Lithium insertion into Li4V3O8

Solid State Ionics 120 (1999) 109–116

Lithium insertion into Li V O4 3 8

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

223-8522, Japan

Received 12 November 1998; accepted 4 December 1998

Abstract

The lithium insertion characteristics of lithium vanadate, Li V O , were investigated using LiV O prepared by the4 3 8 3 8

precipitation technique as the starting material. The Li V O phase was formed by lithiation over x 5 1.5 in Li V O , and4 3 8 11x 3 8

the diffusion of lithium in this phase determined the reaction rate of insertion more than x 5 1.5. Improvement of insertionkinetics in the Li V O phase extended the lithium insertion limit from x 5 3.2 to x 5 4.0, compared with the case of LiV O4 3 8 3 8

by conventional high temperature synthesis. Lithium insertion proceeds as the single-phase reaction in the range of3.2 , x , 4.0. 1999 Elsevier Science B.V. All rights reserved.

Keywords: Vanadate; Lithium; Insertion; Transition; Diffusion

1. Introduction and Zhang et al. [7]. This vanadate belongs to amonoclinic system with the space group P2 /m and1

Since Besenhard et al. [1] found that lithium has a layered structure where adjacent layers with the2trivanadate, Li V O can be used as a lithium nominal composition of V O are held together by11x 3 8 3 8

1insertion host, this oxide has been investigated as a Li ions at the octahedral sites in the interlayer.cathode material for rechargeable lithium batteries Excess lithium corresponding to the amount x is[2–4]. The advantages of Li V O are (i) the large accommodated at the tetrahedral sites between the11x 3 8

discharge capacity, (ii) the high rate capability, and layers.(iii) the good cycle characteristics. These are caused Lithium insertion behaviour of Li V O was11x 3 8

by the uptake of more than three moles of lithium reported by Pistoia et al. [4], Hammou et al. [8], andper formula unit, the fast diffusion of lithium in the Raistrick [9]. Lithium insertion to this oxidecompound, and the structural stability against lithium proceeds as a single-phase reaction for 0 , x , 1.5 |insertion and extraction, respectively. 2.0, followed by a two-phase reaction for 1.5 | 2.0 ,

The crystal structure of Li V O (x 5 0 | 0.2) x , 3.2. Lithium insertion limit is about x 5 3.211x 3 8

was characterized by Wadsley [5], Picciotto et al. [6], when lithium is inserted at about room temperatureto high crystalline Li V O prepared by slowly11x 3 8

cooling of a melt of lithium vanadium oxide. Thac-*Corresponding author. Tel.: 1 81-49-711-6891720; fax: 1 81-keray and co-workers [6,10] refined the crystal45-5631141.

E-mail address: [email protected] (J. Kawakita) structure of the lithiated product, Li V O , and4 3 8

0167-2738/99/$ – see front matter 1999 Elsevier Science B.V. All rights reserved.PI I : S0167-2738( 98 )00555-4

110 J. Kawakita et al. / Solid State Ionics 120 (1999) 109 –116

predicted the formation of Li V O where residual described by Pistoia et al. [24]. An equivalent5 3 8

available sites are filled with additional lithium. amount of V O , obtained by thermal decomposition2 5

Manev et al. [11] and the authors [12] showed that of NH VO (Junsei Chemical, . 99.0% purity) at4 3

this value proved to be attainable by using a special- 5008C for 24 h, was added to a 0.5 M aqueously treated Li V O and by carrying out lithiation solution of LiOH (monohydrate, Kanto Chemical,11x 3 8

under more drastic condition, respectively. . 99.0%). The suspension was stirred at 50 | 608CSeveral preparation techniques of the material for 2 days. The resulting dark red gel was heated and

were devised and tried to improve the cell per- evacuated at 908C to evaporate water to dryness. Aformance of Li V O . For a closer wedging of fine powder was obtained by mild grinding of the11x 3 8

particles, a ground methanolic slurry of a fine oxide dried gel using an agate mortar and pestle. Thepowder and additives were dried and compacted reference vanadate, HT LiV O was also prepared by3 8

under a relatively high pressure [13–15]. Ultrasonic melting the mixture of Li CO and V O in an2 3 2 5

treatment was applied to acquire a larger specific appropriate molar ratio at 6808C and by cooling itarea [16]. Modification of the host skeleton such as slowly down to room temperature. All ground pow-substitution and control of stoichiometry was der samples were sieved under 38 mm in particleattempted [14,17–21]. A favorable result, however, size.could not be obtained except for the case of glassy or Thermogravimetry and differential thermal analy-amorphous Li V O prepared by quenching sis (TG-DTA, Mac Science TGDTA 2000) were11x 3 8

