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Chemical intercalation of lithium into a V6O13 host
SOLID STATE ELSEVIER
Solid State Ionics 81 (1995) 189-199
IONICS
Chemical intercalation of lithium into a V60,, host Christina Lampe-onnerud
a, Per Nordblad b, John 0. Thomas a
a Institute of Chemistry, Uppsala University, Box 531, S-751 21 Uppsala, Sweden ’ Department of Technology, Uppsala University, Box 534, S-751 21 Uppsala, Sweden Received 13 January 1995; accepted for publication 1 August 1995
Abstract Chemical lithium insertion into five different types of V,O,,-based intercalation hosts have been performed in this study. Lii,5V6013, Li,V,O,, and Li,V,O,,; the latter phase representing the highest degree Four phases were identified: Li,,V,O,,, of intercalation. These phases are crystallographically and magnetically different not only from the phase-pure V,O,, host, but also from one another. The presence of other VO,-phases (10 mol% VO, or V,O,) caused slower lithium intercalation into V,O,,, different final phases and poor stability in the presence of water. Keywords: Cathode material; Intercalation; XRD; Magnetization measurements; Magnetic susceptibility; Butyllithium.
1. Introduction
In spite of the fact that V,O,, has been one of the most commonly used active cathode materials in modem thin-film battery design, the lithium insertion properties are still not properly understood. Its crystallographic and magnetic properties have been well characterized [ 1,2], but there would seem to be little agreement as to the lithium mechanisms, phases formed, and the maximum degree of intercalation. In 1979, Murphy and co-workers [3] performed topochemical reactions at room temperature and sugto be the maxigested Li,V,O,, and - Li,,,V,O,, mum lithium uptake for stoichiometric and nonstoichiometric V,O,,, respectively. They also found multiphase behaviour for x < 3 in Li,V,O,, , and a non-stoichiometric single-phase for x > 3. Abraham et al. [4] showed that 2-3 different phases were formed as the intercalation of lithium proceeded. The maximum x in Li,V,O,, was shown to vary be-
tween 4 and 8, x being higher for the non-stoichiometric than stoichiometric case. They also found an irreversible maximum uptake of 14 lithium atoms into V,O,, by electrochemical insertion. If all vanadium atoms in V60,, are reduced to oxidation state + 3, eight lithium atoms can be intercalated into V,O,,. This was found by West et al. [5] using butyl-lithiation; they also made a determination of the maximum uptake of lithium as a function of increasing oxygen content. X-ray data indicated that all phases were monoclinic with the space group C2/m. Electrochemical measurements showed three reversible intercalation phases: x = 1, 4 and ’ 8 in Li,V,O,, [6]. It was later concluded [7] that a single-phase reaction takes place for small lithium content (up to x - 2.51, and that ii,VO,(B) should form thereafter. Recent studies of mass-change accompanying the electrochemical insertion of lithium into V,O,, show discrepancies when more than one Li ion is intercalated per V60,, unit [8]. Battery
0167-2738/95/$09.50 0 1995 Elsevier Science B.V. All rights reserved SSDI 0167-2738(95)00181-6
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State Ionics 81 (199.7) 189-199
studies by Koksbang et al. [9] have shown that 8 Li/V,O,, was only possible during the first cycle, and 6 Li/V,O,, thereafter. We have previously described the difficulties experienced in obtaining phase-pure V,O,, [lo], and determined the reaction mechanisms for the formation of various vanadium oxides by thermal decomposition of NH,VO, [II]. We present here the Li,V,O,, phases formed as x is increased, and compare the results obtained using single-phase and VO,,-contaminated V,O,,. These same materials have subsequently been incorporated in lithium-polymer batteries; see Ref. [12].
annealed V,O,, (Table 1). Powders cl), (3) and (4) were synthesized without any pre-treatment by thermal d~omposition of NH,VO, powder (Gesellschaft fur Elek~omet~lurgie, MBH, 99.9%). Synthesis of the standard V,O,, (1) was performed in a specially designed reaction chamber for a maximum over-pressure of 1.5 MPa and a heating rate of O.S’C/min in the range 25-500°C [12]. Powder (2) was made by grinding powder (1) in an agate mortar prior to lithiation in order to study the effects of strain and grain-size. Powder (3) containing VO, was made using a slightly higher over-pressure ( N 3 MPa) during the thermal decomposition. Powder (4) (V,O,, containing V,O,) was made by heating the NH,VO, in flowing N, atmosphere at l”C/min from ambient to 43O*C, and then holding this temperature for 10 h. Appropriate amounts of powders (3) and (4) were annealed at 600°C in evacuated quartz tubes for 48 h to obtain the last type of V,O,, (5).
