When it gets cold, the performance of electric cars usually suffers, reducing their range and increasing their charging times. This is due to the greater use of energy to heat the passenger compartment and the chemical reactions of the battery, which slow down.
As the temperature drops, the electrolyte’s resistance to the flow of ions increases, which directly affects the range of the car. Of course, this effect varies with cell chemistry: while lithium batteries are very sensitive to cold, sodium batteries often perform nearly as well.
With this problem in mind, a team of scientists at the US Department of Energy’s Argonne and Lawrence Berkeley National Laboratories has developed an electrolyte capable of performing well at sub-zero temperatures. This “antifreeze” electrolyte contains fluorine and has shown promising performance in preliminary testing.
During laboratory tests, cells equipped with this fluorinated electrolyte maintained a stable energy storage capacity during 400 charge and discharge cycles at -20 °C. The results show a capacity comparable to that of a conventional cell with an electrolyte based on carbonates at room temperature.
This “antifreeze” electrolyte shows promising performance
“Our research demonstrated how to optimize new electrolytes for suboptimal temperatures by manipulating the atomic structure of electrolyte solvents,” explains Zhengcheng “John” Zhang, senior chemist and group leader in Argonne’s Chemical Sciences and Engineering Division. “We are patenting our electrolyte and are looking for an industrial partner to adapt one of our designs for lithium-ion batteries.”
Another attraction of this fluorinated electrolyte is its high safety index, as it is not flammable. According to those responsible for the research, their technology could work interchangeably in electric vehicle batteries, stationary energy storage systems and consumer electronics (computers, smartphones, etc.).
The researchers also determined at the atomic scale why this particular structure works so well. “Not only did our team find an antifreeze electrolyte whose performance didn’t drop at minus 4 degrees Fahrenheit, but we also discovered, at the atomic level, what makes it so effective.” This is apparently due to the position and number of fluorine atoms within each solvent molecule.
