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. <EOS>