A Multi-Analytical Approach for the Surface Reactivity Characterisation of Pristine NMC811: Towards Gassing Comprehension

The urgent demand of the EV industry for high energy density cathode materials is currently leading the battery market towards Ni-rich NMCs. Despite that, the gassing phenomenon that affects these materials has huge impacts on their electrochemical properties and causes security issues that prevent the commercialization of 80% Ni-rich NMC. In order to obtain a fundamental understanding of this gassing generation, we decided to focus on the surface reactivity of the pristine NMC811 provided by Umicore, with emphasis on the material surface’s and bulk’s changes during the native contamination layer formation. A multi-analytical approach is thus required to analyse all the aspects of such a complex system. The sapient use of high field 7Li MAS-NMR allowed us to successfully filter the signal of the diamagnetic compounds at the surface of the material and to quantify the corresponding environments. The speciation of these compounds, not being possible by MAS-NMR, was defined by low temperature XPS experiments. It was thence possible to characterise the reactive surface of the primary particles in contact with this contamination layer at the nanometric scale by STEM-EELS with both high energy and high spatial resolutions. The oxidation state and the crystalline phase were successfully determined crossing the high quality experimental spectra recorder with the K2 counting direct detector (Gatan) installed on our new Themis Z G3 (Thermo Fisher Scientific) and EELS edges simulations. On the other hand, low field 1H MAS-NMR gave us a new insight on the proton environments enabling us to clearly see the presence of a proton chemically bonded inside the material for the first time and to correlate it with the surface reactivity investigated with the other techniques. The combined use of these advanced characterisation techniques, all available in the IMN, allowed us to shed a new light on the understanding of the pristine industrial NMC811 with always the same material history.