As a further improvement of the present invention, in step 4, the polyionic liquid solution is filled into the porous inorganic ceramic by titration permeation method.

[0018] To achieve the above objectives, the present invention also provides a composite solid electrolyte, which is prepared using the composite solid electrolyte preparation method described above.

[0019] To achieve the above objectives, the present invention also provides a solid-state lithium metal battery, comprising a positive electrode material, a negative electrode material, and a composite solid electrolyte, wherein the composite solid electrolyte is disposed between the positive electrode material and the negative electrode material, the positive electrode material being lithium iron phosphate, and the composite solid electrolyte being prepared using the composite solid electrolyte preparation method described above.

[0020] The beneficial effects of this invention are: this invention has a high lithium-ion conductivity, which can reduce the crystallinity of the polymer, thereby achieving the purpose of improving the room temperature ionic conductivity of the polymer. Attached Figure Description

[0021] Figure 1 The images shown are photographs and scanning electron microscope (SEM) images of the three-dimensional porous organic-inorganic composite solid electrolyte and its precursor in the embodiments; wherein, (a) is a photograph of LATP and NaCl mixed, ground, and pressed into ceramic electrolyte discs; (b) is a photograph of the pre-sintered ceramic electrolyte; (c) is a photograph of the porous ceramic electrolyte; (d) is a high-magnification SEM image of the porous ceramic electrolyte; and (e) is an image of the composite electrolyte with added PIL.

[0022] Figure 2 These are electrochemical performance diagrams of the three-dimensional porous organic-inorganic composite solid electrolyte in the embodiments; where (a) and (b) are intrinsic impedance diagrams and ionic conductivity bar charts of the three-dimensional porous organic-inorganic composite solid electrolyte at different temperatures, and (c) and (d) are polarization and impedance diagrams in the lithium ion transference number curve of the three-dimensional porous organic-inorganic composite solid electrolyte at room temperature.

[0023] Figure 3 This is a graph showing the cycling performance of a solid lithium metal symmetric battery prepared from the organic-inorganic composite solid electrolyte film in the examples at a current density of 0.05 mA cm⁻².

[0024] Figure 4 The figures show the electrochemical performance of the solid lithium metal half-cell prepared from the organic-inorganic composite solid electrolyte film in the examples; where (a) is the charge-discharge curve of the battery at the first, tenth, fiftieth and one hundredth cycles; and (b) is the cycle efficiency at 0.2C rate.

[0025] Figure 5 This is a schematic diagram of the ionic conductivity of the comparative example of the present invention at room temperature. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0027] It should be noted that, in order to avoid obscuring the present invention with unnecessary details, only the structures and / or processing steps closely related to the present invention are shown in the accompanying drawings, while other details that are not closely related to the present invention are omitted.

[0028] Additionally, it should be noted that the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0029] like Figures 1 to 5 As shown, this invention discloses a composite solid-state electrolyte, its preparation method, and a solid-state lithium metal battery. The solid-state lithium metal battery includes a positive electrode material, a negative electrode material, and a composite solid-state electrolyte, wherein the composite solid-state electrolyte is disposed between the positive electrode material and the negative electrode material. The positive electrode material is lithium iron phosphate, and the composite solid-state electrolyte is prepared using the aforementioned method. The preparation method of the composite solid-state electrolyte mainly includes the following steps:

[0030] Step 1: Grind the pore-forming agent and compress it into tablets to obtain mixed electrolyte discs;

[0031] Step 2: Place the mixed electrolyte discs into a tube furnace for pre-sintering. After placing the pre-sintered electrolyte into deionized water, place it into the tube furnace again for sintering to obtain porous inorganic ceramics.

[0032] Step 3: Mix the unexchanged anion polyionic liquid with lithium salt and place it in water for continuous stirring to carry out ion exchange, thereby obtaining a polyionic liquid solution.

[0033] Step 4: Place the polyionic liquid solution and porous inorganic ceramic in a glove box under an argon atmosphere. Drop the polyionic liquid solution onto the surface of the porous inorganic ceramic and heat and dry it in a heating chamber under an argon atmosphere to obtain an organic-inorganic composite solid electrolyte.

