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

Graphical Special K : Low-cost K 4 Fe(CN) 6 was studied as a cathode for potassium-ion batteries, which exhibit a high voltage of approximately 3.6 V and long lifespan of 400 cycles with an average capacity decay of 0.063 % per cycle. These are endowed by the highly reversible [Fe(CN)] 3−/4− redox couple for charge compensation, with enhanced ionic and electrical conductivity. 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.