POSITIVE ELECTRODE ACTIVE MATERIAL, PREPARATION METHOD THEREFOR, POSITIVE ELECTRODE SHEET, LITHIUM ION SECONDARY BATTERY AND RELATED BATTERY MODULE, BATTERY PACK AND DEVICE THEREOF

The present application discloses a positive electrode active material and a preparation method thereof, a positive electrode plate, a lithium-ion secondary battery and a battery module, a battery pack and an apparatus related thereto. The positive electrode active material includes a lithium nickel cobalt manganese oxide, the molar content of nickel in the lithium nickel cobalt manganese oxide accounts for 60% - 90% of the total molar content of nickel, cobalt and manganese, and the lithium nickel cobalt manganese oxide has a layered crystal structure of a space group R 3m; a transition metal layer of the lithium nickel cobalt manganese oxide includes a doping element, and the local mass concentration of the doping element in particles of the positive electrode active material has a relative deviation of 20% or less; and in a differential scanning calorimetry spectrum of the positive electrode active material in a 78% delithiation state, an initial exothermic temperature of a main exothermic peak is 200°C or more, and an integral area of the main exothermic peak is 100 J/g or less.