Laser-directed energy deposition to achieve high-aspect-ratio micropillar arrays for 3D interdigitated microsupercapacitors

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Microsupercapacitors (MSCs) are promising micropower sources. High-performance active electrode materials have been extensively developed for them because MSC capacitances are critically determined by the electrochemical features of active materials. However, the limited two-dimensional spaces of conventional MSCs pose a substantial challenge in rational electrode design for fully exploiting the active material performances. Therefore, the development of three-dimensional (3D) MSCs has garnered considerable research interest. Herein, 3D interdigitated metal current collectors for 3D MSCs are successfully microfabricated using laser-directed energy deposition (LDED) of Inconel 625 powder. High-aspect-ratio (∼14) micropillars (diameter, 110 µm) are printed on a stainless-steel substrate, thus significantly increasing the surface area for active material deposition. Finally, reduced graphene oxide and polyaniline are electrodeposited as active materials on this 3D platform to boost MSC capacitance. The resulting 3D MSC exhibits substantially high electrochemical performance, with an energy and power densities of 18.76 μWh/cm2 and 0.395 mW/cm2, respectively, and high areal capacitances of 120.7–216.2 mF/cm2 at 1 mA/cm2 depending on the thickness of polyaniline. These inspiring results not only suggest a new route for using high-throughput LDED for high-performance MSCs but also suggest a new 3D fabrication strategy for next-generation micropower sources.