Synthesis, characterization, and electrochemical properties of nanocrystalline silver thin films obtained by spray pyrolysis

Article abstract of DOI:10.1149/1.1632476

Silver thin films were prepared using a spray pyrolysis method, silver acetate as the precursor, and stainless steel, heated at 225 and 300°C, as the substrate. Structural and morphological analyses carried out using X-ray diffraction, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy methods revealed the formation of highly homogeneous, porous coatings ca. 1 μm thick and with nanometric Ag particles as the main component. The presence of small amounts of Ag₂O was also inferred from XPS data. The reduction process of these films, which are used as electrodes over the potential range 3.0-0.0 V in lithium cells, consisted of several steps involving the formation of a solid electrolyte interface between 1.5 and 0.2 V, and at least two Ag-Li alloys below 0.2 V, the patterns of which were indexed in the cubic and tetragonal systems, respectively. The alloying/dealloying processes are reversible, and the cell can deliver a capacity of 600 Ah kg^-1 in the potential window 1.0-0.0 V.

Full text of DOI:10.1149/1.1632476

Journal of The Electrochemical Society, 151 ͑1͒ A151-A157 ͑2004͒
A151
0013-4651/2003/151͑1͒/A151/7/$7.00 © The Electrochemical Society, Inc.
Synthesis, Characterization, and Electrochemical
Properties of Nanocrystalline Silver Thin Films
Obtained by Spray Pyrolysis
a,z
b
b,
b
J. Morales,a, L. Sanchez, F. Martın, J. R. Ramos-Barrado, and M. Sanchez
´
´
´
*
*
a
´
´
´
´
Departamento de Quımica Inorganica e Ingenierıa Quımica, Facultad de Ciencias,
´
´
Universidad de Cordoba, 14071 Cordoba, Spain
bLaboratorio de Materiales y Superficie (Unidad Asociada al Consejo Superior
´
´
de Investigaciones Cientificas), Universidad de Malaga, Malaga, Spain
Silver thin films were prepared using a spray pyrolysis method, silver acetate as the precursor, and stainless steel, heated at 225
and 300°C, as the substrate. Structural and morphological analyses carried out using X-ray diffraction, X-ray photoelectron
spectroscopy ͑XPS͒, and scanning electron microscopy methods revealed the formation of highly homogeneous, porous coatings
ca. 1 ␮m thick and with nanometric Ag particles as the main component. The presence of small amounts of Ag2O was also
inferred from XPS data. The reduction process of these films, which are used as electrodes over the potential range 3.0-0.0 V in
lithium cells, consisted of several steps involving the formation of a solid electrolyte interface between 1.5 and 0.2 V, and at least
two Ag-Li alloys below 0.2 V, the patterns of which were indexed in the cubic and tetragonal systems, respectively. The
alloying/dealloying processes are reversible, and the cell can deliver a capacity of 600 Ah kgϪ1 in the potential window 1.0-0.0 V.
© 2003 The Electrochemical Society. ͓DOI: 10.1149/1.1632476͔ All rights reserved.
Manuscript submitted February 10, 2003; revised manuscript received July 25, 2003. Available electronically December 9, 2003.
In the last few years, lithium-based alloys have aroused increas-
ing interest as promising choices for use as negative electrodes in
Li-ion batteries, particularly since the inception of the Stalion
lithium-ion cell1 developed by Fuji Photo Film Celltec. Co. ͑Japan͒,
which showed that tin-based systems exhibit high specific capacities
as anode materials by virtue of their ability to form LixSn alloys,
ler. The substrate was moved forward and backward at a fixed fre-
quency by an electronically controlled step motor. An aqueous so-
lution of 0.05 M Ag(CH3COO) was used as precursor. The solution
was pumped into the airstream in the spray nozzle at a rate of
50 mL hϪ1 with a syringe pump for a preset time of 20 min. An
airstream of 25 L minϪ1 measured at 1.25 bar was used to atomize
the solution. Circular disks 0.4 mm thick and of 7.5 mm diam of
commercial 304 stainless steel were used as substrates. They were
kept at temperatures over the range 225-300°C.
