Reversible Phase Transition in Ruddlesden-Popper-type Oxysulfide Y<sub>2</sub>Ti<sub>2</sub>O<sub>5</sub>S<sub>2</sub> for Lithium-Ion Battery Anodes

Oxysulfides have the potential for battery electrodes to have durability and rate capability due to their rigid structures and electronic conductivity. Herein, we focus on the Ruddlesden-Popper phase oxysulfide Y2Ti2O5S2 and investigate the phase evolution of Y2Ti2O5S2 during electrochemical Li+ intercalation and deintercalation. The tetragonal structure is maintained down to 0.35 V during the lithiation process. A two-phase reaction between the tetragonal phase and the orthorhombic phase was observed at a voltage plateau region between 0.35 and 0.3 V. Subsequently, the tetragonal phase recovers for further lithiation process. The relatively low lattice volume change of 5 % compared with graphite anode leads to stable cycling performances.