Modeling Competitive Reaction Heat Sources and Variable Cooling Rates Applicable to Thermal Runaway Onset in Lithium-Ion Batteries

Abstract

Two main types of exothermic processes are known to initiate thermal runaway in Lithium-Ion batteries. If mechanical failure of the separator causes an electrical short circuit, the cell’s energy can be released through electrochemical discharge reactions. The full stored energy can be released as heat within the cell for internal short circuits, raising the cell temperature by several hundred degrees Celsius. Different thermochemical reactions occur when Lithium-Ion cells are heated; the anode and cathode materials decomposing with the electrolyte can result in similarly large temperature rises. Our work shows that thermodynamics constrain key reactant species for both decomposition paths to be in common. Interactions and competition between these chemical pathways for heat release are considered in this modeling study, including relative magnitudes of thermal contributions from each reaction pathway and limiting reactant effects. An effective oven temperature concept is defined, which allows thermal runaway initiation via internal short circuits versus external heating to be compared. Temperature and reaction inhomogeneities occurring in the presence of internal localized internal short circuits lead to variations in the balance between electrochemical and thermochemical reactions across the domain of the cell. A simple homogeneous analysis is compared to a higher-dimensional inhomogeneous analysis. The effectiveness external cooling strategies to mitigate an internal short circuit event is investigated. Acknowledgements: This article has been authored by an employee of National Technology & Engineering Solutions of Sandia, LLC under Contract No. DE-NA0003525 with the U.S. Department of Energy (DOE). The employee owns all right, title and interest in and to the article and is solely responsible for its contents. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this article or allow others to do so, for United States Government purposes. The DOE will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan https://www.energy.gov/downloads/doe-public-access-plan. This abstract has been approved for release as SAND2023-01585A.