X-ray diffraction ͑XRD͒ patterns were recorded on a Siemens
D5000 X-ray diffractometer, using Cu K␣ radiation and a graphite
monochromator, in steps of 0.02° and 1.2 s. Scanning electron mi-
croscopy ͑SEM͒ images were obtained on a Jeol JMS-5300 micro-
scope. A Visiolog 5.2 software, from NOESIS, was used to charac-
terize particle size by image processing. Thermogravimetric ͑TG͒
measurements were made on a CAHN 2000 thermobalance by heat-
ing from 25 to 600°C at a rate of 5°C minϪ1 under ambient condi-
tions.
X-ray photoelectron spectroscopy ͑XPS͒ spectra were recorded
on a Physical Electronics PHI 5700 spectrometer using nonmono-
chromated Mg K␣ radiation and a hemispherical analyzer operating
in the constant pass mode at 29.35 eV. Binding energies ͑BEs͒ were
referred to the Ag 3d5/2 peak at 368.3 eV. Samples were mounted on
a holder without adhesive tape and kept under high vacuum in the
preparation chamber overnight before they were transferred to the
analysis chamber of the spectrometer. Survey spectra over the range
0-1200 eV were recorded at a 187.85 pass energy, each region being
scanned several times to ensure an adequate signal-to-noise ratio. A
3 ϫ 3 mm sample area was sputtered by 4 keV Arϩ; the sputter rate
was assumed to be ϳ3 nm minϪ1, as determined for Ta2O5 under
identical sputtering conditions. Spectra were handled by PHI-Access
V.6 and Multipak software, both from Physical Electronics. Curve
fitting of high resolution spectra was carried out after Shirley back-
ground correction and satellite subtraction. The atomic concentra-
tion was determined from C 1s, O 1s, and Ag 3d peak areas, using
Shirley background subtraction and sensitivity factors provided by
the spectrometer manufacturer ͑Physical Electronics͒. An Arϩ ion
beam of 4 keV was used for depth profiling, the composition being
determined from the integrated intensities of the XPS spectra.
Electrochemical experiments were carried out in two-electrode
cells, using lithium as the anode. The electrolyte used was a Merck
battery electrolyte LP 40, ethylene carbonate ͑EC͒:diethyl carbonate
(DEC) ϭ 1:1 w/w, 1 M LiPF6). The stainless steel circular disks
coated with the active material were used as working electrodes.
Ͻ
Ͻ
1.0
x
4.4.
The reaction of these systems with lithium is well known and
involves a decomposition step that yields Li2O and Sn, followed by
the formation of various Li-Sn alloys.2-5 The decomposition reaction
is electrochemically irreversible, so most of the initial discharge
capacity cannot be recovered. Unfortunately, pure Sn tends not to
react electrochemically with lithium. An alternative approach is to
use tin-based intermetallic composites as electrodes in lithium cells.
Good results have been obtained in this respect with Sn-Fe,6 Cu-Sn,7
Sn-Sb,8 Ni-Sn,9 and Sn-Ca10 systems, where the elements accompa-
nying tin act as inert matrices and help mitigate disintegration and
mechanical failure of the electrode through the significant volume
changes resulting from the formation of the LixSn alloy. Also, many
researchers have focused on other elements capable of reversibly
storing variable amounts of Li: Bi,11 Mg,12 Sb,13 Si,14 Zn,15 and
Pb.16
Silver is one other element capable of alloying with lithium to
form AgLix compounds (x Ϸ 3.3, theoretical capacity
17
827 Ah kgϪ1 ͒. Moreover, there is much experience in silver com-
pounds used as electrodes in primary button cells, and the element
can be easily obtained with simple conventional techniques, requir-
ing no inert atmosphere. These advantageous features are attractive
enough to test this element as an electrode material in rechargeable
lithium cells. Silver has so far been used as a diluting matrix to
retard the aggregation of tin in Sn18 and Sn-Sb19 electrodes. This
communication explores the reactivity of silver films in lithium
cells. Preliminary electrochemical tests exposed the potential of el-
emental Ag as an anodic material for electrochemical devices.
