A secondary battery, comprising: a housing being in a quadrangular prism shape and comprising an accommodating hole with an opening, the housing comprising a first side plate and a second side plate connected to each other, and the housing comprising a bottom plate being arranged opposite to a top cover assembly in the axial direction; the top cover assembly connected to the housing in a sealed manner to cover and close the opening; an electrode assembly arranged in the accommodating hole, the electrode assembly comprising more than two electrode units, an electrode unit being of a coiled structure, comprising a first electrode piece, a second electrode piece, and a membrane, and having a wide surface, a narrow surface and a coiled end face, the more than two electrode units being laminated in an axial direction of the accommodating hole, and the wide surface of the electrode unit being arranged facing the top cover assembly, the first side plate being arranged facing the narrow surface, the second side plate being arranged facing the coiled end face, and a thickness of the first side plate is less than that of the second side plate, wherein the top cover assembly is spaced apart from the electrode assembly to form a first buffer gap, the first buffer gap is configured to buffer an amount of expansion deformation of the electrode assembly in the axial direction, a first gap is provided as a separation distance between two adjacent coils of the first electrode piece and is measured in a direction Y perpendicular to the narrow surface and to the first plate, a second gap is provided as a separation distance between the two adjacent coils of the first electrode piece and is measured in the axial direction perpendicular to the wide surface and to the bottom plate, and a size of the first gap being greater than a size of the second gap. a housing being in a quadrangular prism shape and comprising an accommodating hole with an opening, the housing comprising a first side plate and a second side plate connected to each other, and the housing comprising a bottom plate being arranged opposite to a top cover assembly in the axial direction; the top cover assembly connected to the housing in a sealed manner to cover and close the opening; an electrode assembly arranged in the accommodating hole, the electrode assembly comprising more than two electrode units, an electrode unit being of a coiled structure, comprising a first electrode piece, a second electrode piece, and a membrane, and having a wide surface, a narrow surface and a coiled end face, the more than two electrode units being laminated in an axial direction of the accommodating hole, and the wide surface of the electrode unit being arranged facing the top cover assembly, the first side plate being arranged facing the narrow surface, the second side plate being arranged facing the coiled end face, and a thickness of the first side plate is less than that of the second side plate, wherein the top cover assembly is spaced apart from the electrode assembly to form a first buffer gap, the first buffer gap is configured to buffer an amount of expansion deformation of the electrode assembly in the axial direction, a first gap is provided as a separation distance between two adjacent coils of the first electrode piece and is measured in a direction Y perpendicular to the narrow surface and to the first plate, a second gap is provided as a separation distance between the two adjacent coils of the first electrode piece and is measured in the axial direction perpendicular to the wide surface and to the bottom plate, and a size of the first gap being greater than a size of the second gap.