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

An ultrasonic horn reduces the likelihood of damaging a plurality of stacked sheets of metal foil when the stacked sheets and a metal member are ultrasonically bonded by applying ultrasonic vibration to the stacked sheets. An ultrasonic horn is used for ultrasonically bonding a plurality of stacked sheets of negative electrode foil and a negative electrode collector plate by applying ultrasonic vibration to the stacked sheets of negative electrode foil. The horn includes a horn body, a first protrusion having a first surface that is a curved surface and protruding from an opposing surface of the horn body facing the anvil toward the anvil, and a second protrusion provided at a center of the first surface of the first protrusion and protruding toward the anvil. The second protrusion includes an end surface that is a planar surface and a second surface connecting the end surface and the first surface.