Degradation behavior of Ah-level Li-ion pouch cell during repeated fast charging within a wide temperature region

Quantifying the impact of temperature on the degradation behavior of the pouch cell during repeated fast charging is crucial for improving its fast-charging performance, especially in extreme conditions. Here, critical factors including electrochemical behavior, dynamic limitation, interfacial chemistry, structure evolution, and gas production affecting the battery degradation mechanisms have been explored and quantified based on the Ah-level LiNi_0.5Co_0.2Mn_0.3O₂||graphite pouch cells. The battery delivers high specific capacity and acceptable reversibility in the early cycles at 50 °C, and capacity decay occurs with the increased cycles; at 0 °C, the battery shows high polarization, low specific capacity, and poor cycle stability. As revealed by electrochemical analysis, the battery performance at 0 °C is mainly limited by the sluggish interfacial kinetics and the uneven SEI layer with a low proportion of LiF and a high content of Li_xO_y. In contrast, high temperature accelerates the side reaction between electrolyte and cathode, inducing electrolyte decomposition, gas generation, and mechanical pulverization. Moreover, theoretical simulation reveals that the average cell temperature at 273 K is the highest. Both NCM523 cathode and graphite anode at 273 K have the greatest stress and deformation after one cycle at 8C, and the most cracks found on the cycled NCM523 particles at 323 K are mainly due to its severe side reaction. Based on these results, strategies for achieving fast-charging LIBs at extreme conditions can be proposed.