Donut Lab Battery Shows Strong Performance at 100°C

Independent testing by VTT reveals Donut Lab’s solid-state battery delivers over 100% capacity and remains stable at temperatures up to 100°C.

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Donut Lab has released the results of a second independent evaluation of its production-ready solid-state battery, and the findings suggest the technology performs remarkably well under extreme heat. The internationally recognised VTT Technical Research Centre of Finland conducted the testing, focusing specifically on how the battery cell behaves at elevated temperatures.

Heat has long been a critical weakness in traditional lithium-ion batteries. Most operate safely up to around 60 to 70 degrees Celsius, beyond which the risk of degradation, internal damage and even thermal runaway increases significantly. Because lithium-ion cells rely on flammable liquid electrolytes, high temperatures can accelerate unwanted chemical reactions and shorten overall lifespan.

Donut Lab’s solid-state design removes that vulnerability. Without flammable liquid electrolytes, the battery is engineered to tolerate substantially higher operating temperatures. The latest test set out to measure just how well it could perform at 80 and 100 degrees Celsius.

Researchers began the process by measuring the battery’s baseline performance at room temperature, running a standard discharge test to determine its nominal capacity. They then heated the cell to 80 degrees Celsius, allowed it to stabilise, and repeated the discharge cycle. After cooling and recharging the battery, they raised the temperature to 100 degrees Celsius and conducted the same procedure again, before finally recharging it at room temperature to confirm that its performance remained intact.

The results exceeded previous expectations. At 80 degrees Celsius, the battery was able to utilise up to 110 percent of its nominal capacity, operating with greater efficiency than at room temperature. At 100 degrees Celsius, it delivered approximately 107 percent of its nominal capacity. The improved efficiency was attributed to lower internal resistance at higher temperatures, which reduced voltage drop during discharge.

Importantly, the battery continued to function normally after both tests. Even at 100 degrees Celsius, where the external pouch lost its vacuum, the active materials remained fully operational and the cell recharged to the same 4.15 volts as it did under standard conditions. There was no abnormal temperature rise during discharge, and the battery’s core properties remained unchanged.

For industries where thermal stability is critical, such as electric vehicles, energy storage systems and high-performance applications, these findings highlight the potential advantages of solid-state architecture. Independent validation from VTT strengthens Donut Lab’s position as it advances toward commercialisation.

Donut Lab has made the full technical report available on its website, providing detailed insight into a battery that proves not only resilient in extreme heat, but unexpectedly stronger because of it.