Measuring Dynamic Changes in Si SEI Chemistry

In this presentation we will present experimental in situ measurements of the thickness and chemistry of the SEI layer that forms over amorphous silicon electrodes as a function of state-of-charge and cycle.  These measurements were performed using neutron reflectometry which was supported by XPS, IR and electrochemical measurements.  We will show the thickness of the Si SEI layer changes as a function of state-of-charge becoming thicker with lower states of lithiation and thinner with greater lithiation.  Furthermore, the chemistry changes with cycle from more LiF rich at higher states-of-charge to more polymeric when delithiated.  The thickness and the chemistry of the SEI layer changes with the addition of electrolyte additives, like fluorinated ethylene carbonate. Together these results help develop an understanding of additive chemistry and will direct the development of new additives.

This research was supported by the Materials Sciences and Engineering Division, Office of Basic Energy Sciences, U.S. Department of Energy under contract with UT-Battelle, LLC (GMV, TF, RLS – XPS, NR data collection, electrochemistry). Neutron reflectometry measurements were carried out on the Liquids Reflectometer at the Spallation Neutron Source which is sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy (JFB, MD – Data collection and analysis).