Andrew J. Gmitter

Formation, dynamics, and implication of solid electrolyte interphase in high voltage reversible conversion fluoride nanocomposites

Metal fluoride nanocomposites are uniquely suited as an alternative pathway to provide very high energy density cathodes for lithium batteries. Contrasted with modern intercalation compounds, they undergo conversion upon discharge into nanodomains of lithium fluoride and highly active metal. The nanosized metal formed during the discharge process along with the dynamic nature of the crystal structure may have considerable impact on the stability of any solid state interphase formed through reaction with the electrolyte. This is in contrast to the more macrocrystalline and stable crystal structure of traditional intercalation compounds. It has been found that the cyclic carbonates are susceptible to decomposition on the nanometal surfaces at potentials as high as 2.00 V vs. Li, and the products have been identified with Field Emission Scanning Electron Microscopy (FESEM), Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR), and X-ray Photoelectron Spectroscopy (XPS) as lithium carbonate species. Of greater importance is the impact of these decomposition products on the reversible cycling of the metal fluoride. Through a series of potentiodynamic and galvanostatic cycling trials, a clear relationship has been developed for the bismuth fluoride nanocomposites, the decomposition of the electrolyte solvent, and the cycle life. Acyclic organic carbonate solvents have been found to have minimal interaction and exhibited better long-term cycling performance than cyclic solvents.

Hollow CU-coated plastic waveguides for the delivery of THz radiation

Terahertz (THz) radiation has important applications in spectroscopy, imaging, and space science. For some of these applications, in particular spectroscopy, a flexible fiber optic could potentially simplify the THz system and enable the user to transmit radiation to remote locations without excessive absorption by atmospheric moisture. To date THz fiber optics and waveguides have been limited to rigid hollow metallic waveguides, solid wires, or short lengths of solid-core transparent dielectrics such as sapphire and plastic. In this paper we report on flexible, hollow polycarbonate waveguides with interior Cu coatings for broadband THz transmission fabricated using simple liquid-phase chemistry techniques. The losses for these hollow-core guides were measured using a tunable, cw single-mode far IR laser. The losses for the best guides were found to be less than four dB/m and the single mode of the laser was preserved for the smaller bore waveguides. Loss calculations of the loss for the HE11 mode reveal that the metal-coated hollow waveguides have much higher loss than for waveguides coated with both metallic and dielectric thin films.