Experimental
A spray pyrolysis method was used to prepare the Ag coatings.
Compressed atmospheric air was used to atomize a solution contain-
ing the precursor compound through a spray nozzle over the heated
substrate.20 The substrate holder was equipped with thermocouples
and heating elements, the latter governed by a temperature control-
* Electrochemical Society Active Member.
z E-mail: iq2sagrl@uco.es
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A152
Journal of The Electrochemical Society, 151 ͑1͒ A151-A157 ͑2004͒
Figure 1. TG curve for silver acetate.
*
Figure 2. XRD patterns for the Ag thin film electrodes. ͑ are substrate
reflections.͒
Figure 3. SEM images obtained for ͑a, b͒ sample A and ͑c͒ sample B.
Unless otherwise noted, a 0.05 mA mgϪ1 current density was ap-
plied to the cells for electrochemical measurements, controlled via a
MacPile II potentiostat-galvanostat. Cyclic voltammetric tests were
performed at a scan rate of 40 ␮V sϪ1, using a Schlumberger SI-
1286 potentiostat.
Table I. Substrate temperature during precursor deposition,
amount deposited „w…, and structural parameters for the Ag thin
film electrodes.
Results and Discussion
w (mg cmϪ2
)
a ͑Å͒
L ͑nm͒
Compound
Temperature ͑°C͒
Two different coatings were prepared by heating the substrate at
225 and 300°C, resulting in samples A and B, respectively. These
temperatures were chosen from TG measurements of
Sample A
Sample B
225
300
0.60
0.20
432
593
4.0782
4.0782
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Journal of The Electrochemical Society, 151 ͑1͒ A151-A157 ͑2004͒
A153
Figure 4. Particle size distribution of ͑᭝, ᭡͒ sample A and ͑᭺, ᭹͒
sample B.
Figure 5. O 1s, Ag 3d5/2 , and C 1s XPS spectra corresponding to ͑a͒ pure
silver acetate, ͑b͒ sample A, ͑c͒ sample B, ͑d͒ sample A after 2 min of argon
etching, and ͑e͒ sample B after 2 min of argon etching.
Ag(CH3COO), the weight loss of which fell within the previous
temperature range ͑see Fig. 1͒. A short heating time ͑15 min͒ was
used to obtain nanoparticle films of pure Ag ͑as inferred from the
XRD patterns͒. Figure 2 shows the XRD patterns for the coatings,
with the typical reflections for Ag. The remaining peaks were as-
signed to the substrate, and no additional peaks belonging to the
undecomposed precursor were observed. The unit cell parameters,
shown in Table I, are consistent with those reported for Ag. Crys-
tallite sizes were obtained using the Scherrer equation21 and are also
included in Table I; they increased with increasing temperature.
Moreover, the amount of material deposited decreased with increas-
ing temperature, probably because a drop of the precursor solution
burst and spilled part of its component off the substrate. This phe-
nomenon has often been observed in the preparation of various ox-
ides by spray pyrolysis.22
Figure 3 shows the SEM images obtained. Thorough coating of
the substrate is apparent from the cross-sectional image obtained for
sample A, from which the film thickness can be estimated to be
around 1 ␮m. The silver grains tend to be round. Figure 4 shows the
size frequencies ͑open symbols͒ and cumulative percentages ͑solid
symbols͒ corresponding to the particle size distribution for the two
samples. The particle size for sample A ranged from 300 to 500 nm;
that for the sample sprayed at higher temperatures ͑sample B͒
ranged from 500 to 900 nm. These values are fairly consistent with
those obtained from X-ray peak broadening ͑see Table I͒. Thus, the
SEM images show that, when the sprayed solution is deposited on
the heated substrate, the films consist of nanosized particles that
form a highly porous framework. The smaller particle size of sample
A must lead to a more compact film and hence to a higher apparent
thin film density. One also observes an interconnected system of
channels close to the steel surface that results from sintering of Ag
particles as suggested by the XPS data discussed in the next para-
graph. The coating is defined by this gel-like layer where quasi-
spherical grains stand out, and the thickness is essentially dictated
by the size of these round particles ͑Fig. 3a͒.
