## 3 Results
The Rc values of both the S\(-\)C\(+\)(57.3 \(\mathrm{ohm/cm^{2}}\)) and S\(+\)C\(-\)(50.2 \(\mathrm{ohm/cm^{2}}\)) cells were relatively smaller than that of the TRG (388.2 \(\mathrm{ohm/cm^{2}}\)) cell. Interestingly, TRG exhibits the highest Rc of 388.2 \(\mathrm{ohm/cm^{2}}\). This might be due to the apparent precipitation of the TRG solution during the dispersion of TRG electrodes. The Rp value of the TRG cell is large and out of scope for this measurement. It was found that the Rp values of the S\(-\)C\(+\) and S\(+\)C\(-\) cells were 6.2 and 5.5 \(\mathrm{ohm/cm^{2}}\), respectively. Since both cells have the same composition materials, a similar Rp value was expected. Thus, the total internal resistance values of the S\(-\)C\(+\) and S\(+\)C\(-\) cells were 66.3 and 58.5 \(\mathrm{ohm/cm^{2}}\), respectively.. As Rc represents the electron conduction of a cell, the Rc values of both the S\(-\)C\(+\) and S\(+\)C\(-\) cells were selected to be as close as possible for the further charging-discharge comparison. Figure 8 plots the cyclic voltammetry (CV) curves of TRG, and the S\(-\)C\(+\) and S\(+\) C\(-\) cells. The cell current was measured in response to an applied voltage from 0 to 3.2 V. The accumulated charge (Q) with an applied voltage (V), follows Q = CV, where C is the capacitance. The response current follows I = C \(\times\) dV/dt. For an ideal capacitance, such as for the S\(-\)C\(+\) cell (Figure 8c), under a constant voltage  
Figure 7: The impedance spectra of the TRG, S\(-\)C\(+\) cell and S\(+\)C\(-\) cell. scan rate, a constant current should be observed resulting in a rectangular shape for the CV curve. However, we must consider that the capacitor is in series with an equivalent internal resistor (R = Rs + Rc + Rp) [27]. As with the TRG cell (Figure 8a), the charging or discharging current of the capacitor required a time constant (RC) to reach the steady state current [28]. With a large RC, it took more time to reach the steady state and, thus, it collapsed the rectangular profile of the current response in Figure 8a [29; 30]. On the other hand, increasing the scan rate meant reducing the response time, which also caused collapsed results, as observed in Figure 8a-c. Figure 8d plots the capacitance against voltage profiles, in which the CV current at 100 mV/s was divided by the same scan rate. As can be seen, except for TRG, both S\(-\)C+ and S+C\(-\) cells showed a more rectangular-like capacitance response, indicating that they are closer to being ideal capacitors. The capacitance response of the cell was proportional to the accessible surface area for the IL electrolyte. In addition, these results suggested that the capacitance values of these cells were in the sequence of S\(-\)C+ > S+C\(-\)>TRG. Due to the wide electrochemical window of EMI-TFSI, the operation voltage of all the cells could be operated at 3.2 V. Figure 9 plots the galvanostatic discharge currents vs. time of the TRG, S\(-\)C+ and S\(+\)C\(-\) cells As can be seen in Figure 9a, the voltage drop at the beginning of the discharging current is a result of voltage loss when the current across an equivalent resistance which is related to internal resistance R. Therefore, as expected TRG had the highest initial voltage drop among all the samples. The gravimetric specific capacitances (Cs) of the active materials on the electrodes were extracted from the gravimetric discharge curve, following [31; 32; 33]:  
\[C_{S}=\frac{4C}{m}=\frac{4I\Delta t}{m\Delta V}\]  
where \(m\) is the total weight of active materials on two electrodes, \(C\) is the capacitance of the cell, \(I\) is the constant current, \(\Delta t\) is the discharging time, and \(\Delta V\) is the potential change (excluding the initial voltage drop) during discharging. Figure 10 plots the capacitance value deduced from the discharging current. As shown in the plot, all the capacitance responses decreased as a function of the specific current density.