Seems like Form Energy has come up with a better method, also iron-based but no combustion.
The Future of Energy Storage - Professor Yet-Ming Chiang, MIT
https://www.youtube.com/watch?v=E76q-9q7ZDg
Professor Yet-Ming Chiang, one of the world’s most prominent researchers in energy storage, will give a personal perspective on some of the challenges and opportunities for better and cheaper energy storage. From a historical perspective, battery performance has improved steadily, but now the divergent needs for batteries in high energy density applications such as EVs (and, coming soon, electric aviation), and those for grid storage, which emphasizes ultra-low cost and earth-abundant materials, are becoming clear.
He will give examples of emerging innovations that may address these different needs, including solid-state and other batteries that use alkali metal electrodes, and approaches that make use of the most widely available electroactive elements.
Battery technologies are notoriously difficult to scale given high technology risk and high development costs. Yet-Ming will share some of the unique lessons learned at startups he has co-founded, including A123, 24M, and most recently Form Energy.
https://www.spglobal.com/marketintelligence/en/news-insights...
It's being sold as a complementary solution to more efficient LFP cells (for evening peak shifting), and as an alternative to pumped hydro and peaking gas turbines.
It would be better to waste the energy than to let them have it for free.
I really want them to succeed for the sake of the planet, but it's another "revolutionary new battery just five years away" story.
As solar gets cheaper and cheaper, the ability to mitigate efficiency loss by just increasing the size of the solar installation gets easier and easier.