Sodium fluoride, a fluorine compound, is an important ingredient in many toothpastes. This substance serves to protect teeth from tooth decay. But fluorine-containing compounds have other practical uses, including e-mobility. Scientists at the US Department of Energy’s Argonne National Laboratory have discovered a fluoride electrolyte that could protect next-generation electric car batteries from degrading, reports Science Daily.
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Researchers use new electrolyte
“An exciting new generation of electric vehicle battery types beyond lithium-ion is on the horizon,” says Zhengcheng Zhang, group leader in Argonne’s Department of Chemical Sciences. Non-lithium-ion battery chemistry offers twice or more stored energy compared to lithium-ion for the same volume or weight. They could power cars much longer distances and even one day power long-haul trucks and airplanes. The problem is that their high energy density quickly decreases with repeated charging and discharging.
However, the Argonne team has now developed a solution that involves changing the electrolyte. In batteries, electrolytes are the liquid through which the lithium ions move between the cathode and anode to achieve charging and discharging. In lithium metal batteries, the electrolyte is a liquid composed of a lithium-containing salt dissolved in a solvent. The problem is that it does not form a sufficient protective layer on the anode surface.
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Elastic protective layer on batteries
The researchers discovered a new fluoride solvent that maintains a robust protective layer for hundreds of cycles. It combines a positively charged fluorinated component (cation) with another negatively charged fluorinated component (anion). This is referred to as an ionic liquid, i.e. a liquid that consists of positive and negative ions.
“The crucial difference in our new electrolyte is the replacement of hydrogen atoms by fluorine in the ring-shaped structure of the cation part of the ionic liquid,” says Zhang. “This made the crucial difference in maintaining high performance over hundreds of cycles in a lithium-metal test cell.” Simulations showed that fluorine cations adhere to and accumulate on the anode and cathode surfaces before a charge discharge cycle takes place. An elastic protective layer is then formed in the early phases of the cycle, which is said to be better than what is possible with previous electrolytes.
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Substance should be safer and more environmentally friendly
According to the research team, the electrolyte offers many other benefits. First, the substance is inexpensive because it can be produced in one simple step with extremely high purity and yield. Second, the electrolyte is said to be environmentally friendly because it requires far fewer solvents, which are volatile and can release pollutants into the environment. Third, the liquid is safer than other solutions because it is non-flammable.
“Lithium-metal batteries with our fluorinated cation electrolyte could significantly advance the electric vehicle industry,” Zhang said. “And the usefulness of this electrolyte undoubtedly extends to other types of advanced battery systems beyond lithium-ion.”