Donut Lab recently announced the latest test results of its solid-state batteries. The test focused on the safety of the damaged cells, which, according to the Finnish company, would have "serious consequences" for traditional lithium-ion batteries ". Following the module-level charging test on the Verge Motorcycles electric motorcycle last week, the fifth test of the Donut Lab "I don't believe in donuts (I Donut Believe)" campaign has now been completed. This test focuses on the cell labeled "DL2" issued in the previous high temperature test.

During charging at 100 degrees Celsius, the cell lost its vacuum state due to damage to the vacuum structure around the battery. Outside observers at the time concluded that the cell must have contained a conventional liquid electrolyte, as the solid electrolyte allegedly present in the Donut cell did not normally result in gas release or the observed cell expansion. However, Donut Lab now attributes the swelling to a different material failure, rather than electrolyte gas release. The company said in a press release: "The battery cells used in the tests were made of materials and adhesives from the lithium-ion battery industry, which are not designed for operation at 100 degrees Celsius. It is widely believed that the battery is completely damaged and will undergo thermal runaway, which is a possible result of lithium-ion batteries."

In order to prove the safety of its solid-state cells-and indirectly confirm that they are indeed solid-state cells-the Finnish company decided to continue discharging the damaged battery cells. The reason is as follows: if the adhesive joint of the soft pack cell with the liquid electrolyte is damaged to such an extent that air can penetrate, it is highly likely that the liquid electrolyte will at least partially leak, leading to dangerous consequences. Ville Piippo, chief technology officer of Donut Lab, explains: "In a similar failure of a conventional lithium-ion battery, the consequences would be severe. The liquid electrolyte would leak and the active material would come into contact with oxygen, possibly causing a fire or thermal runaway. After the vacuum structure collapses, the lithium-ion battery would not function. Since the Donut battery is a completely solid-state battery, it is not affected by such reactions."

The damaged DL2 cell not only received a continuous discharge after the damage caused by the thermal test. In the subsequent safety test, the battery cell first underwent five standard 1C charge and discharge cycles. Donut Lab said: "In these cycles, despite the damage to the vacuum structure, the battery cells can still operate normally and safely." Subsequently, the cell was charged for more than 50 cycles at a charge rate of 5C, equivalent to 12 minutes of full charge. The test was carried out at 25 degrees Celsius, and the cooling plates used in the previous test were installed above and below the soft pack cells. "The Finnish side reported that during these cycles, the battery capacity stabilized at about 11 amperes, compared to the original capacity of 25 amperes. But during the five 1C cycles at the end of the measurement, the battery showed a slight recovery." "The key revelation of this test is that although the damage to the housing caused early performance degradation, it still ensures consistent and safe operation of the battery cells without temperature spikes or fire hazards."