Tailoring Primary Particle Size Distribution to Suppress Microcracks in Ni-Rich Cathodes via Controlled Grain Coarsening

Crystallinity and microstructure, fundamental properties of cathode materials, are determined during the calcination process. Increasing the calcination temperature to improve crystallinity induces grain coarsening in multiple directions, resulting in the polygonal primary particles with heterogeneous size distribution. Here, grain coarsening was controlled by introducing Nb segregated at grain boundaries, and a microstructure with homogeneous primary particles evolved under a balanced coarsening force. The homogeneous size distribution of the primary particles improved not only the mechanical stability of the cathode particles but also the resistance to microcrack propagation during cycling. The Nb-doped Ni-rich cathode with homogeneous primary particle size retained 90.0% of its initial capacity after 500 cycles by suppressing electrolyte infiltration along the microcracks and subsequent degradation. This study demonstrates that improving the mechanical stability of cathode particles by tightly packing homogeneous primary particles is a key factor in improving the cycling stability of Ni-rich cathodes.