Battery Cell Finishing Dust Control

Failing to maintain a clean, dust-free environment for cell finishing processes can lead to several problems, including: 

• Short circuits: Dust particles can cause short circuits between the electrodes and the separator, which can lead to reduced battery performance or even failure.
• Reduced insulation: Dust particles can also reduce the effectiveness of the insulation between the positive and negative electrodes, which can lead to reduced battery life or even a safety hazard.
• Contamination of electrolyte: Dust can contaminate the electrolyte, which can impact the chemical reactions that take place within the battery. This can lead to reduced battery performance or even failure.
• Reduced efficiency: Dust particles can also cause an increase in resistance within the battery, which can lead to reduced efficiency and lower overall performance.

Cell finishing looks different for each type of battery. Generally speaking, cell finishing refers to the final manufacturing steps that are performed on individual cells to ensure their quality and reliability. The finishing process is critical to the performance and safety of the battery. Depending on the battery type, these processes may include: 

• Roll pressing: Li-ion pouch batteries undergo a roll-pressing process, in which the electrodes are stacked with the separator and passed through a set of steel rollers. This process ensures good contact between the electrodes and separator, improved structural integrity and reduced internal resistance. 
• Formation: Most battery types—including Lithium-Ion, Nickel-Cadmium, Alkaline, and Lead-Acid—must go through a formation process to ensure safe and consistent performance over their lifetime. This step involves cycling the cell through several charge and discharge cycles to activate the electrode materials, stabilize battery performance and ensure that the battery operates at its rated capacity.
• Degassing: For Li-ion pouch batteries, degassing is an important step in the finishing process. Degassing involves removing any excess gas from the battery to ensure that it operates safely and reliably. During the manufacturing process, small amounts of gas—including hydrogen (H2), carbon dioxide (CO2), and volatile organic compounds (VOCs)—can be generated within the battery, which can cause swelling and potentially lead to safety hazards. The primary gas captured during degassing is hydrogen gas, which is highly flammable and can be hazardous if not properly handled. Degassing generally involves placing the battery pouch in a vacuum-sealed bag connected to a vacuum pump, which goes through several cycles of pressurizing and depressurizing to collect gases.
• Sealing: After the formation process, the cell is sealed to prevent leakage and maintain the integrity of the cell. The sealing process depends on the type of battery and may involve heat-sealing, crimping, or other methods. 
• Tab welding and terminal attachment: The cell is fitted with metal tabs that are used to connect the cell to external devices. The tabs are typically welded onto the cell using a laser or ultrasonic welding process. After the tabs are welded, a Li-ion cell is fitted with a terminal block for easy connection to other cells or battery packs. These processes will generate some weld fume, which may require a fume collection system.
• Insulation and labeling: The cell is fitted with an insulating sleeve and labeled with relevant information, such as the cell model and capacity.

• Exposure to hazardous chemicals such as solvents, acids and other chemicals used in the electrolyte solution. Workers may be exposed to these chemicals through inhalation or skin contact, which can lead to health effects such as respiratory irritation, skin irritation, and chemical burns.
• Exposure to toxic weld fumes created during tab welding and terminal attachment. Laser welding can create very tiny particulate that can be inhaled deeply into the lungs, creating health problems such as lung and respiratory system irritation, metal fume fever, kidney and neurological damage, and cancer.

• Worker health and safety: The Occupational Health and Safety Administration (OSHA) sets legally enforceable Permissible Exposure Limits (PELs) for respirable materials in the U.S. That means employers must keep exposure levels for regulated materials below the PEL for all workers at all times. Manufacturers can find the PEL specific to the materials they are working with in OSHA’s Annotated PEL Tables. Manufacturers should also be aware of Threshold Value Limits (TLVs) from the American Conference of Governmental Industrial Hygienists (ACGIH) and Recommended Exposure Limits (RELs) from the National Institute of Occupational Safety and Health (NIOSH). Though these (often lower) limits do not carry the force of law, many manufacturers choose to aim for the lower thresholds to ensure worker safety and prepare for future regulatory changes.
• Environmental protection: Emissions produced during battery manufacturing may be subject to Environmental Protection Agency (EPA) regulations, including the Clean Air Act, Clean Water Act, and Resource Conservation and Recovery Act (RCRA). These rules govern how hazardous materials are handled and stored, how waste material is disposed of (including particulate collected in the dust collection system), and how much material may be emitted into the atmosphere.
• Fire and explosion protection: If dust and emissions produced during battery cell finishing are combustible, manufacturers must also comply with OSHA and National Fire Protection Association (NFPA) standards for handling combustible materials. This includes standards for dust control and dust collection system design, which manufacturers are legally required to follow in most jurisdictions. Combustible dust is likely to be a bigger problem at other stages of battery manufacturing; if there is enough dust to create a combustion risk, the environment is nowhere near clean enough for battery finishing processes. However, hydrogen gas collected during degassing is highly flammable. Systems for collection of hydrogen gas must comply with all NFPA standards for handling flammable and explosive gases.

Before designing a dust collection system, it is important to consider several elements, including the type and volume of dust (and where it is coming from), the requirements of the manufacturing environment, and any constraints on system design. Some considerations include: 

• Cleanroom isolation: One of the most important elements is preventing dust from earlier manufacturing processes from migrating into the cleanroom environment. This may require a combination of physical barriers or enclosures and the use of positive and negative pressure zones to keep dust from moving from dirtier spaces into cleaner ones.
• Filtration selection: Filters selection is also very important when designing a dust containment system for sensitive battery applications. Dust particles may include highly charged, ultrafine dust and nanomaterials used in electrode production. Specialized antistatic filters and HEPA filtration may be required to effectively control battery dust. 
• Gases and vapors: Dust from battery cell assembly and finishing processes may be mixed with aerosols, gases and vapors from the electrolytes and manufacturing processes, such as volatile organic compounds (VOCs) and hydrogen gas that must be collected during degassing. Specialized molecular filtration strategies, such as activated carbon filters, may be required to control gaseous emissions and aerosolized vapors.
• Space constraints: Battery cell finishing lines can have limited space for installing large-scale dust control systems. Designing compact and efficient dust collection equipment that can be easily integrated into the assembly line is essential.