plete at the two temperatures studied. This is also reflected in the O
1s emission spectrum, the intensity of which is significantly de-
creased ͑the atomic percentage is nearly one-half, Table II͒. More-
over, this peak becomes more asymmetric as discussed below. The
value of the Ag 3d5/2 BE obtained for the acetate precursor and
deposited silver is virtually the same, 384.4 eV, which makes it
difficult to discriminate between Ag0, as found by XRD, and Agϩ.
Identifying the valence states of silver from the BE values is not
easy because they are closely spaced. Thus, values for the BE of the
Ag 3d5/2 photoemission between 368.1 and 368.4 eV have been re-
ported for Ag, and values over the ranges 367.3-367.6 and 367.8-
368.0 eV have been obtained for Ag2O and AgO, respectively.
Greater differences exist in the Auger AgMNN peak, which appears at
358.0, 350.6, and 355.5 eV on the kinetic energy scale for Ag,
Ag2O, and AgO, respectively.23 The value obtained from the films,
whichever the preparation temperature, is better explained by as-
suming the formation of metallic silver, a conclusion that is also
consistent with the XRD data.
The O 1s peak for the films is complex, with many components
corresponding to different chemical states. The peak profile was
fitted to four components, as shown in Fig. 6. The peak near 532.0
eV ͑curve 1͒ can be assigned to hydroxyl or water species.24,25 The
second peak, centered at 531.6 eV ͑curve 2͒, could be assigned to
traces of undecomposed silver acetate or an intermediate species
that maintains a CuO bond ͑viz. CO32Ϫ). The C 1s photoemission
peak exhibits a reduced intensity peak at 288.15 eV, a value similar
to that for the carboxyl group. However, the oxygen-to-carbon in-
tensity ratios found in the film samples are greater than that for pure
silver acetate, so this oxygen species is also bonded to other species.
Atomic oxygen on a metallic silver surface and dissolved subsurface
atomic oxygen have been shown to posses a BE near 531 eV24,26
͑curve 3͒. Finally, the peak at the highest energy ͑529.2 eV͒ can be
assigned to oxygen forming Ag2O rather than AgO, the O 1s peak
for which appears at 528 eV.23
Figure 5 shows the XPS spectra for films subjected to various
treatments. The XPS spectrum for silver acetate was also recorded
for comparison. The C 1s XPS spectrum for pure silver acetate
exhibits two peaks, one centered at 288.3 eV23 and assigned to the
carboxylate group, and the other at 284.8 eV and due to the methyl
group. The increased area under the latter peak is a result of the
additional contribution of adventitious carbon. The atomic compo-
sitions obtained ͑Table II͒ reveal a carbon content nearly twice as
high as that in the nominal acetate stoichiometry. While this peak is
maintained in the spectra for the films, the former virtually disap-
pears ͑only a weak signal, nearly coincident with the background, is
detected͒. This reveals that acetate decomposition is virtually com-
Table II. Atomic compositions obtained from XPS data.
Compound
C 1s ͑%͒
O 1s ͑%͒
Ag 3d ͑%͒
58
59
64
4
26
15
12
7
16
26
24
89
Ag(CH3COO)
Sample A
Sample B
Sample A
͑2 min Ar etching͒
Sample B
5
7
88
͑2 min Ar etching͒
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A154
Journal of The Electrochemical Society, 151 ͑1͒ A151-A157 ͑2004͒
Figure 6. O 1s and C 1s peak curve fitting: ͑a͒ pure silver acetate, ͑b͒ sample A, and ͑c͒ sample A after 2 min of argon etching.
