Thermal runaways, triggered by oxygen release from the oxide cathode materials, pose a major safety concern for widespread application of lithium ion batteries. To allow for a deeper understanding of the processes leading to the thermal runaway, a combined modeling and experimental work of phase transformation and the subsequent oxygen release in LiCoO₂ electrodes was undertaken. This contribution presents the modeling part and the accompanied abstract in this meeting reports the experimental details, thus only a brief experimental description is given here. Commercially available and chemically de-lithiated LiCoO₂ samples were used. Utilizing in-situ aberration-corrected scanning transmission electron microscopy (STEM) and in-situ electron energy loss spectroscopy (EELS) techniques, phase transformation and the oxygen release from LiCoO₂ samples were investigated in the temperature range between 25 °C and 450 °C.¹

In order to interpret the experimental measurements and to identify factors governing phase transformation and the subsequent oxygen release, a multiphase-field model (PFM) is established to represent the coupled mechanical, chemical and transport behavior occurring in the LiCoO₂ electrodes. The PFM was developed using the MOOSE framework.^2,3 The model captures both the kinetics of the oxygen release by employing Fick’s diffusion law, as well as the stress build-up. This is achieved by coupling the evolution equation of the phase-field variables (i.e., oxygen concentration, existed phases) to the mechanical equations allowing to study diffusion induced phase transformation and stress generation. The model was validated against the above described experimental measurements by comparing the rate of phases growth and their thicknesses. This comparison allows the PFM to predict the oxygen composition depth and the stress profile in the layered, spinel and rock salt structures of the LiCoO₂ during the heating. The simulation results indicate that the generated stress slows down the oxygen release, and changes the local oxygen concentration within the phases. In addition, the temperature ranges of the critical oxygen release were identified. Thus, this combined work provides suggestions for a safe operating window of the LiCoO₂ electrodes.

References

1. S. R. Sharifi-Asl, F. Soto, A. Nie, Y. Yuan, H. Asayesh-Ardakani, T. Foroozan, V. Yurkiv, B. Song, F. Mashayek, R. Klie, K. Amine, J. Lu, P. Balbuena, R. Shahbazian-Yassar, Nano Lett., 17, 2165-2171 (2017).

2. M. R. Tonks, D. Gaston, P. C. Millett, D. Andrs, and P. Talbot, Comput. Mater. Sci., 51, 20–29 (2012).

3. D. Schwen, L. K. Aagesen, J. W. Peterson, and M. R. Tonks, Comput. Mater. Sci., 132, 36–45 (2017)