Cathode Design Based on Nitrogen Redox and Linear Coordination of Cu Center for All-Solid-State Fluoride-Ion Batteries.

All-solid-state fluoride-ion batteries (FIBs) have attracted extensive attention as candidates for next-generation energy storage devices; however, promising cathodes with high energy density are still lacking. In this study, CuN is investigated as a cathode material for all-solid-state fluoride-ion batteries, which offers enough anionic vacancies around the 2-fold coordinated Cu center for F intercalation, thereby enabling a multielectron-transferred fluorination process. The contribution of both cationic and anionic redox to charge compensation, in particular, the generation of molecular nitrogen species in highly charged states, has been proved by several synchrotron-radiation-based spectroscopic technologies. As a result, CuN exhibits a high reversible capacity of ∼550 mAh g, exceeding many conventional fluoride-ion cathodes. It is believed that the new charge compensation chemistry as well as the unique intercalation behaviors of novel mixed-anion Cu-N/F local structures could bring new insights into energy storage materials.