High-performance aqueous potassium ion asymmetric supercapacitors based on tunable 2D transition metal oxides

Rechargeable aqueous potassium ion asymmetric supercapacitors are emerging as a promising alternative to lithium ion batteries due to their low cost and high safety. However, the large size of the potassium ions tends to lead to large deformations and even irreversible shattering of the active material during the insertion/extraction process. In this paper, amorphous/crystalline biphasic KxV2O5 (ac-KxV2O5) is synthesized by electrochemical deposition on three-dimensional nanoporous nickel tube collectors. The amorphous K0.25V2O5∙nH2O acts as a molecular column to maintain the large interlayer spacing of crystalline V2O5 bilayer, providing sufficient space to accommodate as much hydrated potassium ions as possible and their rapid transport, effectively alleviating structural damage to the host material. Benefiting from the large work function difference between V2O5 and MnO2, an aqueous potassium ion asymmetric supercapacitor is assembled using KxV2O5∙nH2O anode and KxMnO2∙nH2O cathode to obtain a volumetric energy of 32.7 mWh cm−3, which is superior not only to commercial energy storage devices but also to previously reported aqueous alkaline ion batteries and supercapacitors.