Designing a battery is a three-part process. You need a positive electrode, you need a negative electrode, and—importantly—you need an electrolyte that works with both electrodes.
An electrolyte is the battery component that transfers ions—charge-carrying particles—back and forth between the battery’s two electrodes, causing the battery to charge and discharge. For today’s lithium-ion batteries, electrolyte chemistry is relatively well-defined. For future generations of batteries being developed around the world and at the U.S. Department of Energy’s (DOE) Argonne National Laboratory, however, the question of electrolyte design is wide open.
“While we are locked into a particular concept for electrolytes that will work with today’s commercial batteries, for beyond-lithium-ion batteries the design and development of different electrolytes will be crucial,” said Y. Shirley Meng, professor of molecular engineering at the University of Chicago’s Pritzker School of Molecular Engineering and chief scientist at the Argonne Collaborative Center for Energy Storage Science (ACCESS). “Electrolyte development is one key to the progress we will achieve in making these cheaper, longer-lasting and more powerful batteries a reality, and taking one major step towards continuing to decarbonize our economy.”
In a new paper published in Science, Meng and colleagues laid out their vision for electrolyte design in future generations of batteries.
Even relatively small departures from today’s batteries will require a rethinking of electrolyte design, according to Meng. Switching from a nickel-containing oxide to a sulfur-based material as the main constituent of a lithium-ion battery’s positive electrode could yield significant performance benefits and reduce costs if scientists can figure out how to rejigger the electrolyte, she said.
For other beyond-lithium-ion battery chemistries, like rechargeable sodium-ion or lithium-oxygen, scientists will similarly have to devote considerable attention to the question of the electrolyte.
One major factor that scientists are considering in the development of new electrolytes is how they tend to form an intermediary layer called an interphase, which harnesses the reactivity of the electrodes.
“Interphases are crucially important to the functioning of a battery because they control how the selective ions flow into and out of the electrodes,” Meng said. “Interphases function like a gate to the rest of the battery; if your gate doesn’t function properly, the selective transport doesn’t work.”
The near-term goal, according to the team, is to design electrolytes with the right chemical and electrochemical properties to enable the optimal formation of interphases at both the battery’s positive and negative electrodes. Ultimately, however, researchers believe that they may be able to develop a group of solid electrolytes that would be stable at extreme (both high and low) temperatures and enable batteries with high energy to have much longer lifetimes.