This was inevitable. lithium and sodium are both Alkali Metals, column 1 of the Periodic Table of Elements, and they are only one row apart, so they share many characteristics. Lithium is actually very common, but current demand for lithium-ion batteries is stretching the supply to the limit and driving up pricing. Sodium is much more common than lithium, so it is unlikely that any surge in demand for these would ever significantly elevate pricing. That is only where advantages of sodium-ion batteries start.