Maximized crystal water content and charge-shielding effect in layered vanadate render superior aqueous zinc-ion battery

Emerging as a promising candidate for grid-scale energy storage, aqueous zinc-ion batteries are challenged by both sluggish Zn2+ migration kinetics and poor cyclic stability of cathode materials . Herein, a maximized crystal water content of 14.8 wt% is reported for layered Na 5V12O32·11.9H2O as the new cathode material. Such a content has enlarged the lattice space up to 12.75 A providing spacious channels for rapid Zn2+ migration. The charge-shielding effect of crystal water alleviates the electrostatic interactions between Zn 2+ and the cathode framework, enhancing ionic conductivity . The density functional theory calculation reveals that the high crystal water content facilitates the electrical conductivity . These should promote the Zn 2+ migration kinetics and cyclic stability. Through characterizations by ex situ X-ray photoelectron spectroscopy and near edge X-ray absorption fine structure analysis, the high crystal water content is found to associate with two-electron redox reactions during Zn 2+ (de)intercalation. As a result, the Na5V12O32·11.9H2O cathode presents a reversible capacity of 430.52 mA h/g at 0.1 A/g with 103.7% retention of initial capacity over 3,862 cycles at 1 A/g.