[Tossrock]

I've said for a while that electric planes are the perfect use case for aluminum-air batteries. Aluminum-air batteries have up to 8x the energy density of lithium ion, but are not rechargeable, so using them only makes sense if you have a system to recycle the used batteries. This doesn't make a ton of sense with cars, because cars are constantly going from random place to random place, and having to include a stop at a battery recycling center every ~1000km or whatever would be impractical.

But planes go between very limited sets of known points, with huge amounts of infrastructure. Adding in the capability to do Al-air battery swaps / recycling would be easy, and the benefits for the use case (huge weight savings, faster turnaround times by swapping vs charging) are big.

[EastLondonCoder]

Apparently Eviation is looking into aluminium air batteries https://en.wikipedia.org/wiki/Eviation_Alice

[throwawayboise]

Small tertiary airports often served by short regional flights don't have a lot of infrastructure. They have a couple of fuel trucks and a gate agent/security screener/baggage handler who might all be the same person.

[ars]

So instead of a fuel truck you have a battery swapper.

You'll have to ship the batteries somewhere they can charge/reprocess, but you also need to ship fuel, so it's a 1-to-1 tradeoff (you can ship the batteries by land).

[throwawayboise]

Is it 1:1? There are a lot more KWh in a tanker truckload of jet fuel than in the same volume of batteries.

[Tossrock]

Not that much more (theoretically) - Al-air batteries could reach up to ~8kWh/kg, which is in the same range as jet fuel's 12ish. Aluminum is also denser than jet fuel, so per unit volume it could be even closer.

[otterley]

What's the process for recycling an aluminum-air battery? And is it cost/energy effective to do so?

(If you think about it, closed-loop recycling of energy storage is just another form of recharging, but with extra steps.)

[Infernal]

From wikipedia[0] "it is possible to mechanically recharge the battery with new aluminium anodes made from recycling the hydrated aluminium oxide". I've found a few papers regarding recovery of aluminum from aluminum oxides, but I don't have the background to interpret them with an eye towards that process's impact on the overall efficiency of the battery.

[0] https://en.wikipedia.org/wiki/Aluminium–air_battery

[throwawayboise]

Production of aluminum metal from aluminum oxide is hugely energy-intensive. Aluminum plants often have an on-site utility-size power plant to provide the electricity. Is this same energy needed to recycle the oxide from the batteries? If so it seems like a non-starter, maybe unless it could be done with solar generation.

[ars]

> Is this same energy needed to recycle the oxide from the batteries?

The energy delivered by the battery in flight, is what you need to use to restore it back to fresh. The more energy you need the better your battery.

Why does it need to be specifically solar? Use electric from the grid, and as the entire grid changes over to other power sources so will this.

[Infernal]

The real question here is the ratio of energy delivered over the life of a fresh anode as it is fully converted to aluminum oxide, to the amount of energy required to turn that same aluminum oxide back into a pure aluminum anode.

[throwawayboise]

> Why does it need to be specifically solar? Use electric from the grid,

The vast majority of grid electricity is still produced from fossil fuels (at least where I live).

[eyelovewe]

And that must and is changing. Green transport is predicated upon a green grid.

Additionally, a “wasteful” process, like electrolysis of water to make hydrogen, can be usefully inserted at onsite wind generation sites for when the grid isn’t requiring/buying vs sitting idle. When you see large wind turbines stopped and you know that there is a constant stream of wind at 50m above that ridge line it’s simply because the grid is not buying atm. I’m positing that aluminum air batteries are viable for aviation for the same reason.

[mapt]

There is no "recharging" an aluminum-air battery, you add the energy back through recycling (smelting) it.

One of the big synergies is with renewables: With the right industrial process, you can treat this smelting process as a way to dump excess energy in peak production times.

[Hypx_]

It's the same idea of green hydrogen. Only hydrogen allows you to use pipelines instead of physically hauling everything. You also don't have to worry about the battery physically gaining weight as you fly.

[ComputerGuru]

I remember 20 years back, hydrogen was going to be it. There were prototype cars manufactured, calls for hydrogen fueling stations to be built, everyone scrambling to get on the hydrogen train. Then it all just fizzled out. It was probably one of the promised techs I most wish had lived up to the hype.

[Hypx_]

It's going to live up to the hype. It just didn't happen in that timeframe.

[otterley]

Doesn't smelting generate a ton of waste heat, though? Sounds like a process that uses far more energy than the aluminum-air battery can hold.

[Hypx_]

Because aluminum-air batteries are not rechargeable, they're fundamentally inferior to hydrogen fuel cells (which work in nearly the same way!). At least with hydrogen you can refuel the airplanes with a liquid instead of having to use a physical battery swap. Also, even higher energy density that doesn't gain weight during flight.