Spatial quantification of dynamic inter and intra particle crystallographic heterogeneities within lithium ion electrodes

Dynamic chemical and structural heterogeneities within electrodes are known to lead to battery degradation and failure. Here, the authors show that X-ray diffraction computed tomography can be used to spatially quantify the dynamic crystallographic states of electrodes as they operate and degrade. The performance of lithium ion electrodes is hindered by unfavorable chemical heterogeneities that pre-exist or develop during operation. Time-resolved spatial descriptions are needed to understand the link between such heterogeneities and a cell's performance. Here, operando high-resolution X-ray diffraction-computed tomography is used to spatially and temporally quantify crystallographic heterogeneities within and between particles throughout both fresh and degraded LixMn2O4 electrodes. This imaging technique facilitates identification of stoichiometric differences between particles and stoichiometric gradients and phase heterogeneities within particles. Through radial quantification of phase fractions, the response of distinct particles to lithiation is found to vary; most particles contain localized regions that transition to rock salt LiMnO2 within the first cycle. Other particles contain monoclinic Li2MnO3 near the surface and almost pure spinel LixMn2O4 near the core. Following 150 cycles, concentrations of LiMnO2 and Li2MnO3 significantly increase and widely vary between particles.