High energy density of flexible graphene supercapacitors with discharge times controlled by silica microparticles

Abstract

This work reports the electrochemical performance of flexible symmetric supercapacitors which employs two flexible graphene electrodes (FGEs) and silica microparticles (SiO2-MPs) in the electrolyte solution. The discharging time of the supercapacitors increased up to six times after increasing the SiO2-MPs content from 10 to 30 wt%. The introduction of SiO2-MPs played two main roles: i) to enhance the specific surface area of the electrodes (up to 145 % with respect to the electrodes without SiO2- MPs), which in turn, raises the capacity for the ion storage in the devices; and, ii) to generate the SiO, SiOH, SiOC chemical bonds and defects sites, which in turn, enhanced the charge storage by redox (faradaic) reactions. The supercapacitors presented a high energy density value of 748 Wh/kg and specific capacitance of 1663.3 F/g due to the charge storage by the redox reactions and to the high specific surface area available in the FGEs. The long discharge times, high energy densities and flexibility of the supercapacitors, suggest that they could be useful for applications of portable devices which need long operating times.