Afaik, an important component of battery degradadation is the deformation of the anode and cathode as ions migrate between the two electrodes. Sodium ions are m

Afaik, an important component of battery degradadation is the deformation of the anode and cathode as ions migrate between the two electrodes. Sodium ions are much larger that Lithium so this issue is much more pronounced. So in addition to energy/mass, there is another metric that prevents them from catching up to Lithium.