Scanning Electrochemical Cell Microscopy in a Glovebox: Structure-Activity Correlations in the Early Stages of Solid-Electrolyte Interphase Formation on Graphite

Understanding the formation and properties of the solid-electrolyte interphase (SEI) will enable the development of enhanced Li-ion batteries (LiBs) and other battery types. Herein, we report scanning electrochemical cell microscopy (SECCM) in a glovebox to characterize the SEI formation on the basal surface of highly oriented pyrolytic graphite (HOPG) as a model system of negative LiB electrodes with nonaqueous electrolytes. Different grades of HOPG have been studied, which provide a range of step edge densities on the basal surface. The high-throughput and spatially-resolved character of SECCM allows thousands of measurements across a surface, revealing how surface heterogeneity in graphite affects the early stages of the SEI formation and its properties. Step edges promote electrolyte reduction resulting in a more passivating SEI than that formed on smoother surfaces. A strongly insulating but relatively unstable SEI is detected under fast formation conditions, while slow formation rates induce the steady growth of an increasingly passivating SEI. This work provides new insights on the SEI dynamic formation and demonstrates SECCM as a powerful technique to probe the effect of local structure in heterogeneous battery materials under inert atmosphere. The demonstration that SECCM can readily be deployed in a glovebox serves as a foundation for future experiments to explore high resolution electrochemical imaging of battery electrode materials.

Automated summary

This study uses scanning electrochemical cell microscopy (SECCM) to investigate the formation of solid-electrolyte interphase (SEI) on graphite surfaces in Li-ion batteries. The presence of step edges on the surface promotes the formation of a more passivating SEI. The study also shows that an unstable SEI can be detected under fast formation conditions, while a slow formation rate leads to the growth of an increasingly passivating SEI.