Sodium-sulfur batteries do exist, and are currently used. Did anyone read the wiki article i linked?
NGK even sells this things:
https://www.ngk.co.jp/nas/specs/ Those are probably the ones with the "brittle ceramic separator" mentioned in the video.
As i understand, the battery insides would be solid when discharged and molten when charged. I suppose that they have a hell of a thermal insulation, or the charge wouldn't last.
Ambri seems to have removed the ceramic separator in favor for another layer of molten material which keeps the anode and cathodes apart.
I suppose that if the case breaches, it's fireworks time with the molten sodium. In fact, you can read about a fire incident with NGK batteries here:
https://www.ngk-insulators.com/en/news/20120425_9322.htmlSo, while i'm no expert in this, the claims that nothing will happen if the case is shot at, do sound like bullshit. Take a look at the hazards of sodium-sulfur batteries here, page 3:
https://www.nrel.gov/docs/legosti/old/4678.pdfThat's unless i got the video wrong, and they're actually using something else. I think he said that they mixed the sodium with another metal, or something like that? Maybe that makes it less explosive, or something.
70% efficiency is quite reasonable (but not the best in battery technologies). Hydrogen cell fuels have typically lower efficiency than that, unless you use the waste heat for something useful, which won't be the case in a car. And the hydrogen needs to be produced by electrolysis, if you want it clean, and right now the efficiency of around 70 to 80%, i think. Then you need to compress the hydrogen, which again requires energy, Here seems to be a good explanation:
https://cleantechnica.com/2018/08/11/hydrogen-fuel-cell-battery-electric-vehicles-technology-rundown/Hydrogen does have a big advantage, and it's that is fast to charge, and with excellent range.
And this video is great also, down from the same webpage:
Something interesting to note, however, is that it should be quite easy to make a pluggable hydrogen / battery hybrid vehicle. If you have enough battery range for normal everyday use, and you just have to use hydrogen occasionally for long trips, or emergencies, then that looks quite interesting to me. But would that kind of use be enough for the hydrogen stations to make a profit?