Phase-separated polymer electrolytes with dual-interface enhancement effect for high-loading lithium metal batteries

Solid polymer electrolytes (SPEs) offered enhanced safety and superior lithium dendrite suppression compared to liquid electrolytes, yet suffered from inadequate ionic conductivity and poor interfacial stability. Phase-separated polymer electrolytes (PSPEs) partially addressed these limitations but introduced dual-interface challenges, including insufficient electrode contact and inhomogeneous phase distribution. This work presented a novel BSF composite electrolyte fabricated through in situ polymerization of a PSPEs system comprising butyl acrylate (BA), succinonitrile (SN), and LiTFSI, with fluoroethylene carbonate (FEC) as a critical additive. This design simultaneously enhanced the compatibility between the polymerized BA matrix and the SN liquid phase, established continuous ion transport pathways, improved interfacial wettability, and generated stable LiF-rich interphases at both electrodes. The structural evolution and interfacial chemistry were systematically verified through Raman mapping, HAADF-STEM, and TOF-SIMS analyses. Electrochemical evaluation demonstrated exceptional performance. The constructed Li|BSF|Li symmetric cells achieved stable cycling for over 2000 h at 0.5 mA/cm² with a critical current density (CCD) of 4.2 mA/cm². Moreover, Li|BSF|NCM811 full cells with a high mass loading (18 mg/cm²) retained 80.5% of their capacity after 100 cycles. These results represented state-of-the-art performance among polymer-based solid electrolytes, underscoring the potential of the BSF system for high-energy–density lithium metal batteries.