Passivated Li7La3Zr2O12 (LLZO) particles, tape casting powders and slip compositions including the particles, methods of forming the particles, methods of tape casting using the particles, green tapes including the particles, cast LLZO films formed from the particles, and lithium batteries including the cast LLZO film. A passivated LLZO particle includes an LLZO core, wherein the LLZO is optionally doped with one or more elements. The passivated LLZO particle also includes a shell including H-LLZO, H3O+-LLZO, and/or Li2CO3.