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

Abstract

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 Zn²⁺ diffusion. Here, an electrochemically induced phase transformation strategy is proposed to mitigate and overcome these barriers. <i>In situ</i> X-ray diffraction analysis confirms the complete transformation of tunnel-like structural V₆O₁₃ into layered V₅O₁₂·6H₂O during the initial electrochemical charging process. Theoretical calculations reveal that the phase transformation is crucial to reducing the Zn²⁺ migration energy barrier and facilitating fast charge storage kinetics. The calculated band structures indicate that the bandgap of V₅O₁₂·6H₂O (0.0006 eV) is lower than that of V₆O₁₃ (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 V₅O₁₂·6H₂O delivers a high capacity of 609 mA h g^-1 at 0.1 A g^-1, superior rate performance (300 mA h g^-1 at 20 A g^-1), fast-charging capability (<7 min charging for 465 mA h g^-1), and excellent cycling stability with a reversible capacity of 346 mA h g^-1 at 5 A g^-1 after 5000 cycles.