Multifunctional polyoxometalate-modified separator enabling superior Na ion transport kinetics and dendrite-free sodium metal batteries

The performance of sodium metal batteries (SMBs) is fundamentally dictated by ionic transport. Here, a polyoxometalate (Na3PW12O40)@Zein/polyacrylonitrile-modified polypropylene separator (PZP) is designed to boost Na+ transport kinetics and transference number. Results indicate that the unique shared oxygen bridge structure of Na3PW12O40 significantly increases Na+ transference number (tNa+ = 0.75) and diffusion kinetics, thereby achieving dendrite-free sodium metal deposition and a robust solid electrolyte interphase. Specifically, a symmetric cell using the PZP separator could stably cycle for 5000 h at 1 mA cm−2, 1 mAh cm−2, and 12 000 cycles at high current density (25 mA cm−2, 1 mAh cm−2). Furthermore, the assembled NaǁPZPǁNa3V2(PO4)3@C full cell could stably cycle for 2000 cycles at a current density of 500 mA g−1, providing a reversible capacity of 85 mAh g−1 along with a capacity retention of 95.1%. All these results demonstrate the potential of polyoxometalate-functionalized separators for practical applications in SMBs.