288997 Growth of Nanowires On Bulk Metal Foils: Opportunities and Challenges towards High-Throughput, Catalyst-Free Nanowire Production
Silicon and germanium nanowires are promising building blocks for a variety of proposed nanomaterial-enabled technologies. Recently, nanowires have drawn significant interest as a high performance anode materials for next-generation lithium ion batteries. Challenges between high-throughput production, ease of applicability, and cycling performance present restriction to bring this promise towards technological fruition. We have studied high-throughput nanowire growth directly on bulk metal films. This approach obviates the need for noble metal seed catalyst particles and facilitates direct integration of nanowires on macroscopic contacts. This configuration has significant advantages for the potential application of nanowire-based anodes since the direct contact to the current collecting metal foil avoids the need for a conducting binder and thereby reduced overall weight of the battery cell. This synthesis method has been observed to produce high-yields of good quality nanowires that are epitaxially attached to a conductive surfaces, and could be adapted to a roll to roll process--addressing the key restrictions to implementation.
In contrast to nanowires grown from metal seed particles via the vapor-liquid-solid mechanism, the growth mechanism underlying the formation of nanowires on bulk metal foils is poorly understood. A better mechanistic understanding of the nanowires grown on bulk foils is required to optimize the nanowire yield and to explore opportunities for controlled synthesis of nanowires with predefined growth direction, diameter and length. We report our investigation of the fundamental growth mechanism based on nanowire growth on metal films with controlled composition and thickness. We investigated the composition of the metal seed foil using X-ray photoelectron spectroscopy depth profiling. The physiochemical properties of the nanowire surface are a critical determinant of their electrical properties; this is particularly critical in the formation of stable solid-electrolyte interfaces in the application of nanowire-based anodes. We investigated chemical and physical surface modification techniques and established the relationship between surface chemistry and electrochemical performance.