(680a) Aramid Nanofibers for Structural Enhancement of Capacitors and Batteries

Structural energy and power is a concept that aims to combine the mechanical properties of structural composites with the energy storage properties of capacitors and batteries. The ultimate goal is to achieve savings in mass and volume for aircraft, spacecraft, and ground transportation. We approach this concept at the materials level, where the focus is on imparting superior mechanical properties to the electrode or electrolyte components. One of the major challenges in this area is the inherent tradeoff in mechanical and energy storage performance. This is because many additives for mechanical enhancement dilute the electroactive material, thus reducing the energy density or specific energy. Here we discuss the synthesis, processing, and structure-property-performance tradeoffs of capacitor and battery electrodes containing Kevlar^® aramid nanofibers (ANFs). These nanoscale building blocks are derived from the chemical dissolution of Kevlar^® thread into 40 nm diameter nanofibers. ANFs are combined with reduced graphene oxide sheets via vaccuum filtration to create mechanically robust capacitor electrodes. Here, we show that graphene paper supercapacitor electrodes containing aramid nanofibers as guest materials exhibit extraordinarily high tensile strength (100.6 MPa) and excellent electrochemical stability. This is achieved by extensive hydrogen bonding and π−π interactions between the graphene sheets and aramid nanofibers. The trade-off between capacitance and mechanical properties is evaluated as a function of aramid nanofiber loading, where it is shown that these electrodes exhibit multifunctionality superior to that of other graphene-based supercapacitors, nearly rivaling those of graphene-based pseudocapacitors. These non-covalent interactions are further manipulated by modification at the graphene sheet face to further enhance the mechanical properties. We also show the incorporation of ANFs into Li-ion batteries and the impact at the electrode level. We anticipate these composite electrodes to be a starting point for structural energy and power systems that harness the mechanical properties of aramid nanofibers.