Coordination electrochemistry taming reversible hypervalent bromine redox for energetic six-electron-transfer lithium-bromine battery.

Conversion-type static bromine batteries demonstrate promise in high output voltage and large capacity for rechargeable energy storage due to the inherent polyvalent reaction potential. Nevertheless, the combination of the limited two-electron 2Br-/Br2 redox couple and the redox-inactive organic ligands presents a fundamental bottleneck for the overall specific energy. Herein, ethyl viologen dibromide is developed as an energetically active positive electrode for organic lithium-bromine batteries by efficient coordination chemistry, featuring an advanced six-electron redox mechanism triggered by both intercalation and conversion reactions. The activated redox couple of 2Br-/2Br+ incubates a collaborative increase in capacity (632.8 mAh g-1Br) and discharge voltage (3.7 V). Besides, ethyl viologen undergoes reversible two-step intercalation and extraction of Li+ ions, contributing to additional energy storage. Reciprocal spectroscopic characterizations and computational electrochemistry indicate the chemisorption effect and interhalogen confinement and detail the dynamic mass-charge transfer pathway. This work sets a paradigm worth emulating for designing high-performance halogen batteries.