In short
- Fluorine is the common thread: it comes from the LiPF6 electrolyte salt and the PVDF binder.
- Each process stage produces a different off-gas, so treatment has to be designed stage by stage.
- EU recovery targets mean many pilot lines will need to scale, so the off-gas design should scale with them.
Black mass is the shredded, separated mix of cathode and anode material recovered from spent lithium-ion cells. Turning it into battery-grade metals is a major industrial opportunity across the UK and Europe. It is also a process that releases some of the most aggressive gases we deal with.
This article sets out what comes off each stage of a typical recycling route, so engineers and EHS managers can plan their off-gas treatment early rather than retrofit it after a permit condition or a corroded duct.
Where the fluorine comes from
Researchers at the University of Birmingham, writing for IOM3, point to two main sources of fluorine in a lithium-ion cell: the polyvinylidene fluoride (PVDF) binder and the lithium hexafluorophosphate (LiPF6) electrolyte salt. When LiPF6 meets moisture during disassembly and pre-treatment it can hydrolyse to form hydrogen fluoride. At high temperature, both PVDF and LiPF6 decompose into fluorocarbons and HF, which they describe as needing additional off-gas treatment systems.
Hydrogen fluoride is highly toxic and corrosive. It also attacks glass and silica, which rules out some materials that are common elsewhere in process plant.
What each stage releases
| Stage | What happens | Typical off-gas components | Usual treatment |
|---|---|---|---|
| Discharge and shredding | Cells are opened, often under inert gas or liquid | Electrolyte solvent vapour, HF, fine particulate | Particulate capture, caustic scrubbing; solvents need their own stage |
| Pyrolysis or thermal pre-treatment | Heat drives off binder and electrolyte | HF and other fluorine species, fluorinated organics, CO | Thermal oxidiser for organics, then quench and caustic scrubber |
| Hydrometallurgical leaching | Black mass is dissolved and metals separated | Acid mist, plus SO2, NOx or chlorine depending on the leach chemistry | Packed or multi-stage scrubber with pH and ORP control |
The exact mix depends on cell chemistry, state of charge, and how your process is run, so these are starting points for a design conversation rather than a specification.
Piloting one of these stages now?
Tell us which stage and what you are measuring. We will tell you what the off-gas train needs.
Pyrolysis needs a train, not a single scrubber
Pyrolysis off-gas is hot, carries organics and is rich in fluorine. A caustic scrubber removes acid gases such as HF very effectively, but it will not destroy the organic fraction. The usual answer is a thermal oxidiser to deal with the organics, followed by a quench to bring the gas down to a temperature plastics can tolerate, then a caustic packed tower and a mist eliminator before the fan and stack.
Getting the quench right matters. Polypropylene is commonly rated to around 80°C and PVDF to around 100°C in chemical service, so the scrubber materials and the quench design have to be chosen together.
Engineer's note
On pilot lines the off-gas changes from run to run as cell chemistry and state of charge change. We size for the worst run you expect rather than the average, and fit instruments that log inlet conditions, so the commercial design is based on what the pilot actually saw.
Why scale-up is coming
The EU Batteries Regulation (2023/1542) sets material recovery targets for waste batteries. For lithium, the target is 50% recovery by the end of 2027, rising to 80% by the end of 2031. Cobalt, copper and nickel targets rise from 90% to 95% over the same period.
Those targets are a large part of why so many pilot and demonstration plants are being built now. A pilot that proves its off-gas performance with measured data gives a much shorter route to a permitted commercial plant.
Designing a pilot that has to scale? Our battery recycling page sets out how we approach skid-mounted pilot packages.
See battery recycling scrubbersQuestions to settle early
- Which stages vent to atmosphere, and which can share a scrubber? Incompatible streams should not be mixed.
- Is there solvent vapour that needs an oxidiser or carbon before the scrubber?
- What does your permit regime require you to measure, and where will the sample ports go?
- How will spent liquor containing fluoride be handled on site?
Common questions
Is HF the only problem gas in battery recycling?
No. HF is the most common concern, but pyrolysis also produces fluorinated organics and carbon monoxide, and leaching can release acid mist, SO2, NOx or chlorine depending on the reagents used.
Can one scrubber treat the whole plant?
Sometimes, but often not. Streams with very different chemistry, or that could react together, are better treated separately. We look at each vent before deciding.
Can you work under our NDA?
Yes. Most recycling processes are proprietary, and we are happy to sign your NDA before any process data is shared.