Correlating local materials properties with global battery electrochemistry is nontrivial because battery particles and electrodes are heterogeneous and defect-rich. Pinpointing the root cause of battery performance improvement or degradation can be challenging. In this presentation, we discuss our recent progress in understanding electrode heterogeneities and structural defects in Li ion ion cathodes ranging from individual particles to electrode ensembles. We hope to shed light on these questions: How heterogeneous are the electrochemical reactions within and among active particles? What are the roles of structural defects (point defects, dislocations, grain boundaries, cracks) in directing electrochemical reactions? Are analytical techniques capable of characterizing these heterogeneities with good statistical representativeness? How will the characterization results inform better design of chemical heterogeneity, such as engineered dopant distribution, to improve battery performance? Can we tailor structural defects to improve battery performance? We will also showcase some examples of our low/no-cobalt cathode developments.