Tracking Passivation and Cation Flux at Incipient Solid-Electrolyte Interphases on Multi-Layer Graphene using High Resolution Scanning Electrochemical Microscopy

The solid electrolyte interphase (SEI) is a dynamic, electronically insulating film that forms on the negative electrode of Li+ batteries (LIBs) and enables ion movement to/from the interface while preventing electrolyte breakdown. However, there is limited comparative understanding of LIB SEIs with respect to those formed on Na+ and K+ electrolytes for emerging battery concepts. We used scanning electrochemical microscopy (SECM) for the in situ interfacial analysis of incipient SEIs in Li+, K+ and Na+ electrolytes formed on multi-layer graphene. Feedback images using 300 nm SECM probes and ion-sensitive measurements indicated a superior passivation and highest cation flux for a Li+-SEI in contrast to Na+ and K+-SEIs. Ex situ X-ray photoelectron spectroscopy indicated significant fluoride formation for only Li+ and Na+-SEIs, enabling correlation to in situ SECM measurements. While SEI chemistry remains complex, these electroanalytical methods reveal links between chemical variables and the interfacial properties of materials for energy storage.

Automated summary

This study investigates the solid electrolyte interphase (SEI) in Li+ batteries (LIBs) and compares them to SEIs formed on Na+ and K+ electrolytes. The researchers used scanning electrochemical microscopy (SECM) to analyze the incipient SEIs in Li+, K+, and Na+ electrolytes on multi-layer graphene. The results show that Li+-SEI exhibits superior passivation and the highest cation flux compared to Na+ and K+-SEIs. Additionally, significant fluoride formation was observed in Li+ and Na+-SEIs.