r/DonutLab

I don't remember DonutLab ever saying out loud they have a third party 'Cooperation Partner', but the NDA for the latest test report does say it. I assume this refers to CT Coating.

>The purpose of this Agreement is to protect the confidentiality of certain confidential information that the Company intends to make available to the Recipient, separately from any information made publicly available by the Company, including a confidential video and/or reports containing information subject to confidentiality obligations relating to the Company’s cooperation with a third party (the “Cooperation Partner”)

The video and test report itself could, according to the NDA, come from both the Cooperation Partner and another third party.

>The confidential video and/or reports made available to the Recipient separately from the Public Video may have been prepared by or on behalf of, or provided by, the Cooperation Partner or another third party, and the Company is making such information available to the Recipient subject to the confidentiality obligations applicable to such information and pursuant to its obligations towards the Cooperation Partner or such other third party.

Bit weird that this NDA allows the video to come from CT Coating instead of the testing company.

Full NDA text:
https://pastebin.com/vPvjjq3P

https://preview.redd.it/ysqgu5saqwjh1.png?width=1102&format=png&auto=webp&s=8636ae9216665beb456116d56eadb6cf53bd1465

Firstly, IANAL, what do people need to be conscious of before discussing these NDAs?

I suspect it wouldn't make sense for Donut Lab or anyone else to actually try and enforce NDAs that they have let anyone sign up to on the internet, it just seems hopeless to try and actually enforce, and it is likely just a marketing stunt/stalling tactic anyway*. That said, it might not be the smartest idea to comment that you signed the NDA and then directly leak the contents, so unless someone with more than a layman's familiarity with the legalities of this situation can advise on this, I'm going to discourage anyone from doing that on this post. As I understand it, if someone has leaked it to you, and you haven't signed the NDA, you might be okay to comment with the details, but again, IANAL.

Last Thursday Lehtimaki said they would probably send out the NDAs the next day, has anyone heard anything about whether they did actually send anything out?

If you get sent an NDA, but do not sign it, can you share the contents of the NDA?

* Yes it might not be Donut Lab who put the NDA in place, but I don't really understand why a third party would insist on an NDA but then have such lax restrictions on how the NDA is signed up for.

What a bipolar cell is. Instead of discrete cells wired in series with tabs and busbars, you coat the cathode on one side of a current collector plate and the anode on the other, then stack N of these plates. The series connection happens through the plate itself. You save tab mass, interconnect resistance, and packaging volume, and you can pick your stack voltage by picking N. That's the whole trick, and it's a good one.

Why bipolar does not require a solid electrolyte. Bipolar is an architecture. The electrolyte state is a separate variable. Proof by production hardware: Toyota has been shipping bipolar NiMH as the traction battery of the Aqua since mid-2021, built with Toyota Industries at the Kyowa and Ishihama plants, tens of thousands of packs per month. NiMH is an aqueous system, roughly 6 M KOH. A liquid, and a nastily creepy one at that. Toyota's next step is bipolar LFP, the "popularization" battery on their 2026-2027 BEV roadmap, again a conventional liquid-electrolyte lithium chemistry, plus a bipolar high-nickel variant for 2027-2028. And the concept is old: bipolar lead-acid goes back to the 1920s, and bipolar Li-ion with a standard LiPF6 carbonate electrolyte was patented in 1997.

• Toyota Industries, bipolar NiMH for Aqua: https://www.toyota-industries.com/products/automobile/batteries/index.html
• Toyota battery roadmap, bipolar LFP 2026-2027: https://global.toyota/en/newsroom/corporate/39330500.html
• Bipolar Li-ion with liquid carbonate electrolyte, US5595839 (1997): https://patents.google.com/patent/US5595839A
• Review on bipolar sodium-ion, incl. history from 1923 Pb-acid onward: https://www.sciencedirect.com/science/article/abs/pii/S2352152X23005364
• Sakuu showing Munro physical bipolar lithium-metal stacks: https://www.youtube.com/watch?v=yZhKqpleAXM
• Good general explainer: https://www.batterydesign.net/chemistry/bipolar-battery/

The actual hard problem in bipolar has never been "the electrolyte is liquid." It is that every layer must be ionically isolated from its neighbours. Any shared electrolyte path around the edge of a plate is a shunt across a series junction: self-discharge plus plate corrosion. The fix is a sealed frame around the perimeter of every layer, which is why most of the bipolar patent literature is sealing patents (see e.g. CEA's US10497941). A solid electrolyte makes sealing easier because nothing wicks. Easier, not uniquely possible. A semi-solid or gel design sits in exactly the same category. So "our cells are bipolar, therefore solid-state" is an argument that Toyota's KOH-soaked Aqua pack disproves at a rate of 40,000 units a month.

The part nobody demos on a bench: balancing. A bipolar stack is a series string. Physics doesn't care whether the series connection runs through a busbar or through a shared collector plate: the current through every layer is identical either way, and the reasons cells drift apart are identical too. Differential self-discharge, differential coulombic efficiency, and capacity spread turning equal Ah throughput into unequal ΔSOC. These accumulate in one direction with no restoring force.

In a normal lithium pack the BMS handles this. Every series element gets a voltage sense lead, and a balancing circuit bleeds charge off the high cells, typically some tens to hundreds of mA. Now try that inside a bipolar stack. Every sense lead and every balancing conductor is a feedthrough breaching the perimeter seal, which was the hard part of the design to begin with. Sensing is arguably manageable, a sense lead carries microamps and could be a thin foil extension of the plate. But balancing needs real current through a real conductor with real dissipation, per layer, inside the stack. At that point you have rebuilt a module BMS in the least accessible location imaginable and thrown away most of the packaging win you built the thing for.

Why NiMH gets away without any of this. NiMH has a built-in chemical balancer. On overcharge, the positive electrode evolves oxygen, which diffuses to the negative and recombines. The excess current turns into heat instead of voltage rise, so a layer that gets ahead clamps itself and the string equalises automatically. Lead-acid has an equivalent gassing shunt. This is precisely why Toyota commercialised bipolar NiMH first: you can treat the whole stack as one monolithic cell, monitor only the terminals, and the chemistry forgives you.

Lithium has no such sink. Overcharge in a lithium cell is not self-limiting, it's destructive. And before anyone points out that Donut says their battery contains no lithium: sodium-ion has exactly the same problem. No overcharge recombination mechanism, no chemical self-balancing, same one-way drift, same destructive endpoint. Whatever intercalation chemistry you pick, a monolithic bipolar stack without per-layer access is a series string that is simultaneously unbalanceable and unobservable. On a flat-plateau chemistry, one layer can quietly walk toward overcharge while the terminal voltage of the stack looks perfectly normal. I have no idea how SAKUU solved this as they use some lithium metal chemistry.

So the interesting question was never "can you make three cells read three voltages." The question is what happens to layer-to-layer drift over the claimed 100,000 cycles in a chemistry with no chemical overcharge sink and no published balancing scheme. Either the layers are tapped, in which case "one cell, any voltage" is doing some heavy lifting as a description, or they aren't, and then the cycle-life claim needs an explanation nobody has offered yet.

I was waiting for the next Idonutbelieve video to land today as announced but it was just pushed to tomorrow.

I mean, just give me a link to them when uploaded somewhere else.