Electrochemical Properties of Trimethylammonium Tetrafluoroborate in Electrochemical Double-Layer Capacitors

Trimethylammonium tetrafluoroborate (TriMA BF4), consisting of the smallest trialkylammonium ion, was investigated for use in electrochemical double-layer capacitors. Despite the presence of a proton in TriMA, cycle life tests in acetonitrile (AN) and -butyrolactone (GBL) showed a good capacity retention with a 1.8 V cut-off voltage. The rate of electrolysis of TriMA BF4 in GBL was lower than that in AN because of the lower conductivity in GBL. As a consequence, the cells based on GBL achieved a higher capacitance and longer life than those with AN. TriMA BF4 had a higher conductivity and lower viscosity than the quaternary salt tetraethylammonium tetrafluoroborate in GBL, as well as higher ionic mobility, these factors resulted in a higher rate capability.