Reversible Hydration Enabling High-Rate Aqueous Li-ion Batteries

Two-dimensional TiS2 has been proposed as a versatile host material for various battery chemistries. Nevertheless, its compatibility with aqueous electrolytes has not been thoroughly understood. Herein, we report on a reversible hydration process to account for the electrochemical activity and structural evolution of TiS2 in a dilute electrolyte for sustainable aqueous Li-ion batteries. Solvated water molecules intercalate into TiS2 layers together with Li+ cations, forming a hydrated phase with a nominal formula unit of Li0.38(H2O)2 δTiS2 as the end product. We unambiguously confirm the presence of two layers of intercalated water by complementary electrochemical cycling, operando structural characterization, and computational simulation. Such a process is fast and reversible, delivering 60 mAh g-1 discharge capacity at a current density of 1250 mA g-1. Our work provides further design principles for high-rate aqueous Li-ion batteries based on reversible water co-intercalation.