Formation\nCycle Control for Enhanced Structural Stability\nof Ni-Rich LiNi<sub><i>x</i></sub>Co<sub><i>y</i></sub>Mn<sub>1‑x‑y</sub>O<sub>2</sub> Cathodes

Nickel-rich\nNCM cathode materials promise lithium-ion batteries\nwith a high energy density. However, an increased Ni fraction in the\ncathode leads to complex phase transformations with electrode–electrolyte\nside reactions, which cause rapid capacity fading. Here, we show that\nan initial formation cycle at 0.1 C with a higher cutoff voltage (≥4.35\nV) increases the stability of Ni-rich NCM (LiNi<sub>0.88</sub>Co<sub>0.08</sub>Mn<sub>0.04</sub>O<sub>2</sub>) particles during cycling\nat 1 C. We unveil that the formation of intragranular nanovoids is\ndirectly associated with the initial formation cycle at a lower charging\ncutoff voltage when oxygen vacancies are introduced at the Ni-rich\nNCM particle surface, due to irreversible electrolyte decomposition\nat the cathode–electrolyte interface. Nanovoid evolution of\nthe Ni-rich NCM particles after 50 cycles increases the NiO-like rock\nsalt phase; it results in intragranular cracks, which cause structural\ninstability via heterogeneous phase distribution. This work demonstrates\nthe importance of controlling Ni-rich NCM surface chemistry from the\ninitial formation cycle to achieve better cycling stability.