Oct 21 2019

Aluminum Air Batteries

An article about a new battery is making the rounds and I am getting a lot of questions about it – Ex-Navy officer turned inventor signs a multi-million deal to produce his electric car battery that will take drivers 1,500 miles without needing to charge. As stated, that sounds like a significant advance, about a 5 fold improvement over the current lithium-ion batteries powering a Tesla, for example.

That would certainly be a huge advantage and give the electric car industry a significant boost. Increased range would alleviate “range anxiety” and also mean the recharging could happen once a week rather than every night. It would also make electric vehicles easier to use on long trips. Further, increased range is the same as smaller batteries. Instead of a range of 1,500 miles, you cold have a battery with a 300 mile range that weighs one-fifth as much. (I am assuming that when they state the range they are comparing batteries of the same size.) That would make the vehicle more efficient and potentially cheaper.

But as always, the devil is in the details. What exactly are they talking about? There are lots of red flags in this article, starting with the fact that it is in the Daily Mail, which doesn’t exactly have a good reputation for high quality journalism. Also it makes it seem like this is the invention of one guy, rather than a lab, company, or even industry. That’s not realistic. There is also this:

Few will have heard of Jackson’s extraordinary invention. The reason, he says, is that since he and his company Metalectrique Ltd came up with a prototype a decade ago, he has faced determined opposition from the automobile industry establishment.

Sorry, but this conspiracy theory does not pass the smell test. New battery tech would not threaten the automotive industry, it would be a new option.

In any case, regardless of the sensational reporting, what are the actual facts of the battery itself. The inventor is Trevor Jackson, who claims to have made a breakthrough in aluminum-air (al-air) batteries. This technology is not new, it has been around since the 1960s, and is actually being used in some settings, like the military. This might be better described as a fuel cell than a battery, however. First – it is not rechargable. The energy comes from oxidizing aluminum:

This battery uses the oxidation of aluminum at the anode and the reduction of oxygen at the cathode to form a galvanic cell. In the process the aluminum is completely consumed to produce aluminum hydroxide. The metal air battery has a very attractive energy density because part of the reactants come from the air.

Aluminum is also a light metal, with good energy density. One technical limitation to widespread use of an al-air cell is that the electrolyte solution is very toxic. This is the breakthrough that Jackson claims, that he developed a new electrolyte solution that is so non-toxic you can drink it. He is not revealing his formula, saying it is proprietary, but he claims he has demonstrated his fuel cell to third parties. OK – let’s assume his core claim is true, that he has a new version of the al-air battery with a non-toxic electrolyte. Is this a good option for the next fleet of automobiles?

I think there are good reasons the automotive industry remains skeptical. There are practical considerations here. A Telsa lithium ion battery pack weighs 540 kg (1,200 lbs). Even at five times the energy density, a pack with a 300 mile range would weigh 240 pounds. Since the battery cannot be recharged, it would need to be swapped out. The driver would not be expected to lift a 240 pound battery, or more for longer range vehicles. You could break it up into many 20 pound batteries, or require a station with equipment to lift out the spent battery. Either way, this would require a new infrastructure that is not trivial.

All these spent batteries can be recycled to reclaim the aluminum, but that is an energy-dependent process. Basically you have to put more energy back in than what you got out from the battery. This is another required infrastructure. Requiring new infrastructure is not a deal-killer, if the advantages are worth it, but it is a significant barrier.

The potential advantages are the good energy density, and the fact that aluminum is cheap and abundant. You could use aluminum recycled from cans, for example, to make the batteries. But the non-rechargeable thing is a huge drawback. This would require an entirely new approach to electric vehicles, at the very least delaying adoption. You get a chicken-and-egg problem – will people buy the car before the infrastructure is ready, and who will build the infrastructure until there are enough users on the road? Such situations are frequent, and they can be bootstrapped by early adopters and industry and government investments to boost the infrastructure enough to lure in users. If we decide that this is the best way to go, we can make it happen.

But I am just not seeing the advantages necessary to make such a huge investment in a fairly dedicated infrastructure. Swapping out hundreds of pounds of batteries every few days doesn’t seem practical.

Meanwhile, research is ongoing into new battery tech. Much of that research does focus on metal-air batteries, because of their high potential energy density. Aluminum also may be the battery material of the future, replacing lithium – it’s cheaper and more abundant, and more energy dense. But we need to work out all the details. One bad feature can be a deal-killer with battery tech. Batteries need to simultaneously have good energy density, fast enough discharge power to power a car, fast enough recharge speed, be safe and stable in a wide range of environments, and have many charge-recharge cycles. They also need to use affordable and abundant materials. The perfect battery made from platinum won’t help.

We have not hit upon the successor to lithium-ion yet, and not for lack of trying. Meanwhile, the lithium-ion technology is slowly and incrementally advancing, but enough to keep raising the bar for any potential competitor. We will eventually get to a replacement technology for lithium-ion, if for no other reason than supplies of lithium will run short. Again, aluminum may be the way to go. But the technology is not there yet, and Jackson’s breakthrough, while nice, is not enough.

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