• Donut Lab released its second independent solid-state battery test result Monday.
• The pouch cell was subjected to extreme temperatures as high as 212 degrees Fahrenheit.
• It appeared to perform well at elevated heat, but one battery scientist said the limited data revealed little about its real-world performance.

Finnish startup Donut Lab has released its second independent test result for what it claims is the world’s first all-solid-state battery. Once again, the data is raising as many questions as it answers.

This latest test puts the cell through its paces at high-temperatures of 80 and 100 degrees Celsius (176-212 degrees Fahrenheit), roughly double the maximum operating temperature of conventional lithium-ion batteries. 

On the surface, the results look promising. But experts urged caution, pointing to data they say is far too thin to mean much. Some of Donut’s biggest claims, like all-important battery chemistry and energy density, are still unverified. 

Eric Wachsman, a professor at the University of Maryland’s Department of Materials Science and Engineering who specializes in solid-state batteries and solid oxide fuel cells, said the insufficient data does not represent real-world usage in automotive applications. 

“The cells are not violating any law of thermodynamics,” Wachsman told me in an email. “But the data presented leaves a lot to be desired for many reasons,” he said.

A 2.4 kilogram steel plate was placed on the Donut Lab solid-state cell for mechanical pressure while charging and discharging.

Photo by: Donut Lab

Researchers say solid-state batteries are a “holy grail” technology that can unlock superior driving range compared to today’s lithium-ion batteries, while substantially reducing charging times and fire risk. At least on paper, the technology has the potential to vanquish range and charging anxieties and unlock broader EV adoption.

Battery companies and automakers are racing to develop the technology, but mass manufacturing of solid-state batteries without defects is extremely challenging. Several solid-state battery startup CEOs InsideEVs has interviewed have said it’s an unresolved problem.

That’s why Donut Lab’s claims took the internet by storm early this year. The Helsinki-based startup says it has developed the world’s first all-solid-state battery that’s production-ready. It will power Verge Motorcycles EVs starting this quarter. 

The specs it’s put forward are extraordinary: 400 watt-hours of energy density (roughly double today’s lithium-ion cells), a five-minute charge time, an operating range of -30C to 100C (-22F to 212F), a 100,000-cycle lifespan, and zero rare earth materials.

Photo by: Donut Lab

The announcement was met with deep skepticism from industry experts for making bold claims without providing any proof, patent disclosures, or live demonstrations. The company is now responding to the blowback by releasing independent test results from the VTT Technical Research Centre of Finland.

After demonstrating its fast-charging capabilities in a lab test last week, the company released a second independent test on Monday. This one showcases the cell’s apparent stability at temperatures as high as 80C and 100C (176F and 212F). 

At 80C (176F), the cell appeared to have delivered more energy than at 20C (68F), reaching 110.5% of its normal capacity. It basically suggests that the chemistry is possibly running more efficiently at elevated heat. After the high-temperature discharge, it recharged without any visible damage, indicating normal performance.

The battery was then pushed even harder. The agency raised the temperature of the testing chamber to 100C (212F), which is the boiling point of water. Again, the cell performed better than it did at room temperature, delivering 107% of its normal capacity. And it was able to charge up normally again thereafter.

That’s impressive because regular lithium-ion batteries don’t handle heat all that well. As temperatures climb, they lose efficiency. And if you push far enough, they can become unstable or sustain permanent damage. Studies suggest that the optimal operating range for lithium-ion batteries is between 25-40C (77-104F). The Donut Lab cell was able to survive in temperatures over twice of that.

However, there was one notable development after the 100C test: the Donut battery’s outer pouch lost its “vacuum.” Wachsman said the pouch issue was a potential red flag. The loss of vacuum, he explained, may indicate that the cell lost its “hermetic seal,” the barrier that keeps outside air away from the sensitive internal chemistry.

“Pouch cells will tend to expand due to internal pressure as they can give off gas during cycling,” Wachsman said. “It’s clear they experienced excessive swell after a few cycles,” he said after comparing the fast-charging images from last week’s test to this week’s high-temperature results.

Potential swelling on the Donut Lab solid-state EV battery cell after a discharge test at 100 degrees Celsius (212 degrees Fahrenheit)

Whether this is a major safety issue or something that’s expected on solid-state cells remains unclear. However, the broader consensus is consistent among experts. Neither test reveals meaningful pack-level performance over the thousands of cycles that actually matter for real-world use. 

“To be commercially relevant, the cells need to be stable with less than 10-20% of capacity fade for thousands of cycles,” Wachsman said. “Without that, the tests are essentially meaningless.”

