Cryogenic imaging and spectroscopic study of electrochemically formed solid interphases - from nano to meso scale.

Our work demonstrated that the chemical and morphological information of Li metal can be largely preserved during cross-sectional TEM specimen preparation via cryo-FIB by mitigating the local heating damage and ion implantation, which has enabled the quantitative analysis of the impact of electrolyte on the nucleation and morphology of Li metal. Cryo-FIB has also shown potential to elucidate the structure and chemistry of Li metal/electrolyte interfaces when coupled with cryo-TEM. Now we have developed unique in situ and cryogenic analytic electron microscopy techniques to probe dynamic phase changes and interfaces of susceptible materials for electrochemical devices. Intrinsic chemical reactivity and beam sensitivity of Li metal and solid electrolyte interphase (SEI) impede mechanistic studies by electron microscopy. Solar cells with hybrid perovskite materials are also beam sensitive and their degradation issues need to be studied upon operation under the electrical bias. To study these materials, prerequisite techniques are required including cryogenic focused ion beam (cryo-FIB) and cryogenic transmission electron microscopy (cryo-TEM).