Rechargeable lithium metal batteries with increased energy density, performance, and safety may be possible with a newly-developed, solid-electrolyte interphase (SEI), according to Penn State researchers.

The SEI is key to the stabilization of lithium metal anodes for rechargeable batteries; however, the SEI is constantly reforming and consuming electrolyte with cycling. The SEI is plagued by a failure to control its structure and stability.

In a paper in Nature Materials, the Penn State team reports a molecular-level SEI design using a reactive polymer composite, which effectively suppresses electrolyte consumption in the formation and maintenance of the SEI.

A reactive polymer composite, picturing the electrochemical interface between lithium metal anode and electrolyte is stabilized by the use of a reactive polymer composite, enabling high-performance rechargeable lithium metal batteries. Credit: Donghai Wang,Penn State

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.

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 of mechanical and chemical engineering and corresponding author

The new SEI layer consists of a polymeric lithium salt, lithium fluoride nanoparticles and graphene oxide sheets. This structure differs from conventional electrolyte-derived SEIs and has excellent passivation properties, homogeneity and mechanical strength.

The team reported that the use of the polymer–inorganic SEI enables high-efficiency Li deposition and stable cycling of 4 V Li|LiNi_0.5Co_0.2Mn_0.3O₂ cells under lean electrolyte, limited Li excess and high capacity conditions. The same approach was also applied to design stable SEI layers for sodium and zinc anodes.

There is a lot of molecular-level control that is needed to achieve a stable lithium interface. The polymer that [lead author Yue Gao] 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

Using both chemistry and engineering design, the collaboration between fields enabled the technology to control the lithium surface at the atomic scale.

The reactive polymer also decreases the weight and manufacturing cost, further enhancing the future of lithium metal batteries.

This research represents the latest innovation generated by Wang, a member of the Institutes of Energy and the Environment (IEE) and the Battery Energy and Storage Technology (BEST) Center, a leading research institute in energy storage.

The Office of Vehicle Technologies in the US Department of Energy and the National Science Foundation supported this work.

Resources

• Yue Gao, Zhifei Yan, Jennifer L. Gray, Xin He, Daiwei Wang, Tianhang Chen, Qingquan Huang, Yuguang C. Li, Haiying Wang, Seong H. Kim, Thomas E. Mallouk & Donghai Wang (2019) “Polymer–inorganic solid–electrolyte interphase for stable lithium metal batteries under lean electrolyte conditions” Nature Materials doi: 10.1038/s41563-019-0305-8