Na-Ion can be a lot less expensive. But it’s a lot heavier. (Not a problem for grid-storage.)
As a native English speaker, I don’t think I’ve ever heard someone call NaCl just “Sodium”, it’s always called “Sodium Chloride”.
I’m a PhD candidate in chemistry. I’ve never once seen sodium refer to the salt, sodium chloride. Sodium is the metallic form or the atom.
However, why sodium, tungsten, lead, antimony, tin, silver, gold, mercury, iron, and potassium and not their Latin forms? Natrium, wolfram, plumbum, stibium, stannum, argentum, aurum, hydrargyrum, Ferrum and kalium? I don’t really know. Mostly it’s just fun trivia for me to tell the undergrads.