LiNiO2 with Ni defects in the 3b sites (named “Ni defected” LiNiO2) was prepared and characterized using electrochemical calorimetry. Different from conventionally prepared “Standard” LiNiO2, “Ni defected” LiNiO2 exhibited high reversibility. The 1st coulombic efficiency was recorded to be 101% due to minimization from the Ni ion substitution at the Li 3a sites. The reversible capacity was 212 mAh g−1 in the 1st cycle with 87% capacity retention after 80 cycles because Li+ ordering and Jahn-Teller distortion during the charge and discharge cycle were suppressed by introducing the Ni defect 3b sites. The proposed simple defect design concept introduced the development of a high capacity and highly reversible LiNiO2 material without metal substitutions and without increasing the charge cut-off voltage.