Guest Seminar - Visualization of the lithium sulfur electrochemistry

Taken advantage of a high theoretical energy density of 2567 Wh kg-1, lithium sulfur batteries (LSBs) have been considered promising candidates for next-generation energy storage systems. Tremendous efforts have been devoted to improving the battery performance by preparing smart nanostructures. However, detailed reaction mechanisms and the principles of tailoring reaction paths remain unclear. In-situ transmission electron microscopy (TEM) is a powerful technique to probe the dynamic processes of electrochemical reactions at a high spatial resolution and in real-time. Through in-situ TEM study with a solid cell, we revealed the correlation between sulfur volume expansion and the porosity of carbon nanofibers. Further, by developing an in-situ TEM equiped with a graphene-based liquid cell (GLC), where liquid electrolyte and TiN-C/S nanoparticles are encapsulated between two graphene sheets, we disclosed the nucleation and growth dynamics of solid Li2S from soluble polysulfides. Very recently, using operando optical microscopy, we found liquid sulfur droplets formation during charging at room temperature, which is much lower than the melting point of sulfur. The liquid sulfur indicates superior kinetic features from its flowing and reshaping natures. More interestingly, the preservation of liquid sulfur is strongly linked to the substrate chemistry, where solid sulfur forms from the edge of 2D materials. It is believed that in-situ microscopic investigation of sulfur cathodes would not only shed new light on understanding of reaction mechanisms but also provide fundamental guidelines to design better LSBs.