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Purifying emissions from battery recycling and production

The transition from fossil fuels to greener forms of energy is driving a huge expansion in lithium-ion battery production and recycling capacity in Europe. DESOTEC’s activated carbon filters offer simple and effective solutions to treat air emissions and wastewater in the battery industry.

The market and drivers

By 2040, battery demand from electric vehicles (EVs) produced in Europe is projected to rise to 1 200 GWh per year. For the EU alone, the European Commission’s Green Deal describes batteries as a major pillar for climate neutrality in 2050, not only for battery electric vehicles but also for energy storage from wind, solar and hydropower for use in European national grids. Yet globally, just 100 GWh annual battery production was seen in 2021. However, production capacities of more than 450 GWh per year will be needed from 2030 to achieve the EU targets.

Furthermore, in the past year, awareness has grown of the need to recycle used batteries to avert a future energy crisis. The EU’s Green Deal, the circular economy act and the Battery Directive also enhances the need to quickly develop recycling capacities. A Greenpeace study in late 2020 found that almost 13 million tonnes of EV batteries will come to the end of their lives between 2021-2030. In that time, battery production will consume 30% of the world’s known cobalt reserves, and lithium use will also rise dramatically.

Although the vast majority of large battery production facilities exceeding a battery output of 1 GWh per year (gigafactories) are currently in Asia, Europe is rapidly catching up and is projected to reach 600 GWh by 2030. Concerns about supply chain disruption and sustainability are also prompting European car manufacturers to build battery production and recycling facilities closer to home. At the beginning of 2022, more than 40 gigafactories have been announced to open all over Europe by 2030, whereas more than 50 recycling facilities were planned, also all over Europe.

Polluted emissions

Battery production and recycling both cause contaminated emissions which must be treated before they can be discharged to the environment. In battery production, contaminated air emissions are the bigger issue; while in recycling, both polluted air and wastewater may be a concern.

Important pollutants from battery production and recycling:

  • N-methyl-2-pyrrolidone (NMP) from the coating process;
  • Carbonic acid esters such as dimethyl carbonate (DMC) and ethylmethyl carbonate (EMC) as electrolyte solvents in the cell filling process.
  • Hydrogen fluoride (HF) when the conductive salts e.g. LiPF6 come in contact with moisture or the binder PVDF decays, especially seen in the recycling process

NMP is classified as a substance of very high concern due to its toxicity, and therefore subject to very strict emissions limits, often way below standard VOC limits. To deal with these emissions, companies either have to install an efficient purification set-up or switch to alternative molecules. Today, NMP is the preferred coating solvent for its proven processability. Alternative solvents for the coating process such as triethyl phosphate (TEP) or ethyl acetoacetate (EAA) may be less harmful, although their operability at full scale is not yet proven. Although they are not subject to such strict emissions limits as NMP, they are still of concern to companies on sustainability grounds.

DMC and EMC are less dangerous but highly volatile and photosensitive. Just like the emissions from the coating process, they still have to be removed. HF is corrosive and toxic and should therefore be purified.

Relevant BREFs related to battery recycling

A Best Available Technology (BAT) REFerence (BREF) document does not exist for battery recycling. Therefore, the BREF Waste Treatment (category 16 - Wastes not otherwise specified) may be considered as the relevant source for the Best Available Technologies – Associated Emission Levels (BAT-AEL) for emission control [5,6]. In addition to the general conclusions on emission minimization (BAT 1-25), the BAT of different waste treatment categories may be considered as well, such as those for:

  • Mechanical treatment in shredders of metal waste (BAT 26-28)
  • Treatment of WEEE containing VFCs and/ or VHCs (BAT 29-30)
  • Physico-chemical treatment of solid and/or pasty waste (BAT 40-41)
  • Thermal treatment of spent activated carbon, waste catalysts and excavated contaminated soil (BAT 48-49).

BAT-AEL concentrations are the values that are usually taken over by national legislators and included in the emission requirements for issuing an operating permit. Table 1 illustrates that adsorption of pollutants on granular activated carbon is considered to be one of the best available technologies. It can also be seen, that the emission levels of the aforementioned components of lithium batteries are very low. In most process flowcharts a combination of technologies such as wet alkaline scrubbing followed by activated carbon adsorption is used to reach these low levels.

Table 1: Regulated pollutants relevant in Lithium battery recycling, best available technology and achievable clean gas concentration [6]

Chart

Air emissions

Battery production: There are several stages of the production process which cause contaminated air emissions.

These include: venting of the solvent tanks (NMP, DMC/EMC), the coating of the cathodes (NMP); the injection of electrolytes into the battery (DMC/EMC) and the internal recycling of already filled batteries which generally releases DMC and EMC.

Flow rates vary between the different stages but can be high, even up to 30-40 000 m³/h. Concentrations in these air flows are usually low, at around 2-30 mg/Nm³. However, emission limits of 1 mg/Nm³ NMP and 10 mg/Nm³ DMC/EMC have been observed in the market.