2, Experimental Five different intercalation hosts were studied: (1) standard V,O,,, (2) ground V,O,,, (3) V60,s containing VO,, (4) V,O,, containing V,O, and (5)
Table I The various V,O,,-based intercalation hosts used for chemical lithiation Powder
Annealed
Standard
Ground
%0,3
WI3
(1)
(2) powder (1) ground
(3) thermal decomp. of NH,VG,
(4) thermal decomp. of NH,VO,
(5) annealed mixture of powders (3) and (4)
WA3
+ vo2
WA3
+ w,
‘6Ol3
preparation
thermal decomp. of NH.,VG,
mean oxidation state (titration)
4.30 f 0.01
4.30 rt 0.01
4.30 * 0.02 (calculated from molar ratios)
4.40 f 0.03 (calculated from molar ratios)
4.35 * 0.01
grain-size
5-25 pm
5-25 pm
2-10 pm
lo-25 pm
5-15 Pm
effect of sintering CXM)
agglomerate 300 pm
no agglomerate
aggIomerate 200 pm
agglomerate 200 pm
no aggio~mte
WA3
Yio13
90% v,o,, 10% vo,
phase analysis
+
90% v,o,,
i
10% v,o,
V&s
(XRD)
v,Gl, unit cell
a = 11.933(7) A b = 3.672(3) A c = 10.139(4) w @= 100X2(3)” V = 436.3(6) A s
11.8780) 3.673(2) 10.131(11) 100.68(6) 434.4(7)
11.923(6) 3.683(2) 10.150(7) 101.78(4) 436.3(S)
11.942(9) 3.685(3) 10.171(10) 100.60(6) 439.9(9)
I 1.943(8) 3.686(3) 10.180(7) 100.86(6) 440.X6)
C. Lampe-&nerud
et al./Solid
Chemical lithiation was performed in 25 mL glass bottles, each sealed with a replaceable teflon-silicon septum as the vanadium oxide was weighed in. The powder was then completely covered with freshly distilled hexane (4-5 mL) and the atmosphere changed to dry Ar or N, before transferring the bottle to a glovebox ( < 1 ppm H,O and 0,). The lithiation was performed by slowly adding n-butyllithium (Merck, 1.6 M in hexane) under the hexane surface using a Hamilton syringe (1 .OOO+ 0.005 mL) fitted with exchangeable needles. The lithium/ vanadium molar ratio was varied: 0.5
State Ionics 81 (1995) 189-199
191
120°C prior to each experiment. Each lithiation reaction was interrupted by evaporating the hexane at 70°C under a flowing Ar atmosphere, and immediately transferring the samples back to the glovebox. The effects of ageing were tested with regard to spontaneous decomposition (both in a glovebox and in air), and to stability with respect to water (by adding 15 mL water followed by an equilibration time of lo-20 h). The total concentrations of vanadium and lithium were determined for experiments performed with standard V,O,, (1) using inductively coupled plasma atomic emission spectrometry (Spectroflame, Spectra Kleve). lo-20 mg samples were boiled to complete solvation in HCl(6 mL, 12 M) and HNO, (2 mL, 14 M), and diluted with milliQ-filtered water (Millipore Bedford, MD) on cooling. The emission from vanadium and lithium was measured for 3 X 10 s at 3 11.071 and 670.784 nm, respectively. Standard cali-
a
b
30
40
50
60
70
80
-2e+ Fig. 1. X-ray diffractograms for various single-phase V,O,, powders used in this study: (a) an annealed stoichiometric mixture (V,O,,, powder 5) (0 0 l-reflections marked); (b) the result of thermal decomposition of NH,VO, (standard V,O,,, powder 1) and (c) a ground V,O,, (powder 2). All diffractograms can be compared with a calculated diffraction pattern cd).
192
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bration solutions (Referensmaterial AB, Sweden) were prepared in the same reagent matrix. Duplicate samples were analyzed to check homogeneity. All samples were characterized in terms of phase and degree of crystallinity by X-ray diffraction (XRD) using a STOE & CIE GmbH STADI powder diffractometer (CuKa, radiation) fitted with a 45” curved position-sensitive detector. The stabilities of the different phases formed upon lithiation were assessed; exposure times varied from 10 min to 10 h. The grain-size and morphology of the starting vanadium oxides were also studied in a Zeiss DSM 960A scanning electron microscope (SEM). The VO,, contamination levels were determined by establishing reference diffractograms using weighed-in mixtures of single-phase V,O,,, VO, and V,O, [I 1,131. Potentiometric titrations [13] were made to determine the mean vanadium oxidation state in the single-phase V,O,,. Magnetization versus temperature (5 kG; 5-50 K) was recorded using a Quantum Design MPMS SQUID-magnetometer for the three different singlephase V,O,, samples ((11, (2) and (5)) and for the standard lithiated V,O,, series (1).
3. Results 3.1. The vanadium oxide phases All three single-phase V,O,, samples contained the same thin (< 1 pm), needle-like crystallites, while only the standard V,O,, sintered into agglomerates (- 300 pm>. The V,O,, (5) was single-phase (Fig. la), showing good agreement with the calculated V,O,, diffractogram (Fig. Id). Titrations gave the mean oxidation state of vanadium as 4.35 f 0.01, corresponding to the slightly oxygen-rich stoichiometry V,O,,,s,. On the other hand, the standard V,O,, (5) was found to be oxygen deficient, with a mean oxidation state of 4.30 f 0.01 (V,O,,,,). The corresponding X-ray diffractogram (Fig. lb) indicated a crystalline single-phase V,O,, with somewhat lower 0 0 I-reflection intensities. This effect is much more pronounced in the ground powder (Fig. lc), and a smaller crystallographic a-axis could be noted (Table 1). The magnetization measurements on the different single-phase V60,, samples (11, (2) and (5)
State Ionics 81 (1995) 189-199
M (emu/g)
0
I
/
’
!
I
I
0
50
100
150
I
I
1
200 T(K)
250
I
I
I
I
300
350
400
Fig. 2. Magnetisation versus temperature for the various singlephase V,O,, powders (1, 2 and 5) used in this study (H = 5 kOe).
exhibited certain differences compared to earlier studies [2,3] (Fig. 2). The metal-insulator transition (at 150 K) is broadened for the standard and annealed V,O,, samples compared to the ground sample. The decrease in the susceptibility at 60 K can be related to the antiferromagnetic transition described in [2]. A very weak anomaly around 340 K indicates that minor amounts of VO, may be present in the thermally decomposed V,O t s. The mixed-phase oxides were determined ( f 2%) from the reference diffractograms to be 90 mol% V,O,, and 10 mol% VO, or V,O,, respectively. Both powders had sintered into N 200 pm agglomerates, but contained crystallites of very different morphology. The powder containing VO, resembled closely single-phase V60,s, with small needle-like crystallites (< 5 pm3); whereas the powder containing V,O, were regularly shaped crystallites (N 15 p,m3). XRD showed that both powders were crystalline, but that the oxide containing V,O, had broader peaks and lower intensities for the V60L3 (0 0 Z&reflections, indicating the introduction of preferred orientation or some type of structural disorder. 3.2. Lithiated V, O,, All samples, regardless of their V,O,, starting material, were black after intercalation. Four different Li,V,O,, phases can be identified on lithiating the standard single-phase V60,3, none of which ex-
et al. /Solid State ionics 81 (1995) 189-199
,
I
I
,
20
30
40
50
60
-----r-----------r-------
IO
193
C. Lumpe-&nerud
Fig. :3. X-ray diffractograms for the lithium intercalation products formed from standard single-phase V,O,, (powder 1): (a) Li,,V,0,3, Li,,,VhO,,, (c) Li3V,0,, and (d) Li,V,O,,.
