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.

Structural batteries and supercapacitors combine energy storage and structural functionalities in a single unit, leading to lighter and more efficient electric vehicles. However, conventional electrodes for batteries and supercapacitors are optimized for high energy storage and suffer from poor mechanical properties. More specifically, commercial lithium-ion battery anodes and cathodes demonstrate tensile strength values <4 MPa and Young’s modulus of <1 GPa. Here, we show that using branched aramid nanofibers (BANFs) or nanoscale Kevlar fibers as a binder leads to mechanically stronger lithium-ion battery electrodes. BANFs are combined with lithium iron phosphate (LFP, cathode) or silicon (Si, anode) particles and reduced graphene oxide (rGO). Hydrogen-bonding interactions between rGO and BANFs are harnessed to accommodate load transfer within the nanocomposite electrodes. Overall, we obtained up to 2 orders of magnitude improvements in Young’s modulus and tensile strength compared to commercial battery electrodes while maintaining good energy storage capabilities. This work demonstrates an efficient route for designing structural lithium-ion battery cathodes and anodes with enhanced mechanical properties using BANFs as a binder.

Noncovalent bonding of graphene/aramid nanofiber electrodes with tannic acid leads to enhanced mechanical properties while maintaining good energy storage.

Reduced graphene oxide/aramid nanofiber (rGO/ANF) supercapacitor electrodes have a good combination of energy storage and mechanical properties, but ion transport remains an issue toward achieving higher energy densities at high current because of the tightly packed electrode structure. Herein, carbon nanotubes (CNTs) are introduced to prevent rGO flake stacking to improve the rate capability of the rGO/ANF structural supercapacitor. The effect of CNTs on the rGO/ANF composite electrode’s mechanical and electrochemical properties is investigated by varying the composition. The addition of 20 wt % CNTs led to an increase in Young’s modulus up to 10.3 ± 1.8 GPa, while a maximum in ultimate strain and strength of 1.3 ± 0.14% and 55 ± 6.8 MPa, respectively, was found at a loading of 2.5 wt % CNTs. At low specific currents, the electrodes performed similarly (160–170 F g–1), but at high specific currents (5 A g–1), the addition of 20 wt % CNTs led to a significantly higher capacitance (76 F g–1) as compared to that of rGO/ANF electrodes without CNTs (26 F g–1). In addition, the energy density also improved significantly at high power from 1.4 to 5.1 W h L–1 with the addition of CNTs. The improvement in mechanical properties is attributed to the introduction of additional hydrogen-bonding and π–π interactions from the carboxylic acid-functionalized CNTs. The increase in capacitance at higher discharge rates is due to improved ion transport from the CNTs. Finally, in situ electrochemomechanical testing examines how capacitance varies with strain in these structural electrodes for the first time.

Strong electrodes with good energy storage capabilities are necessary to accommodate the current needs for structural and flexible electronics. To this end, conjugated polymers such as polyaniline (PANI) have attracted...