In situ X-ray photoelectron and Auger electron spectroscopic characterization of reaction mechanisms during Li-ion cycling.

The complex nature of Li-ion battery reactions along with their sensitivity to environmental exposure necessitates in situ characterization, particularly for surface sensitive methods. In this work, we demonstrate in situ X-ray photoelectron spectroscopy and in situ Auger electron spectroscopy applied to characterize the evolution of bonding and chemistry during cycling of nanoparticle electrodes. We apply the method to study the conversion reaction associated with Li insertion and extraction from CuO nanoparticle electrodes. This approach circumvents the need for ion sputtering and mechanical erosion, previously required to remove solid electrolyte interphase during ex situ measurements. This allows the elucidation of the changes in Cu oxidation state, during initial Li insertion, without the introduction of artifacts that have caused prior disagreement in the published literature.