Advances in technology are changing how we weld batteries
As customers seek better performance and higher currents from their battery packs, one area of focus has been on battery tab design – specifically looking at thicker, more conductive tab material. Traditionally, battery tabs are made of nickel due to its weldability using electrical current. Developments in tab material design exploits the weldability of nickel and the higher conductivity of copper, resulting in, for example, the material SigmaCLAD; this layered material allows for a thicker more conductive tab than when using nickel only.
However, with these new materials come new challenges in welding. The thicker tabs require a greater force to put the tab material in intimate contact with the cell and avoid material expulsion. This means the battery cell also needs to withstand additional force —which is generally the case. If the caps of the battery are too thin, this might lead to deformation and blow outs.
In addition, even though the outside layers of this composite material are nickel, we need a higher current power supply with fast, closed loop feedback to weld them. The Amada Weld Tech IPB-5000A-MU puts out up to 6,000 amps of current addressing tab thickness up to about 0.020” (0.5 mm).
Safety is another concern that should be considered when welding batteries—especially lithium ion. If the battery can is punctured during the welding process, the outgassing lithium is harmful for the operator, causing skin and eyes to burn.The IPB-5000A-MU weld control has built in closed loop feedback to ensure consistent output; it samples the current, voltage, or both at a 5 kHz sampling rate, providing accurate feedback to ensure success. Typically, battery packs are welded in voltage feedback mode, but in some applications, you may need multiple pulses, and it is recommended to use current-voltage combination. In addition, Amada Weld Tech also recommends pairing any resistance welding equipment with a weld process monitor, like the MM-400A. This can flag welds that go outside of the set limits providing another layer of security and safety.
For thick tabs up to 0.02” (0.5 mm), Amada Weld Tech recommends a TL-089A-EZ weld head which is an air actuated, precision, low inertia, force-fired weld head with a thin profile to conserve workbench space. It offers 40 lb force per electrode and allows independent adjustment of the left and right forces to optimize heat balance between the two weld nuggets that form. Its pneumatic control actuates the electrodes and maintains a pre-set firing force.
Indeed, welding thicker, more conductive battery tab material common in today’s higher capacity battery packs can be challenging, but welding success can be achieved by designing the parts correctly and selecting the equipment best suited to the application. SMT
This article was contributed by Amada WeldTech.