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Laser Welding

Battery tab welding still comes down to the copper problem

Copper reflects most of the light a 1 µm source produces until it melts, then absorbs it suddenly. Green and blue sources exist because that transition is hard to control.

By LasersNews Desk··2 min read
Workers in a metal workshop engaged in active construction and welding tasks.
Photo by Hoang NC on Pexels

Joining copper with a near-infrared laser is a problem of absorption. At room temperature, copper reflects roughly ninety-five per cent of light at 1 µm. As it heats and melts, absorption climbs steeply. The process therefore sits on an unstable threshold: too little power and nothing happens, slightly more and the material suddenly couples, absorbs strongly and can eject molten metal.

Why this matters for batteries

Cell-to-busbar and tab connections are copper or copper-aluminium, thin, numerous and electrically critical. A weld with excessive spatter risks conductive debris inside a cell assembly. A weld with inconsistent penetration produces variable resistance, which becomes heat, which becomes a reliability problem over thousands of cycles.

Volume compounds it. A pack may contain thousands of joints, and process capability has to hold across all of them.

The wavelength answer

Copper absorbs green light at 515 nm far more readily than infrared, and blue diode sources at around 450 nm better still. Starting with high absorption removes the unstable threshold: coupling is predictable from the first moment, and the process window widens considerably.

The trade is cost and available power. Green and blue sources remain more expensive per watt than mature 1 µm fiber lasers, and the highest powers are still found in the infrared.

The hybrid approaches

Two practical compromises are widely used. The first is beam shaping — a ring-mode or dual-core beam that preheats the surface with a surrounding annulus while a central core drives penetration, stabilising coupling without changing wavelength. The second is short pre-pulses that raise surface temperature into the absorbing regime before the main pulse arrives.

Both narrow the gap enough that infrared sources remain viable for many copper joints, which matters because infrared is where the installed base, the service network and the cost curve already are.

What decides the choice

For thin tabs at very high volume with tight spatter limits, green and blue increasingly win on process capability. For thicker busbars where absolute power matters, infrared with beam shaping still dominates. The decision is rarely about which is better in principle and almost always about which produces a stable process on the specific joint at the required rate.

This article was produced by the LasersNews AI desk and reviewed by our editors.

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