Lithium insertion behaviour of silver vanadium bronze

Solid State Ionics 99 (1997) 71–78

Lithium insertion behaviour of silver vanadium bronze

*Jin Kawakita , Yasushi Katayama, Takashi Miura, Tomiya KishiDepartment of Applied Chemistry, Faculty of Science and Technology, Keio University, Hiyoshi 3-14-1, Kohoku-ku, Yokohama 223,

Japan

Received 28 August 1996; accepted 4 February 1997

Abstract

Ag V O has been prepared by the ion exchange reaction in the molten salt of AgNO using Na V O . This oxide has11x 3 8 3 1.2 3 8

a similar layer structure to M V O (M 5 Li and Na), and its lattice parameter has been determined. Up to four moles of11x 3 8

lithium (x 5 4) in Li Ag V O are accommodated electrochemically. The discharge process showed that after deposition ofx 1.2 3 8

metallic silver by reduction of Ag(I) prior to V(V) and simultaneous occupation of the octahedral site by inserted Li(I),additional lithium was inserted into Li V O . The charging process showed extraction of three lithiums from Li V O and1.2 3 8 4 3 8

no return of the silver element back to the original structure with oxidation.

Keywords: Silver; Vanadium; Lithium; Molten salts; Insertion

1. Introduction destruction of the structure on lithium insertion andextraction [5,6]. The diffusion coefficient of lithium

˜Vanadium oxides, such as V O and V O , are (D ) in Li V O is higher than that in V O and2 5 6 13 Li 11x 3 8 2 51regarded as promising candidates of the cathode V O because Li ions in the octahedral sites do not6 13

1active materials for lithium secondary batteries [1– interfere with the jump of the inserted Li ions from3]. Lithium vanadate, Li V O , is an attractive a tetrahedral site to the neighboring one [5]. It was11x 3 8

˜material in terms of the specific energy and re- reported that increases of D are also observedLi

versibility on discharge and charge [4–6]. It has a accompanying expansion of the layer distances by1 1layer structure and Li ions in the octahedral sites introduction of the alkali metal ions, such as Na

2 1are surrounded by oxygen atoms of V O , in which and K ions, into the octahedral sites between the3 8

the vanadium elements are in pentavalent state. The layers [7–9]. Such an enhancement is expected forlayer structure is stabilized by a strong bonding the complex compound of V O and Ag O, i.e.2 5 2

1between the Li ion and the layer, resulting in little Ag V O . However, reduction and oxidation of2 4 11

silver prior to those of vanadium occur in Ag V O2 4 11

on discharge and charge, respectively [10–13].In this paper the authors report a new preparation

* method of Ag V O having the layered structureCorresponding author. Tel: (181-45) 563-1141; fax: (181- 11x 3 8

45) 563-0446; e-mail: [email protected] similar to M V O (M 5 Li and Na) by ion11x 3 8

0167-2738/97/$17.00 1997 Elsevier Science B.V. All rights reservedPII S0167-2738( 97 )00120-3

72 J. Kawakita et al. / Solid State Ionics 99 (1997) 71 –78

1 1exchange of Na ions in Na V O with Ag ions LiClO /PC (Mitsubishi Chemical, water content11x 3 8 4

in molten salts, and the electrochemical lithium [H O] , 20 ppm) solution was used as an elec-2

insertion and extraction processes of this compound trolyte. Vanadium oxide powder ( , 38 mm),were investigated. acetylene black (Denka black, Denkikagaku Kogyo)

and poly(tetrafluoroethylene) (PTFE) were mixed asa weight ratio of 80:15:5 and pressed on a porous

4 222. Experimental nickel net at 2 3 10 N ? cm to prepare the pellets.The pellets were used as the working electrodes with

2V O was prepared by thermal decomposition of surface areas of 1.96 cm . The surfaces, except the2 5

NH VO (Soekawa Chemicals, . 99% purity) at working electrode areas, were insulated with silicone4 3

5008C. Na V O was used as a starting material for resin. All the test cells were fabricated in a glove box1.2 3 8

the reason described later. It was synthesized as filled with argon gas. Galvanostatic discharge was22described by Pistoia et al. [7]. Na CO (Junsei performed at the current density of 0.1 mA ? cm2 3

