Fast Zn2+ kinetics of vanadium oxide nanotubes in high-performance rechargeable zinc-ion batteries

Mild aqueous rechargeable Zn-ion batteries emerge as potential grid energy storage devices due to excellent cycling stability, high Coulombic efficiency and low cost. However, reliable cathodes with high rate capability still need to be optimized. Previous vanadium oxide cathodes generally show the mechanism of Zn2+ intercalation into crystal layers, during which the lattice structure of active materials keeps stable. Different from this intercalation mechanism, here, we report a special conversion mechanism of Zn2+ storage. Vanadium oxide nanotubes with interlaminar dodecylamine are employed as the cathode. During the initial activation process, the cathode is fully converted to layered zinc pyrovanadate with amorphous zones induced by protonated dodecylamine, while the discharge process results in reversible formation of an amorphous-phase product during cycling. Layered zinc pyrovanadate can be electrochemically recovered from the amorphous phase after the Zn2+ de-intercalation. Despite an armorphous phase as the discharge product, this active material shows high cycling stability and fast Zn2+ kinetics. In addition, this cathode displays a specific energy density of ~242.5 Wh kg−1 and shows capacity retention of 80.5% after 950 cycles at 2.4 A g−1. Even at a high current density of 9.6 A g−1, the cathode delivers a specific energy of ~50 Wh kg−1 (5460 W kg−1) in 33 s. Although vanadium oxide nanotubes with interlaminar dodecylamine ions show little success in Li/Na-ion batteries with non-aqueous electrolytes, a mild aqueous Zn-ion system rejuvenates this material.