| AVS 63rd International Symposium & Exhibition | |
| Electronic Materials and Photonics | Thursday Sessions |
| Session EM+SS+TF-ThA |
| Session: | Materials and Interfaces for Energy Storage |
| Presenter: | Joshua Fain, Vanderbilt University |
| Authors: | J.S. Fain, Vanderbilt University J.W. Mares, Vanderbilt University S.M. Weiss, Vanderbilt University |
| Correspondent: | Click to Email |
We report on silicon (Si) compatible energy-storage supercapacitors (SCs) that incorporate pseudocapacitive nickel hydroxide [Ni(OH)2] coupled with an electric double layer capacitance (EDLC) contributed by constituent Ni(OH)2 and carbon layers. SCs can charge and discharge their energy much more rapidly than conventional batteries (within a few seconds to minutes), while possessing a higher energy storage capability than traditional capacitors (specific capacitances can reach thousands of F/g). Although SCs have made a commercial impact in regenerative breaking, there remains untapped potential for this technology in on-chip energy storage that could lead to reduced size and weight of microelectronic devices. However, advancements in Si-based on-chip energy storage has been hindered due to the rapid corrosion of Si by most electrolytes necessary for energy storage. Recently, it has been shown that conformal carbonization of high surface area porous silicon (PSi) electrodes protects the Si matrix from corrosion while also contributing to energy-storage EDLC behavior. Here, we show that functionalization of carbonized PSi with pseudocapacitive Ni(OH)2 leads to significantly improved energy-storage capabilities of the SC electrode from a few to over 100F/g (with respect to the mass of the entire electrode), and up to 1400 F/g (with respect to the mass of only the Ni(OH)2 - corrected for EDL contribution of the carbon). The electrodes were fabricated by electrochemical etching of PSi, followed by carbonization using chemical vapor deposition, and finally inclusion of Ni(OH)2 into the matrix via a sol-gel process or electrochemical deposition. Cyclic voltammetry (CV) and charge/discharge experiments were carried out to investigate the energy storage capabilities of composite pseudocapacitive electrodes prepared with varying sol-gel concentrations and different electrochemical deposition parameters. Scan rates of 1-50 mV/s were used. Clear oxidation and reduction peaks were evident in the CV curves along with the EDLC contribution. We observed a tradeoff between specific surface area and Ni(OH)2 quantity: the higher the Ni(OH)2 coverage in the PSi matrix, the lower the accessible surface area. The highest specific capacitance of 1400 F/g was measured on an electrode with a modest concentration of Ni(OH)2 (5 mg/mL nickel acetate tetrahydrate:2-methoxyethanol) at 50 mV/s. The results of these studies suggest that PSi is an excellent high surface area host template for Ni(OH)2 that enables high specific capacitance to be achieved on a Si-compatible platform that could be directly integrated into microelectronic devices.