Ultrafast Zn²⁺ Intercalation and Deintercalation in Vanadium Dioxide

Although rechargeable aqueous zinc-ion batteries have attracted extensive interest due to their environmental friendliness and low cost, they still lack suitable cathodes with high rate capabilities, which are hampered by the intense charge repulsion of bivalent Zn²⁺. Here, a novel intercalation pseudocapacitance behavior and ultrafast kinetics of Zn²⁺ into the unique tunnels of VO₂ (B) nanofibers in aqueous electrolyte are demonstrated via in situ X-ray diffraction and various electrochemical measurements. Because VO₂ (B) nanofibers possess unique tunnel transport pathways with big sizes (0.82 and 0.5 nm² along the b- and c-axes) and little structural change on Zn²⁺ intercalation, the limitation from solid-state diffusion in the vanadium dioxide electrode is eliminated. Thus, VO₂ (B) nanofibers exhibit a high reversible capacity of 357 mAh g⁻¹, excellent rate capability (171 mAh g⁻¹ at 300 C), and high energy and power densities as applied for zinc-ion storage.