Supercapacitor Electrodes Based on Three-Dimensional Copper Structures with Precisely Controlled Dimensions

There is a high demand for energy-storage devices with both high power and energy densities. Numerous studies have focused on the design of materials that enable a simultaneous improvement in both aspects. These studies mainly involve enhancing the power densities of batteries or the energy densities of supercapacitors. Improvements to energy density can be achieved by improved energy-storage materials and/or increasing the percentage of mass or volume in the system devoted to the energy-storage material. Power density, on the other hand, is limited by the transport of ionic and electronic species from one electrode to the other, as well as the reaction kinetics at the electrodes. Multiple factors play vital roles in the energy-transfer rate. Certain factors, such as the diffusivity and conductivity of the system components, are determined by the choice of electrode materials, electrolytes, and operating conditions of the system. Other factors, however, mainly rely on geometric design choices such as surface area, porosity, active material thickness, and interelectrode distance. Improvements in power density require an optimization process that takes these multiple factors into account. Ideally, high-power electrochemical devices should possess large electrode surface area and minimum thickness of the active material, in order to maintain their high-power capabilities. The maximization of the surface area per unit mass or volume is important, as it increases the amount of active material located at or near the electrode–electrolyte interface. The active material thickness, on the other hand, sets the diffusion and conduction path lengths for ions and electrons, respectively. These path lengths determine the internal resistance of the system during the charge and discharge processes. Hence, the minimization of these path lengths plays a vital role in the performance of the device. Examples of approaches to maximize electrode surface area include various structures constructed from metal networks, nanotubes, aerogels, and xerogels. These structures offer complex geometries with extremely high surface area, yet they are mainly fabricated in a non-deterministic way, which limits the control over their critical dimensions, as well as over their uniform reproducibility and scalability. Herein, we present a method for fabricating and characterizing well-ordered, scalable, and high-surface-area 3D Cu architectures suitable for use as current collectors in electrochemical energy-storage applications. These Cu architectures feature precisely controlled characteristic lengths that address the aforementioned critical factors and ultimately determine the device performance. The method involves robotically assisted sequential electrodeposition of alternating Cu and Ni layers to form a multilayer structure of desired thickness. Performing Well-ordered three-dimensional Cu architectures serving as low-resistance current collectors for supercapacitor applications are fabricated by combining microfabrication and electrochemical techniques. These techniques enable the realization of electrodes with precisely controlled characteristic dimensions, including the surface area, thickness of the active material, and interlayer spacing. Highly laminated Cu structures are formed by through-mold electrodeposition of alternating Ni and Cu layers followed by selective electrochemical removal of Ni layers. Underpotential deposition is utilized to precisely measure the electrochemically accessible surface area of the resultant Cu structure. A conformal, thin layer of nickel hydroxide is electrodeposited onto the Cu backbone, forming the supercapacitor electrode. The resulting electrodes exhibit a high specific capacitance value of 733 Fg . In cycle testing, the electrodes deliver 94% of their capacitance after over 1000 cycles. The supercapacitor is also shown to deliver 69% of its 5 mVs 1 capacity at rates as high as 25 mVs . These results illustrate the benefits of using well-ordered metal architectures as current collectors for advanced electrochemical energy storage applications.