Solid phase synthesis method of positive electrode active material of nickel-rich lithium composite transition metal oxide in a form of a single particle, positive electrode active material of nickel-rich lithium composite transition metal oxide in a form of a single particle formed therefrom, positive electrode and lithium secondary battery containing the same

A method of making a positive electrode active material by solid phase synthesis, comprising:

• (S1) mixing transition metal raw powders with a first lithium raw material to prepare a first mixture, wherein the first mixture has a molar ratio of lithium to total transition metals of 0.95 to 1.02, and wherein the transition metal powders comprise a nickel raw powder, wherein a molar ratio of nickel to total transition metals is 80 mol % or more;
• (S2) primary sintering the first mixture at a temperature of 760° C. to 900° C. in an oxygen-containing atmosphere to cause solid phase reaction, and cooling the sintered first mixture to obtain a first sintered product;
• (S3) mixing the first sintered product with a second lithium raw material to prepare a second mixture, wherein the second mixture has a molar ratio of lithium to total transition metals of 1.00 to 1.09;
• and
• (S4) secondary sintering the second mixture at a temperature of 760° C. to 900° C. in the oxygen-containing atmosphere to prepare a lithium composite transition metal oxide in the form of a single particle.