From the perspective of welding, the most important aspect of battery lug welding is the thickness and material of the lug and terminal. Conductivity is the name of the game, so the battery lug is usually made of aluminum or copper, sometimes nickel or tin-plated. The terminal can be cold rolled steel, aluminum, or copper, depending on the physical size of the finished battery.
The most common battery types are cylindrical lithium-ion batteries with the size of 18650 (18mm x 65mm), large prismatic batteries, and lithium polymer soft packs. Each battery type has a different set of welding requirements.
Cylindrical cell laser welding
The key to welding the cylindrical battery type is to weld the negative terminal. The battery lug is directly welded to the tank instead of a separate platform on the positive side. The weld on the negative terminal shall not penetrate the can-body thickness, which is usually about 0.015 inches (0.3 mm). The thickness of the can determine the thickness of the tab - according to experience, the tab should be 50-60% of the thickness of the can. The cylindrical battery shell material is usually nickel-plated steel, and the lug material is nickel or tin-plated copper. Nickel plating is better than tin plating because it is more stable; The extremely low boiling point of tin will lead to welding pores and excessive spatter.
Large prismatic cell laser welding
These high-capacity batteries need thick plates to ensure sufficient current-carrying cross-section to provide battery output. The tab connection only needs to handle the capacity of a single cell. Therefore, thinning or "stamping" thick joint material to achieve lap welding or creating through holes for fillet welds can greatly reduce the size of the required weld. This in turn reduces the heat input to the tank, which is always a problem when welding thicker joints.
For lap weld geometry, reducing the thickness of the lug to 0.01-0.02 inch can provide sufficient welding area to obtain strength and capacity while maintaining a sufficiently low temperature during welding to avoid battery damage. The material selection of terminals and lugs is usually aluminum - the recommended lug materials are 1080 and 1100. Avoid using aluminum alloy 6061, which will crack when welding. If this material has been specified and cannot be changed, 4047 prefabricated parts will be used as the third material, which will introduce a large amount of silicon in the weld to prevent the weld from cracking.
Lithium polymer battery laser welding
These thin flexible batteries with rectangular packaging are indeed becoming more and more popular in consumer electronics. The terminals on these batteries are composed of thin layers of copper foil and aluminum foil, which are welded to copper sheet and aluminum sheet by laser respectively. Due to the need to weld a stack of foil, this welding is traditionally carried out using ultrasonic technology, but now optical fiber laser welding machine is used to improve the welding quality and strength. The key to the success of using fiber lasers in this application is to ensure (a) close contact with the foil, and (b) the use of pulse lasers to avoid overheating.
The RS-SWF-80/150 80W & 150W & 300W fiber laser welding machine is catering to the demand for high-quality high-speed laser welding for lithium battery cells. It can weld a wide range of materials and can realize the welding between different materials. such as steel, aluminum, copper, nickel, etc