KFe(C2O4)F: A Fluoro‐oxalate Cathode Material for Li/Na‐Ion Batteries.

The iron‐based polyanionic fluoro‐oxalate material, KFe(C2O4)F (KFCF), has been synthesized by hydrothermal methods. This compound shows promising reversible lithium and sodium insertion properties as a cathode material. The material delivered a first‐cycle discharge capacity of 120 mAh g−1 at ∼3.3 V (Li+/Li) and 97.4 mAh g−1 at ∼3.0 V (Na+/Na) in LIB and NIB, respectively. Stable cycling performance was observed in both cases. The involvement of reversible Fe2+/Fe3+ redox was confirmed by ex‐situ Mössbauer spectroscopy supported by first‐principles calculations. This study reveals promising performance from a mixed oxalate‐fluoride based polyanionic material thereby opening up further possibilities for materials discovery in the design of new electrode materials. [ABSTRACT FROM AUTHOR]