Cell assembly in battery manufacturing relies heavily on the quality and reliability of tab welding and interconnection technologies. These processes ensure electrical conductivity and mechanical stability between electrodes and external terminals. The most common methods include ultrasonic welding, laser welding, and mechanical crimping, each with distinct advantages and limitations. The choice of method depends on material compatibility, production speed, and joint performance requirements.

Ultrasonic welding is widely used for joining battery tabs due to its ability to create solid-state bonds without melting the base material. The process involves high-frequency vibrations (typically 20-40 kHz) applied under pressure, causing localized plastic deformation and atomic diffusion. Key parameters include amplitude (5-50 µm), welding force (100-1000 N), and energy input (50-500 J). Excessive energy can lead to cracks or voids, while insufficient energy results in weak joints. Aluminum tabs weld more easily than copper due to lower hardness, but copper requires higher energy input. Joint conductivity correlates with weld area and interfacial bonding quality, with resistance values typically below 50 µΩ for well-formed joints. Mechanical strength is measured by peel force, often exceeding 10 N/mm for reliable connections.

Laser welding offers precision and speed, making it suitable for high-volume production. The process uses focused laser beams (fiber or pulsed lasers) to melt and fuse materials. Parameters such as power (50-500 W), pulse duration (1-20 ms), and spot size (0.1-0.5 mm) must be optimized to avoid defects like spatter or incomplete penetration. Laser welding works well for copper and aluminum but requires careful parameter adjustment due to their different thermal conductivities and reflectivity. Copper's high reflectivity necessitates higher power settings, while aluminum's rapid heat dissipation demands precise control. Joint resistance in laser welding can achieve values below 20 µΩ, with shear strength often exceeding 15 N/mm². However, the heat-affected zone may weaken adjacent materials, requiring thermal management strategies.

Mechanical crimping provides a non-thermal alternative, relying on compressive force to form cold welds between tabs and terminals. This method avoids heat-related defects but requires precise control of crimping force and geometry. Typical crimping forces range from 500-3000 N, depending on material thickness and hardness. Joint performance depends on surface cleanliness and oxide removal, as contaminants increase contact resistance. Crimped joints exhibit higher resistance (100-500 µΩ) compared to welded ones but are less prone to thermal degradation. Mechanical strength is determined by interlocking deformation, with pull-out forces often exceeding 20 N/mm.

Material compatibility poses significant challenges, particularly when joining dissimilar metals like copper and aluminum. Galvanic corrosion can occur in humid environments, increasing resistance over time. Solutions include using intermediate layers or coatings to mitigate corrosion. High-speed production exacerbates these issues, as process windows narrow to maintain quality. Ultrasonic welding in high-speed lines may require adaptive control to compensate for material variations, while laser welding demands real-time monitoring to prevent defects.

Tab welding differs from pack-level welding in scale and complexity. Cell assembly focuses on individual connections with minimal thermal impact on sensitive components, whereas pack-level welding involves larger structures and higher energy inputs. Pack welding often employs laser or resistance welding for busbars and module interconnects, where joint durability and current-carrying capacity are critical. The precision required in cell assembly is higher due to smaller tolerances and the need to avoid damaging adjacent materials.

Process optimization requires balancing speed, quality, and cost. Ultrasonic welding is cost-effective for aluminum but struggles with copper at high speeds. Laser welding offers faster cycle times but at higher equipment and maintenance costs. Mechanical crimping is the least energy-intensive but may not meet resistance requirements for high-performance cells. Advanced monitoring systems, such as in-line resistance measurement or optical inspection, are increasingly used to ensure consistency in mass production.

Emerging trends include hybrid methods combining ultrasonic and laser techniques to improve joint quality, particularly for dissimilar materials. Adaptive control algorithms adjust parameters in real time based on sensor feedback, reducing defect rates. Material innovations, such as coated tabs or composite foils, also enhance weldability and long-term stability. The industry continues to explore alternatives to traditional welding, including conductive adhesives or nanoscale interconnects, though these are not yet mainstream.

The future of tab welding lies in increasing automation and precision while reducing energy consumption. Integration with Industry 4.0 systems enables predictive maintenance and data-driven optimization, further improving yield and reliability. As battery designs evolve toward higher energy densities and faster charging, interconnection technologies must keep pace to meet stringent performance and safety standards.