I guess grid scale storage is a solved problem then? And Tesla battery wall is pointless.
A typical UK household uses close to 50kWh of energy a day, most of it on heating and cars. So, in a zero-carbon future, you'd need a 10-foot shipping container per 20 homes to give them each a single day of storage. You'd need >10x that to ride out a windless cold snap (common in the UK where I am—we even had 2 weeks of no wind power in the height of summer last year so ran 60% gas during the hottest week ever recorded).
Grid-scale storage is tens of TWh, still way beyond any battery technology. These are MWh-scale systems. Useful, but not grid-scale storage. A grid would need tens of millions of these. At $17/kWh we're talking $500 billion.
They would be useful for keeping the air-con running on hot nights in solar-powered countries though.
Ambri has existed for 10+ years now and they are only gone deploy their first grid battery in 1-2 years.
They might have a great product, but they are far away from impacting the market to such a degree that any other battery company is 'pointless'.
Basically storing heat and converting it back to electricity, you are going to lose quite a bit of energy. And that's before you consider cooling effects. Heating up a large mass is not particularly fast. It takes some time. And then getting a lot of energy out rapidly is also not really that easy.
A lithium ion battery has probably well over 90-95% efficiency. It keeps its charge. And you can charge/discharge rapidly. Basically, you cans switch them on fast enough that switching from the grid to a battery when there's an outage, you probably won't notice the switch over.
Both have their strong and weak points and there is probably going to be a use for both on the grid.