alt Hacker NewsSodium has greater density than lithium, while most other materials used in a battery have similar densities regardless if sodium or lithium is used, so if a Na-ion battery and a LFP battery have about the same mass and stored energy, it is likely that the sodium-ion battery has a smaller volume.
that doesn't check out, capacity depends on surface area, if the element that is on the surface is heavier then, all other things equal, the battery will be heavier for same kWh.
Sodium would need to be more efficient to be lighter, which it isn't