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Donut Lab battery tests, part 3

The third tranche of independent test results on the Donut Lab solid state battery technology has dropped.

Wow... if this is all they've got then I think we can consign this "breakthrough" techology to the hyperbole bin.

Of all the things that people really don't care about in a high energy, high capacity battery, the self-discharge rate is probably ranked number one.

The type of application that this battery will find itself in really doesn't care about self-discharge. These batteries will likely be discharged within hours of being charged so nobody cares if that self-discharge rate is 1 percent per day or 5 percent per day.

So why did they even bother testing this aspect of the battery's performance?

Well according to the company, it was to prove that their batteries aren't just big supercapacitors.

Err.. excuse me but anyone with even the most basic understanding of electrical theory will have already worked out that these aren't supercapacitors, simply by looking at the charge/discharge current/voltage curves provided in the first tranche of data.

A supercapacitor with this kind of energy density would also be a 45-fold improvement over existing supercap technology -- rather unlikely.

Interestingly enough, although they tout a low-self-discharge in these tests, the reality is that the Donut Lab solid state cells seem to have a rate that is significantly higher than existing conventional lithium-ion chemistries.

As I mentioned earlier, this is not realy a problem for EVs or electric-flight, it could be an issue if you were perhaps going away for a period of time and had to leave your car in storage. A regular recharge would be required for protracted periods to avoid the battery going flat -- something most chemistries are rather unforgiving of.

No, I'm picking that this is simply an attempt to delay the *really* important data.

That really important data is the energy density and the cycle-life of these cells.

Are they saving the best until last?

I doubt it. Rather, I suspect they're trying to keep disappointment at bay for as long as they can.

Chances are that they will somehow fudge or simply not release the super-critical tests that would verify the 400W/Kg energy density or 100,000 cycle-life claims.

I'm picking that for cycle-life, they'll conduct a few hundred charge/discharge cycles and then extrapolate that to the point where 80% of the capacity remains. This is a deeply flawed technique since many chemistries have a rather non-linear degradation and the degree of this non-linearity would not be apparent in such a limited test.

As for the 400WH/Kg, they may opt to measure energy-in rather than energy actually stored and delivered. Alternatively, they will measure the weight of the bare cell which is again, not really a true result because bare cells will not deliver on the charge or discharge rates being claimed previously because that would cause overheating without some form of heatsink or active thermal management.

Once you add the essential thermal management the actual *real-world* energy density will likely fall far below the figures currently being claimed and even then, not able to be delivered at the "5-minute charge" rate.

Putting my cynic's hat on again, I think that if this battery tech was all they claim it to be then they would already have begun licensing it to third parties. Why go to all the hassle of engaging in marketing stunts like this drip-fed test data if you could already be raking in billions of dollars for simply allowing others to build your patented battery cells?

Sorry, this doesn't pass the sniff test.

If you're interested, the third tranche of test data can be found here.

Carpe Diem folks!

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