In practical silicon electrodes the coupled mechanical and chemical degradation of the solid electrolyte interphase (SEI) is a critical issue. During electrochemical cycling, the extremely large mechanical strains that are applied to the SEI on Si are a primary factor that limits cycle life. However, the effect of particle size on these strains has not been investigated in prior work.

To address this, we have integrated measurements on silicon nanoparticle composite electrodes with an in situ method for applying controlled mechanical strains to SEI during electrochemical cycling and a finite element model (FEM). Comparisons of electrodes with different particle sizes show lower capacity loss with smaller particles. This finding is explained with the FEM. Variations in the SEI formation were also investigated, using different cycling conditions and electrolyte additives.