Rational Design of Anthraquinone Homogeneous Bidirectional Catalysts for Lithium-Sulfur Battery

Lithium-sulfur (Li-S) batteries are highly promising for high-specific-energy batteries due to high energy density and low cost. However, the dissolved lithium polysulfide (LiPSs) together with sluggish reaction kinetics and pronounced LiPSs shuttling, bring about severely limiting battery performance. Herein, an anthraquinone (AQ)-based homogeneous catalytic strategy is proposed to accelerate sulfur redox conversion, employing soluble 2-bromoanthraquinone (2-BT) as a bifunctional redox mediator. By introducing a bromo substituent, a redox mediator with well-matched potentials for catalyzing Li₂S oxidation and sulfur reduction was obtained, thereby promoting the solid-liquid-solid conversion of sulfur and suppressing the polysulfide shuttle effect and polarization. In situ Raman results further reveal that 2-BT accelerates sulfur reduction and elevates the formation potential of polysulfides, thereby effectively promoting the solid–liquid conversion process in Li-S batteries. Furthermore, DRT analysis demonstrates that, during charging, the introduction of 2-BT reduces the interfacial resistance associated with the solid–liquid conversion during Li₂S oxidation. Therefore, the Li-S cells containing 2-BT deliver an initial specific capacity of 832 mAh g⁻¹ at 1 C, retaining 96.3% of capacity after 450 cycles. This work provides a rational molecular design strategy for an AQ-based homogeneous catalyst and offers an effective approach to improving the reaction kinetics and interfacial stability of Li-S batteries.