Enhanced redox kinetics of polysulfides by nano-rod FeOOH for ultrastable lithium–sulfur batteries

Abstract

Lithium–sulfur batteries (LSBs) have been exploited as advanced energy storage systems owing to their high theoretical specific capacity. However, the shuttle effect from lithium polysulfides (LiPSs) and the sluggish redox kinetics are the main obstacles hindering LSBs' commercialization. In this study, an efficient host material to adsorb LiPSs and regulate their redox conversion was designed. Nano-rod iron hydroxide/electrochemical exfoliated graphene (FeOOH/EG) composites were synthesized by a traditional hydrothermal method. After ball-milling and annealing with modified sulfur, the FeOOH/EG-S composite presents that the sulfur particle is surrounded by FeOOH/EG sheets. As evidenced by XPS results, the FeOOH/EG composite provides strong chemical bonding towards LiPSs with Fe–S, Li–O and S–C bonds. Potentiostatic discharging tests demonstrated that FeOOH/EG promotes the precipitation of solid-state Li₂S. First-principle (DFT) calculations revealed that LiPSs are adsorbed by FeOOH within a range of adsorption energies from −1.07 eV to −5.7 eV, indicating that FeOOH has favourable affinity towards polysulfides. Meanwhile, the low diffusion energy barrier (0.07 eV and 0.11 eV) enables the fast diffusion of LiPSs across FeOOH, enhancing the redox reaction kinetics during the charge/discharge process. As a result, the prepared FeOOH/EG-S electrode delivers a reversible capacity of 1323 mA h g⁻¹ at a current density of 0.1C. After charging/discharging for 500 cycles at a current density of 2C, the FeOOH/EG-S electrode displays a capacity of 733 mA h g⁻¹, which shows a low capacity decay rate of ∼0.027% per cycle. This work will be quite inspiring to promote the commercialization of LSBs.