Aluminium-air (Al-air) batteries for cars are an innovative technology that automakers and policy-makers should take a close look at, say Helena Uhde and Veronika Spurná at ECECP. Although a battery, they behave more like an engine: the fuel is the aluminium which reacts with the air via an electrolyte to produce electric power. Al-air has big advantages over a lithium-ion battery, the favoured choice for EVs. It has a travel range similar to that of gasoline powered cars. Its energy density is far higher than a lithium-ion battery. The battery pack is much lighter, opening a door to electric planes too. And aluminium is an inexpensive and abundant metal, unlike lithium. It requires battery swapping, not re-charging, so it faces infrastructure and logistical challenges… as do all the other technologies. But that gets around the grid capacity issues faced by the growth of EVs. However, it lacks policy support, mainly because it’s not officially classed as a battery. With the right policy support and attention from automakers it’s another technology that could become mainstream. Development continues. But, as the article points out, the science has been around for a while: the space shuttle’s solid rocket boosters were powered by aluminium powder.
Accounting for 24% of direct CO2 emissions from fuel combustion, the transport sector is set to play a critical role in the global decarbonisation effort. Almost three-quarters of these emissions derive from road vehicles, while, despite the impact of the Covid-19 pandemic, emissions from aviation and shipping continue to increase. There are a number of alternative fuels and technologies that are cleaner than combustion vehicles, including biodiesel, biogas, electric, hybrid or hydrogen powered vehicles. Another technology that is rarely publicised, but which is believed to have great potential, is aluminium-air (Al-air) battery technology.
Aluminium + air = power
Al-air batteries are an inexpensive, light and powerful source of energy. The formula is quite simple: aluminium + air = power. A reaction of oxygen and aluminium in the air creates electricity and leads to a charge that can be used, for example, in passenger cars. ‘It’s half-way between a battery and a fuel cell. It takes the best bits of both, I like to say’, says Trevor Jackson, a former Rolls Royce engineer and officer in the UK’s Royal Navy who founded Métalectrique, an Al-air battery development company that has got significant media attention in the last couple of years.
Lithium-ion batteries have drawbacks
At present, the world is betting on lithium-ion powered electric vehicles as a way to achieve climate goals. In 2020, the year of the pandemic, almost 1.4 million battery electric vehicles and plug-in hybrids (together also referred to as xEVs) were registered in Europe, 137% more than in 2019. According to Carbon Brief, xEVs produced up to three times lower emissions than conventional vehicles in 2019, with variations depending on electricity sources during manufacturing and charging.
Despite the proven advantages of xEVs, powering the global car fleet with batteries comes with caveats: the life of a battery is guaranteed for between five and eight years; recycling is notoriously difficult (currently the recycling rate is less than 5%); the electricity source may not be clean; and charging xEVs at scale may put strain on the electricity grid. Last but not least, the rare earth minerals required for xEVs pose supply chain risks.
A report published by the European Commission in 2020 on the environmental impact of conventional and alternatively fuelled vehicles concluded that xEVs have significantly lower environmental impact across all vehicle types. However, that impact depends largely on regional and operational circumstances, given that the energy mix varies widely from country to country. Furthermore, the use of copper and electronic components in xEVs continues to represent a challenge to the environment. By contrast, Al-air battery technology promises to address the sustainability, recycling, and sourcing aspects of low-carbon transport.
Al-air technology breakthrough
Almost 20 years ago, scientists predicted that the combination of Al-air batteries and xEVs would be one of the most promising technologies for future passenger vehicles in terms of travel range, purchase price, fuel cost, and life cycle cost. ‘The behaviour of the battery and the cost performance makes it an affordable alternative to fossil fuels,’ says Jackson. Al-air batteries allow a travel range similar to that of gasoline powered cars, currently estimated at 1,600 km per tank. Why has this technology been so slow to come to public attention?
The barriers standing in the way of commercialisation have long been intrinsic to the technology itself: In 2020, scientists were still maintaining that poor performance and high costs for the cathode, anode, electrolyte and other battery components made the technology unsuitable for scalability and commercialisation due to issues such as anode corrosion or pore blockage.
However, Jackson believes he has managed to address those issues: ‘By a happy accident I developed an electrolyte system which seemed to address the main problems. The battery gets the best performance, with an energy density of 1.35kWh/kg at pack level, which is about nine times the energy of lithium-ion batteries.’
How it works
According to Jackson, the best description for the technology is an ‘electric engine’. It is neither a battery nor an engine, but rather an electric equivalent of an engine. In this ‘engine’, the ‘fuel’ is aluminium metal (the anode), which reacts with the oxygen (the cathode) around it to create power. Since the cathode is just oxygen from the surrounding air, there is no need to carry the weight of another metal like a conventional battery, and this makes it considerably lighter.
‘It is a very safe and boring system. It quietly delivers the power constantly until the fuel is gone, unlike with a pre-charged battery where you have to cope with the loss of voltage (and therefore power) as it discharges. This is a particular problem in electric aviation where full power is always required in case of aborted landings. This is why, rather than a battery, it’s more like an engine that uses fuel. We have done tests for 1,500 miles (2,414 km) and power has been constant all the way. And right now, it costs between 29 and 35 euros per kWh for the manufacturer and 0.15 cents per kilometre for the driver,’ he says.
Jackson believes that Al-air batteries are a very appropriate extension for xEVs. ‘In my opinion, people don’t want to wait for an electric car to charge up when they need to go somewhere. Whereas with our battery, we have a 90 second swapping system. Mobility to us is a very important freedom. That’s our philosophy,’ he tells us.
