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|1. (WO2018159197) SECONDARY BATTERY|
|Applicants:||HITACHI AUTOMOTIVE SYSTEMS, LTD.
The purpose of the present invention is to improve the product reliability and safety of a secondary battery, while maintaining joint strength. Provided is a secondary battery including: an electrode in which an electrode having a metal foil exposed part on one end and a separator are mutually laminated; and a current collector having an ultrasonic welded part which is connected to the metal foil exposed part by ultrasonic welding. The secondary battery is characterized by the following: a junction portion of the ultrasonic welded part has a shape having multiple projections, each projection being formed of sloped portions and a top surface portion; and formula (1) is satisfied when "A" denotes the sum of the length of one sloped portion and a half length of the top surface portion, and "B" denotes the length from the bottom of the projection to half of the top surface portion if the one sloped portion and the top surface portion are projected in the current-collector direction. Formula (1): A ≤ B × C (C is the stretch rate of the metal foil)