James S. Daubert

Solvate Structures and Spectroscopic Characterization of LiTFSI Electrolytes

A Raman spectroscopic evaluation of numerous crystalline solvates with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI or LiN(SO2CF3)2) has been conducted over a wide temperature range. Four new crystalline solvate structures-(PHEN)3:LiTFSI, (2,9-DMPHEN)2:LiTFSI, (G3)1:LiTFSI and (2,6-DMPy)1/2:LiTFSI with phenanthroline, 2,9-dimethyl[1,10]phenanthroline, triglyme, and 2,6-dimethylpyridine, respectively-have been determined to aid in this study. The spectroscopic data have been correlated with varying modes of TFSI(-)···Li(+) cation coordination within the solvate structures to create an electrolyte characterization tool to facilitate the Raman band deconvolution assignments for the determination of ionic association interactions within electrolytes containing LiTFSI. It is found, however, that significant difficulties may be encountered when identifying the distributions of specific forms of TFSI(-) anion coordination present in liquid electrolyte mixtures due to the wide range of TFSI(-)···Li(+) cation interactions possible and the overlap of the corresponding spectroscopic data signatures.

Corrosion Protection of Copper Using Al2O3, TiO2, ZnO, HfO2, and ZrO2 Atomic Layer Deposition

Atomic layer deposition (ALD) is a viable means to add corrosion protection to copper metal. Ultrathin films of Al2O3, TiO2, ZnO, HfO2, and ZrO2 were deposited on copper metal using ALD, and their corrosion protection properties were measured using electrochemical impedance spectroscopy (EIS) and linear sweep voltammetry (LSV). Analysis of ∼50 nm thick films of each metal oxide demonstrated low electrochemical porosity and provided enhanced corrosion protection from aqueous NaCl solution. The surface pretreatment and roughness was found to affect the extent of the corrosion protection. Films of Al2O3 or HfO2 provided the highest level of initial corrosion protection, but films of HfO2 exhibited the best coating quality after extended exposure. This is the first reported instance of using ultrathin films of HfO2 or ZrO2 produced with ALD for corrosion protection, and both are promising materials for corrosion protection.

Intrinsic limitations of atomic layer deposition for pseudocapacitive metal oxides in porous electrochemical capacitor electrodes

By comparing the pseudocapacitive performance of ALD V2O5 in micro-, meso-, and macro-porous carbon electrodes, we describe the fundamental limits to ALD in very fine pores for pseudocapacitive charge storage. Comparing experimental trends with an ALD coating model, we find that the thermal V2O5 ALD process using vanadium triisopropoxide (VTIP) and water is unable to deposit in pores where the pore diameter is below a critical diameter of 13 A. By adding the ALD V2O5 layer onto activated carbon electrodes, we find that the energy storage capacity could be increased by 144% for carbon with micropores and macropores, whereas for carbon black powder containing only macropores (i.e. a low surface area resulting in a relatively small starting capacity) the ALD coating increased the capacity more than 40-fold. To understand the ALD coating limits, the pores of the carbon electrodes were modeled as a series of connected tubes, and the volume of V2O5 deposited determined experimentally was compared to the calculated deposition limit. Pores below this critical diameter were sealed and decreased the accessible volume for V2O5 deposition by more than half, decreasing the maximum capacity. The effect of the pore sealing by the ALD process on the capacitive response of the activated carbon based electrodes was also studied. This work highlights the intrinsic capabilities and limitations of coating microporous materials using ALD.

Corrosion mitigation coatings for RF sources and components

Most all high power RF sources and components require liquid cooling, usually high purity water. Copper and associated braze alloys are susceptible to corrosion if the water contains impurities or modest levels of oxygen. Unfortunately, high purity water is not readily available in many locations, including developing countries, remote sites, and naval vessels. The U.S. Navy is funding development of protective coatings to reduce or eliminate corrosion in copper coolant channels in RF sources and solenoids. This presentation will describe procedures for applying corrosion mitigation coatings in RF sources and associated components and equipment.