- Oct 18, 2021 8:02 pm GMT
As the website summary for the link below indicates, aluminum-air battery technology has been making headlines. This video does a pretty good job of explaining the pros and cons.
The only point that Joe fumbles, I believe, is in talking about the ease of recycling aluminum as a mitigating factor for the non-rechargeability of aluminum-air batteries. Aluminum, as a metal, is easily recycled. But when an aluminum-air battery discharges, the end product is not aluminum metal. It's an aluminum hydroxide gel -- hydrated aluminum oxide. If you're not into chemistry, skip the next paragraph to get to the bottom line.
Hydrated aluminum oxide from spent aluminum-air batteries is the same thing as what's made in the Bayer process for refining bauxite ore. The hydrated aluminum oxide is calcined to drive off the water and produce aluminum oxide powder. That powder is then dissolved in molten cryolyte to be reduced to molten aluminum via the Hall-Heroult process. The Hall-Heroult process is an electrolytic process that uses a consumable carbon anode. Oxidation of the anode emits a mixed stream of CO2 and CO. If the overall process is to be green, it must be paired with fuel synthesis or other processes to utilize the waste stream and keep carbon emissions out of the atmosphere. In principle, it's possible to use inert anodes that produce oxygen rather than CO2 and CO. The cell voltage and hence to energy cost per ton of aluminum would be higher, and AFAIK, a zero-carbon alternative to the Hall-Heroult process has never been commercially deployed.
The bottom line is that not only are aluminum-air batteries not rechargeable, but the process for recycling a spent aluminum-air battery to produce a new replacement would be quite expensive. It's energetically equivalent to producing fresh metal for the aluminum anodes from ore. If aluminum-air batteries were to be routinely used to power EVs, it would require at least an order of magnitude increase in new aluminum production capacity.
That said, I can see a couple of applications where aluminum-air batteries could make a lot of sense. One would be the hybrid EV application that Joe refers to near the end of his video. An EV could carry a swappable Aluminum-air batter with a capacity for 3 or 4 hundred miles of range, paired with a somewhat reduced lithium-ion battery pack good for 200 miles of range. 200 miles is ample for most driving needs; for occasions when it isn't the aluminum-air batter could be tapped for an additional 3 or 4 hundred miles. That disposes of the "range anxiety" issue from having only 200 miles in the rechargeable battery pack.
The other application would be for power backup in hospitals, commercial facilities, and micro-grids. The aluminum-air batteries would replace the diesel powered generators currently used. They'd be cleaner, more reliable, and probably a good deal more economical than a diesel-powered backup generator. The key to feasibility is that they would only be used for power emergencies. Once their charge was used up, they'd have to be replaced. However, the energy density of aluminum-air is high enough that trucking in a megawatt-hour replacement battery would be no big deal.
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