A quiet revolution is unfolding in the world of electric aviation — one that promises to rewrite the rules of flight endurance, efficiency, and affordability. This revolution centers around an extraordinary technology that has recently caught the attention of the UK Ministry of Defence: the Aluminium-Air (Al-Air) battery. Unlike many battery technologies still trapped in laboratories, Al-Air batteries are here, being tested in real-world aviation scenarios.
The Long Quest for the Right Battery
For years, aircraft manufacturers have been held back by one major challenge — finding the right battery. While some pinned their hopes on incremental improvements in lithium-ion (Li-ion) batteries, others awaited the elusive breakthrough in solid-state technology. The problem? Energy density.
Elon Musk famously remarked in 2020 that electric aircraft would only surpass fossil fuel performance if batteries reached 400 Wh/kg energy density. Since then, the world has been waiting. Li-ion batteries have inched closer but remain stuck around 300 Wh/kg. Alternatives like lithium-silicon and lithium-sulfur have shown promise but suffer from practical limitations — low cycle life, expansion issues, and high degradation.
Enter Aluminium-Air: A Game-Changer
Aluminium-Air batteries quietly stand apart from this crowd. Boasting an energy density upwards of 1200 Wh/kg, and with potential to reach 2000 Wh/kg, they offer more than four times the energy storage of the best lithium-ion batteries. Despite being around since the 1960s, they’ve remained largely overlooked due to several historical drawbacks: non-rechargeability, toxic electrolytes, high costs, and limited efficiency.
However, recent advancements have tackled these limitations head-on:
- Non-toxic electrolytes have replaced harmful chemicals.
- Lower purity, cheaper aluminium alloys can now be used.
- Significant improvements in coulombic efficiency.
- Emerging swap-and-go battery pack models that eliminate the need for recharging.
Practical Advantages Already in Flight Testing
In India, 25 kWh Al-Air battery packs have been built weighing just 15 kg — translating to an impressive 1666 Wh/kg at the pack level. These packs do not require cooling systems and offer a unique benefit: they are safe, with no risk of thermal runaway thanks to water-based electrolytes.
Costs are also encouraging. Despite slightly higher running costs (mainly due to aluminium production energy demands), Al-Air batteries offer a cost-per-mile lower than fossil fuels — approximately half the cost of diesel or petrol.
Aluminium-Air: Transforming Aviation Possibilities
In aviation, where weight is paramount, the ultra-lightweight nature of Al-Air batteries makes them ideal. While traditional batteries offer flight times of 15-20 minutes in personal aircraft like the Jetson One or Pivotal Helix, Al-Air technology could extend this beyond one hour — transforming these crafts from mere recreational vehicles into practical tools for commuting, medical evacuation, and cargo transport.
Larger applications look even more promising. A two-seater trainer aircraft like Swift, tested under the UK’s Project Monet, could achieve 11 hours of flight time with Al-Air batteries at a flying cost of just $29 per hour. Drone tests in the UK have already clocked a staggering 17 hours of flight endurance using Al-Air systems.
A New Design Philosophy
Aluminium-Air batteries open up new design possibilities:
- Aircraft like Pipistrel Velis Electro could see flight times jump from 1.5 hours to over 6 hours.
- Distributed propulsion systems, easier with electric motors, gain more utility with longer flight times.
- Al-Air’s swappable nature means quick turnaround times — critical for both commercial and military applications.
The Simplicity Behind the Power
According to Trevor Jackson, a former naval officer and CEO of MAL Research, the simplicity of Al-Air batteries is part of their appeal. Roughly a third of their weight comes from aluminium alloy plates, a third from non-toxic electrolytes, and a third from structural components. Despite slightly lower power density (around 500 W/kg), their sustained output and safety profile make them ideal for long-endurance fixed-wing aircraft.
The Verdict: Ready for Takeoff
Aluminium-Air batteries may not replace lithium-ion across every application — especially where high bursts of power are required. But for electric aviation, particularly regional transport, training aircraft, drones, and personal flying vehicles, they present a practical, efficient, and ready-to-deploy solution. With lower costs, unparalleled energy density, and safer chemistry, Al-Air batteries could be the key to unlocking the next generation of electric aviation.