The film may be formed by contacting the active metal (e.g., Li) surface with a diluted solution of the following individual acids: H3PO4, HPO3, their active metal acidic salts (i.e., XH2PO4, X2HPO4 where X is an atom of the active metal (e.g., Li)) and mixtures thereof and mixtures thereof with one or more of H2SO4 and LiHSO4 in a dry organic solvent compatible with the active metal.