• • JNS@PBI achieves a porosity of 71.3% and electrolyte uptake of 451%, enabling high ionic conductivity of 1.80 mS cm−1, which is critical for reducing internal resistance and supporting high-rate operation.
• • The Janus design with conductive CPPNFs and insulating PPNFs homogenizes current distribution and heat dissipation, suppressing dendrite growth and enhancing safety under high-rate cycling.
• • Full cells with LiFePO4/graphite deliver capacity retention of 85.2% after 700 cycles at 1 C and 90.3% after 1500 cycles at 3 C, demonstrating superior long-term cycling stability compared to conventional separators.
• • Stable polarization voltage over 2000 h of plating/stripping cycles confirms exceptional interfacial stability, which is essential for practical LMB applications.