Air Storage Impact\non Surface Evolution of Stoichiometric\nand Li-Rich NMC811

In recent years, a type of layered oxide, LiNi<sub><i>x</i></sub>Mn<sub><i>y</i></sub>Co<sub><i>z</i></sub>O<sub>2</sub> (NMC) where <i>x</i>+<i>y</i>+<i>z</i> = 1, has become the preferred cathode material\nfor electric\nvehicle (EV) batteries. Despite some disorder in the crystal structure\ndue to Li<sup>+</sup>/Ni<sup>2+</sup> cation mixing, the composition\noffers a high specific capacity of up to 200 mAh g<sup>–1</sup> at 4.3 V vs Li|Li<sup>+</sup>. The objective of this study is to\ncomprehensively evaluate the structural and electrochemical changes\nin NMC811 after storage in ambient conditions. In this report, we\nstudy stoichiometric and Li-rich NMC811 in terms of their structural,\nmorphological, and electrochemical differences. Following literature\nreports, a rigorous aqueous washing procedure was used alternatively\nto remove a possible lithium excess from the NMC surface. The findings\nof this study hold immense significance as they focus on the potential\nchallenges that may arise due to the remaining lithium content or\nLi<sup>+</sup> extraction from the near-surface NMC811 materials.\nThere is no consensus in the literature on whether excess lithium\ncan harm the material’s structural and electrochemical properties,\nreduce performance and safety concerns, or be beneficial regarding\nits protective properties, for Ni-rich NMC. Proper treatment of as-synthesized\nNi-rich NMCs helps to develop procedures to address the residual lithium\ncompounds issues, leading to enhanced performance and safety. Here\nwith this report, we show another aspect not being considered in the\nliterature before, regarding morphological NMC811 reshaping and a\nmechanism of LRC transition and growth due to aging. In addition,\nwe linked the selected structural parameters to the electrochemical\nperformance of various NMC811 materials. We discuss the well-known\nstructural factors and their limitations and introduce a doublet resolution\ncriterion that can help in predicting electrochemical performance.