Abstract: Provided is a battery cell having a structure in which outer circumferential sides of a cell case are sealed by heat fusion in a state in which an electrode assembly including a cathode, an anode, and a separator is housed in a cell case together with an electrolyte solution, wherein the electrode assembly and the cell case have a structure in which both ends at positions opposite to each other are together curved in the same direction so that a curved surface is formed on an outer surface of the battery cell, and at least one of the heat-fused outer circumferential sides of the cell case is curved to adhere to a curved surface while forming an inner surface.