Advanced K3V2(PO4)2O2F cathode for rechargeable potassium-ion batteries with high energy density

Potassium-ion batteries (PIBs) have emerged as promising candidates for cost-effective and sustainable energy-storage systems. Nevertheless, limited by the large K+ radius, PIBs have great difficulty in figuring out and designing suitable host materials. Herein, a suitable cathode material K3V2(PO4)2O2F (KVPOF) for PIBs has been carefully prepared. It exhibits a high specific capacity close to the theoretical value, 116.3 mAh/g at 20 mA/g within the voltage window of 2.0–4.5 V vs K+/K, corresponding to a de-/intercalation process of ∼2 mol K+ per formula unit. In addition, it presents an average operating voltage plateau of about 3.5 V, resulting in an energy density of about 410 Wh/kg. The crystal structure and phase transition are revealed by in situ x-ray diffraction, and the structure is found to be fully reversible during the de-/intercalation of K+. Furthermore, the potential of KVPOF cathode for applications at low temperatures was explored, and the full cell matched with graphite anode demonstrated fair electrochemical performance. The experimental results suggest the feasibility of using KVPOF as cathode material for rechargeable PIBs.