You can't really get them in the sort of energy density you need for an ESS at any comparable price to LFP right now, so they only really make sense in really limited spots.

Ex - the closest I can find is something like: https://batteryfinds.com/product/3-1v-210ah-sodium-ionna-ion...

but just compare against LFP: https://www.18650batterystore.com/products/eve-mb31-grade-a-...

So...

LFP: 4.0KWh @ $275.00 Sodium: 2.6KWh @ $568.00

Right now, it's older generations of the chemistry, and you end up paying twice as much for half the power. So yeah... unless you really need the temperature extremes, it makes a lot more sense to stick with LFP.

But CATL at least is claiming they have cells in the pipeline for this year that get NA+ down to comparable $/KWh as LFP, and then yes - I'd much prefer to use the newer chemistry.

If sodium follows the same trend as LFP did, they'll get much cheaper at scale, and performance will go up markedly over the next 15 years. I won't be at all surprised to see them end up completely dominating the space in the long run, but we're not yet at the spot where they're better than LFP (at its most mature).