All-Solid-State Reduced Graphene Oxide Supercapacitor with Large Volumetric Capacitance and Ultralong Stability Prepared by Electrophoretic Deposition Method

Portable energy storage devices have gained special attention due to the growing demand for portable electronics. Herein, an all-solid-state supercapacitor is successfully fabricated based on a poly­(vinyl alcohol)-H₃PO₄ (PVA–H₃PO₄) polymer electrolyte and a reduced graphene oxide (RGO) membrane electrode prepared by electrophoretic deposition (EPD). The RGO electrode fabricated by EPD contains an in-plane layer-by-layer alignment and a moderate porosity that accommodate the electrolyte ions. The all-solid-state RGO supercapacitor is thoroughly tested to give high specific volumetric capacitance (108 F cm^–3) and excellent energy and power densities (7.5 Wh cm^–3 and 2.9 W cm^–3, respectively). In addition, the all-solid-state RGO supercapacitor exhibits an ultralong lifetime for as long as 180 days (335 000 cycles), which is an ultrahigh cycling capability for a solid-state supercapacitor. The RGO is also tested for being used as a transparent supercapacitor electrode demonstrating its possible use in various transparent optoelectronic devices. Due to the facile scale-up capability of the EPD process and RGO dispersion, the developed all-solid-state supercapacitor is highly applicable to large-area portable energy storage devices.