δ-MnO2 nanofiber/single-walled carbon nanotube hybrid film for all-solid-state flexible supercapacitors with high performance

Abstract

δ-MnO₂ ultralong nanofibres with smooth surface, good dispersion and a large length-to-width ratio were first controllably prepared by hydrothermally treating δ-MnO₂ with low crystallinity at 150 °C for 20 h in 1 M NaOH. δ-MnO₂ nanofiber/single-walled carbon nanotube (SWCNT) hybrid film electrodes with excellent flexibility and high capacitance were obtained between the δ-MnO₂ nanofibre and SWCNTs via a simple vacuum filtration method. The formed regular fibrous network structure and a synergistic effect between the SWCNTs and δ-MnO₂ nanofiber make the δ-MnO₂/SWCNT-15 hybrid film electrode show a larger areal specific capacitance of 964 mF cm⁻² at a current density of 1 mA cm⁻² and excellent capacity retention of 81% when the current density was increased from 1 to 10 mA cm⁻². By using δ-MnO₂/SWCNT-15 film electrodes, a flexible all-solid-state δ-MnO₂/SWCNT-15 hybrid supercapacitor was assembled by sandwiching the PVA–KOH solid-state electrolyte, which not only showed good flexibility and mechanical properties, but also gave a high energy density of 31.8 μW h cm⁻² at a power density of 0.815 mW cm⁻². δ-MnO₂ nanofibre/SWCNTs hybrid film flexible supercapacitors have great potential in future portable and wearable electronic applications due to their excellent flexibility, high energy density, good cycle life and coulombic efficiency.