Binary room-temperature complex electrolytes based on LiClO4 and organic compounds with acylamino group and its characterization for electric double layer capacitors

Binary room-temperature complex electrolytes have been synthesized based on lithium perchlorate (LiClO4) and organic molecules with acylamino groups, including acetamide, ethyleneurea, 2-oxazolidinone (OZO), urea. methylurea (NMU) and 1,3-dimethylurea (DMU). Both LiClO4 and all organic molecules with acylamino groups are solid at room-temperature, but their mixtures at the proper molar ratio are liquid with a liquidus temperature about below 25 degrees C characterized by differential scanning calorimetry (DSC). Infrared spectroscopic studies show that the organic molecules can coordinate with the Li+ cation and the ClO4- anion via their polar groups (the C = O and NH groups). Such strong interactions lead to the dissociation of LiClO4 and the breakage of the hydrogen bonds among the organic molecules, resulting in the formation of the complex systems. Electrochemical performances of the complex electrolytes are evaluated with ac impedance spectroscopy, cyclic voltammetry (CV). and in a test electric double layer capacitor (EDLC), respectively. The LiClO4-acetamide electrolyte at molar ratio 1:5.5 exhibits the highest ionic conductivity, 1.25 x 10(-3) S cm(-1) at 25 degrees C and 11.5 x 10(-3) S cm(-1) at 80 degrees C. The analysis for the CV behavior indicates that the electrochemical stability window of these electrolytes is above 3 V. The results demonstrate that these complex systems are promising electrolyte candidates for supercapacitor and probably other electrochemical devices. (c) 2008 Elsevier B.V. All rights reserved.