Investigations of the Structural and Electrochemical Properties of Partially Abused Li-ion Batteries for Advanced Diagnostics

Abstract

Establishing a framework for understanding the degradation mechanisms of lithium-ion batteries (LIBs) subjected to abusive conditions has become increasingly important in recent years, as LIBs continue to capture new markets involving an array of abuse-prone applications such as electric vehicles, aircraft, and mobile energy storage systems. Characterization techniques used to identify the state-of-health (SoH) of LIBs can identify a range of degradation mechanisms, which can be broadly categorized as loss of lithium inventory (LLI), loss of active material (LAM), and conductivity loss (CL). These degradation mechanisms, which have been well characterized in literature, are established using a variety of in-situ and ex-situ techniques. The most common in-situ technique for determining cell SoH involves monitoring temperature and voltage as a function of state of charge (SOC) throughout cell cycling. For abusive conditions, however, this measurement is a particularly poor indicator of battery SoH and does not provide valuable insight into cell degradation until failure is imminent. It is particularly difficult to determine SoH for LIBs, as the voltage curve maintains a relatively uniform profile until moments before cell failure. A more versatile in-situ technique capable of monitoring battery degradation mechanisms is Electrochemical Impedance Spectroscopy (EIS), which quantifies cell SoH by measuring system response to a range of sinusoidal excitation signals at varying frequencies. Although extensive characterization of battery degradation has been conducted using traditional EIS hardware, no research has been conducted on impedance analysis of active load cells subjected to abusive conditions. This work attempts to identify failure markers by linking impedance measurements captured using the EIS toolbox to previously established degradation mechanisms for abused cells. In-situ EIS measurements were collected, followed by identification of failure markers using ex-situ material characterization of harvested electrodes. Failure markers were established by linking degradation behavior identified by material characterization methods to changes in impedance behavior observed by the toolbox. This data can be extrapolated for use with general LIB chemistries in a wide range of BMS’s. Although data extrapolation is outside the scope of this work, data obtained will help facilitate future extrapolation of failure markers to a wide range of LIB chemistries. 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.