High-purity 13C-labeled mesoporous carbon electrodes decouple degradation pathways in Li-O2 batteries with polymorphic Ru catalysts

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While solid-state catalysts are commonly used to reduce the charge potential, their influence on the cycle stability of Li-O 2 batteries remains controversial. The underlying problem is to decouple the degradation from the electrolyte and the electrode. In this work, a high-purity 13 C-labeled graphene mesosponge ( 13 C-GMS) with a high-surface-area and few-edge-sites has been synthesized. Furthermore, 13 C-GMS loaded with polymorphic Ru catalysts were prepared, allowing the distinction between cathode and electrolyte degradation in Li-O 2 batteries. Comprehensive in situ characterization and theoretical simulations show that the lower charge potential only mitigates the degradation of the carbon cathode, while the different Ru catalysts trigger different degrees of degradation of the electrolyte. The carbon cathode or the electrolyte may serve as the “weakest link” limiting the cycle life of Li-O 2 batteries. This work provides insight into the pending debate on whether solid-state catalysts improve or worsen the cyclability of Li-O 2 batteries. • High purity 13 C mesoporous carbon with high surface area and edge-site-free properties was synthesized to decouple side reactions from cathode and electrolyte. • Ru-fcc catalyzes lower charge potential than Ru-hcp due to its lower adsorption energy towards LiO 2 as revealed by Density Functional Theory. • Ru-fcc triggers more severe side reactions in the electrolyte, leading to the accumulation of more side products than Ru-hcp as confirmed by in situ XAFS. • A lower overpotential leads to better cathode stability but cannot guarantee better cycle life, an insight that explains the enduring controversy over solid-state catalyst effects in Li-O 2 batteries.

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