[0034] Steps 1-4 will be explained in detail below.

[0035] In step 1, the pore-forming agent is a mixture of inorganic ceramic powder and sodium chloride (NaCl), wherein the ratio of inorganic ceramic powder to NaCl is any one of 2:3, 1:1 or 3:2.

[0036] Step 1 uses the template method: the pore-forming agent NaCl is mixed and ground with inorganic ceramic powder in different proportions and then pressed into tablets. The tablet pressing method is to mix and grind the ceramic powder with NaCl, take 0.24-0.26g of the mixed powder and pour it into a metal mold, press it with a powder tablet press at 16-18MP for 3-5min, and then obtain mixed electrolyte discs.

[0037] In step 2, the obtained mixed electrolyte discs are pre-sintered at 250-350℃, then subjected to a water bath at 30-50℃ for 3-5 hours to remove NaCl, leaving pores, and finally sintered at 700-800℃ to obtain porous inorganic ceramics, wherein the porous inorganic ceramics are LATP(Li 1.3 Al 0.3 Ti 1.7 P3O 12 ) or LAGP (Li 1.5 Al 0.5 Ge 1.5 P3O 12 Any one of them.

[0038] In step 3, the polyionic liquid (PIL) is poly(1-ethyl-3-acrylate) imidazole bis(trifluoromethanesulfonyl)imide salt, which is also applicable to other conventional polymers such as PEO (polyethylene oxide), PVDF (polyvinylidene fluoride), and PVDF-HFP (poly(vinylidene fluoride-co-hexafluoropropylene)).

[0039] In step 3, the solvent used in the solution stirring method is N-methylpyrrolidone. The solution stirring method involves dissolving 0.08-0.12g of PIL and 0.02-0.03g of lithium salt in 0.5-1.0g of NMP (N-methylpyrrolidone); the stirring speed is 600-800 r / min, and the stirring time is 12-18h.

[0040] In step 3, the polyionic liquid contains lithium salt by dissolving LiTFSI at a concentration of 1 mmol g. -1 The concentration is dissolved in an NMP solution of the polyionic liquid. The lithium salt is lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0041] In step 4, the polyionic liquid (PIL) is filled into the porous ceramic using a titration permeation method. The titration permeation method involves adding 0.01g-0.015g of PIL to the porous ceramic via a syringe and soaking for 0.5-1 hour. The stirred solution is then dropped onto the porous ceramic and soaked for 30 minutes. The ceramic is then dried in a vacuum drying oven at 60-80℃ for 4 hours. After drying, the battery is assembled.

[0042] The following will be described in conjunction with the embodiments.

[0043] Example 1:

[0044] Taking inorganic ceramics as an example, organic-inorganic composite solid electrolytes were prepared using the NaCl template method and the PIL titration permeation method.

[0045] First, LATP and NaCl were mixed and ground in a 3:2 ratio for 30 minutes. Then, 240 mg of the mixed powder was poured into a 16 mm diameter metal mold and compressed into tablets using a tablet press. The mixed powder was compressed into tablets with a diameter of 16 mm by maintaining a pressure of 16 MPa for 4 minutes.

[0046] The sheet was pre-sintered in a tube furnace at 300°C for 2 hours to improve its mechanical strength. Then, the pre-sintered electrolyte was placed in a deionized water bath at 40°C for 4 hours to remove NaCl and leave pores, forming porous LATP. At this point, the porous LATP was sintered again in a tube furnace at 750°C for 3 hours to obtain the final porous LATP.

[0047] Preparation of polyionic liquid: First, the unexchanged anion polyionic liquid was mixed with lithium salt and placed in water and stirred continuously for 12 hours at a speed of 600 r / min to perform ion exchange, obtaining PIL. Then, 100 mg of the obtained PIL and 57.4 mg of lithium salt were added to NMP and stirred for 12 hours to obtain the polyionic liquid solution.