Chemical Co. Ltd., . 99.5% purity) and V O were with a potentiostat (Toho Technical Research, 20922 5

mixed in an agate mortar in a molar ratio of 1.2:3, and PS-08). Cyclic voltammetry was performed at21and melted at 6208C for 24 h in the air. After the the scan speed of 0.01 mV? s using the potentiostat

melt was cooled slowly down to room temperature, described above and a function generator (HokutoNa V O was obtained. Ag Na V O with vari- Denko, HB-104).1.2 3 8 y 1.22y 3 8

ous y values was prepared by reacting Na V O1.2 3 8

with excess molten AgNO (Wako, . 99.8% purity)3

in a molar ratio of 1:30 in an alumina crucible for 3. Results and discussion0.5 | 8 h in air at a temperature (2258C) above themelting point of AgNO . Silver contents ( y) in the 3.1. Preparation of Ag V O3 1.2 3 8

samples were determined by atomic absorption anal-ysis (Hitachi, 180-55 AAS) for silver. Ag V O as Casalot et al. synthesized Ag V O by the solid1.2 3 8 11x 3 8

the reference material was synthesized by the solid state reaction of V O and Ag O [14]. The crystal2 5 2

state reaction as follows: Ag O (Kojima Chemical structure has not been determined yet. The lattice2

Co. Ltd., . 98% purity) and V O were mixed in a parameters of Ag V O were refined in this work.2 5 11x 3 8

molar ratio of 1.2:3 and heated at 5308C for 24 h The unit cell parameters of Ag V O was deter-1.2 3 8

under O atmosphere. The samples were character- mined from the data of the sample obtained by the2

ized by X-ray powder diffraction (XRD, Rigaku, solid state reaction. The lattice parameters ofRINT-1300) using Cu Ka radiation with Ni filter and M V O (M 5 Ag, Na [15] and Li [16]) are1.2 3 8

infrared (IR) spectroscopic methods (Bio-Rad, FTS- compared in Table 1, and observed and calculated65, KBr disk method). crystal data of Ag V O is listed in Table 2. The1.2 3 8

Electrochemical measurements were performed determination of the detailed crystal structure ofwith a cylindrical glass cell. Lithium wires (Aldrich, Ag V O is under way.11x 3 8

1. 99.9% purity, 3.2 mm in diameter) were used as The authors intended to substitute Li ions in

23 1the counter and reference electrodes. A 1 mol ? dm Li V O with Ag ions in order to prepare11x 3 8

Table 1Unit cell parameters of M V O (M5Ag, Na, and Li)1.2 3 8

a bM5Ag M5Ag M5Na [15] M5Li [16]

˚a (A) 7.37(1) 7.29(7) 7.36(1) 6.68(2)˚b (A) 3.60(3) 3.59(9) 3.61(4) 3.60(1)˚c (A) 12.23(3) 12.24(1) 12.19(1) 12.03(2)

b (deg.) 107.2(7) 107.1(6) 107.7(9) 107.8a Solid state reaction.b Ion exchange reaction.

J. Kawakita et al. / Solid State Ionics 99 (1997) 71 –78 73

Table 2Observed and calculated spacing hkl for Ag V O by solid state1.2 3 8

reaction

˚ ˚hkl Calcd. (A) Obs. (A) I /I0

¯101 7.020 7.008 S¯102 5.341 5.330 M¯103 3.938 3.933 M¯201 3.685 3.679 M

200 3.519 3.516 VS011 3.444 3.440 M

¯111 3.206 3.204 W¯203 3.110 3.106 S

111 2.992 2.990 M202 2.683 2.681 M112 2.664 2.662 M

¯211 2.577 2.574 W¯105 2.445 2.441 M

300 2.35 2.344 S¯303 2.346 2.339 S¯114 2.321 2.319 M¯205 2.284 2.294 M¯214 2.146 2.144 M

114 2.027 2.036 W¯311 2.023 2.021 M¯305 1.974 1.971 M

311 1.865 1.863 M¯402 1.843 1.841 M

020 1.802 1.801 M312 1.737 1.737 M

¯412 1.641 1.638 M¯222 1.603 1.602 S

Fig. 1. XRD patterns of the ion-exchanged samples,Ag Na V O . (a) y50 (starting material), (b) y50.8 (0.5 h),y 1.22y 3 8

(c) y51.0 (1.0 h), (d) y51.2 (2.0 h), (e) y51.2 (4.0 h), (f) y51.2(solid state reaction).Ag V O by the ion exchange reaction in the11x 3 8

molten salt. When Li V O was used as the11x 3 81starting material, Li ions were unable to be substi- samples obtained by the reaction for more than two

1 1tuted with Ag ions. Li ions in the octahedral sites hours gave the identical XRD patterns, and their22were bonded strongly to O ions since the radius of silver contents did not increase more than y 5 1.2.

