Benefiting from the excellent lithium ions diffusion kinetics and considerable discharge specific capacity, Ni-rich layered oxides have become the preferred selection cathode active materials (CAMs) for high energy density Li-ion batteries. However, due to the distinctive electronic structure of nickel ions (Ni^2+/3+/4+) and the strict criteria for sintering conditions, the Ni-rich CAMs inherently suffer from notorious deterioration when in contact with the ambient air. This review provides a comprehensive and critical overview of air instability for Ni-rich CAMs, a neglected but critical issue for large-scale application. The fundamental understanding of derivation of air instability and characterizations is first given, followed by a discussion of evolution behaviors and the corresponding negative influence on fabricating properties of electrodes and electrochemical/safety performance of batteries. Afterward, various material modification strategies for improving air storage stability including pre-treatment by doping and coating and post-treatment by gas, wash, and heat are overviewed. Finally, some perspectives for further exploration to address the air instability issue and pave ways toward Ni-rich CAMs’ practical applications are also proposed.

中文翻译：

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富镍层状氧化物的空气不稳定性——大规模应用的障碍

得益于优异的锂离子扩散动力学和可观的放电比容量，富镍层状氧化物已成为高能量密度锂离子电池的首选正极活性材料（CAM）。然而，由于镍离子独特的电子结构（Ni ^2+/3+/4+) 和严格的烧结条件标准，富镍 CAM 在与环境空气接触时会发生固有的劣化。这篇综述全面而重要地概述了富镍 CAM 的空气不稳定性，这是一个被忽视但对大规模应用至关重要的问题。首先给出了对空气不稳定性的推导和表征的基本理解，然后讨论了演化行为以及相应的对电极制造性能和电池电化学/安全性能的负面影响。之后，概述了用于提高空气储存稳定性的各种材料改性策略，包括通过掺杂和涂层进行的预处理以及通过气体、洗涤和加热进行的后处理。最后，