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

Abstract

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 Na₅V₁₂O₃₂·11.9H₂O as the new cathode material. Such a content has enlarged the lattice space up to 12.75 Å providing spacious channels for rapid Zn²⁺ migration. The charge-shielding effect of crystal water alleviates the electrostatic interactions between Zn²⁺ 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 Zn²⁺ 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 Zn²⁺ (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.