Unraveling the Formation of Amorphous MoS₂ Nanograins during the Electrochemical Delithiation Process

Molybdenum disulfide (MoS₂) is a promising high-capacity anode for lithium-ion batteries. However, the conversion reaction mechanism of MoS₂ (the delithiation pathway in particular) has been controversial, which limits the rational optimization of its electrochemical performance. The main challenge is how to precisely identify the amorphous nanomaterials generated during lithiation/delithiation. Here, the structural evolutions of MoS₂ during lithiation/delithiation are systematically investigated using synchrotron X-ray absorption spectroscopy at Mo K-edge and S K-edge and Raman spectroscopy. It is revealed that amorphous MoS₂ nanograins rather than sulfur as previously suggested, are formed after delithiation, and that the fully lithiated MoS₂ electrode contains additional Mo-S related phases besides the known Mo and Li₂S. Density functional theory simulations suggest that the Mo nanoparticles formed during lithiation are very reactive with Li₂S, thus enabling the regeneration of MoS₂ upon delithiation. These findings deepen the understanding of the lithiation/delithiation mechanism of MoS₂, which will pave the way for the rational design of advanced MoS₂-based electrodes.