This work examines the application of Electrochemical Impedance Spectroscopy (EIS) and Differential Capacity calculations (dQ/dV) as tools for determining the state of stability (SOS) of an electrochemical cell or battery. The cells used for this study were commercial 10 Ah NMC cells and 10Ah LFP cells subjected to electrical abuse coupled with EIS monitoring. This aims to not only provide a deeper understanding of how abused cells and batteries fail, but also form the technical basis of a tool that could ultimately be used to interrogate cells of an unknown stability and even monitor active cells for early signs of damage or failure. Fast impedance monitoring hardware previously developed at Idaho National Laboratory is used to provide not only monitoring after an abusive battery test but also look for changes in the cell while abusive conditions are applied. Differential capacity calculations are explored both before tests and after moderate levels of overcharge to explore any observable changes that may be monitored during charge and discharge operations. Lastly, X-ray diffraction measurements were performed on the cathode/anode before and after the abuse test to understand the effect of overcharge in the structural changes. Figure 1 presents the measurements for the NMC cells that were partially abused from 20-60% OC. These three markers could then be potentially applied to cross-examine batteries of an unknown stability as well as provide the basis for an active diagnostic method as part of a battery management system.
Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia LLC, a wholly owned subsidiary of Honeywell International Inc. for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.