In situ fabrication of AN/EMA-based gel polymer electrolyte integrated with commercial polypropylene separator for long-cycling lithium metal batteries

Polyacrylonitrile (PAN)-based gel polymer electrolytes (GPEs) exhibit favorable electrochemical stability owing to nitrile (-C N) groups; however, excessive rigidity of nitrile-containing networks remains challenging for constructing thin separator-integrated electrolytes. Herein, a thin AN/EMA-based gel polymer electrolyte (AN/EMA-GPE) is fabricated through in situ thermal copolymerization of acrylonitrile (AN) and ethyl methacrylate (EMA) on commercial polypropylene (PP) separators. The flexible EMA segments mitigate polymer network rigidity, while AN units provide polar sites to regulate Li + transport within the gel framework. The resulting separator-supported electrolyte forms a thin gel layer of approximately 25 μm after polymerization, exhibiting a lithium-ion transference number of 0.52 and an anodic stability window of 5.32 V vs. Li + /Li. Benefiting from the integrated gel architecture and improved ion-transport characteristics, Li|AN/EMA-GPE|Li symmetric cells, the interfacial charge-transfer resistance is measured to be approximately 200 Ω with a critical current density of 1.6 mA cm -2 ; steady Li stripping/plating is recorded over 2000 h under 0.1 mA cm -2 , outperforming EMA-GPE and liquid electrolyte controls. Post-cycling morphology and impedance analyses further reveal a more stable lithium/electrolyte interfacial evolution. When coupled with LiFePO 4 cathodes, Li|AN/EMA-GPE|LFP cells retain 84% capacity after 900 cycles at 2 C with an average Coulombic efficiency above 99%. This work provides a feasible strategy for designing thin separator-supported gel electrolytes with balanced ion transport and lithium-metal compatibility.