(Invited) Mechanisms and Material Impacts of Overcharge in Lithium Ion Batteries

Abstract

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 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 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 pouch cells and 10Ah LFP cells subjected to electrical and thermal 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 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 abuse to explore any noticeable changes that may be monitored during charge and discharge operations. The electrochemical techniques are supported with materials evaluations to further understand the impact of abusive conditions on the constituent materials. 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.