Issue 15, 2024

A bipolar-type covalent organic framework on carbon nanotubes with enhanced density of redox-active sites for high-performance lithium-ion batteries

Abstract

As a special class of crystalline porous polymers, covalent organic frameworks (COFs) containing electrochemical redox-active centers are attractive electrode materials for Li-ion batteries. However, designing and synthesizing COF-based electrode materials with a high loading density of redox-active groups, high redox potential, and increased conductivity to enhance their specific capacities and energy densities is extremely challenging. Herein, a series of novel bipolar-type composite cathodes (denoted as TAPP-Pz-COF-XCNTs, where X = 10, 20, 30 and 40 wt% of CNTs) were prepared by in situ condensation of a new p-type phenazine (Pz)-based building block (5,10-dimethyl-5,10-dihydrophenazine-2,7-dicarbaldehyde, Pz) with a bipolar-type semiconductor (5,10,15,20-tetra(p-aminophenyl) porphyrin, TAPP) in the presence of carbon nanotubes to address these challenges. TAPP-Pz-COF-40%CNTs possessing exceptional conductivity (7.48 × 10−3 S m−1) and a mesoporous channel of 2.1 nm enable stable and rapid ion transport. This, in combination with the plentiful p-, n-, and bipolar-type redox active sites, endows the TAPP-Pz-COF-40%CNT cathode with a specific capacity of up to 314 mA h g−1 at 200 mA g−1, a record energy density of 737.5 W h kg−1, which is the highest energy density among the thus far reported organic polymer and COF cathodes for Li-ion batteries, superior ion transport dynamics (10−12 to 10−8 cm2 s−1), and excellent long-term cycling stability (88% after 10 000 cycles at 10 000 mA g−1). Using a series of ex situ characterization studies and density functional theory (DFT) calculations, the reversible conversion of bipolar-type redox-active centers of TAPP-Pz-COF-40%CNTs was revealed and an overall 6 PF6/6 Li+ redox mechanism per asymmetric unit was rationalized.

Graphical abstract: A bipolar-type covalent organic framework on carbon nanotubes with enhanced density of redox-active sites for high-performance lithium-ion batteries

Supplementary files

Article information

Article type
Paper
Submitted
01 Feb 2024
Accepted
10 Jun 2024
First published
14 Jun 2024

Energy Environ. Sci., 2024,17, 5451-5460

A bipolar-type covalent organic framework on carbon nanotubes with enhanced density of redox-active sites for high-performance lithium-ion batteries

Q. Xu, Z. Liu, Y. Jin, X. Yang, T. Sun, T. Zheng, N. Li, Y. Wang, T. Li, K. Wang and J. Jiang, Energy Environ. Sci., 2024, 17, 5451 DOI: 10.1039/D4EE00520A

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