MIT’s new sodium fuel cell beats lithium three-to-one for regional aviation

Researchers have chased practical electric aviation for decades, especially for short‑haul routes, but progress remains slow. Projects such as all-electric helicopter Sikorsky Firefly (2010), the Airbus E-Fan (2017), the experimental aircraft NASA’s X-57 Maxwell (2023), and nine-passenger commuter Tecnam’s P-Volt (2023) stalled when current batteries proved too heavy, delivered too little energy, or degraded faster than operators could tolerate.

But that landscape could be poised for a shift, thanks to a novel sodium-air fuel cell that MIT researchers announced and published in the journal Joule.

Identifying sodium metal as “a low-cost, high energy density fuel,” the MIT team developed a fuel cell uniquely operating on humidified air. In the end, their lab-scale stack delivered approximately 1,500 Wh/kg, roughly triple today’s best lithium-ion battery packs and comfortably exceeding the 1,000 Wh/kg “tipping point” analysts consider crucial for regional jets.

The authors estimate that the production cost of the sodium metal to be in the range of “$0.8–$1/kg-Na at scale using a capex/opex ratio similar to that for hydrogen production.”

Functioning like a true fuel cell rather than a sealed battery, the system consumes liquid sodium metal that is oxidized to produce electricity; spent sodium cartridges can then be swapped out and refilled. The cathode draws its oxygen from ambient air through a porous ceramic membrane. This design means the only rapidly consumed material is the sodium itself, an abundant commodity derived from ordinary rock salt.

Lead author Yet-Ming Chiang conceded in a statement that the concept “totally crazy” to some, but argues it solves three chronic aviation headaches at once: weight, cost and safety. And because only one reactant is flammable at any moment, the runaway-fire risk that plagues lithium cells is sharply reduced.

In addition to the ability to bypass traditional fuels, there’s another green twist: The exhaust from this sodium-air fuel cell system is primarily sodium oxide. This compound then spontaneously reacts with atmospheric CO₂ and water vapor to form sodium bicarbonate, essentially baking soda. This process means flights could effectively capture a small amount of carbon dioxide, offering a carbon-capture credit rather than a penalty. As an added benefit, if this alkaline byproduct eventually reaches the ocean, it could help nudge seawater pH upward, thus combatting acidification.

The work is still at the prototype stage. The current device is a small, lab-scale prototype, and scaling it up for aviation could pose engineering challenges. For instance, the researchers noted that air-fed cells were more prone to cathode flooding, an issue where excess liquid hinders oxygen transport. The researchers believe electrode optimization and improved flow field design can help address the issue. Managing the highly reactive nature of sodium metal, even with the fuel cell’s inherently safer design compared to some batteries, could be another challenge as sodium metal must be well protected as sodium, like lithium, can spontaneously ignite when exposed to moisture. “Whenever you have a very high energy density battery, safety is always a concern, because if there’s a rupture of the membrane that separates the two reactants, you can have a runaway reaction,” said Chiang in a release.

Despite such inherent challenges in developing novel energy systems, the vision for this technology remains clear. If the team at MIT and its commercial spin-off, Propel Aero, can successfully navigate the path from lab-scale innovation to real-world application, the impact on aviation could be significant.

Perhaps in the not so distant future, the pre-flight checklist could add one new item: “Insert sodium cartridges.” If that line ever makes it into an FAA manual, today’s “crazy” idea will have stuck the landing.