Development of tysonite-type fluoride conducting thin film electrolytes for fluoride ion batteries

Thin films of La1 − xBaxF3 − x (0 ≤ x ≤ 0.15) have been fabricated via a sol-gel spin coating method on stainless steel substrates. The films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and electrochemical impedance spectroscopy (EIS). All the compositions possessed a tysonite-type structure without any detectable impurity; the thickness of the films was 5-6 μm. Fluoride ion conductivity of LaF3 was greatly improved by BaF2 doping. Similar to bulk material, La0.9Ba0.1F2.9 showed the highest ionic conductivity within the measured compositions. An ionic conductivity of 8.8 × 10− 5 S·cm− 1 was observed at 170 °C. Apparent activation energy for the ion conduction measured from 60 °C to 170 °C was determined, as well.