Design of a sandwich-structured cellulose separator with PAN/Al2O3 electrospun layers for high-performance sodium-ion batteries

Cellulose-based separators offer sustainability and renewability, yet their poor mechanical strength and large pore size often result in insufficient cycling stability and safety risks in sodium-ion batteries (SIBs). In this work, a sandwich-structured separator (LF-ALO), consisting of a cellulose-based paper (LF) core coated on both sides with electrospun polyacrylonitrile (PAN)/aluminum oxide (Al 2 O 3 ) layers. Compared with LF, LF-ALO exhibits elevated mechanical strength (19.7 MPa), and markedly improved electrolyte wettability (316 %) owing to the robust interconnected fibrous network constructed by PAN and Al 2 O 3 , which facilitate uniform Na + transport and reduce short-circuit risks by optimizing the pore structure of LF. LF-ALO also achieves a high Na + transference number (t Na+  = 0.85), reducing internal resistance and enhancing charge-discharge efficiency. A half-cell with NaNi 1/3 Fe 1/3 Mn 1/3 O 2 (NFM) cathode delivers 130 mAh g −1 at 0.1C, retains 95.86 mAh g −1 after 100 cycles, and demonstrates superior rate capability. The high mechanical strength, uniform pore structure, and efficient Na + transport of LF-ALO enhance long-term cycling and contribute to safe operation, highlighting cellulose-based composites for next-generation SIBs.