Donut Battery’s second test results published
Donut Lab commissioned the VTT Technical Research Centre of Finland to measure the properties of the world’s first solid-state battery ready for production vehicles developed by the company under independent conditions. The test measured the battery’s performance at high temperatures and demonstrated that the Donut Battery can withstand heat extremely well and offers even greater capacity at high temperatures
Donut Lab has published the results of the second test measuring the properties of its solid-state battery. The test evaluated the battery cell’s capacity performance under hot conditions. The report is available for download at: I Donut Believe – Presenting Third Party Results
Ville Piippo, CTO at Donut Lab, said, “Traditional lithium-ion batteries are very sensitive to heat, and their upper operating temperature limit is typically around 60 to 70 degrees Celsius. High temperatures increase the risk of damage to battery cells and shorten their service life. High temperatures can also cause accelerated reactions inside the cell, and in the worst case, the risk of thermal runaway increases significantly. For the Donut Battery, the baseline situation is already quite different, as it does not contain flammable liquid electrolytes, which is why the maximum operating temperature is higher.”
The test setup involved a battery cell placed on an aluminium profile, with a steel plate placed on top to apply light pressure, hold the cell in place, and reduce so-called hot spots. The capacity of the Donut Battery was measured in stages using this setup at 80 and 100 degrees Celsius.
The test began with a standard 1C discharge test to a cutoff of 2.7 volts to determine the cell's nominal capacity at room temperature. The cell was then charged back to the original 4.15 volts, and the test chamber temperature was raised to 80 degrees, with the cell kept at that temperature for two hours to stabilise.
After this, the same 1C discharge test was repeated to obtain a high temperature reference value. The chamber was then cooled, and the cell was left in it for an hour to cool completely. The battery cell was then recharged to 4.15 volts. After an hour of rest, the cell was discharged at 12 amps to the same cutoff of 2.7 volts, defining the nominal 0.5C capacity at room temperature.
The battery was then charged back to 4.15 volts, after which the cell temperature was allowed to equilibrate for an hour, and the chamber temperature was raised to 100 degrees. After the battery cell temperature had been allowed to equilibrate for two hours, the same 0.5C discharge test was repeated. The chamber temperature was then lowered to 20 degrees, and the battery was charged back to 4.15 volts, ensuring it still reached the same charge capacity.
The results found that the Donut Battery can perform even better under high temperature stress than previously reported. When tested at 80 degrees, the battery cell utilised up to 110% of its capacity with better efficiency than at room temperature. This is due to the cell's internal resistance being lower at high temperatures, resulting in a lower voltage drop during discharge than at room temperature. The battery also continued to function normally after the test, with no visible changes.
In the 100 degree test, the Donut Battery utilised 107% of its capacity with better efficiency than at room temperature. It also charged back to 4.15 volts with the same charge capacity as at room temperature. The battery and its active materials were still fully functional, despite the cell’s external pouch losing its vacuum at 100 degrees.
Piippo said, “The battery’s full capacity was utilised with excellent results at both 80 and 100 degrees Celsius, and it was possible to discharge it at a 1C discharge rate at 80 degrees and a 0.5C discharge rate at 100 degrees without any increase in temperature. The battery’s properties did not change even at 100 degrees, and it functioned normally when recharged, which demonstrates the convincing performance of the Donut Battery even in extremely hot conditions. This confirms that the battery is exceptional not only in terms of performance but also in terms of safety.”
