A method for preparing positive electrode active material, comprising the following steps: mixing a positive electrode active material precursor, a lithium source, and a doping element precursor to obtain a mixture, wherein the positive electrode active material precursor is selected from one or more of an oxide, hydroxide, or carbonate that contains Ni, Co, and Mn, the number of moles of nickel accounts for 50% to 95% of the total number of moles of nickel, cobalt, and manganese, and at least part of doping element in the doping element precursor has not reached its highest valence state; and sintering the mixture in an oxygen-containing atmosphere at a temperature of 600°C to 1000°C to obtain a positive electrode active material, wherein the positive electrode active material comprises a lithium nickel cobalt manganese oxide, wherein 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, and the lithium nickel cobalt manganese oxide has a layered crystal structure with a space group R 3 m; and the lithium nickel cobalt manganese oxide comprises a doping element, wherein 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; wherein the doping element precursor is selected from the group, consisting of one or more of a titanium oxide, a vanadium oxide, a chromium oxide, a selenium oxide, a niobium oxide, a molybdenum oxide, a ruthenium oxide, a rhodium oxide, a palladium oxide, an antimony oxide, a tellurium oxide, a cerium oxide, and a tungsten oxide; wherein the doping element precursor comprises a first doping element oxide and a second doping element oxide, a valence α of a doping element in the first doping element oxide is less than or equal to 4, and a valence β of a doping element in the second doping element oxide is greater than or equal to 4; and β > α. mixing a positive electrode active material precursor, a lithium source, and a doping element precursor to obtain a mixture, wherein the positive electrode active material precursor is selected from one or more of an oxide, hydroxide, or carbonate that contains Ni, Co, and Mn, the number of moles of nickel accounts for 50% to 95% of the total number of moles of nickel, cobalt, and manganese, and at least part of doping element in the doping element precursor has not reached its highest valence state; and sintering the mixture in an oxygen-containing atmosphere at a temperature of 600°C to 1000°C to obtain a positive electrode active material, wherein the positive electrode active material comprises a lithium nickel cobalt manganese oxide, wherein 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, and the lithium nickel cobalt manganese oxide has a layered crystal structure with a space group R 3 m; and the lithium nickel cobalt manganese oxide comprises a doping element, wherein 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; wherein the doping element precursor is selected from the group, consisting of one or more of a titanium oxide, a vanadium oxide, a chromium oxide, a selenium oxide, a niobium oxide, a molybdenum oxide, a ruthenium oxide, a rhodium oxide, a palladium oxide, an antimony oxide, a tellurium oxide, a cerium oxide, and a tungsten oxide; wherein the doping element precursor comprises a first doping element oxide and a second doping element oxide, a valence α of a doping element in the first doping element oxide is less than or equal to 4, and a valence β of a doping element in the second doping element oxide is greater than or equal to 4; and β > α.