Electrochemical and Optical Properties of Lithium Ion Conducting LiPSON Solid Electrolyte Films

Abstract

Lithium phosphorous sulfuric oxynitrides (LiPSON) with different compositions have been prepared by rf‐sputtering using sputter targets with various mixtures of Li 3 PO 4 and Li 2 SO 4 . Morphology, composition, and electrochromic properties of the fabricated thin films were investigated using solid state analysis methods like scanning electron microscopy (SEM), X‐ray photoelectron spectroscopy (XPS), optical transmission spectroscopy, and electrochemical impedance spectroscopy. The composition of the thin films changes due to the varying fractions of process gases. The highest fraction of sulfur is about 1.3 at% validated using XPS. The optical bandgap shifts in the range of 3.7 eV up to 5.3 eV for the different fractions of process gases. Transmission in the UV range is above 60% for most of the sputtered solid electrolyte thin films whereas in the visible range of the electromagnetic spectrum a transmission above 80% is observed. The highest ionic conductivity is identified for the thin films with 4 sccm nitrogen and no additional argon as process gas. However, ionic conductivity is expected to increase with increasing sulfur content and with change of the ratio between different nitrogen coordinations.