Synergistic Catalysts for Lithium-Sulfur Batteries: Ni Single Atom and MoC Nanoclusters Composites

Abstract

The practical application of sulfur (S) cathodes in lithium-sulfur (Li-S) batteries is hindered by the shuttling of soluble lithium polysulfides (LiPSs) and sluggish sulfur redox kinetics. Addressing these challenges requires advanced catalytic host materials capable of trapping LiPSs and accelerating Li-S redox reactions. However, single-site catalysts struggle to effectively mediate the complex multi-step and multi-phase sulfur conversion processes. In this study, we present a novel dual-site catalyst, Ni-MoC-NC, featuring nickel single atoms anchored to nitrogen sites (Ni-N₄) within a carbon nitride (NC) matrix and molybdenum carbide (MoC) nanoclusters. Experimental and theoretical analyses reveal that MoC sites efficiently catalyze the reduction of long-chain LiPSs (Li₂S₈ to Li₂S₄), while Ni-N₄ sites drive the reduction of short-chain LiPSs (Li₂S₄ to Li₂S), resulting in a synergistic enhancement of the complete Li-S redox process. When incorporated as a coating on the cathode side of a commercial polypropylene (PP) separator, the Ni-MoC-NC catalyst enhances sulfur utilization, suppresses LiPSs shuttling, and facilitates a uniform Li⁺-ion distribution, effectively mitigating the uncontrolled growth of lithium dendrites. Thereby, Li-S batteries employing an S/Ni-MoC-NC cathode and a Ni-MoC-NC@PP separator demonstrate outstanding performance, including an initial capacity of 1624 mAh g⁻¹ at 0.2C and 1142 mAh g⁻¹ at 1C, retaining 590 mAh g⁻¹ after 800 cycles. At a sulfur loading of 8.3 mg cm⁻² and an electrolyte/sulfur ratio of 6 µL mg⁻¹, the system achieves an initial areal capacity of 9.57 mAh cm⁻² at 0.1C, showcasing significant promise for practical applications.