Poly(ionic liquid)s/Electrospun Nanofiber Composite Polymer Electrolytes for High Energy Density and Safe Li Metal Batteries

Solid-state electrolytes with mechanical integrity and high ionic conductivity are important components in high performance all-solid-state lithium (Li) batteries. Relative to these electrolytes, ionic liquid-based composite polymer electrolytes exhibit high ionic conductivity and improved safety. However, the incorporation of large concentration of nonactive ions and the presence of a liquid phase lead to relatively low Li⁺ transference number and poor mechanical properties. In this study, poly(ionic liquid)s or polymerized ionic liquids (polyILs) are combined with an electrospun fibrous support to afford electrolytes with high ionic liquid content and greatly increased Li⁺ transference number. The incorporation of electrospun PVDF nanofibers effectively improves the mechanical strength of the composite polymer electrolytes, and consequently, flexible electrolytes with superior mechanical properties are described. Finally, we demonstrate the performance of high energy density Li metal batteries under high-voltage operation (up to 4.5 V) using LiNiMnCoO₂ (NMC) and LiNi_0.8Co_0.15Al_0.05O₂ (NCA) cathodes with an areal capacity up to 1.1 mAh cm^-2