Surface and in-depth characterization of lithium-ion battery cathodes at different cycle states using confocal micro-X-ray fluorescence-X-ray absorption near edge structure analysis

•The potential of confocal micro-XRF-XANES for spatial resolved species analysis in a part of a working system is shown.•The spatial resolution enables differentiation of the oxidized interface from deeper layers.•With the analytical technique confocal micro-XRF-XANES 3D in-situ analyses of working systems are feasible.•The multidimensional and nondestructive analysis of Li-ion battery cathodes is shown.•The analysis will allow for a deeper understanding of processes at interfaces in battery science and others.

The cathode material LiNi0.5Mn1.5O4 for lithium-ion batteries has been studied with confocal micro-X-ray fluorescence (CMXRF) combined with X-ray absorption near edge structure (XANES) at the Mn-K edge and the Ni-K edge. This technique allows for a non-destructive, spatially resolved (x, y and z) investigation of the oxidation states of surface areas and to some extent of deeper layers of the electrode. Until now CMXRF-XANES has been applied to a limited number of applications, mainly geo-science. Here, we introduce this technique to material science applications and show its performance to study a part of a working system. A novel mesoporous LiNi0.5Mn1.5O4 material was cycled (charged and discharged) to investigate the effects on the oxidation states at the cathode/electrolyte interface. With this approach the degradation of Mn3 + to Mn4 + only observable at the surface of the electrode could be directly shown. The spatially resolved non-destructive analysis provides knowledge helpful for further understanding of deterioration and the development of high voltage battery materials, because of its nondestructive nature it will be also suitable to monitor processes during battery cycling.