we assume a depth of 10 nm per min of ion Arϩ etching͒.27 The O
1s peak disappeared after 5 min of etching; however, for sample A,
such a peak continued to be detected after longer periods ͑more than
20 min͒. The silver concentration initially increased through re-
moval of adventitious carbon and oxygen and then remained essen-
tially constant up to 20 min of ion sputtering. Beyond that point, the
silver concentration decreased gradually. The average rate of silver
removal was lower for sample A, which is consistent with the larger
amount deposited ͑see Table I͒. However, the thickness obtained
from these depth profiles, 1-2 ␮m, is consistent with that inferred
from the SEM images. Iron was detected after 20 min of sputtering,
when the silver content started to decrease. These results suggest
that the gel-like silver coating is very thin (Ͻ200 nm thick͒. When
the silver content declines, the extracted silver comes from the
grains. Except for the above-described subtle compositional diver-
gences, no differences such as impurities or distinct phases in the
samples were apparent from these depth profiles.
Figure 8 shows the first galvanostatic discharges performed on
Li/Ag cells. While discharging, the potentials of the films rapidly
drop to 1.5 V, which is followed by a negative slope to a cathode
potential of 0.2 V and, finally, an extensive, nearly horizontal se-
quence up to 0.0 V. A subtle slope change is observed at 2.5 V
which, based on XPS data, could be assigned to the reduction of
Agϩ. The region between 1.5 and 0.2 V, which exhibits an almost
linear decrease in potential with the faradaic yield, can be assigned
to the formation of a solid electrolyte interface ͑SEI͒ film resulting
from the reduction of electrolyte solvent, as reported for noble met-
To shed additional light on the previous findings, films were
sputtered with Arϩ for 2 min. The XPS spectra for these samples are
depicted in Fig. 5 and 6. The most salient changes were as follows.
(i) The C 1s peak almost disappeared. The atomic concentration
dropped to 4-5% ͑see Table II͒, which confirms its assignation to
adventitious carbon. (ii) The O 1s peak was markedly weaker and
more symmetric. The atomic percentage dropped to 7%, and only
the peak centered at 529.0 eV ͑in our opinion associated to silver
oxide͒ was detected. (iii) The Ag 3d photoemission remained
highly symmetric, and its BE hardly shifted. From these results, the
following conclusions can be drawn on the surface structure of the
films: virtually complete decomposition of acetate is observed at the
temperatures used; also, the C 1s peak obtained is due mainly to
adventitious carbon. The main component of the films is metallic
silver, which, based on the O 1s peak deconvolution, is accompanied
by a small amount of Ag2O. Direct identification from the Auger
transition failed because no signal could be identified around 350 eV
on the kinetic energy scale. The two oxidation states of silver are
indistinguishable from the BE of the 3d photoemission peak. No
peaks belonging to the main substrate components ͑Fe, Cr͒ were
detected in this analysis. This means that silver is also the compo-
nent of the black background of the SEM images previously de-
scribed as an interconnected channel system.
The XPS concentration depth profiles for silver, iron, oxygen,
and carbon are shown in Fig. 7. After a few minutes of etching, the
oxygen concentration could not be measured. This suggests that the
Ag2O film was very thin, particularly for sample B ͑around 50 nm if
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Journal of The Electrochemical Society, 151 ͑1͒ A151-A157 ͑2004͒
A155
silver; however, no new peaks were observed. This is consistent
with the cathodic scan as the reduction peaks start to develop below
this potential. Only partial silver amorphization can be inferred from
the pattern. At 0.0 V, the diffractogram changes significantly: new
lines appear, the spacings of which are shown in Table III. This set
of lines, that of low intensity at 26.7° ͑2␪͒ excluded, can be indexed
in a tetragonal system with the following cell parameters: a
ϭ 5.41(1) and c ϭ 5.60(2) Å. Besides these lines, one can detect
a set of reflections located at Bragg angles somewhat smaller than
those for pure silver. These reflections can be indexed in a cubic
system with a ϭ 4.042(3) Å ͑Table IV͒. Compared with silver
͑Table I͒, the unit cell has contracted. In our opinion, these data
define a new Ag-Li alloy, probably with a small lithium content,
rather than pure Ag. Thus, the reduction with lithium up to 0.0 V
leads to the formation of at least two alloys, one tetragonal (AgLiy)
and the other cubic (AgLix). Unfortunately, it is very difficult to
accurately determine their lithium contents from electrochemical
measurements, as x ϩ y ϭ 2.4. None of these alloys coincides with
those reported in the Joint Committee on Powder Diffraction Stan-
dards ͑JCPDS͒ files ͓AgLi ͑card no. 4-805͒ and Ag3Li10 ͑card no.
