▎ 摘　　要

NOVELTY - A composite solid electrolyte comprises lithium-lanthanum-zirconium oxide (LLZO) (I), a binder, and a plasticizer. USE - Composite solid electrolyte used for manufacturing all-solid lithium secondary battery (claimed). Uses include but are not limited to electric industry (electric vehicle, hybrid vehicle, and plug-in hybrid electric vehicle), electronic industry, telecommunication industry, computer industry, environmentally-friendly automobile, and energy storage market. ADVANTAGE - The composite solid electrolyte provides all-solid lithium secondary battery having improved ionic conductivity, excellent safety, and low operating temperature. DETAILED DESCRIPTION - A composite solid electrolyte comprises lithium-lanthanum-zirconium oxide (LLZO) of formula: LixAlpGaqLayZrzO12 (I), where x is 5-9, p is 0-4, q is 0-4, y is 2-4, and z is 1-3, a binder, and a plasticizer. INDEPENDENT CLAIMS are included for the following: (1) an all-solid lithium secondary battery, which comprises a positive electrode comprising a positive electrode active material, lithium-lanthanum-zirconium oxide (LLZO) (L1), and a binder (b1), a composite solid electrolyte layer arranged on the positive electrode and including lithium-lanthanum-zirconium oxide (LLZO) (L2), a binder (b2), and a plasticizer (p2), and a negative electrode positioned on the composite solid electrolyte layer and including a negative electrode active material; and (2) manufacture of the all-solid lithium secondary battery.