Physical Vapor Deposition of Li7La3Zr2O12 for All-Solid-State Thin Film Li Batteries

The liquid solvents used as electrolytes in conventional Li ion batteries limit the operating temperature range and cause safety problems due to insufficient electrochemical stability. With purpose to avoid these disadvantages solid electrolytes, like lithium conducting oxides, sulfides or phosphates can be used. A promising oxide is the garnet-like Li₇La₃Zr₂O₁₂ that shows one of the highest total Li ion conductivities (about 10^-4 S cm^-1 at room temperature) in this class of materials. It also enables a wide application range due to its thermal stability and chemical resistance against possible electrode materials, e.g. metallic Lithium.

In order to compensate the lower Li ion conductivity compared to liquid electrolytes current work is focused on thin electrolyte layers. Hence, main research aspect of the presented work is the thin film processing of Li₇La₃Zr₂O₁₂ with physical vapor deposition methods, especially RF magnetron sputtering. The growth conditions are optimized with regard to synthesize stoichiometric, crack-free and smooth thin films. Deposition is followed by thermal treatment of the as-grown samples to improve the crystallinity which should in turn improve the Li ion conductivity. The composition, structure and the electrochemical behavior of the resulting thin films are analyzed in order to deposit all-solid-state thin film batteries.