A Li₂S-TiS₂-Electrolyte Composite for Stable Li₂S-Based Lithium–Sulfur Batteries

Li₂S is a fully lithiated sulfur-based cathode with a high theoretical capacity of 1166 mAh g⁻¹ that can be coupled with lithium-free anodes to develop high-energy-density lithium–sulfur batteries. Although various approaches have been pursued to obtain a high-performance Li₂S cathode, there are still formidable challenges with it (e.g., low conductivity, high overpotential, and irreversible polysulfide diffusion) and associated fabrication processes (e.g., insufficient Li₂S, excess electrolyte, and low reversible capacity), which have prevented the realization of high electrochemical utilization and stability. Here, a new cathode design composed of a homogeneous Li₂S-TiS₂-electrolyte composite that is prepared by a simple two-step dry/wet-mixing process is demonstrated, allowing the liquid electrolyte to wet the powder mixture consisting of insulating Li₂S and conductive TiS₂. The close-contact, three-phase boundary of this system improves the Li₂S-activation efficiency and provides fast redox-reaction kinetics, enabling the Li₂S-TiS₂-electrolyte cathode to attain stable cyclability at C/7 to C/3 rates, superior long-term cyclability over 500 cycles, and promising high-rate performance up to 1C rate. More importantly, this improved performance results from a cell design attaining a high Li₂S loading of 6 mg cm⁻², a high Li₂S content of 75 wt%, and a low electrolyte/Li₂S ratio of 6.