Electrochemical properties of CNT-PANI nanofiber/MXene buckypaper superflexible electrodes and all-solid-state superflexible supercapacitors

Most of the reported carbon-polyaniline (PANI) electrode composites are powders or require flexible substrates, which hinders their potential applications in the flexible wearable electronics. Moreover, PANI structure collapses and shed loss due to the lack of effective support and protection results in low capacity retention. In this study, superflexible, binder-free and substrate-free carbon nanotube-polyaniline nanofibers/MXene (CP_nfM) buckypaper were prepared by ultrasonic dispersion self-assembly and directional pressure filtration. In the buckypaper, polyaniline nanofibers (PANI_nf) were in situ growth on carbon nanotubes (CNTs), and the CNTs-PANI_nf was inserted between the MXene nanosheets that were ultrasonically separated. Some MXene nanosheets were cut into fragments by ultrasonic waves and self-assembled into nanoflowers on the CNTs-PANI_nf. The CP_nfM electrode had an excellent capacitance of 479 F g⁻¹ at 1 A g⁻¹. The superflexible solid-state supercapacitors (FSSCs) assembled with the electrode had a capacitance of 110 F g⁻¹ at 1 A g⁻¹, a high energy density of 15.3 Wh Kg⁻¹ at a power density of 0.5 kW Kg⁻¹. The capacitance of the FSSC did not decrease but increased during the charge–discharge cycle, with a capacitance retention of 104% after 5000 cycles. Its capacitance retention was 90% after folding 200 times in half along the sharp crease. One-dimensional CNTs and two-dimensional MXene nanosheets collaboratively constructed the superflexible porous skeleton, alleviating the stress damage caused by volume changes of the PANI_nf in the cycles. MXene nanosheets trapped the shed PANI nanoparticles. This work provides a way for potential application of high-performance energy storage devices in wearable electronics.