Long-life lithium batteries enabled by a pseudo-oversaturated electrolyte

The specific energy of Li metal batteries (LMBs) can be improved by using high-voltage cathode materials; however, achieving long-term stable cycling performance in the corresponding system is particularly challenging for the liquid electrolyte. Herein, a novel pseudo-oversaturated electrolyte (POSE) is prepared by introducing 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) to adjust the coordination structure between diglyme (G2) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). Surprisingly, although TTE shows little solubility to LiTFSI, the molar ratio between LiTFSI and G2 in the POSE can be increased to 1:1, which is much higher than that of the saturation state, 1:2.8. Simulation and experimental results prove that TTE promotes closer contact of the G2 molecular with Li+ in the POSE. Moreover, it also participates in the formation of electrolyte/electrode interphases. The electrolyte shows outstanding compatibility with both the Li metal anode and typical high-voltage cathodes. Li||Li symmetric cells show a long life of more than 2000 h at 1 mA cm(-2), 1 mAh cm(-2). In the meantime, Li||LiNi0.8Co0.1Mn0.1O2 (NCM811) cell with the POSE shows a high reversible capacity of 134.8 mAh g(-1) after 900 cycles at 4.5 V, 1 C rate. The concept of POSE can provide new insight into the Li+ solvation structure and in the design of advanced electrolytes for LMBs.