A long-standing method for cryogenic solvent recovery could become a crucial part of the lithium battery recycling process, says Jon Trembley, technology manager, Cryogenic Applications, from Air Products.

Europe’s EV battery recycling industry is developing quickly as it makes significant progress in working towards ambitious 2030 targets for the recovery of valuable metals such as nickel, lithium and cobalt. However, an unresolved challenge remains: managing and recovering the harmful solvent
vapours released during these battery recycling operations.

Over the next decade, the global volume share of end-of-life batteries from light electric vehicles that will be available for recycling instead of reuse will increase dramatically from 27% to 79% in 2035. The abatement and recovery of the solvents released during this mass recycling operation will become a critical priority across the industry, both for the environment and the development of a circular battery economy.

Battery recycling plants are already grappling with the harmful emissions generated when batteries are cracked open, with current regulations primarily requiring them to monitor rather than mitigate them. This has revealed that a range of harmful solvents are being released into the atmosphere, a concern that is likely to drive future regulatory action as the drive towards a circular, sustainable recycling economy intensifies.

A proven method for recovery and abatement of harmful solvent vapours is already well established. Cryogenic condensation, widely used to capture and recycle solvents from appliances such as refrigerators, offers a promising solution for the battery recycling sector. There is now strong potential to adapt this well-established technology as the battery recycling industry comes to terms with its latest challenge.

The challenges of recycling solvents in EV batteries

The three main processes for recycling EV car batteries – pyrometallurgical, hydrometallurgical, and direct recycling – all raise environmental concerns when it comes to solvent emissions.

Pyrometallurgical recycling, which relies on high-temperature smelting, not only emits significant CO₂ but can also release toxic solvent vapours into the atmosphere. Hydrometallurgical recycling, while less carbon-intensive, uses strong acid solutions to extract valuable metals. This process generates hazardous liquid waste and, if not properly controlled, can also release harmful solvents into the environment.

The most pressing concern arises from recycling the electrolyte, a key component of EV batteries made up of lithium salts such as lithium hexafluorophosphate (LiPF₆), dissolved in organic solvents. These include dimethoxyethane (DME), dimethyl carbonate (DMC), 2-methyltetrahydrofuran (2-Me-THF), and ethyl methyl carbonate (EMC). All are volatile, and present significant operational and environmental hazards, as confirmed by monitoring of such a recycling operation using a Fourier Transform Infrared (FTIR) analyser. A monitoring study carried out by Air Products was set-up with a reference spectrum for 13 different compounds, all of which were measured and present a significant environmental hazard. The FTIR analyser also indicated other additional compounds present in the process gas stream.

Additionally, shredding processes that apply high temperatures to remove solvents can trigger dangerous chemical reactions. When fluorinated electrolytes, such as those containing LiPF₆, come into contact with air and moisture, they can form hydrogen fluoride (HF) gas – a highly toxic and corrosive compound that poses severe risks to both workers and the environment. Without strict containment and emission controls, these recycling methods can lead to significant air and water pollution.

Adapting a long-standing proven method for recovery and abatement

Given the release of harmful solvent vapours in the battery recycling process, there is growing interest in using cryogenic condensation as a recovery and abatement method. This has been used since the 1980s and has become the leading method for recycling solvents from white goods with over 50 sites located across the world.

Abatement methods using controlled temperatures and pressures already exist. For example, Duesenfeld, a German battery recycling company, employs a proprietary temperature vacuum process to recover solvents from lithium-ion batteries. However, this is only effective for 90% recovery and further treatment technology will be required to achieve and meet the required environmental limits. For small scale battery recycling operations working at lower rates of throughput (<2T/hr), spent carbon may be an acceptable and economically viable alternative to treat the final 10%.

However, in large scale recycling plants operating at rates around 4-10T/hr, the use of spent carbon will not be suitable for the remaining 10% of solvents. Cryogenic condensation is a process familiar to larger scale recycling plants for white goods and refrigerators. Liquid nitrogen is used in a heat exchanger to indirectly cool down the process gas released during battery recycling processes. This cooling causes volatile organic compounds (VOCs) in the gas phase to condense, allowing them to be collected by a sorting system. The process also produces inert gases that can be further utilised within the recycling process. Combined with the use of molecular sieves this process can achieve 99.99% solvent recovery rates.

Cryogenic systems have proved highly adaptable and work well not only for new plants but as ‘add-ons’ to existing recycling plants, with systems tailored to the size and requirements of the plant’s battery throughput. Cryogenic condensation is effective at recovering a wide range of volatile organic compounds and organic solvents, particularly those with relatively high vapour pressures and low boiling points.

In the context of EV battery recycling, it can be used to capture and recycle key electrolyte solvents that are released during recycling. These include dimethyl carbonate (DMC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC), all harmful solvents that have been measured at recycling sites.

As the volume of spent batteries being recycled increases from a variety of different markets, there will likely be some uncertainty regarding the exact composition of solvents released during the process. To ensure effective emission control, recycling plants will need to analyse their gas emissions and adjust their cryogenic condensation systems accordingly.

Portable FTIR measurement technology has been successfully used in solvent recycling to identify the full spectrum of emitted solvents. Using this data, recycling facilities can accurately model solvent compositions and design abatement systems that integrate both cryogenic condensation for solvent recovery and dry scrubbing for final purification.

Next stages in the abatement and recovery of solvents from lithium batteries

While EU Battery Regulation (2013/56/EU) primarily focuses on recycling efficiency and reducing hazardous substances, it does not yet impose strict emission limits for solvents released during the recycling process. In the absence of a dedicated framework – such as WEEELABEX for battery solvent emissions – Germany’s TA Luft (Technical Instructions on Air Quality Control) currently serves as the prevailing standard.

Yet, as awareness of harmful solvent emissions increases and the battery recycling industry scales up to meet the dramatic increase in throughput, the industry will need to adopt more advanced emission monitoring and mitigation strategies. Cryogenic condensation, in combination with scrubbing, presents a particularly effective solution due to its ability to capture and recover a broad range of solvents as an add-on process to existing plants.

These techniques not only minimise environmental impact but also improve the economic viability of battery recycling by enabling solvent reuse. By integrating this long-standing industry proven technology, recycling facilities can proactively align with future regulatory demands, reduce hazardous emissions, and contribute to a more sustainable and circular battery industry.