A high-capacity organic cathode based on active N atoms for aqueous zinc-ion batteries

Organic materials are attractive for energy storage due to the structural versatility and green sustainability. Recently, the organic material based on polyaniline has exhibited an enormous potential for zinc-ion batteries (ZIBs). However, their advancement still suffers from limited capacities and unstable voltage plateaus. Herein, we have, for the first time, developed the poly(o-phenylenediamine) (PoPD) organic cathode for aqueous ZIBs. The PoPD with phenazine-like structures can integrate sufficient C=N bonds for zinc storage. The PoPD cathode shows a high reversible capacity (318 mAh g(-1) at 0.05 A g(-1)) and stable charge/discharge voltage platforms around 0.67 and 0.58 V. The PoPD cathode prepared under an acidic condition possesses a long cycle life up to 3000 cycles with a high capacity retention of 66.2% at 1 A g(-1). Furthermore, the mechanism of zinc storage in phenazine-like units of the PoPD has been investigated by ex-situ X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectrometer (FTIR) spectra. For each phenazine-like unit, one zinc ion can coordinate with two C=N bonds reversibly. Such a coordination process maintains the stable conjugated structure of PoPD and enables the steady charge/discharge platforms. This work has paved a way for the design of novel organic materials for ZIBs.