[22,23], mainly because of a difficulty in making a performed on the powder sample of LT LiV O3 8

powder for the desirable electrode caused by the heated at 908C.hardness and toughness of high crystalline Lithium insertion into LT and HT LiV O was3 8

Li V O . carried out using both electrochemical and chemical11x 3 8

In 1990, Pistoia et al. [24] reported a new syn- methods by means of a cylindrical glass cell withthesis route of amorphous Li V O using a precipi- three electrodes and a n-butyl lithium / n-hexane11x 3 8

tation technique in an alkaline aqueous solution. This solution, respectively. All the procedures for bothmaterial showed a better electrochemical perform- methods were presented in detail elsewhere [12].ance than crystalline Li V O , and in particular the The lithium content of chemically lithiated oxides11x 3 8

amount of inserted lithium reached x 5 4.5. Other was determined by elemental analysis for Li and Vresearchers presented a high capacity corresponding using atomic absorption analysis (Hitachi, 180-55to x 5 4.0 [25–27] and a good reversibility [25,26] AAS). In the case of the electrochemical method, theof a finely dispersed form by dehydration of precipi- amount of inserted lithium was calculated from thetated LiV O gels. In the following part, the lithium quantity of the electricity passed through the working3 8

trivanadate obtained by the precipitation technique electrode.and the conventional high temperature synthesis are The crystal structure of all the samples wastermed a low temperature (LT) and a high tempera- characterized by X-ray powder diffraction (XRD)ture (HT) LiV O , respectively. measurement using the Rigaku apparatus (RINT-3 8

To clarify the difference in the lithium insertion 1300) with CuKa radiation source filtered by Ni thinlimit between LT and HT LiV O , the authors have plate. The infrared absorption spectra of as-prepared3 8

focused on lithium insertion behaviour in the region and chemically lithiated oxides were obtained by theof 3.0 , x , 4.0 in Li V O . Insertion characteris- KBr disk method using a Bio-Rad FTS-165 Fourier11x 3 8

tics of LT and HT LiV O were investigated in terms transform infrared (FT-IR) spectrometer. The powder3 8

of the insertion kinetics in addition to structural and sample for these measurements was set to eachopen circuit potential changes. sample holder in a glove box filled with argon gas.

Electrochemical properties were investigated bythe galvanostatic discharge and the discharge /charge

2. Experimental cycle experiments at the current density of 2 0.05 |221.0 mA ? cm . The open circuit potential (OCP) of

Low temperature lithium trivanadate (LT LiV O ) chemically lithiated samples was measured using the3 8

was prepared using the precipitation technique, as electrochemical cell described above. The chemical

J. Kawakita et al. / Solid State Ionics 120 (1999) 109 –116 111

˜diffusion coefficient of lithium (D ) was determinedLi

by the galvanostatic intermittent titration technique(GITT) [28]. In this paper, the discharge capacity isrepresented by x in Li V O .11x 3 8

3. Results and discussion

3.1. Preparation of LT LiV O3 8

Fig. 1 shows TG and DTA curves of LT LiV O3 8

heated at 908C. The weight of the sample decreasesgradually up to about 3008C and then keeps almostconstant. On the other hand, no obvious peak isobserved on the DTA curve around 2808C, at whichcrystallization begins [24]. The sample subjected tothe TG-DTA measurement, however, crystallized tosome extent. Therefore, in our experiment, dehy-

Fig. 2. IR spectra of LT LiV O dehydrated at (a) 90 and (b)3 8drated LT LiV O was obtained by heating the3 83508C, and (c) HT LiV O .3 8sample at 3508C for 12 h.

