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 (Z); 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 (Z) 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 (Z), 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 (Z) perpendicular to the wide surface and to the bottom plate , and a size (L1) of the first gap being greater than a size (L2) 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 (Z); 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 (Z) 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 (Z), 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 (Z) perpendicular to the wide surface and to the bottom plate , and a size (L1) of the first gap being greater than a size (L2) of the second gap . <EOS>