A secondary battery comprising: a case comprising an opening ; an electrode assembly disposed within the case , the electrode assembly comprising a main body and two tabs , the two tabs respectively extending outwards from both sides of the main body in an axial direction (X) of the main body , the two tabs being both disposed facing the case ; and a cap assembly comprising a cap plate , a lower insulating member and an explosion-proof valve , the cap plate sealing the opening , the explosion-proof valve being disposed on the cap plate , the lower insulating member being disposed on a side of the cap plate close to the electrode assembly , the lower insulating member comprising an inner side surface facing the main body , an outer side surface facing the cap plate , and a concave portion recessed from the inner side surface toward the outer side surface , and the concave portion being in position corresponding to the explosion-proof valve , wherein the concave portion comprises a first inclined surface and a second inclined surface which are distributed along the axial direction (X), the first inclined surface and the second inclined surface are both inclined from the inner side surface toward the outer side surface , the explosion-proof valve is located between the first inclined surface and the second inclined surface , and the first inclined surface and the second inclined surface become close to each other in a direction from the inner side surface to the outer side surface , and wherein the first inclined surface and the inner side surface are both flat surfaces, and an angle (α) formed between the first inclined surface and the inner side surface is from 120° to 170°; and/or, the second inclined surface and the inner side surface are flat surfaces, and an angle (β) formed between the second inclined surface and the inner side surface is from 120° to 170°. a case comprising an opening ; an electrode assembly disposed within the case , the electrode assembly comprising a main body and two tabs , the two tabs respectively extending outwards from both sides of the main body in an axial direction (X) of the main body , the two tabs being both disposed facing the case ; and a cap assembly comprising a cap plate , a lower insulating member and an explosion-proof valve , the cap plate sealing the opening , the explosion-proof valve being disposed on the cap plate , the lower insulating member being disposed on a side of the cap plate close to the electrode assembly , the lower insulating member comprising an inner side surface facing the main body , an outer side surface facing the cap plate , and a concave portion recessed from the inner side surface toward the outer side surface , and the concave portion being in position corresponding to the explosion-proof valve , wherein the concave portion comprises a first inclined surface and a second inclined surface which are distributed along the axial direction (X), the first inclined surface and the second inclined surface are both inclined from the inner side surface toward the outer side surface , the explosion-proof valve is located between the first inclined surface and the second inclined surface , and the first inclined surface and the second inclined surface become close to each other in a direction from the inner side surface to the outer side surface , and wherein the first inclined surface and the inner side surface are both flat surfaces, and an angle (α) formed between the first inclined surface and the inner side surface is from 120° to 170°; and/or, the second inclined surface and the inner side surface are flat surfaces, and an angle (β) formed between the second inclined surface and the inner side surface is from 120° to 170°. <EOS>