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

Abstract

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.