Understanding LiI-LiBr Catalyst Activity for Solid State Li₂S/S Reactions in an All-Solid-State Lithium Battery

Li||MoS₂ solid-state batteries have higher volumetric energy density and power density than Li||Li₂S batteries. However, they suffer from energy and power decay due to the formation of lithium sulfide that has low ionic/electronic conductivity and a strong Li-S bond. Herein, we overcome these challenges by incorporating the catalytic LiI-LiBr compound and carbon black into MoS₂. The comprehensive simulations, characterizations, and electrochemical evaluations demonstrated that LiI-LiBr significantly reduces Li⁺/S^2- interaction and increases the ionic conductivity of Li₂S, thus enhancing the reaction kinetics and Li₂S/S redox reversibility. MoS₂@LiI-LiBr@C||Li cells with an areal capacity of 0.87 mAh cm^-2 provide a reversible capacity of 816.2 mAh g^-1 at 200 mA g^-1 and maintain 604.8 mAh g^-1 (based on the mass of MoS₂) for 100 cycles. At a high areal capacity of 2 mAh cm^-2, the battery still delivers reversible capacity of 498 mAh g^-1. LiI-LiBr-carbon additive can be broadly applied for all transition-metal sulfide cathodes to enhance the cyclic and rate performance.