 The researchers developed a new technique called depth-sensitive plasmon-enhanced Raman spectroscopy, DSPAS, which allows them to observe the formation of solid electrolyte interphase, SEI, in real time. This technique uses nanostructures made up of copper, gold, and lithium to create a strong electromagnetic field when light hits it. This field can be used to detect changes in the chemical composition of the SEI as it forms and evolves over time. By using this technique, they were able to observe how the SEI formed differently depending on whether the battery was charged with a carbonate or an ethylene glycol electrolyte. They also observed how the SEI changed during repeated cycles of charging and discharging. These findings provide valuable insight into the role of the SEI in lithium metal batteries and could lead to improved designs for these types of batteries. This article was authored by UGU, Yenming Yu, Jenderlin, and others.