Exceptional Lithium‐Ion Storage Performance on an Azo‐Bridged Covalent Heptazine Framework

Abstract

Graphitic carbon nitride (g‐C3N4) possesses rich pyridine nitrogens, which is helpful for facilitating electrochemical capability in Li+ storage; however, its poor conductivity is still the main challenge. Based on the knowledge of its intrinsic merits and defects, here, it is proposed to integrate active heptazine (HEP) species with functional linkers into orderly molecular structures for improved performance. As the first proof‐of‐concept, a unique azo‐linked covalent heptazine framework (Azo‐CHF) where two HEP units are bridged with azo linkages, is ingeniously designed and prepared to enhance the inherent charge conductivity for Li+ storage. Attributing to the deeply extended conjugation along overlapping azo nitrogens and the aromatic π system of HEP cores, Azo‐CHF with the lowest bandgap (2.58 eV) exhibits enhanced Li+/e− transport than g‐C3N4 through density functional theory calculations. Therefore, the Azo‐CHF anode exhibits an unprecedented performance with a large reversible capacity (1723.0 mAh g−1 at 0.1 A g−1), superior rate capability (824.0 mAh g−1 at 10 A g−1), and impressive cyclability (756.5 mAh g−1 undergoing 1000 cycles at 10 A g−1). This study not only demonstrates the great application prospect of Azo‐CHF for Li+ storage, but also opens a fantastic window to further explore high‐performance electrodes by integrating HEP with other active motifs.

Covalent Organic Framework Functionalized with Fluorescein Isothiocyanate for the Selective and Sensitive Detection of Toxic Mycotoxin

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