Researchers Develop Lithium-Ion Battery That Could Perform Better in Low Temperatures

Scientists at Argonne National Laboratory and Lawrence Berkeley National Laboratory have developed a new electrolyte for lithium-ion batteries. The safer electrolyte can work just as well in sub-zero temperatures as it does around room temperature, or 68 to 77 degrees Fahrenheit.

Lithium-ion batteries have a liquid electrolyte, which is important for carrying ions through the battery’s electrodes in order to power a vehicle or device and recharge. But the liquid electrolyte freezes when temperatures drop below freezing point, which can make it more difficult to recharge an EV in cold regions.

The scientists developed an electrolyte containing fluorine and shared their findings in a study published in Advanced Energy Materials.

“Our team not only found an antifreeze electrolyte whose charging performance does not decline at minus 4 degrees Fahrenheit, but we also discovered, at the atomic level, what makes it so effective,” Zhengcheng “John” Zhang, senior chemist and group leader in Argonne’s Chemical Sciences and Engineering division, said in a statement.

Currently, lithium-ion batteries have an electrolyte made with a type of salt, lithium hexafluorophosphate, along with carbonate solvents, like ethylene carbonate, which dissolve the salt into a liquid.

The electrolyte in its liquid form allows ions to flow from the cathode through the electrolyte and finally to the anode. When ions go through the electrolyte, they encounter solvents. The solvents are in clusters and form a protective layer, known as the solid-electrolyte interphase, when they strike the anode surface. This protective layer lets the ions pass through, but not the solvents. Lithium atoms store up in the graphite anode while charging. The vehicle powers up when electrochemical reactions release electrons from the lithium to create electricity.

When temperatures are cold, however, the electrolyte and its carbon solvents start freezing and can no longer move lithium ions to the anode. 

So scientists have been testing other solvents that could better withstand the cold. The team of scientists at Argonne and Lawrence Berkeley national laboratories found a composition of solvent containing fluorine that requires the lowest amount of energy possible to release the lithium ions from the solvent clusters when temperatures are below zero. 

Even at -4 degrees Fahrenheit, the newly developed electrolyte had the same capacity as a conventional electrolyte at room temperature. Additonally, this electrolyte is safer, as it won’t catch on fire the way that carbonate-based electrolytes can.

The development is promising for more effective lithium-ion batteries for everything from smart devices to electric vehicles that will charge and discharge even in below-freezing temperatures.

According to Zhang, the team is patenting the electrolyte and currently searching for an industry partner to utilize the electrolyte in the design of a lithium-ion battery.