High-performance MoS2 quantum dots/graphene functionalized separator and its failure analysis under high sulfur loading

Abstract

Although functionalized separators have been proved to effectively mitigate the shuttle of lithium polysulfides (LiPSs), the capacity degradation of lithium-sulfur (Li-S) batteries with functionalized separators under high sulfur loading still hasn’t been detailed investigated totally. Herein, the synergistic inhibition effect of ultralight MoS2 quantum dots decorated nitrogen doped reduction of graphene oxides composites (MoS2 QDs-NRGO) modified separator on polysulfides shuttling is achieved. The Li-S batteries with this functional separator exhibit an impressive drop in cycle performance under high sulfur loading that the capacity retention at 71.5 % under sulfur loading of 2 mg cm−2, and only 53.1 % under 6 mg cm−2. Through the in-situ/ex-situ Raman spectroscopy investigation, kinetics analysis and electrochemical performance test, we discover that the inhomogeneous deposition of Li2S is seriously on the separator modified layer under high sulfur loading, which blocks the lithium-ion diffusion kinetics in the separator and increases the reaction between Li2S and lithium anode, leading to the fast capacity fading of Li-S batteries. Afterward, we find an appropriate area-loading of the modified layer can effectively mitigate the deposition of the Li2S, thereby improving the cycling stability of Li-S batteries under the high sulfur loading.