The method disclosed includes: a step (I) of preparing a dispersion liquid (S) including an aluminum compound (A); a step (II) of mixing the dispersion liquid (S) and a predetermined phosphorus compound (B) so as to prepare a coating liquid (U); a step (III) of applying the coating liquid (U) onto the base (X) so as to form a precursor layer of the layer (Y); and a step (IV) of subjecting the precursor layer to heat treatment at a temperature of 110°C or more so as to form the layer (Y). The aluminum compound (A) can be formed by adding an acid to a solution including an aluminate. The number of moles (N M ) of aluminum atoms derived from the aluminum compound (A) and the number of moles (N P ) of phosphorus atoms derived from the phosphorus compound (B) satisfy 0.8 ‰¤ (N M )/(N P ) ‰¤ 4.5.