A new kind of polymeric ionic liquid (PIL) membrane based on guanidinium ionic liquid (IL) with ester and alkyl groups was synthesized. On addition of guanidinium IL, lithium salt, and nano silica in the PIL, a gel PIL electrolyte was prepared. The chemical structure of the PIL and the properties of gel electrolytes were characterized. The ionic conductivity of the gel electrolyte was 5.07 × 10−6 and 1.92 × 10−4 S cm−1 at 30 and 80 °C, respectively. The gel electrolyte had a low glass transition temperature (Tg) under −60 °C and a high decomposition temperature of 310 °C. When the gel polymer electrolyte was used in the Li/LiFePO4 cell, the cell delivered 142 mAh g−1 after 40 cycles at the current rates of 0.1 C and 80 °C.
