The chemical diffusion coefficients of lithium ions (D Li) in spherical Li[Ni0.5Mn0.3Co0.2]O2 are systematically determined by galvanostatic intermittent titration technique (GITT) and electrochemical impedance spectroscopy (EIS). The D Li obtained from GITT are greatly dependent on the lithium content and cell potential. In the charge process, the D Li values are in the range of 9.0×10−11 to 3.3×10−9 cm2 s−1. In the discharge process, the D Li values are in the range of 1.9×10−11 to 3.9×10−9 cm2 s−1. In addition, the minimum values in the D Li are observed at the stoichiometry x ≈0.25 for Li1−x [Ni0.5Mn0.3Co0.2]O2, which coincide with the voltage-plateau region at about 3.75V. The D Li obtained from EIS are in the range of 1.7×10−11 to 6.5×10−9 cm2 s−1 and the variation tendency with cell potential is consistent with the results obtained from GITT during the charge process.