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

Fluoride-ion batteries (FIBs), which use F– ion migration to drive charge–discharge cycles, have recently gained academic attention as the next generation of rechargeable batteries. Copper difluoride (CuF2) represents a promising positive electrode material for FIBs owing to its high theoretical capacity and high redox potential. In this study, the high-temperature electrochemical reversibility of a CuF2 composite electrode in a bulk-type all-solid-state FIB is evaluated. The CuF2 composite electrode showed high reversible capacities during the initial cycling at operation temperatures as high as 200 °C and relatively good capacity retention up to the 30th cycle, even at 140 °C. It is suggested that the bulk-type battery operates through reversible fluoride-ion shuttling between CuF2 and the counter electrode via an F– ion-conducting solid electrolyte. Furthermore, this study indicates that maintaining a CuF2/Cu particle size of less than 50 nm is important in fabricating bulk-type FIBs with good electrochemical performance.