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. K_0.486V₂O₅ 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 K_0.486V₂O₅ cathodes cycled between 1.5 and 4.2 V. The analyses reveal the highly reversible structural evolution of K_0.486V₂O₅, in which the chemically inserted K⁺ ions partially remain between VO layers charged at high voltage serving as stabilizing species to prevent phase transformations. K_0.486V₂O₅ 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.