Amorphous Li–B–W–O solid-state electrolyte thin film for a solid-state ionic power sources

Li–B–W–O thin film serving as a solid-state electrolyte layer for a solid-state thin film battery has been deposited on a stainless steel (SUS)/Si substrate by thermal evaporation deposition at room temperature. By energy dispersive X-ray spectroscopy and inductively coupled plasma-atomic emission spectrometer measurements, the as-grown thin film showed a stoichiometry of Li_2.99BW_1.8O₉. The as-grown Li–B–W–O solid-state electrolyte thin film possessed an amorphous structure as confirmed by X-ray diffraction. Field emission scanning electron microscopy measurements of the film cross section showed a dense structure that did not have any large defects such as cracks or voids. For a cell structure of SUS/Li–B–W–O/SUS/Si, an impedance measurement conducted at room temperature revealed an ionic conductivity of 2.15 × 10⁻⁷ S cm⁻¹ with activation energy of 0.52 eV, which suggests that Li–B–W–O thin film can possibly be used as an electrolyte in solid-state thin film batteries.