Preparation of polymer electrolytes using ionic liquids and evaluation of physicochemical properties

To achieve high safety and good cycle performance of lithium polymer batteries, it is important to develop novel polymer electrolytes based on ionic liquids (ILs). In this study, a number of polymer electrolytes were prepared by applying various [Ls to polymethylmethacrylate-type polymers, and the physicochemical properties of the systems were evaluated. The temperature-dependence of the conductivity of the polymer electrolytes obeyed the Arrhenius relation, indicating free migration of the ionic species inside the polymer electrolytes and that ionic conduction proceeded by a conduction mechanism similar to that of the solution system. The conductivity of the phosphonium-type polymer electrolyte at 30 degrees C was three-fold higher than that of the corresponding ammonium-type polymer electrolyte ([P-225][TFSA] (gel): 1.46 x 10(-4) S cm(-2), [N-2224]FSA[(gel): 5,01 x 10(-5) S cm(-2). [P-4441][TFSA] (gel): 7.94 x 10(-5) S cm(-2), [N-4441][TFSA] (gel): 2.32 x 10(-5) S cm(-2)). For application to the lithium ion battery, the polymer electrolyte containing lithium ions was prepared and the physicochemical properties were evaluated, Even in the presence of a lithium salt, the phosphonium-type polymer electrolytes showed higher conductivity than the corresponding ammonium-type polymer electrolytes. The electrolyte underwent sequential two-stage thermal decomposition. The decomposition of the IL component was observed after thermal decomposition of the polymer component. From analysis of the charge distribution of the phosphonium and ammonium cations by MP2 calculation, the proportion of positive charges in the alkyl chain of the ammonium cation was larger than that of the phosphonium cation. This suggests that the cations in the ammonium-type polymer electrolytes enhance the interaction with the polymer chains and crosslinking sites to a greater extent than the phosphonium cations. (C) 2018 Elsevier B.V. All rights reserved.