DESOTEC has installed different-sized filters for some of the different stages, namely several Aircon 2000 and 3000, two AIRCON V-XL and Aircon V-L with Airconnect system at European battery production facilities to treat aforementioned emissions.

Battery recycling:

Again, emissions can be released at several stages. The shredding process is a significant source. This entails separating solids from liquids by crushing the batteries into a granulate, then, evaporating acidic gases like hydrofluoric acid and solvents. However, especially when moisture or oxygen is present, acidic gases like hydrofluoric acid or phosphoryl trifluoride are formed e.g. from conducting salt LiPF6 or polymers like PVDF. The organic compounds like binder, foil and electrolytes may lead to a complex decomposition products emission, containing, for example, ethene. Therefore, wet alkaline scrubbers are often employed for removal of HF. Effective removal of the Volatile Organic Compounds can then be achieved through downstream application of activated carbon.

Flowrates are low, usually around a couple of hundred m³/h; but VOC concentrations are high, often around 1-10 g/m³.

The evaporated electrolyte solvents (DMC/EMC etc.) can be condensed and stored in tanks, which release emissions through vents. The dried granulate (often referred to as black mass) contains metals, including aluminium, nickel, cobalt, lithium and also graphite. The metals are extracted from the black mass via thermal or hydrothermal processes. In the latter hydrometallurgical treatment, solvents are used, which can end up in air and water emissions

While today, the recycling focus is first on the heavy metals, the EU Green Deal and the Battery Directive has set ambitious recycling targets to also address lithium. However, many companies also assess feasibility of the recovery of electrolytes and graphite. During the metal extraction process solvents or solubility modifiers may also be used, which may be found in the air emissions. This is another potential application of activated carbon filtration.

DESOTEC can supply either one large filter unit, or a few smaller filters in series. This depends largely on the client’s needs, including the availability of space at the site.

Wastewater

Wastewater pollution can occur during the washing and rinsing of components. Rainwater run-off can also pick up contamination. Because of the high energy nature of the batteries, catching fire is possible and therefore recycling facilities may have cooling or fire extinguish run-offs in the drainage water.

The wastewater will contain a mixture of components of electrolytes, coatings, and cleaning agents, so contamination is measured in terms of overall chemical oxygen demand (COD) levels.

Chemicals

In battery production or recycling, organic solvents or electrolytes that had been evaporated are condensed and fed back into the production. However, with increasing efficiency of that process, less mock-up solvent or electrolyte will have to be employed. This may lead to an eventual enrichment of impurities in the circulated organics, which in turn can have a negative impact on the product. Activated carbon is known to effectively remove impurities in organic solvents like aromatic or halogenated compounds.

The hydrometallurgical separation of Lithium from the heavy metals via hydroxyl precipitation leaves a Lithium sulfate containing brine with organic impurities from the electrolytes, fluorine or phosporus-containing decomposition products measured as TOC, total organic carbon. Filtration of that solution with Activated Carbon before further processing has been proven very promising.

Advantages of DESOTEC solutions

Battery production and recycling are fast-changing and –growing sectors. Technology is continually improving, making it possible both to electrify transport fleets, and to recover increasing amounts of precious components from spent batteries. Knowledge of the carbon footprint of products and operations and compliance within so-called performance categories is clearly mandated in the amendment proposal of the EU Battery directive.

At DESOTEC, we support this sector, and are already supplying filters to two European battery production and recycling facilities. Our filters are ideal for sites that are under pressure to get up and running as swiftly, smoothly and safely as possible. Moreover, we offer low carbon footprint activated carbons and through reactivation of the used activated carbons have clear and reportable visibilities on the carbon footprint of your emission cleaning and product purification step.

Our filters are mobile, so can be installed very quickly. Many alternative technologies, like regenerative thermal oxidisers (RTOs), require several months of planning and engineering, and can be subject to supply chain delays. By contrast, the lead time for our filters is usually a couple of weeks, or sooner in urgent cases. Our varying filter sizes allow for ideal use of space at the customer’s premises. Moreover, volatile prices of natural gas may pose a risk on the operating cost of thermal oxidation treatment systems.

Our filters start working straight away. Activated carbon is a straightforward technology: if contamination is present, the filters will adsorb it. Unlike some alternative technologies, it does not require a steady flow to operate efficiently, so is ideal for new factories where production might stop and start. Once the factory is running smoothly, the filters can be optimised if necessary.

DESOTEC handles all waste, so companies can focus on production. Filter exchanges are simple, and can be carried out with no production downtime. Our technicians then transport the spent carbon away from the customer’s site in the closed filter unit, making for a safe and hassle-free process. It is reactivated at our facilities in Belgium, closing the loop and boosting sustainability. DESOTEC has knowledge of the carbon footprint of all products. As a result, you are future proof for EU’s 2024 requirement of carbon footprint reporting with our mobile filters. 

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