Modelling and Simulation of the Solid Electrolyte Interphase with varying Porosity

Kurzfassung

The solid electrolyte interphase (SEI) grows continuously during the lifetime of lithium ion batteries [1,2] and acts as a passivating film between the negative electrode and the electrolyte. To this point several models have been created to describe its formation process [2-4]. These models assume a single rate limiting transport mechanism for the SEI growth, in return they remain inconclusive with respect to the actual rate limiting process. We present and evaluate a new model of the SEI growth with the goal of reaching a more significant statement in this regard. The model is obtained by coupling the transport processes inside this porous layer with the reaction kinetics of SEI formation. Contrary to existing models [2-4] we treat the porosity as a time-dependent variable. The influence of spatially varying porosity on the transport processes has been taken into account and is described with the Bruggemann ansatz. This novel approach allows us to investigate the SEI morphology. Simulations show that the model results in a √t like growth of the SEI thickness, consistent with current experimental observations [1-2]. By fitting the results to measured growth curves [2] we obtain an estimate for the conductivity of the major SEI component assumed in the model such as lithium carbonate [5] or lithium ethylene dicarbonate [6,7]. The model reveals that the SEI volume fraction attains a constant value. We are able to derive analytic expressions for this value and the time evolution of the SEI thickness based on justified assumptions. These expressions show that the transport parameters of electrons and electrolyte are directly connected to SEI morphology and thickness. Their derivations allow new insights into the SEI formation process. [1] A.J. Smith, et al, Journal of the Electrochemical Society, 158 (2011), A447. [2] M.B. Pinson, et al., Journal of the Electrochemical Society, 160 (2012), A243-A250. [3] H.J. Ploehn, et al., Journal of the Electrochemical Society, 151 (2004), A456. [4] J. Christensen, et al., Journal of the Electrochemical Society, 151 (2004), A1977. [5] Peng Lu, et al., Journal of Physical Chemistry, 118 (2014), 896-903. [6] G. V. Zhuang, Journal of Physical Chemistry, 109 (2005), 17567-17573. [7] Kang Xu, et al., American Chemical Society, 111 (2007), 7411-7421. [8] E. Karaca, Modeling Growth of the Solid Electrolyte Interphase, Master Thesis at the University of Ulm (2014).