Functionalized graphene microspheres for high volumetric energy density supercapacitors

Abstract

The development of electrode materials with high packing density and superior volumetric performance is crucial to address the growing demand for compact supercapacitors in wearable electronics and electric vehicles. However, the low packing density of graphene limits its volumetric capacitance. To overcome this challenge, functionalized graphene microspheres (FGR) were synthesized through processes such as ozone oxidation, H₂O₂ etching, CNT incorporation, spray drying, and carbonization of graphene oxide ribbons (IGOR) with abundant edge sites. The resulting FGR provides numerous active sites, efficient electron and ion transport pathways, stable oxygen-containing functional groups, and a compact structure. These properties enable FGR to achieve high volumetric capacitance and excellent rate performance (442.8 and 308.0 F cm⁻³ at 1 and 100 A g⁻¹, respectively), high mass loadings (12 mg cm⁻²) and packing density (1.02 g cm⁻³). FGR-assembled symmetric supercapacitors (FGR//FGR) deliver a high volumetric energy density of 30.2 W h L⁻¹ at 120.9 W L⁻¹. These features make FGR-based supercapacitors highly relevant for industrial applications, including portable electronics, electric vehicles, and grid energy systems. The scalable synthesis approach and robust design further emphasize their potential for widespread industrial adoption.