[0048] The prepared solution and porous LATP were placed in a glove box under an argon atmosphere. 0.2 ml of PIL was dropped onto the surface of the porous LATP and allowed to permeate for 30 min. Then, the solution was placed in a heating chamber under an argon atmosphere and heated at 80 °C for 4 h to dry, resulting in an organic-inorganic composite solid electrolyte (denoted as 3:2).

[0049] The assembly steps for solid-state lithium batteries are as follows:

[0050] A certain amount of lithium iron phosphate powder, Super P, and PVDF powder were weighed out, with a weight ratio of 8:1:1. The mixture was ground in a mortar for 30 minutes to ensure uniform mixing. An appropriate amount of NMP (N-methylpyrrolidone) was added to form a slurry, which was then coated onto an Al foil and vacuum dried at 60°C for 24 hours. A solid-state lithium battery device was assembled in the following order: positive electrode, solid electrolyte film prepared using the above method, lithium metal, steel sheet, and spring sheet.

[0051] Figure 1 These are photographs and scanning electron microscope images of the organic-inorganic composite solid electrolyte in the embodiments; Figure 1(a) is a photograph of the electrolyte after LATP and NaCl are mixed and compressed into a tablet; (b) is a photograph of the mixed electrolyte after pre-sintering at 300℃; (c) is a photograph of porous LATP after sintering at 750℃; (d) is a high-magnification scanning electron microscope image of porous LATP after sintering at 750℃; and (e) is a high-magnification scanning electron microscope image of the organic-inorganic composite solid electrolyte after adding PIL to porous LATP.

[0052] Figure 2 These are electrochemical performance graphs of the organic-inorganic composite solid electrolyte in the embodiments; where (a) and (b) are intrinsic impedance diagrams and ionic conductivity histograms of the organic-inorganic composite solid electrolyte at different temperatures. (c) and (d) are polarization and impedance diagrams of the lithium-ion transport number graph of the organic-inorganic composite solid electrolyte at room temperature. It can be seen that the ionic conductivity reaches 10 at temperatures of 10℃ and above. -4 S cm -1 Based on the above calculations, the lithium-ion transference number is 0.67.

[0053] Figure 3 The figure shows the electrochemical performance of a solid-state lithium metal symmetric battery prepared using the organic-inorganic composite solid electrolyte in the examples; the figure shows the symmetric battery at 0.05 mA cm⁻¹. -2 Cyclic performance diagram at current density;

[0054] Figure 4 The figures show the electrochemical performance of the solid lithium metal half-cell prepared from the organic-inorganic composite solid electrolyte film in the examples; where (a) is the charge-discharge curve of the first, tenth, fiftieth and one hundredth cycles at 0.2C rate; and (b) is the cycle efficiency at 0.2C rate.

[0055] The solid-state lithium battery prepared in this embodiment operates at 0.1 mA cm⁻¹. 2 At a current density, it can stably cycle with lithium metal for over 1000 cycles (2000 hours), and maintain a specific capacity of 120 mAh g at room temperature (0.2C). -1 Stable cycle of more than 100 times.

[0056] Example 2:

[0057] In this embodiment, the inorganic ceramic used is LAGP. The organic-inorganic composite solid electrolyte was prepared using the NaCl template method and the PIL titration permeation method.

[0058] First, LAGP and NaCl are mixed and ground in a 3:2 ratio for 30 minutes. Then, 240 mg of the mixed powder is poured into a 16 mm diameter metal mold and compressed into a tablet using a tablet press. The mixed powder is compressed into tablets with a diameter of 16 mm by maintaining a pressure of 16 MPa for 4 minutes.

[0059] The sheet was pre-sintered in a tube furnace at 300°C for 2 hours to improve its mechanical strength. Then, the pre-sintered electrolyte was placed in a deionized water bath at 40°C for 4 hours to remove NaCl and leave pores, forming porous LAGP. At this point, the porous LAGP was sintered again in a tube furnace at 750°C for 3 hours to obtain the final porous LAGP.

