As the global demand for lithium-ion batteries grows — driven by electric mobility and renewable energy — so does the need for advanced battery recycling technologies. Among the most critical enablers of safe and efficient recycling is vacuum technology. Vacuum technologies play an essential role across several key process steps, from material preparation to solvent recovery and quality assurance.
This article examines how different types of vacuum technologies contribute to the performance, safety and environmental integrity of modern battery recycling. Rather than proposing a one-size-fits-all solution, the article highlights the specific vacuum requirements of five different process stages and discusses the advantages and limitations of available solutions.
Image Source: Busch Vacuum Solutions
1. Enhanced safety in shredding
After the used battery has been fully discharged, it is shredded to break down the components. Shredding used batteries can be hazardous, due to the volatile nature of the liquid electrolyte and other materials. Sparks during shredding can ignite the electrolyte, leading to potentially explosive conditions.
Dry vacuum pumps: claw and screw technologies. Dry vacuum pumps, such as claw and screw vacuum pumps, are often the first choice for creating an inert and contaminant-free atmosphere in the shredding process. They effectively evacuate ambient air to allow the injection of inert gases like nitrogen, which drastically reduces the risk of ignition. Due to their oil-free operation, they are insensitive to contamination of the operating fluid by process gases, depending on the gases introduced. It makes them ideal where cleanliness and gas purity are essential.
Additionally, dry vacuum pumps are energy-efficient, especially in continuous operation, due to the absence of sealing liquids or oils. However, they come with certain limitations: exposure to corrosive vapors or particulates released during shredding may lead to wear unless corrosion-resistant coatings or materials are used. Furthermore, the initial investment is typically higher than for vacuum pumps running with an operating fluid, such as oil-lubricated or liquid ring vacuum pumps.
Liquid ring vacuum pumps: robust handling of wet gases. When transitioning from dry gas to vapor handling, liquid ring vacuum pumps become relevant. These vacuum pumps are excellent at managing the wet gases that emerge during the shredding process. Their lack of small gaps (and therefore lack of mechanical friction) makes them easier to assess in terms of ignition risk.
While liquid ring vacuum pumps generally consume more energy than dry vacuum pumps of comparable size when handling non-condensable gases, they can be more energy efficient when pumping condensable vapors, because the condensation within the liquid reduces the gas volume to be evacuated. This allows for smaller vacuum-pump sizing and lower energy consumption. However, they require the management of operating fluids, which can be a drawback in terms of operational efficiency and environmental impact.
Oil-lubricated rotary vane pumps: a compromise solution. Positioned between dry and liquid-based technologies, oil-lubricated rotary vane vacuum pumps present a pragmatic solution for the shredding process. They are mechanically simple, cost-effective, and capable of handling moderate vapor loads while delivering stable vacuum levels.
However, their reliance on oil introduces risk of contamination and necessitates additional components like oil mist filters and regular maintenance routines. Moreover, they are less suited for explosive atmospheres or applications demanding absolute cleanliness, limiting their use in direct contact with volatile shredding environments.
Consideration of ATEX requirements. In potentially explosive shredding environments, the use of ATEX-certified vacuum systems or vacuum pumps may be required to mitigate ignition risks and ensure compliance with European safety directives. However, ATEX certification is not necessarily mandatory. The responsibility to perform a comprehensive risk assessment and decide on the necessity of certified equipment rests with the operator. Depending on process-specific hazards, such as the concentration of flammable gases or the potential for spark generation, ATEX-certified solutions can offer an additional layer of safety and legal assurance. The choice of vacuum pump must align with the specific operational and safety requirements of the shredding step — factoring in gas composition, flammability risk, environmental controls and cost structure.
2. Efficient electrolyte removal during drying
The drying phase is crucial for removing the electrolyte following the shredding process. Vacuum drying lowers the boiling points of volatile components, facilitating evaporation at lower temperatures. The achievable base pressure of a vacuum system is fundamentally limited by the pumping principle of the technology used; to reach deeper vacuum levels — especially for removing solvents with low vapor pressure — it is often necessary to combine different vacuum technologies, because individual vacuum pumps tend to lose suction performance near their ultimate pressure.
