A π-conjugated N-containing compound as a high-capacity cathode for fast aqueous and flexible Zn-ion batteries

Aqueous zinc-ion battery is recognized as a strong and potential alternative to lithium-ion batteries in the fields of grid-scale energy storage and wearable electronics, due to its low cost and high safety. For developing new cathode materials of zinc-ion batteries with high-capacity, herein, trinitrohexaazanaphthalene (TNHATN) was synthesized and firstly evaluated as the cathode materials. Because of its multiple redox active sites, π-conjugated structure containing electron-withdrawing groups (nitro, -NO2) and insolubility in aqueous electrolytes, the TNHATN electrode exhibits a high specific capacity of 3246 mAh g-1 at a current density of 0.04 A g-1 during the first discharge, high rate-performance (239 mAh g-1 remains at 20 A g-1) and better cycling stability (67.3% capacity retention after 1000 cycles). Density functional theory (DFT) calculations and various ex situ tests disclose that the uptake and removal of Zn2+ and H+ ions may be involved in the electrochemical reaction of the TNHATN electrode. Meanwhile, the fabricated flexible aqueous Zn//TNHATN battery also has long cycle life (71% capacity retention after 1000 cycles), excellent volumetric energy density (21.36 mWh cm-3), and excellent mechanical flexibility, displaying its application potential in wearable electronics.