Passivated LLZO particles and tape casting of LLZO films

A method of tape casting, the method comprising

• tape casting a tape casting slip composition to form a green tape, the tape casting slip composition comprising a plurality of passivated Li7La3Zr2O12 (LLZO) particles each comprising:
• an LLZO core, wherein the LLZO is optionally doped with one or more elements,
• a shell comprising Li2CO3, and
• an H3O+-LLZO and/or H-LLZO layer between the core and the shell,
• wherein the tape casting slip composition comprises an excess lithium source in sufficient quantity such that the tape casting slip composition comprises an amount of Li that is 1% to 40% in excess based on a stoichiometric amount of Li in the LLZO core, wherein the excess lithium source comprises Li2CO3, LiOH, Li2O, LiCl, LiNO3, Li-citrate, Li-acetate, Li-oleate, LiF, Li2SO4, or combinations thereof;
• drying the green tape;
• and
• sintering the green tape in the absence of a mother powder.