It was the battery claim of the decade. Donut Lab introduced solid-state cells that shocked the battery world with their efficiency and blistering charging times. Now, it turns out that it was just a decent liquid lithium-ion cell with an ambitious press release. Finnish financial and criminal authorities are reportedly looking into the matter.
Alarm bells
A comprehensive investigation published this week has delivered definitive proof that Donut Lab’s ‘solid-state battery’ is a conventional lithium-ion cell.
Previously, the battery drew headlines at CES 2026, claiming solid-state sodium-ion technology with the promises of 400 Wh/kg, 100,000 charge cycles, and a five-minute fast charge. It turned out to be a scam.
The battery industry is notorious for bold lab statements that raise questions about viability in real life. As for Donut Labs, alarm bells had been ringing for some time.
Even though five independent test reports from Finland’s VTT Technical Research Center confirmed some peripheral claims: fast charging and high-temperature survival.
What the test doesn’t show
But battery experts were not convinced not just by what the VTT tests showed, but by what they conspicuously did not show. The cell also swelled visibly during charging, after just four cycles.
Not a minor detail. Liquid electrolytes swell, solids don’t. Systematically, the tests also avoided the two specs that actually mattered: energy density and cycle life. Measuring energy density takes a scale and a basic discharge test. VTT never did it.
In April, Donut Lab’s former Chief Commercial Officer filed a criminal complaint in Finland, alleging the specs were never achieved.
Subsequently, battery researcher Ziroth coordinated an investigation involving more than 20 independent battery experts, including researchers from Fraunhofer and two European universities. Every single one reached the same conclusion: the tested cell is a lithium-ion cell with high-nickel NCM chemistry.
Two pieces of evidence
Two pieces of electrochemical evidence are hard to argue with. First, the voltage curves place the cell at 3.7-3.8 V at 50% state of charge. This is exactly where NCM lithium-ion cells operate. Sodium-ion cells, which Donut Lab claimed to use, do not exceed 3.5 V at that point.
Second, the cell shows a distinctive kink in its anode expansion curve around 50-70% charge. That’s the fingerprint of lithium ions reordering inside graphite’s layered structure.
Sodium ions are physically too large to fit between graphite layers. Their presence would make that kink impossible. But the cell shows it, providing undeniable evidence that the chemistry is lithium-ion. For clarity’s sake: lithium-ion can be solid state, but that was never Donut Lab’s take.
In conclusion, the real-world energy density is approximately 298 Wh/kg. This is respectable for a high-performance lithium-ion cell, but it is not the 400 Wh/kg that helped raise $25 million of investment from over 1,300 mostly small investors.
Small investors take the bullit
That is the most uncomfortable part of the story—many individuals invested via a crowdfunding round. After CES 2026, when the revolutionary specs were unveiled, the company’s claimed valuation jumped to $1.25 billion. CEO Marko Lehtimäki wrote to investors and promised “a potential return on investment of up to 10x in just 12 to 18 months.”
In reality, many labs are pursuing solid-state as the Holy Grail, and the Finnish fraud case should not slow down legitimate development in general. But it might color public perception and definitely casts a shadow over the already shaky reliability of battery start-ups, their industrial road maps, and their technological promises.
Yang Hongxin, chairman of the Chinese high-tech battery company SVOLT, was already critical about Donut Lab’s announcement at CES. “That battery doesn’t exist in the world,” he said, “All the parameters are contradictory. Any technician with basic knowledge would recognize it as a scam.”
Turns out he was right. The Finnish authorities will now decide what happens next.
