A new type of battery can stand being left out in the cold.
This rechargeable battery churns out charge even at –70° Celsius, a temperature where the typical lithium-ion batteries that power many of today’s cell phones, electric cars and other devices don’t work. Batteries that withstand such frigid conditions could help build electronics that function in some of the coldest places on Earth or on space rovers that cruise around other planets.
Inside lithium-ion batteries, ions flow between positive and negative electrodes, where the ions are embedded and then released to travel back through a substance called an electrolyte to the other end. As the temperature drops, the ions move sluggishly through the electrolyte. The cold also makes it harder for ions to shed the electrolyte material that gloms onto them as they cross the battery. Ions must slough off the matter to fit into the electrode material, explains study coauthor Xiaoli Dong, a battery researcher at Fudan University in Shanghai.
Such cold conditions make conventional lithium-ion batteries less effective. At –40° C, these batteries deliver about 12 percent of the charge they do at room temperature; at –70° C, they don’t work at all.
The new battery, described online February 28 in Joule, contains a special kind of electrolyte that allows ions to flow easily between electrodes even in the bitter cold. The researchers also fitted their battery with electrodes made of organic compounds, rather than the typical transition-metal-rich materials. Ions can lodge themselves in this organic material without having to strip off the electrolyte material stuck to them. So these organic electrodes catch and release ions more easily than electrodes in normal batteries, even at low temps, Dong says.
Because the ions flow better and connect more readily with the electrodes at lower temperatures, the battery retains about 70 percent of its room-temperature charging capacity even at –70° C.
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Still, battery cells in the new design pack less energy per gram than standard lithium-ion batteries, says Shirley Meng, a materials scientist at the University of California, San Diego, not involved in the work. She would like to see whether a more energy-dense version of the battery can be built.