A Better Electrolyte Promises Less Fluorine, More Power From Future Lithium-Metal Batteries

Researchers from the Electrochemical Energy Systems Laboratory at ETH Zurich, the State University of New York, and Ariel University, working with the DEVCOM Army Research Laboratory, have come up with a new electrolyte for lithium-metal batteries — which, they say, delivers more energy while lessening their environmental impact.

The team's research focuses on lithium-metal, rather than the more common lithium-ion or lithium-polymer, battery chemistry. Lithium-metal batteries deliver more than twice the energy capacity of lithium-ion equivalents, but at a cost: to offer a similar longevity they require fluorinated solvents and salts in their electrolyte, resulting in a high environmental impact for each battery produced.

The fluorinated compounds are there to protect the battery's negative electrode from damage by forming a protective layer around it. "This protective layer can be compared to the enamel of a tooth," co-corresponding author and project lead Maria Lukatskaya explains. "It protects the metallic lithium from continuous reaction with electrolyte components."

To reduce the fluorine required, the team approached the problem from a different direction: using electrostatic attraction to bring charged fluorinated molecules into forced contact with the electrode, rather than relying on the molecules being evenly distributed throughout the electrolytic solution. By doing this, the team's electrolyte require only 0.1 percent as much fluorine — 20 times less than the next-best approach to the same problem — while delivering the same protective effect.

The team states that its work, published in the journal Energy & Environmental Science under open-access terms, "can notably reduce costs and environmental footprint of implementing high energy batteries" — though has not yet disclosed a roadmap to commercialization.