A method comprising providing, on a substrate, a stack for an energy storage device, the stack comprising a first electrode layer, a second electrode layer, and an electrolyte layer between the first electrode layer and the second electrode layer. A groove is formed at least through the second electrode layer and the electrolyte layer such that the groove is wider in the second electrode layer than in the electrolyte layer. An electrically insulating material is provided in the groove. An electrically conductive material is provided in the groove, on the electrically insulating material.