High‐Capacity Aqueous Potassium‐Ion Batteries for Large‐Scale Energy Storage

A potassium iron (II) hexacyanoferrate nanocube cathode material is reported, which operates with an aqueous electrolyte to deliver exceptionally high capacities (up to 120 mA h g-1 ). The cathode material exhibits excellent structural integrity, leading to fast kinetics and highly reversible properties. All of the battery materials are safe, inexpensive, and provide superior high-rate, long-cycle-life electrochemical performance.