Donut Lab cell reaches 409.3 Wh/kg in VTT test

At Finland’s VTT Technical Research Centre, the object under scrutiny was not a vehicle but a single Donut Battery V1.5 cell, designated DL6. VTT discharged it across its full 2.3–4.25V range at a 0.1C rate and 25°C. Energy divided by mass produced 409.3 Wh/kg; energy divided by volume produced 804.7 Wh/L. It is the first energy-density figure Donut Lab has put on record after months of scrutiny, and a legitimate measurement of that cell.

The calendar puts the number in a sharper frame. At CES in January, Donut Lab’s headline claim was not simply a high-density battery, but a solid-state cell ready for original-equipment vehicle manufacturing. The company said Verge Motorcycles would be the first production vehicle to use it, with first deliveries in Q1 2026. It is now September, and no production EV is running Donut Lab’s battery. Electrek’s June investigation found that the motorcycles described as production units were still being used to refine manufacturing; CEO Marko Lehtimäki later told Finnish media that the tested cell was not the one intended for customers.

The density figure also does not establish the chemistry. Amprius already sells a conventional liquid-electrolyte, silicon-anode lithium-ion cell rated at 450 Wh/kg. Top commercial high-nickel cells sit around 250–300 Wh/kg, while solid-state pilots from QuantumScape, Toyota and Samsung SDI target 350–450 Wh/kg. Donut Lab’s result is therefore a strong cell-level measurement, but it sits within figures advanced lithium-ion technology can already reach.

So, concretely, vehicle makers gain a number they can examine, not a production battery they can order for a vehicle. Drivers gain nothing immediate: the test covered one cell, and there is still no production EV on the road using Donut Lab’s technology. The test conditions matter too. An earlier VTT capacity test used a 1C discharge down to 2.7V; the new test discharged 10 times more slowly and reached 0.4V deeper, choices that increase the energy extracted from the cell.

The two hardest questions remain open. Across six independent tests, Donut Lab has published no cycle-life data for its claim of up to 100,000 cycles; this test ran only two capacity cycles. Intertek reportedly confirmed a bipolar internal structure, meaning layers connected in series, but not that the electrolyte is solid. That was also a different cell. VTT made no chemistry determination: in its report, solid-state appears only in the customer’s project name. The result is real laboratory data, but it does not yet turn a cell into a vehicle.