Activation of an ionic liquid electrolyte for electric double layer capacitors by addition of BaTiO 3 to carbon electrodes

Abstract

To increase the capacitance of an electric double layer capacitor (EDLC) containing 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF 4) as an ionic liquid electrolyte, barium titanium oxide (BaTiO 3) as a ferroelectric material is incorporated into activated carbon electrodes. An EDLC composed of BaTiO 3 powder/activated carbon composite electrodes and the ionic liquid electrolyte EMIBF 4 exhibits a large capacitance when compared to the corresponding EDLC without BaTiO 3. Moreover, the rate performance of the EDLC containing BaTiO 3 is improved when the electrodes are prepared by an improved method, i.e., vacuum penetration of BaTiO 3-dispersed EMIBF 4 into the activated carbon electrodes. No positive addition effect of BaTiO 3 is observed for the corresponding EDLC with a typical organic electrolyte composed of a tetraalkylammonium salt and propylene carbonate as a solvent. These results suggest that BaTiO 3 incorporated into the electrodes would improve the dissociation of the ionic liquid EMIBF 4, and hence increase the carrier concentration available for the formation of an electric double layer.