Preparation and structural optimization of vanadium oxide nanotubes as cathode materials for PIBs with improved performance†

In this work, we synthesized hollow multi-walled vanadium oxide nanotubes (VO_x-NT) using a soft template technique under hydrothermal reaction conditions. By replacing organic templates, which do not contribute to electrochemical potassium storage, with K⁺ in a solution environment, we effectively retained the original hollow multi-walled structure of VO_x-NT while obtaining the K-VO_x-NT material. We conducted systematic characterizations of the microstructure, morphology, and composition of these materials and evaluated their potassium storage performance. Compared to the original VO_x-NT, K-VO_x-NT exhibited significantly enhanced cycling stability and rate performance when serving as the cathode in potassium-ion batteries (PIBs). It demonstrated a reversible discharge specific capacity of 75.7 mA h g⁻¹ for the 1st cycle at a current density of 50 mA g⁻¹ within a voltage range of 1.5–3.8 V (vs. K⁺/K) and retained 62.2 mA h g⁻¹ after the 50th cycle. When a current density of 600 mA g⁻¹ was applied, it could still deliver a capacity of 44.3 mA h g⁻¹. Furthermore, the storage and degradation mechanisms of K⁺ in K-VO_x-NT were elucidated. In addition, using hard carbon as the anode, the K-VO_x-NT full-cell was tested to further evaluate its practical performance. This work provides insight into the design and modification of vanadium-based cathode materials for future PIBs.