Organosulfide-Based Deep Eutectic Electrolyte for Lithium Batteries.

Deep eutectic electrolytes (DEEs) are a new class of electrolytes with unique properties. However, the intermolecular interactions of DEEs are mostly dominated by Li⋅⋅⋅O interactions, limiting the diversity of chemical space and material constituents. Herein, we report a new class of DEEs induced by Li⋅⋅⋅N interactions between 2,2'-dipyridyl disulfide (DpyDS) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). The strong ion-dipole interaction triggers the deep eutectic phenomenon, thus liberating the Li+ from LiTFSI and endowing the DEEs with promising ionic conductivity. These DEEs show admirable intrinsic safety, which cannot be ignited by flame. The DEE at the molar ratio of DpyDS:LiTFSI=4:1 (abbreviated as DEE-4:1) is electrochemically stable between 2.1 and 4.0 V vs. Li/Li+ , and exhibits an ionic conductivity of 1.5×10-4  S cm-1 at 50 °C. The Li/LiFePO4 half cell with DEE-4:1 can provide a reversible capacity of 130 mAh g-1 and Coulombic efficiency above 98 % at 50 °C.