for the SSA experiments are split into four main sections here. For negative charging: charge the supercapacitor to -0.8 V at a constant current, hold the cell voltage at -0.8 V for 5 minutes, discharge the supercapacitor back to 0 V at a constant current of the same magnitude as the charge step, and finally hold the cell voltage at 0 V for 5 minutes. This protocol was also applied for the positive and switching experiments but with different voltage windows. This protocol was also used for the long voltage hold experiments but here with a limited voltage window of ± 0.4 V and cell voltage holds of 6 hours instead of 5 minutes. A modified protocol was used for varying the current density where a voltage window of ± 0.8 V was used but there was no cell voltage hold applied in between charging/discharging steps to exaggerate the effect of the current density on the results.