Prepotassiated V2O5 as the Cathode Material for High‐Voltage Potassium‐Ion Batteries

The voltage and capacity of cathodes are critical factors for energy density of batteries. However, the cutoff voltage of cathode materials in potassium‐ion batteries (PIBs) is usually 4.0 V, causing structural transformations in the electrode materials in the course of repeated insertion/extraction of K+ ions with a large radius (1.38 Å). Materials with large interlayer spacing and short ion diffusion paths show promise to overcome this issue. K0.486V2O5 nanobelts, prepared by preinserting K+ ions into V2O5, are used as cathode materials in high‐voltage PIBs. Various analysis methods are used to understand the insertion/extraction behavior of K+ ions in K0.486V2O5 cathodes cycled between 1.5 and 4.2 V. The analyses reveal the highly reversible structural evolution of K0.486V2O5, in which the chemically inserted K+ ions partially remain between VO layers charged at high voltage serving as stabilizing species to prevent phase transformations. K0.486V2O5 cathodes exhibit a high specific capacity of 159 mAh g−1 at 20 mA g−1 with good cycling stability of 67.4% after 100 cycles at 100 mAh g−1 in the half K‐ion cell. The results provide guidelines for designing layered transition metal oxides to be used as cathode materials for high‐voltage PIBs with high energy density. K0.486V2O5 nanobelts are synthesized by a novel hydrothermal method. The K0.486V2O5 nanobelts are used as the cathode of nonaqueous high‐voltage potassium‐ion batteries (PIBs). The stabilization of K+ ions remaining between VO layers at 4.2 V is revealed by in situ Raman and ex situ X‐ray powder diffraction (XRD).