Structural Supercapacitors Based on Graphene Composite Film Electrodes

Structural energy storage devices, capable of storing energy while simultaneously bearing mechanical loads, are gaining significant interest in aerospace, electric vehicles, and portable electronics. However, the commonly used carbon fiber fabric current collector/reinforcement occupies a disproportionately large share of the device’s mass and volume, thereby limiting the overall energy density of the device. In this paper, we present a device architecture in which an integrated graphene/conducting polymer composite film is used to replace the conventional carbon fiber fabrics to serve as both the current collector and mechanical reinforcement in structural supercapacitors. Owing to the high specific capacitance of the composite film, the new devices exhibit a high specific capacitance of 62.5 mF cm–2 and energy density of 6.1 μW h cm–2 at a current density of 0.2 mA cm–2, corresponding to volumetric energy density of 0.14 mW h cm–3, and gravimetric energy density of 31.2 mW h kg–1. Those values far surpass those of the counterparts using carbon fiber fabrics. To further enhance load-bearing and energy storage performance, multilayer devices are developed. A seven-layer device demonstrated a flexural strength of 19.0 MPa and, through series-parallel connections of internal electrodes, achieved a large working voltage of 4.5 V, or a high specific capacitance of 161.1 mF cm–2 and energy density of 14 μW h cm–2. This work demonstrates the potential of graphene composite film electrodes in structural energy storage applications and provides a new pathway toward achieving high-performance structural energy storage devices.