Lithium - The Lightest Metal.

I've been contacted by a number of folks recently asking about lithium. Most of them seem to be Wall Street types interested in my opinion on the usage of lithium for battery manufacturing. At the risk of violating a rule proposed by Einstein ("everything should be made as simple as possible, but not simpler") I thought I'd throw down some facts about Element Number 3.

Lithium is a metal, but lacks a lot of the properties that most of us associate with its more structural cousins. Almost structurally bankrupt, lithium can be cut with a knife, with a consistency resembling chilled butter. It finds structural applications only when alloyed (the external tank of the Space Shuttle is made from aluminum-lithium alloy) where it improves the mechanical properties while reducing mass due to its extremely low density. Lithium floats in even the lightest of mineral oils, and would handily do so on water as well if not for another of its unusual properties, an extremely high reactivity. Lithium reacts with water, tarnishes on contact with atmospheric oxygen and will even burn in nitrogen. It is happy to give its outermost valence electron to anyone who will take it, disrupting even the highly stable triple bond in molecular nitrogen. Lithium is also capable of intercalation into the crystal structure of other materials, notably graphite and metal oxides. Without the sturdy mechanical properties of its transition metal cousins, lithium has found some more unusual applications, and its low density, high reactivity and ability to infiltrate other crystalline materials, lithium is the charge carrier for most high-energy battery systems produced today.

The way in which this lithium can be used in the anode and cathode of the batteries is a field of relatively fertile development with active searches for new materials yielding new discoveries every year. What doesn't change too much, however, are the relatively simple mathematics of lithium usage. As strange a substance as metallic lithium can be, it has to follow the rules of chemistry and physics just like everyone else.

Lithium has an atomic mass of 6.93 g/mol. One mol of anything has 6.023 x 10^23 of those things. Each lithium atom has that one valence electron. So in 6.93 grams of lithium, you can liberate 6.023 x 10^23 unwanted valence electrons.

With those 6.023 x 10^23 valence electrons (each with 1.6 x 10^-19 coulombs) we get 96485 coulombs (or Faraday's constant) per gram of lithium.

But of course, we battery people never talk about coulombs and joules, but rather about amp-hours and watt-hours. There are 3600 joules in a watt-hour, and 3600 coulombs (or amp-seconds) in an amp hour. If a T-Rex was a useful unit of energy, there are 3600 T-Rex-seconds in a T-Rex-hour. Or pretty much any unit you can think of.

Therefore, those 96485 coulombs (or 1 F) that we got from those 6.93 grams of lithium turn out to be 26.8 amp-hours. Or dividing the two we get 3.867 Ah per gram of lithium.

Nothing that you, nor I, nor anyone on Wall Street, nor Dmitri Mendelev himself can do will change any of this.

A typical 18650 lithium-ion cell is around 3.6 Ah. Assuming for a moment that there is no surplus lithium above what's cyclable and that some small number approximations hold (I know, this is flirting dangerously with the "too simple" part of the quote), that 18650 cell contains about a gram of cyclable lithium.

Now of course many would say that we need watt-hours to do useful work, not only amp-hours, and therefore we need to multiply those amp-hours by a nominal cell voltage to get the watt-hours for each cell. Technically the voltage seen at the cell terminal is a function of how both the anode and cathode store the lithium, but increasing the cell voltage requires not only appropriate materials but other improvements like electrolyte stability at higher voltages. The typical lithium ion cell voltage hasn't moved too much in the last decade or so. Some 4.3 and 4.4 volt designs exist now, but most cells are typically considered 'fully charged' at 4.2 V, and have what I call a "capacity weighted voltage" (the voltage at which the energy of a hypothetical cell with a constant voltage would equal the energy of the real cell) around 3.6-3.7 V.

Therefore, with one gram of lithium, you can store somewhere around 13 watt-hours of energy. Or 46 kJ. Don't ask me to convert to T-Rex.

With that 13 watt-hours of energy we can propel a vehicle. If it was the influential 1990's EV1, we needed about 190 Wh to drive a mile. Many smaller EVs might use 250-300 Wh/mile, and larger SUVs might need 350-450 Wh/mile. If we assume that 300 Wh/mile is a good number to use, I need about 23 grams of cyclable lithium to drive one mile.

If you assume that mediocre EVs might have less than 100 miles of range, decent ones might have 200 miles of range, and great ones would have more than 300 miles of range, you might end up with a range of 2.3-6.9 kg of lithium per EV.

So if you want to understand the annual world market for battery grade lithium, you just need to take all the above numbers and simply combine them with the number of EVs sold per year.

Figuring out that number, of course, is another matter entirely. I'll stick to what I'm good at.