High-Performance Flexible Asymmetric Fiber-Shaped Supercapacitor Based on CF/PPy and CNT/MnO₂ Composite Electrodes

Fiber-shaped supercapacitors (FSSs) are identified as promising facilities in flexible and wearable energy storage fields. In this study, an electrode with excellent formability was accomplished by depositing polypyrrole on highly aligned discontinuous carbon fiber (CF/PPy). For the FSS with core–sheath structure, CF/PPy fiber was the core electrode, LiCl/PVA was the electrolyte, and carbon nanotube/MnO2 (CNT/MnO2) film was the opposite electrode. The charge of core and opposite electrodes was paired by adjusting the electrochemical reaction times of MnO2 and PPy. The obtained FSS had an areal capacitance of 66.27 mF cm–2 (lineal capacitance of 13.52 mF cm–1 and volumetric capacitance of 4.08 F cm–3) and a broadened potential window of 1.6 V, which resulted in a maximum energy density of 23.56 μWh cm–2. The cycling stability was evaluated by charge–discharge test, and it retained 83% of its initial capacitance after 5000 cycles. Furthermore, the FSS showed exceptional flexibility and it retained above 90% of its capacitance after 200 repeated bending tests, illustrating excellent mechanical stability.