They actually are.
https://www.geeky-gadgets.com/bluetti-sodium-ion-portable-power-station/
Not yet at price parity with Lithium Ion, if you go by total charge capacity, and they are heavier and larger per watt hout charge capacity...
... but they can cycle a considerablely greater number of times, they have longer expected lifespans, work better in cold weather, can charge and discharge faster.
EDIT
Derp, ok, the above isn't solid state... but it is a viable product, without being solid state.
Given the rate of adoption and research going into sodium ion related tech, solid state sodium ion may be a thing in under two years... a hell of a lot of people are actively working on solving basically assembly line and industrial use specific problems right now.