From natural cotton thread to sewable energy dense supercapacitors
Considering cost and flexibility, cotton thread is an ideal material to fabricate wearable and portable electronics. However, the capacitance of cotton thread based supercapacitors remain extremely low (below 50 mF/cm2) due to the insufficient capacitive utilization of active materials. In this work, ordered mesoporous carbon (OMC) membrane are rationally coupled with chemical vapour deposition derived graphene (CVD gr), to form highly conductive carbon coatings around cotton yarns. In this material design, OMC membrane act as hydrophilic nanoporous “ion reservoirs” to accumulate sufficient cations from gel electrolyte, while CVD gr endows the composite thread low liner resistance (3.7 Ω cm-1) and high mechanical strength. Using butyl-3-methylimidazolium chloride modified gel as ionic conducting electrolyte, the efficiency in capacitive utilization of coated MnO2 microparticles has been doubled, delivering an areal capacitance of 1.1 F cm2 with a volumetric energy of 2.7 mWh cm-3. Such supercapacitor thread is lightweight, sewable, durable in bending fatigue tests, and can be fabricated through facile dip-coating method. Impressively, this device can power a photodetector based on TiO2 nanowires without applying any external bias voltage, which opens up new opportunity for development of wearable and self-powered nanodevices in near future.