Detection of Li Deposition on Si/Graphite Anodes from Commercial Li-Ion Cells: A Post-Mortem GD-OES Depth Profiling Study

Abstract

A new semi-quantitative method was developed to detect Li deposition on Si/graphite anodes. This method is based on Post-Mortem glow discharge optical emission spectroscopy (GD-OES) depth profiling. Based on the contents of Si, Li, and O in the GD-OES depth profiles, we define a corridor, in which the minimum amount of metallic Li on the anode is located. This method was applied to three types of commercial 18650 cells with Si/graphite anodes in the fresh state and with Li plating intentionally produced by cycling at low temperatures. Additional cells were cycling aged at 45 °C to 80% SOH. The main aging mechanisms at 45 °C were determined using differential voltage analysis (DVA), SEM, and half cell experiments. Subsequently, the cells aged at 45 °C were further cycled under the conditions that had led to Li deposition for the fresh cells. Furthermore, the anode coating thickness for 18 types of commercial Li-ion cells are correlated with the specific energy, while distinguishing between graphite anodes and Si/graphite anodes. Our extensive Post-Mortem study gives deep insights into the aging behavior of state-of-the-art Li-ion cells with Si/graphite anodes.