Semiliquid Lithium Metal Anode Developed for Lithium-Ion Batteries

June 17, 2019 by Scott McMahan

Carnegie Mellon University researchers have created a semiliquid lithium metal-based anode that could offer a new paradigm in battery design. Lithium batteries constructed using this new type of electrode could have a higher capacity and be much safer than conventional lithium metal-based batteries that employ lithium foil as anode material.

The interdisciplinary research team detailed their findings in the current issue of Joule.

Lithium-based batteries are among the most common types of rechargeable batteries in modern electronics because of their capacity to store large amounts of energy. Conventionally, these batteries are made of combustible liquid electrolytes and have two electrodes, an anode and a cathode separated by a membrane.

After repeated charge and discharge cycles, strands of lithium called dendrites can form on the surface of the electrode. The dendrites can pierce through the membrane separating the two electrodes. This penetration allows contact between the anode and cathode, which can a battery to short circuit, and in worst case scenarios, catch fire.

"Incorporating a metallic lithium anode into lithium-ion batteries has the theoretical potential to create a battery with much more capacity than a battery with a graphite anode," said Krzysztof Matyjaszewski, J.C. Warner University Professor of Natural Sciences in Carnegie Mellon's Department of Chemistry. "But, the most important thing we need to do is make sure that the battery we create is safe."

One suggested solution to the potentially flammable liquid electrolytes used in lithium-ion batteries is to replace them with solid ceramic electrolytes. Solid ceramic electrolytes are highly conductive, non-combustible, and can resist dendrite penetration.

However, researchers have observed that the contact between the ceramic electrolyte and a solid lithium anode is inadequate for storing and providing the power needed for most electronics.

Han Wang, a doctoral student in Carnegie Mellon's Department of Materials Science and Engineering, and, Sipei Li, a doctoral student in Carnegie Mellon's Department of Chemistry, were able to overcome this issue by developing a new class of material that can be used as a semiliquid metal anode.

Collaborating with the Mellon College of Science's Matyjaszewski, an expert in polymer chemistry and materials science, and Jay Whitacre, Trustee Professor in Energy in the College of Engineering, who is renowned for his work developing new energy storage and generation technologies, Li and Wang created a dual-conductive polymer/carbon composite matrix that features evenly distributed lithium microparticles.

The matrix continues to be liquid at room temperatures, which allows a sufficient level of contact with the solid electrolyte.

With the combination of garnet-based solid ceramic electrolyte with the semiliquid metal anode, they successfully cycled the cell at 10 times higher current density than cells with a solid electrolyte and a conventional lithium foil anode. This cell also demonstrated a considerably longer cycle-life than traditional cells.

"This new processing route leads to a lithium metal-based battery anode that is flowable and has very appealing safety and performance compared to ordinary lithium metal. Implementing new material like this could lead to step change in lithium-based rechargeable batteries, and we are working hard to see how this works in a range of battery architectures," said Whitacre.

The researchers believe that their approach could be employed to make high capacity batteries for electric vehicles as well as specialized batteries for use in wearable devices that need flexible batteries. They also believe that their strategies could be extended beyond lithium to other rechargeable battery systems, such as sodium metal batteries and potassium metal batteries and might be useful in grid-scale energy storage.

Funding for this research came from the National Institutes of Health and the National Science Foundation.

Additional study authors include: Tong Liu and Julia Cuthbert from the Carnegie Mellon Department of Chemistry.