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

Lithium sulfide (Li 2 S) is a promising electrode material with high specific capacity and can be paired with commercial anode materials such as graphite. However, bulk Li 2 S 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 Li 2 S by altering the oxidation pathway in the initial charge process. It enables Li 2 S to release normal capacity over the general voltage range (1.5–3 V). The composite cathode with the Li 2 S: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 Li 7 P 3 S 11 sulfide electrolyte and In–Li anode (the corresponding capacity based on Li 2 S 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 Li 2 S is 844.2 mAh g −1 ). This work will contribute to the further development of Li 2 S‐based all‐solid‐state Li–S batteries.