Electrochemical performances of azo dyes as organic cathodes for lithium-ion batteries

Organic electrode materials present a promising pathway toward green and sustainable lithium-ion batteries (LIBs) due to their abundant resources, high theoretical capacities, molecular diversity, and environmental sustainability. In this study, we systematically investigate a set of commercially available azo dyes to explore their electrochemical performances as organic cathode materials, with a particular focus on methyl orange (MO), which shows the best performance and lowest cost within the set. Ex situ structural characterizations during discharge-charge tests, including X-ray diffraction (XRD), Raman spectroscopy, Fourier-transform infrared (FTIR) spectroscopy, and X-ray photoelectron spectroscopy (XPS) characterization, confirm that MO undergoes reversible lithiation/delithiation at the azo group. Furthermore, to address issues of dissolution and capacity fading during cycling, MO has been encapsulated within BP2000 conductive porous carbon. The resulting MO@BP2000 composite shows significantly improved cycling stability and rate capability, achieving an initial reversible capacity of 150 mAh g −1 and retaining 121 mAh g −1 after 50 cycles at 30 mA g −1 . These findings clarify the redox behavior of azo dyes in LIBs and provide mechanistic insights that can potentially guide the molecular design of high-performance azo-based cathode materials. • Four commercial azo dyes are evaluated as cathode materials for lithium-ion batteries. • Methyl orange (MO) shows the best balance of cost and electrochemical performance. • The redox mechanism of MO is revealed via ex situ spectroscopic characterization. • Encapsulation with BP2000 further enhances the cycling stability of MO.