hibited the metal-insulator transition at 150 K. The X-ray diffractogram for theofirst phase, LiO.dV,O,, (Fig. 3a) (a = 11.930(5) A, b = 3.680(2) A, c = 10.147(6) A, @= 100.85(5)0, V= 437.5(3) .k3>, resembles closely the non-intercalated V6013; it can be indexed in the same C2/m space group and almost the same cell [ 141. The magnetization measurements (Fig. 4) exhibit a continuous increase in magnetization as the temperature is lowered. The next phase, which begins to form immediately as the lithium content is raised above x = 0.5, reaches fuI1 intercalation at Li,,5V60,3. New XRD peaks appear (Fig. 3b), and the space group and cell have changed dramatically. Magnetic measurements contain a new feature; a weak bump at 40 K, indicating some antiferromagnetic ordering (Fig. 4). An increase of the magnetization was observed with decreasing temperature. This antiferromagnetic behaviour was more pronounced for the third phase, Li,V,O,,, and an increase in magnetization could be seen at the lowest temperatures measured. XRD suggested sig-
(b)
nificant structural rearrangement with respect to Li1.5V6013(Fig. 3c), with both positions and intensities of reflections changing. A final phase begins to M bmu/p) I
J ,+ \
0 0
10
+
+
*
1
20
f
.f
-i
/
,
30
40
$
..
50
T m Fig. 4. Magnetisation versus temperature for the LixV,OIB phases (x = 0.5, 1.5, 3 and 6) compared with non-intercalated V,0,3
(x=OO)(H=5kOd.
194
C. Lmnpe-herud
et al./Solid
form for x > 3; higher background and only a few broad peaks appear in the X-ray diffractograms, suggesting a decrease in the degree of crystallinity (Fig. 3d). The magnetic measurements were temperature independent at low temperatures, but showed a higher response than for pure V,O,, (Fig. 4). When samples with x > 6 (x,,, = 10) were exposed to air, either white particles formed or the sample ignited. The white particles were identified by XRD as LiOH. The diffractograms (Fig. 3d) and the chemical analyses (after the removal of LiOH)
h .s E z.
State Ionics 81 (1995) 189-199
for all higher values of x (up to x = 10) were the same as for x = 6. This final phase was therefore concluded to be Li,V,O,,. A slight increase in crystallinity could also be noted for samples intercalated for a longer time. Chemical analysis indicated a lower x-value in Li,V,O,, compared to the amount of butyl-lithium added, and also revealed some inhomogeneity in the lithium content of the intercalated samples (Table 2). The ground V,O,, samples showed the same sequence of four lithiated phases. However, the diffrac-
b
6000
5000
4000
Fig. 5. The final Li,V,O,, obtained from intercalation into (a) single-phase V,O,,; containing V,O, (90/10 mol%). The inset (22.5’ < 20 < 24.3’) shows a systematic
(b) V,O,, containing VO, (90/10 shift in the strongest reflection.
mol%), (c) V,O,,
Table 2 Results from chemically lithiated standard V,O,, Bu-Li added for x Li/V,O,, 0.50 0.75 1.00 I .25 1.50
1.75 2.00 3.00 4.00 5.00 6.00 7.00 t 8.00
Li/V, ratio from chemical analysis 0.44 * 0.01 0.74f 0.01 0.95 f 0.03 1.17+0.01 1.2140.03 1.51 fO.01 1.9s+o.12 3.1410.21 3.44f0.52 4.99 f 0.08 5.33+0.05 5.87f.O.01 a sample ignited ’
’ White LiOH formed.
tograms showed that the preferred orientation or grinding-induced disorder remained, and some peak intensities were consistently lower than the as-made
V,O,, intercalation host. A slightly higher lithium content could he noted in intercalated samples, and some inhomogeneity was still observed. Similar results were obtained for lithiation of the annealed V,0t3. For x > 6, the sample again ignited or white LiOH was formed. Generally, sharper peaks with higher peak-to-background ratios were seen by XRD for this series compared to the standard series.
Some differences were noted in the lithium intercalation of V,O,, containing VO, (powder (3)) and V,O, (powder (4)) compared to the standard singlephase V,O,, case. XRD measurements showed that VO, and Vz05 were intercalated simultaneously with the single-phase V,O,,, and disappeared gradually as x approached N 5. The lithiation of the V,O,, phase much resembled the standard experiment, although some differences were noted: diffraction peaks were
b
Fig.6. The effect of water on intercalated single-phase V,O,, achieving - Li,,.,V,013 (a) before water addition; (b) after water addition and Cc>comparison with Li,,V,0,3.
2600 h 2400 *t: 2 2
2200
5
2000 1800
I
I
I
t
/
,
,
t
5
10
15
20
25
30
35
-20”-“---+ Fig. 7. The effect of water on intercalated single-phase V,O,, achieving - Li,V,O,, (a) before water addition; (b) after water addition and (c) comparison with Li,V,O,,.
generally broader, less detail could be seen in the diffractograms, and some LiXV60,3 peaks were missing for higher X. Also, when saturating the samples with lithium at x = 7, the crystallographic unit cell for the final Li,V,O,,-phase was slightly different for the single-phase V,O,, compared to the contaminated case (Fig. 5). The differences were more pronounced for powder (4) than for powder (3), and the disorder observed earlier in the V,O,, host remained. LiOH formation or ignition of organic lithium-containing species was seen for addition of x > 7. 3.4. Sensitivity
scope of this present work, some observations of the effect of H,O on the Li,V60,, phases can be stated here without any further discussion. On exposure to water, Li0.5V6O,3 returned to single-phase V,O,,, and LI,V~O,~ in the range 0.75 < x < 1.5 to L&&O,, (Fig. 6). For 2
LiX”6%
to water
Intercalated samples confined to a glovebox remained stabIe throughout the study, as ascertained by XRD measurements. Samples decomposed slightly in air after several weeks. Similar sensitivity to water was found for the standard and annealed V,O,, intercalation hosts ((1) and (5)). While a controlled study of the Li,V,O,,-water system lies outside the
Li,V,O,, + H,O 0
1
2
3
4
5
6
Fig. 8. Schematic rep~seatat~on of the influence of water on various Li,V,O,,-phases synthesized from single-phase V,O,,.
