Positive electrode active material and preparation method therefor, secondary battery and electric device

A preparation method for a positive electrode active material, comprising the following:

• mixing a raw material comprising a sodium source, an iron source, and a phosphorus source with a solvent to obtain a mixed slurry, wherein optionally, the raw material further comprises an M source;
• and
• drying and calcinating the mixed slurry to obtain a positive electrode active material, wherein the positive electrode active material comprises a polyanionic compound having a general formula shown in formula I, and the positive electrode active material has a crystallinity of 0.8-1,
• NaxFey1My2(PO4)z(P2O7)k Formula I
• wherein M comprises at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Sn, Hf, Ta, W, and Pb;
• 1≤x≤7, 1≤y1+y2≤4, 1≤z≤2, and 1≤k≤4.