Provided are a positive electrode active material, a method for the preparation thereof and a positive electrode plate, a secondary battery and an electrical device containing the same. The positive electrode active material has a core-shell structure, including a core and a shell cladding the core, wherein the core includes Li1+xMn1−yAyP1−zRzO4, the shell includes a first cladding layer cladding the core, a second cladding layer cladding the first cladding layer and a third cladding layer cladding the second cladding layer. The positive electrode active material of the present application enables the secondary battery to have a relatively high energy density, and good rate performance, cycling performance and safety performance.