Achieving high robust laser conduction welding and enhanced joint conductivity in pure copper foil stacks using a flat-top blue laser

The innovation of energy storage battery manufacturing technology, particularly the welding process of current collector pure copper foil stacks, is crucial for the development of the e-Mobility industry. This work aims to achieve high robust blue laser conduction welding (B-LCW) and enhance the joint conductivity of pure copper foil stacks. The conventional keyhole mode is replaced by blue laser conduction mode with a flat-top uniform energy distribution. The parameter, molten pool characteristics, surface morphology, microstructure, and conductivity were analyzed, and the correlation factors were examined. The results demonstrate that the high robust laser conduction welding of high-reflectivity/high-thermally-sensitive pure copper foil stacks was achieved, by which obtaining superior foil fusion connection and surface morphology compared to conventional infrared laser keyhole welding. Moreover, benefit from the high absorptivity (53.1%) and flat-top energy distribution of the blue laser, a high-stability molten pool and smooth welding seam were obtained. Meanwhile, the microstructure of the welding seam changes from small block-α-phase crystals to coarse columnar crystals with preferred orientation in the welding direction. The conductivity of the welding seam exceeds that of the base foil stacks, exhibiting a strong correlation with surface morphology and microstructure. Therefore, the high robust B-LCW process has considerable advantages in the welding of specific high-reflectivity foil stacks, which can promote the development of the new energy e-Mobility industry.