High Voltage Compatible Bi-Functional Electrolyte for Li Metal Batteries

In a few decades, the huge advancement was achieved via successful commercialization of Li ion batteries. As the demand for more stable energy supply source grows, the necessity to replace the conventional carbon anode also is being increased. Lithium metal has been suggested as one of the candidates. However, it has few critical barriers regarding the safety which must be overcome to be successful alternative for the next generation batteries. Among diverse approaches, introducing a safe electrolyte to the system could be one step forward for Lithium metal to be used as the next generation batteries. In this study, the glyme based electrolyte was formulated by simply making a solution with Lithium bis(fluorosulfonyl)imde (LiFSI), 1-2, dimethoxy ethane and the fluorinated ether. This mono-glyme has been known to be effective to restrain Lithium dendritic growth1. Also, it can dissolve LiFSI salt up to 9.6 mol. Since, highly concentrated electrolyte is able to put up with relatively high electrochemical stability2, thus, it could be a favorable solvent for the electrolyte. On the other hand, the fluorinated part of the electrolyte (1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether) could not dissolve the salt at all, but, it functions as an anti-oxidation agent and a viscosity lowering agent at the same time. In Figure 1(a), it was proven that the electrolyte comprising those two components is quite effective to maintain the stability within the practical voltage window ranged from 3.0 ~ 4.5 V (vs. Li/Li+) via cyclic voltammetry (CV). Based on the stability, it also shows the full cell test results indicating outstanding cycle performance over 200 cycle even with highly packed cathode (c.a. 4g/cc) as illustrated in Fig. 1(b). The extended performance is attributed to the synergistic contribution from each component of the electrolyte.