Lithium Plating–a Life-Limiting and Safety Issue in a Li-Ion Cell

Abstract

Despite their advances and widespread use in various applications for the last two decades, Li-ion batteries continue to exhibit occasional failures from Li plating on the anode. Li plating can have immediate effects on performance and more devastating effects upon the safety, if the Li plating occurs in a dendritic form that could pierce through the separator causing an internal short. Even in a benign form, plated Li—lacking the protective SEI that protects the carbon anode —tends to react with electrolyte which results in a rapid growth in interfacial impedance and capacity loss during cycling. Li plating will manifest whenever intercalation kinetics (into carbon) are slower compared to lithium plating over carbon, despite the lower reversible potential of the latter. Poor cell design factors, i.e., improper matching of anode and cathode in terms of electrochemical capacities and geometric aspects with localized hotspots in current distribution, and inappropriate electrolyte, can cause Li plating on the anode. The nature of the anode, electrolyte and SEI are among the most important factors that can influence Li plating.1 Apart from the design/chemical abnormalities, lithium plating is also triggered by the operational conditions, such as fast charge rates and low operating temperatures relevant to planetary space missions. In our earlier study, we have demonstrated that the choice of the electrolyte is critical in determining the propensity towards lithium plating.2 Specifically, these studies indicate that the Li intercalation kinetics are mainly dictated by the anode surface films (SEI), which in turn could be controlled by a judicious selection of electrolyte solution, i.e., both solvent and salt. We have established a correlation between the poor lithium intercalation kinetics and the propensity towards lithium plating using different electrolytes with different solvent blends and different electrolyte additives. Recently, Li plating was observed in cells upon extended cycling at ambient temperature in a Low Earth Orbit (LEO) satellite simulation condition, involving 30 minutes of discharge and 60 minutes of charge continuously, possibly due to impeded intercalation kinetics at the anode. Likewise, exposure to high intensity radiation environments may have led to Li plating in prototype 18650 cells upon subsequent cycling. In this paper, we will discuss the Li plating phenomenon in these specific examples, and with reference to anode/cathode interfacial kinetics at low temperatures in different electrolytes. ACKNOWLEDGEMENT The work described here was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration (NASA). REFERENCES B. V. Ratnakumar and M. C. Smart, ECS Trans. 25 (36), 241 (2010).M. C. Smart and B. V. Ratnakumar, J. Electrochem. Soc. 2011, 158 (4), A379.