Towards Synergistic Transport of Ions and Electrons at the Interface between Janus Nanofiber Separators and Solid Electrolyte Interphase
Localized overheating in high-rate lithium-ion batteries (LIBs) or lithium metal batteries (LMBs) accelerates dendrite formation, disrupting current density and thermal distribution uniformity. This study constructs a Janus-structured, polybenzimidazole (PBI)-welded separator (JNS@PBI) with polypropylene nanofibers (PPNFs) on one face and nanoscale carbon black-modified PPNFs (CPPNFs) on the other. The CPPNFs layer provides electronic conductivity to homogenize interfacial current distribution and heat dissipation, while the PPNFs layer ensures electronic insulation. PBI, serving as a welding agent with intrinsic ionic conductivity, enhances mechanical properties and lithium-ion transport. This design enables synergistic transport of ions and electrons at the JNS@PBI/SEI interface. Density functional theory (DFT) calculations 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 confirm exceptional interfacial stability, with stable polarization voltage over 2000 h of plating/stripping cycles. Remarkable rate capability and cycling endurance are observed: high-capacity retention rates of 85.2% after 700 cycles at 1 C and 90.3% after 1500 cycles at 3 C in assembled LiFePO4/graphite full cells. This work provides a promising approach for next-generation separators for high-safety LIBs or LMBs.