Self‐Healing UPy‐Functionalized Polyethylene Networks: A Robust Platform for Resilient and High‐Performance Lithium Battery Separators

Conventional polyolefin separators exhibit limited mechanical resilience and poor damage tolerance, leading to performance degradation and critical safety concerns. To overcome these limitations, we developed supramolecular self-healing separators based on polyethylene-hydroxyethyl methacrylate (PE-HEMA) copolymers functionalized with ureidopyrimidinone (UPy) units. The UPy motifs undergo reversible dimerization through quadruple hydrogen bonding within the polymer matrix, forming a dynamic supramolecular network capable of autonomously repairing mechanical defects. Three copolymers with varying UPy grafting densities were synthesized and blended with high-molecular-weight polyethylene oxide (PEO) to significantly enhance electrolyte affinity and ionic transport. Composite membranes (35-40 µm) were subsequently produced via a rapid, solvent-free hot-pressing process. Due to increased amorphous character and enhanced polymer chain mobility, the resulting materials exhibit efficient self-healing at mild temperatures (40°C), improved electrolyte wettability, and high ionic conductivity. Electrochemical testing in Li|Li symmetric cells demonstrate that the separators successfully recover functionality after dendrite-induced short circuits through network reorganization. When implemented in LiFePO4-based full cells, the optimized separator enables stable cycling, delivering a discharge capacity of ≈130 mAh g- 1 after 1000 cycles with up to 81.5% capacity retention, alongside improved thermal safety. These results highlight the promise of UPy-based supramolecular separators for next-generation lithium-based batteries.