Donut Lab has released a second set of independent test results for its solid-state battery, confirming its fast-charging capability and high-temperature tolerance. The new report, conducted by VTT Technical Research Centre of Finland, adds another data point in favor of Donut Lab's claims. However, the most extraordinary specs remain unverified, including energy density and cycle life. To hit 400 Wh/kg, the cell would need to weigh approximately 235 grams, according to VTT's report, which does not include the cell's weight. This claim cannot be verified from the available data.
The test results show that the cell delivered more energy at elevated temperatures, exceeding its room-temperature capacity at +80°C and +100°C. In both cases, the cell charged normally at room temperature afterward. This is consistent with solid-state electrolyte behavior, where ionic conductivity improves with heat because there is no flammable liquid electrolyte to decompose. However, the fact that the cell pouch lost its vacuum after the 100°C discharge raises questions about long-term durability.
Donut Lab's claims of over 99% capacity retention at -30°C remain untested by independent parties. The company had originally claimed the battery operates safely from -30°C to 100°C with over 99% capacity retention, but VTT did not test at this temperature. The pouch losing vacuum at 100°C is also a yellow flag, which may be a simple packaging issue or point to gas generation in the cell chemistry at extreme temperatures.
The pace of Donut Lab's releases is worth noting, with two independent VTT test reports in two weeks, both confirming specific claims. This level of transparency is more common in the battery industry than most startups have ever offered. However, the pattern is also clear: Donut Lab is proving the easier claims first, such as fast charging and high-temperature tolerance.
The biggest established players in solid-state batteries, including Toyota, Samsung SDI, CATL, and BYD, are all targeting 2027 or later for initial production of their own solid-state cells. None of them claim to have a production-ready cell matching all of Donut Lab's specifications simultaneously. CEO Marko Lehtimäki staked his reputation on shipping Verge Motorcycles with these cells in Q1 2026, which is now weeks away.
We have to give Donut Lab credit where it is due for releasing VTT test results at a rate of about one per week. However, the fact that the energy density and cycle life claims remain untested by independent parties raises questions about their validity. Further verification is needed to confirm Donut Lab's claims.
The high-temperature results are particularly meaningful, surviving and gaining capacity at +80°C and +100°C is not something conventional lithium-ion cells can do, and it is consistent with the behavior you would expect from a genuine solid-state electrolyte. However, this achievement does not necessarily mean that Donut Lab's battery will revolutionize the industry.
The pouch losing vacuum at 100°C is a yellow flag that may be a simple packaging issue or point to gas generation in the cell chemistry at extreme temperatures. This raises questions about long-term durability and whether Donut Lab's claims are entirely accurate. Further testing is needed to confirm the validity of its claims.
In conclusion, while the test results are promising, further verification is needed to confirm Donut Lab's claims. The fast-charging and temperature data are real and independently verified, but if the energy density or longevity do not hold up, this is an interesting cell, not the world-changing breakthrough Donut Lab pitched to the world at CES.
While the test results are promising, further verification is needed to confirm Donut Lab's claims.
