An exterior material for a lithium ion battery comprising at least a substrate layer, a metal foil layer, and a sealant layer in that order, wherein the sealant layer comprises an anionic functional group-containing layer containing a compound having an anionic functional group, and the concentration of the anionic functional group contained in the anionic functional group-containing layer is about 1.0 mass % or more based on the total amount of the components constituting the anionic functional group-containing layer.