Preparation method of modified positive electrode active material

1. A preparation method of a modified positive electrode active material, which comprising steps of:

dispersing a positive electrode active material matrix into an alcohol solvent to form a positive electrode active material matrix suspension;

dissolving an alcohol-soluble aluminum salt in an alcohol solvent to form an alcohol-soluble aluminum salt solution;

dissolving an alcohol-soluble phosphorous compound in an alcohol solvent to form an alcohol-soluble phosphorous compound solution;

mixing the alcohol-soluble aluminum salt solution and the alcohol-soluble phosphorous compound solution and heating to react, obtaining a liquid-phase coating solution which contains aluminum phosphate after the reaction is finished;

mixing and stirring the positive electrode active material matrix suspension and the liquid-phase coating solution which contains aluminum phosphate, extraction filtrating and obtaining a filter cake after the stirring is finished, then drying and baking the filter cake, finally obtaining a modified positive electrode active material in which an aluminum phosphate layer is uniformly coated on a surface of the positive electrode active material matrix;

wherein, in the positive electrode active material matrix suspension, a mass ratio of the alcohol solvent is from 30% to 70% of a mass of the positive electrode active material matrix; and

a general formula of the positive electrode active material matrix is Li a Ni x M 1-x O z , where, 0.9≤a≤1.2, 0.5≤x<1, M is one or more selected from the group consisting of Co, Mn, Al, Mg, Fe, Cr, V, Ti, Cu, B, Ca, Zn, Zr, Nb, Mo, Sr, Sb, W and Bi.

2. The preparation method of the modified positive electrode active material according to claim 1 , wherein in the obtained modified positive electrode active material, a mass ratio of the aluminum phosphate layer is from 0.03% to 0.3% of a mass of the positive electrode active material matrix.

3. The preparation method of the modified positive electrode active material according to claim 1 , wherein in the obtained modified positive electrode active material, a thickness of the aluminum phosphate layer ranges from 5 nm to 70 nm.

4. The preparation method of the modified positive electrode active material according to claim 1 , wherein the alcohol solvent is one or more selected from a group consisting of methanol, ethanol, 1-propanol, isopropanol and 1-butanol.

5. The preparation method of the modified positive electrode active material according to claim 4 , wherein the alcohol solvent is ethanol.

6. The preparation method of the modified positive electrode active material according to claim 1 , wherein an acidity regulator is added to adjust pH of reaction system in the step of obtaining a liquid-phase coating solution which contains aluminum phosphate.

7. The preparation method of the modified positive electrode active material according to claim 6 , wherein the acidity regulator is weak acid ammonium.

8. The preparation method of the modified positive electrode active material according to claim 6 , wherein the acidity regulator is one or more selected from a group consisting of ammonium acetate, ammonium bicarbonate and ammonium carbonate.

9. The preparation method of the modified positive electrode active material according to claim 1 , wherein the alcohol-soluble aluminum salt is one or more selected from a group consisting of aluminum chloride, aluminum isopropoxide, aluminum acetylacetonate, trimethylaluminum and aluminum nitrate.

10. The preparation method of the modified positive electrode active material according to claim 1 , wherein the alcohol-soluble phosphorous compound is one or more selected from a group consisting of triethyl phosphate, phosphorous acid and phosphorus pentoxide.

11. The preparation method of the modified positive electrode active material according to claim 1 , wherein a baking temperature ranges from 300° C. to 700° C., a baking time ranges from 1 h to 10 h.