Application of 3DOM PI Separator to Li Metal Battery with Highly Concentrated Ionic Liquid Electrolyte

Abstract

Highly concentrated ionic liquid electrolytes (ILEs) have garnered considerable attention because of the safety of Li metal batteries. However, the use of highly concentrated electrolytes including ILEs is limited by the low affinity to separators. The separator directly contacts the surface of the Li metal anode, which significantly affects the morphology of deposited Li metal. In this study, a three-dimensionally ordered macroporous polyimide (3DOM PI) was proposed as a high-affinity separator for highly concentrated ILE ([lithium bis(fluorosulfonyl)imide]₁[N-methyl-N-propylpyrrolidinium bis(fluorosulfonyl)imide]₁). The 3DOM PI separator is made of polyimide and has a high porosity with a 3D-ordered uniform pore structure. These properties resulted in a higher affinity for highly concentrated ILE and higher ionic conductivity compared with that of conventional separators, making it possible to improve the reversibility of Li deposition/dissolution and the rate capability of the full cells. Moreover, the 3DOM PI separator improved the uniform Li deposition/dissolution and enabled the non-dendritic deposition of Li metal. The 3DOM PI with ILE provided more stable Li metal deposition/dissolution (charge/discharge reaction).