Decomposition dynamics of peroxide by a redox mediator-anchored doped graphene catalyst in a Li-O₂ battery

Li-O₂ batteries are ideal for next-generation energy storage technology due to their high theoretical energy density. However, challenges such as slower charge transfer and sluggish Li₂O₂ decomposition reactions hinder their practical implementation. Combining a redox mediator with a cathode catalyst is a potential strategy for mitigating these challenges. In this study, first principles molecular dynamics simulations were used to investigate the effect of a tetrachloroquinone (TCQ) redox mediator and dimethyl sulfoxide (DMSO) solvent, combined with doped-graphene surfaces, for the oxygen evolution reaction (OER). Our investigation found that upon interaction with TCQ, charge transfer occurs from doped graphene to TCQ, resulting in the oxidation of the doped graphene and the reduction of TCQ. Graphitic-N doped graphene exhibits enhanced charge interaction with TCQ, and the chlorine substituent facilitates the charge transfer. Furthermore, lithium-oxygen-containing compounds like LiO₂ and Li₂O₂ transfer charge to TCQ, indicating their oxidation, which can promote the Li₂O₂ decomposition reaction. The solvent significantly reduces the charge overpotential and influences the potential-determining step of the OER. Our findings demonstrate that DMSO, in combination with TCQ, plays a critical role in dissociating Li₂O₂. Ab initio molecular dynamics simulation shows that the interaction between DMSO-Li₂O₂ and TCQ-Li₂O₂ facilitates the OER by forming the LiO₂(DMSO)₃ complex. This is mainly the Li-O interaction assisted by the oxygen of DMSO and TCQ, which weakens the Li-O bonds of Li₂O₂ and facilitates its conversion to lithium and oxygen. Moreover, the lithium ions tend to coordinate with four DMSOs, forming tetrahedral Li(DMSO)₄ complexes. These findings enhance our understanding of the synergistic effects of redox mediators, solvents, and cathode catalysts on the Li₂O₂ decomposition reaction of Li-O₂ batteries, thereby facilitating their advancement and potential applications in energy storage technologies.