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Welding of Dissimilar Materials for Soft Pack Batteries

Oct 10, 2020

With its energy concentration, high welding efficiency, high processing accuracy, and large weld aspect ratio, laser has become the copper-aluminum welding of power batteries, and even the only technology that can weld electroplated nickel to copper materials. Reasonable selection of welding methods and processes will directly affect the cost, quality, safety and consistency of the battery.

 

Power batteries and energy storage batteries are currently the two major applications of battery technology. Energy storage batteries correspond to solar and other equipment, and power batteries correspond to new energy vehicles. And a long time ago, battery technology companies led by Japanese and South Korean companies classified the types of power battery packaging into three major forms: cylindrical, square, and soft pack batteries.

 

Three power batteries


Soft pack batteries have always been the industry’s first choice for mobile devices, but in automotive applications, they are also valued by car brands because of their volume controllability, especially for plug-in hybrid vehicles, taking into account the overall vehicle layout. In terms of weight and weight, the volume advantage of the soft pack battery is more obvious.

 

pouch cell application


For the welding of dissimilar materials of the soft pack battery, it mainly includes the series connection of the positive and negative lugs, the welding of the positive and negative lugs with the copper bus bar, and the welding of the multilayer negative aluminum and copper bus bars. The thickness of the copper lug is generally 0.2-0.5mm, and the thickness of the aluminum lug is generally 0.2-0.6mm.


The biggest difficulty in copper-aluminum welding:

Because copper and aluminum have a large difference in melting point, they are infinitely mutually soluble in the liquid state, and finitely mutually soluble in the solid state, and can form a variety of solid solution phases based on intermetallic compounds. Therefore, when welding, it is necessary to choose a light source with good beam quality to reduce heat input. Only by shortening the contact time between copper and liquid aluminum can the formation of two intermetallic compounds be reduced, thereby improving the strength of the welded joint.


Considering the difference in melting point of copper and aluminum (difference of 424℃) during welding, the best comprehensive performance is only when the mass fraction of copper in copper-aluminum alloy [ω(Cu)] is below 12%-13%.