Method for Preparing Positive Electrode Additive for Lithium Secondary Battery, and Positive Electrode Additive for Lithium Secondary Battery Prepared Thereby

The present disclosure relates to a method for preparing a positive electrode additive for a lithium secondary battery having a high irreversible capacity and being capable of preventing gelation and reducing gas generation, and a positive electrode additive prepared thereby. The method for preparing the positive electrode additive includes the steps of: mixing a lithium raw material, a nickel raw material and, optionally, a raw material containing an element M, and then heat-treating the mixture, thereby preparing a predetermined lithium nickel oxide, wherein the lithium raw material includes LiO and LiOH, and the LiOH is used in an amount of 5 to 10% by weight with respect to the total weight of the lithium raw material.