Laser cleaning has emerged as a critical pretreatment step for battery welding surfaces, particularly in the manufacturing of lithium-ion cells and packs. The process involves using a pulsed or continuous-wave laser to remove contaminants, oxides, and residues from metal surfaces prior to welding. This method is especially relevant for copper and aluminum current collectors, tabs, and busbars, where surface purity directly impacts weld quality and electrical performance.

The primary objective of laser cleaning is oxide layer removal. Metallic surfaces develop native oxides (e.g., CuO, Al₂O₃) that hinder weld formation by increasing interfacial resistance and causing inconsistent fusion. Studies show that laser cleaning reduces oxide thickness from 50-200 nm to below 5 nm, as verified by X-ray photoelectron spectroscopy (XPS). For copper, oxygen content drops from 8-12 at.% to under 1 at.% after laser treatment. Aluminum surfaces exhibit similar trends, with oxygen concentration decreasing from 15-20 at.% to 2-3 at.%. This reduction is critical because oxides increase contact resistance by up to 40%, which negatively affects weld homogeneity.

Parameter optimization is essential for effective laser cleaning without substrate damage. Key variables include fluence (energy density), pulse overlap, and wavelength. For copper, a fluence range of 2-6 J/cm² is optimal, while aluminum requires 1.5-4 J/cm² due to its lower thermal conductivity and melting point. Pulse overlap ratios of 30-50% ensure uniform cleaning; higher overlap risks heat accumulation, while lower overlap leaves untreated zones. Nanosecond lasers at 1064 nm are commonly used for copper, whereas aluminum benefits from 532 nm due to its higher absorption at shorter wavelengths. Over-cleaning must be avoided, as excessive energy input can roughen surfaces beyond Ra 1.5 µm, which degrades weld quality.

Comparisons with chemical and mechanical cleaning highlight laser advantages. Chemical cleaning (acid pickling, solvents) achieves oxide removal but leaves residues and poses environmental hazards. Mechanical methods (abrasion, brushing) introduce particulates and cold-work the surface, increasing hardness by 10-15% and reducing ductility. Laser cleaning avoids these issues, with residual contamination levels below 0.1 mg/cm², compared to 0.5-1 mg/cm² for chemical methods. Additionally, laser processing is faster, with typical cleaning speeds of 0.5-2 m/s versus 0.1-0.3 m/s for mechanical brushing.

Weld strength improvements are directly measurable after laser pretreatment. For ultrasonic welding of aluminum tabs, laser-cleaned joints exhibit 20-30% higher peel strength (120-150 N/mm vs. 90-110 N/mm for untreated surfaces). Resistance welding of copper shows similar gains, with shear strength increasing from 250-300 MPa to 350-400 MPa. The consistency of welds also improves, with standard deviation in strength reduced by 50% compared to chemically cleaned samples. This reliability is attributed to the elimination of interfacial oxides, which otherwise cause sporadic failure points.

Process control is critical in laser cleaning. Real-time monitoring via photodiodes or spectroscopy ensures complete oxide removal while preventing excessive ablation. Systems integrating laser cleaning with welding in a single workstation achieve throughputs of 10-15 parts per minute, making the technique viable for high-volume production. Energy consumption is modest, at 0.5-1.5 Wh per cleaning cycle, significantly lower than the 5-10 Wh required for equivalent chemical treatment including drying steps.

The impact on electrical performance is equally significant. Contact resistance at laser-cleaned welding interfaces decreases by 60-70%, from 0.8-1.2 mΩ to 0.3-0.5 mΩ for copper-copper joints. This reduction translates to lower heat generation during battery operation, improving energy efficiency by 1-2% in pack-level testing. For aluminum-steel dissimilar welds, laser cleaning enables stable intermetallic compound formation, reducing resistance drift over 500 thermal cycles from 25% to under 10%.

Material-specific considerations dictate parameter adjustments. Thin foils (under 50 µm) require fluence below 3 J/cm² to prevent perforation, while thicker busbars (1-2 mm) tolerate up to 8 J/cm². Alloyed materials like Al 3003 need tailored pulse durations (20-50 ns) to avoid selective vaporization of alloying elements. Pre-cleaning inspections via CCD cameras detect pre-existing defects, allowing dynamic parameter adjustment to avoid exacerbating surface flaws.

Environmental and operational benefits further justify laser adoption. The process generates no liquid waste or volatile organic compounds (VOCs), unlike chemical cleaning. Maintenance is minimal, with optical component lifetimes exceeding 8,000 operating hours. Compared to mechanical methods, laser systems reduce particulate emissions by 90%, as measured by ISO 8573-1 air purity standards.

Limitations exist but are addressable. Initial capital costs for laser systems are higher than conventional cleaning setups, though ROI is achieved within 2-3 years through reduced consumable costs and higher yield. Reflective materials like copper may require beam shaping or multiple passes, but these are mitigated by modern laser sources with adaptive optics.

In summary, laser cleaning provides a precise, repeatable method for preparing battery welding surfaces. By optimizing fluence, overlap, and wavelength, manufacturers achieve oxide-free interfaces that enhance weld strength by 20-30% and reduce electrical resistance by over 60%. The technique outperforms chemical and mechanical alternatives in speed, consistency, and environmental impact, making it increasingly indispensable for high-quality battery production. Future developments may focus on inline quality verification and integration with adaptive welding systems for fully automated processing.