Donut Lab commissioned the internationally recognized Technology Research Centre VTT to independently evaluate its first serially producible solid-state battery. Initial testing has confirmed that the Donut Battery can be fully charged in just five minutes, and Donut Lab has published the results of its first measurements analyzing the battery’s key features.
The tests evaluated the Donut Battery’s charging speed and thermal behavior during charging. They simulated a worst-case scenario in which the battery cell lacks active temperature controls and its temperature can rise freely at extremely high charging rates.
The measurement was done using two passive cooling configurations. In the first, the cell was surrounded by two lightly compressed aluminum cooling plates; in the second, the cell was attached to only one bottom cooling plate. Recharging rates are indicated using C-rates, where 1C means the battery is charged from empty to full in one hour (5C = ~12 min, 11C = ~5-6 min). Traditional lithium-ion batteries typically charge at 1C to 3C with active cooling, whereas in this measurement the charging power rises to significantly higher rates without active cooling. The testing began with a standard discharge capacity test at 1C, which was followed by rapid charging tests (at 5C and 11C) with both cooling configurations.
The results are in line with the five-minute charging time previously announced by the company.
The measurements indicate that the Donut Battery can tolerate high charging rates without active temperature control. Under the specified test conditions, the cell was charged at 5C for more than nine minutes, reaching 80% state of charge in approximately 9.5 minutes and 100% in just over 12 minutes. Following discharge, the cell delivered 100% of the charged capacity.
The battery cell was then recharged rapidly at the extreme speed of 11C. Charging from 0-80% was achieved in 4.5 minutes and a full 100% state of charge in just over seven minutes. When discharged after a full charge, 98.4-99.6% of the battery capacity was available for use.
Even though the testing conditions did not directly simulate cell behavior in a battery pack, the testing demonstrates the benefits of the Donut Battery as part of a pack. The battery cell does not require any particular compressive force and works well with passive cooling, which simplifies the battery pack architecture.
“Unlike other solid-state batteries requiring high compressive pressures and undergoing volume changes of up to 15-20% during recharging cycles, the Donut Battery does not require special compression or more extensive cooling. This greatly simplifies the structure of battery packs and enables solutions that are cost-efficient, powerful and better than traditional lithium-ion batteries in terms of energy and power density,” said Donut Lab CTO Ville Piippo.
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