IR spectra of LT and HT LiV O are compared in3 8

Fig. 2. LT LiV O heated at 908C has absorption absorbance of these bands is considerably small3 821bands near 3400, 1600 and 800 cm ascribed to one compared with LT LiV O heated at 908C, as shown3 8

stretching vibration n(O-H) and two deformation in Fig. 2b. Taking into account TG result, thesevibrations d(O-H) of bonds between oxygen and bands are due to water vapor remaining in thehydrogen atoms, as shown in Fig. 2a. The existence chamber where the sample for the IR measurement isof these bands indicates that water molecules are set. Other absorption bands are observed near 1000

21contained in the sample. When dehydrated at 3508C, and 700 cm ascribed to two kinds of stretchingvibration of bond between vanadium and oxygenatoms, n(V5 O) and n(V-O-V), respectively, asreported by Kera [29]. These bands are consistentwith that of HT LiV O in Fig. 2c with respect to3 8

both wavenumbers and relative absorbances.XRD patterns of LT and HT LiV O are compared3 8

in Fig. 3. Broad and weak diffraction lines areobserved for LT LiV O heated at 908C, as shown in3 8

Fig. 3a. These lines were not assigned to anyone ofalready known vanadium oxides and lithium van-adates. When dehydrated at 3508C as seen in Fig. 3b,however, there are a lot of obvious diffraction lines,and all of them are attributed to a monoclinic system(P2 /m). Accordingly, LT LiV O heated at 908C is1 3 8

a hydrated microcrystal because of no peaks on theDTA curve at the temperature up to 3508C. ThoughLT LiV O dehydrated at 3508C has the same crystal3 8

system and space group as HT LiV O in Fig. 3c, the3 8

relative intensities of the former are considerablydifferent from those of the later. This phenomenonFig. 1. (a) TG and (b) DTA curves of LT LiV O dehydrated at3 8

2 1908C. Heating rate: 108C ? min . was also reported in other literatures [24,25] and


22Fig. 3. XRD patterns of LT LiV O dehydrated at (a) 90 and (b) Fig. 4. Discharge curves at 2 0.1 mA ? cm and OCP plots of LT3 8

3508C, and (c) HT LiV O . and HT LiV O . OCP plots of chemically lithiated products are3 8 3 8

shown here.

explained by the deductions that LT LiV O has3 8

isotropic and strain-free crystallites and that it has The former has two obvious plateaus at the potentialthe smaller grain than HT LiV O . Different media near 2.6 V and 2.3 V beyond x 5 1.5 while the latter3 8

of crystal nucleation and growth for HT and LT decreases less stepwise. This phenomenon is dis-samples might bring about the different manner of cussed later.crystal nucleation and growth for both cases. Fur- IR spectra of lithiated products, Li V O , ob-11x 3 8

thermore, a preferred orientation of the HT sample tained by chemical lithium insertion to LT LiV O3 8

was retained after both chemical and electrochemical are compared in Fig. 5. When the amount of insertedlithium insertion. This phenomenon was not ob- lithium is within x 5 1.5, the absorption bandsserved in the case of LT sample. Apparently, similar ascribed to n(V5 O) are observed between 1000 and

21SEM images of both LiV O were obtained in size 900 cm , as seen in Fig. 5b (for example x 5 1.09)3 8

and morphology of the aggregated particles, for and are shifted to the lower wavenumbers than thoseexample, as presented elsewhere [27]. of the starting material (Fig. 5a). This corresponds to

lowering of bond strengths between vanadium and3.2. Lithium insertion behaviour of LT LiV O oxygen atoms caused by reduction of the vanadium3 8

element accompanied by lithium insertion. For 1.5 ,

Fig. 4 shows the potential versus composition x , 3.2, additional absorption bands appear between21profiles of LT and HT LiV O , including OCP plots 900 and 800 cm , for example, at x 5 2.11 as3 8

of chemically lithiated products and galvanostatic shown in Fig. 5c. The similar IR spectra weredischarge curves of LiV O samples at 2 0.1 mA ? obtained in the case of lithium insertion to HT3 8

22cm . The similar potential changes of OCP plots LiV O up to x 5 3.2. Beyond x 5 3.2 for LT3 8

with x values are observed for both LT and HT LiV O , absorption bands disappear between 10003 821LiV O in the range of 0.2 , x , 3.2. As further and 900 cm and remain between 900 and 8003 8

