step 1) dissolving a water-soluble lithium salt, a water-soluble aluminum salt, and a water-soluble meta-aluminate in deionized water that has been introduced with an inert gas and boiled to remove carbon dioxide, subjecting a resulting mixture to ultrasound or stirring to dissolve, then adding an alkali thereto to adjust a pH of the resulting mixture to 9 to 11, and controlling a temperature at 60° C. to 80° C., and subjecting a resulting adjusted mixture to reaction to produce a lithium aluminum hydrotalcite;

step 2) placing the lithium aluminum hydrotalcite obtained in step 1) under protection of an inert gas, calcining at 100° C. to 150° C. for 2 h to 6 h to remove water between hydrotalcite layers to obtain a calcined sample, then grinding the calcined sample to power to obtain a lithium aluminum hydrotalcite powder;

step 3) preparing a lithium aluminum hydrotalcite-based solid electrolyte slurry for later use by the following operations in a first glove box:

adding an organic solvent, an organic polymer, and a lithium salt into a container, stirring an obtained mixture to complete dissolution, then adding the lithium aluminum hydrotalcite powder to the obtained mixture, subjecting a resulting blend to ultrasound or stirring to homogeneous dispersion, then adding a photoinitiator or a thermal initiator thereto to obtain the lithium aluminum hydrotalcite-based solid electrolyte slurry; and

wherein the organic polymer is polyethylene glycol diacrylate (PEGDA); and

step 4) performing the following operations in a second glove box:

subjecting the lithium aluminum hydrotalcite-based solid electrolyte slurry obtained in step 3) to curing and film-forming to obtain the lithium aluminum hydrotalcite-based solid electrolyte film;

wherein proportions of an inorganic phase and an organic phase in the solid electrolyte film are respectively as follows: a content of an inorganic phase lithium aluminum hydrotalcite is 59.9 wt %, and a content of the organic phase is 40.1%, based on a total mass of a solid electrolyte film after removal of the lithium salt; and

in step 1), the water-soluble lithium salt is lithium chloride; the water-soluble aluminum salt is aluminum chloride; and a molar ratio of lithium to aluminum is in a range of 1:2 to 1:5.