Cylindrical lithium ion secondary battery
A cylindrical lithium ion secondary battery, including a cylindrical can; an electrode assembly in the cylindrical can with an electrolyte solution; and a cap assembly sealing the cylindrical can, the cap assembly including a positive temperature coefficient (PTC) device connected to the electrode assembly, a cap-up connected to the PTC device, solder between the PTC device and the cap-up, and an exterior space without the solder on external circumferences of the PTC device and the cap-up.
1. A cylindrical lithium ion secondary battery, comprising:
a cylindrical can;
an electrode assembly in the cylindrical can with an electrolyte solution; and
a cap assembly sealing the cylindrical can,
the cap assembly including a positive temperature coefficient (PTC) device connected to the electrode assembly, a cap-up connected to the PTC device, solder between the PTC device and the cap-up, and an exterior space without the solder on external circumferences of the PTC device and the cap-up, wherein the cap-up includes an exterior stepped portion protruding toward the exterior space and contacting the PTC device.
2. The cylindrical lithium ion secondary battery as claimed in claim 1 , wherein the exterior space has a width in a range of 0.1 mm to 1.5 mm.
3. The cylindrical lithium ion secondary battery as claimed in claim 1 , wherein a width of the exterior stepped portion is equal to that of the exterior space.
4. The cylindrical lithium ion secondary battery as claimed in claim 1 , wherein the exterior stepped portion includes a plurality of stepped portions spaced apart from each other.
5. The cylindrical lithium ion secondary battery as claimed in claim 1 , wherein the exterior stepped portion includes a plurality of serrations.
6. The cylindrical lithium ion secondary battery as claimed in claim 1 , wherein a top surface of the cap-up corresponding to the PTC device is planar.
7. The cylindrical lithium ion secondary battery as claimed in claim 1 , wherein a top surface of the cap-up corresponding to the PTC device is bent.
8. The cylindrical lithium ion secondary battery as claimed in claim 1 , wherein the cap assembly further includes an interior space without solder on internal circumferences of the PTC device and the cap-up.
9. The cylindrical lithium ion secondary battery as claimed in claim 8 , wherein the cap-up includes an interior stepped portion protruding toward the interior space and contacting the PTC device.