Semi-Interpenetrating Network Polymer Electrolytes with Increased Mechanical Robustness and Ionic Conductivity for Stable Lithium Metal Batteries

Gel polymer electrolytes (GPEs) have attracted considerable attention because of their potential to enhance the safety of rechargeable batteries, including lithium metal batteries. Nonetheless, significant challenges still remain, such as insufficient mechanical strength, limited ionic conductivity, and unstable solid electrolyte interphase (SEI). This study developed a novel GPEs with a polyethylene (PE) separator skeleton, featuring a semi-interpenetrating network (semi-IPN) structure. This is achieved by incorporating crosslinked polyethylene glycol diacrylate (C-PEGDA) into a dual-polymer matrix of poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) and poly (methyl methacrylate) (PMMA). It exhibits outstanding high stress and strain properties (155.2 MPa, 182%) and can remain stable for extended periods at 150 °C. The semi-IPN effectively reduces its crystallinity while suppressing anion migration. As a result, lithium ions can migrate rapidly through coordination with carbonyl (C=O) and ether (C-O-C) groups, leading to a notable enhancement in ionic conductivity (0.64 mS cm-1) in the gel network formed by injection of electrolytes. Furthermore, the nonporous crosslinked architecture significantly broadens the electrochemical window (>4.8 V) and exhibits excellent compatibility with Li metal anodes and effective dendrite suppression. Consequently, Li||Li symmetric cells show stable cycling over 1000 h, and Li||LiFePO₄ cells maintain 96.2% capacity retention after 500 cycles. This study provides critical insights for the development of high-performance energy storage devices with enhanced safety.