Supporting Information
for
Advanced Materials, adma.200600065
Wiley-VCH 2006
69451 Weinheim, Germany
06.06.2006
1
adma200600065_si.doc
Supporting Information
Synthesis of New-Phased VOOH Hollow “Dandelions” and Their Application in
Lithium-Ion Batteries**
By Changzheng^^Wu, Yi^^Xie,* Lanyu^^Lei, Shuangquan^^Hu, Chuanzi^^OuYang
S1. Redox Titration Experiments to Determine the Oxidation State of Vanadium
The oxidation state of vanadium was determined by redox titration on the basis of the
following procedure. First, in an argon gas atmosphere, a definite amount of as-prepared
sample was dissolved quickly in H2SO4 solution (60 mL, 1.7 M), named solution I. The
standard KMnO4 solution (determined by titrating with Na2C2O4), was used to titrate
solution I, where the oxidation state of vanadium in the as-prepared sample could be oxidized
into V(VI) in VO2+ ions. With the addition of KMnO4, the color of solution I became yellow
gradually. A sudden color change from light yellow to deep orange indicates the titration
endpoint. Based on the calculation and analysis of the obtained results, the oxidation state of
vanadium should be 3+ in our case.
S2. XRD Analysis
The close resemblance of the X-ray diffraction (XRD) pattern of orthorhombic FeOOH to the
obtained XRD pattern, as shown in Figure S1, indicates that these two materials possess a
similar crystal structure. First, based on the crystallographic lattice constants (a = 3.8744 Å,
b = 12.7416 Å, c = 3.0468 Å) that are obtained according to the calculation of the d-value for
our hollow “dandelions” and the borrowed corresponding indices of FeOOH crystallographic
planes (JCPDS card no. 74-1877), we used the following equation to confirm that the other
peaks in the XRD pattern can all be indexed in the orthorhombic system with the
crystallographic lattice constants given above:
d=
1
l
k
h
( )2 + ( )2 + ( )2
c
b
a
(S1)
The results are summarized in Table S1, from which one can see that the experimental dvalues agree with the theoretical d-values, confirming that the XRD patterns obtained here
can be indexed in the orthorhombic system with the crystallographic lattice constants
a = 3.8744 Å, b = 12.7416 Å, and c = 3.0468 Å. Based on the close resemblance to FeOOH,
the formula for our vanadium oxide is VOOH from the crystallographic point of view.
06.06.2006
2
adma200600065_si.doc
Figure S1. a) Observed X-ray diffraction pattern for the as-obtained VOOH. b) Standard
orthorhombic FeOOH pattern in JCPDS card no. 74-1877.
Table S1. Summary of the experimental and theoretical d-values calculated according to the
indices of the crystallographic plane for FeOOH (JCPDS card No. 74-1877) for the asobtained new-phased VOOH.
(hkl)
(020)
Theoretical d-value [Å]
6.3780
Experimental d-value [Å]
6.3780
(120)
(031)
(111)
(131)
(051)
(200)
(220)
(151)
(080)
(231)
(022)
(171)
(251)
3.3103
2.4757
2.3537
2.0861
1.9547
1.9372
1.8534
1.7452
1.5927
1.5256
1.4816
1.4491
1.3759
3.3022
2.4747
2.3559
2.0941
1.9372
1.9372
1.8519
1.7368
1.5801
1.5234
1.4860
1.4427
1.3768
06.06.2006
3
adma200600065_si.doc
S3. Comparison Experiments for Understanding the Formation Mechanism of VOOH
Hollow Dandelions
As mentioned in the Communication, the formation of VOOH hollow dandelions is a
hydroxylation and reduction process based on the reaction
-
2 VS 3 + N 2 H 4 + 12 NH 4 OH ® 2 VOOH + N 2 + 6 ( NH 4 ) 2 S + 10 H 2 O
(S2)
Since the in situ–produced N2 bubbles are from the N2H4·H2O, according to Equation S2, the
amount of N2H4·H2O added will certainly influence the amount of N2 in the reaction process.
When no N2H4·H2O is introduced into the system, no nitrogen gas will be produced. Thus, we
can investigate the role of N2 by controlling the amount of N2H4·H2O added in the reaction
process: Without the addition of N2H4·H2O, there are only particles in the final products, and
the phase revealed by XRD is not the new-phased VOOH anymore, indicating that hydrazine
is responsible for both the appearance of hollow structures and the reduction of V5+ to V3+.
