Study Of Correlation Between Electrolyte (Ions Dimension, Solvent) And Electrode Materials (Pore Size, Pore Size Distribution)

Activated carbon with different pore architecture was prepared from petroleum coke by KOH activation and used as electrode materials of electric double-layer capacitor. Non-aqueous electrolytes with different ions dimension and ionic liquid with the various length of the alkyl chain were solvated in solvent propylene carbonate or acetonitrile and acted as electrolytes. The electrochemical behavior was investigated using two-electrode and three-electrode configurations through galvanostatic charge/discharge, cyclic voltammograms, and electrochemical impedance spectroscopy techniques. Results showed an asymmetric capacitance response occurred on each electrode for the material with insufficiently developed porosity of SAC-R1. The charge storage saturation would take place in the negative electrode, observable as an inferior gravimetric capacitance of 7 Fg-1 as compared to that of 113 Fg-1 in the positive electrode. A close fit of pore size distribution of electrode material to the size of bulky terabutylammonium cation suggests a saturation effect on the active surface, observable as a decrease in capacitance current in the negative region. Experimental and calculated maximum charge values present a good correspondence. Results suggest that the insufficiently developed porosity for cation accommodation causes the current decay in the negative electrode. In contrast, pores size is larger than that of terafluoroborate, the saturation effect is not found at the expense of the lower specific area capacitance in the positive electrode. The difference of capacitive behaviours of each electrode became obvious with the increasing of the length of the alkyl chain of ionic liquid. This suggested that there existed strongly dependence between ions dimension and pore size. The variation of capacitive performance with different solvent further confirm the partially desolvated effect would occur in the EDLC process.