NOVELTY - A lithium-ion secondary battery comprises a current collecting disk (7) for collecting current from a foil. A joint portion obtained by joining the current collecting disk and an end portion of the foil is formed to project from a face of the current collecting disk, which faces an electrode group. The current collecting disk includes projecting ridge portions (8) extending from a central portion of the current collecting disk toward an outer edge portion on its face positioned on the side opposite to the electrode group; and flat portions facing the electrode group.    USE - Lithium-ion secondary battery used as a power source for an electric vehicle or a hybrid vehicle.    ADVANTAGE - The current collector and foil are joined to each other securely while damage of the foil is suppressed.    DETAILED DESCRIPTION - A lithium-ion secondary battery is provided with an electrode group, where a positive electrode plate obtained by applying positive electrode mixture including positive electrode active material to a foil and a negative electrode plate obtained by applying negative electrode mixture including negative electrode active material to a foil are disposed to sandwich a separator. An end portion of the foil of the positive electrode plate and/or the negative electrode plate projects from an end face of the electrode group. A current collecting disk for collecting current from the foil is disposed to face the end face of the electrode group. A joint portion obtained by joining the current collecting disk and an end portion of the foil is formed to project from a face of the current collecting disk, which faces the electrode group. The current collecting disk includes projecting ridge portions extending from a central portion of the current collecting disk toward an outer edge portion on its face positioned on the side opposite to the electrode group; and flat portions facing the electrode group and provided at positions corresponding to the projecting ridge portions. The joint portion is formed by causing the end portion of the foil to abut on the flat portions and melting the projecting ridge portions to cause the melted projecting ridge portions to project from the flat portions. The current collecting disk is formed with a pair of grooves (18a, 18b) extending along both sides of the projecting ridge portion.    DESCRIPTION OF DRAWING(S) - The drawing is a perspective view of current collecting disk where a pair of grooves is formed on both sides of a projecting ridge portion.    Current collecting disk (7)    Projecting ridge portions (8)    Slits (9)    Grooves (18a, 18b)