Fine valence regulation of hydrated vanadium oxide as a novel cathode for stable potassium-ion storage.

Layered VO·HO with a large interlayer spacing of 14 Å is hydrothermally synthesized and used as a cathode for potassium-ion batteries. It exhibits a capacity of 110 mA h g with a capacity retention of 99.2% over 700 cycles. Its storage mechanism is identified as pseudo-capacitive intercalation.