Tracing　the　dynamic　process　of　Li-ion　transport　at　the　atomic　scale　has　long　been　attempted　in　solid　state　ionics　and　is　essential　for　battery　material　engineering.　Approaches　via　phase　change,　strain,　and　valence　states　of　redox　species　have　been　developed　to　circumvent　the　technical　challenge　of　direct　imaging　Li;　however,　all　are　limited　by　poor　spatial　resolution　and　weak　correlation　with　state-of-charge　(SOC).　An　ion-exchange　approach　is　adopted　by　sodiating　the　delithiated　cathode　and　probing　Na　distribution　to　trace　the　Li　deintercalation,　which　enables　the　visualization　of　heterogeneous　Li-ion　diffusion　down　to　the　atomic　level.　In　a　model　LiNi1/3Mn1/3Co1/3O2　cathode,　dislocation-mediated　ion　diffusion　is　kinetically　favorable　at　low　SOC　and　planar　diffusion　along　(003)　layers　dominates　at　high　SOC.　These　processes　work　synergistically　to　determine　the　overall　ion-diffusion　dynamics.　The　heterogeneous　nature　of　ion　diffusion　in　battery　materials　is　unveiled　and　the　role　of　defect　engineering　in　tailoring　ion-transport　kinetics　is　stressed.