C. Lampe-hnerud
et al./Solid
Fig. 9. The local vanadium
coordination
Thereafter, samples seemed unaffected by treatment with water. This behaviour is summarized schematically in Fig. 8. For the lithiated samples derived from ground V,O,, and V,O,, containing VO,, a complete deintercalation occurred for x < 2 on exposure to water. The new unidentified phase (discussed above) was also found here for x > 2; peaks were broader and showed some intensity differences compared to the single-phase case. All samples containing V,O, were totally deintercalated on exposure to water for x < 8.
mass-%
VO,
impurity
Fig. 10. Calculated mean oxidation state V,O,, /VO, and V,0,3 /V,O, mixtures.
of
vanadium
State Ionics 81 (199.5) 189-199
for
in V,O,, V,O,,
197
and VO,.
4. Discussion All three vanadium oxide hosts studied here have similar local atomic arrangements, with the vanadium atoms octahedrally coordinated by six oxygens (Fig. 9). Distortion of these octahedra is common; typically, the vanadium atom may not be centred in the octahedron (as in V,O,,>, or one of the six oxygen atoms may be more distant from the central vanadium atom than the rest (as in V,O,>. These octahedra can also be linked together in several ways, which explains the formation of such a large number of different vanadium oxide phases. Phaseanalysis is usually made by XRD, but the similar VO, structures set the general detection level at N 5 mol%. XRD can only be used to identify essentially crystalline material, but complementary magnetic measurements can detect traces of non-crystalline VO, impurities. Spectroscopy, titration and oxidation are methods commonly used to determine the vanadium/oxygen ratio, e.g. [3-71. However, these methods will only give the mean oxidation state of vanadium. There are examples in the literature, e.g. [ 151, where the composition has been given as although VO, could be seen in the magv,O,,.05 netic measurements, indicating that at least three
198
C. L.anpe-&nerud
et al./Solid
VO,.-phases must be present. This is illustrated in Fig. 10, where the calculated mean oxidation state of vanadium is given for different mixtures of V,O,,/VO, and V,O,,/V,O,. An apparently ideal oxidation state of +4.33 can thus be obtained experimentally even at high VO?, contamination levels, if impurity oxides with both higher and lower vanadium oxidation states are present. Bearing in mind the above experimental limitations, it is found that the intercalation of lithium into V,O,, proceeds through the formation of four LiXV,0,3 phases: Li,,V,O,,, Li1.sV60,s, Li3V60,s all of which lack the magnetic metal-’ and Li,V,O,,; insulator transition seen in pure V,O,,. One complication that can arise is phase homogeneity, whereby the vanadium/ oxygen ratio can vary somewhat within a single-phase region. However, the lithium content can also vary for some intercalated phases, and the system should thus be best formulated as Li r*aX013+6. It is clear from the chemical analyses that larger differences are found around x = 3, suggesting a possible region of phase homogeneity. The magnetic measurements also show smooth transitions as x is varied within this region. The immediate formation of LiOH, the ignition of unreacted lithium, and the fact that the only difference found after 54 days of intercalation was a higher degree of crystallinity, combine to suggest that Li6V6O,3 is the final phase formed. No observed differences between the three phase-pure V,O,, powders ((l), (2) and (3)) could be detected, indicating no dependence of the mean vanadium oxidation state if it deviates by +0.04 from the ideal +4.33. However, the V,O,/VO, contaminated with mean vanadium oxidation states in the v,O,,, same region ((1) and (5)), led to important differences on lithium intercalation. Since all vanadium oxides used in this study can be intercalated, the anomalously high maximum level of intercalation can be explained by a high concentration of some “impurity phase” accommodating more than 1 Li/V; e.g. Li,V,O, [16]. The intercalation will also appear less efficient with other VO, species present. In none of the five powders studied is any other vanadium oxide phase formed at any stage of the intercalation. Control of water content during the experimental procedure proved critical throughout the study. The
State Ionics 81 (1995) 189-199
butyl-lithium is itself very sensitive to water; the solution exhibited a range of colours from dark yellow to green, and LiOH particles were often found in fresh bottles. This influences the lithium concentration in the stock solution, so that different experimental x-values will result. A lower lithiation rate was also obtained using glass bottles cleaned as described above, but then stored in atmosphere. It is possible, however, that the treatment of lithium intercalated single-phase V,O,, samples can provide a simple single-phase preparation technique.
Acknowledgements This work has earlier been supported by grants from DARPA (administered by The United States Office of Naval Research (ONR)), and currently by the Swedish Natural Science Research Council (NFR), and the Swedish Board for Technical Development (NUTEK) within the EEC (Joule II) Programme for Non-Nuclear Energy Sources. We would also like to thank Dr. Svante Axelsson and Anna Andersson for their help with the laboratory work and Mats Bexell for his help with the SEM analysis.
References Ill G.J. McCarthy, K.J. Martin, J.M. Holzer, W.M. Syvinski and D.W. Nordland, in: Advances in X-Ray Analysis, ed. C.S. Barrett (Plenum Press, New York, 1992) p. 17. 121AC. Gossard, F.J. Di Salvo, L.C. Erich, J.P. Remeika and H. Yasuoka, Phys. Rev. B 10 (1974) 4178. [31 D.W. Murphy, P.A. Christian, F.J. DiSalvo and J.N. Carides, J. Electrochem. Sot. 126 (1979) 497. [41 K.M. Abraham, J.L. Goldman and M.D. Dempsey, J. Electrochem. Sot. 128 (1981) 2493. and T. Jacobsen, Elec151 K. West, B. Zachau-Christiansen trochim. Acta 28 (1983) 1829. T. Jacobsen and S. Atlung, t61 K. West, B. Zachau-Christiansen, J. Power Sources 14 (1985) 235. 171 NC. Chaklanabish and H.S. Maiti, Solid State tonics 21 (1986) 207. k31H.K. Park, K. Podolski, Z. Munshi, W.H. Smyrl and B.B. Owens, J. Electrochem. Sot. 138 (1991) 627. [91 R. Koksbang, 1.1. Olsen, P.E. Tender, N. Knudsen and D. Fauteux, J. Appl. Electrochem. 21 (1991) 301. T. Gustafsson and J.O. Thomas, MRS 1101C. Lampe-Gnnerud, Proc. 293 (1993) 49.
