Silver(I,III) oxide is the inorganic compound with the formula Ag₄O₄. It is a component of silver oxide-zinc alkaline batteries. It can be prepared by the slow addition of a silver(I) salt to a persulfate solution e.g. AgNO₃ to a Na₂S₂O₈ solution. It adopts an unusual structure, being a mixed-valence compound. It is a dark brown solid that decomposes with evolution of O₂ in water. It dissolves in concentrated nitric acid to give brown solutions containing the Ag ion.