POSITIVE ELECTRODE ACTIVE MATERIAL AND PREPARATION METHOD THEREFOR, POSITIVE ELECTRODE PLATE, LITHIUM ION SECONDARY BATTERY AND BATTERY MODULE COMPRISING LITHIUM ION SECONDARY BATTERY, BATTERY PACK, AND APPARATUS

A positive electrode active material and a preparation method thereof, a positive electrode plate, a lithium-ion secondary battery (5), and a battery module (4), battery pack (1), and apparatus containing such lithium-ion secondary battery (5) are disclosed. The positive electrode active material includes a lithium nickel cobalt manganese oxide. In the lithium nickel cobalt manganese oxide, the number of moles of nickel accounts for 50% to 95% of the total number of moles of nickel, cobalt, and manganese. The lithium nickel cobalt manganese oxide has a layered crystal structure with a space group . The lithium nickel cobalt manganese oxide includes a doping element. When the positive electrode active material is in a 78% delithiated state, the doping element has two or more different valence states, and the amount of doping element in a highest valence state accounts for 40% to 90% of the total amount of doping element.