Battery cell tab connector (tab-to-busbar interconnect)

01

Choose tab and busbar materials and the joining process

A 2025 open-access review in Micromachines (Tab-to-Busbar Interconnections in EV Battery Packs) describes the tab as the cell's main terminal, carrying all energy into and out of the cell, and the busbar as a larger conductor connecting multiple tabs in series or parallel. A high-resistance joint causes I²R losses and local heating that can accelerate degradation of nearby cells and in extreme cases poses a thermal runaway risk, while a mechanically weak joint can fail under vibration and open the circuit. Typical materials are Al, Cu and Ni-plated Cu. [2]

The review compares the three dominant processes: ultrasonic welding is solid-state, suppressing porosity and limiting Al-Cu intermetallics, but is sensitive to thickness, stack geometry and tool wear; laser welding gives high-speed automated production but needs control of spatter, porosity and brittle intermetallics in dissimilar joints; resistance welding is cost-effective and flexible but suffers electrode wear and variability with highly conductive stacks. It concludes no single process is universally superior. [2]

The Warwick study laser-welded 0.3 mm Al, Cu, Cu[Ni] and Ni tabs to 1.5 mm Al and Cu busbars with a 150 W pulsed fibre laser and wobble head. Ni tab to Cu busbar joints gave the highest strength (about 1320 N) and Ni to Al about 930 N; Cu tab to Al busbar (about 560 N) was slightly stronger than Al tab to Cu busbar (about 520 N) because of more CuAl2 intermetallics in the latter. It concluded that Ni tabs make strong joints but perform poorly electrically and thermally and are expensive, while Cu and Cu[Ni] tabs perform well, and that Al busbars can cut busbar weight and cost by 75%. [1]

A 2026 study in Scientific Reports (16:28549) ultrasonically welded 0.5 mm aluminium (AA1100) to 0.3 mm cupro-nickel (UNS C71500) sheets, 75 × 20 mm with a 20 mm overlap, on a 3 kW, 20 kHz welder, varying vibration amplitude (54 and 68 µm), sonotrode pressure (0.22, 0.24 and 0.26 MPa) and weld energy (600–1,500 J). Sonotrode pressure and weld energy affected joint strength more than amplitude. Lap shear strength peaked at 942 N and T-peel strength at 236 N at 1,200 J, then fell sharply at higher energy; at 1,500 J the weld interface reached 375, 384 and 389 °C for the three pressures, and heat thinned the aluminium sheet. Joint resistance decreased as weld energy increased. [3]

Editorial note: because ultrasonic joint strength rises and then falls with weld energy, ask the supplier for the energy window it validated on your tab and busbar stack, with lap-shear, peel and resistance results at both ends of that window. [3]

Give the supplier the cell type and tab material, thickness and plating, cell arrangement (series and parallel counts), busbar material and thickness, current (continuous and peak) and duration, joining process and access (one-sided or both sides), weld pattern, strength and resistance acceptance values, temperature limits, insulation and holder design, and the inspection and test plan for each joint.

02

Check joint resistance and temperature rise at your current

The Warwick study passed 100 A, 150 A and 200 A through the joints for 180 s while measuring resistance and temperature. The lowest resistance was the Cu tab to Cu busbar weld: 0.044, 0.048 and 0.050 mΩ at 100, 150 and 200 A, the rise caused by resistive heating in a positive feedback loop. The highest temperatures were in Ni tab to Al busbar joints (89.9°C at 100 A, 157.8°C at 150 A, with the 200 A case overheating), and the lowest in Cu tab to Cu busbar joints (34°C at 100 A, 46.5°C at 150 A). [1]

Editorial calculation: at 200 A through a 0.050 mΩ joint, heating is I²R = 200² × 0.000050 = 2.0 W per joint; multiply by the number of joints in your module to estimate the joint heat the cooling must remove, and recalculate with the supplier's measured resistance for your materials. [1]

Editorial note: ask for joint resistance and temperature rise measured at your continuous and peak current and duration, not only lap-shear strength.

03

Check Cu–Al joint resistance against the base materials and the cell temperature limit

A 2023 study by the Bayerisches Laserzentrum, FAU Erlangen-Nürnberg and RWTH Aachen welded copper to aluminium in overlap, copper on top, with a 515 nm green laser, which the authors chose because copper absorbs green light far better than infrared. The coupons were 55 × 35 mm: 0.2 mm Cu-ETP with a 2.5 µm electrodeposited nickel coating (tolerance 0.6–3 µm) over 0.3 mm aluminium. Resistance was measured with Kelvin contacts over a 16 mm test length, and temperature with thermocouples 8 mm from the seam. [4]

The authors report that every parameter set gave a resistance between the two base-material values, so the weld did not significantly worsen electrical performance. The abstract reports a parameter window for every strategy, "with the stitched seam achieving the most stable results". Circular beam oscillation increased Cu–Al intermixing and intermetallic formation, and the vertical figure-eight oscillation (parameter set #6) showed the largest amount of intermetallic phases in their micrographs. They cite earlier work that a Cu–Al joint becomes very brittle once the intermetallic layer is thicker than 5 µm. [4]

Editorial calculation: 42.2 µΩ is about 1.5 times the copper reference (28 µΩ) and about 0.77 times the aluminium reference (55 µΩ). The γ1 phase's 14.2 µΩ·cm is about 7.9 times copper's 1.8 µΩ·cm. At 200 A, 42.2 µΩ dissipates about 1.7 W (200² × 0.0000422). Set this against the 0.050 mΩ Cu–Cu figure from the Warwick tests above, and remember that each study used its own test length and geometry. [4] [1]

Ask a busbar supplier which welding strategy and wavelength it uses for Cu–Al joints, the measured joint resistance with its test length, the intermetallic layer thickness from cross-sections, and the temperature measured next to the cell terminal during welding. [4]

04

Trace the interconnect

This is a functional reference built from the sources cited; it is not one maker's design.

05

Fill the specification fields with values for your module

A tab connector quotation needs values for your cells and currents. The table explains each field, gives published values where a reviewed source states them, and says what to obtain from the supplier.

06

Send the cell, current and joint data together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Cells: [type; tab material; thickness; plating]
Layout: [series; parallel; pitch]
Busbar: [Al or Cu; thickness; plating]
Current: [continuous; peak; duration]
Joining: [laser; ultrasonic; resistance; access]
Acceptance: [strength; resistance; temperature rise]
Insulation: [holder; voltage]
Tests: [per-joint inspection; vibration]

See manufacturer records Send an enquiry through CNFX