Air Instability of Ni‐Rich Layered Oxides–A Roadblock to Large Scale Application

Abstract 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.