New ‘cape’ can “extend the life” of electric car batteries

Cui Kehang, an associate professor at the School of Materials Science and Engineering at Shanghai Jiao Tong University, and his collaborators have developed a “cape” that can keep electric vehicles warm in winter and cool in summer, extending battery life. The research was recently published in the new applied physical science journal Device.

When an electric car is parked outdoors, its temperature changes drastically with the change of day and night and season, which can lead to the degradation of the battery. To curb these fluctuations and extend the life of the battery, Cui and collaborators designed an all-weather thermal cloak that can cool electric vehicles by 8°C during hot days and 6.8°C at night.

Image from: Cui Kehang team

The cloak developed by the research team, which is mainly made of silica and aluminum, can do this passively without external energy input and can operate without any modifications in hot or cold weather. “This thermal cloak is like clothing for vehicles, buildings, spacecraft and even alien habitats, keeping it warm in winter and cool in summer.” Cui Kehang said metaphorically.

To suppress natural temperature fluctuations, this cloak isolates the car or any other object underneath the cloak from its surroundings. This cloak consists of two parts: the outer layer effectively reflects sunlight, and the inner layer stores heat inside. No matter how much heat the outer layer absorbs, it is emitted in a way that can easily be dispersed into outer space. This design earned it the name of the “two-faced god” hot cloak, which was inspired by the two-faced Roman god Janus.

“This cloak works on basically the same principle as Earth cooling, that is, cooling by radiation.” Cui Kehang said, “The earth is covered by an atmosphere, and the atmosphere is transparent to a certain range of electromagnetic energy that we radiate.”

While this process is desirable in the summer, it will make the car colder in the winter. “It’s very difficult to develop something that automatically switches on and off without an external energy input.” Cui Kehang said.

The cloak designed by Cui Kehang and team can automatically counteract this effect in winter. This cloak uses an effect called “photon recycling.” Essentially, any energy trapped under the cloak bounces back and forth between the car and the cape, rather than escaping into the outside environment.

To evaluate the performance of this thermal cloak, the researchers tested electric vehicles parked outdoors under typical environmental conditions in Shanghai. At noon, the cabin temperature of unsheltered vehicles reaches 50.5 °C, while the cabin temperature of unsheltered vehicles is 22.8 °C ~ 27.7 °C lower than that of unsheltered vehicles, and 7.8 °C lower than the outdoor temperature. At midnight, the temperature inside the car was 6.8°C warmer than outside, and never fell below 0°C.

“This is the first time we’ve achieved nearly 7 degrees Celsius above ambient temperature at night in winter.” Cui Kehang said, “This also surprised us – without energy input or sunlight, we can still get warmer.” ”

The outer composition of the cloak is made of thin silica fibers and then coated with hexagonal boron nitride sheets, a graphite-like ceramic material that enhances the solar reflectivity of the fibers. These fibers are then woven together to form a fabric and glued to an inner layer made of aluminum alloy.

The team deliberately designed the cloak to make it easier to scale up production in the future. For example, using thinner silica fibers increases the reflectivity of the sun, but they will be less strong and cannot be manufactured with existing high-volume industrial-grade production technologies. In addition, the materials used, including aluminum, silica and boron nitride, are low-cost, making the cloak lightweight, durable, and flame retardant. (Source: China Science News Feng Lifei)

This new material is durable, lightweight, and stretchable. Image from the author

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