Li Plating Quantification in Commercial Graphite‖LiFePO4 cells

Metallic lithium plating (Li plating) is considered one of the most detrimental phenomenon in lithium ion batteries (LIB), as it not only leads to further aging but also to safety deterioration [1], [2]. Li plating occurs during charge, when Li ions deposit on the carbonaceous anode, in place of Li intercalation. Because metallic Li is highly reactive with the electrolyte, it further reacts consuming more lithium and inducing degradation on the electrode surface. These phenomena results in loss of lithium inventory (LLI) and loss of active material (LAM), leading to capacity loss and power fade. Safety deterioration occurs when the metallic Li results in the formation of moss-like deposits and dendrites [3]. Dendrites may eventually grow and pierce the separator, leading to short-circuits than could potentially trigger thermal runaway. Due to the critical impact of Li plating on LIB’s performance and safety, several studies have focused on this topic [4], [5], aiming to further elucidate its effects and provide a proper method for its detection. Despite the recent improvements in this field, to our best knowledge, an advanced, in situ and cost-effective technique to detect and quantify Li plating still remains to be presented. In this study, we will show the analysis to operando estimate and quantify Li plating on a commercial Graphite‖LiFePO4 cell. The cells were tested at ambient temperature (23 ºC) using a stressful – yet realistic – long term cycling testing scheme. First, we coupled incremental capacity (IC) and peak area (PA) analyses to identify and quantify the presence of reversible Li plating from a new IC peak, 0, that eventually emerged after cycle 600 (see Fig. 1). Then, we studied the nature of Li plating origins, to observe that gradual cell degradation, and not a sporadic event, lead to Li plating. To conclude, mechanistic model simulations (‘alawa toolbox with harvested half-cell data) allowed us to identify the ongoing aging modes, estimate the reversible amount of Li plating and project half-cell degradation on each individual electrode throughout cycling (see Fig. 2). The results showed that large LAM on delithiated negative electrode (i.e., LAMdeNE) eventually caused cell imbalance, leading to overcharge the NE subsequently inducing Li plating. The prospect of obtaining these parameters online during cell monitoring in a battery system operation creates remarkable benefits to improve battery management system (BMS) function for battery diagnosis performance. References [1] J. Vetter, P. Novák, M. R. Wagner, C. Veit, K.-C. Möller, J. O. Besenhard, M. Winter, M. Wohlfahrt-Mehrens, C. Vogler, and A. Hammouche, “Ageing mechanisms in lithium-ion batteries,” J. Power Sources, vol. 147, no. 1–2, pp. 269–281, Sep. 2005. [2] M. C. Smart and B. V. Ratnakumar, “Effects of electrolyte composition on lithium plating in lithium-ion cells,” J. Electrochem. Soc., vol. 158, no. 4, p. A379, 2011. [3] M. Dollé, L. Sannier, B. Beaudoin, M. Trentin, and J.-M. Tarascon, “Live scanning electron microscope observations of dendritic growth in lithium/polymer cells,” Electrochem. Solid-State Lett., vol. 5, no. 12, p. A286, 2002. [4] J. C. Burns, D. a. Stevens, and J. R. Dahn, “In-Situ Detection of Lithium Plating Using High Precision Coulometry,” J. Electrochem. Soc., vol. 162, no. 6, pp. A959–A964, 2015. [5] M. Petzl and M. A. Danzer, “Nondestructive detection, characterization, and quantification of lithium plating in commercial lithium-ion batteries,” J. Power Sources, vol. 254, pp. 80–87, May 2014. Fig. 1. Incremental capacity evolution of the test cells at C/25 Fig. 2. Schematic representation of the Graphite‖LFP test cell, showing the evolution with cycle aging of the simulated results Figure 1