The Reaction of Clean Li Surfaces with Small Molecules in Ultrahigh Vacuum: I. Dioxygen

Abstract

The creation of clean Li surfaces by vapor deposition and their subsequent interaction with oxygen have been studied by a combination of ellipsometry and Auger electron spectroscopy in ultrahigh vacuum. The ellipsometric parameters Δ and Ψ for Li thin films vapor‐deposited on a Ni substrate were monotonic functions of the film thickness, and in reasonable agreement with theoretical values calculated for dense (nonporous) films. The clean Li surface is very reactive toward oxygen, with essentially a sticking coefficient of unity at the initial stage of oxidation at 5×10−8 Torr 02 . Oxidation of the entire film (75 Å maximum) into Li20 proceeded with an approximately unit reaction probability. A model of oxidation with in‐plane contraction of the oxide film (continuously exposing fresh Li) is proposed to explain both the high rate of reaction and the observed variation of Δ and Ψ with time of exposure to O2 .

XPS on Li-Battery-Related Compounds: Analysis of Inorganic SEI Phases and a Methodology for Charge Correction

“…Further complicating matters is the fact that many potential reference materials have phase impurities, especially within the information depth of XPS. This is the case for Li2O powder, which is known to convert to LiOH upon exposure to H2O vapor [47][48][49]. In our studies, XPS analysis of Li2O powder (99% purity, Sigma-Aldrich) revealed nearly complete conversion of Li2O to LiOH (spectra and analysis to be discussed in more detail later).…”

Sorption of atmospheric gases by bulk lithium metal

“…In contrast, the mass of sample (E) reached a plateau after five days of exposure, increasing by 22.4 mg, from 8.6 to 31 mg, an increase by a factor of 3.6. Calculations based on the density of lithium (0.53 g/cm 3 ) and Li 2 CO 3 (2.11 g/cm 3 Fig. 3(b) shows the mass gain over 120 hr after smoothing the data after the 7 th data point using a centered 15-point (0.06 hr) moving average.…”

“…Exposures to CO2 or ambient air resulted in an oxidation rate four times smaller than with O 2 or H 2 O [2]. The reaction of 7.5-nm lithium films exposed to O 2 was investigated in a separate study using Auger electron spectroscopy (AES) and ellipsometry and proceeded with an approximately unit reaction probability, though the interpretation of the ellipsometry was complicated by film contraction accompanying the transformation from Li to Li 2 O [3]. Oxidation of thicker lithium films exposed to O 2 was investigated by a quartz crystal microbalance and complete conversion to Li 2 O occurred within 200 s for films up to 100 nm thick [4].…”

Catalysis and Interfacial Chemistry in Lithium Batteries: A Surface Science Approach

“…\10 -11 torr) is extremely rapid, essentially with sticking coefficient of unity, as shown in the AES spectra during dosing shown in Fig. 1 (from [7] ). The surface appears to passivate quickly, but this is only due to the limited escape depth of the Auger electrons, which Fig.…”

“…Inset are raw data recorded as function time scanning rapidly back and forth on the KLL peak in the derivative mode. From [7] attenuate the emission from the underlying lithium metal and saturate the total Auger emission. The in situ ellipsometry reveals the oxidation continues and oxidizes the entire lithium film up to the thickest film used in the study, 20 nm, even at the relatively low pressure of O 2 used, e.g.…”