Reversible Molecular and Ionic Storage Mechanisms in High-Performance Zn0.1V2O5·nH2O Xerogel Cathode for Aqueous Zn-Ion Batteries.

The cathode is a critical component for aqueous Zn-ion batteries (ZIBs) to achieve high capacity and long stability. In this work, we demonstrate a dissolution-free, low-Zn-preinserted bilayer-structured V2O5 xerogel cathode, Zn0.1V2O5·nH2O (ZnVO), with excellent capacity and stability using a low-cost ZnSO4 electrolyte. Its discharge capacity reaches 463 mAh g-1 at 0.2 A g-1 and 240 mAh g-1 at 10 A g-1, while 93% and 88% of its capacity are retained at 0.2 A g-1 for 200 cycles and at 10 A g-1 for 20 000 cycles, respectively. We then show that the outstanding performance of ZnVO is derived from the enlarged gallery spacing by the solvent water intercalation and the water stable V2O5 bilayer structure. We further unveil via ab initio molecular dynamics that H+ is largely originated from the dissociation of the gallery water, while OH- moves out of the gallery to form Zn4(SO4)(OH)6·5H2O with ZnSO4 electrolyte on the surface of ZnVO; the intercalated Zn2+ forms aquo complex [Zn(H2O)6]2+ with the gallery water. Our theoretical analysis also suggests that the gallery water and solvent water in the electrolyte are statistically the same and functionally equivalent. Overall, this study shows the promise of ZnVO as a practical cathode for ZIBs and offers fundamental insights into the roles of gallery water, solvent water, bilayer V2O5 structure, and dual Zn2+/H+ intercalation mechanisms in achieving high capacity and long stability.