Improving energy storage ability of acid-treated carbon fibers via simple sonication and heat treatments for flexible supercapacitors

Abstract

Fiber-type supercapacitor (FSC) is indispensable for soft electronics. Modifying substrate without depositing electroactive material can prevent electroactive material from peeling off and enhance flexibility of FSC. Acid treatment is one of the most effective methods to enhance energy storageability of carbon fiber (CF) via inducing functional groups and creating defects for charge accumulation. In this work, it is firstly to apply sonication and heat treatments on CF electrodes in acid mixture to enhance hydrogen ion diffusion path and acid etching rate. The highest specific capacitance (CL) of 319.0 mF/cm is obtained at 20 mV/s for the CF electrode prepared using full sonication for 45 min and heat treatment at 80 °C at last 25 min, while the untreated CF electrode only shows CL value of 8.3 mF/cm. The FSC with optimized CF electrodes shows maximum energy density of 12 μWh/cm at 250 μW/cm. After 10,000 times repeated charge/discharge process, CL retention of 78% and Coulombic efficiency of 88% are achieved. Excellent flexibility is attained with high CL retentions with bending angle of 180° and bended for 1000 times. Other energy supplying methods are expected to promote the acid treatment on CF and create more efficient FSC in near future.