There are many good reasons to expect sodium batteries to beat li-ion batteries in specific energy. Yes, a sodium charge carrier is ~3.2 times heavier than a li

There are many good reasons to expect sodium batteries to beat li-ion batteries in specific energy. Yes, a sodium charge carrier is ~3.2 times heavier than a lithium ion, and yes, it holds a bit less charge, but none of this has to be relevant because in a normal li-ion battery less than 1% of the total mass is active charge carriers. If you went by the simple properties of charge carriers alone, you'd expect lead-acid batteries to be at least 15 times worse than li-ion ones. However, the best lead-acid batteries are only ~8 times worse than the best li-ion batteries. Because even though the charge carriers are so much worse at doing their job, the chemistry is otherwise much more simple and easy to work with that it lets you pack a lot more charge carrier and lot less support infrastructure into the same battery. Sodium is similar, in that if you have a viable electrolyte, you can expect to utilize a lot more than 1% of the mass of your battery for usable charge carriers. This is why it's absolutely possible for molten salt batteries to have specific energies much higher than the best lithium-ion ones. As far back as 2014 there was a lab-scale prototype that beat every li-ion battery then in existence. The big downside of course is the molten part -- these are stationary batteries not due to low specific energy, but the fact that they have to be heated above ~110C to operate, and it is much more economical to make such batteries as large as possible. And in that segment, the chase is not for the highest specific energy but the lowest cost per Wh.