A method includes stacking unit cells in a stacking direction. Each unit cell includes an electrode structure, a separator structure, and a counter-electrode structure. The electrode structure includes an electrode current collector and an electrode active material layer, and the counter-electrode structure includes a counter-electrode current collector and a counter-electrode active material layer. The electrode and counter-electrode structures extend in a longitudinal direction perpendicular to the stacking direction, and an end portion of the electrode current collector extends past the electrode active material and the separator structure in the longitudinal direction. The end portion of each electrode current collector is bent in a direction orthogonal to the longitudinal direction, an electrode busbar is positioned extending in the stacking direction with a surface adjacent the end portions, and heat and pressure are applied to the electrode busbar to adhere the end portions to the busbar through an adhesive layer.