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[I I] C. lampe-&merud and J.O. Thomas, J. Materials Chem. 5 (1995) 1075. 1123C. urns-~nnemd, J.O. Thomas, M. Hardgrave and S. Yde-Andersen, J. Efectrochem. Sot., to be published. 1131 C. Lampe-Gnnerud and J.O. Thomas, Ear. J. Solid State Inorg. Chem. 32 (1995) 293.
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[I41 K.-A. Wilhelmi, K. Waltersson and L. Kihlborg, Acta Chem. Stand. 25 (1971) 2675, [lSl D.W. M~hy, P. Christian, F.J. DiSalvo, J.N. Carides and J.V. Waszozak, J. Electrochem. Sot. 128 (1981) 2053. 2161 C. Delmas, S. Brethes and M. Menetrier, CR. Acad. Sci. 310 (1990) 1425.
Solid State Ionics 81 (1995) 189-199
IONICS
Chemical intercalation of lithium into a V60,, host Christina Lampe-onnerud
a, Per Nordblad b, John 0. Thomas a
a Institute of Chemistry, Uppsala University, Box 531, S-751 21 Uppsala, Sweden ’ Department of Technology, Uppsala University, Box 534, S-751 21 Uppsala, Sweden Received 13 January 1995; accepted for publication 1 August 1995
Abstract Chemical lithium insertion into five different types of V,O,,-based intercalation hosts have been performed in this study. Lii,5V6013, Li,V,O,, and Li,V,O,,; the latter phase representing the highest degree Four phases were identified: Li,,V,O,,, of intercalation. These phases are crystallographically and magnetically different not only from the phase-pure V,O,, host, but also from one another. The presence of other VO,-phases (10 mol% VO, or V,O,) caused slower lithium intercalation into V,O,,, different final phases and poor stability in the presence of water. Keywords: Cathode material; Intercalation; XRD; Magnetization measurements; Magnetic susceptibility; Butyllithium.
1. Introduction
In spite of the fact that V,O,, has been one of the most commonly used active cathode materials in modem thin-film battery design, the lithium insertion properties are still not properly understood. Its crystallographic and magnetic properties have been well characterized [ 1,2], but there would seem to be little agreement as to the lithium mechanisms, phases formed, and the maximum degree of intercalation. In 1979, Murphy and co-workers [3] performed topochemical reactions at room temperature and sugto be the maxigested Li,V,O,, and - Li,,,V,O,, mum lithium uptake for stoichiometric and nonstoichiometric V,O,,, respectively. They also found multiphase behaviour for x < 3 in Li,V,O,, , and a non-stoichiometric single-phase for x > 3. Abraham et al. [4] showed that 2-3 different phases were formed as the intercalation of lithium proceeded. The maximum x in Li,V,O,, was shown to vary be-
tween 4 and 8, x being higher for the non-stoichiometric than stoichiometric case. They also found an irreversible maximum uptake of 14 lithium atoms into V,O,, by electrochemical insertion. If all vanadium atoms in V60,, are reduced to oxidation state + 3, eight lithium atoms can be intercalated into V,O,,. This was found by West et al. [5] using butyl-lithiation; they also made a determination of the maximum uptake of lithium as a function of increasing oxygen content. X-ray data indicated that all phases were monoclinic with the space group C2/m. Electrochemical measurements showed three reversible intercalation phases: x = 1, 4 and ’ 8 in Li,V,O,, [6]. It was later concluded [7] that a single-phase reaction takes place for small lithium content (up to x - 2.51, and that ii,VO,(B) should form thereafter. Recent studies of mass-change accompanying the electrochemical insertion of lithium into V,O,, show discrepancies when more than one Li ion is intercalated per V60,, unit [8]. Battery
0167-2738/95/$09.50 0 1995 Elsevier Science B.V. All rights reserved SSDI 0167-2738(95)00181-6
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C. Lampc-~nneruder
al./Solid
State Ionics 81 (199.7) 189-199
studies by Koksbang et al. [9] have shown that 8 Li/V,O,, was only possible during the first cycle, and 6 Li/V,O,, thereafter. We have previously described the difficulties experienced in obtaining phase-pure V,O,, [lo], and determined the reaction mechanisms for the formation of various vanadium oxides by thermal decomposition of NH,VO, [II]. We present here the Li,V,O,, phases formed as x is increased, and compare the results obtained using single-phase and VO,,-contaminated V,O,,. These same materials have subsequently been incorporated in lithium-polymer batteries; see Ref. [12].
annealed V,O,, (Table 1). Powders cl), (3) and (4) were synthesized without any pre-treatment by thermal d~omposition of NH,VO, powder (Gesellschaft fur Elek~omet~lurgie, MBH, 99.9%). Synthesis of the standard V,O,, (1) was performed in a specially designed reaction chamber for a maximum over-pressure of 1.5 MPa and a heating rate of O.S’C/min in the range 25-500°C [12]. Powder (2) was made by grinding powder (1) in an agate mortar prior to lithiation in order to study the effects of strain and grain-size. Powder (3) containing VO, was made using a slightly higher over-pressure ( N 3 MPa) during the thermal decomposition. Powder (4) (V,O,, containing V,O,) was made by heating the NH,VO, in flowing N, atmosphere at l”C/min from ambient to 43O*C, and then holding this temperature for 10 h. Appropriate amounts of powders (3) and (4) were annealed at 600°C in evacuated quartz tubes for 48 h to obtain the last type of V,O,, (5).
