Lithium (Li) metal has received much attention as a promising anode candidate in recent years with the increasing demand for high-energy-density rechargeable batteries in industrial fields. However, unlike current graphite anodes where Li ions are intercalated, metallic Li anodes generate Li deposition forming an uneven anode surface and have high reactivity toward organic electrolytes. This can cause safety concerns including cycling instability. Thus, developing a stable electrolyte and its corresponding separator is widely recognized as a major challenge to the practical application of Li metal batteries. Although there remains a need for improving the separator performance because of poor separator wettability for highly viscous electrolytes, little work has been done about the separator structure design to ensure proper wettability and stability [1].

In this study, we propose a high performance composite coated separator for Li metal batteries. A commercial separator was thinly coated with a mixture of block copolymer, ionic liquid, and microspheres. The composite electrolyte coated separator showed significantly enhanced wettability which is sufficient to adsorb highly viscous electrolytes. To improve the mechanical properties of the separator, microspheres with high rigidity and stability to organic electrolyte [2] were used. The tensile strength and thermal stability of the separator were improved by microspheres and block copolymer. This approach appears to be effective in improving battery safety by inhibiting the growth of Li dendrites. Due to the increased wettability and enhanced mechanical properties, the cycle life of the cell was greatly improved when our separator was applied. In addition, unlike the ceramic component with a poor dispersion in the coating solution, our novel coating blend enables cost-effective production with rapid and uniform coatings with its excellent dispersion stability.

[1] M. H. Ryou, Y. M. Lee, J. K. Park, and J. W. Choi, Adv. Mater., 23, 27 (2011).

[2] Y. G. Lee, S. Ryu, T. Sugimoto, T. Yu, W. S. Chang, Y. Yang, C. Jung, J. Woo, S. G. Kang, H. N. Han, S. G Doo, Y. Hwang, H. Chang, J. M. Lee, and J. Y. Sun, Chem. Mater., 29, 14 (2017).