[Physics] Why is there a scarcity of lithium

big-banggeophysicsnuclear-physicsnucleosynthesisstars

One of the major impediments to the widespread adoption of electric cars is a shortage of lithium for the batteries. I read an article a while back that says that there is simply not enough lithium available on the entire planet to make enough batteries to replace every gasoline-powered car with one electric car. And that confuses the heck out of me.

The Big Bang theory says that in the beginning, there was a whole bunch of hydrogen, and then lots of hydrogen started to clump together and form stars, and those stars produced lots of helium through fusion, and then after helium, all the rest of the elements. That's why hydrogen is the most common element in the universe by far, and helium is the second most common.

Well, lithium is #3 on the periodic table. By extrapolation, there ought to be several times more lithium around than, say, iron or aluminum, which there is definitely enough of for us to build plenty of cars with. So why do we have a scarcity of lithium?

Best Answer

Actually, what you've read about the production of nuclei is not quite correct. There are several different processes by which atomic nuclei are produced:

  1. Big Bang nucleosynthesis is the fusion of hydrogen nuclei to form heavier elements in the early stages of the universe, as it cooled from the big bang. There are rather specific thermal requirements for this process to occur, so there was only a short time window in which heavier elements could form, meaning that the only fusion to actually happen in significant amounts was the conversion of hydrogen (and deuterium) to helium, and an extremely tiny amount of lithium.
  2. Stellar nucleosynthesis is the fusion of hydrogen and other nuclei in the cores of stars. This is something separate from big bang cosmology, since stars didn't form until millions of years into the universe's lifetime.

    Now, contrary to what you might have read, not all elements are formed in stellar nucleosynthesis. There are specific "chains" of nuclear reactions that occur, and only the elements that are produced by those reactions will exist in a star in appreciable quantities. Most stars produce their energy using either the proton-proton chain (in lighter stars) or the CNO cycle (in heavier stars), both of which consume hydrogen and form helium. Once most of the hydrogen has been consumed, the star's temperature will increase and it will start to fuse helium into carbon. When the helium runs out, it will fuse carbon into oxygen, then oxygen into silicon, then silicon into iron. (Of course the actual process is more complicated - see the Wikipedia articles for details.) Several other elements are produced or involved along the way, including neon, magnesium, phosphorous, and others, but lithium is not among them. In fact, stars have a tendency to consume lithium, rather than producing it, so stars actually tend to have only small amounts of lithium.

  3. Supernova nucleosynthesis is the fusion of atomic nuclei due to the high-pressure, high-energy conditions that arise when a large star explodes in a type II supernova. There are certain similarities between this and big bang nucleosynthesis, namely the high temperatures and pressures, but the main difference is that an exploding star will have "reserves" of heavy elements built up from a lifetime of nuclear fusion. So instead of just forming a lot of helium as occurred just after the big bang, a supernova will form a whole spectrum of heavy elements. In fact supernovae are the only natural source of elements heavier than iron, since it actually requires an input of energy to produce those elements as fusion products. I believe some amount of lithium would be formed in a supernova along with all the other elements, but since a large star would have used up its hydrogen and helium in the central region where most of the action takes place, lithium is probably not a particularly common reaction product.