(224i) Investigations of Lithium Plating on Thick Graphite Electrodes in Fast Charging Lithium-Ion Batteries

With the rapid growth of the electric vehicle (EV) market, fast charging capability is becoming one of the key features of lithium-ion batteries (LIBs). However, charging traditional LIBs with thick electrodes at high current densities generally adversely impact the electrochemical performance and cause potential safety issues due to the formation of lithium dendrites. The onset of Li dendrite formation is associated with the polarization of cells mainly originated from the retard mass transport across the electrodes. This study investigated the onset of Li plating in the graphite electrodes by using electrochemical analysis. After discharging (lithiating) the graphite electrode to different states of charge (SOC) at various rates, the open-circuit voltage (OCV) during the relaxing period was monitored and the analysis of differential open-circuit (dOCV) was applied to manifest the onset of Li plating. The onset of Li plating was further verified through the analysis of coulombic efficiency (CE) and post-mortem analysis on the cycled electrodes using scanning electron microscopy (SEM). The same approaches were used to study the onset of Li plating in the graphite electrodes with different thicknesses. Based on analysis from these tests, the correlation of Li plating onset, electrode thickness and lithiation rate was established. Furthermore, the experimental observations on the Li plating onset agree well with theoretical predictions obtained with a Newman pseudo-2D model. Therefore, the achievements obtained here will be of both scientific and practical significance in developing LIBs with high energy and power densities.