New solvent might end winter charging blues for EV owners

Subzero temperatures and batteries don't mix – but there may be a solution

Researchers have discovered that using "small molecule" solvents could help improve the performance of lithium-ion batteries, speeding up charging and ensuring they work at low temperatures.

Lithium-ion batteries tend to rely on electrolytes consisting of one or more lithium salts dissolved in an organic solvent.

A team led by Xiulin Fan, a professor at China's Zhejiang University, found that a solvent called fluoroacetonitrile, which is made up of small molecules, improves the way that lithium ions move in the electrolyte, resulting in high conductivity that could facilitate faster charging.

They also found that the recorded conductivity stayed high at -65°C, a leap forward in low temperature rechargeability, the authors said in a paper published in Nature this week.

As the popularity of electric vehicles increases, drivers are coming to terms with their limits. In January, when many US states plunged well below zero, Tesla drivers complained of poor charging performance.

In Illinois, local media reported public charging stations turning into "car graveyards" because motorists were unable to power their vehicles, for example.

Meanwhile, charge times can be a perennial problem for EVs, especially for drivers without off-street parking to charge vehicles overnight.

The scientists used computational modeling to narrow down the electrolyte solvent with the combination of physical properties they were looking for and hit upon the solution of a lithium salt in a solvent called fluoroacetonitrile, or FAN. Sure enough, follow-up experimental testing showed it exhibited some of the properties they were looking for.

In an accompanying article, Chong Yan and Jia-Qi Huang, of the Beijing Institute of Technology, said FAN was a previously unknown form of electrolyte structural transport and could inspire innovative approaches to fast charging and the development of low-temperature batteries.

"Batteries are complex systems that integrate materials science, electrochemical science and intercalation science. Coordinating the many factors that contribute to battery performance is like conducting a symphony, in which each musical instrument has a crucial role. Thus, the authors' transport mechanism will almost certainly need to be used with other design features to develop batteries that charge rapidly and work at low temperatures," they said.

The academics said the team in China had opened up avenues of research for developing the next generation of lithium-ion batteries. ®

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