Structural energy and power systems offer both mechanical and electrochemical performance in a single multifunctional platform. These are of growing interest because they potentially offer reduction in mass and/or volume for aircraft, satellites, and ground transportation. To this end, flexible graphene-based supercapacitors have attracted much attention due to their extraordinary mechanical and electrical properties, yet they suffer from poor strength. This problem may be exacerbated with the inclusion of functional guest materials, often yielding strengths of <15 MPa. 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. We anticipate these composite electrodes to be a starting point for structural energy and power systems that harness the mechanical properties of aramid nanofibers.

5Graphene-containing layer-by-layer (LbL) electrodes are promising for thin film electrochemical energy storage. However, common practice centers on assembly with chemically reduced graphene oxide sheets, which have a tendency to severely aggregate during processing. More direct and facile is the LbL assembly of graphene oxide (GO) sheets and their subsequent electrochemical reduction. Here, we demonstrate porous (void fraction = 0.625) LbL electrodes comprised of electrochemically reduced GO sheets and polyaniline nanofibers (PANI NFs) for use in non-aqueous energy storage systems. Our approach is also promising for deposition onto complex 10 surfaces, as demonstrated here by the successful assembly onto cotton fabric here. Both PANI NFs and ERGO sheets store charge, bear conductivity, and provide a highly porous architecture, which facilitates the mass transport of ions. The nature of PANI NF/GO LbL assembly and growth is first presented, which we find to be affected by assembly pH. The confirmation of the electrochemical reduction step is then discussed, followed by the electrochemical performance of the resulting electrodes in a non-aqueous lithium metal battery. Capacity varies from 85 to 184 mAh/cm 3 (188 to 461 mAh/g) at 0.1 A/g (electrode mass basis), depending on the electrode thickness. 15 The highest specific energy measured was 1395 mWh/g at a specific power of 1590 mW/g, and the highest specific power was 60252 mW/g at a specific energy of 927 mWh/g. These results demonstrate that electroactive polyaniline nanofiber/graphene coatings from aqueous layer-by-layer assembly are attainable for energy storage.