V. Focused Fundamental Research - EERE - U.S. Department of ...

V.E.5 Analysis and Simulation of Electrochemical Energy Systems (LBNL)
Newman – LBNL
were cycled from 3.7 to 0.1 V vs. Li/Li + in a solution of 2
mM ferrocene in 1.0 M LiPF 6 in EC:DEC in order to form
an SEI. The impedance spectra at open circuit were
measured both before and after cycling. Figure V - 204 shows
that, before SEI formation, impedance spectra on both
samples exhibit a straight line of approximately 45 o slope
without any high-frequency semicircles (dashed lines). The
two dashed lines collapse because the kinetics are fast on
both the edge and basal plane. After SEI formation, both
samples show an increased impedance, but the impedance
on the edge plane is much higher than that on the basal
plane, despite higher electronic activity on the edge plane.
More work is required to confirm and explain the results
shown in Figure V - 204. However, these preliminary results
demonstrate the ability of the developed method to
characterize materials found in actual batteries.
-Imaginary impedance, kohm-cm 2
5
4
3
2
1
0
Edge plane
with SEI
No SEI
Basal plane
with SEI
0 0.2 0.4 0.6 0.8 1
Real impedance, kohm-cm 2
Figure V - 204: Comparison of through-film ferrocene impedance on the
edge and basal planes of graphite.
Conclusions and Future Directions
Both RDE and EIS studies on the reduction of
ferrocene will continue. The described work has studied
the SEI formed at 0.6 V versus lithium; we are currently
expanding our studies to the effects of formation voltage
and electrode rotation during SEI formation. We also are
continuing our work on HOPG to see how the
electrochemical behavior of the SEI differs with graphite
orientation. The experimental parameters that we are
varying include the sweep rate for potentiodynamic
formation and the formation voltage. Additionally,
preliminary results have shown major differences in
behavior with different anions; we plan to investigate this
phenomenon further, undertaking non-electrochemical
characterization if necessary.
FY 2011 Publications/Presentations
1. M. Tang and J. Newman, J Electrochem. Soc. 158
(5) A530-A536, 2011.
2. A. Teran, M. Tang, S. Mullin, N. Balsara, Solid State
Ionics, in press.
3. M. Tang and J. Newman, ECS Meeting Abstracts,
1102 348 (2011).
Energy Storage R &D 646 FY 2011 Annual Progress Report