K0.38(H2O)0.82MoS2 as a universal host for rechargeable aqueous cation (K+, Na+, Li+, NH4+, Mg2+, Al3+) batteries

Abstract

Rechargeable aqueous batteries have been widely investigated for large-scale energy storage in view of their high safety and low cost. While tremendous efforts have been devoted to the development of cathode materials, few have focused on the development of anode materials and only limited candidates such as V-based oxides and Ti-based polyanionic compounds have been explored. In this study, for the first time, we discover a hydrated compound of molybdenum based ternary sulfide K_0.38(H₂O)_0.82MoS₂ as a universal host for reversible intercalation of various hydrated cations (K⁺, Na⁺, Li⁺, NH₄⁺, Mg²⁺, Al³⁺, etc.). It undergoes a two-phase reaction during the electrochemical process, showing a stable redox potential of around −0.1 V vs. Ag/AgCl to serve as an anode material and a specific capacity of over 50 mA h g⁻¹ at a current density of 0.5 A g⁻¹. The intercalation of larger hydrated cations during the discharge process results in a lower operation potential and wider interlayer spacing, which has been explained theoretically by Gibbs free energy analysis and valence bond theory. In particular, taking hydrated K⁺ insertion and extraction of K_0.38(H₂O)_0.82MoS₂ as an example, the ex situ XRD and XPS results demonstrate a reversible change in the phase structure and Mo³⁺/Mo⁴⁺ redox couple during the charge–discharge process. Our study provides a promising anode for aqueous batteries using K_0.38(H₂O)_0.82MoS₂ as a universal host.