Donut Battery Passes Extreme Heat And Charge Retention Tests

Technology firm Donut Lab has released new testing data demonstrating the resilience and reliability of its innovative Donut Battery solid-state battery.

To ensure independent verification, Donut Lab is working with Finland’s renowned VTT Technical Research Centre to measure the performance of its production-ready solid-state battery.

The latest results, published in early March, highlight two key capabilities: strong performance under extreme heat and stable energy retention over extended periods—helping address doubts about the technology’s true battery characteristics.

Together, the tests suggest the Donut Battery could offer a safer and more durable alternative to traditional EV battery chemistries.

Exceptional Performance in Extreme Heat

The second round of testing evaluated how the Donut Battery performs in very high temperatures—conditions that typically challenge conventional lithium-ion cells.

Traditional batteries rely on liquid electrolytes that can become unstable when temperatures exceed about 60–70°C. Heat accelerates internal chemical reactions, which can damage cells, shorten lifespan, and in severe cases trigger thermal runaway.

The Donut Battery’s solid-state architecture eliminates flammable liquid electrolytes, allowing it to operate at significantly higher temperatures.

During testing, a battery cell was mounted on an aluminum profile with a steel plate applying light pressure to stabilize the cell and reduce hot spots. Engineers then measured capacity at progressively higher temperatures.

The procedure included:

– A baseline capacity measurement at room temperature
– Heating the test chamber to 80°C and repeating the discharge test
– Cooling and recharging the battery
– Raising the chamber temperature to 100°C for further testing

Donut Lab says the results were striking.

At 80°C, the battery delivered up to 110% of its nominal capacity with improved efficiency compared with room temperature. This improvement was attributed to lower internal resistance at higher temperatures, reducing voltage drop during discharge.

Even at 100°C, the battery maintained around 107% capacity, while still charging back to its original voltage without degradation. Engineers reported that the battery’s active materials remained fully functional despite the external pouch losing vacuum at that temperature.

According to Donut Lab’s CTO, the cell maintained normal operation and showed no visible damage after the tests—demonstrating strong thermal stability.

Third Test Confirms It’s a True Battery

A separate independent test released a week later addressed speculation that the Donut Battery might behave more like a supercapacitor than a traditional battery.

Supercapacitors are known for rapid charging and discharging but lose their stored energy quickly when idle. To verify the Donut Battery’s characteristics, researchers conducted a charge-retention experiment.

The procedure was straightforward:

– The battery underwent a standard capacity test
– It was then charged to about 50% capacity
– The cell remained connected to a testing system that measured voltage every 10 seconds
– After 10 days, the battery was discharged to determine remaining energy

The data showed the battery’s voltage stabilized during the first 10 hours after charging and remained largely stable for the remainder of the testing period. A final capacity measurement confirmed that the small voltage drop matched the expected energy loss for a typical battery.

If the device had been a supercapacitor, the stored energy would have declined far more quickly and in a nearly linear fashion.

The full VTT test report can be downloaded from the I Donut Believe website.

Implications for Electric Vehicles

Donut Lab says the tests support its claim that the Donut Battery is the world’s first solid-state battery ready for production vehicles.

If the technology scales successfully, its characteristics could offer several advantages for electric vehicles:

– Improved safety due to the absence of flammable liquid electrolytes
– Better performance at high temperatures, reducing cooling requirements
– Stable energy storage, confirming conventional battery behavior

While commercial deployment timelines remain unclear, the results suggest solid-state designs like the Donut Battery could play a significant role in the next generation of EV powertrains.

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