NOVELTY - The lithium ion secondary battery comprises a metallic outer can, a wound electrode group (2) accommodated in the outer can in a direction perpendicular to a winding axis, a positive electrode-lead (3), a negative electrode-lead (4), a metallic lid (5) that comprises a positive electrode terminal (6) and a negative electrode terminal and is attached to an opening portion of the outer can, a positive electrode insulating cover, a negative electrode insulating cover, and a rectangular protruding portion.    USE - The lithium ion secondary battery is useful as a power source for electric cars, hybrid vehicles, electric motor cycles and forklifts.    ADVANTAGE - The highly safe sealed lithium ion secondary battery exhibits high energy density and reliability, reduced weight, and improved volumetric efficiency.    DETAILED DESCRIPTION - The lithium ion secondary battery comprises a metallic outer can, a wound electrode group (2) accommodated in the outer can in a direction perpendicular to a winding axis, a positive electrode-lead (3), a negative electrode-lead (4), a metallic lid (5) that comprises a positive electrode terminal (6) and a negative electrode terminal and is attached to an opening portion of the outer can, a positive electrode insulating cover, a negative electrode insulating cover, and a rectangular protruding portion. A wound positive electrode current-collecting tab is provided at one end of the wound electrode group, and a wound negative electrode current-collecting tab is provided at the other end of the wound electrode group. The positive electrode-lead is connected to the positive electrode current-collecting tab. The negative electrode-lead is connected to the negative electrode current-collecting tab. The positive electrode insulating cover is engaged with one end portion including the positive electrode current-collecting tab of the wound electrode group. The negative electrode insulating cover is engaged with the other end portion including the negative electrode current-collecting tab of the wound electrode group. The positive electrode-lead comprises a connection portion connected to the positive electrode terminal, and first and second sandwiching portions that extend from the connection portion to the wound electrode group in the direction perpendicular to the winding axis to sandwich the wound positive electrode current-collecting tab. The negative electrode-lead comprises a connection portion connected to the negative electrode terminal, and first and second sandwiching portions that extend from the connection portion to the wound electrode group in the direction perpendicular to the winding axis to sandwich the wound negative electrode current-collecting tab. The positive electrode insulating cover comprises: a U-shaped member that has first and second sidewalls facing each other; a back surface member; and a sandwiching member configured to sandwich the first sandwiching portion of the positive electrode-lead and the wound positive electrode current-collecting tab portion that faces the first sandwiching portion and to sandwich the second sandwiching portion of the positive electrode-lead and the positive electrode current-collecting tab portion that faces the second sandwiching portion. The negative electrode insulating cover comprises: a U-shaped member that has first and second sidewalls facing each other; a back surface member; and a sandwiching member configured to sandwich the first sandwiching portion of the negative electrode-lead and the wound negative electrode current-collecting tab portion that faces the first sandwiching portion and to sandwich the second sandwiching portion of the negative electrode-lead and the negative electrode current-collecting tab portion that faces the second sandwiching portion. Each of the sandwiching members of the positive electrode insulating cover and the negative electrode insulating cover comprises a rectangular thick portion provided on each of the first and second sidewalls. The rectangular protruding portion is provided on the back surface member, and is located between the thick portions, where a length from the back surface member to a surface opposite to the member is less than a width of the sidewall of the U-shaped member.    DESCRIPTION OF DRAWING(S) - The diagram shows a schematic exploded view of a battery.    Wound electrode group (2)    Positive electrode-lead (3)    Negative electrode-lead (4)    Metallic lid (5)    Positive electrode terminal. (6)