Competing reduction induced homogeneous oxygen doping to unlock MoS₂ basal planes for faster polysulfides conversion

The parasitic polysulfides shuttle effect greatly hinders the practical application of lithium sulfur batteries, and this issue can be addressed by promoting polysulfides conversion with catalytic materials such as MoS₂. However, the catalytic activity of MoS₂ mainly relies on edge sites, but is limited by inert basal planes. We herein report a novel, facile, ethylene glycol enabled competing reduction strategy to dope MoS₂ homogeneously with oxygen atoms so that its inert basal planes can be unlocked. Ethylene glycol works as a reducing agent and competes with thiourea to react with ammonium molybdate, leading to insufficient sulfuration of Mo, and consequent formation of O-MoS₂. Our theoretical and experimental investigations indicate that the homogeneously distributed O dopants can create abundant adsorption/catalytic sites in the MoS₂ basal planes, enlarge the inter-plane distance to promote ion transport, and thus enhance the catalytic conversion of polysulfides. The oxygen doped MoS₂ (O-MoS₂) is supported on carbon nanosheets (CNS) and the composite (O-MoS₂/CNS) is employed to modify the separator of Li–S battery. It gives the battery an initial discharge capacity of 1537 mAh g⁻¹ at 0.2 C, and the battery retains a discharge capacity of 545 mAh g⁻¹ after ultra-long 2000 cycles at 1 C, corresponding to a very small cyclic decay rate of 0.0237%. Even under a raising sulfur loading of 8.2 mg cm⁻², the Li-S battery also delivers a high discharge capacity (554 mAh g⁻¹) with outstanding cycle stability (84.6% capacity retention) after 100 cycles at 0.5 C. Our work provides a novel, facile approach to fabricate highly catalytically active oxygen-doped MoS₂ for advanced Li–S batteries.