New polymerized ionic liquid (PIL) gel electrolyte membranes based on tetraalkylammonium cations for lithium ion batteries

New polymerized ionic liquids (PILs) based on tetraalkylammonium cations with N(CF₃SO₂)₂^- (TFSI^-) anions are synthesized by homopolymerization and anion exchange reaction. Furthermore, a gel polymer electrolyte membrane based on the PILs as polymer host is prepared incorporating a tetraalkylammonium ionic liquid, LiTFSI salt and nano-size SiO₂. The gel polymer electrolyte membranes show exceptional thermal and electrochemical properties. They are found to be thermally stable up to 336°C. With the increase of the IL, T_g of the PIL-based electrolyte samples decreases obviously. When the IL concentration is 25wt%, the ionic conductivity of the electrolytes reaches 4.9×10^-4Scm^-1 at 60°C. After 130 cycles, the Li/LiFePO₄ battery with the gel polymer electrolyte membranes at 60°C has discharge capacity of 122mAhg^-1 at 0.1 current rates.