Power batteries and energy storage batteries are the two major scenarios for the application of battery technology at present. Energy storage batteries correspond to solar energy and other equipment, and power batteries correspond to new energy vehicles.

The packaging types of power batteries are classified into three types: cylindrical, square and soft packs. The soft pack battery has always been the first choice for mobile devices in the industry, but in automotive applications, it is also valued by car brands because of its volume controllability, especially for plug-in hybrid vehicles. When it comes to weight and weight, the volume advantage of the soft pack battery is more obvious.

With its advantages of concentrated energy, high welding efficiency, high processing precision, and large weld seam 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 batteries.

Pouch battery dissimilar material welding

For the welding of dissimilar materials of soft pack batteries, it mainly includes the series connection of positive and negative lugs, the welding of positive and negative lugs and copper busbars, and the welding of multi-layer anode aluminum and copper busbars. The thickness of copper tabs is generally 0.2-0.5mm, and the thickness of aluminum tabs is generally 0.2-0.6mm.

The biggest difficulty in the welding of copper-aluminum materials by laser welding of soft pack batteries

Due to the large difference in melting point between copper and aluminum, they are infinitely soluble in each other in liquid state and limited in mutual solubility in solid state, and can form a variety of solid solution phases based on intermetallic compounds. Therefore, when welding, try to choose a light source with good beam quality and reduce heat input. Shortening the time that copper is in contact with liquid aluminum can reduce the formation of two intermetallic compounds, thereby increasing the strength of the welded joint.

Difficulties of Laser Welding Process

High reflection/thermal conductivity material - requires large laser power density, high welding reflectivity, and high requirements for laser stability and reliability.

Materials with high carbon content - when the carbon content is greater than 0.77%, due to the fast cooling and fast heating characteristics of the laser, cracks are easily formed in the center of the weld and the heat affected zone; containing low boiling point elements - such as materials containing Mg, Zn and other elements When the ionization energy of such elements is low, a large amount of evaporation occurs during the laser welding process, and even continues to absorb capacity and becomes plasma, which will change the microstructure type and chemical composition of the weld, and seriously deteriorate the weld performance.