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.