Battery Chemists Recommend Fluoride To Make Electric Cars Go Farther

Alternative chemistries, such as lithium metal, have the potential to provide up to twice the energy density of lithium-ion batteries, which currently power the longest-range EVs. This advancement holds the promise of smaller, lighter battery packs, which will result in increased efficiency and travel distances for EVs. 

Nonetheless, one major limitation of lithium metal batteries is their inability to maintain high energy density over time. Their performance degrades during charge and discharge cycles, eventually eroding the impressive density after only a few hundred cycles, which is a major concern for EV drivers.

To address this issue, a team of researchers led by Zhengcheng Zhang from the Argonne National Laboratory's Chemical Sciences and Engineering division developed a promising approach by leveraging fluoride, an ingredient commonly found in toothpaste for enamel strengthening to extend the lifespan of lithium metal batteries.

These batteries differ from lithium-ion batteries in that their negative electrode (anode) is made of lithium rather than graphite. An electrolytic liquid transports lithium ions between the anode and cathode of the battery. Traditional electrolytes, which are made up of solvents and lithium-containing salts, fail to form a protective layer on the anode, resulting in rapid degradation.

The solution devised by the research team involved substituting fluorine for hydrogen atoms in the ring-like structure of the cation portion of the electrolyte's ionic liquid. This novel adjustment was critical in sustaining high performance over hundreds of cycles in a test lithium metal cell.

The researchers meticulously fine-tuned the ratios to create an ideal protective layer using a high-resolution electron microscope. The new electrolytic liquid is easy to manufacture, making it cost-effective, while also requiring significantly less solvent than traditional alternatives, contributing to its environmental friendliness.

"The substitution of fluorine atoms for hydrogen atoms in the ionic liquid's cation structure was the key differentiator in our novel electrolyte," Zhang explained. "This critical modification allowed lithium metal cells to maintain high performance for an extended period of time during testing." Zhang emphasised the potential impact of lithium metal batteries with fluorinated cation electrolytes, claiming that they could significantly advance the electric vehicle industry. Furthermore, the utility of this electrolyte extends beyond lithium-ion batteries, opening up possibilities for a variety of advanced battery systems.

As the findings of the research team pave the way for more durable and long-lasting lithium metal batteries, the electric vehicle industry anticipates positive implications for improved driving ranges, increased efficiency, and, ultimately, the acceleration of sustainable transportation.