All electrochemical measurements were conducted in a two-electrode configuration with a Biologic BCS-805 potentiostat. Cyclic voltammograms of the cells were first obtained at a scan rate of 10 mV/s with a fixed potential window of 0-2.5 V for at least 5 cycles. For constant charge-discharge measurements, each cell was measured under different current densities at 0.05, 0.1, 0.2, 0.5, 0.75 and 1 A/g with a potential window of 0-2.5 V for at least 3 cycles under each current density. For each type of carbon in each electrolyte system, at least two cells were made. For most carbons three repeat cells were made. The capacitance of each cell was calculated through galvanostatic charge discharge measurements from the slope of the second half of the discharge curve in the last cycle. The representative capacitance for each carbon was the average of repetitive cells with a standard deviation of less than 5 F/g. The error bars in corresponding figures represent the standard deviations between the repetitive cells.