Anion Immobilization-Induced Enhancement of Li+ Transport at the Polymer Electrolyte–Separator Interface

Abstract

Abstract In situ polymerized electrolytes have garnered widespread attention owing to their high ionic conductivity and excellent interface compatibility. However, conventional polyethylene (PE) or polypropylene (PP) separators incorporated to maintain structural integrity typically serve merely as mechanical scaffolds, lacking interfacial functionalities to facilitate ion transport and thereby limiting Li+ transport. Herein, we propose an anion immobilization strategy by employing a PP separator coated with aramid layers on both sides (AP) as the supporting scaffold, followed by in situ polymerization to construct an anion-immobilizing polymer electrolyte (APVD). In this composite architecture, the N–H groups in the aramid layers immobilize TFSI– through hydrogen-bonding interactions, establishing a local Li+ concentration gradient at the electrolyte/separator interfaces that assists Li+ transport. Benefiting from the anion immobilization effect, APVD delivers a high Li+ transference number of 0.78, representing an approximately 81% increase over that of the control sample (0.43). Moreover, the Li||APVD||Li symmetric cell maintains a stable polarization voltage below 100 mV after 900 cycles at 0.3 mA cm–2, demonstrating efficient Li+ transport and robust interfacial stability. This work highlights the potential of transforming supporting separators from passive mechanical scaffolds into active ion-transport-regulating interfaces, providing an effective strategy for the rational design of high-performance in situ polymerized electrolytes.