i think the big issue is asymmetry. they charge at 3C, but they discharge at 8C. so you need the significantly overbuild.

Ambri had a massive molten salt battery that was cheap for grid storage. They went broke. Sadoway gave a great lecture on how actual solutions are fighting corruption and old money.

1 C is defined relative to 1 hour for full discharge and 3 C means a 3x faster discharge rate (full capacity can safely be discharged in 1/3 hour, or you can discharge 3 cells sequentially in an hour). Good lithium cells tend to be above 5C, can reach 10C for peak load or if cooled.

For a large enough battery it doesn't really matter, but for dense portable ones a lower C rating means you have to discharge from more cells simultaneously to maintain a given output. That makes it more complicated, and you have less headroom to the battery's maximum Watt output if you need to accelerate a car hard suddenly.

Kind of, yes. But more importantly, it also means it can only push enough power to run at 3c. And that's probably not for the full charge of the battery.

So a 100 amp hour battery rated at 3c can push out 300 amps. Which also means that if the grid needs a short spike in power, it might be limited.

It shouldn't be too hard to get a 15c LiPo battery, which could push 5x as much energy at peak demand.

You'd probably kill the battery if you charged it from 0-100 at 15c, but for short bursts of charging and discharging, it should handle it just fine.