Well intentioned policy like this can have the reverse effect.
If you limit lithium usage you will limit demand, which can reduce the effort expended to build new mines.
https://www.weforum.org/agenda/2022/07/electric-vehicles-wor...
And let's not forget about all the problems that "innovative" methods of oil extraction such as fracking have created, over and above the fact that it's provided more oil to burn. Lithium mining itself is already an environmental disaster, and it seems highly unlikely that increased demand for the product is going to improve the environmental impact of extracting it. You know, tragedy of the commons and all. The fact that "peak oil" came and went is not a capitalist success story.
A comparable case in point: commercial space launch companies. Arguably, commercial large-scale aviation, too.
It's not only about money-expensive. If it gets more energy-expensive to produce/store/route/... energy than the amount of energy we end up with in the end, the game is over.
So, in practice, there are limits to reserves. There is, of course, the possibility that these limits can change with new technologies, which in turn depends on money-cost as you mention.
It does not exclude easily accessible material. It only excludes material not assessed yet because there has been no need to, as existing reserves will last more than long enough to perform further surveys.
We've just started looking for the thing at the scales we need it now, prospecting and extracting and processing it will improve.
Even if the research is being done, we've got decades before something commercially viable comes out. The need exists now. Anything that isn't essentially ready to go by 2030 probably isn't going to do squat to help us.
What the number shows is that there is no possibility of ever tapping out all available lithium, no matter how many batteries are manufactured. Once the world is saturated, used-up batteries will become the main source for materials to build new batteries from.
The more immediate limitation is rate of manufacture of batteries, because building battery factories takes a long time.
For the most part you are correct. But building the mines, refining, supply chains, etc takes time. So you are perhaps missing one of the main points I was trying, maybe unsuccessfully, to make: we need to deal with the 'right now' and not just worry about how we'll be fine in 50 years.
Lithium is a perfect example. We have plenty in the ground. We don't have plenty of mines. We should be allocating Li carefully until those issues are resolved in 5-10 years.
If we only base our energy policy on how things will be in a decade we will delay the transition while inflicting maximum pain on the population(energy and food shortages, rampant inflation, lower standard of living, etc).