Gr. Zhuang et al., XPS CHARACTERIZATION OF THE REACTIONS OF LI WITH TETRAHYDROFURAN AND PROPYLENE CARBONATE, Surface science, 387(1-3), 1997, pp. 199-212
The reaction of tetrahydrofuran (THF) and propylene carbonate with thi
n (6-10 nm) films of Li vapor deposited an Al(111) al 120-135 K was st
udied in UHV by C 1s and O 1s core-level photoemission. THF and PC con
densate layers were formed by dosing the Li overlayer surfaces at 120-
135 K, with the reaction observed by subsequent warming of the sample.
Activation of the first layer of THF molecules by Li, probably as rin
g-opening, starts at a temperature as low as 120 K. Polymerization of
THF (forming poly-THF) occurs upon melting near 180 K, but is accompan
ied by chain-terminating reactions that form Li alkoxide(s) and hydroc
arbon gas(es), such as ethylene and/or propylene. Between 180 and 320
K, there is progressively greater conversion of poly-THF to alkoxide s
uch that at 320 K, the surface film is almost entirely composed of alk
oxide. Only a few monolayers of the Li film react with the THF under t
hese conditions. Al or near its bulk melting temperature of 220 K, ess
entially all of the PC remaining on the surface has reacted with Li to
form an alkyl carbonate. With increasing temperature, part (25-33%) o
f the alkyl carbonate decomposes to form an alkoxide, and in the tempe
rature interval of 270-320 K there may be a small amount (<5% of the c
arbon present) of Li carbonate formed. The alkyl group in the organo-L
i compounds derived from PC is most probably propylene. There is no ev
idence of the formation of any gaseous products at temperatures below
320 K under the conditions of these experiments. As with THF, only a f
ew monolayers of the Li film have reacted with the PC. Of particular r
elevance to battery technology, however, is the fact that in both case
s the organo-Li layers that have formed at 270 K were formed in the pr
esence of excess (unreacted) Li. (C) 1997 Elsevier Science B.V.