In the present study, we analyze the impact of ambient air contact on NMC811 in comparison to NMC111. It will be shown that in contrast to NMC111, NMC811 is very sensitive when stored under ambient conditions and that the formation of surface impurities detrimentally affects the performance of both, NMC811/Li and NMC811/graphite cells. We will critically investigate the chemical nature of the formed surface species and present a simple method to quantify them. Finally, we will demonstrate that a proper handling of NMC811 is much more challenging compared to NMC111 and if the latter is to be replaced by NMC811, it is of primary importance to control the amounts of surface impurities on Ni-rich NMC cathode materials to allow for low impedance and good cycling stability.
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