Azo coupling enables isomeric anthraquinone porous organic polymers with enhanced lithium-ion battery performance

Abstract

Redox-active anthraquinone porous organic polymers (AQ-POPs) have emerged as sustainable electrode materials for lithium–organic batteries. Despite significant progress in synthetic methodologies, challenges such as limited redox-active sites, sluggish charge transport, and complex synthesis routes continue to hinder battery performance. Here, we report the use of AQ-POPs synthesized via a straightforward azo coupling reaction between diaminoanthraquinone (DAAQ) isomers with 2,6-, 1,4-, and 1,5-linkage positions and phloroglucinol to address these challenges. The resulting crosslinked polymers exhibit tailored porosity, abundant CO and CN functional groups, and robust electrochemical performance. Among them, AQ-POP-1 (synthesized from 2,6-DAAQ) delivered the highest reversible capacity of 971 mAh g⁻¹ at 50 mA g⁻¹, with excellent rate capability and long-term cycling stability. Cyclic voltammetry revealed that the isomeric structure of the DAAQ unit significantly influences redox behavior, capacitive contribution, and charge transport kinetics, shedding light on the structure–property relationships in which the steric hindrance of the DAAQ precursor plays an important role. Furthermore, ex situ Fourier-transform infrared, Raman, and X-ray photoelectron spectroscopy analyses provide insights into reversible transformations between CN/C–N and CO/C–O redox pairs associated with α-hydrazoketone and anthraquinone units, accounting for its superior performance. This work demonstrates the ease of azo coupling polymerization and provides guidelines for designing high-capacity, long-cycle-life organic electrodes for next-generation lithium–organic batteries.