Low‐Cost K₄Fe(CN)₆ as a High‐Voltage Cathode for Potassium‐Ion Batteries

Potassium‐ion batteries (KIBs) are of interest for large‐scale electrical energy storage, owing to the abundance of K resources and potential high energy density. Low‐cost cathodes with high performance are crucial for KIBs. Herein, K 4 Fe(CN) 6 is shown to be a low‐cost and high‐voltage cathode for KIBs. It can deliver a high voltage of approximately 3.6 V and a discharge capacity of 65.5 mAh g −1 with a lifespan of 400 cycles of discharge and charge. This is attributed to the strong σ bonds between C atoms and Fe and to the reduced particle size and good contact with conductive carbon brought about by ball milling, which benefit both the K + ion and the electronic conduction. The [Fe(CN) 6 ] 3−/4− redox couple is found to be responsible for charge compensation upon reversible extraction/insertion of K + from/into K 4 Fe(CN) 6 . The high voltage and stability of K 4 Fe(CN) 6 will make it a promising low‐cost cathode for KIBs and encourage more investigations into high‐performance cathode materials.