The VTT Technical Research Centre of Finland has independently tested a solid-state EV battery developed by Finnish technology startup Donut Lab, with results indicating the company’s prototype can achieve extremely fast charging times under controlled conditions.
According to Donut Lab, VTT was commissioned to measure the performance of its first serially producible solid-state battery cell. The initial round of testing focused on charging speed and thermal behaviour during charging.
The tests were designed to simulate a worst-case scenario in which the battery cell had no active temperature control, allowing its temperature to rise freely at very high charging rates.
Two passive cooling configurations were used during the measurements. In the first setup, the 26Ah cell was surrounded by two lightly compressed aluminium cooling plates. In the second, the cell was attached to a single bottom cooling plate.
Charging performance was measured using C-rates, where 1C represents a full charge in one hour. In comparison, 5C equates to about 12 minutes and 11C to about five to six minutes. Traditional lithium-ion batteries typically charge at rates between 1C and 3C and rely on sophisticated active cooling systems often using some kind of liquid.
Testing began with a standard discharge capacity test at 1C, followed by rapid charging tests at 5C and 11C using both cooling configurations.
At a 5C charging rate, the battery cell reached 80% state of charge in about nine-and-a-half minutes and achieved a full charge in just more than 12 minutes. When discharged after charging, 100% of the charged capacity was available.
The cell was then charged at 11C. Under these conditions, it reached 80% charge in four-and-a-half minutes and 100% in just more than seven minutes. When discharged after a full charge, between 98.4% and 99.6% of the battery capacity was available.
Though the test conditions did not directly replicate behaviour within a full battery pack usually fitted to EVs, Donut Lab said the results indicate potential benefits when the cell is integrated into a pack configuration.
The company said the battery cell does not require specific compressive force and performs with passive cooling — attributes that could simplify battery pack architecture in electric and hybrid electric vehicles.
“Unlike other solid state batteries requiring high compressive pressures and undergoing volume changes of up to 15% to 20% during recharging cycles, the Donut Battery does not require special compression or more extensive cooling,” said Donut Lab CTO Ville Piippo.
“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.”
