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.