Donut Lab publishes results from its second VTT-backed test, claiming strong performance at extreme temperatures.
Finnish startup Donut Lab is pushing back against industry skepticism by releasing new independent test data showing its solid-state battery performs unusually well in extreme heat.The results follow a wave of criticism from battery experts and rivals who questioned the legitimacy of Donut Lab ’s earlier claims of breakthrough performance and production readiness.
The battery maker, which has claimed its cells can charge in minutes and offer high energy density, faced accusations from competitors that its technology might be overstated or even a “scam.”Now, Donut Lab says new independent results from VTT Technical Research Centre of Finland show the battery can handle extreme heat and still perform at a high level.High heat performance validatedThe tests focused on how well the Donut Battery handled temperatures far above what most lithium-ion cells tolerate.Standard lithium-ion batteries typically begin to suffer performance loss and safety risks past 140–158°F . At higher temperatures, they can degrade faster or even enter dangerous thermal runaway.“Traditional lithium-ion batteries are very sensitive to heat, and their upper operating temperature limit is typically around 60 to 70 degrees Celsius. High temperatures increase the risk of damage to battery cells and shorten their service life. High temperatures can also cause accelerated reactions inside the cell, and in the worst case, the risk of thermal runaway increases significantly.”He added context about Donut’s design.“For the Donut Battery, the baseline situation is already quite different, as it does not contain flammable liquid electrolytes, which is why the maximum operating temperature is higher,” explains Ville Piippo, CTO at Donut Lab.In testing, engineers evaluated the battery at 80°C and 100°C . They placed the cell on an aluminum profile and secured a steel plate on top to apply light pressure and reduce hot spots. They then measured capacity in stages.At 176°F, the battery delivered about 110% of its rated capacity. It also showed better efficiency than at room temperature. Lower internal resistance at higher temperatures reduced voltage drop during discharge. The cell showed no visible changes after the test.At 212°F, the battery used roughly 107% of its capacity. It recharged back to 4.15 volts with the same capacity as at room temperature. Although the pouch lost vacuum at that temperature, the active materials remained fully functional.Scrutiny drives independent testingDonut Lab released these results amid continued scrutiny from industry leaders and battery analysts. Some competitors publicly challenged the company’s earlier claims of ultra-fast charging and production readiness.The startup responded by commissioning independent evaluations and publishing the data publicly. This high-temperature test forms part of that broader effort.“The battery’s full capacity was utilised with excellent results at both 80 and 100 degrees Celsius, and it was possible to discharge it at a 1C discharge rate at 80 degrees and a 0.5C discharge rate at 100 degrees without any increase in temperature.”He continued with performance details.“The battery’s properties did not change even at 100 degrees, and it functioned normally when recharged, which demonstrates the convincing performance of the Donut Battery even in extremely hot conditions. This confirms that the battery is exceptional not only in terms of performance but also in terms of safety,” Piippo states.For US automakers and energy storage firms, thermal resilience remains critical. Batteries that withstand extreme heat could reduce cooling system demands and improve safety margins in hot climates such as Arizona, Texas, and Nevada.Whether Donut Lab’s technology proves durable at scale remains an open question. But the company has clearly shifted its strategy. Instead of bold claims alone, it now points to third-party test data to defend its case.
Donut Lab Second Independent Test Solid-State Battery VTT Technical Research Centre Of Finland
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