Constructing High-Energy-Density Aqueous Supercapacitors with Potassium Iodide-Doped Electrolytes by a Pre-Charging 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 c...