Harnessing Asymmetric Electrode Dissolution for Highly Reversible Fluorination of Trivalent Metals to Enable Long-Life F-Ion Batteries

Abstract

Fluoride-ion batteries (FIBs), owing to high theoretical energy density, are regarded as a key developmental direction for next-generation energy storage systems. However, during cycling, FIBs suffer from the dissolution loss of active materials and the formation of electron–ion insulated fluorination products, which severely hinders interfacial reaction kinetics and cycle stability. To address these challenges, we propose a synergistic strategy that integrates multiscale solvent screening with the regulation of asymmetric electrode dissolution mechanism, enabling highly reversible and low-polarization fluorination-defluorination in trivalent metal electrodes. We identify an ideal weakly coordinating solvent that ensure sufficient dissociation of fluoride salt while optimizing the chemical environment at electrolyte–electrode interface. On the cathode side, a solid-state migration-fluorination-defluorination mechanism is established to minimize active-material dissolution, thus fundamentally improving the cycling stability. On the anode side, leveraging the high charge density and strong F–-coordination affinity of Al3+, we convert the insoluble AlF3 to soluble Al–F complexes and construct a complexation-dissolution-redeposition mechanism. This prevents the fluorinated passivation commonly observed in Zn/Mg anodes and markedly lowers the interfacial electron/ion transport barriers. Benefiting from this approach, the FeF3||Pb full cell retains at least 2000 cycles, and the reversible operation of Al anodes in FIBs is demonstrated for the first time.