Fluorinated solvents for high-voltage electrolyte in lithium-ion battery

The major obstacle for the application of high-voltage cathode materials is the anodic instability of the electrolyte. On the guidance of density functional theory calculation, we develop a new high-voltage electrolyte comprising 1 mol L−1 LiPF6 dissolved in fluoroethylene carbonate (FEC) and ethyl difluoroacetate (DFEAc) (FEC/DFEAc = 3:7 in wt.% ratio). It shows a high conductivity (9.48 mS cm−1) and high anodic stability compared with the conventional electrolyte of 1 mol L−1 LiPF6 dissolved in ethylene carbonate (EC) and ethyl-methyl carbonate (EMC) (EC/EMC = 3:7 in wt.% ratio). In addition, Li/LiNi0.5Co0.2Mn0.3O2 half-cells with the new electrolyte display an excellent cycling ability with capacity retention of 89.23% after 100 cycles at 4.6 V (vs. Li/Li+). Although the electrolyte still will be oxidized at the cathode surface, the Li2CO3 and carbon-fluoride species originated from DFEAc and FEC are beneficial to building a stable cathode/electrolyte interface as revealed by the TEM and XPS results.