Method for reducing waste by recovering transition metals from lithium secondary battery

A method for reducing waste by recovering a transition metal of a lithium secondary battery, comprising:

• preparing a cathode active material from a cathode of a lithium secondary battery, wherein the cathode active material comprises a lithium transition metal oxide containing nickel, cobalt and manganese as transition metals;
• producing a first leachate by treating the cathode active material with a first acidic solution containing a first reducing agent in an amount less than an amount corresponding to a reaction equivalent of the cathode active material, wherein a content (wt %) of nickel or cobalt in the first leachate is greater than a content (wt %) of manganese in the first leachate;
• and
• producing a second leachate by treating a remaining cathode active material, which excludes a fraction included in the first leachate, with a second acidic solution containing a second reducing agent, wherein a content (wt %) of manganese in the second leachate is greater than a content (wt %) of nickel or cobalt in the second leachate.