Al-doped hydrated V6O13 cathode materials with enhanced rate and cycling properties for aqueous zinc-ion batteries

Vanadium oxides with unique crystal structure and excellent zinc storage capacity are highly attractive in aqueous zinc ion batteries (ZIBs), but plagued by their sluggish Zn2+ diffusion kinetics and poor cyclability. Herein, to settle these problems, we propose to insert Al3+ ions into a newly developed V6O13 via a facile one-step hydrothermal method, during which the bound water is also intercalated. The incorporation of Al3+, as illustrated by first-principles calculations, not only narrows the energy band gap but also enlarges the diffusion channels and lowers the Zn2+ migration energy barriers in the host structure, thereby improving the transportation efficiency of both electrons and Zn2+ ions. Consequently, the Al-doped hydrated V6O13 (HV6O13) exhibits an extraordinary rate performance, delivering a specific capacity as high as 243 mAh g−1 at 10 A g−1, which is much superior to bare HV6O13 (202 mAh g−1 at 10 A g−1) and most other vanadium oxides. Besides, in sharp contrast to bare HV6O13 which can only maintain 58.8 % of its initial capacity after 1000 cycles at 10 A g−1, the Al-doped HV6O13 shows an activation process initially and thus delivers almost the same capacity as the first cycle after being cycled for 1000 times. This well illustrates the stabilization effect of the inserted Al3+ "pillars" on the structure of V6O13 upon repeated Zn2+ extraction/insertion. Given the few investigations of V6O13, our work may blaze a new trail to further boost the performance of vanadium oxide-based cathode materials for ZIBs.