Practical Reversibility of CuF₂ in a Bulk-Type All-Solid-State Fluoride-Ion Battery

Fluoride-ion batteries (FIBs), which use F- ionmigration to drive charge-discharge cycles, have recently gainedacademic attention as the next generation of rechargeable batteries.Copper difluoride (CuF2) represents a promising positiveelectrode material for FIBs owing to its high theoretical capacityand high redox potential. In this study, the high-temperature electrochemicalreversibility of a CuF2 composite electrode in a bulk-typeall-solid-state FIB is evaluated. The CuF2 composite electrodeshowed high reversible capacities during the initial cycling at operationtemperatures as high as 200 degrees C and relatively good capacity retentionup to the 30th cycle, even at 140 degrees C. It is suggested that thebulk-type battery operates through reversible fluoride-ion shuttlingbetween CuF2 and the counter electrode via an F- ion-conducting solid electrolyte. Furthermore, this study indicatesthat maintaining a CuF2/Cu particle size of less than 50nm is important in fabricating bulk-type FIBs with good electrochemicalperformance.