IMLB 2006, Abstract # 0396.pdf
Isocyanate Compounds as Electrolyte Additives for
Lithium-Ion Batteries
Isocyanate compounds have been patented in various
purposes for LIB`s. [7,8]
C. Korepp(1)*, K.-C. Möller(1), E. A. Lanzer(1),
M. O. Sternad(1), P. R. Raimann(1), M. R. Schweiger(1)
N. S. Hochgatterer(1), D.-T. Shieh(2), J. O. Besenhard(1),
M. Yang(2), M. Winter(1)
In recent investigations we focused on the role of linear
and aromatic isocyanates as additives for lithium-ion
batteries in PC-, EC-DMC- and EC-EMC-based
electrolytes.
(1)
Linear as well as aromatic isocyanates form proper SEI
films on the electrode surface to not only make graphite
compatible with PC but also to improve cycling
performance in EC-EMC and EC-DMC electrolyte. It
can be shown by scanning electron microscopy, the first
charge plots and constant current cycling.
Liquid nonaqueous solvents have found numerous
applications in electrolytes for lithium-ion batteries
(LIB). The choice of solvent mixtures is usually a
compromise between the desired physical (e.g.
electrolyte conductivity, volatility, flammability, wetting
ability, etc.) and electrochemical properties (reduction
and oxidation at the respective electrode/electrolyte
interfaces, solid electrolyte interphase (SEI) formation
behavior, etc.).
An elegant way to overcome the inevitable limitations of
this compromise is the use of electrolyte additives, which
even in small amounts improve the electrolyte properties
in the desired direction. Among many additive
applications, such as overcharge protection and cell
safety improvement, electrolyte additives for improved
film formation processes at anode and cathode have
found particular interest.
Electrolyte decomposition and SEI formation can take
place via different mechanisms. One mechanism is the
electrochemical polymerization via reduction or
oxidation of vinylene monomers [1,2]. Previously we
suggested that the first step of the electrochemically
induced reduction (= cathodically induced electro
polymerization) of vinylene compounds is the electron
transfer from the electrode to the double bond, which
starts a chain reaction via addition of the formed reactive
species to the double bonds of other monomers or other
solvent components present in the electrolyte. Only the
first electron transfer step is an electrochemical one, thus
charge consuming step. The subsequent reactions are
apparently only of chemical nature.
Acrylic acid nitrile (AAN) has already been presented [3]
as a novel example out of the large class of vinylene
group containing film forming additives for anodes in
lithium ion batteries. The outstanding filming properties
of vinylene compounds such as AAN allow using
graphitic carbon anodes in propylene carbonate-(PC)
based electrolytes even with only 1 % of the additive.
2-Cyanofurane is another advantageous vinylene
additive [4]. A similar reaction mechanism can be
expected by using isocyanate as electrolyte additives.
From early investigations in the field of preparative
organic electrochemistry the reductive film-forming
polymerization of isocyanates is well known. [5,6]
Both, linear and aromatic compounds have been
investigated by cyclic voltammetry, constant current
cycling experiments, in-situ FTIR spectroscopy and
online mass spectrometry. Furthermore, the influence of
aromatic compounds on the thermal stability of the
formed SEI layer at elevated temperature will be shown.
2 wt% benzyl isocyanate
1 M LiClO4 / PC
Transmission
Institute for Chemistry and Technology of Inorganic
Materials, Graz University of Technology
Stremayrgasse 16, A-8010 Graz, Austria
(2)
Materials Research Laboratories ITRI, Chutung,
Hsin-Chu, Taiwan 310, R.O.C.
[email protected]
4000
0.5 V
0.6 V
0.75 V
1.0 V
1.1 V
1.3 V
1.7 V
2.0 V
2.5 V
OCV
3500
decrease of -NCO band
-1
at 2275 cm
3000
2500
2000
1500
1000
500
-1
ν / cm
Figure 1: IR spectra of the electrolyte PC/ LiClO4 at the
glassy carbon electrode with 2 wt % benzyl isocyanate –
decrease of asymmetric –NCO stretching vibration at
2275 cm-1.
[1] J. W. Breitenbach, O. F. Olaj, F. Sommer, Adv.
Polym. Sci. 1972, 9, 47.
[2] K.-C. Möller, S. C. Skrabl, M. Winter and J. O.
Besenhard, 3rd Hawaii Battery Conference, Hawaii,
2001.
[3] C. Korepp, H.J. Santner, T. Fujii, M. Ue, J.O.
Besenhard, K.-C. Möller, M. Winter, J. Power
Sources, 2005, article in press.
[4] K. -C. Möller, H. J. Santner, W. Kern, S.
Yamaguchi, J. O. Besenhard and M. Winter, J.
Power Sources, 2003, 119-121, 561.
[5] G. S. Shapoval, Ukr. Khim. Zhur. 1967, 33, 946.
[6] U. Akbulut, Makromol. Chem. 1979, 180, 1073.
[7] M. Schmidt, A. Kühner, M. Niemann, Ger. Pat.
DE 100 42 149 A 1 1999.
[8] T. R. Jow, S. Zhang, K. Xu, M. S. Ding , US Pat. No
6,905,762 B1 2005.
Support by the Austrian Science Funds through the
special research program "Electroactive Materials" is
gratefully acknowledged.