Fluoride‐Ion Batteries: Unraveling the Fundamental Science for Next‐Generation Energy Storage

ABSTRACT Fluoride‐ion batteries (FIBs) have recently gained scientific interest, primarily driven by the potential high‐energy‐density advantage. The considerable gap between fundamental knowledge and functional performance stems from unresolved scientific challenges intrinsic to the fluoride shuttle principle. Critical issues such as severe volume expansion in conversion‐type electrodes, poor fluoride‐ion mobility in solid electrolytes, and metastable electrode‐electrolyte interfaces represent critical scientific bottlenecks that limit electrochemical reversibility and cycle life. Moreover, the absence of consensus regarding evaluation methodologies and mechanistic descriptors prevents direct comparability across scientific investigations. In this Review, we discuss the fundamental electrochemistry of fluoride‐ion batteries, with a particular focus on charge‐transfer mechanisms, ion‐transport kinetics, and structural evolution in electrode and electrolyte materials. We further highlight the critical role of advanced characterization techniques in probing underlying reaction pathways and interfacial phenomena. Finally, we consider essential research directions required to establish a reliable knowledge base for this emerging field.