21lithium insertion to LT LiV O proceeds beyond cm , for example at x 5 4.00, as shown in Fig. 5d.3 8

x 5 3.2, a slow inclination of its OCP is observed. The remaining bands are shifted to the lowerThe discharge potential of LT LiV O changes in wavenumbers, compared with those of x 5 2.11 (Fig.3 8

similar manner as that of HT LiV O for x , 1.5. 5c). These results indicate that additional lithium for3 8


Fig. 5. IR spectra of Li V O (LT) by chemical lithium Fig. 6. XRD patterns of Li V O (LT) by chemical lithium11x 3 8 11x 3 8

insertion, (a: x 5 0.22, b: x 5 1.09, c: x 5 2.ll and d: x 5 4.00). insertion, (a: x 5 0.22, b: x 5 1.09, c: x 5 2.11 and d: x 5 4.00).

x . 3.2 is inserted to the single Li V O phase,4 3 8

which is formed by the phase transition upon lithia-tion after coexistence of the original LiV O phase.3 8

XRD patterns of lithiated products, Li V O ,11x 3 8

obtained by chemical lithium insertion to LT LiV O3 8

are compared in Fig. 6. For x . 1.5, all the diffrac-tion lines in the pattern are attributed to the originalLiV O , as seen in Fig. 6b (for example at x 5 1.09)3 8

and 6a. Note that broad peaks near 128 and 268 in 2u

are due to Mylar film, which covers the sampleduring the XRD measurement. In the region of 1.5 ,

x , 3.2, additional diffraction lines in the patternwere ascribed to the Li V O phase, and so two4 3 8

phases coexisted in this region. Some of them areseen clearly near 168 and 328 at x 5 2.11, as shownin Fig. 6c. Beyond x 5 3.2, diffraction lines ascribedto the original LiV O phase disappeared and only3 8

the second Li V O phase was observed in the4 3 8

pattern. As shown in Fig. 6c and 6d, however, somelines in the second phase at x 5 4.0 are shifted toeither the lower or the higher angle than those atx 5 2.11, indicating a modification of the crystal

Fig. 7. Dependence of lattice constants on x in Li V O , (d:11x 3 8lattice caused by further lithiation. To clarify this, the original phase of LT, s: second phase of LT, m: original phase oflattice constants were calculated from the XRD HT, n: second phase of HT, 1 : by Wadsley [5], and 3 : bypatterns and their dependence on x values (Fig. 7) is Picciotto et al. [6]).


Table 1studied. Similarly to the case of HT LiV O [12], all3 8 ˜Chemical diffusion coefficient of lithium (D ) of Li V OLi 11x 3 8the lattice constants of LT LiV O have an approxi-3 8

Sample x 5 0.2 (LiV O phase) x 5 3.2 (Li V O phase)mately linear relationship against x in the single 3 8 4 3 8

2 8 29phase region of 0.2 , x , 1.5, and keep almost LT 8.88 3 10 6.33 3 1028 211constant for each phase in the two phase region of HT 2.03 3 10 7.11 3 10

1.5 , x , 3.2. In addition, lattice constants changewith x upon further lithiation beyond x 5 3.2.Though a axis shrinks and b angle approaches 908, b other hand, the former is considerably larger in twoand c axes extend, leading to a swelling of the lattice orders of magnitude than the latter at x 5 3.2, i.e. involume by about 1% at x 5 4.0 compared with at the second Li V O phase, although the coefficient4 3 8

x 5 3.2. This result is explained by an increase of the of the Li V O phase decreases compared with that4 3 8

repulsive interaction between cations. Accordingly, of the LiV O one. Accordingly, actual lithium3 8

the structural studies using the XRD measurement insertion process is determined by the slow diffusivi-revealed that lithium insertion into the Li V O ty of lithium in the Li V O phase. This fact is4 3 8 4 3 8

phase proceeds as the single phase reaction for 3.2 , confirmed by a large gap between OCP and dis-x , 4.0. charge potential for HT LiV O beyond x 5 1.5 and3 8

