SECONDARY BATTERY

A positive-electrode core laminate of a portion of a positive-electrode core on which no positive-electrode active material layer is formed is bonded to a positive-electrode current collector by ultrasonic bonding. A core recess is formed in a bonding region of the positive-electrode core laminate bonded to the positive-electrode current collector by ultrasonic bonding, a region of the positive-electrode core laminate in which the core recess is formed includes a solid-state bonding layer and a central layer, the solid-state bonding layer being formed by solid-state bonding between layers of the positive-electrode core, the central layer being disposed between the solid-state bonding layers formed on both faces of the positive-electrode core, and the first average grain size of metal crystal grains constituting the solid-state bonding layer is smaller than the second average grain size of metal crystal grains constituting the central layer.