Iron air batteries

Wendy said:

Still, it would be interesting to see a comparison between lithium and steel air batteries. Is there anywhere close this make a nice alternate for cars? Time will tell,and I don't have the IQ to figure out what is which. I'm pretty sure that the fire risk between the two is pretty significant.

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There's very little in the way of a meaningful comparison -- they server two completely different purposes and almost any situation that lends itself to one almost certainly makes the other an unsuitable choice.

For instance, in a car you need the battery to respond very quickly to changes in demands (millisecond time scales), but iron-air batteries respond to changes in minutes, which is acceptable for grid storage applications.

The mass-density of Li-Ion is three to four times higher than iron-air, while the volume-density is 30x to 50x higher.

The round-trip-efficiency for Li-Ion is something like 50% better than iron-air. That's important for mobile applications as it impacts range. Static applications are less sensitive to it.

Iron-air batteries are much safer, while we are becoming a lot more aware of just how dangerous lithium-ion batteries are. While we seem to be willing to live with the piecemeal dangers of cars and phones catching fire (and, let's face it, we accept other small-scale disasters like homes blowing up from natural gas or cars catching fire at a gas pump), imagine the impact of a huge grid-service battery bank going up.

Li-Ion batteries are intended for repeated very deep cycle applications. While Iron-air batteries are capable of being deep cycles, the are best suited for infrequent deep cycling that occurs slowly (over days, not hours).