Insights into Cycling Aging of LiNi0.80Co0.15Al0.05O2 Cathode Induced by Surface Inhomogeneity: A Post-mortem Analysis

A comprehensive post-mortem study is conducted on the power-optimized LiNi _0.80Co _0.15Al _0.05O ₂ (NCA) cathode material harvested from large-format commercial pouch cells with different aging conditions. Uneven degradation phenomena are observed in the harvested NCA electrode during the post-mortem analysis. A schematic model, which is associated with the surface inhomogeneity, is proposed to interpret the formation of uneven degradation phenomena. On the basis of the model, the detrimental impact caused by an elevated cycling temperature is related to the fact that the high cycling temperature facilitates the local overcharge reaction and further accelerates the uneven degradation of the NCA electrodes. This work provides experimental evidence and an in-depth discussion concerning the cycling aging induced from the surface heterogeneity of the electrode material. Additionally, we emphasize the necessity of carrying out a reliable aging study on thin-coated battery electrodes.