During lithium-ion battery packing, joining between battery cases and tabs is challenging for manufacturers due to dissimilar materials of the battery case and the tab, as well as their thicknesses. Laser welding, which has proven to produce a good weld with high productivity and low electrical resistance, is introduced to weld these materials. The weld was conducted with nanosecond-pulsed fiber laser and the effect of laser powers on mechanical and electrical properties as well as microstructure of the joint is investigated. The weld bead at the low laser power exhibited several blowholes on the surface, while the formation of voids including centerline and root cavities was observed through the cross-section. Moreover, the phenomenon of upward penetration (UP) was observed in all laser powers and recoil pressure which was generated by metal evaporation was supposed to cause the formation of an upward flow of the lower material. A hardness test was performed on both horizontal and vertical directions through the fusion zone. Additionally, the increase of upward penetration (UP) resulted in higher strength and lower electrical resistance of the weld.
Given the drawbacks of the conventional welding methods in joining the battery case and tab in the lithium-ion battery, the laser welding technique using the metal tube has been introduced for the weld. The metal tube is supposed to contribute a positive effect including protection to the outside structure by blocking the injection of the spatters, and minimization of the contact gap between the battery case and table. However, the use of the metal tube is believed to cause the plume trapped inside and affect the intensity distribution of the laser gaussian beam. Through the observation and analysis in this study, both advantages and disadvantages of the application of the metal tube on the weld have been analyzed. The use of the metal tube prevents the ejection of the spatter to the outside of the welding zone, as well as minimize the air gap between the battery case and tab in the lap joint weld is also minimized. On the other hand, the trapped plume inside the metal tube and the reduction of the energy of the laser beam have been considered to cause significant changes in the morphology, mechanical, and electrical properties of the weld.
Joining dissimilar metals is critically challenging due to the difference in properties of the metals themselves which leads to the formation of brittle intermetallic compounds (IMCs). Aluminum (Al) and copper (Cu) are well-known materials for electrical application as they attribute to various advantageous characteristics. In lithium-ion batteries, to obtain most of the features of the metals, combinations of these metals are highly recommended. However, with such high reflective metals and heat-sensitive characteristics in the battery, the joint of these metals needs to be processed with an advanced method. In this study, a pulsed fiber laser source that suits to process for heat-sensitive components is utilized to weld two overlap configurations of Al/Cu and Cu/Al, separately. Different ranges of laser power are designated for each welding configuration separately. Thus, the quality of the two welds is evaluated in terms of microstructure and mechanical properties. Consequently, it is found that the growth of IMCs with dendritic structure towards the Al side is observed in both cases. Moreover, the weld of Al/Cu shows a better connection strength as well as fewer imperfections than the weld of Cu/Al.
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