Enhancing sulfur oxidation reaction by overcoming redox barriers with FeSe2@C for lithium–sulfur batteries†
Abstract
The electrocatalytic sulfur oxidation reaction (SOR), marked by a multifaceted 16-electron transfer, stands as a pivotal advancement in lithium–sulfur battery technology. In this process, the initial conversion of Li2S to Li2S2 during the charging phase is identified as the rate-determining step, characterized by a significant energy barrier. The integration of a nanoflower-shaped transition metal selenide catalyst on carbon (FeSe2@C) catalyzes the SOR. The synergistic effect of d–p orbital hybridization in the Fe–S bond and the redox cycling between Fe2+ and Fe3+ facilitates electron transfer, thereby lowering the decomposition barrier of Li2S. This has been confirmed through both density functional theory (DFT) calculations and experimental electrocatalysis. The oxidation of Li2S is reliant on an efficient charge transfer mechanism, where electrons are progressively transferred to intermediate species, leading to direct interactions with Li2S and the formation of Li2S2. This conversion is corroborated by in situ Raman spectroscopy. The FeSe2@C catalyst significantly reduces the activation energy by enhancing charge transfer efficiency. At a current density of 1C, the battery exhibited an initial capacity of 581.3 mA h g−1, with a remarkable capacity retention of 97.5% after 600 cycles and a minimal capacity decay rate of 0.004% per cycle, indicative of superior cyclability. This research propels the electrocatalysis of Li2S in the charging phase of lithium–sulfur batteries, thereby accelerating the kinetics of the SOR and contributing to the field's progress.