Meaning
High-precision fusion weld created using a non-consumable tungsten electrode under an inert gas shield provides a hermetic seal for steel or aluminum battery housings. This welding technique, commonly called a tungsten inert gas seal, is used to close the fill port or join the cap of cylindrical and prismatic cells. It prevents the leakage of volatile electrolyte solvents and blocks the entry of atmospheric moisture and oxygen.
Welding Mechanism
An electric arc is established between the tungsten electrode and the metal casing, melting the edges to fuse them together under a protective flow of argon or helium gas. The inert gas prevents oxidation of the molten metal, which would otherwise create a porous and weak seam. This method produces clean welds with minimal spatter, which is essential to avoid introducing conductive metal particles into the cell.
Purchase Quality
Sourcing agreements for prismatic lithium-ion cells require automated leak testing of these welded seals using helium mass spectrometry. A leaky weld allows electrolyte dry-out and leads to rapid cell degradation and potential safety hazards. Sourcing managers require the weld seam to meet specific leak rate limits before accepting the production batches.
Welding Heat
Internal components and polymer seals can suffer damage if the thermal energy from the arc spreads beyond the joint boundaries. Weld designs must use copper heat sinks or pulsed-current profiles to keep the temperature of the internal cell components below eighty degrees Celsius.
