Li₄GeS₄–Li₃PS₄ electrolyte thin films with highly ion-conductive crystals prepared by pulsed laser deposition

Abstract

Highly ion-conductive thin films in the pseudobinary system Li₄GeS₄–Li₃PS₄ were prepared by pulsed laser deposition (PLD). Raman spectra showed that the obtained thin films were mainly composed of Li⁺, (PS₄)³⁻, (GeS₄)⁴⁻ and (GeS_1/2S₃)³⁻ ions. The 33Li₄GeS₄·67Li₃PS₄ (mol %) thin film showed glass transition phenomenon at about 160°C, suggesting that the obtained amorphous thin film was in a glassy state. The thin film exhibited higher ionic conductivity than the Li₄GeS₄ and Li₃PS₄ thin films because of the so-called “mixed anion effect”. Furthermore, the structural rearrangement and crystallization after heat treatment for the thin film increased ionic conductivity from 1.1 × 10⁻⁴ to 1.8 × 10⁻³ S cm⁻¹ at 25°C, and decreased activation energy from 42 to 28 kJ mol⁻¹. Highly lithium-ion conductive thin films prepared in this study are promising for the application to bulk-type all-solid-state lithium secondary batteries.