Vertically Aligned Carbon Nanofibers Coupled with Organosilicon Electrolytes: Electrical Properties of a High-Stability Nanostructured Electrochemical Interface

Abstract

Organosilicon compounds can form novel electrolytes having a number of unusual properties, including high electrochemical stability, high thermal stability, and low viscosity. Vertically aligned carbon nanofibers can act as exceptionally good nanostructured electrodes, with the vertical orientation and presence of edge-plane graphite along the sidewalls providing desirable electrochemical properties. We have explored the electrical properties of the interfaces of VACNF electrodes with a model organosilicon electrolyte solution. The compound 1-(3-{2-[2-(2-methoxy-ethoxy)-ethoxy]-ethoxy}-propyl)-1,1,3,3,3-pentamethyl-disiloxane (2SM3) with added lithium bis-oxalato-borate (LiBOB) was used. Forests of vertically aligned carbon nanofibers (VACNFs) ∼80 nm in diameter grown by plasma-enhanced chemical vapor deposition (PECVD) were used as electrodes. Our results show that the resulting interfaces yield interfacial capacitances equal to the increase in geometric area, indicating full electrochemical accessibility of the nanofiber sidewalls. Measurements as a function of potential perfect stability at applied voltages up to 3 V. Some initial Faradaic reactions arise near 3.5 V, but these decrease within a few cycles to produce interfaces that exhibit excellent stability up to 5 V while yielding >1000 μF/cm2 from nanofibers only 2 μm long. The results show that the organosilicon electrolyte combined with VACNFs provides excellent electrochemical properties. The results have implications for understanding the ability to integrate organosilicon electrolytes with high-surface-area carbon materials for applications such as electrochemical double-layer capacitors and lithium-ion batteries.