Direct tracking the interfacial processes at nanoscale in a working battery is important to reveal the reaction mechanism and further create the structure-reactivity correlations, which is of great significance for interfacial engineering and prospective optimization of lithium-ion batteries (LIBs).

Recently, a research team led by Prof. WEN Rui and Prof. ZHENG Jian at Institute of Chemistry of the Chinese Academy of Sciences elucidated the structural evolution and reaction mechanism on ultra-flat monolayer molybdenum disulfide (MoS₂) electrode upon charging/discharging. The study was published in Nature Communications.

Using in situ electrochemical atomic force microscopy (EC-AFM), the researchers intensively studied the interfacial processes on large-area ultra-flat MoS₂ anode in the presence and absence of fluoroethylene carbonate (FEC) additives. The successive nucleation and growth of ultra-thin FEC-derived solid electrolyte interphase (SEI) film with thickness of 0.7 ± 0.1 nm was directly captured and quantitatively analyzed, revealing the surface effect of the electrolyte additive.

Furthermore, they observed the appearance/retention of wrinkles, resulting from the phase transition of 2H MoS₂ to 1T LixMoS₂, upon lithiation/delithiation, elucidating the intrinsic flexibility of MoS₂ and failure mechanism of MoS₂-based LIBs.

These results provided a comprehensive understanding of the quantitative live formation and interphasial morphology of ultra-thin SEIs derived from additives, as well as the micro-mechanism of wrinkling process on the MoS₂ anodes.

This work was supported by the Ministry of Science and Technology of China, the National Natural Science Foundation of China and the Chinese Academy of Sciences.

Video of in situ EC-AFM recording the initial process of formation of the ultra-thin FEC-derived SEI film upon charging. The scale bar is 600 nm. (Image by Prof. WEN Rui)