It is a shame that your "sources" never studied chemistry at...

It is a shame that your "sources" never studied chemistry at school. Both Lithium and Sodium are reactive elements but it is well documented and known that Sodium is more prone to react with water, or even oxygen with moisture, than Lithium. Maybe Britanncia might be easy for you to read: "Generally, elemental sodium is more reactive than lithium, and it reacts with water to form a strong base, sodium hydroxide (NaOH). Its chemistry is well explored." (Sodium - Chemical Properties, Reactions, Uses | Britannica). So in other words if there is a car accident and the Sodium is exposed to the external environment, it can be said with fair reason, that it would pose a greater degree of danger to the public, than if it was Lithium.

As for your energy density claim, it is also well documented and known that Sodium will never be able to be an equivalent substitute to Lithium based on scientific elemental properties. You can go educate yourself on this one.