(414f) Multi-Physics Safety Modeling of Li-Ion Battery Pouch Cells Abused By Mechanical Indentation: Self-Inhibition of Electrical Shorting through Gas Lubrication

The safety concern stemming from the unstoppable thermal runaway (TR) of abused Li-ion batteries remains a critical challenge for the wide deployment of electric vehicles and battery energy storage systems. In this work, we analyze the thermo-electrochemical failure response of battery pouch cells tested using a single-side mechanical indentation protocol at Oak Ridge National Laboratory across electrode chemistries and state-of-charge (SOC). Mechanical indentation triggers a local internal short circuit (ISC), leading to rapid voltage decay and temperature rise. Although the theoretical timescales for microscopic thermal and electrochemical transport phenomena occur over O(1s), complex voltage and temperature dynamics are measured on the timescale of O(100s). This time scale anomaly coincides with unexplored continuous gas generation.

Here, we develop a multi-scale physical model to explain the dynamic cell voltage and surface temperature obtained from mechanical indentation of commercial LiCoO2-Graphite pouch cells spanning SOCs 0% (Fully Discharged) to 100% SOC (Fully Charged). At the microscopic scale, the ISC results in the propagation of the thermo-electrochemical front (TEF), which transports the energy generated by Joule heating and exothermic degradation reactions to the intact region of the pouch cell. Gas is generated from exothermic reactions and naturally advected to the indenter’s fracture line interface. At the macroscopic scale, the evolved gas flows through a lubricating channel along the fracture surface, disconnecting the ISC. The gas flow across these different scales acts as a negative feedback loop on the ISC, which is a critical driving factor of the long experimental timescales of O(100s). This work synthesizes various sectors of battery modeling, from porous electrode modeling [1], thermal degradation modeling [2], to novel descriptions of gas transport phenomena - all of which contribute to the observed TEF propagation.

By simulating over multiple length and timescales, the presented multi-scale modeling elucidates the following features obtained from the mechanical indentation tests on LIB pouch cells: 1) SOC-dependent voltage recovery and 2) transitions in maximum temperature rise over different SOCs. In doing so, this work demonstrates the importance of accurately capturing the gas generation and transport in ISC-driven battery failure and establishes a basis for safety analysis and thermal runaway risk prediction for mechanically abused large-format Li-ion batteries.

1. Smith, Raymond B., and Martin Z. Bazant. "Multiphase porous electrode theory." Journal of The Electrochemical Society 164, no. 11 (2017): E3291.

2. Hatchard, T. D., D. D. MacNeil, A. Basu, and J. R. Dahn. "Thermal model of cylindrical and prismatic lithium-ion cells." Journal of The Electrochemical Society148, no. 7 (2001): A755.