Oil-lubricated rotary vane pumps: cost-effective solution. Rotary vane vacuum pumps can typically reach ultimate pressures between 0.1 and 1 hPa (mbar), offering a good balance between performance and cost for moderate drying requirements. Rotary vane vacuum pumps are available in single-stage or multi-stage versions. Multi-stage versions can reach a lower ultimate pressure, but these versions encounter more problems with condensation because there is less oil per chamber.
Liquid-ring vacuum pumps: vapor-tolerant and chemically robust. Limited by the vapor pressure of the sealing liquid (typically water), liquid ring vacuum pumps achieve ultimate pressures around 30 hPa (mbar), depending on operating temperature and fluid management. This makes them suitable for pre-drying or bulk vapor removal.
Dry screw and claw vacuum pumps: clean and high performance. Among all vacuum technologies considered (except dual-stage rotary vane vacuum pumps), dry screw vacuum pumps achieve the deepest vacuum levels, capable of reaching pressures below 0.01 hPa (mbar).
Due to their relatively high ultimate pressure (10-60 hPa (mbar)) and limited tolerance for condensable vapors, single-stage claw vacuum pumps can be ruled out for drying applications where deep vacuum and solvent handling are critical. However, a two-stage version of the claw vacuum pumps allows for pressures lower than 10 hPa (mbar) and can therefore be considered.
Vacuum boosters: extending vacuum performance. To overcome the pressure limitations of the primary vacuum pumps previously mentioned and to maintain a defined pressure, vacuum boosters can be added upstream of the main vacuum stage. Vacuum boosters are dry, positive-displacement vacuum pumps. Their main task is to increase the pumping speed at working pressure. They increase the available pumping speed in lower pressure ranges where the efficiency of the backing pumps is already decreasing. When properly configured, the combination of booster and backing pumps can significantly enhance pumping speed and enable the system to reach much lower pressures than the backing pump alone — often by an order of magnitude. However, the achievable performance strongly depends on the specific ratio between the booster and backing pump, which must be carefully matched to process parameters such as gas composition, expected throughput, operating temperatures and pressure setpoints. The design of the booster separates the gearbox and bearings from the vacuum chamber, allowing oil-free, contactless operation. Single-stage vacuum boosters cannot be used directly against atmospheric pressure, as too-high pressure differences can cause overheating and lobe expansion. To prevent this, booster systems require a bypass control during startup to prevent overload and ensure system protection.
Consideration of ATEX requirements. As with other steps in battery recycling, compliance with ATEX directives is not automatically required, but depends on a risk analysis performed by the operator. If ATEX is required, the system must be considered as a whole.
3. Improved purity through vacuum distillation
Following the drying process, the vaporized electrolyte must be condensed and purified for reuse. Vacuum distillation enables this by separating electrolyte components based on differences in their boiling points — without requiring extreme temperatures that might degrade sensitive substances. This process step requires stable, deep vacuum levels and high chemical resistance, especially when dealing with complex electrolyte mixtures.
Both dry and wet vacuum technologies play critical roles in enabling efficient and precise separation, depending on the specific system design, required vacuum depth and tolerance to chemical or thermal stresses.
Oil-lubricated rotary vane vacuum pumps. Rotary-vane vacuum pumps can be a viable option for vacuum distillation, offering stable performance and competitive acquisition costs. However, their use is limited by the sensitivity of the operating fluid (oil) to contamination from process media. Chemical compatibility must be carefully evaluated, as exposure to aggressive or condensable vapors can degrade the oil, increase maintenance needs and compromise vacuum performance. Therefore, their applicability is restricted to media that do not adversely interact with the lubrication system.
Dry screw and claw vacuum pumps: clean and controlled separation
Dry screw vacuum pumps are the most effective dry technology for vacuum distillation. They achieve deep, stable vacuum levels critical for lowering boiling points and enabling precise separation without thermal decomposition. Their oil-free operation eliminates the risk of contamination, making them ideal for high-purity recovery of valuable electrolyte components.
