Enhanced stability of sodium anodes by amino-functioned macroporous two-dimensional nanodiamond coated polypropylene separators

The abundance and cost-effectiveness of sodium metal present a promising foundation for the widespread adoption of sodium-metal batteries (SMBs). However, the dendrite formation during the repeated Na deposition/stripping process impedes the long-term stable operation of the batteries. To tackle these concerns, a separator structure is designed by coating commercial polypropylene (PP) with amino (NH2) functionalized two-dimensional diamonds (diamane) with macroporous structure. As a result, the Na symmetric cell incorporating the PP/NH2-diamane separator exhibits sustained stability for 3200 h at 5 mA cm−2 with 1 mAh cm−2, and 1800 h at a high current density of 20 mA cm−2 with 1 mAh cm−2. The excellent electrochemical performance of the cell with the PP/NH2-diamane separator can be attributed not only to the sodiophilic NH2 functional groups facilitating the uniform deposition of Na ion, but also to the homogeneously macroporous channels formed on the PP separators, enabling uniform and rapid transportation of sodium ions through the separator. Moreover, the PP/NH2-diamane separator also enhances the rate capability and long-cycle stability of Na metal batteries. This cost-effective strategy offers a promising avenue for engineering stable SMBs through simply separator modifications.