If price was the only factor that matters, we could be using nickel-metal-hydride batteries. They also last longer.

A more important aspect where Sodium would be better than Lithium for batteries is that it doesn't catch fire that easily. Lithium batteries are prone to thermal runaway, where if you increase their temperature that makes them release more energy and increase their temperature even more until they combust violently.

A graphic example to this is where Grand Tour's Richard Hammond recently crashed an electric car, which then continued to spontaneously catch fire five days after the crash (https://www.total-croatia-news.com/made-in-croatia/23852-the...)