K_0.83V₂O₅: A New Layered Compound as a Stable Cathode Material for Potassium-Ion Batteries

Recently, potassium-ion batteries (PIBs) are being actively investigated. The development of PIBs calls for cathode materials with a rigid framework, reversible electrochemical reactivity, and a high amount of extractable K ions, which is extremely challenging due to the large size of potassium. Herein, a new layered compound K0.83V2O5 is reported as a potential cathode material for PIBs. It delivers an initial depotassiation capacity of 86 mAh g–1 and exhibits a reversible capacity of 90 mAh g–1 with a high redox potential of 3.5 V (vs K+/K) and a capacity retention of more than 80% after 200 cycles. Experimental investigations combined with theoretical calculation indicate that depotassiation–potassiation is accommodated by contraction–expansion of the interlayer spacing along with unpuckering–puckering of the layers. Additionally, the calculated electronic structure suggests the (semi)metallic feature of KxV2O5 (0 < x ≤ 0.875) and K-ion transport in the material is predicted to be one-dimensional with the experimentally estimated chemical diffusion coefficient in the order of 10–15–10–12 cm2 s–1. Finally, a K-ion full cell consisting of the K0.83V2O5 cathode and a graphite anode is demonstrated to deliver an energy density of 136 Wh kg–1. This study will provide insights for further designing novel layered cathodes with high K-ion content for PIBs.