Lithium Methyl Carbonate as a Reaction Product of Metallic Lithiumand Dimethyl Carbonate Page: 2 of 24
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Introduction
In a seminal paper, Aurbach et al.1 proposed that surface films formed on metallic
lithium in propylene carbonate (PC) are not composed primarily of lithium carbonate, as
suggested in earlier work by Bro2 and Dey3, but of lithium alkyl carbonates, ROCO2Li,
where R = alkyl group. This conclusion was reached based on ex-situ FTIR analysis of
the surface layers, and comparison with spectra for reference compounds taken either
from the literature or from compounds synthesized in the course of that study. In addition
to PC, some experiments were also described for the linear carbonate, diethylcarbonate
(DEC), using the same procedures. It was reported that lithium metal is not passivated in
DEC, but dissolves completely to form a dark brown solution. The products were
isolated, analyzed by FTIR and reported to be a mixture of lithium ethylcarbonate
(CH3CH2OCO2Li) and lithium ethoxide (CH3CH2OLi). This paper was pioneering and
formed the basis for later work, especially by Aurbach and co-workers 4. However, the
actual IR spectra of the lithium alkyl carbonate reference compounds were not published
either in reference 1 or in later work, only tabulations of frequencies and relative
intensities (s = strong, m = medium, w = weak) were given. Comparison of any
experimental spectra with these tabulations is therefore very subjective.
In the present work, we present for the first time a complete IR spectrum for an
important reference compound, lithium methyl carbonate, and relate this spectrum to that
from the surface of metallic lithium immersed from dimethyl carbonate (DMC). The
expected chemical reduction path of DMC on metallic Li surface, based on the studies by
both Aurbach and co-workers' and previous work from this laboratory6 is:
2CH30CO2CH3 + 2e~ + 2Li0 -> 2LiOCO2CH3 +CH3CH3T (1)2
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Zhuang, Guorong V.; Yang, Hui; Ross Jr., Philip N.; Xu, Kang & Jow, T. Richard. Lithium Methyl Carbonate as a Reaction Product of Metallic Lithiumand Dimethyl Carbonate, article, October 16, 2005; Berkeley, California. (https://digital.library.unt.edu/ark:/67531/metadc878637/m1/2/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.