K 2 Fe(C 2 O 4 ) 2 : An Oxalate Cathode for Li/Na-Ion Batteries Exhibiting a Combination of Multielectron Cation and Anion Redox.

The development of multielectron redox-active cathode materials is a top priority for achieving high energy density with long cycle life in the next-generation secondary battery applications. Triggering anion redox activity is regarded as a promising strategy to enhance the energy density of polyanionic cathodes for Li/Na-ion batteries. Herein, K 2 Fe(C 2 O 4 ) 2 is shown to be a promising new cathode material that combines metal redox activity with oxalate anion (C 2 O 4 2- ) redox. This compound reveals specific discharge capacities of 116 and 60 mAh g -1 for sodium-ion batterie (NIB) and lithium-ion batterie (LIB) cathode applications, respectively, at a rate of 10 mA g -1 , with excellent cycling stability. The experimental results are complemented by density functional theory (DFT) calculations of the average atomic charges.