Metallic MoS2 Nanosheets for Lithium-Sulfur Batteries

Abstract

This thesis addresses challenges in the development of lithium-sulfur (Li-S) batteries using metallic MoS2 nanosheets as functional host materials. While our prior research established lithiated MoS2 (LixMoS2) as an effective sulfur host for Li-S batteries, two major barriers remain to practical implementation of LixMoS2: incomplete understanding its stability and its scalable synthesis. Therefore, the initial focus of this thesis was to comprehensively investigate the thermal and environmental stability of LixMoS2. This part of the thesis revealed that lithiation dramatically enhances the thermal stability of the meta-stable metallic 1T phase, preserving it up to 250 °C in dry air—well above the conventional phase transformation temperature of ~100 °C. We establish that moisture is the primary degradation factor, enabling conventional fabrication methods in dry-room conditions rather than requiring costly fully inert environments. Second part of the thesis involves microwave-assisted chemical exfoliation (MWCE), a novel synthesis approach that dramatically reduces reaction time from 48-72 h to just 30 s while achieving near-complete conversion to the desirable 1T phase. By incorporating carbon-based microwave susceptors and replacing conventional conduction heating with microwave heating, effective reaction temperature increases from 66 °C to 144 °C, significantly accelerating phase transformation kinetics. The enhanced understanding of stability mechanisms and improved synthesis methods enable high-performance Li-S batteries. We employ melt-diffusion method to incorporate sulfur into the 1T MoS2 host structure, creating composite cathodes that maintain excellent electrochemical performance even under commercially relevant conditions. The scalability of MWCE further enables the fabrication of Ampere-hour pouch cells that deliver impressive initial capacities of 1245 mAh g⁻¹ with stable cycling under lean electrolyte conditions.