TiO2 crystalline structure and electrochemical performance in two-ply yarn CNT/TiO2 asymmetric supercapacitors

Solid-state flexible energy storage devices play a crucial role in the development of wearable electronic textiles. In this study, we fabricated flexible asymmetric two-ply yarn supercapacitors from carbon nanotube yarns and surface-oxidized titanium filament. The crystalline structure of the TiO 2 surface layer can be adjusted to amorphous, anatase and rutile states by altering the annealing temperature. The titanium filament with a rutile TiO 2 surface layer produced at high annealing temperature showed far superior electrochemical performance over the filaments with amorphous and anatase TiO 2 surface layers. The as-prepared asymmetric two-ply yarn supercapacitors in aqueous gel electrolyte can achieve a durable operating voltage up to 1.4 V, with a maximum energy density of 11.7 Wh kg −1 and a maximum power density of 2060 W kg −1 . The asymmetric two-ply yarn supercapacitors exhibited excellent flexibility and cycling stability over 1200 cycles at straight, twisted and bent states.