Polymer-Ionic liquid Electrolytes for Electrochemical Capacitors.

摘要

Polymer electrolyte, comprised of ionic conductors, polymer matrix, and additives, is one of the key components that control the performance of solid flexible electrochemical capacitors (ECs). Ionic liquids (ILs) are highly promising ionic conductors for next generation polymer electrolytes due to their excellent electrochemical and thermal stability. Fluorinated ILs are the most commonly applied in polymer--IL electrolytes. Although possessing high conductivity, these ILs have low environmental favorability. The aim of this work was to develop environmentally benign polymer--ILs for both electrochemical double-layer capacitors (EDLCs) and pseudocapacitors, and to provide insights into the influence of constituent materials on the ion conduction mechanism and the structural stability of the polymer--IL electrolytes.;Two types of inorganic nanofillers were incorporated into these polymer electrolytes. The effects of SiO2 and TiO2 nanofillers on ionic conductivity, crystallinity, and dielectric properties of PEO--EMIHSO4 were studied over a temperature range from --10 °C and 80 °C. Using an electrochemical capacitor model, impedance (complex capacitance) and dielectric analyses were performed to understand the ionic conduction process with and without fillers in both semi-crystalline and amorphous states of the polymer electrolytes. Despite their different nanostructures, both SiO2 and TiO 2 promoted an amorphous structure in PEO-- EMIHSO4 and increased the ionic conductivity 2-fold. While in the amorphous state, the dielectric constant characteristic of the fillers contributed to the increased conductivity and cell capacitance. Leveraging the fillers, the ionic conductivity of the environmentally friendly polymer--ILs approached the level of the polymer--fluorinated IL at room temperature, and exceeded the latter at high temperature.;Another approach to improve the performance of polymer electrolytes was undertaken through the development of protic ILs (PILs) and polymer--PIL electrolytes for pseudocapacitors. Binary eutectic systems of PILs were investigated, and the proton conduction of the eutectic systems was characterized in both liquid and polymer states. Devices enabled by PEO--EMIHSO4 and PEO--binary PILs demonstrated a comparable energy density to that with polymer--fluorinated ILs.;Solid polymer electrolytes composed of poly(ethylene oxide) (PEO) and 1&