Donut Lab says more independent results are coming in the weeks ahead. Energy density figures and battery chemistry disclosures remain the two things worth watching for. Until those surface, the jury is firmly still out.

Contact the author: suvrat.kothari@insideevs.com

Earlier this month, a little-known Finnish startup shocked the world when it claimed to have beaten Toyota, Samsung, LG Energy, Quantumscape and any number of Chinese automakers at commercializing the Holy Grail of electric-vehicle power: solid-state batteries.

Helsinki-based Donut Lab said at CES 2026 that it has a class-leading solid-state battery ready to go in an upcoming electric motorcycle, boasting five-minute fast-charging and unprecedented energy density. Hopes ran high that this could be a breakthrough for a battery technology widely seen as capable of changing the world. But then, the doubts started to emerge.

“People love seeing strategic partnerships and manufacturing scale-up,” Jiayan Shi, an associate at research firm BloombergNEF specializing in electrochemistry, told InsideEVs. “It would be nice to have data for performance and safety validation,” she added.

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Source: Patrick George

For their part, Donut Lab executives maintain the technology is real, yet shrouded in mystery to protect their trade secrets. The company says the battery will soon be used in a new two-wheel EV from Verge Motorcycles. “The Donut battery surpasses what most of the industry is still planning for years from now,” Marko Lehtimaki, the co-founder and CEO of Donut Lab, said on the company’s YouTube channel. “These batteries are shipping today.”

Donut Lab and Verge Motorcycles did not respond to a detailed list of questions from InsideEVs about the technology, nor grant interviews with executives to respond to these claims. 

Battery researchers have long described solid-state batteries as a key to solving many, if not most, of the problems with current battery chemistries. They swap out the liquid chemical-based electrolyte with a solid one, promising to eliminate range anxiety, enable ultra-fast charging speeds, perform flawlessly in extreme weather and deliver unmatched safety thanks to its fireproof properties.

On paper, an all-solid-state battery would have no trade-offs, which would be a dream come true for battery engineers and consumers alike. But making them at scale without defects and at a lower cost than lithium-ion batteries is extraordinarily difficult, battery executives have previously told InsideEVs.

The Donut Labs solid-state cell on display at CES 2026.

Photo by: Patrick George

That backdrop helps explain why Donut Lab’s claims generated such extensive media attention during CES, including coverage by InsideEVs. But before diving deep, here’s a list of the company’s claims:

• The battery has 400 watt-hours per kilogram of energy density, much higher than 200-300 Wh/kg of today’s lithium-ion packs. 
• It can charge in as little as five minutes, depending on the size of the pack. 
• It can last 100,000 cycles, significantly more than today’s lithium-ion batteries, which last around 1,500-3,000 cycles. 
• No toxic or rare earth materials are involved.
• Its operating temperature ranges between -30 degrees Celsius (-22 degrees Fahrenheit) to 100C (212F).
• Costs are similar to today’s nickel-manganese-cobalt batteries, according to the company.
• The start-up has been working on the tech since 2018.

What most clearly sets Donut Lab apart from other solid-state battery announcements is its timeline. Many large battery manufacturers say the technology is unlikely to mature before the end of the decade. Donut Lab, by contrast, says its batteries will be on the road in a matter of weeks. 

Photo by: Patrick George

Verge Motorcycles’ TS Pro models equipped with its all-solid-state batteries will be delivered to customers in the U.S. and Europe starting this quarter, the company said. The Tron-inspired electric motorcycle claims to offer 370 miles of range and charge to 80% in under 10 minutes.

Battery experts and industry analysts, however, have urged caution. 

Why Experts Are Skeptical Of These Claims

“Producing all-solid-state battery cells at high yield and high volumes is significantly more complex than lithium-ion batteries,” BloombergNEF’s Shi said. “Equipment providers have not yet developed standardized commercial production lines for the diverse range of all-solid-state battery technologies.”

Moreover, the company has disclosed little about its battery chemistry or manufacturing process. There are no approved patents tied to the technology, no publicly disclosed production facility and no independent testing for the batteries just yet.

Photo by: Patrick George

Some industry analysts are skeptical, too. “Without detailed chemistry disclosure or independent testing, it’s unclear whether this technology is directly comparable to the lithium-metal solid-state batteries that Toyota and QuantumScape are developing,” Stephanie Valdez-Streaty, the director of market insights at Cox Automotive, told InsideEVs.

