A Comparative Analysis of the Capacity Fading Mechanisms in Ni-Rich Single-Crystal and Polycrystalline Cathodes

Abstract

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.