Development of BiFeO₃‑Enhanced Cellulose Separators via Electrospinning for High-Performance Lithium-Ion Batteries

Lithium-ion battery (LIB) performance and safety are strongly dictated by the properties of the separator, which governs ion transport, interfacial stability, and resistance to dendrite penetration. In recent years, cellulose and its derivatives have emerged as a sustainable and high-performance alternative to commercial polypropylene separators for LIBs. Their polar, electrolyte-philic molecular structure improves wettability and ionic transport, promoting uniform Li-ion flux, and reduces the probability of dendrite formation. In this work, we developed a regenerated cellulose separator enhanced with ferroelectric BiFeO₃ (BFO) nanoparticles via electrospinning followed by an alkaline hydrolysis process. The cellulose acetate precursor produced a highly porous and polar fibrous network that facilitated electrolyte uptake and ionic transport, while the ferroelectric properties of BFO contributed to internal electric field redistribution at the electrode-separator interface, mitigating dendrite nucleation and growth. This synergistic effect led to significant improvements in interfacial stability and ion transport. Structural, chemical, and morphological analyses (FT-IR, EDS, and SEM) confirmed successful regeneration and uniform nanoparticle incorporation. Electrochemical benchmarking against RE:C, RE:C-Bi₂O₃, and RE:Fe₂O₃ separators, as well as pristine regenerated cellulose fibers and commercial polypropylene separators, demonstrated a clear performance advantage for the RE:C-BFO separator. With an average thickness of 40 μm, this separator exhibited a 1.91 factor improvement in electrolyte wettability and nearly a 2 orders of magnitude enhancement in ionic conductivity. Electrochemical testing revealed a low charge transfer resistance of 48 Ω and excellent cycling stability, maintaining ∼78% capacity retention after 100 cycles and enabling stable operation for up to 500 cycles. The discharge capacity of the RE:C-BFO separator decreased from 326 mAh/g at a current density of 0.2 mA/cm² to 252 mAh/g after 100 cycles at 0.5 mA/cm², representing significantly better performance compared with the control separators and approaching the theoretical specific capacity of graphite (372 mAh/g). Overall, these results highlight the strong potential of oxide-enhanced regenerated cellulose (RE:C-MFO) separators to improve electrolyte wetting, enhance Li-ion conduction, and suppress dendrite nucleation through internal electric field homogenization, providing a promising pathway toward safer, more durable next-generation LIBs.