Self-branched Nb2O5 nanoarrays as “electron-ion reservoirs” to enhance the conversion of polysulfides in flexible Li–S batteries

Abstract

Li–S batteries (LSBs) are promising next-generation energy-storage devices due to their high theoretical capacity and cost effectiveness. However, the widespread use of LSBs is still impeded by the low conductivity of sulfur, the volume expansion of active materials, and the shuttle effect of lithium polysulfides (LiPSs) in practical conditions. In this work, a novel sulfur matrix integrating self-branched Nb₂O₅ nanoarrays and flexible carbon cloth (NBCC) is designed and prepared. The conformal S@NBCC composite provides surface-to-surface contact between sulfur and the catalytic mediator, thus exposing more active sites for trapping LiPSs. Meanwhile, the selected Nb₂O₅ nanoarrays with ultrafast Li⁺ motion capability can work as “electron-ion reservoirs” to further accelerate the conversion reaction of LiPSs. Moreover, the extra-free space among the branched nanoarrays can not only facilitate the infiltration of the liquid electrolyte, but also enhance its tolerance to volume expansion of sulfur during the lithiation process. Benefitting from these synergistic effects, the self-supported S@NBCC shows a high specific capacity of 1262.5 mA h g⁻¹ at 0.1 C and maintains an impressive specific capacity of 759.6 mA h g⁻¹ even after 300 cycles at 1 C, showing great potential in promoting the practical application of flexible LSBs.