Reconfiguring Sodium Intercalation Process of TiS₂ Electrode for Sodium-Ion Batteries by a Partial Solvent Cointercalation

Titanium disulfide (TiS2), a first-generation cathode in lithium batteries, has also attracted a broad interest as a sodium-ion battery electrode due to fast sodium intercalation kinetics and large theoretical capacity. However, the reversibility of sodium de/intercalation is far inferior to that of lithium because of the unfavorable intermediate phase formation. Herein, we demonstrate that reconfiguring sodium intercalation via partial solvent cointercalation alters the phase-transition paths for the entire reactions of NaxTiS2 (0 < x < 1), detouring the formation of the unfavorable intermediates. Additionally, it unexpectedly results in a remarkable enhancement of sodium intercalation reversibility, boosting the cycle stability (1000 cycles) accompanying high power capability (10C rate). Comparative investigations reveal that the sodium intercalation in ether-based electrolyte involves a preintercalation of solvent molecules, which is subsequently dissimilar to the bare sodium intercalation in conventional electrolytes. Rediscovery of the intercalation behavior of TiS2 offers a new insight in revisiting the reversibility and kinetics of the commonly known electrodes for batteries.