Polymer binders play a critical role in the fabrication of composite electrodes. This is particularly true for silicon electrode materials where due to the large volume expansion during cycling a mechanically robust binder is needed to minimize Si pulverization and prevent electronic isolation. Currently, the most widely used binder is polyacrylic acid (PAA); however, there is very little knowledge of the effect any polymer binder has on the formation and composition of the solid-electrolyte interface (SEI). In this work we report on the formation and growth of the SEI layer as probed with in situ neutron reflectivity. We also explore the effect of adding an electronically conductive binder, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) on SEI formation on thin film Si anodes. In addition to the in situ reflectivity measurements at open circuit voltage and as a function of the state of charge, x-ray photoelectron spectroscopy (XPS) and infrared spectroscopy studies were used to study the elemental composition of the SEI layer formed. Electrochemical impedance spectroscopy (EIS) was also performed to better understand how the Li-ion is transported through the polymer layer into the Si.

Acknowledgement: This research was supported by the Vehicle Technologies Office, Hybrid Electric Systems Program, David Howell (Manager), Battery R&D, Brian Cunningham and Peter Faguy (Technology Managers), at the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy. 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.