Crystal-Water-Free Potassium Vanadium Bronze (K_0.5V₂O₅) as a Cathode Material for Ca-Ion Batteries

The research to discover a suitable cathode material for calcium-ion batteries (CIBs) remains challenging, despite their potential advantages of high energy density and cost-effectiveness. Herein, we report K0.5V2O5 as a cathode material for CIBs. During the initial charging of the electrode, potassium ions were replaced with 0.12 Ca. The calcium-exchanged electrode exhibited a reversible discharge capacity of ∼100 mAh g–1 at 0.1 C rate at room temperature with an average voltage of ∼3.0 V (vs Ca/Ca2+). The reversible capacity is higher than any reported cathode materials without crystal water, demonstrating the feasibility of further development of high-capacity crystal-water-free CIB cathode materials.