Nano-carbon supported B/N-coordinated Fe single atoms with a tuned electronic structure for long lifespan zinc–iodine batteries†

Abstract

Single-atom catalysts (SACs) have great potential to boost the sluggish iodine redox kinetics and alleviate the polyiodide shuttle in aqueous zinc–iodine (Zn–I₂) batteries. Nevertheless, it is a big challenge to improve the catalytic activity of traditional metal nitrogen (M–N₄) SACs by adjusting the microenvironment to enhance iodine redox kinetics. Herein, asymmetric B/N-coordinated Fe single atoms (Fe–B₂N₂) immobilized on carbon nanotube forests (denoted as Fe-SAs@BNCF) are prepared by a one-pot calcination method and used as the iodine host in Zn–I₂ batteries. Theoretical calculation results have revealed that the B sites function to increase the electron density by disrupting the symmetrical electron distribution around the Fe sites compared to traditional Fe–N₄. Correspondingly, the as-synthesized Fe–B₂N₂ SACs significantly improve polyiodide adsorption and electrocatalytic activities in Zn–I₂ batteries. Moreover, carbon nanotube forests provide more adsorption sites for polyiodides. Consequently, the Zn–I₂ batteries with Fe-SAs@BNCF as a host enable a superb long lifespan (78% retention over 60 000 cycles at 5 A g⁻¹) and a high rate capability (147 mA h g⁻¹ at 10 A g⁻¹). This work provides a promising strategy for designing advanced I₂ cathodes with asymmetric single atoms for long-life Zn–I₂ batteries.