Charge–Discharge Behavior of Bismuth in a Liquid Electrolyte for Rechargeable Batteries Based on a Fluoride Shuttle

Rechargeable batteries based on fluoride transfer have attracted attention because of the possibility of achieving high energy densities surpassing those of current lithium-ion batteries. Although the batteries of this type, fluoride shuttle batteries (FSBs), have been developed using solid electrolytes, most operate at relatively high temperatures, greater than 423 K. In addition, in attempts to fabricate FSBs using liquid electrolytes, only the discharge reactions have been investigated, and they still suffer from serious issues of reversibility. In the present study, we have prepared a fluoride-conducting liquid electrolyte by dissolving an organic fluoride in a room-temperature ionic liquid, yielding a FSB electrolyte with a high fluoride concentration (0.35 mol dm–3) and conductivity (2.5 mS cm–1). By using this electrolyte, we have demonstrated a rechargeable FSB working at room temperature that is constructed from Bi|BiF3 and PbF2|Pb couples as the positive and negative electrodes, respectively.