Electrochemical potassium-ion intercalation in NaxCoO2: a novel cathode material for potassium-ion batteries.

Reversible electrochemical potassium-ion intercalation in P2-type NaxCoO2 was examined for the first time. Hexagonal Na0.84CoO2 platelets prepared by a solution combustion synthesis technique were found to work as an efficient host for K+ intercalation. They deliver a high reversible capacity of 82 mA h g-1, good rate capability and excellent cycling performance up to 50 cycles.