Tuning functional two-dimensional MXene nanosheets to enable efficient sulfur utilization in lithium-sulfur batteries

Abstract

Practicality of lithium-sulfur batteries is severely hindered by the notorious polysulfide-shuttle phenomenon, leading to rapid capacity fade. This issue is aggravated with increase in sulfur loading, causing low-coulombic efficiency and cycle life. Herein, we present a facile strategy to combine hydrophobic sulfur and hydrophilic, conductive Ti 3 C 2 T z -MXene via one-step surface functionalization using di(hydrogenated tallow)benzylmethyl ammonium chloride (DHT). The latter renders the Ti 3 C 2 T z surface hydrophobic, making it readily dispersible in sulfur dissolved in a carbon disulfide (CS 2 ) solvent. By evaporating the solvent, we conformally coat the DHT-Ti 3 C 2 T z (DMX) with sulfur. The developed composite, with higher available active area, enables effective trapping of lithium polysulfides (LiPs) on the electroactive sites within the cathode, leading to improvement in electrochemical performance at higher sulfur loadings. The DMX/S cathodes function with high sulfur loading of ∼10.7 mg·cm −2 and deliver a stable areal capacity of ∼7 mAh·cm −2 for 150 cycles. Moreover, a DMX/S cathode in a pouch-cell configuration retains ∼770 mAh·g −1 after ∼200 cycles at 0.2C (85.5% retention). Ex situ studies elucidate the nature of the LiPs-MXene interaction and the effect of surface functionalization towards improved performance. DHT functionalized hydrophobic MXenes (DMX) form a stable colloidal solution in CS 2 Atomically thin, metallically conductive DMX improves sulfur utilization in composites DMX/S cathode delivers good cycling stability at a high sulfur loading of 10.7 mg·cm −2 Emphasis on cathode development, pouch-cell performance, and nature of the interactions Rechargeable lithium-sulfur (Li-S) batteries have the potential to replace lithium-ion batteries because of their higher specific energy. Pai et al. report a surface fictionalization strategy to enable maximum sheet-surface area use of 2D-MXenes in Li-S batteries, which enables high sulfur loading, capacity retention, and long cycle life.