A secondary battery comprising: a first electrode structure (E100); a second electrode structure (E200) spaced apart from the first electrode structure; and an electrolyte layer (E150) disposed between the first electrode structure and the second electrode structure, wherein the first electrode structure comprises: a current collector layer (CL10); and a plurality of first active material plates (AP13) electrically connected to the current collector layer, protruding from the current collector layer, and comprising a first active material, wherein each first active material plate of the plurality of first active material plates has a width (W) and a length (L) greater than the width, and the plurality of first active material plates are spaced apart from one another in a widthwise direction (d1) and in a lengthwise direction (d2), and wherein the electrolyte layer extends into gaps between the plurality of first active material plates along the lengthwise direction; characterized in that the plurality of first active material plates comprises a first group (AP13-3) of plates, and a second to fifth group (AP13-1; AP13-2; AP13-4; AP13-5) of plates spaced apart from the first group of plates in the lengthwise direction (Y), said first group of plates being located at or around the centre portion of the electrode structure, wherein the second to fifth group of plates, each being closer to a first end portion and/or a second opposite end portion of the first electrode structure in the lengthwise direction (Y) than the first group of plates, and a length of each of the plate in the second to fifth group of plates decreases from the centre portion being the first group (AP13-3) of plates of the electrode structure toward the first end and/or the second opposite end thereof. a first electrode structure (E100); a second electrode structure (E200) spaced apart from the first electrode structure; and an electrolyte layer (E150) disposed between the first electrode structure and the second electrode structure, wherein the first electrode structure comprises: a current collector layer (CL10); and a plurality of first active material plates (AP13) electrically connected to the current collector layer, protruding from the current collector layer, and comprising a first active material, a current collector layer (CL10); and a plurality of first active material plates (AP13) electrically connected to the current collector layer, protruding from the current collector layer, and comprising a first active material, wherein each first active material plate of the plurality of first active material plates has a width (W) and a length (L) greater than the width, and the plurality of first active material plates are spaced apart from one another in a widthwise direction (d1) and in a lengthwise direction (d2), and wherein the electrolyte layer extends into gaps between the plurality of first active material plates along the lengthwise direction; characterized in that the plurality of first active material plates comprises a first group (AP13-3) of plates, and a second to fifth group (AP13-1; AP13-2; AP13-4; AP13-5) of plates spaced apart from the first group of plates in the lengthwise direction (Y), said first group of plates being located at or around the centre portion of the electrode structure, wherein the second to fifth group of plates, each being closer to a first end portion and/or a second opposite end portion of the first electrode structure in the lengthwise direction (Y) than the first group of plates, and a length of each of the plate in the second to fifth group of plates decreases from the centre portion being the first group (AP13-3) of plates of the electrode structure toward the first end and/or the second opposite end thereof. <EOS>