Investigation of Voltage Range and Self-discharge in Aqueous Zinc Ion Hybrid Supercapacitors

Aqueous zinc ion hybrid supercapacitors are attracting extensive interest as a promising energy storage technology due to their high safety, low cost and long stability. At present, however, there is a lack of understanding of the potential window and self-discharge of this aqueous energy storage technology. Here, we report the first systematic investigation of the potential window of this device by cyclic voltammetry and galvanostatic charge-discharge. Hybrid supercapacitors based on commercial activated carbon (AC) have demonstrated a wide and stable potential window (0.2 V to 1.8 V), high specific capacitances (308 F g-1 at 0.5 A g-1 and 110 F g-1 at 30 A g-1), good cycling stability (10,000 cycles with 95.1% capacitance retention) and a high energy density 104.8 Wh kg-1 at 383.5 W kg-1, based on the active materials. The corresponding mechanism involves the simultaneous adsorption/desorption of ions on the AC cathode and zinc ion plating/stripping on the Zn anode. Our work leads to a better understanding of this device and will aid the future development of practical high-performance aqueous zinc ion hybrid supercapacitors based on commercial carbon materials, thus accelerating the deployment of these hybrid supercapacitors and filling the gap between supercapacitors and batteries. Furthermore, the simple methods used in this work could also be applied to effectively determine a rational potential window for other aqueous energy storage devices.