Field of the Invention
The present invention relates to a method for welding electrode taps of a secondary battery which improves insulation defects generated during welding between the electrode taps and lead parts of the secondary battery and an electrode assembly manufactured thereby.
Description of the Related Art
As demand for mobile devices rapidly increases, demand for secondary batteries applied to mobile devices increases and thus technical research on secondary batteries is vigorously carried out.
In general, secondary batteries are rechargeable and may be small-sized and large-sized, and a lithium (Li) battery is representatively used as a secondary battery.
However, although secondary batteries are rechargeable and used as an eco-friendly energy source, as described above, they have a problem regarding stability thereof.
That is, various chemical reactions in a secondary battery are caused by temperature rise due to abnormal energy conversion in the secondary battery. Thereby, lowering of stability of the secondary battery, i.e., ignition and explosion, may occur.
In more detail, if the secondary battery is exposed to high temperature or a high intensity of current flows in the secondary battery within a short time due to external short circuit, the secondary battery is heated by IR heating and a dangerous state, such as heating, ignition, explosion, etc., may be caused. Therefore, durability of secondary batteries needs to be improved.
A conventional secondary battery includes an electrode assembly 2 in which anode plates, separator films, and cathode plates are alternately stacked, installed within a battery case 1, as exemplarily shown in FIG. 1. Among the electrode assembly 2, the anode plate is formed of aluminum or an aluminum alloy as a base material, and the cathode plate is formed of copper as a base material.
Further, electrode taps 3 protruding one side of the electrode assembly 2 for connection to lead parts 4 are provided at the respective plates. The lead parts 4 serve to connect the respective plates to external terminals, the lead parts 4 and the electrode taps 3 are mainly connected by welding, and welding parts W are formed through welding.
However, during a resistance welding process, a plurality of nuggets is generated between the electrode taps 3 and the lead parts 4 due to fusion of the welding parts W by welding rods. During such a process, foreign substances, such as fine metal particles, are dispersed and move to the lead parts 4 and thus destroy a lead film 4′ during a subsequent process, i.e., sealing of the battery case 1, thereby causing insulation defects.