Synthesis of Fluorine-Free Polymer Electrolyte Having Lithium Bissulfonimide Unit

Abstract

Polymer electrolytes are important materials of Li ion batteries enabling leakage resistance, miniaturization, and thinning. However, the ion conductivities of polymer electrolytes lower than general electrolyte solutions of Li ion battery, limit the performance of cells. To develop novel polymer electrolytes with good ionic conductivity, we focused on the structure of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). LiTFSI is a widely used Li electrolyte salt having high ion conductivity, and its organic structure can be chemically modified. Hence, some polymer electrolytes bearing similar structures were synthesized. However, their ion conductivity are in an insufficient range of 10-5S/cm probably due to their very high Li ion concentrations and high glass-transition temperature (T g). Herein, we describe the synthesis of a novel polymer electrolytes exhibiting high ion conductivity by copolymerization of lithium N-methanesulfonylvinylsulfoneimide (LiMSVSI) for the electrolyte component with poly(ethylene glycol) methyl ether acrylate (PEGMA) for low T gand ion conductive pathway (Scheme 1).The copolymerization of LiMSVSI with PEGMA was carried out by a two-stage heating method. The first stage in ethanol at 60 ºC gave a mixture of the copolymer and the residual monomers. The second stage at 100 ºC after evaporating solvent converted the monomers in quantitatively. The T gof the copolymer was determined as –62 ºC by differential scanning calorimetry (DSC) analysis. The copolymer exhibited good ionic conductivity in the range of 10-4–10-5 S/cm due to its labile ionic structure and low T g. In this paper, we will also describe the copolymerization behavior of LiMSVSI with other comonomers. Figure 1