2, Experimental Five different intercalation hosts were studied: (1) standard V,O,,, (2) ground V,O,,, (3) V60,s containing VO,, (4) V,O,, containing V,O, and (5)
Table I The various V,O,,-based intercalation hosts used for chemical lithiation Powder
Annealed
Standard
Ground
%0,3
WI3
(1)
(2) powder (1) ground
(3) thermal decomp. of NH,VG,
(4) thermal decomp. of NH,VO,
(5) annealed mixture of powders (3) and (4)
WA3
+ vo2
WA3
+ w,
‘6Ol3
preparation
thermal decomp. of NH.,VG,
mean oxidation state (titration)
4.30 f 0.01
4.30 rt 0.01
4.30 * 0.02 (calculated from molar ratios)
4.40 f 0.03 (calculated from molar ratios)
4.35 * 0.01
grain-size
5-25 pm
5-25 pm
2-10 pm
lo-25 pm
5-15 Pm
effect of sintering CXM)
agglomerate 300 pm
no agglomerate
aggIomerate 200 pm
agglomerate 200 pm
no aggio~mte
WA3
Yio13
90% v,o,, 10% vo,
phase analysis
+
90% v,o,,
i
10% v,o,
V&s
(XRD)
v,Gl, unit cell
a = 11.933(7) A b = 3.672(3) A c = 10.139(4) w @= 100X2(3)” V = 436.3(6) A s
11.8780) 3.673(2) 10.131(11) 100.68(6) 434.4(7)
11.923(6) 3.683(2) 10.150(7) 101.78(4) 436.3(S)
11.942(9) 3.685(3) 10.171(10) 100.60(6) 439.9(9)
I 1.943(8) 3.686(3) 10.180(7) 100.86(6) 440.X6)
C. Lampe-&nerud
et al./Solid
Chemical lithiation was performed in 25 mL glass bottles, each sealed with a replaceable teflon-silicon septum as the vanadium oxide was weighed in. The powder was then completely covered with freshly distilled hexane (4-5 mL) and the atmosphere changed to dry Ar or N, before transferring the bottle to a glovebox ( < 1 ppm H,O and 0,). The lithiation was performed by slowly adding n-butyllithium (Merck, 1.6 M in hexane) under the hexane surface using a Hamilton syringe (1 .OOO+ 0.005 mL) fitted with exchangeable needles. The lithium/ vanadium molar ratio was varied: 0.5
State Ionics 81 (1995) 189-199
191
120°C prior to each experiment. Each lithiation reaction was interrupted by evaporating the hexane at 70°C under a flowing Ar atmosphere, and immediately transferring the samples back to the glovebox. The effects of ageing were tested with regard to spontaneous decomposition (both in a glovebox and in air), and to stability with respect to water (by adding 15 mL water followed by an equilibration time of lo-20 h). The total concentrations of vanadium and lithium were determined for experiments performed with standard V,O,, (1) using inductively coupled plasma atomic emission spectrometry (Spectroflame, Spectra Kleve). lo-20 mg samples were boiled to complete solvation in HCl(6 mL, 12 M) and HNO, (2 mL, 14 M), and diluted with milliQ-filtered water (Millipore Bedford, MD) on cooling. The emission from vanadium and lithium was measured for 3 X 10 s at 3 11.071 and 670.784 nm, respectively. Standard cali-
a
b
30
40
50
60
70
80
-2e+ Fig. 1. X-ray diffractograms for various single-phase V,O,, powders used in this study: (a) an annealed stoichiometric mixture (V,O,,, powder 5) (0 0 l-reflections marked); (b) the result of thermal decomposition of NH,VO, (standard V,O,,, powder 1) and (c) a ground V,O,, (powder 2). All diffractograms can be compared with a calculated diffraction pattern cd).
192
C. Lmnpe-6nnerud
et al./Solid
bration solutions (Referensmaterial AB, Sweden) were prepared in the same reagent matrix. Duplicate samples were analyzed to check homogeneity. All samples were characterized in terms of phase and degree of crystallinity by X-ray diffraction (XRD) using a STOE & CIE GmbH STADI powder diffractometer (CuKa, radiation) fitted with a 45” curved position-sensitive detector. The stabilities of the different phases formed upon lithiation were assessed; exposure times varied from 10 min to 10 h. The grain-size and morphology of the starting vanadium oxides were also studied in a Zeiss DSM 960A scanning electron microscope (SEM). The VO,, contamination levels were determined by establishing reference diffractograms using weighed-in mixtures of single-phase V,O,,, VO, and V,O, [I 1,131. Potentiometric titrations [13] were made to determine the mean vanadium oxidation state in the single-phase V,O,,. Magnetization versus temperature (5 kG; 5-50 K) was recorded using a Quantum Design MPMS SQUID-magnetometer for the three different singlephase V,O,, samples ((11, (2) and (5)) and for the standard lithiated V,O,, series (1).
3. Results 3.1. The vanadium oxide phases All three single-phase V,O,, samples contained the same thin (< 1 pm), needle-like crystallites, while only the standard V,O,, sintered into agglomerates (- 300 pm>. The V,O,, (5) was single-phase (Fig. la), showing good agreement with the calculated V,O,, diffractogram (Fig. Id). Titrations gave the mean oxidation state of vanadium as 4.35 f 0.01, corresponding to the slightly oxygen-rich stoichiometry V,O,,,s,. On the other hand, the standard V,O,, (5) was found to be oxygen deficient, with a mean oxidation state of 4.30 f 0.01 (V,O,,,,). The corresponding X-ray diffractogram (Fig. lb) indicated a crystalline single-phase V,O,, with somewhat lower 0 0 I-reflection intensities. This effect is much more pronounced in the ground powder (Fig. lc), and a smaller crystallographic a-axis could be noted (Table 1). The magnetization measurements on the different single-phase V60,, samples (11, (2) and (5)
State Ionics 81 (1995) 189-199
M (emu/g)
0
I
/
’
!
I
I
0
50
100
150
I
I
1
200 T(K)
250
I
I
I
I
300
350
400
Fig. 2. Magnetisation versus temperature for the various singlephase V,O,, powders (1, 2 and 5) used in this study (H = 5 kOe).
exhibited certain differences compared to earlier studies [2,3] (Fig. 2). The metal-insulator transition (at 150 K) is broadened for the standard and annealed V,O,, samples compared to the ground sample. The decrease in the susceptibility at 60 K can be related to the antiferromagnetic transition described in [2]. A very weak anomaly around 340 K indicates that minor amounts of VO, may be present in the thermally decomposed V,O t s. The mixed-phase oxides were determined ( f 2%) from the reference diffractograms to be 90 mol% V,O,, and 10 mol% VO, or V,O,, respectively. Both powders had sintered into N 200 pm agglomerates, but contained crystallites of very different morphology. The powder containing VO, resembled closely single-phase V60,s, with small needle-like crystallites (< 5 pm3); whereas the powder containing V,O, were regularly shaped crystallites (N 15 p,m3). XRD showed that both powders were crystalline, but that the oxide containing V,O, had broader peaks and lower intensities for the V60L3 (0 0 Z&reflections, indicating the introduction of preferred orientation or some type of structural disorder. 3.2. Lithiated V, O,, All samples, regardless of their V,O,, starting material, were black after intercalation. Four different Li,V,O,, phases can be identified on lithiating the standard single-phase V60,3, none of which ex-
et al. /Solid State ionics 81 (1995) 189-199
,
I
I
,
20
30
40
50
60
-----r-----------r-------
IO
193
C. Lumpe-&nerud
Fig. :3. X-ray diffractograms for the lithium intercalation products formed from standard single-phase V,O,, (powder 1): (a) Li,,V,0,3, Li,,,VhO,,, (c) Li3V,0,, and (d) Li,V,O,,.
