Reversible Hydration Enabling High-Rate Aqueous Li-Ion Batteries

Layered 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 relatively dilute electrolyte for sustainable aqueous Li-ion batteries. Solvated water molecules intercalate in TiS₂ layers together with Li⁺ cations, forming a hydrated phase with a nominal formula unit of Li_0.38(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 cointercalation.