Irreversible Additive Comprised in Cathode Material for Secondary Battery, Cathode Material Comprising the Same, and Secondary Battery Comprising Cathode Material

Provided is an irreversible additive contained in a cathode material for a secondary battery, wherein the irreversible additive is an oxide represented by the following Chemical Formula 1, and wherein the oxide has a trigonal crystal structure, a cathode material including the same, and a secondary battery including the cathode material, LiNiMO (1)