Form Energy in the US is also developing this technology, though they haven't deployed to the grid yet.

As electricity grids get nearer to being 100% renewables, they need to account for <5% of times both solar & wind don't meet peak electricity demand. Lithium-Ion batteries, which only store electricity for a few hours, aren't much use here, but Iron-Air batteries will be.

They can store days worth of electricity, and not only that, they are stable and non-flammable. The only chemical reaction taking place is iron oxidizing (rusting).

Ore Energy connects world’s first grid-connected iron-air battery in Delft