Evidence for the Coexistence of Polysulfide and Conversion Reactions in the Lithium Storage Mechanism of MoS2 Anode Material

Numerous studies have been conducted on a MoS2 material owing to its high capacity and good rate capability as a promising substitute for commercial graphite materials in lithium-ion batteries. However, contrary to the continuous improvement in performance, the mechanism of the reversible lithium-ion storage in MoS2 remains still unclear. Herein, we carried out an in-depth study about the lithium storage behavior of MoS2 during the lithiation/delithiation process. The conversion reaction was verified by monitoring the reversible formation of the MoS2 phase through the X-ray absorption and X-ray photoelectron spectroscopies. Moreover, reversible polysulfide reactions were demonstrated by investigating the sulfur redox reaction through the voltage profile comparison and X-ray photoelectron spectroscopy deconvolution. The results of systematic approach to the reaction mechanism present clear evidence that both the polysulfide reaction (S + 2Li+ + 2e− ↔ Li2S) and the conversion reaction (MoS2 + 4Li+ + 4e− ↔ Mo + 2Li2S) contribute to the initial obtained capacities. Furthermore, these reactions were confirmed to occur not only in the initial cycle but also during subsequent cycles. The findings help to understand the distinct reaction mechanism of MoS2 and provide crucial guidelines for developing promising conversion-based anode materials as next-generation rechargeable batteries.