Tracking the solid-electrolyte-interphase (SEI) formation on Amorphous Si and Sn anodes for li-ion batteries

Neutron reflectometry provides a detailed method in which to investigate the solid-electrolyte interphase (SEI) throughout its initial formation and under dynamic cycling conditions in lithium-ion batteries. Amorphous silicon (a-Si) and tin are investigated to demonstrate both the thickness and scattering length density of the SEI layer considering a fluoroethylene carbonate (FEC) electrolyte additive. Distinct differences and similarities between the two systems have been identified; both a-Si and Sn observe a reversible contraction/growth of the SEI layer throughout charge/discharge cycles originating from the buildup and dissolution of organic components at the electrolyte surface. a-Si observes a clear tendancy to form an initial Li₂O/Li₂CO₃ layer based on a chemical reaction that occurs between the native oxide and the electrolyte prior to electrochemical cycling. Whereas the native tin oxide appears to remain intact, forming an SEI of different composition as a result.