Pseudo Over Saturated Electrolyte for High Voltage Lithium Batteries

The specific energy of Li metal batteries (LMBs) can be improved by using high voltage cathode materials, however, achieving stable cycling at high voltages is of particularly challenging to the electrolyte. Here, we prepare a novel pseudo over saturated electrolyte (POSE) by the introduction of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) to adjust the coordination structure between diglyme (G2) and lithium bis(triflfluoromethanesulfonimide) (LiTFSI). Surprisingly, although TTE shows little solubility to LiTFSI, while the molar ratio between G2 and LiTFSI in the POSE can be enhanced to 1:1, which is much higher than that in the saturation state, 1:2.8. We prove that TTE propel the G2 molecular to closer contact with Li + in the POSE, moreover, it also strongly coordinate with the solvated couples, Li[G2]TFSI. The electrolyte demonstrates outstanding compatibility with both Li metal anode and typical high voltage cathodes, it can be stably cycled in Li||Li batteries at 1 mA cm -2 , 1 mAh cm -2 for 2000 h. And meantime, Li|| LiNi 0.8 Co 0.1 Mn 0.1 O 2 cell with the POSE shows a high reversible capacity of 134.8 mAh g -1 after 900 cycles at 4.5V, 1C rate. We believe the concept of POSE can provide new insight into the Li + solvation structure, as well as the design of advanced electrolytes for LMBs.