Methacrylic-based solid polymer electrolyte membranes for lithium-based batteries by a rapid UV-curing process

The present communication describes solid polymer electrolyte (SPE) membranes prepared by the direct free radical photo-polymerisation (UV-curing) of poly(ethyleglycol)methacrylic oligomers in the presence of a lithium salt. The highly mobile pendant ethoxy chains, constituting a considerable fraction of the whole polymer matrix, can provide a large density of coordination sites for the Li+ ions and make the material an interesting solvent-free ion conducting medium for high temperature application. The production process is simple and versatile; the resulting membranes demonstrate mechanical integrity due to the cross-linked nature of the polymer network, and wide thermal stability. The electrolytes produced are extra soft, non-crystalline, transparent solids, do not contain volatile matter and show sufficient ionic conductivity along with a wide electrochemical stability window. Differential scanning calorimetry (DSC), Fourier-transform infrared spectroscopy (FT-IR), and electrochemical impedance spectroscopy (EIS) are employed to characterise the polymers, monitor its phase changes and control the conductivity of the electrolytes as a function of lithium bis(trifluoromethane)sulfonimide salt (LiTFSI) concentration. The temperature dependence of the ionic conductivity follows the Vogel-Tamman-Fulcher (VTF) equation, and the ionic conductivity at 60 °C reaches values higher than 10−4 S cm−1.