Structural Supercapacitors Based on Graphene Nanoplatelet-Coated Carbon Fiber Electrodes

Rising CO2 emissions and fossil fuel depletion have driven interest in energy storage systems aligned with complementary technologies. The aerospace and automotive sectors seek lightweight composites to reduce fuel consumption as well as energy storage for electrification. Nanomaterials, and nanocomposites in particular, are ideally suited to tackling this challenge of multifunctional applications. Structural supercapacitors (SSCs) offer promising solutions by combining lightweight load-bearing materials with energy storage functionality. Here, we have designed, fabricated, and characterized multicell SSCs (up to five cells) that utilize the multifunctional beneficial properties of graphene, aimed to increase specific capacitance compared to the single-cell architecture by reducing the electrode weight. Two distinct solid polymer electrolyte matrix systems, ionic salt-based (LiTFSI/PC) and ionic liquid-based (EMIMTFSI), were investigated to identify a functional matrix for the multicell design. The carbon fiber electrodes for the SSCs were coated with graphene nanoplatelets (GNPs) at varying weight ratios (3, 6, 10, and 15 wt %), utilizing their ultrahigh surface area and exceptional mechanical properties to enhance both electrochemical and mechanical performance. Experimental results indicated that a significant increase of up to 59% in specific capacitance could be achieved by the multicell design compared to single-cell SSCs. Coating the carbon fiber electrodes with GNPs significantly enhanced the flexural strength by 23% and stiffness by 12% in single-cell SSCs, along with a 4.1% increase in capacitance, despite a slight reduction in specific capacitance due to the added mass.