Atomic-scale processes are critical to improving the performance of lithium-ion batteries. How lithium atoms move around is one important aspect. Combining x-ray spectroscopic imaging and phase-field modeling, the lithium transport dynamics in a cathode (olivine lithium iron phosphate) are now better understood. Lithium diffusion results in a lithium-deficient phase (blue) that grows at the expense of a lithium-rich phase (red). The presence of the resulting anti-site defects (a disorder in the lithium and iron atom sites in the crystal structure) enables lithium transport over much more surface area than in a defect-free crystal.