Criticalities in the Laser Welding of Li-ion Batteries

Li-ion batteries of higher capacities are fabricated in prismatic-shaped aluminium container-lid assembly and are laser weld for leak-proof design. Hermetic sealing of the Li-ion cells is essential for the consistent cycle life and capacity of the Li-ion cells. Laser welding of aluminium alloys poses several problems due to their high reflectivity and thermal conductivity, and several defects are commonly observed. Pore formation is one of the major defects observed in the laser welding of Li-ion cells causing cell leaking and deteriorating the electrochemical performance. The methodology for minimizing the pores, the reasons for their formation, and the optimization of laser welding parameters for minimizing these defects in prismatic Li-ion cells are discussed in this paper. The reasons attributing to pore formation have been categorized into contaminants, weld practices, laser parameter and discussed in detail. It is observed that pore formation from contaminants could be avoided by use of non-dyed anodized containers. Use of weld practices like slower weld speed of 0.1 mm/s ensures complete fusion. Ending the laser beyond the weld prevents the formation of craters containing pores. A slightly defocused beam of 500 µm spot size prevents spatter formation. Optimum laser energy of 12 J ensures complete depth of fusion preventing leaks due to through pores. Hermetic sealing of the prismatic cells with lower that 10⁻⁶ cc s⁻¹ leak rate could be finally achieved by adopting these measures.