z ]O 2 (NCMA) cathodes have attracted public attention owing to their improved durability by leveraging the advantages of NCM and NCA cathodes. As the Ni content approaches 90%, however, it is challenging to realize high-energy Ni-rich NCMA cathodes without sacrificing durability. Herein, we improve the cycling stability of a Ni-rich Li[Ni 0.93 Co 0.03 Mn 0.03 Al 0.01 ]O 2 (NCMA93) cathode using a combination strategy involving microstructural refinement and surface modification. The F-coating-induced protective layer of the Fcoated, Sb-doped NCMA93 cathode combined with its engineered microstructure enables the formation of a robust cathode−electrolyte interphase (CEI) layer on the cathode surface, which suppresses surface degradation to afford a long battery life. However, the F coating alone does not significantly improve the cycling stability of cathode because it suffers severe microcracking during cycling owing to its suboptimal microstructure. To realize a cathode with a long lifespan, a robust CEI layer should be generated and maintained on the cathode without severe microcracking.

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Layered [Ni1–x–yCox(Mn or Al)y]O2 (NCM or NCA) oxides are the main cathode materials for powering current electric vehicles. Increasing the Ni fraction is the primary approach to increase the energy density of NCM and NCA cathodes, and thus enhancing the driving range of associated electric vehicles. However, high–Ni NCM and NCA cathodes with Ni contents near 90% suffer from inherent structural instability, especially in the deeply charged state, resulting in rapid capacity fading and high thermal instability. One method to address this inherent structural instability involves removing the interparticle boundaries by growing a single-crystal cathode. Single-crystal cathodes, free from interparticle microcracking, are regarded to improve cycling and thermal stability by minimizing parasitic surface degradation. Despite mechanical stability, the single-crystal cathode has some problems. In this presentation, we report a comprehensive evaluation of the fundamental properties of single-crystal and polycrystalline cathodes with a wide range of Ni-rich compositions. The electrochemical performances of single-crystal and polycrystalline cathodes are correlated with their structural changes to elucidate the dominant capacity fading mechanism of single-crystal cathodes.