Ultrathin Coating of Nitrogen and Sulfur Co-Doped Graphene Nanosheets on Polymer Separator for Suppressing Dendritic Lithium Growth in Lithium Metal Batteries

The advent of electric vehicles and other high energy density applications has intensified the research efforts on lithium metal-based batteries, as metallic lithium can provide a high specific capacity (~3,862 mAh g -1 ), enabling it as a promising negative electrode for next-generation battery systems [1,2]. However, the instability of lithium electrodes is one of the greatest challenges hindering the successful development of lithium metal batteries. Lithium metal is unstable against nearly all chemical species and reacts with organic solvents and salts in liquid electrolytes. Moreover, continuous deposition and stripping of lithium may induce uncontrollable dendritic Li growth, which in turn leads to internal short circuits, failure, and eventually explosions. In this work, we demonstrated that an ultrathin nitrogen and sulfur co-doped graphene (NSG) layer deposited on a PE separator could effectively stabilize the lithium electrode surface, suppress dendrite formation, and improve the cycling stability of lithium metal batteries. The NSG coating layer is very thin as compared to other ceramic coatings in micrometer scales, which can provide higher energy density of the cell with NSG separator. The incorporation of heteroatom dopants could induce structural deformations due to local strains induced in the carbon framework, thereby allowing for easy ionic migration while maintaining a uniform ionic flux on the Li metal surface. Moreover, the lone pair electrons in the heteroatom dopants led to the generation of negative charge, resulting in enhanced interfacial interactions between the NSG-coated separator and the lithium electrode. The NSG coating also imparted thermal stability to the PE separator, thus preventing thermal shrinkage of the separator at elevated temperature and enhancing battery safety. The cycling performance of the lithium metal cell employing a NSG coated separator was remarkably improved as compared to the cell with a pristine PE separator. References [1] J. -M. Tarascon, M. Armand, Nature 2001 , 414, 359–367. [2] W. Xu, J. Wang, F. Ding, X. Chen, E. Nasybulin, Y. Zhang, J. G. Zhang,. Energy Environ. Sci. 2014 , 7, 513–537.