Fly ash as a high-capacity, high-rate performance, and low-cost cathode material for lithium-sulfur batteries

Abstract

Lithium-sulfur batteries with a higher theoretical specific capacity (1675 mA h g⁻¹) and a higher energy density (2600 W h kg⁻¹) are considered to be the next-generation energy storage system. However, lithium-sulfur batteries have disadvantages for poor cycle performance, low Coulomb efficiency, and low utilization of active materials. Therefore, the graphene-fly ash-sulfur composite cathode materials are prepared for lithium-sulfur batteries to improve the performance in this study, and the performances of lithium-sulfur batteries with different fly ash doping levels are analyzed. The results show that the cycle stability and high-rate performance of the composite material after adding fly ash are significantly improved. When the composite material with 5 % fly ash cycles 100 times at 0.2 C and 0.5 C current density, its reversible specific capacity can reach 416.8 mA h g⁻¹ and 524 mA h g⁻¹, the cycle efficiency is 98.3 % and 90.6 %, and the capacity retention rate is 56.2 % and 78.8 % respectively, indicating that the composite material has good cycle stability under high-rate conditions. Furthermore, the adsorption experiments and the density functional theory (DFT) calculation of the fly ash to Li₂S_x indicate that the shuttle effect of the polysulfide is inhibited by fly ash particles mainly through ion adsorption and intermolecular force.