Synergies of vertical graphene and manganese dioxide in enhancing the energy density of carbon fibre-based structural supercapacitors

Structural supercapacitor is a promising solution for reducing the overall weight of electric vehicles. To maximum the energy storage capacity of a load-carrying structure, we present a technique to create carbon fibre (CF) electrodes modified with vertical graphene (VG) and manganese dioxide (MnO₂). The results show that the hybridisation of VG and MnO₂ generates a significant synergistic effect in increasing the areal capacitance of electrode. This synergistic effect is attributed to the dual effects of VG in increasing effective surface area and the electrical conductivity, which enable a better distribution of MnO₂ as well as a highly conductive network. A structural supercapacitor, based on the CF/VG/MnO₂ hybrid electrode and a polymer electrolyte, exhibits an areal capacitance of 30.7 mF/cm², energy density of 12.2 mW h/kg, and power density of 2210.3 mW/kg. Moreover, mechanical characterisations demonstrate a tensile strength of 86 MPa and a flexural strength of 32 MPa for this structural supercapacitor. The high electrical energy density and mechanical properties of this supercapacitor pave a way of developing advanced carbon fibre multifunctional composites with excellent structural performance and energy storage capability.