Hard X‐ray spectromicroscopy of Ni‐rich cathodes under in situ liquid heating conditions

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Abstract In situ microscopy involves imaging of samples under real reaction conditions. For electron microscopy, micro‐electromechanical systems (MEMS) chips have previously been developed that can hold a liquid or gas inside the vacuum of the electron microscope, with electrical contacts that allow for heating or biasing of the sample. These chips have paved the way for high‐resolution imaging of dynamic chemical reactions. Here, we report the use of such MEMS chips in an in‐house developed setup for a hard X‐ray nanoprobe, applied to Ni‐rich cathode materials. We investigate the chemical and structural changes in nickel‐rich cathodes upon exposure to electrolyte and under heating conditions using hard X‐ray spectromicroscopy. As such, we find marked differences in the behaviour of pure LiNiO 2 compared to Co and Mn substituted material, NMC811. The use of hard X‐ray spectromicroscopy allows for imaging and observation of: (i) the oxidation state of nickel, changing from Ni 3+ to Ni 2+ , (ii) the effect of a preexisting fracture in the sample and (iii) the structural degradation of the sample during accelerated aging.

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