Per a 2023 Nature article: https://www.nature.com/articles/s43017-022-00387-5

> The locations of suitable continental brines are also geographically restricted, with an estimated 50–85% of lithium-rich continental brine deposits located in the Lithium Triangle and with China as the next richest source. Hard-rock ores are also geographically concentrated in Australia and China

Lithium in a form that is economical to mine/process is indeed quite rare. Which is why 3 countries produce 90% of it.

And it is extremely environmentally costly which is treated as an economic externality. It takes 1.9m litres to mine one ton of lithium and solvent chemicals like hydrochloric acid contaminates groundwater, making the entire site toxic and unlivable.

Entire governments have been overthrown for access to this resource.

And yes Sodium is fine for most applications where it can be a little heavier (grid uses, maybe cars) which is where most of it is projected to be needed.

Here's how much of everything we mined in 2022. Lithium is bottom left corner just above Gold.