AbstractThe 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 Li_xMn₂O₄ 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 Li_xMn₂O₄ near the core. Following 150 cycles, concentrations of LiMnO₂ and Li₂MnO₃ significantly increase and widely vary between particles.