Most of today’s batteries are made up of two solid layers, separated by a liquid or gel electrolyte. But some researchers are beginning to move away from that traditional battery in favor of an all-solid-state battery, which some researchers believe could enhance battery energy density and safety. While there are many barriers to overcome when pursing a feasible all-solid-state battery, researchers from MIT believe they are headed in the right direction.
This from MIT:
For the first time, a team at MIT has probed the mechanical properties of a sulfide-based solid electrolyte material, to determine its mechanical performance when incorporated into batteries.
“Batteries with components that are all solid are attractive options for performance and safety, but several challenges remain,” says Van Vliet, co-author of the paper. “[Today’s batteries are very efficient, but] the liquid electrolytes tend to be chemically unstable, and can even be flammable. So if the electrolyte was solid, it could be safer, as well as smaller and lighter.”
But to move forward in developing an all-solid-state battery, researchers have to first understand the mechanical stresses that may occur during charge and discharge cycles. Because ions cause the electrode to swell as they move, a solid electrolyte could face very high stress levels. If the electrolyte is too brittle, there is high likelihood of performance degradation.
Until now, though, the sulfide’s extreme sensitivity to normal lab air has posed a challenge to measuring mechanical properties including its fracture toughness. To circumvent this problem, members of the research team conducted the mechanical testing in a bath of mineral oil, protecting the sample from any chemical interactions with air or moisture. Using that technique, they were able to obtain detailed measurements of the mechanical properties of the lithium-conducting sulfide, which is considered a promising candidate for electrolytes in all-solid-state batteries.
“The cycle life of state-of-the-art Li-ion batteries is primarily limited by the chemical/electrochemical stability of the liquid electrolyte and how it interacts with the electrodes,” says Jeff Sakamoto, a professor of mechanical engineering at the University of Michigan, who was not involved in this work. “However, in solid-state batteries, mechanical degradation will likely govern stability or durability. Thus, understanding the mechanical properties of solid-state electrolytes is very important.”