pi-Conjugated N-heterocyclic compound with redox-active quinone and pyrazine moieties as a high-capacity organic cathode for aqueous zinc-ion batteries

Organic cathode materials have been widely used for aqueous zinc-ion batteries (ZIBs) due to their designable molecular structures and diverse redox groups. However, there are still many challenges that need to be over-come, such as limited specific capacity and utilization, inadequate electrical conductivity, unsatisfactory cycle durability and unclear charge storage mechanism. Herein, we report a pi-conjugated N-heterocyclic compound containing dual-redox active groups (i.e. quinone and pyrazine), benzo[b]phenazine-6,11-dione (BPD), which are employed as a cathode material in aqueous ZIBs. The BPD cathode shows a high capacity of up to 429 mAh g-1 at 0.05 A g-1, 100 % capacity utilization and excellent cycling performance upon 10,000 cycles. The aqueous ZIB full cell with the BPD cathode delivers an energy density of 276 Wh kg -1, higher than the most previously re-ported organic cathode materials. Moreover, ex-situ characterizations, electrochemical experiments, and theo-retical calculations, clearly illustrate that H+ and Zn2+ are co-inserted during the charge/discharge process. The high utilization and stability of BPD cathode is due to the high insolubility of both BPD and its discharge products. This work provides a reasonable strategy and unique perspective for the design and synthesis of novel high-performance organic cathode materials for aqueous ZIBs.