Hybridization-tuned dual-chain conjugated polythioether quinones for high-energy rechargeable magnesium batteries

Organic conjugated polymers featuring abundant redox-active moieties and flexible framework architectures represent promising cathode materials for rechargeable Mg batteries, but reported organic cathodes have struggled to achieve both high reversible capacity and high energy density simultaneously. Herein, three conjugated carbonyl polymers (25PBQS, 26PBQS, and 2356PBQS) are rationally designed by varying the conjugated thioether connectivity patterns of high-capacity, high-voltage benzoquinone units. The benzoquinone units enable high energy density through efficient two-electron redox reactions. The partial sp³ hybridization of sulfur atoms enhances molecular conformational flexibility, facilitating coordination with Mg²⁺, while partial sp² hybridization promotes charge delocalization and carbonyl enolization. Compared to single-chain 25PBQS and 26PBQS, dual-chain 2356PBQS with extended π-conjugation demonstrates exceptional active-site utilization (85%), delivering a high reversible capacity of 272 mAh g^-1 (50 mA g^-1), a high energy density of 339 Wh kg^-1 (360 W kg^-1), and stable cycling performance with 93.7% capacity retention after 200 cycles. This work provides critical insights into the rational design of organic cathodes with balanced energy and power densities for high-performance rechargeable Mg batteries.