Boehmite/PAN nanocomposite fibrous separators with superior wettability and thermal properties for sodium-ion batteries with high electrochemical performances

Sodium-ion batteries (SIBs) have attracted significant attention as alternative power sources for lithium-ion batteries (LIBs) because of the abundance of sodium resources, and the electrochemical properties of these batteries are analogous to those of LIBs. However, the polyethylene (PE) separator conventionally employed in LIBs has poor affinity with the polar solvent used in SIBs; therefore, glass fiber (GF) separators with high porosity and wettability are widely used in the lab-scale development of SIBs despite their fatal drawbacks including high thicknesses, high costs, and low flexibility. For the commercialization of SIBs, a separator design that accommodates both the advantages of a thin PE separator and the open-pore structure and polar properties of a GF separator is necessary. Herein, we propose a thin, custom-made separator (PAN-AlOOH separator) with highly polar properties and an open-pore structure for SIBs, in which highly polar boehmite (AlOOH) particles are homogeneously integrated in a polyacrylonitrile (PAN) separator using electrospinning. The integration of AlOOH particles in the PAN-AlOOH separator can greatly contribute to ensuring thermal and dimensional stability at elevated temperatures above 270 ℃. Concurrently, AlOOH particles in the PAN-AlOOH separator improve its affinity toward the polar electrolyte of SIBs and alter the solvation structure around the Na⁺ ions in the electrolyte solution, thereby allowing for outstanding wettability and ionic conductivity. Therefore, the PAN-AlOOH separator may be used to achieve an excellent rate capability and cycle performance for SIBs; further, its performance is better than that of Na full cells employing a GF separator.