Soft-hard strategy achieves self-healing and strong polymer electrolytes for long cycle all solid-state lithium metal...

Solid Polymer Electrolytes (SPEs) are pivotal for the next generation of lithium metal batteries, enabling improved safety and energy density. The key challenge lies in balancing mechanical strength from cross-linked structures (restricting polymer chain mobility) with high ionic conductivity. Herein, a "soft-hard combination" strategy is adopted to fabricate a novel self-healing SPE. By incorporating Polyoxyethylene bis(amine) (PGD) for facilitating lithium salt dissociation/conduction and 4,4'-Diaminodiphenyl ether (ODA) for enhancing mechanical properties, a polyurea (PU)-based electrolyte with 9.2 MPa tensile strength is developed. The nitrogen/oxygen functional groups in the polymer form hydrogen bonds, endowing excellent self-healing ability. This PU electrolyte features a wide electrochemical window, integrating self-healing property with high toughness. The Li|PU|Li symmetric cell shows stable cycling over 1100 h without obvious polarization increase, while the LiFePO₄|PU|Li full cell retains negligible capacity loss after 500 cycles, demonstrating great potential for all-solid-state battery applications.