A Novel Approach to Study the Chemo-Mechanical Stability of the Solid Electrolyte Interphase (SEI) in Lithium-Ion Batteries

It has been recognized that a stable solid electrolyte interphase (SEI) is critical in operation of rechargeable Li-ion batteries. A clear understanding of SEI formation, evolution and mechanical response will make it possible to tailor better passivation layers that can improve battery performance. In this work we present a novel approach that is based on patterned Si islands, with measurements that include galvanostatic cycling, electrochemical impedance spectroscopy (EIS), in situ optical microcopy, and in situ stress measurements. By calibrating the expansion and contraction of these islands, it is possible to systematically investigate the impact that large volume changes have on the SEI stability. Comparisons between these islands and continuous Si films then make it possible to correlate the irreversible capacity loss with expansion strain in the underlying Si. These galvanostatic experiments on island samples provide a novel mechanical testing configuration for investigating the stability of thin SEI layers.