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.

Proton‐Conductive Supramolecular Hydrogen‐Bonded Organic Superstructures for High‐Performance Zinc‐Organic Batteries

“…Besides, the reversible formation of ZHTS functions as a pH buffer and hold the solution pH-value constant within a certain range. [28] Consequently, Zn anode is not influenced by proton uptake/removal in HBOS cathodes and shows the typical surface geometry of Zndeposition/stripping without zinc dendrites and byproducts (Figure S21).…”

Molecular Engineering Design for High-Performance Aqueous Zinc-Organic Battery

“…S10 and 2b. The energy gaps between LUMO and HOMO for 4S4Q and 4S6Q are smaller than other organic monomers, reflecting a good ability for electron transfer [ 25 , 27 , 37 ]. That is to say, introducing –S– bonds to an organic skeleton can significantly raise its electronic conductivity.…”

“…S11, the 4S4Q and 4S6Q show high electric conductivity of 8.87 and 9.45 S cm −1 , which are in agreement well with the DFT calculations. Additionally, the 4S6Q displays a lower energy level of LUMO, indicating that 4S6Q has a higher electron affinity and higher reduction potential [ 25 , 38 ]. The HOMO plots of organic molecules can provide information on the ability to achieve maximum capacity [ 39 ].…”

Recent advances in zinc–air batteries: self-standing inorganic nanoporous metal films as air cathodes

“…The long-term stability of ZABs is usually assessed by continuous charge/discharge cycling tests, the test times of more than 500 hours are recommended with a relatively high charge/discharge current density 43,54,59 (for example, 10 mA cm −2 ). And the round-trip overpotentials of ZABs before and after long-term stability are compared to check the rechargeability and durability.…”