Patent ID: 8974931
Filing Date: 2015-03-10
Classification: H01M,Y02E,Y02P,Y02T

Abstract:
1. A cylindrical lithium ion secondary battery comprising: a cylindrical can; an electrode assembly accommodated in the cylindrical can with an electrolyte; and a cap assembly sealing the cylindrical can, wherein the cylindrical can has a cylindrical bottom portion and a side portion extending from the bottom portion to the cap assembly, and a safety vent having a thickness gradient is formed on the bottom portion, wherein the cylindrical bottom portion of the cylindrical can includes a first surface directed toward the electrode assembly, a second surface opposite to the first surface and being planar, and the safety vent is formed on the second surface, wherein the safety vent further includes a third surface disposed between the first surface and the second surface and a pair of spaced-apart fourth surfaces connecting the third surface and the second surface, and wherein the safety vent includes a first region having a thickness between the first surface and the third surface being 10% to 20% of a thickness between the first surface and the second surface, and a second region having a thickness between the first surface and the third surface being 30% to 40% of a thickness between the first surface and the second surface and the third surface between the first region and the second region has a gradient with respect to the first surface.