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

Abstract: 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, K₄Fe(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 K₄Fe(CN)₆. The high voltage and stability of K₄Fe(CN)₆ will make it a promising low‐cost cathode for KIBs and encourage more investigations into high‐performance cathode materials. [ABSTRACT FROM AUTHOR]