Nanoscale Mechanics of the Solid Electrolyte Interphase on Lithiated-Silicon Electrodes.

The ∼300% volume changes of lithiated silicon electrodes (LixSi) during electrochemical cycling lead to cracking of the solid electrolyte interface (SEI). Here, we report how strain is transferred from LixSi to two primary inorganic SEI components: LiF and Li2O. Our first principle calculations show that LiF, effectively bonded on LixSi at x > 1, enables the entire interface structure to deform plastically by forming delocalized stable voids. In contrast, Li2O tightly bonded to LixSi is stiffer, and deforms rigidly across all x. Our results explain the significantly improved ductility of SEI with higher LiF versus Li2O content observed experimentally.