Researchers at MIT and their collaborators have marked a major step forward for electric aviation, offering a new energy storage solution that surpasses today’s lithium-ion batteries in energy density
The new fuel cell design utilises liquid sodium metal as the fuel and ordinary air as the oxidiseroxidiser, with a solid ceramic electrolyte separating the two.
This setup provides a lightweight and energy-dense system capable of delivering more than three times the energy per kilogram compared to current electric vehicle batteries. For aviation, where weight and efficiency are critical, this development could be transformative.
How sodium air-fueled cell works
Traditional lithium-ion batteries, although effective in cars, reach their limits in aircraft and other high-demand applications due to their low energy density.
They typically top out at around 300 watt-hours per kilogram, well below the threshold of 1,000 watt-hours per kilogram considered necessary for realistic regional electric aviation.
The new sodium-based fuel cells exceed this mark in lab testing, with early prototypes achieving over 1,500 watt-hours per kilogram at the component level.
Unlike conventional batteries, which are sealed systems that require recharging, this technology operates more like a fuel cell. It uses refillable cartridges filled with sodium metal.
Zero carbon emissions
As power is drawn, the sodium reacts with oxygen from the air to generate electricity, producing a byproduct that is vented, similar to jet exhaust. Still, with a key difference: the emissions contain no carbon dioxide. Instead, the chemical reaction produces sodium compounds that naturally absorb CO₂ from the air, converting it into sodium bicarbonate, also known as baking soda. If released into the ocean, these compounds could help reduce water acidity, offering potential environmental benefits beyond just zero-emission flight.
The researchers have already built working prototypes in both vertical and horizontal configurations, successfully testing them under controlled humidity to optimise performance. Moist air is crucial, as it facilitates the conversion of discharge byproducts into a liquid form that can be easily removed, thereby maintaining the system’s efficiency over time.
In addition to aviation, the technology could be valuable in other sectors such as shipping, rail transport, and heavy-duty trucking, industries that also demand high energy density and low cost. Sodium is widely available, extracted from common salt, and previously produced at large scale for industrial applications. This makes it a promising alternative to more expensive and less abundant materials like lithium.
Safety is another strong advantage of the fuel cell design. While sodium metal is highly reactive, the system is engineered to separate the fuel from the air until energy is needed, reducing the risk of uncontrolled reactions. The use of a ceramic electrolyte and the absence of two concentrated reactants nearby enhance the safety profile compared to high-energy lithium batteries.
Applications past aviation
The team plans to demonstrate a brick-sized version of the fuel cell capable of powering a large drone, targeting applications in agriculture and logistics as an early use case. The startup Propel Aero, launched by members of the research team and housed at MIT’s incubator The Engine, will lead the effort to commercialise the technology.
With strong backing from organisations like ARPA-E and Breakthrough Energy Ventures, this innovation could be a pivotal step toward cleaner, more efficient transportation systems and a future where electric aircraft are no longer a distant dream.
