In Operando Raman Reveals Voltage-Driven SEI Chemistry in Fluorinated Gel Electrolytes

A particular advantage of gel polymer electrolytes (GPEs) has been their ability to incorporate chemical moieties that create stable electrode–electrolyte interfaces that guide uniform deposition and stripping of lithium. Understanding the chemical dynamics at these interfaces remains challenging. Previously, we reported that polyvinylidene fluoride-cohexafluoropropylene (PVDF-HFP) GPEs with an ether cosolvent showed greater stability in lithium metal symmetric cells. In this work, we used a Cu|PVDF-HFP|Li cell design along with in operando Raman spectroscopy to conduct a thorough characterization of the electrolyte–electrode interface to observe the chemical dynamics at work during electrode polarization, lithium plating, and stripping. We observe that PVDF-HFP, cosolvent, and supporting salt all contribute to the initial SEI formation prior to plating. The spectral and electrochemical data using this method allow us to understand the contribution of different chemical species in the evolution of interfaces in lithium metal batteries.