Traditional monitoring of electrochemical cells and batteries has been limited to observation of voltage and temperature of the cell or cells. While this monitoring can be very robust, there are limits to how predictive voltage and temperature behavior can be prior to a thermal runaway event. Ultimately, voltage and temperature changes are often lagging indicators or symptoms of battery failure, and by the time a noticeable change is detected it is too late to arrest cell failure with intervention or maintenance. Further, instantaneous voltage and temperature monitoring are often inadequate to determine the state of a battery at rest, particularly if the battery has been previously subjected to an abusive condition. Knowledge of the level of stability of a damaged battery would allow for both safer and more efficient handling of the abused battery.

This work examines the application of Electrochemical Impedance Spectroscopy (EIS) and Differential Capacity calculations (dQ/dV) as a tool for determining the state of stability (SOS) of an electrochemical cell or battery. The cells for this study were subjected to thermal and electrical abuse coupled with EIS monitoring at differing levels of battery abuse. 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 after tests and during moderate levels of overcharge to explore any observable changes that may be monitored during charge and discharge operations. These 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 multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.