Vanadium Monoxide-Based Free-Standing Nanofiber Hosts for High-Loading Lithium-Sulfur Batteries

Abstract

We report the fabrication of free-standing vanadium monoxide-based carbon nanofiber/sulfur (VO-CNFs/S) cathodes via electrospinning and in situ carbothermal reduction reaction followed by sulfur impregnation using an ultrarapid (<90 s) hybrid solution/melt deposition technique. The assembled Li-S batteries using VO-CNFs/S cathodes delivered a stable capacity of 950 mAh·g-1 with 97% retention after 200 cycles at a 0.5 C rate with a moderate electrolyte/sulfur ratio of 20 mL·g-1 of sulfur. Additionally, we develop cathodes with a high sulfur loading of 8.32 mg·cm-2 that exhibits a stable capacity of 900 mAh·g-1 after a few cycles with near 100% retention over 100 cycles. These cells correspond to a stable aerial capacity of 7.5 mAh·cm-2. We integrate our fabrication and electrochemical performance study with fundamental investigations of Li+ diffusion kinetics, in situ visual monitoring of polysulfides, and ex situ post-mortem X-ray photoelectron spectroscopy study to elucidate polysulfide shuttling and polysulfide-host interactions. The unique integration of oxide and nitride groups in this work results in a synergistic effect of strong Lewis acid-base interactions originating from the vacant d-orbitals of the vanadium monoxide phase and improved conductivity originating from the nitrogen doping in CNFs from a polymeric precursor, thus offering active sites for strong polysulfide binding as well as faster reaction kinetics.