Constructing High-Energy-Density Aqueous Supercapacitors with Potassium Iodide-Doped Electrolytes by a Precharging Method

Aqueous supercapacitors (SCs) are safe and environmentally friendly with a high power density while having low-voltage windows and a low energy density. To address these challenges, poly(vinyl alcohol) potassium borate (PVAPB) gel polymer electrolytes (GPEs), which have demonstrated good electrochemical stability and wettability with electrodes, were prepared by in situ electrodeposition and then doped with potassium iodide (KI). SCs based on commercial active carbon electrodes and KI-doped PVAPB GPEs could work stably at 1.6 V and achieve a specific capacitance of 164.7 F g(-1) and an energy density of 14.38 Wh kg(-1) at a current density of 1 A g(-1), which are both significantly higher than for SCs without KI of 69.9 F g(-1) and 4.38 Wh kg(-1). Meanwhile, the SC prepared with KI-doped PVAPB GPEs has a high ionic conductivity of 1.7 mS cm(-1) (more than 200% higher than for the traditional organic electrolyte) with a power density of 3.55 kW kg(-1). Subsequently, we propose a precharging method to further boost the capacitance and energy of SCs with KI-doped PVAPB GPEs, which could deliver an excellent specific capacitance of 228.2 F g(-1) with an energy density of 17.3 Wh kg(-1) at 1 A g(-1). More importantly, this precharging method works for the KI-KOH electrolyte system as well, which can effectively contribute to constructing high-energy-density SCs with KI-doped electrolytes.