Battery tabs seem to have been getting thicker and more conductive over the last several years, as customers seek better performance and higher currents from their battery packs. These thicker battery tabs are usually made of nickel, but nickel-plated copper tabs are gaining in popularity due to their higher conductivity. We’ve had success welding the thicker nickel tabs, but have found the nickel-plated copper to be very difficult to weld. How to overcome that? Add slots and projections to the tab design to focus the current and minimize current shunting. Welding success also depends, in part, on the battery itself; those with thick caps can easily handle the high force and current needed to weld the thicker tabs. If the battery caps are too thin, however, they may get deformed or blown through.
We’ve had the most success welding thicker tabs using our IPB-5000A Inverter, a resistance welding power supply that delivers superior control for a wide range of micro welding applications. It features 5kHz fast feedback, and operates in constant current, voltage or power feedback modes. Voltage feedback is the typical mode of choice when welding battery packs, but the IPB-5000A can also weld in “combo mode” (current and voltage) to address even the most challenging battery welding applications. It is capable of a maximum output of 6000 amps, making it ideal for welding thicker tabs.
Safety is another concern when selecting resistance welding equipment for battery welding. For example, if not welded properly, the chemicals contained in lithium ion batteries (you’ve heard about this in the news recently, associated with the new Boeing 787 aircraft) can leak out, burning eyes and skin. To avoid this hazardous situation, it is essential to use a closed loop power supply like the IPB-5000A, which includes features used to check weld resistance prior to applying the high welding current.
We also recommend using an 89A/EZ Weld Head which offers 40 lbs. per electrode, and allows independent adjustment of the left and right forces to optimize heat balance between the two weld nuggets. It is supplied with Dual EZ-AIR, a pneumatic control that actuates the electrodes and maintains a preset firing force. At the predetermined firing force, EZ-AIR automatically closes the inlet and outlet valves to the weld head actuation cylinders, eliminating overforce.
In summary, welding the thicker, more conductive tabs used in today’s more efficient, higher capacity battery packs can be challenging, but welding success can be achieved by designing the parts correctly and selecting equipment that is best suited to the application.
For more information read Battery Welding Solutions Using Laser & Resistance Technologies.