Potassium intercalation into graphite to realize high-voltage/high-power potassium-ion batteries and potassium-ion capacitors

Highly reversible potassium intercalation into graphite in carbonate ester solution at room temperature is achieved by electrochemical reduction at the potential approaching to K+/K standard potential which is lower than that of Li+/Li. The intercalation results in formation of stage-1 KC8 compound with delivering 244 mAh g− 1 of reversible capacity. The initial irreversible capacity is suppressed by polycarboxylate binder compared to poly(vinyledene fluoride) binder. The lower potential, good cyclability, and excellent rate capability are first demonstrated for energy storage applications. Because of the lowest potential and weakest solvation among Li+, Na+, K+, Mg2 +, and Ca2 + ion carriers, potassium shuttlecock mechanism between two insertion materials as “potassium-ion battery” is advantageous for higher-voltage/-power rechargeable batteries. The excellent rate performance is beneficial for the application to hybrid-type capacitor, “potassium-ion capacitor,” as an alternative to lithium-ion capacitors.