An Aqueous Eutectic Electrolyte for Low-Cost, Safe Energy Storage with an Operational Temperature Range of 150 °C, from −70 to 80 °C
Wesley Viola, Trisha L. Andrew
Abstract
The performance of conventional energy storage devices greatly suffers at low temperatures. Here, we show that aqueous electrolytes represent an unexpectedly promising solution to this low-temperature issue. The high solubility of lithium chloride in water greatly lowers the freezing point at the eutectic concentration, allowing for a liquid aqueous electrolyte to exist at −74 °C. This electrolyte is used to support low-temperature energy storage in supercapacitors containing an industry-standard activated carbon, retaining 72% of room temperature capacity (28 F/g) at −70 °C and 42% at −80 °C. Since the electrolyte is nonflammable, a high-temperature operation is also possible up to 80 °C, amounting to a broad 150 °C temperature range which covers the most extreme conditions on earth. At −70 °C, the electrolyte has a remarkably high conductivity (1.83 mS/cm) and a broad three-volt stability window. By blending in poly(vinyl alcohol), a polymer electrolyte is made which retains much of the low-temperature performance and is used to make a device capable of lighting an LED at −70 °C for more than a minute. The devices made here excel at low-temperature energy storage and use only safe, low-cost commodity materials.