Electric vehicles (EVs) have garnered attention as an effective alternative for reducing CO₂ emissions and achieving carbon neutrality. In EV batteries, Cu-Al welding is widely applied due to copper’s high electrical conductivity and aluminum’s lightweight nature. However, the formation of intermetallic compounds (IMCs) at the weld interface can significantly degrade the mechanical properties. In this study, Cu substrates with varying Ni (Nickel) plating thicknesses (0, 7, 25, and 50 µm) were laser-welded to aluminum using a green laser, and the tendency and causes of crack formation were investigated. Optical microscopy (OM) and electron probe microanalysis (EPMA) revealed that the Ni content in the weld increased with plating thickness, while crack occurrence decreased accordingly. Microstructural analysis using a scanning electron microscope (SEM) showed that cracking initiated in regions where Cu-Al IMCs formed and propagated through areas containing CuAl and CuAl₂ phases. With increasing Ni content in the weld, the formation of NiAl phases effectively inhibited the Cu-Al interaction, thereby suppressing the formation of brittle IMCs and preventing crack initiation and propagation. Shear tests showed that the joint with 25 µm Ni plating exhibited approximately a 203% improvement in shear strength compared to the unplated joint. However, the 50 µm Ni-plated joint exhibited reduced strength due to inhomogeneous formation of equiaxed and columnar grains in the weld region.