Battery recyclers have their head in the clouds

E-mobility is one of the most impactful trends of our time, changing how we transport people and goods. E-cars, e-buses and e-bikes are a familiar sight. The next stop: electrifying the global aviation industry.

It is a tall order, especially for recyclers, insists Dutch aircraft recycling expert Derk-Jan van Heerden. He ran the company AELS for over 20 years before starting the Aethos Foundation, highlighting aircraft recycling breakthroughs and bottlenecks. ‘Reuse of components and metal scrap recycling is already very successful,’ van Heerden says. ‘I want to make sure that what remains, such as batteries, also finds its way back into the loop. Batteries are already essential for aircraft.’

Multi-billion potential

He co-wrote a report on the topic with start-up Back to Battery. Their findings include there is no ‘one size fits all’ solution for end-of-life batteries, least of all in aviation. That is partly because aeroplanes use various battery types and sizes depending on the aircraft. They contain the following:

• Main and auxiliary power units (Aux/APU) to start the engines and supply back-up power for critical equipment and flight control instruments.
• Emergency equipment such as locator beacons, flight data recorders and cockpit voice recorders, commonly known as the black boxes.
• Mobile devices for the crew, such as torches and communication devices with cells in memory circuits.

‘At the moment, e-flying mostly applies to drones and is in the development phase for small two-seaters or for short-haul flights or lessons,’ Van Heerden observes. Batteries keep them in the air for up to three hours. A NASA pilot project has carried up to four people for 40 minutes. Other trials by Heart Aerospace and Eviation Alice have flown 10 passengers and crew for 300km.

Last available data from SkyQuest puts the market value of the global aviation battery recycling sector at EUR 1.3 billion in 2024. The figure will likely reach EUR 4 billion by 2032. Meanwhile, the electric aircraft sector was worth EUR 14.6 billion, estimated to reach almost EUR 35 billion by 2032, according to analysts at Market Research Future.

Reuse and recertification

‘Aircraft that are scrapped have a lot of reusable parts. Since every flight requires a fully functional Aux/APU battery, for example, these are always in good condition.’ Van Heerden explains they are typically sold for reuse after first passing a strict testing procedure to check every cell. Good cells are reused while poor ones are replaced with a refurbished battery module or pack.

At regular intervals during their lives, aircraft batteries are also tested, known as Part 145 certification, during maintenance. ‘The odds are almost zero that these aviation batteries cannot be re-certified, which is arranged by a dedicated certification specialist,’ the recycler explains. ‘Once in a while, batteries don’t pass the test and are sent off to be destroyed – or recycled – by an expert in the area.’

OEM Saft, based in France, advises replacing the battery if five cells or more are in an insufficient state of health. ‘Replacing all cells is not economically viable and therefore the battery is considered beyond repair,’ explains the company, which holds an 80% market share in the nickel-cadmium segment.

Market analysts predict the aircraft battery reuse market will see 15% compound annual growth in the period 2023 to 2033. This reflects the rising appeal of the multi-billion-Euro parts reuse sector.

Overcoming recycling obstacles

Various factors limit the recycling of aviation batteries, including:

• Metallic lithium reacts violently with water to form hydrogen gas
• Thionyl chloride (SOCl₂) is highly reactive and corrosive, also posing significant hazards
• Li-SOCl₂ batteries are typically used in niche applications and produced in small quantities, offering limited opportunity for a viable business model
• Recycled products have limited economic value so a viable business model depends on subsidies or gate fees

‘Something I found surprising is that that our study confirmed that batteries inside cockpit voice recorders and flight data recorders are not yet recyclable,’ Van Heerden says. ‘They’re legacy products that contain old technology. It’s not commercial to treat them.’

The recycler argues the best solution for aircraft batteries is up for debate as ‘battery’ in this setting is an ‘oversimplification’. For Pb-acid batteries and NiCd the only option is a pyrometallurgical process, while for NiMH and Li-ion both pyrometallurgical and hydrometallurgical routes are possible.

The latter requires extensive pre-treatment, including discharging, dismantling, electrolyte removal, shredding and physical separation.

Which route?

Aethos’ report points out that the first-generation sulphate hydro-processes solve one problem but create a new one. In this case, it is the production of sodium sulphate (Na₂SO4), which represents about 1 kg of waste per kg of battery. ‘With the rapid growth of the battery market to support the energy transition, it has become a huge waste stream,’ Van Heerden laments.

It is also expensive to deal with because it requires an energy intensive crystallisation step. Crystalised Na₂SO4 is difficult to landfill because it is highly soluble in water. However, next generation hydrometallurgical technology pioneered by Back To Battery eliminates the production of sodium sulphate (Na₂SO4) by using closed reagent cycles to minimise chemical use.

For lithium-based metal batteries, such as lithium thionyl chloride, no sustainable recycling option is yet available. End-of-life batteries are piling up in expensive containers designed to mitigate risks associated with storage of these batteries, notably fires.

‘It’s clear that recycling technology needs to evolve and adapt to the times,’ Van Heerden concludes. ‘The advantage of recycling is that we know what is put on the market and we have the lifetime of the product to find a solution before large volumes reach the end-of-life. On the other hand, production scrap, prototypes and warranty recall need an earlier solution.’