2x More Efficient Lithium Metal Batteries Closer To Reality

Poised as the replacement for the standard that are lithium-ion batteries, Lithium metal batteries offer double the energy storage per unit volume. This technology could enable lower charging rates, with electric vehicles covering double the distance and phones lasting twice as long.

At present, lithium metal batteries are unable to go into production because of one drawback: the liquid electrolyte requires the addition of significant amounts of fluorinated solvents and fluorinated salts, which brings up its environmental footprint. The fluorinated compounds from electrolytes are needed to help the formation of a protective layer around the metallic lithium at the negative electrode of the battery. The protective layer protects the metallic lithium from continuously reacting with the electrolyte components. Without it, the electrolyte would quickly get depleted during cycling, the cell would fail and the lack of a stable layer would result in the formation of lithium metal whiskers- ‘dendrites’ -which could touch the positive electrode, causing a short circuit which would likely lead to the battery heating up so much that it’d ignite.

A research group led by Maria Lukatskaya, Professor of Electrochemical Energy Systems at ETH Zurich has now developed a new method that dramatically reduces the amount of fluorine required in lithium metal batteries, thereby rendering them more environmentally friendly, simplifying their manufacturing process and making them more cost effective. One of the biggest challenges posed to Lukatskaya’s team was to find the right molecule to which fluorine could be attached such that it would decompose again under the right conditions once it had reached the lithium metal. The method makes use of electrostatic attraction to achieve the desired reaction. Here, electrically charged fluorinated molecules serve as a vehicle to transport the fluorine to the protective layer. This means that only 0.1% by weight of fluorine is required in the liquid electrolyte, at least 20 times lower than in prior studies.

A big advantage of the new method is that it can be seamlessly integrated into the existing battery production process without generating additional costs to change the production setup. Currently, tests have been successful on coin-sized batteries. The team looks to move on to pouch cells used in smartphones next to test the method’s stability. If research efforts are fruitful then we might get to see battery sizes balloon up in the next decade.

The work has been published in the Energy & Environmental Science journal. An application for a patent has been made as well.

 

Yash Singh