1 ˚the Li ion (0.90 A [17]) was smaller than that of But XRD pattern of Ag V O prepared by the ion1.2 3 81 ˚the Ag ion (1.29 A [17]). Alternatively, Na V O exchange reaction had additional peaks marked by11x 3 8

having a layer structure similar to that of Li V O filled circles which were not observed in that of11x 3 8

was used as a starting material for preparing Ag V O prepared by the solid state reaction.1.2 3 81Ag V O by the ion exchange reaction. Na ions These peaks might be derived from some impurities11x 3 8

22in Na V O were linked less strongly to the O such as Ag O and AgVO . Furthermore, some peaks11x 3 8 2 3

ions in the octahedral sites than in the case of in the XRD pattern of the former were shifting to a1 ˚Li V O , since the radius of Na (1.16 A [17]) higher angle compared with that of the latter. The11x 3 8

1was only a little smaller than that of Ag ion. lattice parameters of Ag V O prepared by the ion1.2 3 8

Fig. 1 shows the change of XRD patterns of the exchange reaction were calculated from the patternobtained samples, Ag Na V O , and Ag V O in Fig. 1e except some peaks attributed to impurities,y 1.22y 3 8 1.2 3 8

obtained by the solid state reaction. Some additional and listed in Table 1. It was found that a-axis ofpeaks other than Na V O were observed in the Ag V O prepared by the ion exchange reaction11x 3 8 1.2 3 8

sample prepared by the ion exchange reaction. The was shorter than that by the solid state reaction while


the substantial difference was not found for other three obvious peaks described above, which shiftedparameters, b, c-axis and b-angle. A possible expla- to lower wave numbers compared to Na V O .1.2 3 8

nation was that the amount of AgNO used as When Ag atoms between the layers were bound to3

molten salt seemed not to be in excess enough to the oxygen atoms by covalent bonding, the bond1 1substitute Ag ions for Na ions completely, and strength between vanadium and oxygen atoms was1that some Na ions remained between the layers. considered to be weakened. As substitution of silver

The y value determined as 1.2 by chemical analysis for sodium proceeded, however, all these absorptionwas considered to be the sum of Ag V O includ- bands became broader for y , 1.0, and some addi-1.2 3 8

1ing Na in the matrix and silver compounds existing tional peaks also appeared at y 5 1.2. The differenceas some impurities. These results revealed that observed between the samples obtained by ionAg V O has a layered structure similar to exchange and by the solid state reaction seen in IR11x 3 8

Li V O . spectra might be also caused by the remaining of11x 3 81IR spectra of Ag Na V O are shown in Fig. Na ions between the layers and by contaminationy 1.22y 3 8

2. It is known that the absorption bands near 950 | of impurities such as AgVO in the former.3211000 and 740 cm are attributed to the stretching

vibration between vanadium and oxygen [18]. 3.2. Electrochemical measurement of Ag V O by1.2 3 8

Ag V O obtained by the solid state reaction had solid state reaction1.2 3 8

The discharge curves of M V O (M 5 Li, Na1.2 3 8

and Ag) samples prepared by the solid state reactionare shown in Fig. 3. The potential of silver vanadatewas the highest during discharge, and the amount ofinserted lithium increased with reduction of Ag(I) toAg(0), and four moles of lithium per formula unitwere accommodated. XRD patterns of the lithiatedsamples, Li Ag V O , are shown in Fig. 4. Deposi-x 1.2 3 8

tion of metallic silver (marked by arrows) indicated

Fig. 2. IR spectra of the ion-exchanged samples, Ag Na V O .y 1.22y 3 8

(a) y50 (starting material), (b) y50.8 (0.5 h), (c) y51.0 (1.0 h),(d) y51.2 (2.0 h), (e) y51.2 (4.0 h), (f) y51.2 (solid state Fig. 3. Discharge curves of M V O . (a) M5Na, (b) M5Li, (c)1.2 3 8

reaction). M5Ag (solid state reaction).


