New Solid-Electrolyte Interphase to Enhance Lithium Metal Batteries

Researchers from Penn State recently highlighted the likelihood of developing rechargeable lithium metal batteries with increased energy density, safety, and performance. They plan to use a newly developed, solid-electrolyte interphase (SEI) to achieve this.

With the growing demand for higher-energy-density lithium metal batteries (used for drones, smartphones, and electric vehicles), the very stability of the SEI has indeed been a vital issue preventing their advancement because a salt layer present on the surface of the battery’s lithium electrode has been observed to insulate it and conduct lithium ions.

This layer is very important and is naturally formed by the reaction between the lithium and the electrolyte in the battery. But it doesn’t behave very well, which causes a lot of problems.

Donghai Wang, Professor, Mechanical and Chemical Engineering, Penn State.

The degradation of the SEI backs the development of dendrites—a component of lithium metal batteries that has been least understood. Dendrites are needle-like formations growing from the lithium electrode of the battery and they negatively affect safety and performance. An approach to this problem was published by the researchers in Nature Materials on March 11^th, 2019.

This is why lithium metal batteries don’t last longer—the interphase grows and it’s not stable. In this project, we used a polymer composite to create a much better SEI.

Donghai Wang, Professor, Mechanical and Chemical Engineering, Penn State.

Headed by Yue Gao, a chemistry doctoral student, the improved SEI is a reactive polymer composite made up of lithium fluoride nanoparticles, graphene oxide sheets, and polymeric lithium salt. The unique construction of this battery component contains thin layers of these materials, and it is in this area that Thomas E. Mallouk, Evan Pugh University Professor of Chemistry, contributed his knowledge.

There is a lot of molecular-level control that is needed to achieve a stable lithium interface. The polymer that Yue and Donghai designed reacts to make a claw-like bond to the lithium metal surface. It gives the lithium surface what it wants in a passive way so that it doesn’t react with the molecules in the electrolyte. The nanosheets in the composite act as a mechanical barrier to prevent dendrites from forming from the lithium metal.

Thomas E. Mallouk, Evan Pugh University Professor of Chemistry, Penn State.

Employing both engineering design and chemistry, the association between fields assisted the technology to regulate the lithium surface at the atomic scale.

When we engineer batteries, we don’t necessarily think like chemists, all the way down to the molecular level, but that’s what we needed to do here.

Thomas E. Mallouk, Evan Pugh University Professor of Chemistry, Penn State.

The reactive polymer is also capable of reducing the manufacturing cost and weight, thus further improving the prospects of lithium metal batteries.

With a more stable SEI, it’s possible to double the energy density of current batteries, while making them last longer and be safer.

Donghai Wang, Professor, Mechanical and Chemical Engineering, Penn State.

This study represents the most recent innovation developed by Wang, a member of the Institutes of Energy and the Environment (IEE) and the Battery Energy and Storage Technology (BEST) Center, a prominent research institute in energy storage.

Penn State researchers who additionally contributed to the project include: Zheifei Yan, graduate student; Jennifer L. Gray, research associate; Xin He, graduate student; Daiwei Wang, graduate student; Tianhang Chen, graduate student; Qingquan Huang, post-doctoral researcher; Yuguang C. Li, graduate student; Haiying Wang, technical staff member; and Seong H. Kim, professor of chemical engineering and materials science and engineering.

This research was financially supported by the Office of Vehicle Technologies in the U.S. Department of Energy and the National Science Foundation.