(Invited) Rapid, Large Area Preparation of Few-Layer Graphene Films Using Xenon Flash Lamp Pyrolysis for High-Performance Structural Micro-Supercapacitors

Abstract

Graphene offers excellent electrical conductivity and very high surface area, which holds great promise for energy storage applications including supercapacitors. Current preparation methods for graphene require relatively long processing times, extremely high temperatures within controlled atmospheres, and/or involve multi-step reactions that present challenges for high throughput fabrication of graphene-based energy storage devices. We report a novel photothermal route to large-scale production of graphene within milliseconds using a commercially available polymers (polybenzoxazine, polyacrylonitrile and polyaniline) and a high intensity xenon flash lamp on various substrates, including carbon fibers, at ambient conditions. The xenon flash lamp provides large-area illumination and a wide emission band (300 nm –1100 nm) that was used to convert the polymeric material directly into few layer graphene upon millisecond exposures. The precursor material is heated to extremely high temperatures in a fraction of a second – a duration that is much shorter than the timescale for thermal equilibrium. This enabled the conversion of the polymeric material into few layer graphene in air and at room temperature, and without thermally damaging the substrate. Conversion to few-layer graphene was strongly dependent on pulse energy and the local temperature which was controlled via pulse power modulation. The obtained graphene composites at optimized conditions exhibited excellent conductivity (0.1 ohm-cm) with ID/IG ratio of 0.3 (Figure 1a). Particularly, graphene derived from polyaniline resulted in the formation of macroporous network (Figure 1b) with good adhesion to the carbon fiber, all of which facilitate the transport of ions through the material. The fabricated supercapacitor devices exhibited a very high areal capacitance of 200 mF/cm2 at 10 mV/s with retention of more than 70% of their capacitance, even at scan rates up to 100 mV/s. Moreover, mechanically, and structurally stable graphene derived from polyaniline on carbon fiber was utilized for the preparation of structural energy storage devices. We assembled symmetric structural supercapacitor comprised of carbonaceous material (carbon fiber and few-layer graphene) and polymer gel electrolyte. This resulted in the preparation of large area device (40 cm2) as shown in the Figure 1c with the capacitance exceeding 2000 mF and almost complete retention of capacitance after 5000 cycles.The preparation of high-quality graphene via photothermal pyrolysis of polymer is amenable to high throughput processing, enabling large-scale production of high performance structural electrochemical energy storage devices. Figure 1