New possibilities for stabilizing interfaces in solid-state lithium-ion battery batteries are now possible.
The solid-state battery is a promising technology in the constant quest to increase the energy density of batteries while reducing their size and weight. These batteries replace the liquid electrolyte, which carries the charges between the electrodes with a solid layer. These batteries may be twice as efficient for their size and could eliminate the risk of fire from lithium-ion batteries. However, one thing is holding back solid-state batteries. Instabilities at the boundary of the solid electrolyte and the electrodes on each side can drastically reduce the battery’s lifespan. Although some studies have used special coatings to increase the bonding between layers, this can lead to additional coating steps during fabrication. Brookhaven National Laboratory and MIT researchers have developed a method to achieve results comparable to or better than the durability of coated surfaces without the need for coatings. This new method eliminates carbon dioxide from the battery materials during a crucial manufacturing step called sintering. In this step, the material is heated to form bonding between the electrolyte and cathode layers. These ceramic compounds are used in the manufacture of battery materials. Even though carbon dioxide is very small in the air (measured in parts per million), its effects can be severe and even fatal. Researchers say that sintering in pure oxygen produces bonds comparable to the best-coated surfaces without the extra cost of coating.
These findings were published in the journal Advanced Energy Materials in a paper written by Younggyu Kim (MIT doctoral student), professor of nuclear science, engineering, and materials science and Engineering Bilge Yildiz and Iradikanari Waluyo at Brookhaven National Laboratory.
Yildiz states that solid-state batteries have long been desired for many reasons. Solid batteries have two key points: they are safer and more energy dense. However, due to low conductivity and interface instability, they have not been commercialized in large quantities.
Yildiz says that the conductivity problem has been successfully addressed, and reasonably high-conductivity materials are already demonstrated. It was much more difficult to overcome the interface instabilities. These instabilities can happen during the manufacturing or electrochemical operation of these batteries. However, the researchers focus on the manufacturing process, specifically the sintering.
Because if ceramic layers are just pressed onto each other, they will not be in contact with one another well. There are too many gaps and high electrical resistance. Sintering is done at temperatures above 1,000 degrees Celsius for ceramic materials. This causes atoms of each material to move into the other and form bonds. Experiments by the team showed that adverse reactions occur at higher temperatures than 100 degrees Celsius. However, this is only true if carbon dioxide is present in small amounts. They found that carbon dioxide can be avoided and that it is possible to maintain a pure oxygen atmosphere for sintering, resulting in excellent bonding at temperatures of 700 degrees.