Irreversible Additive, Positive Electrode Material Including Irreversible Additive, and Lithium Secondary Battery Including Positive Electrode Material

An irreversible additive includes an oxide having a trigonal crystal structure and represented by Formula 1, and a coating layer positioned on a surface of the oxide and including a compound represented by Formula 2. A positive electrode material including the irreversible additive and a lithium secondary battery including the positive electrode material including the irreversible additive are also provided.