Sulfone Modification Enables Merged Multi-Electron Transfer Towards High Voltage Output in Phenoxazine-Based Zinc-Organic Cathodes.

Aqueous zinc-organic batteries are promising for grid-scale energy storage due to their intrinsic safety, low cost, and sustainability, yet their energy density is often constrained by the low operating voltage of organic cathodes. Herein, we introduce strong electron-withdrawing sulfone groups into a phenoxazine backbone, yielding a novel organic cathode material, [(4,4'-sulfonylbis(4,1-phenylene))]bis(10H-phenoxazine) (PXZ-DPS). Theoretical and experimental analyses reveal that sulfone substitution raises the redox potential, deepens frontier orbital levels, and extends π-conjugation, thereby enhancing electronic conductivity and suppressing active material dissolution. Notably, the introduction of the sulfone group enables modulation of the redox kinetics by shifting and merging the two successive one-electron redox processes of two PXZ units (four-electron redox processes in total) at low potentials to higher potentials in PXZ-DPS. As a result, PXZ-DPS delivers a high average discharge voltage of approximately 1.5 V vs. Zn2+/Zn, corresponding to a ∼0.5 V uplift over its phenoxazine analogue, while achieving an impressive specific capacity of 202 mAh g-1 at 0.5 A g-1. These synergistic effects jointly boost the energy density (303 Wh kg-1) of PXZ-DPS||Zn. This work establishes a high‑voltage organic cathode platform and offers a rational strategy to boost the multi‑electron voltage regime in zinc-organic cathodes.