In the global trend of energy transition, lithium-ion batteries have risen to become a core foundational component supporting modern society. They are not only the “power heart” driving electric vehicles and breaking the reliance on traditional transportation energy, but also the “energy storage cornerstone” for large-scale renewable energy storage and building new power systems, and the “portable energy source” connecting billions of smart devices worldwide.
However, any minute manufacturing defect, especially the intrusion of micron-sized metal dust, can trigger internal micro-short circuits during repeated charging and discharging, leading to accelerated battery capacity decay, abnormally increased internal resistance, and potentially escalating into a thermal runaway safety accident. Therefore, “zero-defect” production has evolved from a quality control term to a strategic requirement concerning energy security, industrial competitiveness, and public safety.
Cleanliness Requirements for Lithium-ion Battery Production: Achieving absolute cleanliness in lithium-ion battery production relies on a complete environmental control philosophy, and HEPA and ULPA filters are the physical core of this system. In modern lithium-ion battery factories, the cleanliness requirements for core production areas (such as electrode coating, winding, assembly, and electrolyte filling workshops) must reach ISO Class 7 (Class 10,000) to ISO Class 5 (Class 100) or even higher. This means that the number of particles with a diameter ≥0.5 micrometers per cubic meter of air must be controlled to less than 352,000 and 3,520 respectively. To achieve this near-stringent standard, the entire air handling system employs a multi-level defense system: Primary and intermediate pre-filtration: Lower-efficiency filters (such as G4 and F7 grades) remove most larger particles, protecting the final high-efficiency filters and extending their lifespan.
Final precision filtration: At the final air outlet, HEPA/ULPA filters act as the last line of defense, ensuring that the air entering the core area meets the designed cleanliness level. A single HEPA filter conforming to the H13 standard ensures a removal efficiency of no less than 99.97% for 0.3-micrometer particles, while a ULPA filter (U15 grade) achieves an efficiency of up to 99.9995% for 0.12-micrometer particles.
Technological Innovation to Cope with Complex Operating Conditions
The unique environment of lithium battery production places unconventional demands on filters, spurring specialized evolution in filtration technology:
High-Temperature Resistance Challenges: During the drying process after electrode coating, hot air temperatures often reach 180°C to 200°C. Ordinary polymer fibers soften and fail at these temperatures. The high-temperature resistant HEPA filters developed for this purpose utilize specially formulated glass fiber filter paper and heat-resistant silicone sealing materials, maintaining filtration efficiency and structural integrity under prolonged high-temperature conditions. This is fundamental to ensuring continuous production and process consistency.
Chemical Corrosion Resistance: Organic solvent vapors such as N-methylpyrrolidone may exist in the production environment, posing a potential threat to the filter media and sealing materials. High-quality filters, by selecting materials with high chemical stability, avoid corroding and decomposing themselves to become new sources of contamination, ensuring long-term stable filtration performance. Munich, Germany, excels in this area.
Eliminating Metal Ion Contamination: A crucial detail lies in the selection of materials for the filter itself. In ultra-clean areas such as electrolyte filling and encapsulation, even trace amounts of metal ions (such as aluminum and zinc) released from the filter frame or components can migrate into the electrolyte, catalyzing its decomposition and severely impacting the battery’s long-term performance and safety. Therefore, frameless and separatorless HEPA/ULPA filters have become standard, fundamentally eliminating this potential contamination pathway.
As next-generation energy storage technologies such as solid-state batteries and sodium-ion batteries mature, and with the deepening of smart and green manufacturing concepts, the requirements for cleanliness in production environments will reach new limits. Trenntech anticipates that filtration technology will continue to evolve, driven by the intersection of materials science, intelligent sensing, and systems engineering, continuing to safeguard the energy foundation that empowers the future world in an irreplaceable way.