[0060] Preparation of polyionic liquid: First, the unexchanged anion polyionic liquid was mixed with lithium salt and placed in water and stirred continuously for 12 hours at a speed of 600 r / min to perform ion exchange, obtaining PIL. Then, 100 mg of the obtained PIL and 57.4 mg of lithium salt were added to NMP and stirred for 12 hours to obtain the polyionic liquid solution.

[0061] The prepared solution and porous LAGP were placed in a glove box under an argon atmosphere. 0.2 ml of PIL was dropped onto the surface of the porous LAGP and allowed to permeate for 30 min. Then, the solution was placed in a heating chamber under an argon atmosphere and heated at 80 °C for 4 h to dry, resulting in an organic-inorganic composite solid electrolyte (denoted as 3:2).

[0062] The lithium battery was prepared according to the method and steps in Example 1, and the performance data of the lithium battery obtained were the same as those in Example 1.

[0063] Comparative Example 1:

[0064] The inorganic ceramics used in this embodiment are the same as those in Embodiment 1.

[0065] Organic-inorganic composite solid electrolytes were prepared using the NaCl template method and the PIL titration permeation method. First, LATP and NaCl were mixed in a 2:3 ratio and ground for 30 min. 240 mg of the mixed powder was then poured into a 16 mm diameter metal mold and pressed into tablets using a tablet press. The tablets were pressed at 16 MPa for 4 min to form 16 mm diameter mixed electrolyte discs. The discs were then pre-sintered in a tube furnace at 300 °C for 2 h to improve their mechanical strength. The pre-sintered electrolyte was then placed in a 40 °C deionized water bath for 4 h to remove NaCl and leave pores, forming porous LATP. The porous LATP was then sintered again in a tube furnace at 750 °C for 3 h to obtain the final porous LATP. For the preparation of the polyionic liquid: Unexchanged anion polyionic liquid was mixed with lithium salt and placed in water with continuous stirring for 12 h at a speed of 600 r / min to perform ion exchange, yielding PIL. Then, 100 mg of the obtained PIL and 57.4 mg of lithium salt were added to NMP and stirred for 12 h to obtain a polyionic liquid solution. The prepared solution and porous LATP were placed in a glove box under argon atmosphere. 0.2 ml of PIL was dropped onto the surface of the porous LATP and allowed to permeate for 30 min. Then, it was placed in a heating chamber under argon atmosphere and heated at 80 °C for 4 h to dry, thus obtaining an organic-inorganic composite solid electrolyte (denoted as 2:3).

[0066] The ionic conductivity of this comparative example at room temperature is shown in the figure. Figure 5 .

[0067] Comparative Example 2:

[0068] The inorganic ceramics used in this embodiment are the same as those in Embodiment 1.

[0069] Organic-inorganic composite solid electrolytes were prepared using the NaCl template method and the PIL titration permeation method. First, LATP and NaCl were mixed in a 1:1 ratio and ground for 30 min. 240 mg of the mixed powder was then poured into a 16 mm diameter metal mold and pressed into tablets using a tablet press. The tablets were pressed at 16 MPa for 4 min to form 16 mm diameter mixed electrolyte discs. The discs were then pre-sintered in a tube furnace at 300 °C for 2 h to improve their mechanical strength. The pre-sintered electrolyte was then placed in a 40 °C deionized water bath for 4 h to remove NaCl and leave pores, forming porous LATP. The porous LATP was then sintered again in a tube furnace at 750 °C for 3 h to obtain the final porous LATP. For the preparation of the polyionic liquid: Unexchanged anion polyionic liquid was mixed with lithium salt and placed in water with continuous stirring for 12 h at a speed of 600 r / min to perform ion exchange, yielding PIL. Then, 100 mg of the obtained PIL and 57.4 mg of lithium salt were added to NMP and stirred for 12 h to obtain a polyionic liquid solution. The prepared solution and porous LATP were placed in a glove box under argon atmosphere. 0.2 ml of PIL was dropped onto the surface of the porous LATP and allowed to permeate for 30 min. Then, it was placed in a heating chamber under argon atmosphere and heated at 80 °C for 4 h to dry, thus obtaining an organic-inorganic composite solid electrolyte (denoted as 1:1).

