The spatiotemporal heterogeneity of the state of charge (SOC) within battery electrodes significantly impairs the rate capability and cycle life of lithium-ion batteries. However, mapping this heterogeneity is challenging owing to the lack of experimental methods that quantify the SOC at the electrode scale, while also offering nanoscale resolution for in-depth analyses of individual particles. Herein, this work reports an advanced projection X-ray microscopy that combines nanometric resolution, a large field of view, and high chemical sensitivity using spectroscopic imaging. This method enables the operando imaging of SOC heterogeneity across electrodes containing numerous Ni-rich layered oxide (NRLO) particles, while significantly lessening the radiation dose and maintaining rapid imaging speeds. This work characterizes the SOC heterogeneity in the degraded electrode with a cross-section, thereby revealing the considerable heterogeneity in the battery degradation progresses at the individual-particle-level. Further, this work observes inter- and intra-particle heterogeneity during NRLO particle calcination, thereby identifying rapidly oxidized particles that likely facilitate the calcination process.