Abstract: Disclosed is a manufacturing method for an all-solid-state lithium secondary battery.

Abstract: Disclosed is a method of preparing a solid electrolyte, which includes (a) preparing a solid electrolyte precursor slurry by subjecting a mixed solution including a metal precursor solution, containing a lanthanum precursor, a zirconium precursor and an aluminum precursor, a complexing agent, and a pH controller to coprecipitation, (b) preparing a solid electrolyte precursor by washing and drying the solid electrolyte precursor slurry, (c) preparing a mixture by mixing the solid electrolyte precursor with a lithium source, and (d) preparing an aluminum-doped lithium lanthanum zirconium oxide (LLZO) solid electrolyte by calcining the mixture, and which is also capable of adjusting the aluminum content of a starting material to thus control sintering properties and of adjusting the composition of a precursor and a lithium source to thus control the crystal structure, thereby improving the ionic conductivity of the solid electrolyte.