Understanding the Accelerated Sodium-Ion-Transport Mechanism of an Interfacial Modified Polyacrylonitrile Separator

Sodium-ion batteries (SIBs) are considered as the most attractive candidates for large-scale energy storage systems owing to their low cost and abundant reserves. They need a special separator with rapid Na+ transport for a satisfactory power performance. Herein, an alkaline-solution-treated electrospun polyacrylonitrile separator with an in situ chemical-grafted graphene oxide (denoted as M-PAN-GO) is prepared via regulating the interfacial group. The increased amount and variety of oxygen-containing polar groups −COO–, −COOH–, and −OH in the M-PAN-GO separator not only increase the number of active sites for bonding and transferring Na+ but also produce more H-bonds that impede the migration of PF6–. The obtained M-PAN-GO separator displayed accelerated transmission of Na+ and Li+, and the Na+ transference number is larger than that of Li+ owing to a more efficient binding that can be formed between oxygen-containing functional groups and Na+. DFT calculations demonstrate that a greater binding energy is favorable to binding and promoting ion transport in a certain range. Along with the M-PAN-GO separator’s desolvation capability, high Na+ transference number (0.70) and ion conductivity (4.53 mS cm–1) of the M-PAN-GO separator in 1 M NaPF6 EC DMC electrolyte are obtained. The Na|Na3V2(PO4)3 cells assembled with the M-PAN-GO separator have a superior polarization voltage of 0.76 V rather than 0.97 V at 4 C in SIBs. This work provides a potential high-performance separator for SIBs and lithium-ion batteries.