Unveiling the pattern and progression of reaction extent heterogeneity inside graphite electrodes through real-time monitoring of current density

To improve electrode performance, understanding the complex changes within electrodes when working is vital. The lithiation process in graphite electrodes involves the influx of Li ions from the separator and electrons from the current collector, coupled with materials’ hindrance for charged particle movement, leading to reaction extent heterogeneity. Since capacity is the cumulative effect of current density, real-time monitoring of current density to investigate reaction pathways in different sections of the electrode can enhance our knowledge of the pattern of heterogeneity as the rate increases and progression of reaction extent heterogeneity, aiding in developing mitigation strategies. This study used a pouch cell with a multilayer graphite electrode to monitor current density in real time, revealing patterns associated with increasing rates and the progression of reaction extent heterogeneity inside graphite. The results show that with rate increasing, the current density inside graphite becomes more heterogeneous, leading to more severe reaction extent heterogeneity. Besides, it is shown that heterogeneous current density leads to lithiation of top part in graphite. The resulting additional capacity released from lithium deposition will compensate for the unused capacity of the remaining layers. Consequently, for the graphite, safety has been weakened and lithium inventory has decreased while total capacity remains almost unaffected during the first lithiation.