Layered vanadium oxides; (Na(y)AS(1-y))(2)V4O11 (y = 0.77-0.98) are prepared by substituting part of the silver ions in Ag2V4O11 with sodium ions using an ion-exchange reaction in molten nitrate salts. These oxides exhibit less capacity loss during repeated cycling than non-substituted oxide, Ag2V4O11. This is mainly because the structural change into an amorphous state upon Lithiation is restricted by the pillar effect in which unextractable sodium ions connect adjacent layers during lithium insertion/extraction.