Alkynyl Boosted High-Performance Lithium Storage and Mechanism in Covalent Phenanthroline Framework

The poor conductivity of the pristine bulk covalent organic material is the main challenge for its application in energy storage. The mechanism of symmetric alkynyl bonds (C equivalent to C) in covalent organic materials for lithium storage is still rarely reported. Herein, a nanosized (approximate to 80 nm) alkynyl-linked covalent phenanthroline framework (Alkynyl-CPF) is synthesized for the first time to improve the intrinsic charge conductivity and the insolubility of the covalent organic material in lithium-ion batteries. Because of the high degree of electron conjugation along alkynyl units and N atoms from phenanthroline groups, the Alkynyl-CPF electrodes with the lowest HOMO-LUMO energy gap (Delta E=2.629 eV) show improved intrinsic conductivity by density functional theory (DFT) calculations. As a result, the pristine Alkynyl-CPF electrode delivers superior cycling performance with a large reversible capacity and outstanding rate properties (1068.0 mAh g(-1) after 300 cycles at 100 mA g(-1) and 410.5 mAh g(-1) after 700 cycles at 1000 mA g(-1)). Moreover, by Raman, FT-IR, XPS, EIS, and theoretical simulations, the energy-storage mechanism of C equivalent to C units and phenanthroline groups in the Alkynyl-CPF electrode has been investigated. This work provides new strategies and insights for the design and mechanism investigation of covalent organic materials in electrochemical energy storage.

Automated summary

To address the poor conductivity of pristine bulk covalent organic materials, researchers synthesized a nanosized alkynyl-linked covalent phenanthroline framework (Alkynyl-CPF) for lithium-ion batteries. By improving intrinsic charge conductivity and insolubility, the Alkynyl-CPF electrode demonstrated superior cyclic performance and rate properties due to its low HOMO-LUMO energy gap and high degree of electron conjugation. Investigations into the energy-storage mechanism of C equivalent to C units and phenanthroline groups further provide insights for the design and mechanism investigation of covalent organic materials in electrochemical energy storage.