Electrochemically Induced Phase Transformation in Vanadium Oxide Boosts Zn-Ion Intercalation.

Vanadium oxides are excellent cathode materials with large storage capacities for aqueous zinc-ion batteries, but their further development has been hampered by their low electronic conductivity and slow Zn diffusion. Here, an electrochemically induced phase transformation strategy is proposed to mitigate and overcome these barriers. X-ray diffraction analysis confirms the complete transformation of tunnel-like structural VO into layered VO·6HO during the initial electrochemical charging process. Theoretical calculations reveal that the phase transformation is crucial to reducing the Zn migration energy barrier and facilitating fast charge storage kinetics. The calculated band structures indicate that the bandgap of VO·6HO (0.0006 eV) is lower than that of VO (0.5010 eV), which enhanced the excitation of charge carriers to the conduction band, favoring electron transfer in redox reactions. As a result, the transformed VO·6HO delivers a high capacity of 609 mA h g at 0.1 A g, superior rate performance (300 mA h g at 20 A g), fast-charging capability (<7 min charging for 465 mA h g), and excellent cycling stability with a reversible capacity of 346 mA h g at 5 A g after 5000 cycles.