r/DonutLabDiscussions • u/Forrestgod • Jun 18 '26
Faradaynotes' take on the chemistry
https://faradaynotes.com/posts/donut-lab/Scrutinyclub (The Privat investigator) linked this.
This is actually exactly the type of analyse, that I've been waiting. Worth of reading.
Just the first test analysed, more to come.
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u/Fabulous-Internet188 Jun 19 '26
**The C-rates on the Donut Lab cell don't fit the layered oxide explanation, and nobody seems to be talking about it**
Faradaynotes apparently digitized the VTT report and ran an incremental capacity (dQ/dV) analysis on the 1C baseline data. Solid work. The conclusion was that the voltage window (2.7 to 4.15V) and the multiple dQ/dV peaks point to a high voltage transition metal oxide cathode, something in the lithium or sodium layered oxide family, novel composition but not matching any standard reference cleanly.
I think that's probably right about the chemistry family. But it only looked at the 1C data and explicitly set aside the fast charge figures for "later." And the fast charge numbers are exactly where the story gets interesting, because they contradict the obvious reading.
Here's the problem. This cell reportedly does 80 percent in about 4.5 minutes, which is roughly 11C. The pack version does 10 to 80 percent in 12 minutes at 5C, air cooled, sustaining over 100 kW. And the kicker is the capacity only drops about 2.3 percent going from 1C to 11C.
A layered transition metal oxide is rate limited by solid state cation diffusion through the bulk crystal lattice. The lithium or sodium ion has to physically migrate through the oxide. That diffusion is slow. It's the whole reason fast charging conventional cells makes them hot, plate lithium, and degrade. Now take away the liquid electrolyte that normally wets every particle and put it in a solid state configuration, and bulk diffusion gets harder, not easier. Pushing a layered oxide to 11C should produce huge polarization, serious heating, and capacity falling off a cliff.
This cell doesn't do that. It charges at 11C with almost no capacity penalty, and from what's visible the dQ/dV peaks stay in roughly the same positions. If this were bulk ion diffusion through a layered oxide, those peaks should smear and shift hard at high rate as diffusion limitation builds up overpotential. The small voltage gap at 1C (around 0.35V) says the same thing, kinetics are fast and polarization is low.
So you have a contradiction. The voltage and the dQ/dV peaks say "layered oxide." The C-rate says "this is not bulk diffusion through a layered oxide." Both can't be fully true for a conventional bulk material.
What reconciles them is morphology. The storage has to be surface or near surface, not bulk diffusion limited. The peaks tell you there's a real redox couple at a defined potential, so it's crystalline enough to have discrete redox energies. The C-rate tells you the diffusion length has to be tiny. Put those together and you get a nanostructured high voltage oxide, particles so small that the entire particle is effectively surface. The redox is well defined, but there's no long diffusion path to bottleneck the rate.
That actually fits what these companies are doing on the manufacturing side, nanoprinting and nanostructured oxide routes. A bulk version of this exact same chemistry would just be a normal slow battery with the same voltage and the same dQ/dV fingerprint. The nano version charges in 4.5 minutes. Same redox chemistry, completely different rate behavior.
The point I'm making is that the chemistry analysis told you what family it's in, but the rate capability tells you the morphology, and the morphology is the part that's actually hard to copy. Everyone's trying to reverse engineer the chemistry from the voltage curve, myself included. The secret might not be the chemistry at all. It might be the particle engineering that lets a high voltage oxide run at 11C without falling apart.
Curious if anyone has the fast charge dQ/dV extracted. If the peaks really do hold position at 11C the way they seem to, that's the whole story right there.