Lithium-ion batteries power everything from smartphones and laptops to electric vehicles.
But as the world’s demand for energy storage keeps growing, scientists are searching for battery technologies that can store more energy, cost less, and rely on materials that are widely available.
One promising option is the fluoride shuttle battery.
Although this technology is still in development, it has attracted attention because it could potentially store much more energy than today’s lithium-ion batteries.
It also uses inexpensive materials that are abundant in the Earth’s crust.
Unlike lithium-ion batteries, which move lithium ions back and forth between two electrodes, fluoride shuttle batteries work by transferring fluoride ions. In theory, this process could allow batteries to hold a much larger amount of energy.
However, there has been a major obstacle. The battery relies on two chemical reactions: fluorination and defluorination.
The defluorination process is relatively easy to achieve, but fluorination has proven to be much more difficult.
During fluorination, unwanted side reactions often occur, and some changes become irreversible. These problems reduce battery performance and shorten battery life.
Scientists have been trying to solve this issue for years.
One possible solution is to increase the number of fluoride ions in the battery’s electrolyte. The electrolyte is the material that allows charged particles to move between the battery’s electrodes. Unfortunately, fluoride salts do not dissolve well in many organic liquids used as electrolytes.
Researchers have previously tried using specially designed organic molecules to help dissolve fluoride ions. However, these molecules can be expensive and difficult to make. In some cases, they also hold onto fluoride ions too tightly, making it harder for the battery reactions to happen.
To overcome these problems, a research team tested a different approach. They focused on a stable inorganic compound called potassium tetrafluoroborate, or KBF4.
The researchers mixed KBF4 with cesium fluoride and an organic liquid called tetraglyme. They discovered that adding KBF4 dramatically changed the behavior of the electrolyte. More fluoride salts dissolved successfully, suggesting that KBF4 altered the environment around the fluoride ions.
The team then tested the new electrolyte in experimental batteries. Using several analytical methods, they found that the batteries could repeatedly perform both fluorination and defluorination reactions. This reversibility is essential because rechargeable batteries must be able to undergo the same reactions many times.
The researchers also observed that the fluorination reaction occurred under conditions that differed significantly from previous systems that relied on organic additives. This finding suggests that KBF4 controls fluoride ions in a fundamentally new and potentially better way.
Perhaps most importantly, KBF4 is chemically stable and relatively inexpensive. The researchers believe it may provide a simpler and more practical route for developing fluoride shuttle batteries.
Much work remains before these batteries reach the marketplace. Scientists still need to better understand exactly how the new electrolyte works and further improve battery design and durability.
Still, the study marks an important step forward. If researchers can continue improving fluoride shuttle batteries, they may eventually provide a powerful, low-cost, and sustainable alternative to today’s lithium-ion technology, helping meet the world’s growing energy needs.
