Iron Sulfide Microspheres Supported on Cellulose-Carbon Nanotube Conductive Flexible Film as an Electrode Material for Aqueous-Based Symmetric Supercapacitors with High Voltage.

Nanostructured iron disulfide (FeS) was uniformly deposited on regenerated cellulose (RC) and oxidized carbon nanotube (CNT)-based composite films using a simple chemical bath deposition method to form RC/CNT/FeS composite films. The RC/CNT composite film served as an ideal substrate for the homogeneous deposition of FeS microspheres due to its unique porous architecture, large specific surface area, and high conductivity. Polypyrrole (PPy), a conductive polymer, was coated on the RC/CNT/FeS composite to improve its conductivity and cycling stability. Due to the synergistic effect of FeS with high redox activity and PPy with high stability and conductivity, the RC/CNT/FeS/PPy composite electrode exhibited excellent electrochemical performance. The RC/CNT/0.3FeS/PPy-60 composite electrode tested with NaSO aqueous electrolyte could achieve an excellent areal capacitance of 6543.8 mF cm at a current density of 1 mA cm. The electrode retained 91.1% of its original capacitance after 10,000 charge/discharge cycles. Scanning electron microscopy (SEM) images showed that the ion transfer channels with a pore diameter of 5-30 μm were formed in the RC/CNT/0.3FeS/PPy-60 film after a 10,000 cycle test. A symmetrical supercapacitor device composed of two identical pieces of RC/CNT/0.3FeS/PPy-60 composite electrodes provided a high areal capacitance of 1280 mF cm, a maximum energy density of 329 μWh cm, a maximum power density of 24.9 mW cm, and 86.2% of capacitance retention after 10,000 cycles at 40 mA cm when tested at a wide voltage window of 1.4 V. These results demonstrate the greatest potential of RC/CNT/FeS/PPy composite electrodes for the fabrication of high-performance symmetric supercapacitors with high operating voltages.