Thermo-Electrochemical Simulation of Li-Ion Cells Under Abuse Condition

Safety of lithium-ion cells is one of the most important aspects of battery research [1].     As a pilot study preliminary to building an early-alert heat management system for lithium-ion cells, we present 1D multi-scale simulation of a single cell with exothermic reactions which induce thermal runaway. The thermo-electrochemical model used in this work includes electrochemical and thermochemical kinetics in range from micro to macro scales [2]. Lithium insertion and extraction in active materials are assumed to follow Butler-Volmer kinetics. The model cell in this study has mesocarbon microbeads (MCMB) in anode and a blended electrode of LiMn₂O₄ (LMO) and LiNi_0.8Co_0.15Al_0.05O₂ (NCA) in cathode. The thermodynamic properties of the pure electrode materials are obtained through published half-cell potentials [3,4,5]. The property of blend material is formulated based on an assumption observed through experiments by Tran et al [6].

To simulate runaway events, we take into account thermal degradation mechanisms both at anode and cathode sides at elevated temperature. At the anode, four exothermic reactions are considered; solid electrolyte interface (SEI) decomposition, SEI formation, ethylene oxidation and reaction of lithium with water. Similarly, oxygen release from NCA and oxidation of solvent (ethylene carbonate) are modeled at the cathode. The reactions are assumed to follow Arrhenius behavior and Tafel type expression for non-charge transfer reaction and charge transfer reaction, respectively. The pre-exponential factor and activation energies of the reactions are taken from either literature or fits with published differential scanning calorimetry (DSC) experiments.

Thermal simulations are used to predict the onset of runaway events under cycling from room temperature up to 333 K of ambient temperature. The cycles are tested under current rates of 1, 2, 3 and 4C. Figure 1 shows the heat resulting from cycling with 4C leading to a chain of exothermic reactions approximately at 350 K inducing thermal runaway.

Furthermore, predictions of temperature and kinetic behavior in case of short circuits are presented (Figure 2). The comparison with experimental measurement is discussed.

Acknowledgement

Financial support by the Volkswagen foundation is gratefully acknowledged.

References

[1] D. Doughty, E.P. Roth, ECS Interface, 2012.

[2] N. Tanaka, W. Bessler, Solid State Ionics, http://dx.doi.org/10.1016/j.ssi.2013.10.009 (2013).

[3] Y.F. Reynier, R.Yazami, B. Fultz, J. Electrochem. Soc., 151 (3) (2004) A422-A426.

[4] K.E. Thomas, C. Bogatu, J. Newman, J. Electrochem. Soc., 148 (6) (2001) A570-A575.

[5] H. Yang, J. Prakash, J. Electrochem. Soc., 151 (8) (2004) A1222-A1229.

[6] H.Y. Tran, C. Taubert, M. Fleischhammer, P. Axmann, L. Knuppers, M. Wohlfahrt-Mehrens, J. Electrochem. Soc., 158 (5) (2011) A556-A561.