This isn't correct. This is only true when the battery is first manufactured just like with Li-ion. Once the battery starts functioning, it is ionized metallic Sodium. All the volatility of Na but with corrosion too. There is no Chlorine nor any other halogen in there to engage in an ionic bond. In short, once the battery is functioning, the trick used to keep the Na in an ionic bond stops working (by design). After all, the ionic bond would prevent the battery from functioning.

It should be noted that most manufactures aren't doing pure Na-ion. They are mixing in a little Na with the Li to stretch Li supplies and gather data on the impact of the increased volatility on safety. I wouldn't expect their first use to be in cars. I would expect them to be in grid stabilizing batteries.