Sodium batteries could make electric flight viable

Zero-emissions air travel may be one step closer after scientists at the Massachusetts Institute of Technology unveiled a new type of sodium fuel cell that could one day make electric-powered flight viable.

'Environmental benefits at no cost'

The sodium-air fuel cell – designed by a team led by Yet-Ming Chiang, professor of materials science and engineering at MIT – works by combining liquid sodium metal with oxygen drawn from the air to create a continuous reaction.

The device is "based on well-established electrochemical principles", said The Times. But "unlike conventional batteries, which must be recharged, it is designed to be refuelled, with its energy-rich material being replaced as it is consumed". In this way it is "more similar conceptually to hydrogen fuel cell systems", said MIT Technology Review.

Subscribe to The Week

Escape your echo chamber. Get the facts behind the news, plus analysis from multiple perspectives.

SUBSCRIBE & SAVE

Sign up for The Week's Free Newsletters

From our morning news briefing to a weekly Good News Newsletter, get the best of The Week delivered directly to your inbox.

From our morning news briefing to a weekly Good News Newsletter, get the best of The Week delivered directly to your inbox.

Sign up

Liquid sodium metal "doesn't require the super-cold temperatures or high pressures that hydrogen does, making it potentially more practical for transport". There are also "economic factors working in favour of sodium-based systems" as sodium metal can be made from sodium chloride – commonly known as table salt – which is "incredibly cheap".

The sodium-air cell also produces sodium hydroxide as a chemical by-product, which could be used to absorb CO2 from the atmosphere or turned into sodium bicarbonate for ocean-based carbon removal. It is an "essentially free" by-product, "producing environmental benefits at no cost", said Chiang.

'Within the next year'

With a Boeing 747 estimated to burn around 3,800 gallons of fuel per hour, or about one gallon every second, according to Simple Flying, the aviation industry has long sought a way to make air travel more sustainable (and cheaper).

The focus up to now has been on sustainable aviation fuel (SAF), made from non-petroleum-based renewable sources, such as waste oil and biomass. The International Air Transport Association said it expects the amount of SAF produced globally to double in 2025 to reach 2 million tonnes, said Reuters. Yet this still represents just 0.7% of airlines' total fuel consumption worldwide, with questions around the supply of SAF and its cost, which is far more than traditional jet fuel.

When it comes to electric-powered flight, the energy density of a power source – the amount of energy stored per unit of weight – is "critical", said The Times. Aircraft must be "as light as possible to achieve lift and to maximise range, and the lithium-ion batteries used in electric cars have too low an energy density to power most aircraft. Without a large boost in energy density, electric-powered flight remains impractical for all but the smallest aircraft over short distances."

In laboratory tests, the MIT sodium-air fuel cell prototype delivered more than five times as much energy per kilogram as the lithium-ion batteries currently used in cars.

But even so, sodium-air-powered flight is still some way off. The "next step", said MIT, is to continue research to "improve the cells' performance and energy density, and to start designing small-scale systems", with drones a potential option.

"We'd like to make something fly within the next year," Chiang said.