The battery that promises everything – and why researchers are sceptical

"Everything they are promising is achievable on its own. But not at the same time," says Odne Stokke Burheim.

He studies batteries at the Norwegian University of Science and Technology (NTNU).

Donut Lab's claims about what their battery can do are now being met with strong criticism. The criticism comes from both competitors and researchers.

'The holy grail'

An article in the journal Science examines the conflict surrounding the Finnish company Donut Lab and the solid-state battery it claims to have developed.

According to Science, other battery experts have been much harsher in their criticism of Donut Lab than Burheim at NTNU.

Some have gone as far as to describe the company's battery as a "scam."

Science Norway contacted Donut Lab regarding the allegations, but the company did not respond. Science has not received a response from Donut Lab either.

Solid-state batteries are often described as 'the holy grail' of the battery industry. This is a battery in which the liquid found in conventional lithium-ion batteries has been replaced with a solid material. 

In theory, such a battery should charge faster, store more energy, present a lower fire risk, and last longer.

But the technology has proven difficult to achieve in practice.

Several large companies have spent billions trying to solve this challenge.

Has someone finally succeeded?

Promises ultra-fast charging

Competitors believe Donut Lab is exaggerating what it has achieved. A Finnish competitor has filed a police complaint.

Professor Burheim at NTNU believes the biggest problem is that Donut Lab appears to be promising everything at once.

• extremely fast charging

• extremely long lifespan

• high energy density – making the battery lighter

• high efficiency – ensuring that nearly all supplied energy is actually stored

• strong performance in both cold and hot temperatures

• extremely safe

• cheap to produce

According to Burheim, the problem lies in making all of these promises at once.

Fast charging causes energy loss

When batteries are charged very quickly, heat is generated. You may have experienced this yourself. That heat, in turn, leads to energy loss.

Burheim points out that solid-state batteries typically have higher internal resistance than conventional lithium-ion batteries. 

This makes ultra-fast charging particularly challenging.

“When Donut presented data demonstrating charging from 0 to 80 per cent in under ten minutes, the figures also showed an efficiency of around 80 per cent,” he says.

According to the professor, this highlights a classic battery dilemma:

If you want extremely fast charging, you lose more energy and generate more heat.

If you want very high efficiency, charging usually has to be slower.

Can tolerate high temperatures

Donut Lab has also presented tests in which its batteries become extremely hot – over 90 degrees.

Burheim finds this interesting.

“It could be an indication that they are actually making solid-state batteries,” he says.

One of the advantages of solid-state batteries is their ability to withstand much higher temperatures than today’s lithium-ion batteries.

At the same time, Burheim notes that newer conventional batteries can also tolerate fairly high temperatures.

Dispute over '100,000 cycles'

Perhaps the company's most striking claim is that its battery can endure 100,000 charging cycles.

Here, too, Burheim believes the wording is unclear.

He explains that the battery industry often uses the term 'full equivalent cycles' (FEC). One such cycle means charging a battery from 0 to 100 per cent and then discharging it back to 0 per cent.

But in practice, many batteries operate within a narrower range. For example, electric car batteries are often charged between 20 and 80 per cent. Battery experts refer to this as 0.6 FEC.

Operating within a narrower range significantly reduces battery degradation.

“If a battery is cycled within a limited charge window, it can achieve far more equivalent cycles than if it's repeatedly charged and discharged from 0 to 100 per cent,” Burheim explains.

For that reason, he says it's difficult to interpret claims of '100,000 cycles' without knowing exactly how the tests were conducted.

“This is more a matter of imprecise wording than necessarily dishonesty,” he says.

Testing would've taken many years

The professor highlights another issue:

Testing that many charging cycles in practice takes a very long time.

“If someone charged and discharged a battery twice per hour, reaching 100,000 cycles would take nearly six years," he says.

He therefore questions how long these batteries have actually been tested.

While some researchers have gone so far as to accuse Donut Lab of making false claims, Burheim takes a more nuanced view.

He believes the Finnish company is oversimplifying the picture.

And that it presents its results in a way that makes the numbers appear more spectacular than they may actually be.

———

Translated by Alette Bjordal Gjellesvik

Read the Norwegian version of this article on forskning.no

Reference:

Peplow, M. Whistleblower alleges Finnish startup’s vaunted solid-state battery isn’t what it claims, Science, 2026.

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