2-1097͔͒. Differences in synthetic procedures may account for this
discrepancy. When the cell is charged at 0.2 V, the intensity of the
peaks close to the silver increases, and the unit cell dimension ap-
proaches that for pure Ag. This means that Liϩ is extruded from the
AgLix alloy and the Ag framework as a result. The similarity be-
tween the unit cells of both phases (AgLix and Ag͒ results in slight
polarization between the reduction and oxidation peak. Finally,
when the cell is charged at 1.0 V, most of the peaks belonging to the
tetragonal phase disappear ͑only the more intense reflections at 2.27
and 2.21 Å still remain, but with a reduced intensity͒, and Ag re-
flections are stronger. We can thus assign the oxidation peak at 0.32
V to the extrusion of Li from AgLiy and its conversion into metallic
silver. The fact that the formation peak appears at 0.04 V ͑0.28 V
below the corresponding decomposition peak͒ is indicative of the
greater structural rearrangement required to transform the cubic
phase into a tetragonal phase.
The performance of the Li/Ag cells was studied by analyzing the
specific capacity delivered by the electrodes on cycling ͑Fig. 11͒.
Thus, the Li/Ag cells were discharged up to 0.0 V and then cycled
over the range 0.0-1.0 V. Good capacity retention was observed for
sample A, which retained nearly 95% of its delivered capacity over
the first 12 cycles ͑Fig. 11a͒. By contrast, the capacity retention of
sample B faded rapidly. Additional information can be obtained by
plotting the charge recovery, as the ratio between the specific capac-
ity delivered in each charge process and the previous discharge pro-
cess, against the number of cycles. For sample A, the charge recov-
ery was close to 100%, which testifies to the good reversibility of
the alloying/dealloying processes involved ͑Fig. 11b͒. Conversely,
the cell made from sample B has a low charge recovery ͑Fig. 11b͒.
The increased particle size, together with a greater ability to form
SEI films, may be the origin of the poorer electrochemical response
of this cell, the capacity of which fades after the first six cycles.
Following prolonged cycling, the capacity of sample A also fades,
and the cell delivers only 150 Ah kgϪ1 at the 50th cycle. This ca-
pacity drop can be explained in the light of (i) the volume changes
resulting from alloying/dealloying processes and the subsequent
stress and strain undergone by the active material, and (ii) the lack
of a matrix that can partially mitigate the stress ͑a role played by
Li2O in tin composite electrodes͒. However, the capacity retention
of the Ag electrode is substantially improved relative to other ele-
ments such as Bi,11 Si,31 or Sn32 ͑95 vs. 30-50%͒; these advantages
make Ag thin films potential candidates for use in Li-ion microbat-
teries. Additional efforts must be made to find an inert matrix that
will allow the cycle life of silver thin electrodes to be extended.
