A Highly Tunable Fabrication Process for Binder-Free Three-Dimensional Carbon Nanoarchitectures for Supercapacitor Electrode Via Nanotransfer Printing Technique
Authors: Lee Gun Ho , Park Byung Jun , Jung Yeon Sik 
Published: February 2020

Among various energy storage systems, supercapacitors are known to be excellent candidates with inherent fast charge-discharge characteristics and outstanding cycle stability, but are known to be mediocre in the energy density aspect. In order to realize their full potential, the electrode nanostructure needs to be carefully designed and fabricated, maximizing the surface area for electrochemically active sites while maintaining the conductivity and stability. Here, we report a novel and straightforward fabrication method for a binder-free carbon nanoarchitecture that meets these conditions. Using a solvent-assisted nanotransfer printing technique, a three-dimensional nanoarchitecture is assembled with highly controllable and consistent pore sizes, applicable in both EDLC and pseudocapacitor electrodes.
In this study, arrays of carbon nanowires were transfer-printed using polymer replicas of silicon substrates with linear trenches of various widths and periods, ranging from few hundred nanometers to micrometers. The printing process was repeated multiple times to assemble mesh-like carbon nanoarchitectures with desirable thicknesses. Due the simplicity of the process, the fabrication method is highly versatile, modifiable in numerous elements such as thickness and width of the carbon, pattern size, intersection angles, and so forth. The patterns were fabricated in a wide range of dimensions to investigate the effect of pattern sizes in the electrode performance. Such tunability enables comprehensive analysis of effect of the electrode pore size and structure in supercapacitor performance. The electrochemical performances of the electrodes were tested by manufacturing a series of supercapacitor on CR2032 coin cells. Two symmetric electrodes were isolated using an ion-porous separator and organic solvent was used as the electrolyte. All coin cell assembly was conducted in a dry room with relative humidity lower than 2% to prevent any contamination in the electrolyte.
Furthermore, we report additional processes to widen the application capability of the described fabrication method. Hierarchical structures have been fabricated by printing alternating layers of patterns of different dimensions. Larger nanowires provide apertures that act as pathways for efficient access of electrolyte to the active material, while smaller nanowires contribute to increase the surface area. Moreover, this nanoarchitecture can be modified for pseudocapacitors or other energy storage applications. Metallic nanoparticles can be dispersed and embedded on the carbon surface to form carbon-metal or carbon-metal oxide composite materials, allowing the aforementioned advantages of this structure to be similarly applied in other devices. This three-dimensional nanoarchitecture fabrication process provides a highly tunable and straightforward method based on transfer-printing technique, and further investigations and optimizations can be expected from the high versatility.

Figure 1