Lithium Transition Metal Oxide, Positive Electrode Additive for Lithium Secondary Battery, and Lithium Secondary Battery Comprising the Same

A lithium transition metal oxide which is capable of minimizing a side reaction with an electrolyte, thereby suppressing the generation of gas during charging and discharging of a lithium secondary battery is provided. The lithium transition metal oxide is a lithium cobalt oxide which contains a hetero-element, wherein the hetero-element includes a 4th period transition metal; and at least one selected from the group consisting of a group 2 element, a group 13 element, a group 14 element, a 5th period transition metal, and a 6th period transition metal. The lithium transition metal oxide has a cumulative 50% particle diameter (D50) of 10.0 μm to 25.0 μm and a ratio (D/D) of a maximum particle diameter (D) to a minimum particle diameter (D) of 10.0 to 60.0 when measured by laser diffraction scattering particle size distribution.