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During the discharge of a lithium–sulfur (Li–S) battery, an electronically insulating 2D layer of Li₂S is electrodeposited onto the current collector. Once the current collector is enveloped, the overpotential of the cell increases, and its discharge is arrested, often before reaching the full capacity of the active material. Guided by a new computational platform known as the Electrolyte Genome, we advance and apply benzo[ghi]peryleneimide (BPI) as a redox mediator for the reduction of dissolved polysulfides to Li₂S. With BPI present, we show that it is now possible to electrodeposit Li₂S as porous, 3D deposits onto carbon current collectors during cell discharge. As a result, sulfur utilization improved 220% due to a 6-fold increase in Li₂S formation. To understand the growth mechanism, electrodeposition of Li₂S was carried out under both galvanostatic and potentiostatic control. The observed kinetics under potentiostatic …