A secondary battery including a first electrode structure; a second electrode structure spaced apart from the first electrode structure; and an electrolyte layer disposed between the first electrode structure and the second electrode structure, wherein the first electrode structure includes: a current collector layer; and plurality of first active material plates electrically connected to the current collector layer, protruding from the current collector layer, and including a first active material, wherein each plate of the plurality of first active material plates has a width and a length greater than the width, and the plurality of first active material plates are spaced apart from one another in a widthwise direction and in a lengthwise direction, and wherein the electrolyte layer extends into gaps between the plurality of first active material plates along the lengthwise direction.