hibited the metal-insulator transition at 150 K. The X-ray diffractogram for theofirst phase, LiO.dV,O,, (Fig. 3a) (a = 11.930(5) A, b = 3.680(2) A, c = 10.147(6) A, @= 100.85(5)0, V= 437.5(3) .k3>, resembles closely the non-intercalated V6013; it can be indexed in the same C2/m space group and almost the same cell [ 141. The magnetization measurements (Fig. 4) exhibit a continuous increase in magnetization as the temperature is lowered. The next phase, which begins to form immediately as the lithium content is raised above x = 0.5, reaches fuI1 intercalation at Li,,5V60,3. New XRD peaks appear (Fig. 3b), and the space group and cell have changed dramatically. Magnetic measurements contain a new feature; a weak bump at 40 K, indicating some antiferromagnetic ordering (Fig. 4). An increase of the magnetization was observed with decreasing temperature. This antiferromagnetic behaviour was more pronounced for the third phase, Li,V,O,,, and an increase in magnetization could be seen at the lowest temperatures measured. XRD suggested sig-
(b)
nificant structural rearrangement with respect to Li1.5V6013(Fig. 3c), with both positions and intensities of reflections changing. A final phase begins to M bmu/p) I
J ,+ \
0 0
10
+
+
*
1
20
f
.f
-i
/
,
30
40
$
..
50
T m Fig. 4. Magnetisation versus temperature for the LixV,OIB phases (x = 0.5, 1.5, 3 and 6) compared with non-intercalated V,0,3
(x=OO)(H=5kOd.
194
C. Lmnpe-herud
et al./Solid
form for x > 3; higher background and only a few broad peaks appear in the X-ray diffractograms, suggesting a decrease in the degree of crystallinity (Fig. 3d). The magnetic measurements were temperature independent at low temperatures, but showed a higher response than for pure V,O,, (Fig. 4). When samples with x > 6 (x,,, = 10) were exposed to air, either white particles formed or the sample ignited. The white particles were identified by XRD as LiOH. The diffractograms (Fig. 3d) and the chemical analyses (after the removal of LiOH)
h .s E z.
State Ionics 81 (1995) 189-199
for all higher values of x (up to x = 10) were the same as for x = 6. This final phase was therefore concluded to be Li,V,O,,. A slight increase in crystallinity could also be noted for samples intercalated for a longer time. Chemical analysis indicated a lower x-value in Li,V,O,, compared to the amount of butyl-lithium added, and also revealed some inhomogeneity in the lithium content of the intercalated samples (Table 2). The ground V,O,, samples showed the same sequence of four lithiated phases. However, the diffrac-
b
6000
5000
4000
Fig. 5. The final Li,V,O,, obtained from intercalation into (a) single-phase V,O,,; containing V,O, (90/10 mol%). The inset (22.5’ < 20 < 24.3’) shows a systematic
(b) V,O,, containing VO, (90/10 shift in the strongest reflection.
mol%), (c) V,O,,
Table 2 Results from chemically lithiated standard V,O,, Bu-Li added for x Li/V,O,, 0.50 0.75 1.00 I .25 1.50
1.75 2.00 3.00 4.00 5.00 6.00 7.00 t 8.00
Li/V, ratio from chemical analysis 0.44 * 0.01 0.74f 0.01 0.95 f 0.03 1.17+0.01 1.2140.03 1.51 fO.01 1.9s+o.12 3.1410.21 3.44f0.52 4.99 f 0.08 5.33+0.05 5.87f.O.01 a sample ignited ’
’ White LiOH formed.
tograms showed that the preferred orientation or grinding-induced disorder remained, and some peak intensities were consistently lower than the as-made
V,O,, intercalation host. A slightly higher lithium content could he noted in intercalated samples, and some inhomogeneity was still observed. Similar results were obtained for lithiation of the annealed V,0t3. For x > 6, the sample again ignited or white LiOH was formed. Generally, sharper peaks with higher peak-to-background ratios were seen by XRD for this series compared to the standard series.
Some differences were noted in the lithium intercalation of V,O,, containing VO, (powder (3)) and V,O, (powder (4)) compared to the standard singlephase V,O,, case. XRD measurements showed that VO, and Vz05 were intercalated simultaneously with the single-phase V,O,,, and disappeared gradually as x approached N 5. The lithiation of the V,O,, phase much resembled the standard experiment, although some differences were noted: diffraction peaks were
b
Fig.6. The effect of water on intercalated single-phase V,O,, achieving - Li,,.,V,013 (a) before water addition; (b) after water addition and Cc>comparison with Li,,V,0,3.
2600 h 2400 *t: 2 2
2200
5
2000 1800
I
I
I
t
/
,
,
t
5
10
15
20
25
30
35
-20”-“---+ Fig. 7. The effect of water on intercalated single-phase V,O,, achieving - Li,V,O,, (a) before water addition; (b) after water addition and (c) comparison with Li,V,O,,.
generally broader, less detail could be seen in the diffractograms, and some LiXV60,3 peaks were missing for higher X. Also, when saturating the samples with lithium at x = 7, the crystallographic unit cell for the final Li,V,O,,-phase was slightly different for the single-phase V,O,, compared to the contaminated case (Fig. 5). The differences were more pronounced for powder (4) than for powder (3), and the disorder observed earlier in the V,O,, host remained. LiOH formation or ignition of organic lithium-containing species was seen for addition of x > 7. 3.4. Sensitivity
scope of this present work, some observations of the effect of H,O on the Li,V60,, phases can be stated here without any further discussion. On exposure to water, Li0.5V6O,3 returned to single-phase V,O,,, and LI,V~O,~ in the range 0.75 < x < 1.5 to L&&O,, (Fig. 6). For 2
LiX”6%
to water
Intercalated samples confined to a glovebox remained stabIe throughout the study, as ascertained by XRD measurements. Samples decomposed slightly in air after several weeks. Similar sensitivity to water was found for the standard and annealed V,O,, intercalation hosts ((1) and (5)). While a controlled study of the Li,V,O,,-water system lies outside the
Li,V,O,, + H,O 0
1
2
3
4
5
6
Fig. 8. Schematic rep~seatat~on of the influence of water on various Li,V,O,,-phases synthesized from single-phase V,O,,.
