Crosslinking-enhanced cellulose separator with poly(propylene oxide) and carboxylated cellulose nanofibers for sodium-ion batteries

The performance of sodium-ion batteries (SIBs) is often impeded by the commercial cellulose separators because of their large pore structure and low mechanical strength. Herein, an improved composite cellulose separator is prepared by integrating with bis[(3-methyldimethoxysilyl)propyl]-polypropylene oxide (BSPPO) and carboxylated cellulose nanofibers (C-CNF) via polymerization crosslinking. Multiple interactions between BSPPO and C-CNF synergistically generate high porosity, thereby refining the microporous architecture and providing more space for electrolyte uptake. This result greatly facilitates uniform Na + deposition and fast Na + transport through the BSPPO chain-mediated pore channels. Meanwhile, multiple interconnected networks formed by BSPPO and C-CNF substantially enhance the mechanical strength, with a tensile strength of 22.3 MPa. The optimal separator exhibits an intrinsic resistance of 0.89 Ω, an ionic conductivity of 1.52 mS cm −1 , and a Na + transfer number of 0.72, all markedly superior to those of the commercial cellulose separator. In Na||hard carbon half-cell tests, the separator delivers outstanding rate capability and long-term cycling stability, maintaining a discharge capacity of 68.1 mAh g −1 after 100 cycles at a high rate of 2C. This work tailors composite cellulose separators by combining BSPPO and C-CNF to reinforce their structure and functions, which can help to advance commercial cellulose separator for better practical SIBs applications.