Yeah... I'm not sure what that is. They also conflate mA and mAh a few times. It's kind of confusing.

I think that they are using the weight of lithium metal rather than the actual battery. That's the only thing that makes sense, as the specific energy of PURE LITHIUM is barely above that 10.5 Wh/g figure. The 10.5 must come from the energy drop to sulfur intercalation, which is at .4v. The 8.5 Wh/g figure comes from the reversable voltage range. It's either that or their numbers are off by 100x.

With units of Wh/g (Li metal), my impression is that it's measuring grams of pure lithium.

Yes, but its not a useful measure. Most batteries will have similar specific energy when compared by lithium directly. How effectively the lithium is used is also almost completely irrelevant to the cost, weight and size of the battery. It's just a really weird thing to measure and they don't actually specify what the grams are of- lithium or sulfur are just the only things that make sense.

The grams are specified as "g (Li metal)", so grams of lithium.

Yes, but on first read I thought that they were specifying for the battery using lithium metal as they were also talking about sodium and nonmetallic lithium. It's just so random I didn't read it correctly.

Is lithium the most expensive material in the chemistry?

I made a cursory attempt to find the answer, and I was unsuccessful. I did find this[1], though (from my alma mater).

[1] https://engineering.cmu.edu/media/press/2016/12_13_whitacre_...

That makes sense... Li is typically 4% of the weight of a Li-Ion battery, so that would align pretty well.

I think you're reading it right, or close to it.

It seems like the biggest advance of this one is that the design allows the use of a metallic lithium anode rather than NMC/LMO/LFP etc. They say in the introduction:

"The organic-liquid electrolyte of the lithium-ion battery has an energy-gap window Eg ≈ 3 eV, but its LUMO is below the Fermi level of an alkali-metal anode, it is flammable, and it is not wet by an alkali-metal anode..."

The actual design is lithium metal plated directly onto lithium-doped glass, placed onto sulfur ink on copper as an electrode.

My translation is "The organic-liquid electrolyte will start to spark above 3eV, which is lower than the electron energy if lithium were directly touching it as a metal. Plus, hey, the electrolyte won't wet the metallic lithium anyway so contact is poor."

The glass has a much higher band gap, wets lithium (and sodium, which they also talk about) metal, diffuses sodium and lithium pretty fast, and manufacturability is super high since now you can use all kinds of standard metal working techniques rather than powder handling and sintering -- lithium even melts at 180C, so processing temperatures might be way lower and less costly.

In any case, in this context, the weight density is probably just normalized to anode mass. That would be better to explain clearly what they meant, but it seems fair since the energy density really is higher if you have more lithium in there and that's often the energy density limiting component.

Note: Here's something from just 2014 with a better explanation of why it matters, and a much more complicated sounding solution. https://www.scientificamerican.com/article/pure-lithium-in-b...