Structure and activity of Pt-Co alloys as oxygen reduction electrocatalysts

Carbon supported Pt-Co (3:1 atom ratio) catalysts were prepared in both acid and alkaline aqueous media, followed by heat treatments to promote alloy formation. Both preparations began with a commercial 10% Pt on carbon catalyst with Pt particle sizes of 15 to 30 A. Significantly greater alloying was observed in the acid media prepared catalyst. X-ray diffraction studies of the acid prepared catalyst demonstrated lattice parameters tending away from Pt (3.937 A) and toward that for Pt/sub 3/Co (3.831 A), greatly increased particle sizes, and significant ordering evidenced by the presence of superlattice reflections. In all cases, the base media prepared catalysts were alloyed to a lesser extent, were of moderately increased particle size and gave no indication of alloy ordering. Activity testing under phosphoric acid fuel cell conditions demonstrated that the most highly alloyed catalysts had the greatest activity. Loss of cobalt in the phosphoric acid environment was the lowest in catalysts which were the most alloyed

Redox shuttle additives for overcharge protection in lithium batteries

Seven new redox shuttle additives with shuttle current onset potentials above 4.2 V vs Li/Li+ are reported, along with diffusion coefficients for the neutral additives. The dependence of the limiting shuttle current on the respective diffusion coefficients of the oxidized and reduced forms of an additive is clarified. Overcharge protection in liquid electrolyte Li/LiMn{sub 2}O{sub 4} cells is demonstrated

A study of surface film formation on LiNi0.8Co0.15Al0.05O2 cathodes u sing attenuated total reflection infrared spectroscopy

The surface films formed on commercial LiNi0.8Co0.15Al0.05O2 cathodes (ATD Gen2) charged from 3.75V to 4.2V vs. Li/Li+ in EC:DEC - 1M LiPF6 were analyzed using ex-situ Fourier transform infrared spectroscopy (FTIR) with the attenuated total reflection (ATR) technique. A surface layer of Li2CO3 is present on the virgin cathode, probably from reaction of the active material with air during the cathode preparation procedure. The Li2CO3 layer disappeared even after soaking in the electrolyte, indicating that the layer dissolved into the electrolyte possibly even before potential cycling of the electrode. IR features only from the binder (PVdF) and a trace of polyamide from the Al current collector were observed on the surfaces of cathodes charged to below 4.2 V, i.e., no surface species from electrolyte oxidation. Some new IR features were, however, found on the cathode charged to 4.2 V and higher. An electrolyte oxidation product was observed that appeared to contain dicarbonyl anhydride and (poly)ester functionalities. The reaction appears to be an indirect electrochemical oxidation with overcharging (removal of > 0.6 Li ions) destabilizing oxygen in the oxide lattice resulting in oxygen transfer to the solvent molecules

Failure modes in high-power lithium-ion batteries for use in hybrid electric vehicles

The Advanced Technology Development (ATD) Program seeks to aid the development of high-power lithium-ion batteries for hybrid electric vehicles. Nine 18650-size ATD baseline cells were tested under a variety of conditions. The cells consisted of a carbon anode, LiNi{sub 0.8}Co{sub 0.2}O{sub 2} cathode and DEC-EC-LiPF{sub 6} electrolyte, and they were engineered for high-power applications. Selected instrumental techniques such as synchrotron IR microscopy, Raman spectroscopy, scanning electron microscopy, atomic force microscopy, gas chromatography, etc. were used to characterize the anode, cathode, current collectors and electrolyte from these cells. The goal was to identify detrimental processes which lead to battery failure under a high-current cycling regime as well as during storage at elevated temperatures. The diagnostic results suggest that the following factors contribute to the cell power loss: (a) SEI deterioration and non-uniformity on the anode, (b) morphology changes, increase of impedance and phase separation on the cathode, (c) pitting corrosion on the cathode Al current collector, and (d) decomposition of the LiPF{sub 6} salt in the electrolyte at elevated temperature

Real-time observation of the dry oxidation of the Si (100) surface with ambient pressure x-ray photoelectron spectroscopy

We have applied ambient-pressure x-ray photoelectron spectroscopy with Si 2p chemical shifts to study the real-time dry oxidation of Si(100), using pressures in the range of 0.01-1 Torr and temperatures of 300-530 oC, and examining the oxide thickness range from 0 to ~;;25 Angstrom. The oxidation rate is initially very high (with rates of up to ~;;225 Angstrom/h) and then, after a certain initial thickness of the oxide in the range of 6-22 Angstrom is formed, decreases to a slow state (with rates of ~;;1.5-4.0 Angstrom/h). Neither the rapid nor the slow regime is explained by the standard Deal-Grove model for Si oxidation