I. Core Pain Points in Mass Production of 4680 Large Cylindrical Batteries: Innovation in Thick Copper Full-pole Tab Welding
Blue Lasers & Ring-shaped Beams Solve Processing Challenges of Highly Reflective Materials
As 4680 large cylindrical batteries become the standard configuration for high-end pure electric vehicles, welding stacked multi-layer copper foils for full-pole tabs turns into the primary technical bottleneck. Traditional infrared fiber lasers only achieve 3%~5% light absorption rate on copper, which frequently causes cold joints, localized burn-through and massive metal spatter during welding. Scattered spatter debris falling into cells will create hidden dangers of short circuits and thermal runaway.
Two types of laser light sources achieved commercial mass production in 2026:
1. VBP Variable Beam Profile Ring Adjustable Spot Fiber Laser
This laser allows independent power adjustment for the central beam and outer ring beam. The central beam penetrates thick copper to form a deep penetration keyhole, while the outer ring beam widens the upper edge of the keyhole to discharge bubbles inside the molten pool and trap splashed molten metal back to the weld seam.
This solution reduces spatter generation by 90% when welding 4mm single-layer copper busbars, and controls weld porosity within 0.3%. Meanwhile, the laser source can withstand over 95% reflected laser light, preventing laser source burnout during thick copper welding. Currently, production lines for 4680 cells from Tesla and top domestic cylindrical battery manufacturers are fully equipped with ring-spot laser welding equipment.
2. Domestic Commercial Blue Laser
Blue lasers deliver a 40%~50% absorption rate on copper, 13 times higher than infrared lasers. They can complete lamination welding of hundreds of thin copper foils at the bottom of 4680 cells without ultra-high power input, preventing ultra-thin copper foils from being burnt through.
After the localization of affordable kilowatt-level blue lasers matures in late 2026, they will gradually replace traditional infrared lasers for low-power precision spot welding of pole tabs.
Compared with ultrasonic welding, which was widely adopted before and limited by worn welding horns with a maximum single-line productivity of only 100 PPM, ring-spot laser welding consumes no spare parts. Its production rhythm perfectly matches high-speed stacking processes, making it ideal for gigawatt-hour (GWh) super factories with mass production demands.
II. High-voltage Busbar Welding for Power Packs: Reduce Resistance for Vehicle High-voltage Circuits, Laser Welding Replaces Bolt-fastening Scheme
Thick copper busbars between battery modules are responsible for series-parallel electrical conduction as well as voltage & temperature sampling, directly determining fast-charging efficiency and high-voltage safety of electric vehicles.
Traditional bolt fastening would lead to loosened screws under long-term vehicle vibration, increased contact resistance and excessive heat generation during fast charging. In 2026, new energy vehicle manufacturers widely adopt the integrated laser fusion welding solution for whole-pack busbars:
3000W~6000W high-power VBP ring-spot laser equipment performs overlap autogenous welding on 3~6mm thick copper bars without additional filler metal. The weld forms an integrated metallurgical bond that never loosens. The overall resistance of the vehicle's high-voltage circuit drops by 15%~22%, supporting 800V high-voltage platform ultra-fast charging.
The production line is equipped with CCD vision pre-positioning with ±0.05mm accuracy to automatically compensate dimensional deviations of incoming copper bars. A coaxial fume purification system eliminates tiny copper scraps that may cause creepage risks on busbar surfaces.
III. Cell Sealing Process: Top Cap Circumferential Weld & Sealing Nail Welding
AI-OCT Closed-loop System Eliminates Liquid Leakage Risks
After prismatic cells and 4680 cylindrical cells are filled with electrolyte, sealing nail welding and full peripheral welding of cell top caps determine the service life of batteries. Tiny pinholes on weld seams will cause electrolyte volatilization and leakage, resulting in scrapped cells.
High-end battery production lines completely eliminated post-weld helium sampling leak testing in 2026, and upgraded to the integrated system of OCT Optical Coherence Tomography Scanning + AI Deep Learning Closed-loop Control:
1. The laser welding head integrates a coaxial OCT scanning module, which measures the internal weld penetration depth in real time during welding with axial precision up to 0.02mm;
2. The 1DCNN-BiLSTM AI model analyzes keyhole status instantly. If insufficient penetration (cold joint) or excessive penetration (casing burn-through) is detected, the system will automatically lower or raise laser power within 20 microseconds to correct welding defects in real time;
3. All data including penetration depth, laser power parameters and welding positions are uploaded to the factory MES system for permanent cloud storage, satisfying the full-lifecycle traceability regulations for batteries issued by European and American automobile OEMs.
After intelligent upgrade, the rejection rate of helium inspection for cell sealing welding decreased by 95%, removing the need for large-scale destructive sampling tests and greatly cutting production costs. Moreover, the heat-affected zone of laser welding is controlled within 0.2~0.3mm, avoiding damage to internal separators and active materials inside cells, suppressing lithium precipitation during charging and extending the cycle life of batteries.
IV. Shared Scenario for Energy Storage & Passenger Vehicles: Precision Hermetic Laser Welding for Aluminum Alloy Microchannel Liquid Cooling Trays of Battery Packs
With the popularization of 800V high-voltage EV platforms and large-scale commercial & industrial energy storage power stations, aluminum alloy liquid cold plates have become standard components for battery packs. Dense thin-walled microchannels dissipate massive heat generated during ultra-fast charging.
Traditional brazing and friction stir welding easily deform thin aluminum plates, block flow channels and cause water leakage on welds. Autogenous laser welding has become the preferred manufacturing process for liquid cold plates in 2026, with core advantages as follows:
1. Ultra-low heat input: Concentrated laser energy limits the heat-affected zone to 0.2mm. After welding 1~2mm ultra-thin aluminum cover plates, the overall deformation is less than 0.05mm, preventing microchannel cavities from being squeezed and blocked;
2. Filler-free autogenous welding: The base aluminum material fuses together to form the weld. The weld shares identical material composition with the substrate, without reducing the overall thermal conductivity of cold plates. Weld seams can withstand long-term water pressure testing up to 5 bar;
3. Convenient rework: Portable trolley-type fiber laser welders perform local repair welding on damaged flow channels of finished battery modules directly, without disassembling the entire battery PACK, drastically lowering after-sales maintenance costs for energy storage power stations.
Chinese laser manufacturers have launched dedicated sealing welding workstations for liquid cold plates, integrating pre-weld laser oxide cleaning, hermetic welding and post-weld air tightness preliminary inspection to finish cold plate processing in one-stop workflow.
V. Overall Development Trends of Laser Welding for Power Batteries in 2026
1. Customized Beam Shaping: Factories no longer adopt single Gaussian beam lasers universally. Operators can switch freely between ring spots, flat-top spots and composite beams for different processes, distinguishing applications for thick copper welding and thin aluminum hermetic sealing welding.
2. Front-loaded Quality Inspection: Quality control evolves from post-weld sampling inspection to real-time in-process correction. AI closed-loop monitoring has become a mandatory access threshold for export-oriented battery factories serving overseas markets.
3. Integrated Composite Processes: Dual-function equipment combining laser cleaning and laser welding enters batch trial application. It removes surface oxide and oil contaminants right before welding, simplifying production line layout and reducing factory floor occupation.