[0070] The ionic conductivity of this comparative example at room temperature is shown in the figure. Figure 5 .

[0071] In summary, the method for preparing a three-dimensional porous organic-inorganic composite solid electrolyte provided by this invention involves mixing and grinding NaCl with ceramic powder followed by a water bath, while simultaneously blending PIL with lithium salt and preparing polymer additives using NMP as a solvent. The preparation method and material sourcing are readily available, requiring no hydrothermal or CVD chemical methods, and have low equipment requirements, enabling mass production. Compared to organic electrolytes, it exhibits longer cycle life and more stable voltage hysteresis at the same current density, demonstrating excellent lithium stability. The lithium metal battery prepared from the three-dimensional porous organic-inorganic composite solid electrolyte exhibits superior performance; after 100 cycles at 0.2C, it still maintains a specific capacity of 120 mAh / g and obtains a uniform SEI film, effectively suppressing lithium dendrite formation.

[0072] This invention provides a method for preparing a composite solid electrolyte for lithium metal batteries. The composite solid electrolyte uses porous ceramic as a substrate framework, exhibiting good mechanical properties. The ceramic powder is an inorganic fast ion conductor with a NASICON structure, possessing high lithium-ion conductivity. As a filler for polymers such as PIL, it can reduce the crystallinity of the polymer, thereby improving the room-temperature ionic conductivity of the polymer. Using polymers such as PIL as fillers can improve the compatibility of the electrode-electrolyte interface.

[0073] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a composite solid electrolyte, characterized in that, The main steps include: Step 1: After mixing and grinding the pore-forming agent NaCl with inorganic ceramic powder, 0.24-0.26g of the mixed powder is poured into a metal mold using the template method and pressed at 16-18MP for 3-5 minutes using a powder press to obtain mixed electrolyte discs; wherein, the ratio of inorganic ceramic powder to NaCl is any one of 2:3, 1:1 or 3:

2. Step 2: Place the mixed electrolyte discs into a tube furnace for pre-sintering. After pre-sintering, place the resulting electrolyte into deionized water and then sinter it again in the tube furnace to obtain porous inorganic ceramics. The mixed electrolyte discs are pre-sintered at 250-350 ℃, in a deionized water bath at 30-50 ℃ for 3-5 hours, and then sintered again at 700-800 ℃. Step 3: Mix the unexchanged anion polyionic liquid with lithium salt and place it in water for ion exchange by continuous stirring to obtain a polyionic liquid solution; Step 4: Place the polyionic liquid solution and porous inorganic ceramic in a glove box under an argon atmosphere. Use a titration permeation method to drop the polyionic liquid solution onto the surface of the porous inorganic ceramic. Then heat and dry it in a heating chamber under an argon atmosphere to obtain an organic-inorganic composite solid electrolyte.

2. The method for preparing the composite solid electrolyte according to claim 1, characterized in that: In step 2, the porous inorganic ceramic is Li. 1.3 Al 0.3 Ti 1.7 P3O 12 Or Li 1.5 Al 0.5 Ge 1.5 P3O 12 Any one of them.

3. The method for preparing the composite solid electrolyte according to claim 1, characterized in that: In step 3, the polyionic liquid is poly(1-ethyl-3-acrylate) imidazole bis(trifluoromethanesulfonyl)imide salt.

4. The method for preparing the composite solid electrolyte according to claim 1, characterized in that: In step 3, the lithium salt is lithium bis(trifluoromethanesulfonyl)imide.

5. A composite solid electrolyte, characterized in that: The composite solid electrolyte is prepared using the preparation method of composite solid electrolyte as described in any one of claims 1-4.

6. A solid-state lithium metal battery, characterized in that: The invention includes a positive electrode material, a negative electrode material, and a composite solid electrolyte, wherein the composite solid electrolyte is disposed between the positive electrode material and the negative electrode material, the positive electrode material is lithium iron phosphate, and the composite solid electrolyte is prepared using the preparation method of composite solid electrolyte as described in any one of claims 1-4.

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