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.