In 75 years we won't need to extract more lithium - except the fraction needed to replace permanently-lost batteries.
Incidentally, you should be very careful when talking about "<resource> reserves", because the definition of a reserve is usually "<resource> that is profitable to extract" - and when we "run out", prices will go up and thus currently-unprofitable sources will become profitable, and POOF! Our <resource> reserves have increased, purely through the power of semantics.
Also, over the decades resource extraction becomes cheaper and thus more sources become profitable.
Personally though, I don't think any of that will matter -IMO the future is proton batteries, AKA Hydrogen batteries (which use an electrolyte of "ionic hydrogen", H+, which has 1 proton and 0 electrons - people claim lithium is the lightest metal, but it has 3x the protons of hydrogen). I think that the recent TABQ batteries, or something like it, will become commercially viable within 75 years (although who even knows what batteries will look like in the year 2101).
As for reserves, while you understand the economics you are missing the physics. For example, there is Li (and U) in the ocean. We don't extract Uranium from the ocean not only because it isn't economical, it isn't even energy efficient. This is because moving a billion tonnes of water takes more energy than the 3 tonnes of Uranium you would harvest from doing that. For Li, its takes just as much energy (and money) as its just as rare. In other words, there is a floor on that economic extraction argument specified by a positive EROEI (energy returned on energy invested).
They are always revising estimates up and down a bit. But Li demand just keeps rising and rising. And a single grid scale battery takes 10 years of current Li-ion battery production worldwide to build.
So do we have enough Li at current rates, sure. We don't have anywhere near enough to do anything like replacing even a fraction of FFs with renewables. I guess that's the real headline here. That's why people are experimenting with Na-ion. Putting it in a production car today, that seems...what's the word...homicidal. Making a grid stabilization battery (not for backup) with large amounts of space between cabinets to see what happens, that seems more wise.