C. Lampe-hnerud
et al./Solid
Fig. 9. The local vanadium
coordination
Thereafter, samples seemed unaffected by treatment with water. This behaviour is summarized schematically in Fig. 8. For the lithiated samples derived from ground V,O,, and V,O,, containing VO,, a complete deintercalation occurred for x < 2 on exposure to water. The new unidentified phase (discussed above) was also found here for x > 2; peaks were broader and showed some intensity differences compared to the single-phase case. All samples containing V,O, were totally deintercalated on exposure to water for x < 8.
mass-%
VO,
impurity
Fig. 10. Calculated mean oxidation state V,O,, /VO, and V,0,3 /V,O, mixtures.
of
vanadium
State Ionics 81 (199.5) 189-199
for
in V,O,, V,O,,
197
and VO,.
4. Discussion All three vanadium oxide hosts studied here have similar local atomic arrangements, with the vanadium atoms octahedrally coordinated by six oxygens (Fig. 9). Distortion of these octahedra is common; typically, the vanadium atom may not be centred in the octahedron (as in V,O,,>, or one of the six oxygen atoms may be more distant from the central vanadium atom than the rest (as in V,O,>. These octahedra can also be linked together in several ways, which explains the formation of such a large number of different vanadium oxide phases. Phaseanalysis is usually made by XRD, but the similar VO, structures set the general detection level at N 5 mol%. XRD can only be used to identify essentially crystalline material, but complementary magnetic measurements can detect traces of non-crystalline VO, impurities. Spectroscopy, titration and oxidation are methods commonly used to determine the vanadium/oxygen ratio, e.g. [3-71. However, these methods will only give the mean oxidation state of vanadium. There are examples in the literature, e.g. [ 151, where the composition has been given as although VO, could be seen in the magv,O,,.05 netic measurements, indicating that at least three
198
C. L.anpe-&nerud
et al./Solid
VO,.-phases must be present. This is illustrated in Fig. 10, where the calculated mean oxidation state of vanadium is given for different mixtures of V,O,,/VO, and V,O,,/V,O,. An apparently ideal oxidation state of +4.33 can thus be obtained experimentally even at high VO?, contamination levels, if impurity oxides with both higher and lower vanadium oxidation states are present. Bearing in mind the above experimental limitations, it is found that the intercalation of lithium into V,O,, proceeds through the formation of four LiXV,0,3 phases: Li,,V,O,,, Li1.sV60,s, Li3V60,s all of which lack the magnetic metal-’ and Li,V,O,,; insulator transition seen in pure V,O,,. One complication that can arise is phase homogeneity, whereby the vanadium/ oxygen ratio can vary somewhat within a single-phase region. However, the lithium content can also vary for some intercalated phases, and the system should thus be best formulated as Li r*aX013+6. It is clear from the chemical analyses that larger differences are found around x = 3, suggesting a possible region of phase homogeneity. The magnetic measurements also show smooth transitions as x is varied within this region. The immediate formation of LiOH, the ignition of unreacted lithium, and the fact that the only difference found after 54 days of intercalation was a higher degree of crystallinity, combine to suggest that Li6V6O,3 is the final phase formed. No observed differences between the three phase-pure V,O,, powders ((l), (2) and (3)) could be detected, indicating no dependence of the mean vanadium oxidation state if it deviates by +0.04 from the ideal +4.33. However, the V,O,/VO, contaminated with mean vanadium oxidation states in the v,O,,, same region ((1) and (5)), led to important differences on lithium intercalation. Since all vanadium oxides used in this study can be intercalated, the anomalously high maximum level of intercalation can be explained by a high concentration of some “impurity phase” accommodating more than 1 Li/V; e.g. Li,V,O, [16]. The intercalation will also appear less efficient with other VO, species present. In none of the five powders studied is any other vanadium oxide phase formed at any stage of the intercalation. Control of water content during the experimental procedure proved critical throughout the study. The
State Ionics 81 (1995) 189-199
butyl-lithium is itself very sensitive to water; the solution exhibited a range of colours from dark yellow to green, and LiOH particles were often found in fresh bottles. This influences the lithium concentration in the stock solution, so that different experimental x-values will result. A lower lithiation rate was also obtained using glass bottles cleaned as described above, but then stored in atmosphere. It is possible, however, that the treatment of lithium intercalated single-phase V,O,, samples can provide a simple single-phase preparation technique.
Acknowledgements This work has earlier been supported by grants from DARPA (administered by The United States Office of Naval Research (ONR)), and currently by the Swedish Natural Science Research Council (NFR), and the Swedish Board for Technical Development (NUTEK) within the EEC (Joule II) Programme for Non-Nuclear Energy Sources. We would also like to thank Dr. Svante Axelsson and Anna Andersson for their help with the laboratory work and Mats Bexell for his help with the SEM analysis.
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[I I] C. lampe-&merud and J.O. Thomas, J. Materials Chem. 5 (1995) 1075. 1123C. urns-~nnemd, J.O. Thomas, M. Hardgrave and S. Yde-Andersen, J. Efectrochem. Sot., to be published. 1131 C. Lampe-Gnnerud and J.O. Thomas, Ear. J. Solid State Inorg. Chem. 32 (1995) 293.
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[I41 K.-A. Wilhelmi, K. Waltersson and L. Kihlborg, Acta Chem. Stand. 25 (1971) 2675, [lSl D.W. M~hy, P. Christian, F.J. DiSalvo, J.N. Carides and J.V. Waszozak, J. Electrochem. Sot. 128 (1981) 2053. 2161 C. Delmas, S. Brethes and M. Menetrier, CR. Acad. Sci. 310 (1990) 1425.