Proton-Driven Self-Discharge Causing Chemical Degradation of Benzoquinone in Sulfide All-Solid-State Batteries

High Resolution Image Download MS PowerPoint Slide Benzoquinone (BQ) derivatives are promising organic electrode materials owing to their high theoretical capacities and molecular tunability, but their dissolution in liquid electrolytes limits cycling stability. Sulfide solid electrolytes suppress dissolution yet introduce severe interfacial degradation. Previous studies have proposed two competing degradation scenarios, attributing the degradation either to nucleophilic attack by Li 2 S-derived sulfur species or to lithium-driven self-discharge. However, the dominant pathway and its molecular origin remain unresolved. Here, by varying the BQ-to-Li 6 PS 5 Cl(LPSCl) ratio to capture early-stage reactions, we clarify the initiating degradation chemistry of BQ. Li 2 S-derived sulfur species first attack carbonyl-adjacent carbon sites, forming sulfur-attached intermediates that drive intramolecular proton rearrangement. The migrated protons convert redox-active C=O groups into redox-inactive C–OH moieties, causing proton-driven, rather than lithium-driven, self-discharge. These results reconcile the previously debated mechanisms by showing that nucleophilic attack directly triggers proton-mediated redox deactivation, providing molecular design principles for stable organic electrodes in sulfide all-solid-state batteries.