Lithium metal is being extensively studied as an anode to replace graphite due to its high capacity and the lowest negative electrochemical potential.¹ Current research focus is to mitigate lithium dendrite growth and to increase coulomb efficiency during electrochemical cycling by using various surface coatings or electrolyte additives. Due to the complex reduction reactions of electrolyte components on lithium metal surface, it is highly desirable to develop coating materials with high electrochemical stability.

In this work, we report the synthesis of several Li-alkyl carbonates via a simple one step reaction. These carbonates are known components of solid electrolyte interface (SEI) layers on lithium and graphite anode surfaces. The chemical composition and structural information of these synthetic Li-alkyl carbonates are identified by X-ray diffraction and Infrared Spectroscopy. In one implementation of the reaction, a single-component coating is formed on Li metal in a LiI/organic carbonates (dimethyl carbonate (DMC) and ethylene carbonate (EC)) electrolyte. LiI chemically reacts with dimethyl carbonate to form lithium methyl carbonate, which precipitates and forms a chemically homogeneous coating layer on Li surface. This coating layer is shown to enable dendrite free Li cycling in a symmetric Li||Li cell even at a current density of 3 mA cm^-2. Adding EC to DMC modulates the formation of the lithium methyl carbonate, resulting in a stable coating layer which is essential for long term Li cycling stability. Fig.1 shows the morphology of deposited Li using LiI-EC/DMC electrolytes.² Furthermore, the coating can enable dendrite free, high coulomb efficiency cycling after being transferred to common LiPF₆/carbonates electrolytes which are compatible with metal oxide cathodes. We will show that LiI reacts with a broad range of organic carbonates and ethers to form lithium compounds relevant to high efficiency operations of battery anodes.

Acknowledgements

This work was supported by the Office of Vehicle Technologies of the U.S. Department of Energy through the Advanced Battery Materials Research Program (Battery 500 Consortium) under Contract DE-EE0007764.

Reference

1. W. Xu, J. L. Wang, F. Ding, X. L. Chen, E. Nasybutin, Y. H. Zhang and J. G. Zhang, Energ Environ Sci, 2014, 7, 513-537.
2. H. D. Liu, H. Y. Zhou, B. S. Lee, X. Xing, M. Gonzalez and P. Liu, ACS Appl Mater Inter, 2017, 9, 30635-30642.