As it stands, the charging infrastructure remains one of the main challenges facing replacement of vehicles using the internal combustion engine with xEVs. A 2018 Harvard study suggests that a more accessible, easy to use, and relatively inexpensive charging infrastructure is needed to ensure the commercial success of xEVs. While battery swapping could greatly reduce the waiting time for xEV drivers, the technology is difficult to implement. On the one hand, the batteries are very heavy and have to be fitted precisely; on the other hand, a battery swapping system requires an evenly distributed network of stations that have access to a reliable electricity supply. Several studies anticipate that unregulated charging of even a small number of xEVs could put significant pressure on the local power grid, potentially leading to overload.
For Al-air batteries, the infrastructure requirements are few. ‘In terms of infrastructure, I don’t think we’ve got a big impact. We don’t need a powered and automated swap machine, but if you do implement automated swapping, normal power supplies to a garage forecourt would have enough power to run a swap machine. Our current system is designed for hand swaps, being based on modules of less than 5kg with a carry handle. For this system, the infrastructure is really just a warehousing and transportation logistics system,’ says Jackson.
Al-air adapters can extend the range of xEV cars
In future, with the purchase of an Al-air adapter, customers could turn their xEV into a lithium-aluminium-air hybrid. ‘We have a 4-year-old EV in our lab that only has about 50 miles of range left. The rest of the car is perfect, everything works really well, but with 50 miles it’s a waste, it’s not really a car. With the extender we can give the car 300 extra miles.
Not only will that make the second-hand market more attractive, but it will also accelerate the sales of new EVs, there’s no doubt about that,’ Jackson tells us. It is likely that the technology could extend not just the range, but also the life of the lithium batteries if the Al-air battery adapter reduces the number of charging cycles.
While the recycling of lithium-ion batteries has yet to be developed for the otherwise environmentally friendly xEV technology, recycling of Al-air batteries could be much easier. Aluminium recycling infrastructure already exists.
Beyond the use of aluminium as a power source for electric vehicles, there are other interesting applications: scrap metal recycling applications could use this technology to recycle the scrap metal from, for example, disused aeroplanes, and generate power at the same time. ‘The scrap business has huge potential and it is a bigger conversation to have,’ says Jackson. Another potential application could be recycling the magnesium and aluminium casings on nuclear fuel rods, which is otherwise a highly radioactive, unusable material. This could then be used to produce green power for use on the nuclear site.
Not just for cars
The use of the Al-air battery in passenger vehicles is just the beginning. The amount of energy that can be generated with Al-air batteries is significant and opens up a wide range of possible uses. ‘A lot of people don’t realise that the space shuttle’s solid rocket boosters were powered by aluminium powder. It’s in fireworks and rockets. It has a lot of energy but it’s about how you get the energy out of it,’ explains Jackson.
Possible uses for this bundled power include the marine sector, such as container ships and cruise ships, airport ground support equipment, and powering rural microgrids. Jackson mentions a project that is under consideration in Ghana, where an Al-air powered transport and local power grid could serve remote areas and enable modern communications to schools, and medical facilities, offering remote areas the opportunity to connect economically with larger population centres.
Why isn’t it catching on?
According to the IEA’s Net Zero by 2050 roadmap, half of CO2 emission reductions by 2050 will come from technologies that are in the prototype or demonstration phase today. This means that promising technologies such as the Al-air batteries need to be commercialised at scale.
But so far it has not been easy for Al-air battery companies to launch even with the technological problems resolved and numerous examples of suitable applications. In general, alternative energies that are not included in the definition of ‘battery’ struggle to obtain funding. For instance, in its ‘Sustainable and Smart Mobility Strategy’, the European Commission (2020) names recharging points for xEVs, as well as refilling points for hydrogen as targets in its ‘recharge and refuel’ flagship project, but currently there is no target for refilling batteries, which could use and provide support for the Al-air battery technology.
A similar outlook is evident in China, where xEVs and hydrogen fuel cell vehicles are defined as New Energy Vehicles (NEV) and receive equivalent support, but alternative greenfield technologies struggle to obtain support.
Getting policy-makers to notice
It is therefore all the more important to talk to the right people who believe in the idea. Trevor Jackson was lucky: ‘When I did a demonstration at the French embassy in London, the director was an engineer and he understood the significance. So, I moved to France and set up our company, Métalectrique SAS. We got the electrolyte verified and I developed the working fluid to a level that would solve the engineering problems that were holding back the aluminium air technology. However, it has been a challenging journey without much policy support because lithium-ion batteries are the preferred technology. Without policy backing for AI-Air batteries, car manufacturers go for the safer choice of lithium-ion batteries, which shapes the market for several years ahead.’
With private investment and some funding from the Advanced Propulsion Centre (APC) in Warwick, in 2012 Jackson founded MAL Research & Development limited, the current company. Years of persistence finally seem to be paying off. ‘We have connected with two very large automotive corporations. We’ve also been approached for planes, defence batteries, and remote power on islands. There are a lot of opportunities coming through, we cannot complain. And in addition to that, we have really good results in the lab now with the experiments we have developed to improve the air breathing material. To give you an example: our battery normally runs at 26°C, but we did some temperature power tests and raised it to 40°C and the power went up 30%! It’s a good time,’ says Jackson with a smile.
Tackling the climate crisis requires a diversity of solutions. In the transport sector, the xEV revolution has been a promising development. Yet decarbonisation efforts could be more effective if other alternative technologies, such as the AI-air battery, were employed to help accelerate the transition started by xEVs. With its large energy density at 8.1kWh/kg and resource abundance, Al-air battery technology deserves more attention if it is to reach its potential.
‘Our technology is on the APC roadmap, but only in 20 years‘ time. We’re actually building it now! Our core technology is at the highest level of technology readiness. And yet they say no, it’s disruptive. Yes, it is disruptive. But it works. If you genuinely want to get to the zero net level, you’ve got to be open minded,‘ concludes Jackson.
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