A battery researcher’s investigation, backed by more than 20 independent experts, claims Donut Lab’s much-hyped “solid-state” battery is actually a conventional lithium-ion cell, with voltage curves and expansion data matching high-nickel NCM chemistry rather than the promised sodium-ion solid-state design. Electrek reports the company raised about $25 million from more than 1,300 mostly small investors on claims of 400 Wh/kg energy density, 100,000-cycle life, and 5-minute charging that now appear unsupported. From the report: The investigation consulted over 20 independent battery experts, including Julian Zanau from the Fraunhofer Research Institute, Dr. Yahim San from Justus-Liebig University, Tom Bicha from Leona, and Dr. Yuo Hesca from Seinajoki University of Applied Sciences. Every single one confirmed the tested cell is lithium-ion. There are two key pieces of evidence. First, the voltage curves from VTT testing match high-nickel lithium-ion cells (NCM chemistry). The cell sits at 3.7-3.8 volts at 50% state of charge — right where lithium-ion cells operate. Sodium-ion cells don’t go significantly past 3.5 volts at 50% SOC.
The second piece of evidence is even more damning: VTT’s cell expansion data. When a battery charges, ions squeeze into the anode material, causing it to expand in a predictable pattern. A graphite anode produces a distinctive “kink” in the expansion curve around 50-70% state of charge, caused by how ions reorder themselves in graphite’s layered structure. The Donut Lab cell shows exactly that kink.
This is critical because sodium ions are physically too large to fit into graphite layers. The graphite anode signature proves the cell uses lithium ions. The investigation puts it well: “it’s like we have a slightly noisy fingerprint and a picture of the suspect’s face. And yet again, it’s a match.” The calculated energy density? About 298 Wh/kg — what you’d expect from a good lithium-ion cell, not the 400 Wh/kg claimed.
The investigation reveals that the battery technology traces back to CT Coatings, a German company with an “eclectic” array of patents — including inventions for screen-printed paving slabs, menu folders, and warning triangles. CT Coatings promised Nordic Nano and Donut Lab a screen-printed sodium-ion solid-state battery. What it delivered was a lithium-ion pouch cell.