A top cover assembly for a secondary battery comprising: a top cover plate comprising a lead-out hole and an inside surface forming the lead-out hole; an electrode terminal comprising a cylindrical portion and an annular flange extending in a circumferential direction of the cylindrical portion, wherein the cylindrical portion penetrates through the lead-out hole, and the annular flange extends along a radial direction of the lead-out hole beyond the inside surface; a sealing ring comprising a barrel portion and a ring portion extending in the circumferential direction of the barrel portion, wherein the barrel portion of the sealing ring surrounds the cylindrical portion, the inside surface is connected with the cylindrical portion through the barrel portion in a sealing manner, the ring portion comprises a first ring body and a second ring body successively distributed along the radial direction, the first ring body is connected with the barrel portion, the annular flange is connected with the top cover plate through the first ring body in a sealing manner, and the second ring body does not extend beyond the annular flange; an insulating member comprising a connecting portion and an extension portion, wherein along the axial direction of the lead-out hole, a projection of the connecting portion overlaps with a projection of the second ring body, the connecting portion is connected with the second ring body in a sealing manner, a portion of the insulating member beyond the second ring body forms the extension portion, and along the radial direction, the extension portion extends beyond the annular flange, wherein the top cover assembly further comprises a lower insulating plate, at least part of the lower insulating plate is disposed between the top cover plate and the annular flange of the electrical terminal and a projection of the lower insulating plate and a projection of the extension portion comprises an overlapped area along the axial direction, wherein the insulating member further comprises a cylinder body connected to the extension portion, the cylinder body extends along the axial direction, the cylinder body is disposed around the annular flange, and along the axial direction, an outer peripheral surface of the annular flange is at least partially covered by the cylinder body. a top cover plate comprising a lead-out hole and an inside surface forming the lead-out hole; an electrode terminal comprising a cylindrical portion and an annular flange extending in a circumferential direction of the cylindrical portion, wherein the cylindrical portion penetrates through the lead-out hole, and the annular flange extends along a radial direction of the lead-out hole beyond the inside surface; a sealing ring comprising a barrel portion and a ring portion extending in the circumferential direction of the barrel portion, wherein the barrel portion of the sealing ring surrounds the cylindrical portion, the inside surface is connected with the cylindrical portion through the barrel portion in a sealing manner, the ring portion comprises a first ring body and a second ring body successively distributed along the radial direction, the first ring body is connected with the barrel portion, the annular flange is connected with the top cover plate through the first ring body in a sealing manner, and the second ring body does not extend beyond the annular flange; an insulating member comprising a connecting portion and an extension portion, wherein along the axial direction of the lead-out hole, a projection of the connecting portion overlaps with a projection of the second ring body, the connecting portion is connected with the second ring body in a sealing manner, a portion of the insulating member beyond the second ring body forms the extension portion, and along the radial direction, the extension portion extends beyond the annular flange, wherein the top cover assembly further comprises a lower insulating plate, at least part of the lower insulating plate is disposed between the top cover plate and the annular flange of the electrical terminal and a projection of the lower insulating plate and a projection of the extension portion comprises an overlapped area along the axial direction, wherein the insulating member further comprises a cylinder body connected to the extension portion, the cylinder body extends along the axial direction, the cylinder body is disposed around the annular flange, and along the axial direction, an outer peripheral surface of the annular flange is at least partially covered by the cylinder body.