Ion-Dipole Interaction Driven Alumina-Coated Polyethylene Separator with Enhanced Wettability for High-Performance Rechargeable Aluminum Batteries

Separators are essential for safe and efficient battery operation. Polyolefin separators like polyethylene (PE) are widely used in lithium-ion batteries but are incompatible with strongly polar electrolytes, such as chloroaluminate ionic liquids in rechargeable aluminum batteries (RABs). Glass fiber (GF) membranes are commonly used in RABs due to good wettability, but their excessive thickness, mechanical fragility, and nonuniform macropores limit practicality. This study investigates the feasibility of utilizing an alumina-coated PE (Al₂O₃-PE) separator for RABs. Theoretical and experimental analyses show that the polarizable Al₂O₃ induces strong ion-dipole interactions with RAB electrolytes, imparting exceptional wettability and electrolyte uptake. Combined with its uniform nanopore structure, Al₂O₃-PE enables homogeneous ion flux for reversible Al stripping/plating with dendrite suppression. In RABs with graphene cathodes, Al₂O₃-PE outperforms GF separators, achieving higher capacity, improved rate performance, and long cycling stability. Flexible pouch cells with Al₂O₃-PE demonstrate stable operation under bending, supporting practical application.