Correlating Evolving Local Function and Composition of Solid Electrolyte Interphases by Scanning Electrochemical Microscopy and X-ray Photoelectron Spectroscopy

Solid electrolyte interphases (SEIs) are essential for high-performance lithium and lithium-ion batteries. The SEI is formed by the reductive decomposition of electrolyte components. Ideally, it exhibits ion conductivity but blocks unwanted electron transfer (ET) reactions between the negative electrode materials and electrolyte components. Understanding the relation between functional properties of respective electrodes and the complex composition as well as evolution of the SEI over time and cycling is key for further advances in battery technology. Identical location experiments are demonstrated using scanning electrochemical microscopy (SECM) to probe local reactivity for ET reactions and small-area X-ray photoelectron spectroscopy (XPS) for the analysis of the local chemical surface composition of the SEI on lithium electrodes, both having comparable resolution in the micrometer range. This is enabled by a specially designed sample holder facilitating the cycling of electrodes inside the SECM cell and the inert transfer from the SECM instrument inside a glovebox to another glovebox directly attached to the XPS instrument. The relocation of specific regions, identified in SECM images, in the XPS instrument is enabled by a calibration process of the coordinate transform between the internal coordinates of the SECM and XPS instruments using an overlay of SECM and XPS images from the test samples. This transform is shown to be applicable to other samples. Using the optimized procedures for sample transfer and data acquisition, lithium metal electrodes were studied by SECM and XPS after storage at open circuit potential (OCP) as well as before and after metal deposition-dissolution cycles. The blocking properties improved during storage at the OCP in two kinetically different phases, and cycling caused a temporary strong decrease in the ET blocking and an increase in lateral variation of ET kinetics. The methodology is easily transferable to other samples and other localized techniques, where the relation between local reactivity and chemical surface composition is of interest.