Near‐Atomic‐Scale Evolution of the Surface Chemistry in Li[Ni,Mn,Co]O2 Cathode for Li‐Ion Batteries Stored in Air

Abstract

Layered LiMO2 (M = Ni, Co, Mn, and Al mixture) cathode materials used for Li‐ion batteries are reputed to be highly reactive through their surface, where the chemistry changes rapidly when exposed to ambient air. However, conventional electron/spectroscopy‐based techniques or thermogravimetric analysis fails to capture the underlying atom‐scale chemistry of vulnerable Li species. To study the evolution of the surface composition at the atomic scale, cryogenic atom probe tomography is used herein and the surface species formed during exposure of a LiNi0.8Mn0.1Co0.1O2 (NMC811) cathode material to air are probed. The compositional analysis evidences the formation of Li2CO3. Site‐specific examination from a cracked region of an NMC811 particle also reveals the predominant presence of Li2CO3. These insights will help to design improved protocols for cathode synthesis and cell assembly, as well as critical knowledge for cathode degradation.

Keywords

• ambient oxidation
• atom probe tomography
• Li-ion batteries
• NMC cathodes