Using Internal Pressure Measurements to Fundamentally Understand the Aging of Lithium-Ion Batteries

The sealed nature of lithium-ion batteries makes the in-situ study of their aging mechanisms challenging at best. Typically voltage, current, thermal, and impedance diagnostics are used to characterize cell aging mechanisms as they are cycled and post mortem analysis reveals the most compelling information however further cycling of the cells is of course prohibited. While these are promising, they do not reveal the full story. At the University of Texas at Arlington (UTA), research has been performed to evaluate how cell pressure can be used as a diagnostic to better understand cell aging mechanisms at elevated rates. The cells are punctured in an inert environment and inserted into a sealed chamber where they can be cycled while measuring their internal pressure. The studies presented here have shown a strong correspondence between capacity fade and pressure rise in LiCoO₂ cells across a few different rates. These results as well as some ongoing work in which LiFePO₄ cells are being studied will be presented. Analysis of the impedance growth as well as the gas generated while cycling the cells will also be discussed.