The Quest for Stable Potassium‐Ion Battery Chemistry

Potassium-ion batteries (KIBs) have attracted wide interest for energy storage because of the abundance of the electrode materials involved; however, their electrochemical performances are far behind what can be achieved from lithium-ion batteries (LIBs) or sodium-ion batteries (SIBs). Herein, key promising electrode and electrolyte materials for potassium-ion batteries are identified, the coupled electrochemical reactions in the cell are investigated, and the compatibility between different materials is demonstrated to play the most important role. K2 Mn[Fe(CN)6 ] cathode can deliver a high capacity of ≈125 mAh g-1 and exceptional cycling stability over 61 000 cycles (≈9 months) if the side reactions from the anode can be prevented. Graphite is a good anode material but is subjected to degradation in traditional carbonate electrolytes. New concentrated electrolytes are developed and evaluated. A stable KIB system is demonstrated by coupling a stable K2 Mn[Fe(CN)6 ] cathode, a prepotassiated graphite anode with a concentrated electrolyte to achieve a high energy density of ≈260 Wh kg-1 (based on the active mass of cathode and anode) and good cycling of over 1000 cycles.