Ordered occupation of Ni ions in the Li ion layer (and vice versa) was observed in 0.4 mol % Zr-doped LiNiO2 with R3̅m structure. Although cation mixing is prevalent in LiNiO2 and in other Ni-rich layered cathodes, cation ordering (Li and Ni) has not been previously reported in the as-prepared or fully discharged states. First-principles calculations verified that low-level doping of LiNiO2 with Zr can energetically promote the observed cation ordering. Contrary to previous beliefs, antisite defects (or cation mixing), whose presence is unequivocally justified by the cation ordering, had hardly any negative effect on the electrochemical performance of LiNiO2; both pristine and Zr-doped LiNiO2 delivered 247.5 and 246.5 mAh g–1, respectively, with a Coulombic efficiency of 97%. The capacity retention after 100 cycles was improved by increasing Zr doping to 81% from 74%. The improved cycling stability was attributed to the particle morphology being conducive to Li migration and relieving the deeply charged Li x NiO2 of its inherent structural instability.