Aluminum-Distribution-Dependent Microstructural Evolution of NCA Cathodes: Is Aluminum Homogeneity Really Favorable?

Despite extensive research, the optimal synthesis method and Al concentration for fabricating high-performance Li[NixCoyAl1−x−y]O2 (NCA) cathodes remain to be established. This study provides an in-depth analysis of NCA cathodes prepared using different synthesis methods and Al fractions. Al overdoping (3 mol%) during coprecipitation generates a homogeneous Al distribution in the cathode active material, whereas supplying excess Al during calcination induces a hierarchical spatial arrangement. Interestingly, different Al distributions and concentrations produce strikingly different cathode microstructures, which greatly affect the electrochemical performance of the cathode. Contrary to the common belief that homogeneous Al doping is critical for optimal cycling performance, the electrochemical performance of the cathode is maximized by grain-boundary-segregated Al ions. The proposed Li[Ni0.925Co0.042Al0.033]O2 cathode demonstrates superior cycling performance, retaining 74.1% of its initial capacity after 1000 cycles in a full cell despite cycling under severe operating conditions (3 C and 45°C). These findings redefine the fundamental contribution of the elemental distribution to the engineering of cathode microstructures, thereby providing a viable approach for developing high-performance Ni-rich NCA cathodes for advanced Li-ion batteries.