Contributed Commentary by Rick Kreczmer, RoboVent
July 19, 2023 | Nanomaterials are increasingly important for lithium-ion (Li-ion) battery production. But dust control measures that are designed for larger particulate may not provide adequate control for submicron particles. Dust collection system design must account for the unique physical and chemical properties of nanomaterials used in battery production.
Small Particles, Big Problems
Nanomaterials are defined as particles with a size ranging from 1 to 100 nanometers, or less than 0.1 microns. At this size, materials take on unique properties and create new challenges. In particular:
- Nanomaterials are usually a greater health and safety risk than larger particulate of the same material. Submicron particles are more likely to be inhaled deeply into the lungs and have the potential to cross into the blood and other body systems—sometimes even crossing the blood-brain barrier. Carbon nanomaterials used in battery manufacturing can mimic the behavior of asbestos fibers and damage the lungs.
- Smaller particles create a higher risk of combustion. Because of their light weight, nanomaterials are more likely to stay airborne and accumulate in clouds within production enclosures. They also have more surface area to react with oxygen in the air to sustain a combustion reaction.
- Nanomaterials can escape less-than-airtight enclosures and be carried to distant areas in the facility, creating product contamination concerns if they end up in different parts of the production line. HVAC filtration will not remove nanomaterials from facility air.
It is also important to note that research and regulations have not fully caught up with the proliferation of nanomaterials in battery manufacturing and other industries. OSHA permissible exposure levels (PELs) for materials used in battery production (such as cobalt, nickel, silicon, graphite and magnesium or magnesium oxide) have been set based on research into standard particulate exposure and may not reflect the true risks of nanomaterial exposure.
Designing Dust Collection for Nanomaterials
As li-ion battery manufacturers change production processes to include nanomaterials, they will also need to consider updating dust collection systems. There are several aspects of dust collection system design to consider when dealing with nanomaterials.
- Hood design: When working with nanomaterials, it is preferable to capture fugitive dust as close to the source as possible without disrupting production materials. Where possible, applications should be fully enclosed to contain nanomaterials. Applications that cannot be fully enclosed should have a close capture hood designed to capture material before it can escape into the wider facility.
- Capture velocities: Capture velocities must be carefully calibrated when working with nanomaterials. Because the materials are so light, airflow calibrated for heavier materials may pull in usable, settled material in addition to airborne particulate. The capture velocity needs to be high enough to pull in airborne particulate and prevent the accumulation of clouds of materials in enclosures or ductwork, but not so high that it pulls usable material out of production lines.
- Filter selection: Standard dust collector cartridge filters do not have the filtration efficiency required to collect nanomaterial dust. A high-efficiency particulate air (HEPA) filter or even an ultra-low particulate air (ULPA) filter may be needed to capture extremely small submicron material. A progressive filtration strategy uses lower-efficiency (and lower-cost) cartridge filters to remove heavier materials followed by a higher-efficiency after-filter to remove smaller material.
- Use of positive and negative pressure zones: Positive and negative pressure zones may be used to prevent tiny nanomaterials from escaping into the facility or contaminating other parts of the production line. Keeping enclosures or production areas under slight negative pressure will prevent material migration to higher-pressure zones.
- Fire and explosion safety: Because most of the nanomaterials used in battery production are highly energy-dense and potentially combustible, fire and explosion safety in the dust collection system is essential. The dust collection system provides most of the elements necessary for a combustible dust explosion: lots of airflow (oxygen), a buildup of combustible material, and containment of airborne material. Under these conditions, a single spark—perhaps from a motor short or even static buildup within the dust cloud—can set off a dangerous thermal event. Dust collection systems for combustible nanomaterials must be equipped with an NFPA-compliant deflagration system, including explosion venting, isolation valves to contain a pressure wave, and a rotary airlock to prevent collected material from escaping back into the filter chamber. The dust collector should also have a fire suppression system rated for the type of dust, such as a clean-agent gas system or a Class D fire suppression system for metallic dusts.
Proper dust collection system design and engineering will help battery manufacturers address the challenges presented by nanomaterials in production processes. The right engineering partner can help manufacturers protect people and production processes, ensure the safety and quality of products, and respond to evolving regulations around nanomaterial control.
Rick Kreczmer is an industrial air filtration industry veteran with more than 24 years of experience in executive management. As President of RoboVent, he has led the company through new product innovation and market initiatives to lay the foundation for continued growth and profitability in an evolving manufacturing environment. He can be reached at firstname.lastname@example.org.