Self-Healing UPy-Functionalized Polyethylene Networks: A Robust Platform for Resilient and High-Performance Lithium...

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.