Gr. Zhuang et al., STUDY OF THE REACTIONS OF LI WITH TETRAHYDROFURAN AND PROPYLENE CARBONATE BY PHOTOEMISSION SPECTROSCOPY, Journal of vacuum science & technology. A. Vacuum, surfaces, and films, 16(5), 1998, pp. 3041-3045
Citations number
11
Categorie Soggetti
Physics, Applied","Materials Science, Coatings & Films
The reaction of Li with two organic solvents of technical importance i
n Li batteries, tetrahydrofuran (THF) and propylene carbonate (PC), we
re studied in ultrahigh vacuum by photoemission spectroscopy. The orga
nic condensate layers were formed by dosing thin (6-10 nm) films of Li
at 120-135 K, with the reactions monitored by x-ray photoemission spe
ctroscopy and ultraviolet photoemission spectroscopy upon subsequent w
arming of the sample. Activation of the first layer of THF by Li start
s at a temperature as low as 120 It. Polymerization of tetrahydrofuran
(THF) (forming poly-THF) occurs upon melting near 180 K, but is accom
panied by chain-terminating reactions that form lithium alkoxide(s) an
d hydrocarbon gas(es), such as ethylene and/or propylene. Between 180
and 320 K, there is progressively greater conversion of poly-THF to al
koxide such that at 320 K, the surface film is almost entirely compose
d of alkoxide. At or near its bulk melting temperature of 220 K, essen
tially all of the PC remaining on the surface has reacted with Li to f
orm an alkyl carbonate. With increasing temperature, part (25%-33%) of
the alkyl carbonate decomposes to form an alkoxide. The alkyl group i
n the organo-li compounds derived from PC are most probably propylene.
There is no evidence of the formation of any gaseous products contain
ing carbon or oxygen at temperatures below 320 K under the conditions
of these experiments. Of particular relevance to battery technology, h
owever, is that in both cases the organo-li layers that have formed at
270-320 K were formed in the presence of excess unreacted Li, which i
s the usual circumstance in a real battery, and that no evidence was f
ound of inorganic Li carbonate as a product of the reaction with PC. (
C) 1998 American Vacuum Society. [S0734-2101 (98)00405-9].