Alloy-Regulated Heterointerface Engineering for Kinetics-Driven Sulfur Redox in Li-S Batteries

Lithium-sulfur (Li-S) batteries offer exceptional theoretical energy density, yet their practical deployment is fundamentally constrained by sluggish sulfur redox kinetics and persistent shuttle of polysulfides. Here, we report a NiMo-alloy-assisted quantitative heterointerface engineering strategy that regulates the phase balance, interfacial abundance, and electronic coupling in Mo₂C/MoC heterostructures. By tuning the Ni/Mo ratio as a continuous control parameter, NiMo incorporation drives controlled Mo₂C→MoC phase reconstruction to maximize the density and accessibility of catalytically active Mo₂C/MoC heterointerfaces, while the resulting NiMo domains primarily function as a structural modulator and metallic electron-transport pathway, complementing the conductive nitrogen-doped carbon framework. In situ/ex situ characterizations and density functional theory calculations reveal Mo₂C/MoC heterointerfaces intrinsically exhibit the most favorable polysulfide adsorption strength and the lowest energy barriers for bidirectional sulfur conversion. As a result, Li-S cells equipped with the catalytic separator deliver a high reversible capacity of 1477.8 mAh g^-1 at 0.1 C and sustain long-term cycling with an ultralow decay rate of 0.032% per cycle over 1000 cycles at 0.5 C, enabling an areal capacity of 15.2 mAh cm^-2 at high sulfur loading. This work establishes a quantitative heterointerface design paradigm for regulating sulfur electrochemistry and provides general insights into heterostructure-enabled catalysis in metal-sulfur batteries.