Fig. 5. Discharge and charge curves of Ag V O (solid state1.2 3 8

reaction) with the various cut-off potential. ———: 2.7 V, – –:2.5, ? ? ?: 2.1 V.

essentially similar to that of Li V O . The differ-1.2 3 8

ences in x values on discharge and recharge cyclescorresponded to the amount of metallic silver fromunrechargeable Ag(I) in the oxides, and increase inthe difference at deeper cut-off potential indicated anFig. 4. XRD patterns of the lithiated samples, Li Ag V O . (a)x 1.2 3 8

existence of unextractive Li(I) ions in the oxides.x50 (starting material), (b) x50.5, (c) x51.0, (d) x51.5, (e)x52.0, (f) x54.0. Fig. 7 showed cyclic voltammogram of

Ag V O . Two cathodic peaks near 2.7 and 2.5 V1.2 3 8

that the silver component was reduced prior to the corresponded to lithium insertion and occupation invanadium component. the two respective sites with two different stabiliza-

The discharge and charge curves with various tion energies, and their corresponding anodic peakcut-off potentials are shown in Fig. 5. The x values was observed at 2.8 V. The shoulder-like cathodicon recharging were less than those on discharging by peak near 2.2 V was considered to be assigned tothe amounts 1.2 to 1.5, depending on the cut-off lithium insertion into a defect rock-salt type structurepotential, even when recharging continued up to 3.6 after phase transition to Li V O and the anodic peak4 3 8

V. In the XRD patterns shown in Fig. 6, the peaks which appeared at 2.4 V, found only for Li V O11x 3 8

corresponding to either metallic silver (marked by type oxides [20–22]. The current density in thearrows) and Li V O were observed in the patterns cathodic peak near 2.7 V at first cycle decreased at1.2 3 8

of the recharged samples. These results indicated that the second cycle. Furthermore, metallic silver formedmetallic silver deposited during discharge was not by reduction of Ag(I) at the first cycle was notinserted into the layers of the original structure. This oxidized because the current density in the anodicobservation was different form that reported by West peak near 2.8 V was almost constant and no addition-et al. [19], who described that metallic silver de- al anodic peaks corresponding to Ag(0) → Ag(I)posited during discharge was oxidized on recharge to appeared over 3.0 V at both cycles. These results alsoform Ag V O . The discharge curve of the sample indicated no recovery of metallic silver back to the2 4 11

after the first cycle of discharge and charge was original structure.


Fig. 7. Cyclic voltamograms of Ag V O (solid state reaction)1.2 3 8

———: first cycle, ? ? ?: second cycle.

Fig. 6. XRD patterns of Ag V O after first cycle with the1.2 3 8

various cut-off potentials (a) starting material, (b) 2.9 V, (c) 2.7 V,(d) 2.5 V, (e) 2.1 V, (f) Li V O .1.2 3 8

3.3. Electrochemical measurement of Ag V O by1.2 3 8

ion exchange reaction

The discharge curves of Ag V O obtained by1.2 3 8

both preparation methods are shown in Fig. 8. Theinitial and final stages of the discharge curve weredifferent from each other. This phenomena might becaused by the effect of the impurities, such as the Fig. 8. Discharge curves of Ag V O . (a) ion exchange reaction,1.2 3 8

1 (b) solid state reaction.occupation by Ag ions of the different sites withdifferent preparation method, or the difference in theparticle size for both samples. XRD patterns ofLi Ag V O obtained by the ion exchange reaction potentials at 2.0 and 2.5 V are shown in Fig. 10. Thex 1.2 3 8

were shown in Fig. 9. In this case the deposition of x values on recharging were less than those onmetallic silver (marked by arrows) indicated that discharging, so metallic silver deposited duringreduction from Ag(I) to Ag(0) preceded to that from discharge was not inserted into the layers duringV(V) to V(IV). Appearance of Li V O was not recharging. This consideration was confirmed by the1.2 3 8

clearly confirmed in these patterns. fact that the peaks corresponding to either metallicThe discharge and charge curves with the cut-off silver (marked by arrows) or Li V O , were ob-1.2 3 8


Fig. 10. Discharge and charge curves of Ag V O (ion exchange1.2 3 8

reaction) with the cut-off potentials of 2.5 (———) and 2.0 V(? ? ?).

Fig. 9. XRD patterns of the lithiated samples, Li Ag V O . (a)x 1.2 3 8

x50 (starting material), (b) x50.5, (c) x52.0, (d) x53.0, (e)x54.0.

served in XRD patterns of the recharged sample asshown in Fig. 11.

