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, comprising a core and a shell cladding the core, wherein the core has a chemical formula of Li1+xMn1-yAyP1-zRzO4, the shell comprises a first cladding layer cladding the core, a second cladding layer cladding the first cladding layer, a third cladding layer cladding the second cladding layer and a fourth cladding layer cladding the third cladding layer. The positive electrode active material of the present application enables the secondary battery to have a relatively high energy density, and good cycling performance, rate performance and safety performance.