Diagnosis tools for humidity-born surface contaminants on Li[Ni0.8Mn0.1Co0.1]O2 cathode materials for lithium batteries

Abstract

Ni-rich layered oxides such as Li[Ni0.8Mn0.1Co0.1]O2 (NMC811) are highly sensitive towards moisture. Any contact with humidity leads to the formation of surface contaminants, which reflect into an increased overpotential and cause accelerated capacity loss during cycling. This is particularly relevant when considering large-scale processing. Herein, we report a diagnostic set of tools to rapidly assess the extent of such surface contaminants on Ni-rich NMC materials comprising different titration methods, electron microscopy, and the determination of the reversible and irreversible water adsorption. Based on a series of samples subjected to a controlled humidity for varying times, the formation of carbonate and hydroxide species is investigated and correlated to the eventual electrochemical performance in half-cells and full-cells. The results show that even rather short storage times under humid atmosphere lead to substantial water uptake and surface species formation and that the formation of these surface species has a severe impact on the capacity retention in half-cells and graphite||NMC811 full-cells.