Electrochemical Reaction Mechanism of the MoS₂ Electrode in a Lithium-Ion Cell Revealed by in Situ and Operando X-ray Absorption Spectroscopy

Abstract

As a typical transition metal dichalcogenide, MoS₂ offers numerous advantages for nanoelectronics and electrochemical energy storage due to its unique layered structure and tunable electronic properties. When used as the anode in lithium-ion cells, MoS₂ undergoes intercalation and conversion reactions in sequence upon lithiation, and the reversibility of the conversion reaction is an important but still controversial topic. Here, we clarify unambiguously that the conversion reaction of MoS₂ is not reversible, and the formed Li₂S is converted to sulfur in the first charge process. Li₂S/sulfur becomes the main redox couple in the subsequent cycles and the main contributor to the reversible capacity. In addition, due to the insulating nature of both Li₂S and sulfur, a strong relaxation effect is observed during the cycling process. This study clearly reveals the electrochemical lithiation-delithiation mechanism of MoS₂, which can facilitate further developments of high-performance MoS₂-based electrodes.