SECONDARY BATTERY AND PREPARATION METHOD THEREFOR, AND BATTERY MODULE, BATTERY PACK AND APPARATUS CONTAINING SECONDARY BATTERY

This application provides a secondary battery and a preparation method thereof, and a battery module, battery pack, and apparatus containing a secondary battery. The secondary battery includes a positive electrode plate, the positive electrode plate includes a positive electrode current collector and a positive electrode film layer that is disposed on the positive electrode current collector and that includes a positive electrode active material, where the positive electrode active material includes a first material and a second material, the first material contains lithium transition metal oxide, the second material contains lithium transition metal phosphate, the lithium transition metal phosphate includes secondary particles formed by agglomeration of primary particles, and the second material has a lower discharge platform voltage than the first material with respect to a same type of counter electrode.