A secondary battery including: a plurality of unit cells, wherein each unit cell of the plurality of unit cells includes a cathode extending in a top to bottom direction, an electrolyte membrane surrounding at least three surfaces of the cathode, and an anode surrounding at least a portion of the electrolyte membrane, wherein unit cells of the plurality of unit cells are spaced apart from each other in a left to right direction, with cavities therebetween, and a support member configured to support the plurality of unit cells in the left to right direction and disposed between unit cells of the plurality of unit cells.