The thermal cloak keeps electric vehicles cool in the summer and warm in the winter.

When an electric vehicle is parked outside, the temperature can fluctuate dramatically from day to night and season to season, causing the battery to deteriorate. Researchers developed an all-season thermal cloak that can cool an electric vehicle by 8°C on a hot day and warm it by 6.8°C at night to reduce these variations and extend the battery’s lifespan. The cloak, which is mostly comprised of silica and aluminium, can do so passively without any outside energy input and can function in either hot or cold temperatures. This prototype was described on July 11 in Device, a new application-oriented sister journal to Matter, Joule, and Cell.

“The thermal cloak is like clothes for vehicles, buildings, spacecraft, or even extraterrestrial habitats to keep cool in summer and warm in winter,” explains senior author Kehang Cui, a materials scientist at Shanghai Jiao Tong University. The cloak isolates the car—or any other object beneath it—from the surrounding environment to minimise natural temperature variations. The cloak is made up of two layers: an exterior layer that effectively reflects sunlight and an interior layer that traps heat inside. Whatever heat is absorbed by the outer layer is discharged in such a way that it may be easily dispersed into space. This design has earned it the moniker Janus thermal cloak, after the two-faced Roman god Janus.

“The cloak works in the same way that the earth cools down, through radiative cooling,” Cui explains. “The atmosphere covers the earth, and the atmosphere is transparent to a certain range of electromagnetic energy that we emit.”