A secondary battery, comprising: an electrode assembly, a case and a cap assembly, wherein the case comprises an accommodating cavity, the accommodating cavity comprises an opening, and the electrode assembly is accommodated in the accommodating cavity; the electrode assembly comprises a plurality of electrode units, and the electrode units are stacked in an axial direction of the accommodating cavity; the cap assembly comprises a cap plate and an insulating member provided at an inner side of the cap plate, the cap plate is connected with the case, and the insulating member is positioned at a side of the electrode assembly in the axial direction; and the insulating member is provided with a first surface at a side close to the electrode assembly, and the first surface is a flat surface, wherein the electrode unit comprises a first electrode plate, a second electrode plate and a separator winded together, and comprises wide surfaces and narrow surfaces; the first surface is disposed to face the wide surfaces in the axial direction, every two adjacent electrode units contact each other via respective wide surfaces, and the narrow surfaces are connected with the wide surfaces and positioned at two ends of the electrode unit in a width direction, wherein the cap assembly further comprises electrode terminals and current collecting members, the electrode terminals are provided to the cap plate, and the current collecting members connect the electrode terminals and the electrode assembly; the insulating member is provided with a first groove at a side close to the electrode assembly, the current collecting member comprises a first portion accommodated in the first groove; and the first portion is provided with a second surface at a side close to the electrode assembly, and the second surface is flush with the first surface. the case comprises an accommodating cavity, the accommodating cavity comprises an opening, and the electrode assembly is accommodated in the accommodating cavity; the electrode assembly comprises a plurality of electrode units, and the electrode units are stacked in an axial direction of the accommodating cavity; the cap assembly comprises a cap plate and an insulating member provided at an inner side of the cap plate, the cap plate is connected with the case, and the insulating member is positioned at a side of the electrode assembly in the axial direction; and the insulating member is provided with a first surface at a side close to the electrode assembly, and the first surface is a flat surface, wherein the electrode unit comprises a first electrode plate, a second electrode plate and a separator winded together, and comprises wide surfaces and narrow surfaces; the first surface is disposed to face the wide surfaces in the axial direction, every two adjacent electrode units contact each other via respective wide surfaces, and the narrow surfaces are connected with the wide surfaces and positioned at two ends of the electrode unit in a width direction, wherein the cap assembly further comprises electrode terminals and current collecting members, the electrode terminals are provided to the cap plate, and the current collecting members connect the electrode terminals and the electrode assembly; the insulating member is provided with a first groove at a side close to the electrode assembly, the current collecting member comprises a first portion accommodated in the first groove; and the first portion is provided with a second surface at a side close to the electrode assembly, and the second surface is flush with the first surface.