Activation of Li2S Cathode by an Organoselenide Salt Mediator for All-Solid-State Lithium-Sulfur Batteries

Lithium sulfide (Li2S) is a promising electrode material with high specific capacity and can be paired with commercial anode materials such as graphite. However, bulk Li2S requires a high activation energy during the initial charge due to its inert electrochemical activity, resulting in high charge overpotential. Here, lithium phenyl selenide (PhSeLi) is proposed as a mediator that can effectively activate Li2S by altering the oxidation pathway in the initial charge process. It enables Li2S to release normal capacity over the general voltage range (1.5-3 V). The composite cathode with the Li2S:PhSeLi molar ratio of 4:1 exhibits a high reversible capacity of 615.9 mAh g(-1) at 0.2 A g(-1) after 400 cycles in all-solid-state batteries with Li7P3S11 sulfide electrolyte and In-Li anode (the corresponding capacity based on Li2S is 1016.6 mAh g(-1)). In a full cell with a partially pre-lithiated silicon anode, it can still provide an average discharge capacity of 524 mAh g(-1) at 0.1 A g(-1) (the capacity based on Li2S is 844.2 mAh g(-1)). This work will contribute to the further development of Li2S-based all-solid-state Li-S batteries.