So the battery bank may use more power to maintain the 395-755 deg F. temperature than the power it stores?? Scale it up baby!! Energy density per volume/weight is key in my thinking, and the temp thing plus “... the oxygen-ion battery only achieves about a third of the energy density that one is used to from lithium-ion batteries” sounds like a “tech-killer” to me. We’ll see I guess.
The target market here is utility scale energy storage to back up the intermittent utility scale power sources, not mobile electric power. I don’t think it would take significant power to keep it warm. Thats why elephants dont have fur: the internal metabolic heat released goes as the cube of the animal’s length, and the surface area goes as the square. As you say, scale it up. And/Or put it in a deep mine.
I doubt the technology will go anywhere. If the left’s green new “leap and a net will appear” energy plan continues, the “scientific consensus” will suddenly call nuclear powerplants green. ( Oceania has always been with Eastasia.) Windmills and solar panels are not economic even if we had utility scale energy storage.
Also, the ceramics used in the proof of concept required lots of rare elements, the authors leave solving that as an exercise to the reader. So this is the realm of SciFi. It won’t pay off within the 20 years a US Patent lasts.