Modelling Solid Electrolyte Interphase growth, a Novel Description of Porous Layer Evolution

During the first charge of a fresh lithium ion battery lithium is intercalated into the negative electrode, typically graphite. Simultaneously the electrode potential is lowered and eventually leaves the electrochemical stability window of the electrolyte which is then reduced. The reduction products precipitate on the electrode, forming an electronically passivating but ion conducting layer. This so called solid electrolyte interphase (SEI) prevents further electrolyte reduction thus enabling large cycle numbers of current lithium batteries [1,2]. We simulate the SEI evolution in a continuum model. Porous electrode theory is employed to describe transport through the porous SEI/electrolyte phase. This enables the simulation and study of porosity fluctuations in the direction of film growth. Similar to previous studies [3,4], we predict SEI thickness evolution. However, our novel approach also results in the prediction two SEI morphology properties. We can relate the porosity of the porous SEI layer to transport parameters. Additionally we predict that thickness of the dense and porous SEI layer are related. Analytic treatment reveals that their relative thickness depends on reaction parameters of SEI formation. Both predictions are experimentally observable and could be used for model validation. References: [1] E. Peled, Journal of The Electrochemical Society 126, 2047 (1979). [2] D. Aurbach, Journal of Power Sources 89, 206 (2000). [3] M. B. Pinson and M. Z. Bazant, Journal of the Electrochemical Society 160, A243 (2012). [4] J. Christensen and J. Newman, Journal of The Electrochemical Society 151, A1977 (2004)