POSITIVE ELECTRODE ACTIVE MATERIAL AND PREPARATION METHOD THEREOF, POSITIVE ELECTRODE SHEET, AND SODIUM-ION BATTERY

A positive electrode active material has a chemical formula of NaANiFeMnCuAO, where A is selected from at least one of Zn, Mg, Ca, K, and Li, and the following conditions are satisfied: (1) 0.67≤x≤0.85, 0.01≤y≤0.2, and x+y≤1; (2) 0.11≤a≤0.33, 0.11≤b≤0.33, 0.33≤c≤0.66, 0.11≤d≤0.33, 0≤e≤0.1, and a+b+c+d=1; (3) n satisfies that an algebraic sum of positive and negative valences in the chemical formula equals zero; under same values of x, a, b, c, d, and n, a sodium layer spacing in an unit cell of the positive electrode active material is reduced by 0.005 Å-0.115 Å compared to that of NaNiFeMnCuO.