The Effects of Cell Design on Li Plating in Li-Ion Cells: A Real Insight into Cell Design Optimization for Minimizing Li Plating

Abstract

Li-ion batteries are extensively used in personal electronic devices and electric vehicles (EVs) because of high energy density and high voltage. Although the Li-ion battery technology is satisfying for regular applications, several challenges such as cost, safety, longevity, power density, and energy density remain major hurdles to be overcome for mass production of next generation EVs. Among these challenges, battery lifetime has been recently paid special attention because of detrimental effects that fast charging has on EVs battery lifetime. The main objective of the present work is to study the effects of design parameters on Li-plating on the negative electrode. Li plating is understood to occur during fast charging especially at lower temperatures [1]. Li plating as well as other degradation mechanisms is the main cause of capacity fade and cell degradation [1, 2]. Therefore, understanding the Li-plating phenomena becomes indispensable particularly during aggressive operations of Li-ion cells (fast charging). This knowledge highly proves necessary for cell design and optimization. According to our modeling results Li plating can happen approximately within a distance equal to 35% of the negative electrode thickness, close to the separator. Therefore, the negative electrode design is critical for minimizing Li plating. Design parameters such as type and size of the negative electrode active particles, the negative electrode thickness, along with structural properties, including porosity and tortuosity [1, 3, 4] are primarily factors that influence Li-plating rate during fast charge that should be taken into account for cell design, development, and optimization. Particularly, a hierarchical anode microstructure and its effects on the amount of Li plating under different Crates and temperatures is studied in this work. A hierarchical anode microstructure can be established by moving some portion of the conductive additive and binder towards the negative electrode current collector that results in higher porosity close to the separator and lower porosity close to the current collector. The goal is to design a cell that exhibits little to no Li plating, while being charged (0% SOC to 80% SOC) in less than 45 minutes which is the target for the current EVs charging algorithm [5]. In this work, we deploy a mathematical Multiphysics model, developed in COMSOL Multiphysics 5.4, a finite element based commercial software, to provide in-depth knowledge of the relationship between Li plating amount and the negative electrode design and structural parameters for cell design and optimization purposes. Li plating is considered as an unwanted electrochemical reaction with an equilibrium potential of zero that is coupled with a so-called Pseudo 2D (P2D) Newman-type model [6]. When the Li plating starts (e.g. at high SOC during charge) there is a competition between Li-plating and intercalation currents evaluated by the model and can be changed with different model parameter sets. The fidelity of the model was validated by predicting the experimental data under various cell operations. [1] M.M. Forouzan, B.A. Mazzeo, D.R. Wheeler, J. Electrochem. Soc., 165 (2018) A2127-A2144. [2] A. Barré, B. Deguilhem, S. Grolleau, M. Gérard, F. Suard, D. Riu, Journal of Power Sources, 241 (2013) 680-689. [3] J.E. Vogel, M.M. Forouzan, E.E. Hardy, S.T. Crawford, D.R. Wheeler, B.A. Mazzeo, Electrochimica Acta, (2018). [4] M.M. Forouzan, M. Wray, L. Robertson, D.R. Wheeler, J. Electrochem. Soc., 164 (2017) A3117-A3130. [5] L. Donaldson, Materials Today, 21 (2018) 105-106. [6] T.F. Fuller, M. Doyle, J. Newman, J. Electrochem. Soc., 141 (1994) 1-10.