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More on Donut Labs solid state battery

Yesterday Donut Labs released the second tranch of independent tests on their allegedly revolutionary solid state battery technology.

Sadly, it looks as if my predictions in regards to the "weasel-words" and disappointment associated with this tech are right on the money.

Regular readers will recall that I predicted that these independent tests would validate each of the individual claims made by Donut Labs but only in isolation.

The problem is that you can't enjoy all the benefits at the same time so this tech isn't really going to deliver the rosey future we were promised.

In fact, there are already some tried-and-tested battery technologies that deliver the promises made by Donut's solid state batteries, the only difference being that they're honest about the limitations involved.

This second tranche of data focuses on the cell's performance at high temperatures.

TLDR?

Basically these cells perform well at higher temperatures, delivering at least the rated capacity even when operated at temperatures of 100 degrees C.

It is really important to note however, that the maximum discharge rate during these tests was just 1C -- a paltry 24A.

Note also that the maximum charge rate was also 1C and one test used a 0.5C charge rate. Both of these are a far cry from the 11C (5 minute) charge rate used in the previous tests.

It's also worth noting that one of the cells suffered a physical failure during the test. You'd think they'd carefully test and select those cells submitted for testing so this failure is significant.

I would wager that if you tried to combine the high temperature performance seen in this report with the fast-charging documented in the previous one, the result would be rather incendiary in nature. This is pretty much confirmed by the fact that during the first tests high-speed charging was temporarily paused once the cells approached 90 degrees C.

So you get to have fast-charging *or* high temperatures -- but not both at the same time.

Another worrying omission in this second report (as it was in the first) is the lack of dimensions and weight for the cells under test. Surely, if the claims of 400WH/Kg are true then they would have included at least the weight of the 24AH cell so that this claim could be verified for the cells on test.

I wonder if the cells they submit for the energy density test will be somewhat different to the ones used for the fast-charge test. Generally speaking with most battery technologies, a higher energy density means a lower max-power handling ability both under charge and under load so if you want to "fudge" the figures you provide different versions of the cells for each test.

The fact that there doesn't seem to be a statement that exactly the same set of cells has been used for all tests is perhaps a hint that the validation lab may have been give specifically customised cells for each individual test.

Bottom line: I'm not in the least convinced that we have a "revolutionary" new battery technology here.

To be honest, I think that the Chinese battery giant CATL may be onto something far more practical with their latest claims to have a more evolutionary tech almost ready to roll.

Carpe Diem folks!

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