Key Findings
In tests conducted by VTT, a battery module from Donut Lab retained approximately 93% of its energy at -30°C (-22°F). The module delivered 1,254 watt-hours at this temperature, compared to 1,354 watt-hours at 25°C (77°F). Additionally, the module retained about 97% of its ampere-hour capacity, indicating limited capacity loss under these conditions.
Technical Details
The test utilized a complete module consisting of 14 first-generation Donut Battery cells with a nominal voltage of 48 volts and a small battery management system. To isolate the battery’s inherent performance, the setup excluded all thermal management systems, including heating elements, insulation, and cooling equipment.
- Baseline Test (25°C): Discharged at a 1C rate, delivering 27.77 ampere-hours and 1,354 watt-hours.
- Cold Test (-30°C): After five hours of exposure to the target temperature, the module was discharged at a 1C rate, delivering 26.8 ampere-hours and 1,254 watt-hours.
The discrepancy between charge capacity (97% retention) and energy retention (93% retention) is attributed to a further drop in voltage during cold-weather discharge.
Background & Context
Low temperatures typically slow chemical reactions in batteries, reducing the usable energy available for electric vehicles. While Donut Lab previously claimed 99% capacity retention at -30°C, these VTT results provide a measured figure from a complete module rather than a single cell. Ville Piippo, Donut Lab’s CTO, noted that the company intentionally eliminated all potential advantages, such as insulation, to test the cells’ raw performance.
Significance & Outlook
Donut Lab reported that the module continued to charge and discharge normally following the tests, with no adverse effects observed. However, as these were controlled laboratory tests on a single module, the results do not yet establish the actual driving range of a complete electric vehicle. Donut Lab is now focusing on next-generation battery technologies and further system-level demonstrations.
Source: https://interestingengineering.com/energy/donut-battery-cold-weather-test
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