Promoting Fast Na Ion Transport at Low Temperatures for Sodium Metal Batteries.

Cost concerns have promoted the rise of Na-based batteries as an alternative to Li-based batteries, and the energy density pursuits have brought attention to Na metal anodes. Numerous studies have been conducted on the failure mechanisms and improvement methods of Na metal batteries (NMBs) at room temperature; however, the low-temperature applications are still faced with more complex challenges. On the basis of the concentration effect of the electrolytes, we propose a dilute electrolyte for the low-temperature operation of NMBs. With the low salt concentration and tetrahydrofuran cosolvent, the affinity between Na ions and the solvent molecules is weakened to achieve fast reaction kinetics at low temperatures. The designed electrolyte enables an effectively decreased cell impedance, which improves the cycling stability of Na symmetric cells. As a result, the full cell paired with the Na 3 V 2 (PO 4 ) 3 cathode maintains a capacity of 80 mAh/g over 250 cycles at -20 °C. This work provides an electrolyte design strategy toward low-temperature NMBs.