The present disclosure relates to a method for making a cathode active material coating liquid including steps of forming a phosphate ester solution by adding a phosphate ester in an alcoholic solvent, introducing an aluminum salt to the phosphate ester solution, the aluminum salt being soluble to the alcoholic solvent, and the aluminum salt reacting with the phosphate ester to form a homogeneous clear solution, and adding an acidity regulator to adjust a pH value of the homogenous clear solution to 6 to 7. The present disclosure also relates to a cathode active material coating liquid and a method for coating the cathode active material.