The issue I’ve heard with sodium-ion is that the voltage curves make the power electronics much more expensive for a given efficiency/power level.

[https://www.eevblog.com/forum/projects/sodium-ion-battery-ev...]

Lithium’s curve is nearly flat, which allows for a pretty easy consistent power production (albeit nearly impossible to tell state of charge!) since you only need to target a pretty narrow voltage band.

Overall, that means sodium-ion has to be even cheaper to be competitive, and it makes even less sense in areas where power density matters like electric cars, as you’ll end up with far less power and/or needing much heavier motors and more expensive electronics to compensate when on the lower end of charge.

I don’t want to think of what it would cost to do a 100kw buck-boost power supply that can handle +- 25% (or more!) voltage differences. In reality, I don’t think anyone would try.