Abstract: The present invention relates to a polyimide-based film, a window cover film including the polyimide-based film, and a display panel including the polyimide-based film. More specifically, the present invention relates to a polyimide-based film of which a modulus measured according to ASTM D882 is 5 GPa or more and a rate of change of the modulus, after the polyimide-based film is maintained under a high-temperature and high-humidity condition of 60° C. and 90% RH for 500 hours, is 10% or less.

Abstract: A cylindrical lithium ion secondary battery includes an electrode assembly; a center pin positioned within the electrode assembly and having upper and lower ends that are closed; a can containing the electrode assembly and the center pin; and a cap assembly coupled to the top of the can. The center pin can include a body extending a predetermined length with its upper and lower end open and at least one closure member adapted to close the upper and lower ends of the body and to melt or fracture at a predetermined temperature. The center pin body may also or altematively include a circuit member positioned inside the center pin and adapted to be short-circuited in the case of overcharging and to consume current.

Abstract: Lithium rechargeable batteries having functional center pins are provided. A lithium rechargeable battery has a center pin whose top and bottom ends are blocked by a thermal cut-off composition to reduce the void volume inside a bare cell during initial overcharge. The thermal cut-off composition melts at a temperature within a specific temperature range, e.g. between about 80 and about 250° C. This prevents the battery from exploding and igniting. Thus, the inventive lithium rechargeable batteries have improved thermal stability.

Abstract: A lithium ion secondary battery including an electrode assembly, a center pin positioned within the electrode assembly, a variable-length member coupled to the center pin, the variable-length member adapted to increase in length when an interior temperature of the center pin reaches a critical temperature, a can containing the electrode assembly, the center pin, and the variable-length member, and a cap assembly coupled to the can, the cap assembly having safety means fracturable in response to the variable-length member being increased in length.