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

Rechargeable aqueous batteries have been widely investigated for large-scale energy storage in view of high safety and low cost. While tremendous efforts have been devoted to the cathode materials, few have focused on the 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 K0.38(H2O)0.82MoS2 manifests 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 and shows a stable redox potential around -0.1 V vs. Ag/AgCl to serve as an anode material, which contributes a specific capacity of over 50 mA h g-1 at the current density of 0.5 A g-1. The intercalation of larger hydrated cations during the discharge process results in the lower operation potential and wider interlayer spacing, which has been explained theoretically by Gibbs Free energy and valence bond theory. In particular, taking hydrated K+ insertion and extraction of K0.38(H2O)0.82MoS2 as an example, the ex-situ XRD and XPS results demonstrate reversible change of phase structure and Mo3+/Mo4+ redox couple during the charge-discharge process. Our study points to a promising anode for aqueous batteries using K0.38(H2O)0.82MoS2 as a universal host.