At least one large Chinese battery manufacturer strongly rebuked Donut’s claims. “That battery doesn’t exist in the world,” Yang Hongxin, chairman and CEO of Svolt Energy, told Chinese media last week. “The parameters are contradictory… China’s technology is the most advanced globally. If China can’t produce or perfect it, companies from other countries certainly can’t either.”

Chinese battery manufacturers currently produce some of the world’s most advanced battery packs at a massive scale and low cost. With extensive research budgets and deep manufacturing expertise, several Chinese automakers, including Geely and Chery, seem to be getting close to deploying all-solid-state batteries, but they’re not fully there yet.

BloombergNEF projects that more than 80% of the world’s solid-state battery manufacturing capacity will be concentrated in China in the coming years, so they’re expected to be ahead in developing the tech.

That raises several questions: How could a small Finnish start-up leapfrog the larger companies? Where would these batteries be made? And what technology underpins them? Donut Lab has not provided clear answers, but some clues have emerged from its recent investments and public records.

What Could This Solid-State Battery Chemistry Be?

The Donut Lab battery appears to point toward work done by another Finnish company. Last October, Donut Lab said it made a “significant strategic investment” in renewable energy start-up Nordic Nano, which specializes in nanotechnology—which involves highly precise manufacturing using nanoparticles—for solar and battery applications.

Nordic Nano also said in a report last year that it had developed a “bipolar electrostatic capacitor” for energy storage systems. The specifications described in that report closely resemble Donut Lab’s claims. The capacitor has a similar 400 Wh/kg of energy density and a lifespan of over 50,000 charging cycles with less risk of fire.

Before getting into batteries, Donut Labs developed this hubless rear wheel with an integrated electric motor, a design it claims it pioneered.

Photo by: Patrick George

Capacitors are not new to cars. Lamborghini famously used a supercapacitor in its Sian supercar for instantaneous torque fill and energy recovery. That system, however, was a small hybrid unit paired with a combustion engine.

Capacitors store energy in an electrical field between physical conductive plates, according to a study published on Science Direct, whereas batteries can store energy chemically in small cells. That means capacitors require far more space to store the same amount of energy as batteries, which is why they’re mainly used in energy storage systems.

Nordic Nano also said in that report that it had finished installing pre-production equipment at its facility in Imatra, Finland, near the Russian border in the fourth quarter of last year. Production of its carbon-based solar films and solid-state super capacitors will begin in 2026, the company said.

Donut Labs claims the solid-state battery is not limited to motorcycles. It can be engineered for cars and drones, too.

Photo by: Patrick George

Finland’s local newspaper Yle reported last week that production had started at what it described as a “mysterious factory,” adding that the company had built fencing around the site to prevent “corporate espionage.”

Lehtimaki told The Verge that Nordic Nano was not making this solid-state battery. Nordic Nano did not respond to InsideEVs’ request for comment at the time of writing.

In comments to Yle, Nordic Nano CEO Esa Parjanen said: “We don’t want to reveal where and how we make our products. It’s a trade secret.” He told the outlet that the company was using something called nanomass, which is a carbon-based composite material, in solar panels to collect energy.

The same nanomass technology can be used in battery cells, the report said, replacing lithium with an abundant material common across Europe and the world. “These nanobattery cells can withstand tens of thousands of charging cycles and can hold more energy. They are also fireproof and cannot explode,” Parjanen told the newspaper.

Photo by: Patrick George

According to one theory from EV expert Laycee Schmidtke, who runs the MissGoElectric YouTube Channel, this abundant material could, after all, be sodium. She points to Nordic Nano’s Chief Scientist, Bela Bhuskute, and her research on “titanium dioxide nanostructures” and “carbon nanotubes,” which apparently help prevent dendrites, the sharp needle-like spikes that can damage a battery.

As per her publicly available white paper, the company could be using an anode-free sodium-metal battery instead of the lithium metal anodes U.S. battery start-ups QuantumScape and Factorial are working on. Sodium is indeed far more abundant than lithium, but it doesn’t enjoy the same supply chain advantages as lithium.

If Donut Lab has indeed achieved a breakthrough, it could open a new chapter for the battery world and probably even bring a lot of attention to Europe, which is increasingly relying on Chinese battery makers eager to set up shop on the continent. If not, it could join a long list of failed start-ups that promise bold things and fail to deliver.

The good news is it’s only a matter of weeks, not years, before experts will start tearing down the battery pack and determine whether the solid-state technology is real or not. For now, Donut Lab maintains that it’s the real deal and coming soon: “At Donut Lab, our answer on solid state batteries being ready for use in OEM production vehicles is now, today, not later,” Lehtimaki has said.

Contact the author: suvrat.kothari@insideevs.com