A Li₂S-Based Catholyte/Solid-State-Electrolyte Composite for Electrochemically Stable Lithium-Sulfur Batteries

Li₂S, which features a high theoretical capacity of 1,166 mA·h g^-1, is an attractive cathode material for developing high-energy-density lithium-sulfur batteries. However, pristine Li₂S requires a high activation voltage of 4.0 V, which degrades both the electrolyte and electrode, leading to poor cycling performance. In an effort to reduce the activation overpotential, in this study, we investigate the use of P₂S₅ in an advanced Li₂S-P₂S₅ catholyte and demonstrate a new synthetic approach that enables facile and low-temperature processing. Our findings show the P₂S₅ additive generates two thiophosphates with high ionic conductivities in the catholyte, which improve the activation efficiency and the electrochemical utilization. To further improve this advanced catholyte design, we also investigate two modified Li₂S-P₂S₅ catholytes based on carbon black (to strengthen the conductivity) and dilute polysulfide (Li₂S₆; to amplify the reaction activity). Our analysis indicates that the optimal Li₂S-P₂S₅-Li₂S₆ catholyte attains high ionic conductivity and strong reaction kinetics, achieving a high charge-storage capacity of 700 mA·h g^-1 with a long-term cyclability of 200 cycles.