Researchers demonstrated liquefied gas electrolytes, which can lead to non-flammable lithium-ion batteries in the future. (Image Credit: Baharak Sayahpour)
Energy storage advancements must progress to meet society's growing demand for electrical power. Achieving a zero-emissions world generally requires improved lithium-ion batteries, increasing their energy density, safety, temperature resilience, and environmental sustainability. Researchers at the Pritzker School of Molecular Engineering recently unveiled liquefied gas electrolytes capable of providing those four properties. This work could lead to fire-extinguishing, top-of-the-line batteries that can be developed at scale.
"In 2017, a team of UC San Diego nanoengineers discovered hydrofluorocarbon molecules that are gasses at room temperature and will liquefy under a certain pressure," Yijie Yin, the paper's first co-author, said. "They then invented a new type of electrolyte, which is called 'Liquefied Gas Electrolyte' (LGE)."
"The liquefied gas electrolyte greatly broadens the choice of electrolyte solvent molecules. The screened fluoromethane and difluoromethane small molecules have a low melting point, fast kinetics, and wide voltage window. With the combination of co-solvents, these characteristics make these liquefied gas electrolytes exhibit excellent low-temperature performance (< -60°C), Li metal Coulombic efficiency (>99.8%), and high performance of high-voltage cathodes," the researchers wrote.
Unfortunately, the LGF electrolyte still needs work due to the molecule's high vapor pressure and flammable quality. This still makes it unsafe and can pose a hazard to the environment.
Yin said he wanted to apply dimethyl ether (Me2O) in place of the strong solvating power liquid co-solvents. "As a gas molecule, Me2O can only be used in liquefied gas," said Yin. "It may only work under the pressurized system, and it may provide better lithium metal interface and stability while maintaining fast kinetics."
"If we continue to use the current FM and DFM weakly solvated solvents, the existing high-pressure and flammability shortcomings will not be changed," Yang, a nanoengineering Ph.D. student at UC San Diego, said. "Instead, we should work on searching for molecules with increased fluorinated carbon bonding."
To discover fluorinated molecules with longer carbon chains, they turned to the fluoromethane's structure while also ensuring the liquefied gasses still had a low melting point, low viscosity, and certain polarity. With all that in mind, the two decided to try out 1,1,2 tetrafluoroethane (TFE) and pentafluoroethane pentafluoroethane (PFE).
More surprisingly, both molecules are found in some fire extinguishers. Therefore, these molecules have anti-flammable and fire-extinguishing properties.
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