Internal Short Circuit Modeling: A 3D/2D Multiphysics Coupled Cell Model
Authors: Buzon Didier , Abada Sara 
Published: February 2020

Prediction of the Lithium-ion batteries safety behavior is a key point for the development and diffusion of this technology. Among all the different abuse, overuse state or internal faults, the internal short circuit (ISC) is the most difficult case to investigate and mitigate on a commercial cell via the existed safety test methods.
Investigation: For the investigation prospect, triggering and repeating an ISC scenario with a good control of the short circuit impedance in laboratory is very hard to set up. The ISC results in self discharge in combination with a local temperature increase, but the local physical data evolution during and after the fault are mainly inaccessible via usual experimental set up. According to the ISC severity, exothermic chemical reactions may take place if the temperature exceeds the activation reaction threshold. These chemical reactions reflect the different cell components interaction and decomposition, which lead to accelerated and uncontrolled thermal runaway within the cell.
Thermal runaway mitigation: The evolution and propagation of the thermal runaway inside a cell is directly linked to the internal geometrical and material properties of the battery cell. Actually, battery cell designers have no tools allowing to evaluate and quantify the impact of the internal specifications of a battery cell on its capacity to withstand fault conditions.
In order to get a better knowledge of the way the different involved physics phenomenon and cell specifications can affect the thermal runaway of a lithium-ion cell, a 3D/2D multiphysics coupled model has been developed. The first part of this presentation will focus on the description of this multiphysics coupled model. It includes a 3D thermal model (based on an energy balance), a 2D electrochemical model (based on an electric equivalent circuit) and a chemical decomposition reactions and thermodynamical model (based on Arrhenius equation). The picture gives an overview of the thermal runaway propagation simulation (evolution of the internal temperature and conversion degree of reactant 1, 1.34 and 1.4 seconds after the ISC appearance) obtained on an unrolled 18650 lithium-ion cell triggered by a local internal short circuit applied between the anode and the cathode of the jellyroll. This simulation was performed with the finite element software Comsol.
To go further, this computational tool has been parametrized with all the available data and models of the 18650 commercial cell analyzed in the EVERLASTING European project. This project intends to bring Li-ion technologies closer to automotive actual market requirements by improving many different aspects (driving range improvement and range anxiety reduction via a better prediction, better reliability via an improved thermal and load management, safety problem detection and mitigation, improved BMS development). A large set of safety test is currently realized for this project. The second part of the presentation will focus on a comparison between safety experimental tests data performed on the EVERLASTING’ cell and simulation results from the proposed multiphysics coupled model. First, this analyses allows to evaluate how the proposed tool is able to predict the behavior of a cell in internal short circuit condition. Next, a sensibility analysis of some cell parameters on the thermal runaway is discussed as conclusion and as perspective for further investigations.

Figure 1