Lithium deposition on polycrystalline silver - A comparison between electrochemical and gas-phase environments

The electrochemical properties of clean and oxygen-contaminated polycrystal line Ag surfaces have been examined in LiClO4/polyethylene oxide solutions in ultrahigh vacuum (UHV) environments at temperatures in the range 323-333 K. Unlike the behavior observed for Au and Ni under the same experimental conditions, no clearly defined voltammetric peaks were found during the fir st and subsequent cycles in the range 2.20-0.25 V vs. Li/Li+ initiated at t he open-circuit potential, 1.75 V vs. Li/Li+. instead, the scans in the neg ative direction were characterized by two adjoining regions in which the cu rrent increased linearly with potential, albeit at different rates, and the subsequent scans in the positive direction yielded comparatively much smal ler currents largely independent of the applied potential. Integration of t he voltammetric curves over the potential range 0.25 < E < 2.20 V vs. Li/Li + revealed a pronounced imbalance between the charges obtained in the scans in the negative (Q(-)) and positive (Q(+)) directions. This phenomenon was attributed, by and large, to the high rates of Li dissolution into Ag at t hese temperatures, consistent with the presence of a low-temperature eutect ic in the Li-Ag phase diagram. Additional support for this view was obtaine d from UHV nonelectrochemical measurements involving vapor-deposited Li ont o Ag, for which the amount of Li on the surface, as monitored by Auger elec tron spectroscopy, decreased markedly upon increasing the temperature from ca. 300 to 350 K. The voltammetry of oxygen-contaminated Ag surfaces was ch aracterized by a well-defined peak in the scan in the positive direction ce ntered at ca. 1.3 V, which persisted upon continuous cycling. Although the process responsible for this feature has not yet been identified, it provid es a marker for detecting oxygen impurities on Ag in this electrolyte. (C) 1999 The Electrochemical Society. S0013-4651(98)10-067-8. All rights reserv ed.