A secondary battery comprising: a case comprising a receiving hole having an opening; a cap assembly sealingly connected with the case to close the opening; an electrode assembly disposed in the receiving hole, wherein the electrode assembly comprises two end surfaces opposite to each other in a first direction perpendicular to an axial direction of the receiving hole and tabs extending from respective end surfaces, and there are two or more electrode assemblies which are stacked in the axial direction, the electrode unit comprises a flat shape comprising two wide surfaces and two narrow surfaces connecting the two wide surfaces, wherein the two wide surfaces are disposed opposite to each other in the axial direction, and the wide surfaces and the narrow surfaces are alternately arranged; and a current collector comprising an extending portion and a current collecting portion fixedly connected to the tab, wherein the extending portion extends in the axial direction, wherein, the current collecting portion comprises a connecting end extending in a second direction perpendicular to both the axial direction and the first direction, and the current collecting portion is connected to an end of the extending portion away from the cap assembly through the connecting end, there are two or more extending portions which are spaced apart in the second direction, and the extending portions and the current collecting portions are disposed in one-to-one correspondence, both the number of the extending portions and the number of the current collecting portions are identical with the number of the electrode assemblies, and the extending portions, the current collecting portions and the tabs are disposed in one-to-one correspondence, and the current collecting portions are spaced apart in the axial direction, the tabs are spaced apart in the axial direction, and the current collecting portions do not overlap in the axial direction and the tabs do not overlap in the axial direction. a case comprising a receiving hole having an opening; a cap assembly sealingly connected with the case to close the opening; an electrode assembly disposed in the receiving hole, wherein the electrode assembly comprises two end surfaces opposite to each other in a first direction perpendicular to an axial direction of the receiving hole and tabs extending from respective end surfaces, and there are two or more electrode assemblies which are stacked in the axial direction, the electrode unit comprises a flat shape comprising two wide surfaces and two narrow surfaces connecting the two wide surfaces, wherein the two wide surfaces are disposed opposite to each other in the axial direction, and the wide surfaces and the narrow surfaces are alternately arranged; and a current collector comprising an extending portion and a current collecting portion fixedly connected to the tab, wherein the extending portion extends in the axial direction, wherein, the current collecting portion comprises a connecting end extending in a second direction perpendicular to both the axial direction and the first direction, and the current collecting portion is connected to an end of the extending portion away from the cap assembly through the connecting end, there are two or more extending portions which are spaced apart in the second direction, and the extending portions and the current collecting portions are disposed in one-to-one correspondence, both the number of the extending portions and the number of the current collecting portions are identical with the number of the electrode assemblies, and the extending portions, the current collecting portions and the tabs are disposed in one-to-one correspondence, and the current collecting portions are spaced apart in the axial direction, the tabs are spaced apart in the axial direction, and the current collecting portions do not overlap in the axial direction and the tabs do not overlap in the axial direction.