Effect of crown ether additive on the compatibility of electrolyte and hard carbon anode in sodium ion battery

The addition of additives is an ideal method to form solid electrolyte interface (SEI) and improve electrolyte solvation structure of Sodium-ion batteries. 15-Crown-5 is effective in improving the ionic solvation structure owing to its high coordination ability with Na+. Through physical characterization, it was analyzed that the crown ether molecules reaching the surface of hard carbon anodes driven by the electric field force could reduce the side reaction products of the hard carbon anode surface, lower the degree of polarization of the hard carbon anode, participate in the formation of uniform and smooth SEI films, augment the content of inorganic components in the SEI, and thus improve the sodium conductivity of the SEI. The addition of 15-Crown-5 proved to improve the compatibility between electrolyte and the hard carbon anode 15-Crown-5 and the hard carbon demonstrated excellent cycling performance of 300 cycles on the basis of the electrolyte, achieving a capacity retention of 95.69 % and an 8.87 % higher discharge specific capacity at 50 mA g−1as compared to the cell without the additive.