Anion-Regulated Ionic Liquid–Polymer Electrolytes for High-Performance and Safe Lithium Metal Batteries

Abstract

The development of safe and high-performance polymer electrolytes is critical for advancing lithium metal batteries (LMBs). Herein, we report a PVDF-HFP-based polymer electrolyte incorporating two ionic liquids with different anions FSI− and TFSI−-to investigate their impact on structure and electrochemical behavior. The TFSI−-based system (PPIL) exhibits smaller particle size, reduced crystallinity, and enhanced amorphous β-phase content, enabling improved ion mobility and a lower activation energy (69.0 kJ mol−1). Solid-state NMR and Raman analyses reveal weaker Li+ coordination in PPIL, consistent with its higher ionic conductivity (1.22 × 10−3 S cm−1). Interfacial characterizations show that PPIL promotes the formation of a stable, LiF/Li3N-rich SEI. As a result, LMBs using PPIL achieve over 2000 h of stable cycling, superior rate performance, and excellent thermal and mechanical safety in pouch cells. This work highlights the importance of ionic liquid anion design in optimizing polymer electrolytes for next-generation energy storage systems.