Sputter-Deposited Amorphous Li₃PO₄ Solid Electrolyte Films

This paper reports the thin-film synthesis of Li₃PO₄ solid electrolytes by RF magnetron sputtering. A relatively high ionic conductivity of more than 1 × 10^-6 S cm^-1 is achieved. It is revealed that the crystallization of Li₃PO₄ impedes ionic conduction, and a moderate amount of O₂ addition to Ar suppresses the crystallization and guarantees long-term deposition. Another important finding in this study is that when Li₃PO₄ is deposited on a LiCoO₂ film to construct a thin-film battery, the LiCoO₂ film can be damaged depending on the substrate bias potential relative to the cathode potential propagated through the sputtering plasma. Active control of the bias potential to avoid the damage realizes negligible interface resistance in the thin-film battery.