Freestanding Hollow Ni Microwire Mesh for the Fabrication of High Areal Energy Density Asymmetric Microsupercapacitor

Microsupercapacitors are touted as one of the promising "next frontiers" in energy-storage research and applications. However, significant challenges still exist in terms of physical properties and electrochemical performance, particularly attaining high energy density, stability, ease of synthesis, and feasibility of large-scale production. Most current research presents high energy density values by normalizing the performance to the mass or thickness of active material. These high values are usually several orders of magnitude higher than the real overall device performance. The main problem arising from these results is that when the amount of active material increases to practical levels, the normalized performance decreases rapidly. Here, a new freestanding microporous electrode comprised of deposited Ni on a polymer microwire mesh is presented. The high surface area and conductivity of the electrode makes it suitable for supercapacitor applications. In addition, the Ni electrode is freestanding and serves as the current collector, making the need for supporting substrate and current collector redundant. Next, we have electrochemically deposited MnO₂ and polypyrrole on the Ni electrode in order to assemble an asymmetric supercapacitor with a high voltage window. Using this system of freestanding, conductive, and high surface area electrode, we are able to reduce the total mass and volume of the device, which results in an increase of the overall device energy and power density.