In recent times, a secondary battery refers to a device which converts external electric energy into the form of chemical energy and stores it therein, and then generates electricity as necessary. Such a secondary battery is also called the name of ‘rechargeable battery’ which means a battery capable of being charged many times. Typical secondary batteries include a lead storage battery, nickel cadmium (Ni—Cd) battery, nickel metal hydride (NiMH) battery, lithium ion (Li-ion) battery and a lithium ion (Li-ion) polymer battery. A secondary battery provides both an economical advantage and an environmental advantage as compared to a disposable primary battery.
Currently, a secondary battery is used for some applications requiring low electric power. For example, such applications include a device that helps starting of a car, portable device, instrument and an uninterruptible power supply system. Recently, development of wireless communication technology leads popularization of a portable device. In addition, there is a tendency to convert many conventional systems into wireless systems. Under these circumstances, there is an exploding demand for secondary batteries. Further, hybrid cars and electric cars have been commercialized with a view to preventing environmental pollution. Such next-generation vehicles adopt secondary batteries to reduce the cost and weight and to increase the service life.
In general, secondary batteries are generally provided as cylindrical, prismatic or pouch-type batteries. This is because secondary batteries are manufactured by installing an electrode assembly including a negative electrode, positive electrode and a separator into a cylindrical or prismatic metal can or a pouch-type case made of an aluminum laminate sheet, and then injecting an electrolyte to the electrode assembly. Therefore, a predetermined space for installing a secondary battery is required essentially. Thus, such cylindrical, prismatic or pouch-like shapes of secondary batteries undesirably function as limitations in developing various types of portable devices. As a result, there is a need for a novel type of secondary battery which allows easy deformation.
In this context, a cable-type secondary battery, which has a significantly larger ratio of length to sectional diameter, has been suggested.
A cable-type secondary battery undergoes deformation frequently due to its purpose of use. As a result, the interval between an electrode and a separation layer is increased so that a problem of degradation of fundamental characteristics, such as life characteristics and output, of a battery may occur.