In addition, evidently, the appropriate molar ratio of [N2H4]/[V] is essential for the
formation of hollow dandelions, providing additional evidence for the above mechanism.
Notably, the molar ratio of [N2H4]/[V] in the range from 7:1 to 12:1 favors the formation of
hollow “dandelions”. However, when the molar ratio of [N2H4] /[V] is lower than 5:1,
keeping [V] constant at 1.5 mmol, there are only VOOH small particles and flakes in the final
products (Figs. S2a,b), which may be related to the lack of sufficient N2 bubbles for the
VOOH to aggregate around, and thus the morphology is more messy in the final products,
although the phase remains orthorhombic VOOH. When the [N2H4]/[V] molar ratio is greater
than 15:1, keeping [V] constant at 1.5 mmol, only solid VOOH microparticles are obtained
(Fig. S2c,d), which may be related to the fact that the large amount of N2H4 accelerates the
nucleation process and then the large number of freshly formed VOOH monomers tend to
aggregate with each other directly, rather than aggregate on the surface of the in situ–
produced N2 bubbles.
Consistent with the “aggregation-then-growth” model, our time-dependent experiments
indeed agree with the mechanism mentioned in the Communication; it is found that the
growth process occurs after the hollow spheres have formed. Under the present synthetic
conditions, hollow spheres with a smooth appearance are readily formed after a short reaction
time of 2 h, as shown in Figures S3a and b, where the field effect scanning electron
microscopy (FE-SEM) images show the smooth surface of the spheres and the transmission
electron microscopy (TEM) images (inset in Fig. S3a) reveal the contrast between the dark
edge and pale center and the poor crystallinity, confirming the hollow nature of the
intermediate products at a short reaction time of 2 h. A magnified TEM image is shown in the
inset in Figure S3b, showing the smooth surface of the spheres. With a longer reaction time of
5 h, the VOOH sheets gradually appear on the surface of the spheres, as shown in Figures S3c
and d, where the FE-SEM images show the rough surface and the roughly circular shape of
the hollow spheres, respectively. At a reaction time of 12 h, VOOH “dandelions” are
obtained.
4
(b)
031
020
300
200
250
022
131
100
220
151
150
251
002
200
111
Intensity (a.u.)
adma200600065_si.doc
120
06.06.2006
50
10
20
30
40
50
60
70
2 q (degrees)
(d)
200
031
120
700
020
600
060
500
080
231
022
251
200
220
151
300
131
400
111
Intensity (a.u.)
800
100
0
10
20
30
40
2 q (degrees)
50
60
70
Figure S2. TEM images and the corresponding XRD patterns for the products at different
[N2H4]/[V] molar ratios: a,b) [N2H4]/[V] = 4:1; c,d) [N2H4]/[V] = 15:1.
Figure S3. FE-SEM images of the intermediate products collected at different stages after
reacting for 2 h (a,b) and 5 h (c,d). Inset in (a): Corresponding TEM image, from which one
can see that the hollow spheres are formed at the short reaction time of 2 h.
S4. Phase and Morphology of the VOOH Hollow-Dandelion Electrode after the 20th
Cycle
Figure S4 shows an XRD pattern and FE-SEM image of VOOH hollow dandelions after the
20th lithium ion intercalation/deintercalation cycle. Compared with the sample without
electrochemical measurement (Figs. 2 and 4 in the Communication), the XRD pattern of the
06.06.2006
5
adma200600065_si.doc
VOOH hollow dandelions after intercalation/deintercalation cycling is almost unchanged,
which indicates this new-phased VOOH is stable in the electrochemical process and the
lithium ion intercalation/deintercalation process is reversible. The broad peak at ca. 2θ = 15°
to 30o can be attributed to carbon used in the preparation of the electrode. The starred peaks
are typical peaks for Al substrates. As depicted in the Figure S4b, the morphology of the
hollow dandelions can be clearly seen after 20th charging and discharging cycle. Thus, after
the electrochemical investigation had been performed, only some of the hollow dandelions
retained the hollow-dandelion morphology, while the phase of the VOOH samples remained
unchanged.
*
*
231
*
200
031
Relative Intensity (a.u.)
020
120
(a)
*
10
20
30
40
50
60
70
2q(degrees)
Figure S4. a) XRD pattern and b) FE-SEM image of VOOH hollow dandelions after the 20th
lithium intercalation/deintercalation cycle. The broad peak at ca. 2θ = 15° to 30o can be
attributed to carbon used in the preparation of the electrode. The starred peaks in (a) arise
from the Al substrate.