Lithium is a much coveted element nowadays, since many electric vehicles use them, and all our electronic devices run on lithium-ion cells as well. One would think the supply would be running low by now, but oddly enough we are discovering more and more supplies of the stuff, and recently prices have been dropping like the proverbial flies.
On the other hand rare earths are used for other parts of the cells, but developments are going fast since many companies are thinking up new battery chemistries and optimizations for the anodes and cathodes. Tesla even came up with a different cell size, since this had the highest energy density.