Finnish technology company Donut Lab has released results from a third independent test of its solid-state battery. The test measured charge retention over a 10-day period. Results confirm the Donut Battery behaves as a true battery, not a supercapacitor.
Highlights
- Third independent test completed: VTT Research Centre measured the Donut Battery’s ability to retain charge over 10 days at room temperature.
- Supercapacitor theory dismissed: The battery’s voltage stabilized and held charge, unlike a supercapacitor, which would discharge linearly and rapidly.
- Consistent cell performance: A 1C capacity test confirmed the cell matched previous test samples exactly.
- Full report available: The VTT test report is available for download on the I Donut Believe website.
Test Methodology and Setup
The charge retention test used a straightforward research setup. Donut Lab connected the battery cell to a laboratory battery tester at room temperature. The tester measured cell voltage every 10 seconds throughout the test period.
As in previous tests, researchers began with a 1C capacity test. This step verified the cell was identical to earlier test samples. The battery was then charged to roughly 50 percent and left connected for 10 days.
Results Show Battery-Like Behavior
The cell voltage stabilized during the first 10 hours after charging. Over the following nine days, the voltage curve continued to flatten. A final capacity test confirmed the voltage drop matched the measured energy loss in watt-hours.
“Since we unveiled the Donut Battery, there has been a lot of speculation and theories about whether it is a supercapacitor. In all its simplicity, this test proves that it is a battery. Supercapacitors charge and discharge quickly, but they also lose their charge quickly when not in use. The Donut Battery behaves like a battery and can maintain a charge for significantly longer,” said Ville Piippo, CTO at Donut Lab.
A supercapacitor under the same conditions would have shown a fast, linear voltage drop. Instead, the Donut Battery held its charge consistently. This result aligns with expected solid-state battery behavior.
What Comes Next
Donut Lab has now completed three rounds of independent testing through VTT Research Centre. The company previously published results on capacity and high-temperature performance. Together, these tests build the validation case for what Donut Lab calls the first solid-state battery ready for production vehicles.
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