Instead of a battery, the new concept is a kind of fuel cell — which is similar to a battery but can be quickly refueled rather than recharged. In this case, the fuel is liquid sodium metal, an inexpensive and widely available commodity. The other side of the cell is just ordinary air, which serves as a source of oxygen atoms. In between, a layer of solid ceramic material serves as the electrolyte, allowing sodium ions to pass freely through, and a porous air-facing electrode helps the sodium to chemically react with oxygen and produce electricity.
In a series of experiments with a prototype device, the researchers demonstrated that this cell could carry more than three times as much energy per unit of weight as the lithium-ion batteries used in virtually all electric vehicles today.
A great deal of research has gone into developing lithium-air or sodium-air batteries over the last three decades, but it has been hard to make them fully rechargeable. “People have been aware of the energy density you could get with metal-air batteries for a very long time, and it’s been hugely attractive, but it’s just never been realized in practice,” Chiang says.
By using the same basic electrochemical concept, only making it a fuel cell instead of a battery, the researchers were able to get the advantages of the high energy density in a practical form. Unlike a battery, whose materials are assembled once and sealed in a container, with a fuel cell the energy-carrying materials go in and out.
The researchers envision that to use this system in an aircraft, fuel packs containing stacks of cells, like racks of food trays in a cafeteria, would be inserted into the fuel cells; the sodium metal inside these packs gets chemically transformed as it provides the power. A stream of its chemical byproduct is given off, and in the case of aircraft this would be emitted out the back, not unlike the exhaust from a jet engine.
But there’s a very big difference: There would be no carbon dioxide emissions. Instead the emissions, consisting of sodium oxide, would actually soak up carbon dioxide from the atmosphere. This compound would quickly combine with moisture in the air to make sodium hydroxide — a material commonly used as a drain cleaner — which readily combines with carbon dioxide to form a solid material, sodium carbonate, which in turn forms sodium bicarbonate, otherwise known as baking soda.
“There’s this natural cascade of reactions that happens when you start with sodium metal,” Chiang says. “It’s all spontaneous. We don’t have to do anything to make it happen, we just have to fly the airplane.”
As an added benefit, if the final product, the sodium bicarbonate, ends up in the ocean, it could help to de-acidify the water, countering another of the damaging effects of greenhouse gases.
Initially, the plan is to produce a brick-sized fuel cell that can deliver about 1,000 watt-hours of energy, enough to power a large drone, in order to prove the concept in a practical form that could be used for agriculture, for example. The team hopes to have such a demonstration ready within the next year
It’s a red flag that they don’t compare to H2, which has significant aviation FC prospects/research, and has even higher energy density by weight, and the advantage of exhausting water vapour and so fuel weight goes down during trip.
Sodium is also produced by electrolysis. It can make a lot of H2 and heat by reacting with water. In fact, the reaction of 1 ton makes 1.8mwh of heat, + 1.4mwh of H2 heat value (900kwh electric), where hot H2 might have extra energy potential for electricity or combustion (not sure).
Sodium metal costs $2000/ton. Reaction with water makes 42kg of H2, and so about $46/kg of H2 is too high. The heat would improve the efficiency of SOFCs (described matches article) by getting the heat for free, and maybe 1.2mwh/ton electric. SOFCs have always had the advantage of working with polluted fuel blends.
Perhaps if sodium or H2 production was combined with desalination process, then cost of green sodium or H2 could be lowered.
Fuck the cost. The planet is going to be unfit for human habitation in a generation or two, while ecosystems and ocean current collapse kills everything else.
All that matters is if it’s cleaner. Stop ruling out options because they’re not market friendly.
Hydrogen is clean electrolysis too. Would cost less.
Yep. And I’m a big supporter. We should use the cleanest methods available as appropriate for each application.
The problem is that we don’t yet have a practical alternative to jet fuel, except high speed rail and Zoom. The technologies are all too young.
And it’s not just cost, it’s trying to make them useful enough. Batteries will not take you across a continent, for any cost.
We’re more at the stage of “fuck the cost. Give me another option to try”
The real competitor for green aviation isn’t hydrogen, it’s bio-fuel. Bio-kerosene, bio-gas and bio-ethanol all have useful roles in aviation, and are essentially carbon neutral over their lifecycle. Zero carbon at the proverbial tailpipe is a lot less important when that tailpipe is at 30,000 feet.
bio fuels are not scalable. Much more solar energy (15x+ factor) is created by PV than by ethanol per area, and more efficiently turned into H2 (or e kerosene, btw) than the bio route. Bio route is airline PR to do something, but would make food scarce at scale.
iirc the issue with Hydrogen is that it has very high energy/mass but incredibly low density to the point that the fuel tank to contain a reasonable amount of hydrogen (say comparable to hydrocarbons) is even more prohibitive than battery weight.
300atm compressed H2 has more energy than batteries. 600wh/L electric. 900 wh/L heat. LH2 is equivalent to 1100atm compressed. LH2 is right for aviation because the tanks are light/simple, and they are filled shortly before takeoff. It’s a big weight savings over kerosene.