UC Berkeley

Here we report a new redox-active perylene bisimide (PBI)-polysulfide (PS) gel that overcomes electronic charge-transport bottlenecks common to lithium-sulfur (Li-S) hybrid redox flow batteries designed for long-duration grid-scale energy storage applications. PBI was identified as a supramolecular redox mediator for soluble lithium polysulfides from a library of 85 polycyclic aromatic hydrocarbons by using a high-throughput computational platform; furthermore, these theoretical predictions were validated electrochemically. Challenging conventional wisdom, we found that π-stacked PBI assemblies were stable even in their reduced state through secondary interactions between PBI nanofibers and Li2Sn, which resulted in a redox-active, flowable 3-D gel network. The influence of supramolecular charge-transporting PBI-PS gel networks on Li-S battery performance was investigated in depth and revealed enhanced sulfur utilization and rate performance (C/4 and C/8) at a sulfur loading of 4 mg cm-2 and energy density of 44 Wh L-1 in the absence of conductive carbon additives.