Lithium-stable NASICON-type lithium-ion conducting solid electrolyte film coated with a polymer electrolyte

The NASICON-type doped LiTi(PO 4 ) 3 has high lithium-ion conductivity and is stable in aqueous solution with a high lithium-ion content, but is unstable in contact with lithium metal. Therefore, these electrolytes should be protected by a lithium-stable lithium-ion conductor for a cell with a lithium metal electrode. Here we propose a composite solid electrolyte of a high lithium-ion conducting solid electrolyte film, Li 1.4 Al 0.4 Ge 0.2 Ti 1.4 (PO 4 ) 3 (LAGTP), coated with a thin polyethylene oxide (PEO) based polymer electrolyte layer. LAGTP coated with PEO containing an ionic liquid and an oxide filler of BaTiO 3 (or SiO 2 ) was stable in contact with lithium metal and the interface between the lithium metal and composite electrolyte exhibited low polarization during the lithium deposition and stripping processes. • Lithium-stable solid electrolyte proposed. • Interface resistance of Li/solid electrolyte was as low as 130 Ω cm 2 at 60 °C. • Excellent Li deposition and stripping cyclic performance observed.