Figure 7. XPS depth profiles for ͑᭹͒ silver, ͑᭡͒ iron, ͑᭺͒ oxygen, and
carbon ͑Ã͒.
als used as electrodes in lithium batteries.28,29 This phenomenon is
more marked in sample B, which possesses a greater particle size
and a smaller amount of active material. However, this behavior
does not seem plausible, because the SEI filming reaction generally
is dependent on the surface area and should be favored by an in-
creased value of this parameter. The surface chemical state of the
two samples may provide a more plausible explanation. Oxygen
atoms, the content in which was somewhat higher in sample A ͑see
Table II͒, are strongly bound to the surface of this sample, so their
removal, as noted earlier, requires a more drastic treatment. This
could afford more direct contact between the organic molecules of
the electrolyte and silver atoms, thus facilitating the formation of the
SEI film. When the potential scale is enlarged, two plateaus can be
observed in the 0.2-0.0 V region that are ascribed to Li-Ag alloys.30
These two steps in the reduction process can also be inferred from
the cyclic voltammetric curve of Fig. 9, even though the reduction
peaks ͑particularly that at the lower potential͒ are not completely
resolved under the conditions used. The anodic scan is better de-
fined, with two rather symmetric peaks at 0.12 and 0.32 V in the
voltammogram. This cyclic voltammogram differs from that re-
ported by Wachtler,18 who found a third anodic peak at ca. 0.4 V.
To analyze the structural changes undergone by silver during the
discharging and charging processes, ex situ XRD patterns were re-
corded at different discharge and charge potentials. At a discharge
potential of 1.0 V ͑Fig. 10͒, the main difference of the pattern from
that for the parent film was a decreased intensity in the peaks for
Conclusions
Spray pyrolysis of aqueous silver acetate solutions is a simple,
effective method for preparing silver thin films at moderate tempera-
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Journal of The Electrochemical Society, 151 ͑1͒ A151-A157 ͑2004͒
Figure 8. First-discharge and subsequent charge-discharge galvanostatic curves for Li/Ag cells.
tures. Above 200°C, the organic salt is virtually decomposed, and
the substrate is thoroughly coated with a highly uniform, homoge-
neous film consisting of nanometric, spherical particles. Under these
conditions, the sole crystalline phase detected in the film is Ag;
however, XPS spectra reveal a more complex surface structure con-
taining small amounts of oxidized species ͑probably Ag2O). These
thin films can react reversibly with lithium in a Li/LiPF6 , EC-DEC/
film cell configuration over the potential range 0.0-1.0 V and form
various reversible Ag-Li alloys that can be identified by combining
cyclic voltammetry with ex situ XRD measurements. The good ca-
pacity retention of the cell ͑particularly that made from the film with
smaller particle size͒ together with the very low potential make
these films attractive candidates as anodes for Li-ion microbatteries.
Figure 10. Ex situ XRD patterns recordered at different discharge ͑1.0 and
0.0 V͒ and charge ͑0.2 and 1.0 V͒ cutoff potentials for sample A.
Figure 9. Cyclic voltammogram for a Li/sample A cell over the range 0.0-
1.0 V.
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Journal of The Electrochemical Society, 151 ͑1͒ A151-A157 ͑2004͒
A157
Acknowledgments
This work was supported by Junta de Andalucıa ͑Group FQM-
Table III. Structural parameters assigned to the AgLiy phase.
´
d ͑Å͒
hkl
´
175͒ and Ministerio de Ciencia y Tecnologıa ͑Project MAT2002-
04477-C02-02͒.
Lattice: tetragonal
a ϭ b ϭ 5.41(1) Å
c ϭ 5.60(2) Å
3.1539
2.2750
2.2141
1.9187
1.8675
1.8442
1.5886
1.4484
1.2907
1 1 1
1 1 2
2 1 1
2 2 0
0 0 3
2 1 2
2 2 2
3 2 1
3 0 3
The University of Cordoba assisted in meeting the publication costs of
this article.
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Table IV. Structural parameters assigned to the AgLix phase.
d ͑Å͒
hkl
Lattice: cubic
a ϭ 4.042(3) Å
␣ ϭ 90°
2.3253
2.0214
1.4288
1.2197
1 1 1
2 0 0
2 2 0
3 1 1
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Figure 11. Delivered ͑a͒ specific capacity and ͑b͒ charge recovery on cy-
cling for Li/Ag cells: ͑᭹͒ sample A, ͑ᮀ͒ sample B.
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