As electric devices have been increasingly developed, and the demand for such electric devices has increased, the demand for secondary batteries has also sharply increased in recent years. In addition, new forms of secondary batteries have been required according to various trends in design including a slim type structure or a curved structure of electric devices.
According to such various trends in design, electric devices have been designed such that at least one portion of the outside of each of the electric devices is curved unlike a conventional simple rectangular parallelepiped structure. In addition, each of such electric devices is provided with a larger number of electronic components than conventional electric devices. For this reason, secondary batteries which are more stable and have increased electric capacities are required. Among such secondary batteries is a lithium secondary battery exhibiting high energy density and operating voltage and excellent charge retention and service-life characteristics. The lithium secondary battery has been widely used as an energy source for various electronic products as well as electric devices.
Based on the appearance thereof, the lithium secondary battery may be classified as a cylindrical battery, a prismatic battery, or a pouch-shaped battery. Based on the kind of an electrolyte, the lithium secondary battery may also be classified as a lithium ion battery, a lithium ion polymer battery, or a lithium polymer battery.
A recent trend in the miniaturization of electric devices has increased the demand for a prismatic battery or a pouch-shaped battery, which has a small thickness. In particular, much interest is currently focused on such a pouch-shaped battery because it is easy to modify the shape of the pouch-shaped battery, the manufacturing cost of the pouch-shaped battery is low, and the pouch-shaped battery is lightweight.
Generally, a pouch-shaped battery is a battery having an electrode assembly and an electrolyte in a pouch-shaped battery case, formed of a laminate sheet including a resin layer and a metal layer, in a sealed state. The electrode assembly mounted in the battery case is configured in a jelly-roll (wound) type structure, a stacked type structure, or a combination (stacked/folded) type structure.
FIG. 1 is a view typically showing the structure of a pouch-shaped secondary battery including a stacked type electrode assembly.
Referring to FIG. 1, a pouch-shaped secondary battery 10 is configured to have a structure in which an electrode assembly 30, including cathodes, anodes and separators disposed respectively between the cathodes and the anodes, is mounted in a pouch-shaped battery case 20 in a sealed state such that a cathode lead 40 and an anode lead 41 electrically connected to cathode tabs 31 and anode tabs 32 of the electrode assembly 30 are exposed to the outside.
The battery case 20 includes a case body 21 having a depressed receiving part 23, in which the electrode assembly 30 is located, and a cover 22 integrally connected to the case body 21.
The battery case 20 is formed of a laminate sheet including an outer resin layer 20A constituting the outermost portion of the laminate sheet, an isolation metal layer 20B to prevent penetration of materials, and an inner resin layer 20C for sealing.
The cathode tabs 31 and the anode tabs 32 of the stacked type electrode assembly 30 are respectively coupled to the electrode leads 40 and 41 by welding. In addition, insulative films 50 are attached to the top and bottom of each of the electrode leads 40 and 41 to prevent the occurrence of a short circuit between a thermal welding device (not shown) and the electrode leads 40 and 41 and to achieve sealing between the electrode leads 40 and 41 and the battery case 20 when the upper end 24 of the case body 21 and the upper end of the cover 22 are thermally welded to each other using the thermal welding device.
However, the above-mentioned pouch-shaped secondary battery is generally configured to have a simple rectangular parallelepiped structure. In a case in which the pouch-shaped secondary battery is mounted in various designs of electric devices each having a curved structure, therefore, the inner space of each of the electric devices cannot be fully used or unnecessary dead spaces may be formed in each of the electric devices. In addition, such inefficient use of the inner space of each of the electric devices may increase overall volume of each of the electric devices.
Therefore, there is a high necessity for an electric device configured to have an external appearance based on various designs including a curved structure and to have a secondary battery that is capable of efficiently using the inner space of the electric device mounted therein.