Polymethacrylate-comb-copolymer electrolyte for solid-state energy storage devices

Abstract

We report a highly ion-conductive polymer electrolyte, based on a poly(2-[3-(2H-benzotriazol-2-yl)-4-hydroxyphenyl]ethyl methacrylate)-poly(oxyethylene methacrylate)-comb (PBE-comb) copolymer and the 1-ethyl-3-methylimidazolium dicyanamide (EMIM-DCA) ionic liquid, for use in a solid-state supercapacitor. Selective interactions between the poly(oxyethylene methacrylate) (POEM) chains and the EMIM-DCA induce the formation of a microphase-separated structure, as evidenced by Fourier-transform infrared spectroscopy, transmission electron microscopy, and differential scanning calorimetry. The well-defined nanostructured morphology effectively suppresses the aggregation of EMIM-DCA to provide ion-transport pathways that facilitate the fast diffusion of mobile ions. The capacitance of the solid-state supercapacitor formed with the PBE/EMIM-DCA electrolyte (125.1Fg−1) was much greater than that of the conventional poly(vinyl alcohol) (PVA)/H3PO4 electrolyte (39.5Fg−1) due to its higher ionic conductivity and superior affinity for the electrode. The fast ion-diffusion properties of the PBE/EMIM-DCA electrolyte was confirmed by its high capacitance retention (70%) at a fast scan rate, significantly higher than that observed for the PVA/H3PO4 electrolyte. Moreover, the supercapacitor composed of the PBE/EMIM-DCA electrolyte showed considerable cycling stability (91.1% after 10,000 charge-discharge cycles). The PBE/EMIM-DCA electrolyte is therefore a promising candidate for use in high-performance solid-state supercapacitors and energy-storage systems.