Elucidation of Electrode-Electrolyte Interfaces Using Neutrons

This presentation will describe experimental characterization of the thickness and composition of the reaction products on silicon anode materials and aluminum current collectors measured using neutron reflectometry. NR is a neutron scattering technique highly sensitive to morphological and compositional changes occurring across surfaces and interfaces, including buried interfaces. It can be used to study such changes over lengths scales extending 1 nm to hundreds-of-nanometers. Neutrons, by virtue of their nature, are deeply penetrating and therefore ideally suited as a probe to study materials in complicated environments, such as electrochemical cells. Unlike x-rays, neutrons interact with the nuclear potential of constituent element and are sensitive to light elements like Li and H.

We will show that the SiO_x surface of silicon materials react irreversibly with the electrolyte 1.2M LiPF₆-3:7 wt% ethylene carbonate:dimethyl carbonate.  The reaction product is a complex mixture of Si-O-F-C species.  It is dense and homogenous and has a thickness of about 3.5 nm.  Similar reaction chemistry is observed for Al current collectors.  Insights from these measurements will provide a framework to understand capacity losses with cycling of high energy density materials.

Acknowledgement: 

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 (LB, GMV). This Research at Oak Ridge National Laboratory's Spallation Neutron Source was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U. S. Department of Energy.