Technology company Donut Lab has today published new test results. According to the report by the research organization VTT, the Donut Battery retained 97% of its capacity at -30 degrees Celsius. The cold temperature test did not involve a single cell, but rather an entire battery module assembled from Donut Lab’s first-generation cells.
“Winter is the moment of truth for every battery. All electric vehicle owners know what happens to driving range when the temperature drops. When we unveiled our battery at CES last January, we made one of our boldest claims: our technology retains 99% of its capacity in minus-30-degree conditions,” says Marko Lehtimäki, CEO of Donut Lab.
Cold temperature test demonstrates performance of battery pack under extreme conditions
In the test, a module consisting of 14 battery cells was placed in a temperature chamber at -30 degrees Celsius. The module comprised a 48-volt nominal voltage system and a small battery management system, but without any thermal management. No heating elements, insulation or cooling were used in the test.
VTT did not measure only the ambient air. It placed one temperature sensor inside the module, directly on the surface of a cell, and another on the outside. The measurement results show exactly what was happening inside the cells and demonstrate that the module was indeed frozen through: the cells inside were at -30 degrees Celsius throughout before the dismantling process began.
First, VTT measured the module’s capacity at +25°C by discharging it at a 1C rate. This established a baseline for the test: 27.77 ampere-hours and 1354 watt-hours. Subsequently, the chamber was cooled to -30°C. The module remained in the chamber for a total of five hours until it was frozen throughout. Then, the same discharge process was carried out at a 1C rate. The measurement yielded 26.8 ampere-hours, representing 97% of the ampere-hour capacity previously recorded at +25°C. In terms of watt-hours, the result was 1254, which is approximately 93% of the baseline. This is explained by the fact that voltage drop is naturally greater in freezing temperatures.
The test was deliberately conducted in as challenging conditions as possible. In a real vehicle, the battery module would be in a closed and insulated case. In addition, a functioning battery heats itself; which can be seen directly in VTT’s results, where the cells heat up during discharge despite the extremely cold conditions of the temperature chamber. As the heat stays inside the battery, as in every normal battery, the capacity increases.
“We intentionally eliminated all the potential advantages a battery might normally have. Despite this, the battery remained unaffected by the conditions. A typical lithium-ion battery would struggle to provide power, even for a brief moment, in such cold temperatures. This validates our promise of 99% capacity, which customers can expect from a fully insulated battery module without any heaters or tricks,” explains Ville Piippo, CTO at Donut Lab.
As the report demonstrates, following battery capacity discharges performed during deep-freeze conditions, the module charges and discharges completely normally, with no adverse effects whatsoever resulting from the cold.
Comprehensive series of tests concluded
The test published today represents the final testing of Donut Lab’s Gen1 cells. The tests carried out by VTT have analysed the performance of the Donut Battery across several different areas:
- Rapid charging in five minutes
- High temperature test at 100 degrees Celsius
- Self-discharge test
- Rapid charging of a damaged cell 50 times
- Swelling and pressure tests
- Energy density measurement
- Cold temperature test at -30 degrees Celsius
“Along the way, we have also provided a preview of the next generation of the Donut Battery, such as the cell’s bipolar structure, material analysis and composition as demonstrated through a nail penetration test. Moving forward, our focus will be on new-generation technologies, and several system-level demonstrations are in the pipeline,” Lehtimäki continues.
VTT’s test report is available at Idonutbelieve.com.
