This section provides background information related to the present disclosure which is not necessarily prior art.
With the technical developments and extensive use of mobile devices, electric vehicles, hybrid vehicles, power storages, uninterruptible power supplies or the like, the demands on secondary batteries as an energy source rapidly increase, and batteries capable of coping with various demands are being actively studied.
Generally, a secondary battery is a battery capable of charging and discharging. Particularly, a lithium secondary battery has a high operation voltage, and thus it is more widely used not only for existing high-tech electronic devices such as cellular phones, notebooks, camcorders or the like but also various fields requiring high power and large capacity such as uninterruptible power supplies, electric bicycles, electric wheelchairs, electric vehicles or the like.
The lithium secondary battery generally uses a lithium-based oxide as a positive electrode active material and uses a carbon material as a negative electrode active material. Depending on the kind of electrolyte, the lithium secondary battery is classified into a lithium ion battery using a liquid electrolyte and a lithium polymer battery using a polymer electrolyte. Also, depending on the shape of a can accommodating the electrode assembly, the lithium secondary battery is classified into a cylindrical battery, a rectangular battery and a pouch-type battery.
An electrode assembly of an existing pouch-type secondary battery includes a grid extruding from a laminated electrode plate body and an electrode tab connected to the grid to serve as an electrode terminal of the secondary battery. The electrode assembly is configured so that a positive electrode plate, a separator and a negative electrode plate are laminated or wound in order.
In case of existing secondary batteries, the electrode tab is connected to the grid of the electrode assembly by means of ultrasonic welding or riveting. However, in the ultrasonic welding, as the number of laminated electrode plates increases or the thickness of the current collector foil or the electrode tab increases, overheating or vibration is generated during the welding work, which may deform the separator or easily damage the electrode plate. In case of riveting, a plurality of processes is required, which deteriorates productivity.
Meanwhile, the above problems during the secondary battery manufacturing process are commonly found not only for a pouch-type secondary battery but also all kinds of batteries where several grids are connected to an electrode tab.