Overheating buzz battery: This is all we know about Donut Lab’s battery now

The measurements of the Donut Lab battery made by VTT have attracted enormous interest, and hardly ever has the general public’s hunger for information on the laboratory measurement results of a single battery been so great.

In the report published yesterday, indeed, VTT had a battery or battery cell in the measurements that was capable of the wild charging speeds promised by Donut Lab. In the 11C test, the battery was charged to 80 percent in 4.5 minutes and fully charged in more than seven minutes.

When battery researchers have analyzed the tests in more detail, new features have begun to emerge from the report. One of them is the alarming information that in the 11C charge measurement, which tests the battery the hardest, the battery cell got so hot that the measurement had to be stopped.

Professor of battery chemistry and materials at Aalto University Tanja Kallio had time to review the results of VTT’s report on Monday evening. He commented on the temperature issue as follows:

“In VTT’s measurements, the temperature of the battery rises when the charge-discharge cycles are repeated. In the last (or actually the middle) 11C charge, the temperature of the battery rises above the set safety limit and the measurement is interrupted,” Kallio points out from the report.

According to the report, the safety limit of the test is set at 90 degrees Celsius, which is an extremely high temperature for any battery.

“If a unit cell was used in these measurements, then for the battery of the actual vehicle, several such unit cells would have been needed to store a sufficient amount of energy. Of course, these measurements do not prove, but they nevertheless point in the direction that such a battery should have active cooling when using fast charging”, says Kallio.

Kallio’s analysis contradicts Donut Lab’s Ville Piipon with, who in turn specifically emphasized in the company’s video and press release that Donut Lab’s battery does not need much active cooling. If the battery is to be charged with the promised 11C power, according to the tests, active cooling is indeed needed.

Research and development manager of Seinäjoki University of Applied Sciences Juho Heiska stated the same observation to Alma News Media immediately after the announcement.

“However, with a hard 11C charge, the battery got really warm, which means the resistance in the battery”, Heiska estimates.

Kallio states that the internal resistance of the battery could indicate that the battery is a truly solid electrolyte battery.

“Solid electrolytes often have a higher internal resistance to the transfer of lithium ions than batteries based on liquid electrolytes. In this case, a larger proportion of the energy is converted into heat due to the internal resistance of the battery. The large temperature rise observed in the measurements could therefore be due to the high internal resistance of the solid electrolyte,” Kallio speculates.

Is it a lithium battery?

One of the questions concerning Donut Lab’s battery that has puzzled experts and the general public since the very beginning has been what chemistry or technology the battery is based on. There have been claims from one side to the other, and there have been claims that it could even be a supercapacitor based on a completely different technology.

We asked battery professor Tanja Kallio what chemistry she thinks the Donut Lab battery is based on based on VTT’s tests.

“Based on the charge-discharge curve alone, it is not possible to judge whether it is a lithium battery. The voltage range used is wide, which would indicate, for example, a lithium-ion battery or a sodium-ion battery. However, we do not know whether the cell tested by VTT has only one cell or several. So we do not know whether it is a discharge-charge curve of a unit cell, which is why it is not possible to analyze the matter in more detail,” Kallio opens.

Genuine transparency is missing

The biggest problem with Donut Lab’s and VTT’s tests is linked to this. Although the tests performed by VTT have been carried out correctly and independently, we do not have any further information about the battery used in the test and its contents.

Both Kallio and Heiska’s attention is focused on making a single battery perform as desired in a single charging test by putting certain types of materials into it.

“Lithium-ion batteries can be made from several different materials. When lithium titanate (LTO) is used as the negative electrode (or anode), then 11C charging speeds and even higher speeds can be reached. However, such batteries have a clearly lower energy density than the more commonly used lithium batteries based on carbon anodes,” says Kallio.

Donut Lab’s promised energy density for the battery is at the very top of the industry at 400 Wh/kg. In VTT’s tests published now, the energy density of the battery was not indicated at all. Kallio noted that essential information about the battery was not provided.

“So far, the mass or volume of the battery has not been announced, so claims about the energy and power per volume or weight of the battery have not been verified,” Kallio concludes his analysis.

One battery problem

Juho Heiska announced before the announcement that one and the same battery must be able to verify all of Donut Lab’s claims.

“Donut Lab must be able to demonstrate that one and the same battery cell charges as promised, also lasts the promised 100,000 cycles, also manages in the cold as promised and at the same time fulfills the promise of 400 Wh/kg”, says Heiska about Donut Lab’s battery tests.

So what is required from Donut Lab in the future is strong evidence that the future tests performed on the company’s battery by VTT have been performed on the same battery cell that performed as promised in the fast charging tests.

Also from the United States Electrek website based on a recent analysis, a good performance in the load test is the easiest to achieve. So more tests are needed, which Donut Lab has also promised.

However, Donut Lab has caused skepticism and confusion by announcing the results it wants at a time of its own choosing. So more transparency is needed.

“Big turn”: New information about Donut Lab’s uproar – Should the Nordic countries unite? See Friday’s Financial MorningDonut Lab’s battery charges as promised, but not all promises have been proven yet