Automated degassing equipment plays a critical role in lithium-ion cell manufacturing, particularly after the formation process. During formation, gases such as carbon dioxide, hydrogen, and hydrocarbons evolve due to electrolyte decomposition and solid electrolyte interphase (SEI) layer formation. These gases must be removed to prevent swelling, internal pressure buildup, and performance degradation. Modern degassing systems integrate puncture mechanisms, vacuum systems, gas analysis, and resealing processes while maintaining strict safety protocols.
The puncture mechanism is the first step in degassing. Precision-controlled needles or blades penetrate the cell's sealing area without damaging internal components. The puncture depth and angle are calibrated for different cell formats, whether cylindrical, prismatic, or pouch. For cylindrical cells, the puncture occurs near the fill port, while pouch cells require careful alignment to avoid electrode damage. Force sensors ensure consistent penetration, and servo-driven actuators adjust for cell-to-cell variations in thickness or material properties.
Vacuum systems extract gases efficiently after puncture. Multi-stage rotary vane or dry screw pumps achieve vacuum levels between 10 and 100 Pa, depending on cell chemistry and gas content. The vacuum chamber design minimizes dead volume to enhance gas removal rates. Some systems employ pulsed vacuum cycling, alternating between low and moderate vacuum levels, to improve gas extraction from porous electrodes. Residual gas analyzers (RGAs) or mass spectrometers monitor gas composition in real-time, ensuring complete removal before resealing. Data from these analyzers can correlate gas species with formation process parameters, enabling quality control adjustments.
Gas analysis integration provides insights into cell health and process consistency. Fourier-transform infrared spectroscopy (FTIR) or gas chromatography identifies and quantifies vented species. For instance, ethylene and ethane detection indicates electrolyte reduction, while oxygen presence suggests moisture contamination. Automated systems log gas data for traceability and flag outliers for further inspection. In-line analysis reduces the need for offline testing, accelerating production throughput.
Resealing follows degassing and must restore hermetic integrity. Laser welding is predominant for metallic cell housings, such as aluminum or steel cans in cylindrical and prismatic formats. Fiber lasers with wavelengths of 1070 nm or 808 nm provide precise energy delivery, melting the puncture site material without excessive heat spread. Weld penetration depth typically ranges from 0.3 to 1.2 mm, validated through helium leak testing with sensitivity below 10^-6 mbar·L/s. Pouch cells use epoxy resealing, where automated dispensers apply two-part epoxies or UV-curable adhesives over the puncture site. Curing occurs under controlled temperature and humidity, with bond strength tested via peel or shear tests.
Safety systems mitigate risks from vented gases and dry room conditions. Vent gas handling includes catalytic converters or scrubbers to break down flammable or toxic species like hydrogen fluoride. Explosion-proof electrical components and nitrogen purging prevent ignition in vacuum pumps or analysis equipment. Dry rooms maintain dew points below -40°C to avoid moisture ingress during resealing. Localized gloveboxes with argon atmospheres further protect sensitive components in prismatic or pouch cell production.
Automation synchronizes these steps for high-throughput operation. Robotic arms transfer cells between stations, while programmable logic controllers (PLCs) coordinate timing between puncture, vacuum, analysis, and resealing. Machine vision systems verify puncture and reseal quality, rejecting defective units. A single degassing station can process 20 to 60 cells per minute in cylindrical cell lines, with throughput limited by vacuum pump speed and resealing method.
Process validation ensures consistency across cell formats. Cylindrical cells undergo burst pressure testing post-resealing, with thresholds set above 2 MPa for 18650 or 21700 formats. Prismatic cells require edge weld integrity checks via X-ray imaging, while pouch cells are evaluated for delamination resistance after epoxy curing. Statistical process control tracks key parameters like vacuum time, residual gas levels, and reseal strength, triggering maintenance if deviations exceed predefined limits.
Material compatibility influences equipment design. Vacuum chamber seals use perfluoroelastomers to resist electrolyte solvents, while puncture tools employ tungsten carbide or ceramic coatings to minimize wear. Laser welding optics incorporate protective coatings to prevent contamination from outgassed deposits. These material choices extend equipment lifespan and reduce particulate generation in dry room environments.
Future advancements may focus on closed-loop degassing, where extracted gases are recycled or repurposed. For example, carbon dioxide could be captured for industrial use, while hydrocarbons might feed into energy recovery systems. Such approaches align with sustainability goals but require additional gas separation and purification stages in the degassing workflow.
In summary, automated degassing integrates precision engineering, real-time analytics, and stringent safety measures to ensure lithium-ion cell performance and reliability. The interplay between puncture mechanisms, vacuum technology, and resealing methods adapts to diverse cell formats while maintaining production efficiency. Continuous monitoring and validation uphold quality standards, making degassing a pivotal step in battery manufacturing.