Microscopic Operando Diagnosis of Li Plating During Full Cell Fast Charging

The fast-charging becomes crucial for electronic devices and electric vehicles (EVs). However, it can result in Lithium (Li) plating on the graphite anode that aggravates the cell degradation and increases the safety risk. In this work, we fabricate Li-ion full cells in transparent glass capillaries as the model system for the practical Li-ion sandwich cells to probe the dynamic evolution in graphite anodes during the fast-charging process and under low temperatures. We observed that Li plating can occur before the cell is fully charged even at a low C-rate and at room temperature. The onset of Li plating is always accompanied by some features in the full cell voltage signal. Our <i>operando</i> experiments provide the direct proof that the 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 lithiated graphite and the Li plating. At low temperatures, such polarization becomes stronger and leads to earlier Li plating during the fast charging.