Fig. 8 shows a dependence of the discharge a smaller discharge capacity than LT LiV O (see3 8

capacity of LT and HT LiV O on the current Fig. 4), caused by the formation of the Li V O3 8 4 3 8

density. At each current density, LT LiV O has phase working as if it hindered lithium insertion.3 8

larger capacity than HT LiV O and the gap between Further lithium insertion, however, proceeds beyond3 8

both oxides increases. This phenomenon is mainly x 5 3.2 when the diffusion of lithium in the Li V O4 3 8

due to a difference in the insertion rate of lithium in phase becomes fast enough to be a match for in thethe compound. Apparent chemical diffusion coeffi- LiV O phase, as in the case of LT LiV O , which3 8 3 8

˜cient of lithium (D ) of Li V O is listed in Table has smaller grain size and less preferred orientationLi 11x 3 8

1. At x 5 0.2, i.e. in the original LiV O phase, the of the sample. The latter effect may bring about a3 8

coefficient of LT LiV O is larger than but same feasible rearrangement of the lattice, i.e. a fast3 8

order of magnitude as that of HT LiV O . On the displacement of constituent atoms, accompanied by3 8

the phase transition from the original LiV O phase3 8

to the second Li V O one because of less strain of4 3 8

the crystal lattice on rearrangement by the less long-range order.

Fig. 9 shows first discharge and charge cycle22curves of LT and HT LiV O at 60.1 mA ? cm ,3 8

and current is reversed at 1.5 V. Most steps on thedischarge curve of HT LiV O disappear on the3 8

charging curve. This phenomenon is explained bythe reason that electrochemical lithium extraction ofthe HT sample has a reaction path different frominsertion, yet leading to the return to the originalstructure [30]. In the case of LT LiV O , the3 8

charging curve returns through same shapes of thedischarge curve. In particular, two plateaus areclearly observed on both curves. This result indicatesa reversible nature of lithium insertion and extractionreactions of LT LiV O . When the upper limit of3 8

charging potential is 3.6 V, a small amount of lithiumis remained in the host structure of LT LiV O , as isFig. 8. Dependence of x in Li V O on current density, (a: LT 3 811x 3 8

and b: HT). the same in HT LiV O . It may be extracted if3 8


the electrochemical measurement are presented inFig. 10. The additional peaks of metallic silver in thepatterns are due to a silver paste used for preparationof the working electrode. After first discharge andcharge cycling, both LiV O seem to have the3 8

patterns analogous to those of the starting materials,i.e. samples before cycle. Though all the diffractionlines of samples after cycling are ascribed to theoriginal LiV O , a slight shifting of some diffraction3 8

lines is caused by the remaining lithium in the hoststructure after cycling, as described above. Conse-quently, lithium insertion and extraction reactions ofLT LiV O proceed reversibly.3 8

4. Conclusion

The dehydrated lithium trivanadate, Li V O11x 3 8Fig. 9. Discharge and charge curves of LiV O at 60.10 mA ?3 8 (LT), prepared by the precipitation technique had2 2cm , (a: LT and b: HT).

less preferred orientation than the oxide (HT) byconventional high temperature synthesis. Large dis-

charged up to a higher potential, similarly to the case charge capacity was attained for the LT oxide byof HT LiV O .3 8 lithium insertion beyond x 5 3.2, resulted in accom-

XRD patterns of electrode samples subjected to modation of four moles of lithium per formula unit.In the range of 3.2 , x , 4.0, lithium insertionproceeded as single-phase reaction in the secondLi V O phase, which was formed by lithiation of4 3 8

the original LiV O phase over x 5 1.5. In addition,3 8

the lattice constants in this region were refined in thisstudy. The Li V O phase has much smaller diffu-4 3 8

sion coefficient of lithium in the HT oxide by twoorders of magnitude than the LiV O one. This fact3 8

concerning the HT oxide explained the restriction ofthe whole reaction and the limitation of the amountof inserted lithium to x 5 3.2. Simultaneously, it wasrevealed that lithium insertion proceeded beyondx 5 3.2 by improvement of insertion rate, in par-ticular in the Li V O phase, using the LT oxide4 3 8

with the favorable nature of little preferred orienta-tion.

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Lithium insertion into Li4V3O8