Dry claw pumps, while also oil-free and low-maintenance, cannot reach the same vacuum depths as screw vacuum pumps. As such, they are better suited for preliminary vacuum generation or systems where ultimate pressures of around 20 hPa (mbar) are sufficient. Their simplicity and energy efficiency make them a viable option where deep vacuum is not essential, and they still provide contaminant-free operation that supports high process purity.
Liquid ring vacuum pumps: thermal buffering and vapor tolerance. The general advantages and limitations of liquid ring vacuum pumps have been discussed in the context of shredding and drying. In distillation, their strengths remain relevant — particularly in condensation stages with high solvent content or chemically aggressive media. Their ability to tolerate liquid carryover and stabilize volatile mixtures makes them a practical choice in systems with fluctuating process loads. However, for applications requiring deeper vacuum or higher energy efficiency, their use should be carefully evaluated. The performance advantages of vacuum boosters, particularly in achieving deeper vacuum levels and faster evacuation, have been outlined earlier. These benefits also apply to distillation, where system throughput and pressure stability are critical.
4. Advanced process monitoring in battery recycling
Process monitoring is a critical aspect of refining battery-recycling methods to ensure efficiency and sustainability, particularly when handling complex chemical reactions within thermal treatment processes, such as pyrolysis. One of the key tools in this monitoring is the residual gas analysis (RGA). RGA is a method used to determine which gases are present in a system and in what quantities. It relies on mass spectrometry, where molecules are ionized, and the resulting ions are sorted by their mass-to-charge ratio (m/z) using a quadrupole mass filter. In battery recycling, RGA is employed to analyze the gas phases emitted during the recycling process. This technology enables real-time surveillance and control by identifying and quantifying the gases released, which are indicators of the chemical reactions occurring within the system. Through this analysis, it is possible to gain a deep understanding of the process dynamics, which aids in the optimization of the recycling method and equipment. Mass spectrometry supports the identification of hazardous or corrosive substances, ensuring environmental compliance and worker safety. It also helps in adjusting process parameters to improve efficiency and throughput, leading to a more refined and controlled recycling operation that maximizes material recovery and minimizes harmful emissions.
5. Ensuring system integrity through leak detection
Ensuring high process integrity plays an important role to prevent hazardous conditions and ensure optimal recovery rates. A key component of maintaining high integrity is rigorous leak testing to confirm the tightness of recycling chambers and equipment. The process begins with pressure decay testing, which serves as an initial indicator for potential leaks. This method involves pressurizing a system, then measuring the pressure decrease over time. If the pressure drops beyond a pre-defined threshold, it indicates a potential leak. For pressure decay testing, vacuum gauges provide accurate and reliable measurements to detect any drops in pressure that could signal a leak.
Following a pressure decay test, tracer-gas leak detection is employed to precisely quantify the leak. Tracer-gas leak detection is highly sensitive and suitable for detecting even smallest leaks. A tracer gas, such as helium or hydrogen, is introduced into the system, and a leak detector with an integrated mass-spectrometer analyzer cell identifies and quantifies any escaping gas. The use of helium is particularly effective, due to its small molecular size and inert nature, which allows it to quickly pass through leaks without reacting with the materials involved.
Together, these methods provide a comprehensive approach to maintaining high process integrity in battery recycling facilities.
Conclusion
The integration of vacuum technology in battery recycling processes addresses multiple challenges associated with safety, efficiency and environmental impact. By enhancing process safety through inert atmospheres, enabling efficient material separation via controlled vacuum levels, and ensuring system integrity through advanced leak detection, vacuum technology is at the forefront of driving sustainable practices in battery recycling. As the industry continues to evolve, the role of vacuum technology will expand, further embedding its significance in the sustainable life cycle management of battery technologies. ♦
Edited by Mary Page Bailey
Author
Bastian Schöchert works for Busch Vacuum Solutions as a Market Coordinator for Batteries and Carbon Capture Technologies. Within this position, he helps customers from the battery industry, including battery recycling, to successfully solve demanding vacuum and leak-detection challenges.