Suppressed oxygen extraction and degradation of LiNixMnyCo2O2 cathodes at high charge cut-off voltages

• Published in: 纳米研究：英文版 Vol. 10; no. 12; pp. 4221 - 4231
• Main Author: Jianming Zheng;Pengfei Yan;Jiandong Zhang;Mark H. Engelhard;Zihua Zhu;Bryant J. Polzin;Steve Trask;Jie Xiao;Chongmin Wang;Jiguang Zhang
• Format: Journal Article
• Language: English
• Published: 2017
• ISSN: 1998-0124; 1998-0000

The capacity degradation mechanism in lithium nickel-manganese-cobalt oxide （NMC） cathodes （LiNi1/3Mn1/3Co1/3O2 （NMC333） and LiNi0.4Mn0.4Co0.2O2 （NMC442）） during high-voltage （cut-off of 4.8 V） operation has been investigated. In contrast to NMC442, NMC333 exhibits rapid structural changes including severe micro-crack formation and phase transformation from a layered to a disordered rock-salt structure, as well as interfacial degradation during high-voltage cycling, leading to a rapid increase of the electrode resistance and fast capacity decline. The fundamental reason behind the poor structural and interracial stability of NMC333 was found to be correlated to its high Co content and the significant overlap between the Co3＋/4＋ t2g and O2- 2p bands, resulting in oxygen removal and consequent structural changes at high voltages. In addition, oxidation of the electrolyte solvents by the extracted oxygen species generates acidic species, which then attack the electrode surface and form highly resistive LiF. These findings highlight that both the structural and interfacial stability should be taken into account when tailoring cathode materials for high voltage battery systems.