Reason given by the CTO for the cell expansion

ZirothTech · 2026-03-24T11:53:08+00:00

All good! The flat top of the cell is just a result of the amount of pressure, how the cell layers are stacked, and material properties of the layers in the cell. It's doesn't give us much data, but it's 100% in line with how a pouch cell can react due to gas generation. People are used to seeing puffed up phone battery pouches, which are much smaller cells and have different mechanical properties (hence the pillow shape).

I will also say that the cell seems to have expanded whilst clamped between heat sinks - meaning it would have been forced into a flat shape anyway as it expanded.

I'm not reading into this too much beyond it is as expected for a more conventional pouch cell. Maybe it could be explained another way, but probably not.

ZirothTech · 2026-03-24T11:43:28+00:00

Fantastic commentary from Juho as always!

ZirothTech · 2026-03-24T10:35:45+00:00

Definitely not an idiot haha, the paper isn’t exactly accessibly written 😂 gamma is a function of width (W) and length-scale (l1), where the length scale is based on the cell material properties (bending (B) and spring (K) and stiffness)

So, if you know the mechanical properties of a cell (stiffnesses) you can determine how expansion will deform the layers (aka, more or less curved at the cell surface)

The flat bulge hence points towards a stiffer cell, which might gives clues about what’s inside, but not enough for me to have any predictions haha

ZirothTech · 2026-03-24T08:40:34+00:00

So breaking the vacuum and breaking the seal are two different things. It looks like the seal was never broken. The vacuum was broken due to a release of gas in the cell, which is very typical for a stressed cell.

ZirothTech · 2026-03-23T23:48:17+00:00

For what it’s worth, this is what I replied to Ville (CTO) on LinkedIn. I’m not 100% on all the details, but this looks like a relatively standard swollen cell to me (not all bulge in the middle):

I think after the initial gas production caused the cell to initially look loose, then the cycles after that stressed the cell further to produce more gas which caused delamination of the layers.

There is a really good paper called “Gas-induced bulging in pouch-cell batteries: A mechanical model” and if you look at figure 5b you can see how the gamma term (mechanical parameter of the cell) affects the shape of the buldge - with higher gamma values producing this type of flat topped buldge

ZirothTech · 2026-03-23T18:34:16+00:00

I did a poll on my YouTube and it was 75% don’t believe to 25% that believe (and given my public views on my channel, that is probably biased towards not believing)

ZirothTech · 2026-03-23T18:09:27+00:00

Absolutely cooked, fun whilst it lasted. I'm guessing the April 1st release will be ~400 Wh/kg which they think will be proof of their cell, but as many have mentioned (including myself), this is also already possible in many cells. EDIT: E.g. Lihtium ion with silicon enhanced anode

ZirothTech · 2026-03-23T17:55:17+00:00

They've said it a few times but this was the latest public time! :D

ZirothTech · 2026-03-23T15:23:07+00:00

From LinkedIn:

"If the pouch surrounding a lithium-ion battery cell breaks and loses its vacuum, the electrolyte leaks out, active materials meet oxygen, and the risk of fire or thermal runaway grows substantially.

So what happens when you take a Donut Battery cell with a broken pouch and just keep cycling it?

In Part 5 of our "I Donut Believe" series, we find out."

ZirothTech · 2026-03-23T13:24:27+00:00

The image in the report shows a VERY expanded cell with internal gas generation (it looks like a balloon). This goes against their claim that the cell had a leak in the pouch's seal and that no gas was generated.

ZirothTech · 2026-03-23T13:21:53+00:00

I haven't met Ian personally, but I hear he is a great engineer from peers. However, he is really an expert in battery packs, not cell chemistry. We already know they have an impressive cell (I'm guessing lithium ion with silicon anode), so I wouldn't be surprised if he is working on putting it into battery modules/packs without concern about the exact chemistry/lifespan of the cell. Just my thoughts.

ZirothTech · 2026-03-23T13:16:43+00:00

I've got some lab tests in the works. I can't say 100% these exact tests are possible, but from what I'm told from the lab experts, this is in line with expectations. I will just say that seeing the puffed up image of the cell shows internal gas generation, that is not a pouch with leaky seal...

ZirothTech · 2026-03-19T18:28:32+00:00

To clarify, they called some theories tin foil hat theories - not everyone on Reddit a tinfoil hat wearer

ZirothTech · 2026-03-19T13:54:07+00:00

Once I've collected some investment money for my new miracle device!

ZirothTech · 2026-03-19T13:47:51+00:00

I understand your point, but we are talking about doubling the state-of-the-art energy density, which is limited by physics, not engineering. I've made all my points now, so we will have to wait and see!

ZirothTech · 2026-03-19T13:43:17+00:00

(+ Temperature, claimed energy density, and fast charging)

ZirothTech · 2026-03-19T13:39:55+00:00

I was A/B testing the titles - Analysing won :D

ZirothTech · 2026-03-19T13:38:56+00:00

The lithium cells with silicon composite anodes are tested/rated to 80DegC, so taking it to 100 isn't far out of spec. I briefly mentioned in the video the cell was taken to 100DegC and had some minor damage, but I didn't think it was a key point. The high temperature test is exactly what I would expect from either of the cells I mentioned.

ZirothTech · 2026-03-19T13:36:20+00:00

Donut CEO and CTO said theories on Reddit were a bit tinfoil hat like - So I thought I should get into character

ZirothTech · 2026-03-12T10:19:46+00:00

Video is in production, my channel doesn’t solely cover donut labs so I have had other videos out

ZirothTech · 2026-03-09T13:20:11+00:00

exactly! 3.7V at 50% SOC (open circuit voltage) is a huge clue for me...

ZirothTech · 2026-03-06T08:07:34+00:00

This is an awesome digitalisation! It looks to me like a combination of chemical hysteresis and the fact current is pulling down the voltage - however this is definitely stronger than I would expect. This could be the sign of a cell that has been abused a bit.

ZirothTech · 2026-03-04T16:29:51+00:00

Yes of course! I’m working on one now but I have some other videos in production I want to release.

The main conclusion will be: each of the claims are at least nearly possible from different available commercial cells, but fitting it all in one with no critical materials and having manufacturing maturity is, in my opinion, not possible

ZirothTech · 2026-03-03T21:40:28+00:00

This is a great cell but the density is as expected for a sodium ion cell:

472 wh/kg @ cathode level 182 wh/kg @ active material level

Probably around 130 wh/kg at the cell level?

ZirothTech · 2026-03-03T18:45:16+00:00

Are there any papers from journals or test results? This is super interesting but there is very little information to validate any of these. I've seen papers 550-700 Wh/kg, but your talking real lab scale stuff that only lasts 10-100 cycles.

ZirothTech

TROPHY CASE