A systematic development of 2D alloy catalyst with synergistic performance of high lithium polysulfide (LiPS) binding energy and efficient Li+ ion/electron conduction is presented. The first section of work found that Li+ ions can flow through the percolated ion transport pathway in polycrystalline MoS2, while Na+ and K+ ions can easily flow through the percolated 1D ion channel near the grain boundaries. An unusually high ionic conductivity of extrinsic Li+, Na+, and K+ ions in 2D MoS2 film exceeding 1 S/cm was measured that is more than two orders of magnitude higher than those of conventional solid ionic materials, including 2D ionic materials. The second section of this dissertation focus on catalyzing the transformation of LiPSs to prevent the shuttle effect during the battery cycling by synthesizing 2H (semiconducting) – 1T (metallic) mixed phase 2D Mo0.5W0.5S2 alloy on CNF paper, using two step sputtering and sulfurization method. The lithium sulfur (Li-S) battery cell assembled with the 2D Mo0.5W0.5S2/CNF/S cathode shows a high specific capacity of 1228 mAh g-1 at 0.1C and much higher cyclic stability over 4 times as compared to the pristine cathodes. The high LiPSs binding energy of catalyst efficiently prevents the shuttling effect and corrosion of Li anode after long term stability test for over 400 cycles. The defect engineered MoWS catalyst on CNF showed significantly enhanced polysulfide transformation resulting in specific capacity of 1586 mAh g-1 at 0.05C for the full cell Li-S battery and much higher cyclic stability over 1000 cycles. Stacked layers of D-MoWS-CNF-S cathodes can result in an increased sulfur loading up to 10 mg cm-2 with highest achievable areal capacity of 13.5 mAh/cm2. The efficient sulfur utilization and reduced negative-to-positive capacity (N/P) ratio by D-MoWS catalyst significantly increased the gravimetric energy density to the highest reported value of 1090 Wh kg-1 w.r.t the total weight of anode and cathode.

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