A seal structure is provided for an energy storage device. The seal structure includes a sealing glass joining an ion-conducting first ceramic to an electrically insulating second ceramic. The sealing glass has a composition that includes about 48 weight percent silica, about 20 weight percent to about 25 weight percent boria, about 20 weight percent to about 24 weight percent alumina, and about 8 weight percent to about 12 weight percent sodium oxide based on the total weight of the sealing glass composition. A method for making the seal structure is provided. An article comprising the seal structure is also provided.