Composite solid electrolyte membrane and preparation method thereof

The invention discloses a composite solid electrolyte membrane in the field of lithium ion batteries, the composite solid electrolyte membrane is obtained by coating a porous support material with a composite electrolyte slurry comprising a polymer, an inorganic oxide, a lithium salt and a solvent and drying, and the polymer is one or two of polyvinylidene fluoride-hexafluoropropylene and polyvinylidene fluoride; the inorganic oxide is any one or a mixture of more of lithium lanthanum zirconium oxide, tantalum-doped lithium lanthanum zirconium oxide, lithium lanthanum titanium oxide, lithium aluminum titanium phosphorus and lithium aluminum germanium phosphorus; the lithium salt is any one or a mixture of more of lithium bis (fluorosulfonyl) imide, lithium bis (trifluoromethanesulfonic acid) imide, lithium bis (oxalato) borate, lithium hexafluorophosphate and lithium perchlorate; the solvent is one or more of anhydrous acetonitrile, N, N-dimethyl formamide, N-methyl pyrrolidone and acetone. The composite soli