Application of a novel binder for activated carbon-based electrical double layer capacitors with nonaqueous electrolytes

Abstract

In this work, we have fabricated activated carbon electrodes using the binder LA135 and assembled electrical double layer capacitors with nonaqueous electrolytes of 1 M tetraethyl ammonium tetrafluoroborate (Et4NBF4) in propylene carbonate (PC), 1 M Et4NBF4 in acetonitrile (AN), and 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4) ionic liquid, respectively. The main chemical compositions of the binder are polyacrylonitrile and styrene–butadiene rubber. Scanning electron microscope images show that the conductive agents have been uniformly dispersed on the activated carbons in the electrode. The thermal stabilities of electrodes using different binders are studied by thermogravimetric analysis. The electrochemical properties of cells in different nonaqueous electrolytes are characterized by cyclic voltagramms, electrochemical impedance spectra, galvanostatic charge–discharge, leakage current, and cycle life measurements. The capacitor in Et4NBF4/AN has the lowest internal resistance and superior high-rate capability, and the one in Et4NBF4/PC has the smallest leakage current. The capacitor in EMIMBF4 has the energy density as high as 35.4 Wh kg−1 at a current density of 0.2 A g−1 (based on the total mass of active materials), which is 1.6 times higher than that of capacitor in PC electrolyte. Besides, the electrochemical properties of capacitors with different binders are comparatively studied. The capacitor using LA135 has the highest specific capacitance and moderate internal resistance comparing with the ones using poly(tetrafluoroethylene), sodium carboxymethyl cellulose + styrene–butadiene rubber or poly (vinylidene fluoride).