Cheating :O




The problem is that in cold temperatures, the electrolyte with carbonate solvents begins to freeze. As a result, it loses the ability to transport lithium ions into the anode on charge. This is because the lithium ions are so tightly bound within the solvent clusters. Hence, these ions require much higher energy to evacuate their clusters and penetrate the interface layer than at room temperature. For that reason, scientists have been searching for a better solvent.

The team investigated several fluorine-containing solvents. They were able to identify the composition that had the lowest energy barrier for releasing lithium ions from the clusters at sub-zero temperature. They also determined at the atomic scale why that particular composition worked so well. It depended on the position of the fluorine atoms within each solvent molecule and their number.

In testing with laboratory cells, the team’s fluorinated electrolyte retained stable energy storage capacity for 400 charge-discharge cycles at minus 4 F. Even at that sub-zero temperature, the capacity was equivalent to that of a cell with a conventional carbonate-based electrolyte at room temperature.

“Our research thus demonstrated how to tailor the atomic structure of electrolyte solvents to design new electrolytes for sub-zero temperatures,” Zhang said.

The antifreeze electrolyte has a bonus property. It is much safer than the carbonate-based electrolytes that are currently used, since it will not catch fire.

“We are patenting our low-temperature and safer electrolyte and are now searching for an industrial partner to adapt it to one of their designs for lithium-ion batteries,” Zhang said.

In addition to John Zhang, Argonne authors are Dong-Joo Yoo, Qian Liu and Minkyu Kim. Berkeley Lab authors are Orion Cohen and Kristin Persson.

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