Emerging chemical heterogeneities in a commercial 18650 Li-ion battery during early cycling

X-ray diffraction computed tomography (XRD-CT) was employed to study a commercial 18650 cylindrical LiNi0.8Co0.15Al0.05O2 (NCA) battery under operating conditions and during seven cycles. Multiple chemical heterogeneities related to the lithium distribution were observed in both the cathode and the anode from the analysis of the spatially-resolved diffraction signals. It is shown that during the battery charging, the anode exhibits different degrees of activity regarding the lithiation process. Explicitly, the following three regions were identified: uniform/homogenous lithiation, delayed lithiation and inactive-to-lithiation regions. The delayed lithiation region, observed for the first time, was seen to have a direct impact on the properties of NCA in its close proximity during the battery discharging, preventing its full lithiation by trapping the lithium in the form of LiC30-30+ phase. Further to this, the aluminum tab negatively affected the NCA in direct contact with it, leading to different lattice parameter a and c evolution compared to the rest of the cathode.