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

Provided is an ultrasonic horn 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.