Low-Redox-Barrier Two-Electron p-Type Phenoselenazine Cathode for Superior Zinc-Organic Batteries

Abstract

Organic p-type cathode materials with high redox potentials and fast kinetics have captured widespread attention in propelling Zn-organic batteries (ZOBs). However, their anion-accessible capacity is insufficient due to single electron reaction and/or high energy barrier of each redox-active unit. Here we design two-electron-donating p-type organic chalcogen small molecules (phenoxazine (PO), phenothiazine (PS) and phenoselenazine (PSe)) with tuned charge distributions and electron transfer behaviors as cathode materials for ZOBs. With the decrease of chalcogenide electronegativity (O>S>Se), PSe liberates the strongest coordination activity, efficient electron delocalization, and charge storage kinetics with an ultralow redox activation energy (0.23 vs. 0.34 eV of PS and 0.41 eV of PO), which contributes to high dual-electron utilization of phenazine motifs of 99.2% (vs. 68.8% of PS and 52.7% of PO). Consequently, Zn||PSe battery delivers the highest capacity storage (227 mAh g−1) and energy density (273 Wh kg−1) among the reported p-type cells, along with long life (10,000 cycles). A two-electron redox mechanism is unlocked at amine/selenium sites of PSe, accompanied by reversible uptake of two CF3SO3− anions. This study highlights the considerable potential of low-energy-barrier multielectron design for high-performance organic cathodes towards advanced ZOBs.