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.