Failure progression in the solid electrolyte interphase (SEI) on silicon electrodes

In this in situ, operando study, the authors provide detailed insight into the failure mode of Si anodes for Li-ion batteries. Si anodes promise high capacity but SEI degradation from the large volume change during cycling is widely recognized as a roadblock for their practical use. While many studies have focused on SEI chemistry, this paper provides direct information on mechanical integrity and failure in a well-defined model system of patterned Si islands. In particular, in situ PeakForce Tapping images of the SEI layer show the presence of a bilayer structure and quantify layer modulus. During cycling the softer, mostly organic outer layer develops through thickness cracks and delaminates. The inner layer appears to be a nanocomposite and remarkably stays in place and shows no signs of mechanical degradation. The absence of damage or growth of the inner layer suggests good passivation despite high strains, which makes it a possible avenue to more stable high capacity anodes.