Multi-electron/ion conduction channels enabling high-performance flexible supercapacitors

Abstract

The construction of aqueous flexible supercapacitors with both broad working voltage and high energy density is promising but still challenging. In a supercapacitor, the electron/ion conduction properties of electrodes, whether between the electrode and electrolyte or within the electrode materials, play a critical role in stimulating the capacitive components of active materials, particularly for thicker electrodes used in practical applications. Herein, a three-dimensional porous carbon fiber (CF) uniformly wrapped metal-oxide (M_xO_y) is developed and interconnected by graphene sheets (Gs) to construct multi-electron/ion conduction channel inks (multi-conductive inks). In situ electrochemical impedance combined with in situ potential monitoring reveals that the screen-printed multi-electron/ion conduction channel electrodes not only significantly facilitate electronic and ionic diffusion/transport, but also greatly accelerate the redox kinetics of metal-oxides. As a result, the assembled asymmetric flexible supercapacitor based on M_xO_y/CF@Gs multi-conductive electrodes (e.g., Fe₂O₃/CF@Gs//NiO/CF@Gs) delivers a remarkable areal capacitance of 206.2 mF cm⁻² at 3 mA cm⁻², far higher than that of pure Fe₂O₃//NiO (27.5 mF cm⁻²) and Fe₂O₃/CF//NiO/CF (53 mF cm⁻²). The energy and power density of the multi-conductive supercapacitor reach up to 0.093 mW h cm⁻² and 30 mW cm⁻², respectively. In addition, the screen-printed flexible supercapacitor also exhibits excellent flexibility with a capacitance retention of 89.2% after 1500 bending cycles. More impressively, two printed flexible supercapacitors connected in series can power a timer working for 350 minutes after only 50 seconds of charging, or light up 8 LED arrays even with continuously bending, squeezing, and flapping. Therefore, it opens a new horizon for designing of energy sources for future portable and wearable electronic devices.