James M. Mosby

Direct Electrodeposition of Cu2Sb for Lithium-Ion Battery Anodes

We describe the direct single potential electrodeposition of crystalline Cu2Sb, a promising anode material for lithium-ion batteries, from aqueous solutions at room temperature. The use of citric acid as a complexing agent increases the solubility of antimony salts and shifts the reduction potentials of copper and antimony toward each other, enabling the direct deposition of the intermetallic compound at pH 6. Electrodeposition of Cu2Sb directly onto conducting substrates represents a facile synthetic method for the synthesis of high quality samples with excellent electrical contact to a substrate, which is critical for further battery testing.

Synthesis of copper silicide nanocrystallites embedded in silicon nanowires for enhanced transport properties

Here we report the in situ doping of Si nanowires with Cu, which results in nanowires containing nanocrystalline inclusions of Cu3Si and significantly enhanced electrical conductivity. These nanowires are of interest for use in secondary Li batteries as well as nanowire arrays that can be directly sensitized for photovoltaic applications. This synthesis route is based on controlling the vapour-phase flux of precursor materials into the catalyst tip whereby the flux of the Cu is much less than that of Si. A compositional study utilizing SEM–EDS, XRD, and TEM–EDS techniques of vapour–liquid–solid (VLS) grown Si nanowires in the presence of Cu vapour confirms that the bulk nanowire matrix is Si doped with crystalline Cu3Si and low concentrations of Cu. The electronic transport measurements conducted on single nanowires indicate that the electronic resistivity of the doped nanowires is several orders of magnitude lower than undoped Si, thereby making them more conductive. Based on the data collected from the nanowire growth in conjunction with the in situ VLS doping mechanism, the doping density can be controlled by varying the gas-phase concentration of the dopant or the thermodynamic conditions of the nanowire growth. Both approaches will result in a change in the relative fluxes from the gas phase into the VLS catalyst as well as the kinetics for Cu3Si formation. This is advantageous because dopant density can be used to tune both the electronic and the optical properties of the nanowires.

Evidence of Induced Underpotential Deposition of Crystalline Copper Antimonide via Instantaneous Nucleation

Cu2Sb was electrodeposited onto transmission electron microscopy TEM grids to investigate changes in morphology, composition, and crystal structure during the early stages of nucleation and growth. Multiple transitions were observed within the first second of the deposition, leading to the formation of crystalline Cu2Sb. These transitions were analyzed using TEM, scanning electron microscopy, selected area electron diffraction, and energy-dispersive X-ray spectroscopy. The nucleation sites are initially polycrystalline antimony with amorphous copper, which then transition through a polycrystalline copper intermediate containing some antimony before forming crystalline Cu2Sb. These analyses provide direct evidence that Cu2Sb does not deposit directly from solution but deposits by induced underpotential deposition. This is indicative of the electrodeposition of a typical alloy initially, but what is unusual is that the deposit at longer time scales is a highly crystalline intermetallic. This investigation is unique because TEM grids allow the interface between the deposited material and the substrate to be investigated. This is possible because the composite carbon film on the TEM grid behaves as a transparent substrate. This approach can be extended to other systems, allowing the development of a comprehensive understanding of the electrodeposition of intermetallic compounds.