Design and Synthesis of a π-Conjugated N-Heteroaromatic Material for Aqueous Zinc–Organic Batteries with Ultrahigh Rate and Extremely Long Life

Abstract

Electroactive organic materials with tailored functional groups are of great importance for aqueous Zn–organic batteries due to their green and renewable nature. Herein, a completely new N-heteroaromatic material, hexaazatrinaphthalene-phenazine (HATN-PNZ) is designed and synthesized, by an acid-catalyzed condensation reaction, and its use as an ultrahigh performance cathode for Zn-ion batteries demonstrated. Compared with phenazine monomer, it is revealed that the π-conjugated structure of N-heteroaromatics can effectively increase electron delocalization, thereby improving its electrical conductivity. Furthermore, the enlarged aromatic structure noticeably suppresses its dissolution in aqueous electrolytes, thus enabling high structural stability. As expected, the HATN-PNZ cathode delivers a large reversible capacity of 257 mAh g−1 at 5 A g−1, ultrahigh rate capability of 144 mAh g−1 at 100 A g−1, and an extremely long cycle life of 45 000 cycles at 50 A g−1. Investigation of the charge-storage mechanism demonstrates the synergistic coordination of both Zn2+ and H+ cations with the phenanthroline groups, with Zn2+ first followed by H+, accompanying the reversible formation of zinc hydroxide sulfate hydrate. This work provides a molecular-engineering strategy for superior organic materials and adds new insights to understand the charge-storage behavior of aqueous Zn–organic batteries.