A Nitrogen-Rich Fully Conjugated Covalent Organic Framework as High-Performance Anode Materials for Hybrid Lithium-Ion Capacitors

Abstract

Hybrid lithium-ion capacitors (HLICs) have been found to have significant commercial potential owing to both their high power density and high energy density. However, the kinetic imbalance between electrodes hinders their development. The covalent organic frameworks (COFs) are one of the promising anode materials owing to their rich active sites, highly ordered channels, and flexible structural design, but they still meet the limitation of low electrical conductivity. Herein, we develop a fully conjugated covalent organic framework (TAB-COF) featuring a nitrogen-rich graphene-like structure as anode material for HLICs. Such a fully conjugated structure of TAB-COF significantly enhances the intrinsic conductivity and promotes efficient electron transport, which realizes high practical discharge capacity. Furthermore, the Li+ storage mechanism involving 21-electron storage was systematically investigated through complementary ex situ spectra analyses and theoretical calculations. As a result, the TAB-COF organic electrode delivers an outstanding reversible capacity of 2014 mAh g−1 at 0.1 A g−1, which is superior to most organic anode materials. In addition, the assembled TAB-COF||AC HLICs possess a high energy density of 103.8 Wh kg−1, a high power density of 7310.5 W kg−1, and stable cycling performance with a capacity retention of 87% after 10,000 cycles at 1 A g−1.