LiCoO₂ has been labelled with ¹⁷O from ¹⁷O-enriched water, and then examined via⁷Li, ¹⁷O and ⁵⁹Co solid-state NMR at different charge states. The results reveal the atomic-level environment evolution during the phase transitions, and ¹⁷O NMR is found to be more sensitive to the subtle structural changes.