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

## TL;DR

A new composite electrode material made of iron sulfide and cellulose-carbon nanotube films shows excellent performance in supercapacitors with high voltage and durability.

## Contribution

A novel composite electrode material combining FeS2 microspheres with a cellulose-CNT conductive film is developed for high-voltage symmetric supercapacitors.

## Key findings

- The RC/CNT/FeS2/PPy composite electrode achieved an areal capacitance of 6543.8 mF cm–2 at 1 mA cm–2.
- The electrode retained 91.1% of its capacitance after 10,000 charge/discharge cycles.
- A symmetric supercapacitor using this electrode delivered a maximum energy density of 329 μWh cm–2 and 86.2% capacitance retention after 10,000 cycles.

## Abstract

Nanostructured iron
disulfide (FeS2) 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/FeS2 composite films. The RC/CNT composite
film served as an ideal substrate for the homogeneous deposition of
FeS2 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/FeS2 composite
to improve its conductivity and cycling stability. Due to the synergistic
effect of FeS2 with high redox activity and PPy with high
stability and conductivity, the RC/CNT/FeS2/PPy composite
electrode exhibited excellent electrochemical performance. The RC/CNT/0.3FeS2/PPy-60 composite electrode tested with Na2SO4 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/0.3FeS2/PPy-60 film after a 10,000 cycle test. A symmetrical supercapacitor
device composed of two identical pieces of RC/CNT/0.3FeS2/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/FeS2/PPy composite electrodes for the fabrication
of high-performance symmetric supercapacitors with high operating
voltages.