Single-crystal, conventional, and refined polycrystalline (Li­[Ni0.9Co0.05Mn0.05]­O2) cathodes were prepared, and their performances and capacity fading behaviors in half cells were compared. The rate capability and cycling stability of polycrystalline cathodes are better than those of single-crystal cathodes. Furthermore, the performance of the refined polycrystalline cathode is markedly improved owing to the elongated, radially oriented primary particles of the cathode, which effectively suppresses severe intergranular microcracking during cycling. The rapid capacity fading behavior of single-crystal cathode stems from kinetically hindered Li+ intercalation, resulting from its long Li+ diffusion paths and microstructural damage caused by repeated cycling. The accumulation of internal stress in large single-crystal particles during cycling leads to fracturing and the development of an extensive network of regularly spaced slip bands. Structural damage concentrated in these slip bands causes inhomogeneities in the distribution of Li+ within particles and hinders Li+ diffusion, leading to poor electrochemical performance.

The continuous expansion of the electric vehicle (EV) market is driving the demand for high-energy-density batteries using Ni-rich cathodes. However, the operation of Ni-rich cathodes under extreme-fast-charging (XFC) conditions compromises their structural integrity, resulting in rapid capacity fading; realizing Ni-rich cathodes operable under XFC conditions while maximizing energy density and long-term cycling performance is challenging. This study introduces a Li[Ni0.92Co0.06Al0.01Nb0.01]O2 (Nb-NCA93) cathode with a high energy density of 869 Wh kg–1. The presence of Nb in the Nb-NCA93 cathode induces the grain refinement of its secondary particles, alleviating internal stress and preventing heterogeneity of Li concentration during cycling. A resulting full-cell reaches full charge within 12 min and retains 85.3% of its initial capacity after 1000 cycles (cycled at full depth of discharge). In addition, the Nb-NCA93 cathode generates limited heat under XFC conditions due to its refined microstructure.