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 2 ) 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 2 composite films. The RC/CNT composite film served as an ideal substrate for the homogeneous deposition of FeS 2 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 2 composite to improve its conductivity and cycling stability. Due to the synergistic effect of FeS 2 with high redox activity and PPy with high stability and conductivity, the RC/CNT/FeS 2 /PPy composite electrode exhibited excellent electrochemical performance. The RC/CNT/0.3FeS 2 /PPy-60 composite electrode tested with Na 2 SO 4 aqueous electrolyte could achieve an excellent areal capacitance of 6543.8 mF cm -2 at a current density of 1 mA cm -2 . 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 2 /PPy-60 film after a 10,000 cycle test. A symmetrical supercapacitor device composed of two identical pieces of RC/CNT/0.3FeS 2 /PPy-60 composite electrodes provided a high areal capacitance of 1280 mF cm -2 , a maximum energy density of 329 μWh cm -2 , a maximum power density of 24.9 mW cm -2 , and 86.2% of capacitance retention after 10,000 cycles at 40 mA cm -2 when tested at a wide voltage window of 1.4 V. These results demonstrate the greatest potential of RC/CNT/FeS 2 /PPy composite electrodes for the fabrication of high-performance symmetric supercapacitors with high operating voltages.