Identifying the limiting electrode in lithium ion batteries for extreme fast charging

Lithium ion batteries that are capable of extreme fast charging (XFC) are highly desirable to accelerate adoption of electric vehicles (EVs). To identify the rate limiting factors for XFC, we used both half cells and symmetric cells to investigate the fast charging behavior of the cathode and anode separately. The symmetric cells enabled accurate measurements of charge transfer at each electrode without complications from counter electrodes. The battery materials and electrode design were comparable to the state-of-the-art for EV cells. Under these conditions, the graphite anode is the rate limiting electrode for fast charging in NMC811/Graphite pouch cells. The effective N/P ratio falls below 1.0 at high charging rates, which also causes Li plating. The use of symmetric cells in this study provides new insights to identify the limiting electrode in Li-ion batteries, especially those designated for extreme fast charging applications. Keywords: Symmetric cell, Li-ion battery, Extreme fast charging (XFC), Ni-rich cathode, NMC811, Electric vehicles