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Donut Lab reveal - what happened?

Yesterday I wrote about the pending reveal of independent tests of the revolutionary Donut Lab battery technology.

Today, the first part of that test data dropped.

Has this validated the company's claims?

Let's take a look.

As I suggested yesterday, we didn't get a comprehensive overall validation of the many claims made for this battery. Instead, we got a look at just one aspect of the technology.

This first set of data from the testing company VTT deals only with charge rates.

The Donut claims that their battery can be fast-charged at up to 11C (that's the current capacity of the battery multipled by 11). In the case of this supposed 26AH cell, we're talking about 286 amps.

The figures presented by VTT verify that the cell can handle an 11C charge rate with what appears to be slightly less efficiency than existing tech -- albeit at once stage the cell temperature reached almost 90 degrees C despite a heatsink being attached. Clearly a significant amount of the charge energy is being converted to heat. Traditional Li-Ion chemistry wastes around 10 percent of the charge energy, here' we're almost double that when charging at 11C.

If we look at the numbers, it appears that this nominally 90WH cell wastes around 20WH when charged at 11C. The 90WH discharge capacity actually requires up to 110WH of input energy -- hence the reason for the significant temperature increase.

If we look at the average EV battery capacity of (say) 70KWH, this means that a full charge at 11C will result in some 15KWH of waste heat over the 8 minute charge period.

That is a *lot* of energy to dissipate over a relatively short period of time, significantly more than is the case with existing EV battery and charging technologies.

Even with active cooling, it's going to be a challenge for EV manufacturers to actually realise the potential 11C charging rate that these batteries appear to offer. Dumping 15KW in just 8 minutes is a big ask and chances are that in "the real world", thermal throttling will occur during charging and that will bring the *actual* practical charge rate down to a figure that is more in line with existing technologies.

This will be especially true in regions where daytime ambient temperatures may be tens of degrees higher than that encountered elsewhere.

So, kind of as predicted, although "technically" speaking, the Donut battery tech does appear to live up to the claims in respect to charge-rates, the relative inefficiency when charging at 11C rates points to the claims being "headline claims" and not necessarily representing the whole truth.

There are other battery technologies out there that can be charged at 11C rates or higher -- but there is usually a heavy penalty to be paid in terms of charge-cycle life. These high charge rates tend to result in much reduced lifespan when compared to lithium-ion or LFP chemistries. The data presented today is only a very small part of the whole picture. What we really need to see is how many effective charge-discharge cycles these cells can handle at a 11C charge rate.

My suspicion is that when they deliver the cycle-life testing figures, the company's claims for this aspect of the cell's performance will not apply at the 11C charge rates.

As I suggested in yesterday's column, each of the individual claims may hold up in isolation but I fear that we won't get a battery that delivers on all those claims at once. If it did then why go through this unnecessary staged release of the test data?

Carpe Diem folks!

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