An energy storage device and structure for energy storage cells is provided that includes a plurality of energy storage cells, each of the energy storage cells having side surface areas. The plurality of energy storage cells are arranged in a pattern with each energy storage cell being spaced a specified distance apart from one another. An expandable material is adhered, by an adhesive backing, to at least a portion of the side surface areas of one or more of the energy storage cells, and the expandable material expands within and at least part of the specified distance.