Fig. 12 shows cyclic voltammograms ofAg V O obtained by both preparation methods.1.2 3 8

Ag V O by the ion exchange reaction had addi-1.2 3 8

tional cathodic peaks near 2.9 and 2.3 V, probablyrepresenting reduction of Ag(I) to Ag(0) and lithiuminsertion into new phase, respectively, which wascaused by the above mentioned effect. Othercathodic and anodic peaks appeared at the same Fig. 11. XRD patterns of Ag V O (ion exchange reaction) as the1.2 3 8

starting material (a), after first cycle with the cut-off potentials ofpotential range as for the samples by the solid state2.5 V (b) and Li V O (c).1.2 3 8reaction.

These results are explained by the reduction1 2processes during discharge: [Li] [0.2Ag] V O 1 3Li 1 3eOcta Tetra 3 8

→ 0.2Ag(0) 1 [Li] [3Li] V O , (2)Octa Octa 3 81 2[Ag] [0.2Ag] V O 1 Li 1 eOcta Tetra 3 8

→ Ag(0) 1 [Li] [0.2Ag] V O , (1) and the oxidation process during charge:Octa Tetra 3 8


process occurs, oxidation of deposited silver andformation of Ag V O would not occur during the1.2 3 8

subsequent charge process, but the formation of1Li V O by insertion of Li ions would be prefer-11x 3 8

able.

References

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[5] G. Pistoia, S. Panero, M. Tocci, R.V. Moshtev, V. Manev,Solid State Ionics 13 (1984) 311.

[6] G. Pistoia, M. Pasquali, M. Tocci, R.V. Moshtev,V. Manev, J.Fig. 12. Cyclic voltamograms of Ag V O . ———: ion ex-1.2 3 8Electrochem. Soc. 132 (1985) 281.change reaction, ? ? ?: solid state reaction.

[7] M. Pasquali, G. Pistoia, Electrochim. Acta 36 (1991) 1549.[8] R. Tossici, R. Marassi, M. Berrettoni, S. Stizza, G. Pistoia,1 2[Li] [3Li] V O → [Li] V O 13Li 13e .Octa Tetra 3 8 Octa 3 8 Solid State Ionics 67 (1993) 77.[9] G. Pistoia, G. Wang, D. Zane, Solid State Ionics 76 (1995)(3)

285.[10] E.S. Takeuchi, W.C. Thiebolt III, J. Electrochem. Soc. 135The subscripts ‘Octa’ and ‘Tetra’ in these equations

(1988) 2691.represent the cation occupation of the octahedral and[11] E.S. Takeuchi, W.C. Thiebolt III, J. Electrochem. Soc. 138tetrahedral sites between the layers, respectively.

(1991) L44.[12] R.A. Leising, W.C. Thiebolt III, E.S. Takeuchi, Inorg. Chem.

33 (1994) 5733.[13] A.M. Crespi, P.M. Skarsad, H.W. Zandbergen, J. Power4. Conclusion

Sources 54 (1995) 68.[14] A. Casalot, M. Pouchard, Bull. Soc. Chim. 10 (1967) 3817.Ag V O , having a layer structure, was obtained1.2 3 8 [15] J. Kawakita, K. Makino, Y. Katayama, T. Miura, T. Kishi,

by the ion exchange reaction of Na V O in the1.2 3 8 Solid State Ionics, submitted for publication.molten salt of AgNO at low temperature, and its [16] A.D. Wadsley, Acta Crystallogr. 10 (1957) 261.3

[17] R.D. Shanon, Acta Crystallogr. A32 (1976) 751.structure was similar to that prepared by the solid[18] Y. Kera, J. Solid State Chem. 51 (1984) 205.state reaction of V O and Ag O.2 5 2 [19] K. West, A.M. Crespi, J. Power Sources 54 (1995) 334.The electrochemical measurement indicated the[20] G. Pistoia, M. Pasquali, G. Wang, L. Li, J. Electrochem. Soc.

reduction processes including the deposition of 137 (1990) 2365.metallic silver by reduction with lithium insertion. [21] R. Tossici, R. Marassi, M. Berrettoni, S. Stizza, G. Pistoia,

1 Solid State Ionics 57 (1992) 227.Displacement of Ag ions at the octahedral sites in1 [22] L.A. de Picciotto, K.T. Adendorff, D.C. Liles, M.M. Thac-Ag V O by Li ions occurs accompanying the1.2 3 8 keray, Solid State Ionics 62 (1993) 297.deposition of metallic silver. Once the discharge

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Lithium insertion behaviour of silver vanadium bronze