ULTRASONIC HORN, SECONDARY BATTERY, AND METHOD FOR MANUFACTURING SECONDARY BATTERY

Provided is an ultrasonic horn (510) that can reduce the likelihood of damaging a plurality of stacked sheets of metal foil when the stacked sheets of metal foil and a metal member are ultrasonically bonded by applying ultrasonic vibration to the stacked sheets of metal foil, without using a protective metal plate. A horn (ultrasonic horn) (510) is used for ultrasonically bonding a plurality of stacked sheets of negative electrode foil (302a) and a negative electrode collector plate (4B) by applying ultrasonic vibration to the stacked sheets of negative electrode foil (302a). The horn (510) includes a horn body (511), a first protrusion (512) having a first surface (512a) that is a curved surface and protruding from an opposing surface (511a) of the horn body (511) facing the anvil (520) toward the anvil (520), and a second protrusion (513) provided at a center of the first surface (512a) of the first protrusion (512) and protruding toward the anvil (520). The second protrusion (513) includes an end surface (513b) that is a planar surface and a second surface (513a) connecting the end surface (513b) and the first surface (512a).