Novel Deep Eutectic Electrolyte Induced by Na···N Interactions for Sodium Batteries

Described herein presents a class of novel deep eutectic electrolytes (DEEs) with distinctive properties for sodium batteries. Instead of being limited by the presence of a hydrogen bond donor (HBD) or hydrogen bond acceptor (HBA), the concept of Na···N interactions was first brought in between sodium bis(fluorosulfonyl)imide (NaFSI) and 1,2-dimethylimidazole (DMIm). The deep eutectic phenomenon was caused by the strong ion–dipole interaction, which was conducive to the release of Na⁺ from NaFSI and drove the DEE with a desirable ionic conductivity. Furthermore, the proposed mechanism of Na···N interactions was credibly confirmed by Raman, ²³Na NMR, and theoretical calculations. The half-cell based on NaFSI/DMIm–1/4 can provide a reversible capacity of 316.7 mAh·g^–1 at 0.05 A·g^–1, and Coulombic efficiency remains 91% after 500 charge–discharge cycles at 1.0 A·g^–1 in the application of sodium batteries. It is anticipated that this work will present distinct insights into the extension of electrolytes for sodium batteries.