A secondary battery, comprising: a case; an electrode assembly accommodated in the case, wherein the electrode assembly comprises a transverse transition part extending along a length direction X, and a longitudinal transition part extending along a height direction Z; and a folded insulation plate accommodated in the case and covering an exterior of the electrode assembly, wherein the folded insulation plate comprises: two side portions, wherein each of the two side portions comprises a transverse covering portion and a longitudinal covering portion, the transverse covering portion and the longitudinal covering portion being used to cover the transverse transition part and the longitudinal transition part of the electrode assembly, respectively, characterized in that, the folded insulation plate further comprises a top portion located between the two side portions and provided with hollow regions, wherein the case has an inner wall having a quadrate structure, the electrode assembly is in a wound structure and has an arc surface extending longitudinally, the longitudinal covering portion is arranged at a side of the electrode assembly viewed in a thickness direction of the secondary battery and covers a portion of the arc surface. a case; an electrode assembly accommodated in the case, wherein the electrode assembly comprises a transverse transition part extending along a length direction X, and a longitudinal transition part extending along a height direction Z; and a folded insulation plate accommodated in the case and covering an exterior of the electrode assembly, wherein the folded insulation plate comprises: two side portions, wherein each of the two side portions comprises a transverse covering portion and a longitudinal covering portion, the transverse covering portion and the longitudinal covering portion being used to cover the transverse transition part and the longitudinal transition part of the electrode assembly, respectively, characterized in that, the folded insulation plate further comprises a top portion located between the two side portions and provided with hollow regions, wherein the case has an inner wall having a quadrate structure, the electrode assembly is in a wound structure and has an arc surface extending longitudinally, the longitudinal covering portion is arranged at a side of the electrode assembly viewed in a thickness direction of the secondary battery and covers a portion of the arc surface. two side portions, wherein each of the two side portions comprises a transverse covering portion and a longitudinal covering portion, the transverse covering portion and the longitudinal covering portion being used to cover the transverse transition part and the longitudinal transition part of the electrode assembly, respectively, characterized in that, the folded insulation plate further comprises a top portion located between the two side portions and provided with hollow regions, wherein the case has an inner wall having a quadrate structure, the electrode assembly is in a wound structure and has an arc surface extending longitudinally, the longitudinal covering portion is arranged at a side of the electrode assembly viewed in a thickness direction of the secondary battery and covers a portion of the arc surface.