Strengthened d-p Orbital Hybridization on Metastable Cubic Mo₂C for Highly Stable Lithium-Sulfur Batteries

Suppressing the lithium polysulfide (LiPS) shuttling as well as accelerating the conversion kinetics is extremely crucial yet challenging in designing sulfur hosts for lithium-sulfur (Li-S) batteries. Phase engineering of nanomaterials is an intriguing approach for tuning the electronic structure toward regulating phase-dependent physicochemical properties. In this study, a metastable phase δ-Mo₂C catalyst was elaborately synthesized via a boron doping strategy, which exhibited a phase transfer from hexagonal to cubic structure. The hierarchical tubular structure of the metastable cubic δ-Mo₂C-decorated N-doped carbon nanotube (δ-B-Mo₂C/NCNT) endows fast electron transfer and abundant polar sites for LiPSs. First-principles calculations reveal the strengthened chemical adsorption capability and hybridization between the d orbital of Mo metal and the p orbital of S atoms in LiPSs, contributing to higher electrocatalytic activity. Moreover, in situ Raman analysis manifests accelerated redox conversion kinetics. Consequently, δ-B-Mo₂C/NCNT renders the Li-S battery with a high specific capacity of 1385.6 mAh g^-1 at 0.1 C and a superior rate property of 606.3 mAh g^-1 at 4 C. Impressively, a satisfactory areal capacity of 6.95 mAh cm^-2 is achieved under the high sulfur loading of 6.8 mg cm^-2. This work has gained crucial research significance for metastable catalyst design and phase engineering for Li-S batteries.