A lead tab that includes an insulation cover including a boss unit, which protrudes from a surface of the insulation cover and includes an electrical insulating material; and a thermal cut-off device assembly including: a thermal cut-off device; a first lead and a second lead that are coupled to the thermal cut-off device; and a hole through which a portion of the boss unit of the insulation cover protrudes. Here, the boss unit of the insulation cover includes a coupling portion that is larger than an opening of the hole of the thermal cut-off device assembly to secure the insulation cover to the thermal cut-off device assembly.