Towards synergistic transport of ions and electrons at the interface between Janus nanofiber separators and solid electrolyte interphase

The localized overheating in high-rate lithium-ion battery (LIB) or lithium metal battery (LMB) accelerates dendrite formation, which disrupts the uniformity of current density and thermal distribution. This study constructs a Janus-structured and polybenzimidazole (PBI) welded separator (JNS@PBI) with polypropylene nanofibers (PPNFs) (via multilayer co-extrusion) on one face and nanoscale carbon black-modified PPNFs (CPPNFs) on the other. The CPPNFs layer with electronic conductivity homogenizes the interfacial current distribution and heat dissipation, while the PPNFs layer provides electronic insulation. PBI with welding function and intrinsic ionic conductivity not only improves mechanical properties but also enhances the lithium-ion transport. The synergistic transport of ions and electrons is available at the interface between JNS@PBI and the solid electrolyte interphase. Density functional theory (DFT) calculations further elucidate how JNS@PBI enhances interfacial ion transport and regulates lithium deposition. JNS@PBI exhibits high porosity (71.3%), superior electrolyte uptake (451%), and high ionic conductivity (1.80 mS cm −1 ). Electrochemical tests further confirm the exceptional interfacial stability, stable polarization voltage during 2000 h of plating/stripping cycles, remarkable rate capability and cycling endurance, high-capacity retention rates of 85.2% after 700 cycles at 1 C and 90.3% after 1500 cycles at 3 C high rate are observed in assembled LiFePO 4 /graphite full cells. This provides a promising way for next-generation separators for high-safety LIB or LMB.