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 separator and electrons from current collector, coupled with materials’ hinderance for charged particles movement, leading to reaction extent heterogeneity. Since capacity is the cumulative effect of current density, real-time monitoring current density to investigate reaction pathways in electrode different sections can enhance our knowledge of heterogeneity’s pattern as rate increases and progression, 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 heterogenous, leading to more severe reaction extent heterogeneity. Besides, it is shown that heterogeneous current density leads to lithiation of top part in graphite. The resulted additional capacity released from lithium deposition will compensate the remaining layers’ unused capacity. Consequently, for the graphite, safety has been weakened and lithium inventory has decreased while total capacity remains almost unaffected during the first lithiation.