Push-Pull Engineering Enables Dual-Electron Redox in Phenoxazine Cathodes for Lithium Dual-Ion Batteries

Abstract Phenoxazine-based compounds are valuable cathode materials owing to their high theoretical capacity and robust redox reversibility. However, insufficient intramolecular charge delocalization destabilizes deeply oxidized states and limits dual-electron transfer. Herein, a “push-pull electronic engineering” strategy is developed by incorporating delocalizing electron-deficient units into the phenoxazine framework to regulate frontier molecular orbitals, extend π-electron delocalization, and stabilize deeply oxidized states. Two isomers, 2,7-di(10H-phenoxazin-10-yl) tribenzo[a,c,i]phenazine-10,15-dione (2,7-DPTBD) and its 3,6-substituted counterpart (3,6-DPTBD), are synthesized. Both materials exhibit reversible dual-electron oxidation. Nevertheless, steric hindrance in 3,6-DPTBD weakens the push-pull interaction and reduces its electrochemical performance. Consequently, 2,7-DPTBD delivers a high energy density of 668 Wh kg–1 at an average discharge potential of 2.56 V. Furthermore, a full cell employing graphite anodes achieves a peak discharge capacity of 211 mAh g–1 and maintains stable cycling over 1000 cycles. Symmetric dual-ion batteries are assembled based on the bipolar characteristics of 2,7-DPTBD, which stably operate for 200 cycles.