Lithium Plating Identification and Quantification in Li-Ion Cell from Degradation Behaviors

Abstract

Accelerated stress tests (AST) are widely used to speed up the aging of Li-ion cells. During AST, lithium plating may occur, which is unwanted and even dangerous. Thus, accurately check the occurrence of lithium plating of a cell during AST is vital for charging protocol selection and optimization, degradation mechanism identification, and life prediction. Current methods can hardly examine the lithium plating in product cell on-board. In this study, three methods have been proposed to check the occurrence of lithium plating in product cell on-board based on its degradation behavior. The combination of those methods has the potential to quantify the amount of the plated lithium. The first method is built on Arrhenius’ law, as indicated in Figure 1. During AST, the cell capacity fade is mainly caused by the growth of solid electrolyte interphase (SEI) layer, and lithium plating. If we assume the SEI formation rate follows Arrhenius’ law with temperature [1], then any deviation of the degradation rate from the law indicate the occurrence of lithium plating. The second method is based on the consideration that plated Li may cause less increase in resistance than the SEI corresponding with the same amount of Li. The occurrence of lithium plating could be differentiated from the trajectories of the resistance and capacity variations using R-Q plot. The third method is built on the discovery that cell ages fast with the existence of lithium plating. Thus, capacity fade rate can be used as an indicator for the judgment of lithium plating. Combining the above three methods, one can identify and even quantify the lithium plating of a cell during the AST. Figure 1 Arrhenius’ law is used to judge the occurrence of lithium plating. (T, a, b) in the legend stands for aging condition, in which a is the level of the charging current and b is the level of the cut-off voltage during charging. The levels 1, 2, and 3 for a are 0.4C, 0.7C, and 1C, while for b are 4.05 V, 4.15 V, and 4.25V. The validity of the methods was checked using post-mortem analysis combined with materials identification techniques. Optical methods, like optical microscopy and Raman microscopy, and electron microscopy, including SEM, AFM, and TEM, were used to identify the existence of lithium plating on the surface of cell anode [2]. Those techniques were further utilized to analyze the morphological characteristics of lithium plating. Furthermore, NMR and X-ray techniques, like XPS and XAS, were adopted to quantitatively analyze the composition of the lithium plating [3]. Reference: [1]. Wright, R.B., et al., Calendar-and cycle-life studies of advanced technology development program generation 1 lithium-ion batteries. Journal of Power Sources, 2002. 110(2): p. 445--470. [2]. Zhe Li, Jun Huang, et al., A review of lithium deposition in lithium ion and lithium metal secondary batteries. Journal of Power Sources, 2014, 254: 168-182. [3]. Rangeet Bhattacharyya, et al., In situ NMR observation of formation of metallic lithium microstructures in lithium batteries. Nature Materials, 2010, 9: 504-510. Figure 1