of 10
1
Supporting Information
Three
-
Dimensional Au M
icrolattices as
Positive
E
lectrodes
for Li
-
O
2
B
atteries
Chen Xu,
Betar M. Gallant,
Phillip U. Wunderlich,
§
Timm Lohmann,
§
Julia R. Greer,
Division of Engineering and Applied Science, California
Institute of Technology,
Pasadena, CA 91125
Division of Chemistry and Chemical Engineering, California Institute of Technology,
Pasadena, CA91125
§
Research and Technology Center, Robert Bosch LLC, Palo Alto, CA 94304
2
Figure S1.
Cyclic voltammogram of as
-
fabricated Au microlattice and SEM of the
surface of the sample. (a) CV of hollow Au microlattice in 0.5 M H
2
SO
4
with a scan rate
of 50 mV s
-
1
; (b) SEM image of rough polycrystalline Au surface obtained via constant
current elect
rodeposition.
2%μm%
(b)*
400
600
800
1000
1200
1400
1.5
1
0.5
0
0.5
1
Voltage vs Ag/AgCl [mV]
Current [mA]
(a)*
Oxide**
reduc'on*
Oxide**
forma'on*
3
Figure S
2
. XRD patterns of pristine Au microlattice.
4
Figure S3
. SEM image of the surface of a Au microla
ttice electrode discharged at
21
0
n
A
cm
-
2
true
. No noticeable formation of “toroids”.
1%μm%
5
Figure S
4
. FTIR spectrum of a microlattice after the
first
discharge, taken in a N
2
glovebox. The grey zone indicates Li
2
CO
3
peaks. The
peaks
at 1340 cm
-
1
, 1200 cm
-
1
,
1136 cm
-
1
and 1060 cm
-
1
denoted by “
are attributed to residual LiTFSI. This sample is
not washe
d prior to characterization. The peak LiTFSI locations are
in good agreement
with Gowda
et al
1
.
800
1000
1200
1400
1600
1800
2000
Wavenumber [cm
1
]
Absorbance [a.u.]
Li
2
CO
3
HCO
2
Li
CH
3
CO
2
Li
LiTFSI
*
**
**
**
**
1
st
*discharge*
**
6
Figure S5
. Raman spectra of a microlattices
after the 1
st
charge, 1
st
discharge,
and
after 3
cycles
ending with a
4
th
discharge.
References obtained from commercially available
powders from Sigma Aldrich.
600
700
800
900
1000
1100
1200
Raman shift [ cm
1
]
Intensity [a.u.]
CH
3
CO
2
Li
HCO
2
Li
LiOH
Li
2
CO
3
Li
2
O
2
1
st
%charge%
1
st
%discharge%
4
th
%discharge%
7
The powder references exhibit peaks at Raman shifts of 790 cm
-
1
and 1090 cm
-
1
for
Li
2
O
2
and Li
2
CO
3
, respectively,
which agrees
well with literature
.
2
7
The predominant
product after the
1
st
discharge was Li
2
O
2
, as indicated by a peak in the Raman data at 790
cm
-
1
.
No Li
2
CO
3
peaks were observed.
The
FTIR
spectrum
showed several peaks
centered at 1400 cm
-
1
and 860 cm
-
1
, which
suggests the presence of a
small amount of
Li
2
CO
3
. This discrepancy
between the FTIR and the Raman data
may arise from the C
O
bond being more
infrared a
ctive
than Raman
active.
8,9
The increase
in Li
2
CO
3
can be
readily observed by the emergence of a peak at 1090 cm
-
1
in the Raman data, which was
absent after the
1
st
discharge
(Figure 5)
. This finding is supported by
the
IR data where
the intensity of the Li
2
CO
3
peaks increased, along with
that of
HCO
2
Li and CH
3
CO
2
Li,
with
cycling.
An interesting featured observed in the Raman spectra showed a peak at 750 cm
-
1
,
which
does not coincide with the previously observed peak for Li
2
O
2
at 790 cm
-
1
, nor
does it align with expected side reaction products
such has LiOH, HCO
2
Li and
CH
3
CO
2
Li. One possibility is that the 750 cm
-
1
peak belongs to Li
2
O
2
where the O
O
bond strength is different from that of the Li
2
O
2
formed on the 1
st
cycle. Varying positions
for the O
-
O stretch
in
Li
2
O
2
formed during discharge
have been
reported in literature,
with values between 745 cm
-
1
10
and 808 cm
-
1
10,11
.
The
origins
of this
peak
shift
remain
elusive; several
factors
that
can potentially affect the bonding strength
have been
proposed
,
for example
the
crystallinity of Li
2
O
2
,
which
can
lead to peak broadening or
peak disappearance,
12,13
or hydration of Li
2
O
2
,
which can lead to
a
blue shift of up to 70
8
cm
-
1
.
5,14
It is likely that in this work this shift
is caused by the
local contamination on
Li
2
O
2
surfaces from LiOH or other species.
9
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