More fluorine could unlock cold-climate upside for EVs

News Analysis

22

May

2023

More fluorine could unlock cold-climate upside for EVs

  • Nils Backeberg

Scientists from the U.S. Department of Energy's (DoE) Argonne and Lawrence Berkeley national laboratories developed a fluorine-containing electrolyte for Li-ion batteries that performs well even in sub-zero temperatures.

Lithium-ion batteries are now the go-to technology for electric vehicles (EVs). However, early hybrid electric vehicles (HEVs), such as Toyota’s Prius, kickstarted the industry based on well-established nickel-metal-hydride (NiMH) batteries. Despite the superior performance of Li-ion, Toyota has maintained NiMH in its fleet, especially for HEV models driving in cold climates.

The Li-ion battery performance has a narrower optimal operating temperature compared to NiMH. In the search for a better solvent in Li-ion batteries to improve operating temperature ranges, the research team at the DOE investigated several fluorine-containing solvents, finding an antifreeze electrolyte that, according to the researchers, has a bonus property of improved safety.

Fluorine applications are already baked into the fortunes of the EV market. The electrolyte solution in Li-ion batteries is already usually based on fluorine-containing lithium salts, mainly lithium hexafluorophosphate (LiPF6) but also lithium tetrafluoroborate (LiBF4). In addition, hydrofluoric acid is used in the chemical processing of natural graphite to purify it, in a preliminary step to enable the production of spherical graphite for use in anodes in Li-ion batteries. According to Project Blue data, the compounded exposure of fluorine to the EV growth market will underpin a doubling of the market by 2050. 


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