(Invited) Surface Characterisation of Ni-Rich NMC Materials Stored in Various Environments

In order to obtain higher energy densities for electromobility applications, the market is now heading towards high-nickel content NMCs. However, these materials suffer from severe gassing issues decreasing the cycle life and causing safety problems. While it is agreed that the O2 evolution is coming from oxygen lattice oxidation at the end of charge, the source of CO and CO2 gassing is still under debate. In this context, we report here a systematic study of NMC811 pristine material surface contaminations obtained after storage in different controlled environments. We use a multi-analytical approach involving combined MAS-NMR, XPS and STEM-EELS to provide a full material characterisation before cycling. The chemical environment of the Li present in the paramagnetic bulk of the material is successfully determined by means of 7Li MAS-NMR at low field (200 MHz). High field 7Li MAS-NMR (500 MHz) allows the quantification of the surface diamagnetic Li. Low field 1H MAS-NMR gives insights on the proton bulk and surface environments. STEM-EELS mapping is performed with both high energy and high spatial resolution using our new TEM/STEM Themis Z G3 (Thermo Fisher Scientific) equipped with a double camera GIF spectrometer. We obtain a good multi-elemental chemistry mapping quantification as well as the accurate analysis of the fine structure of the L3/L2 Ni edges thanks to the use of an excited monochromator. Putting together all characterisation results, we achieved a thorough analysis of primary particles surface contamination after different controlled storage conditions, that will be correlated with gassing measurements and cell cycling stability.