The primary current‐collector materials being used in lithium‐ion cells are susceptible to environmental degradation: aluminum to pitting corrosion and copper to environmentally assisted cracking. Localized corrosion occurred on bare aluminum electrodes during simulated ambient‐temperature cycling in an excess of electrolyte. The highly oxidizing potential associated with the positive‐electrode charge condition was the primary factor. The corrosion mechanism differed from the pitting typically observed in aqueous electrolytes because each site was filled with a mixed metal/metal‐oxide product, forming surface mounds or nodules. Electrochemical impedance spectroscopy was shown to be an effective analytical tool for characterizing the corrosion behavior of aluminum under these conditions. Based on X‐ray photoelectron spectroscopy analyses, little difference existed in the composition of the surface film on aluminum and copper after immersion or cycling in LiPF6 electrolytes made with two different solvent formulations. Although Li and P were the predominant adsorbed surface species, the corrosion resistance of aluminum may simply be due to its native oxide. Finally, copper was shown to be susceptible to environmental cracking at or near the lithium potential when specific metallurgical conditions existed (work hardening and large grain size). © 1999 The Electrochemical Society. All rights reserved.

As the size of mechanical systems shrinks from macro- to nanoscales, surface phenomena such as adhesion, friction, and wear become increasingly significant. This paper demonstrates the use of alcohol adsorption as a means of continuously replenishing the lubricating layer on the working device surfaces and elucidates the tribochemical reaction products formed in the sliding contact region. Friction and wear of native silicon oxide were studied over a wide range of length scales from macro- to nanoscales using a ball-on-flat tribometer (millimeter scale), sidewall microelectromechanical system (MEMS) tribometer (micrometer scale), and atomic force microscopy (nanometer scale). In all cases, the alcohol vapor adsorption successfully lubricated and prevented wear. Imaging time-of-flight secondary ion mass spectrometry analysis of the sliding contact region revealed that high molecular weight oligomeric species were formed via tribochemical reactions of the adsorbed linear alcohol molecules. These tribochemical products seemed to enhance the lubrication and wear prevention. In the case of sidewall MEMS tests, the lifetime of the MEMS device was radically increased via vapor-phase lubrication with alcohol.

a †ToF-SIMS spectra are formed by bombarding a surface with a pulse of primary ions and detecting the resultant ionized surface species using a time-of-flight mass spectrometer. Typically, the detector is a time-to-digital converter. Once an ion is detected using such detectors, the detector becomes insensitive to the arrival of additional ions for a period termed as the (detector) dead-time. Under commonly used ToF-SIMS data acquisition conditions, the time interval over which ions arising from a single chemical species reach the detector is on the order of the detector dead-time. Thus, only the first ion reaching the detector at any given mass is counted. The event registered by the data acquisition system, then, is the arrival of one or more ions at the detector. This behavior causes ToF-SIMS data to violate, in the general case, the assumption of linear additivity that underlies many multivariate statistical analysis techniques. In this article, we show that high-mass-resolution ToF-SIMS spectral-image data follow a generalized linear model, and we propose a data transformation and scaling procedure that enables such data sets to be successfully analyzed using standard methods of multivariate image analysis.

The origin and role of tribochemical reaction products formed while sliding silicon oxide surfaces in the presence of adsorbed alcohol molecules in equilibrium with the vapor phase were studied. Wear and friction coefficient studies with varying contact loads and n-pentanol vapor environments were used to determine under what operating conditions the tribochemical reaction species was produced. Imaging time-of-flight secondary ion mass spectrometry and microinfrared spectroscopy found that hydrocarbon species with a molecular weight higher than the starting vapor molecules are produced when there is wear of the SiO(2) surface. When the n-pentanol vapor lubrication is effective and the silicon oxide surface does not wear, then the tribochemical polymerization products are negligible. These results imply that the tribochemical polymerization is associated with the substrate wear process occurring due to insufficient adsorbate supply or high mechanical load. The tribochemical reactions do not seem to be the primary lubrication mechanism for vapor phase lubrication of SiO(2) surfaces with alcohol, although they may lubricate the substrate momentarily upon failure of the alcohol vapor delivery to the sliding contact.