LiNi2/3Sb1/3O2 has been prepared by ion-exchange from NaNi2/3Sb1/3O2. Powder X-ray diffraction (XRD) and single crystal electron diffraction by transmission electron microscopy (TEM) of the material indicate that it is isostructural with α-NaFeO2. Electrochemical test shows that the reversible capacity for Li intercalation and deintercalation drops rapidly with the number of times cycled. Both experimental evidences and first principles calculations point to the migration of nickel as the reason for the poor capacity retention.