A battery module developed by Finnish technology company Donut Lab retained approximately 93 percent of its energy at -30 degrees Celsius (-22 degrees Fahrenheit) without external heating or insulation, according to new test results from VTT, which tested a complete module containing 14 first-generation Donut Battery cells.
The 14-cell module delivered 1,254 watt-hours at -30°C (-22°F), compared with 1,354 watt-hours at 25°C (77°F). It also retained about 97 percent of its ampere-hour capacity, suggesting limited capacity loss under the tested conditions.
The results address a major challenge for electric vehicles, whose batteries typically deliver less usable energy in freezing weather. Low temperatures slow the chemical reactions inside batteries and can reduce their ability to supply power.
Donut Lab, which develops battery technology for electric mobility applications, had previously claimed its battery could retain 99 percent of its capacity at -30°C, although the latest test measured a slightly lower figure.
VTT tested a complete module containing 14 first-generation Donut Battery cells, rather than evaluating a single cell. The module operated at a nominal voltage of 48 volts and included a small battery management system.
It had no heating elements, insulation, cooling equipment, or other thermal management systems.
Researchers first measured its performance at 77°F by discharging it at a 1C rate, equivalent to drawing its rated capacity over approximately one hour. The module delivered 27.77 ampere-hours and 1,354 watt-hours.
They then lowered the chamber temperature to -30°C (-22°F) and kept the module inside for five hours. Sensors positioned on a cell surface inside the module and on its exterior confirmed that the internal temperature had reached the target.
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