Microscopy Diagnosis of the Onset of Lithium Plating in Transparent Lithium-Ion Full Cells.

The fast-charging capability is critical for the wide adoption of electric vehicles (EVs), which, however, can result in lithium (Li) plating on the graphite anode and thus aggravate cell degradation and increase the safety risk. Li plating is also prone to occur during charging at low temperatures. In this work, we fabricate Li-ion full cells in transparent glass capillaries to probe the real-time dynamic evolution of the lithiated phases throughout the graphite anode toward the onset of lithium plating during fast charging and under low temperatures. We observed that Li plating can occur well before 70% state of charge (SOC), even at a low C-rate and at room temperature. Our experiments provide the direct proof that subtle features in the electrochemical responses are caused by the Li plating, which can be utilized to improve battery management strategy. Mathematical simulations confirm that the local overpotential due to the strong concentration polarization is the root cause of the axial reaction heterogeneity in the graphite anode and the Li plating on the fully lithiated particles.