Lithium insertion behaviour of Li1+xV3O8 prepared by precipitation technique in CH3OH

Solid State Ionics 110 (1998) 199–207

Lithium insertion behaviour of Li V O prepared by precipitation11x 3 8

technique in CH OH3

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

Yokohama 223-8522, Japan

Received 27 February 1998; accepted 4 April 1998

Abstract

Li V O (LT-M sample) was obtained by the sol-gel method in CH OH. This sample, prepared at 3508C, possessed a11x 3 8 3

smaller grain size and better electrochemical performance than the HT sample prepared by conventional high temperature21synthesis. High discharge capacity (372 mAh g : x 5 4.0) and reversible discharge and charge cycles were attained owing

to improvement of insertion and extraction kinetics. When heated at 2008C, CH OH molecules remained in the compound3

and crystallinity became lower by lithium insertion over x 5 2.0. The lithium deintercalation was irreversible. 1998Elsevier Science B.V. All rights reserved.

Keywords: Sol-gel; Vanadate; Lithium; Insertion; Extraction

1. Introduction (V O ) [17]. This method is usually called some-2 5

thing such as the precipitation technique or the sol-Lithium vanadium oxide, Li V O , has been gel process. When dehydrated at 2008C, the oxide11x 3 8

studied as one of the cathode materials of lithium showed excellent electrochemical performance as an1secondary batteries since Wadsley reported its crystal amorphous form, accommodating 4.5 moles of Li

structure in 1957 [1]. At the beginning of the studies ions per formula unit. Afterwards, sodium vanadate,on the lithium insertion behaviour of this compound, Na V O , with low crystallinity and sodium potas-11x 3 8

this oxide when used for experiments, was prepared sium mixed vanadate, Na K V O , were also12x x 3 8

by high temperature synthesis, in which slow or synthesized in the same way using alkaline aqueousrapid cooling of a melt of lithium vanadium oxide solutions [18,19]. Cyclic voltammetry and spectro-occurred [2–16]. Hereafter, the Li V O prepared scopic measurement such as X-ray absorption spec-11x 3 8

this way is termed the HT sample in this paper. troscopy (XAS) and FT-IR analysis were applied toIn 1990, Pistoia at al. presented a new synthesis Li V O prepared by the precipitation technique as11x 3 8

route to obtain Li V O in the gel state by well as by conventional high temperature synthesis11x 3 87precipitation from an aqueous solution containing [20]. Furthermore, Li NMR measurement was car-

lithium hydroxide (LiOH) and vanadium pentoxide ried out on Li V O and Na V O in amorphous11x 3 8 11x 3 8

and crystalline forms [21]. These results have shown*Corresponding author. E-mail: [email protected] more homogeneous distances between vanadium and

0167-2738/98/$19.00 1998 Elsevier Science B.V. All rights reserved.PI I : S0167-2738( 98 )00150-7

200 J. Kawakita et al. / Solid State Ionics 110 (1998) 199 –207

1oxygen atoms and faster diffusion of Li ions in the 5008C for 24 h. Then the mixture was stirred at 508Camorphous form than in the crystalline one. Im- for two days under argon atmosphere. Greenishprovement of electrochemical performance was ex- brown solids precipitated, and the mixture wasplained by the fact that the lack of long range order heated and evacuated at 908C for 12 h to evaporate

1caused shorter pathways for motion of Li ions and CH OH to dryness. A fine powder was obtained by3

more symmetric structure of the VO octahedron, mild grinding of the precipitate using an agate mortar61leading to allowance of accommodation of more Li and pestle. This powder was highly hygroscopic. As

ions per unit cell. Recently, thin films for application the reference oxide, Li V O (HT) was also pre-1.2 3 8to micro-batteries were fabricated by utilizing prepared by melting the mixture of Li CO and V O in2 3 2 5cipitated Li V O in a gel state [22]. West et al. a appropriate molar ratio and cooling it slowly down11x 3 8

reported preparation of LiV O in a finely dispersed3 8 to room temperature. All powder samples wereform by dehydration of aqueous lithium vanadate sieved under 38 mm in particle size by grindinggels as well as its electrochemical characteristics using an agate mortar and pestle.[23]. After heat treatment of the dried gels at 3508C, Thermogravimetry and differential thermal analy-this material possessed a high capacity for lithium sis (TG-DTA, Mac Science TG-DTA 2000) were

1insertion, i.e. up to four additional Li ions per carried out on the sample heated at 200 and 3508C.formula unit, and good reversibility when used as TG-DTA data of the sample evacuated at 908C couldelectrode material. The Li V O obtained from11x 3 8 not be obtained owing to its high hygroscopicity.aqueous solution is termed the LT sample in the Accordingly, the heat treatment was carried out infollowing part of this paper. dry air at the temperature cited above, referring to

So far, the LT sample has been synthesized only the report by Pistoia et al. [17].in an aqueous solution. However, water is one of the IVThe content of tetravalent vanadium, V washindrances that has to be excluded from the nonaque- determined using the following redox titration tech-ous lithium cell. Then, the authors invented the

nique, described by Wickham [24]. The powderpreparation of Li V O using methanol (CH OH)11x 3 8 3 sample was dissolved in 10% H SO solution and2 4as a solvent. Of course, lithium methoxide (LiOCH ) IV3 preexisting V was titrated with 0.20mM KMnO4was substituted for LiOH owing to the formation of

(Yoneyama Chemical, .99.3% purity) /H SO solu-2 4H O by reaction of LiOH with V O . Hereafter, V2 2 5 tion. Then all of the pentavalent vanadium, V waslithium vanadium oxide obtained by this method is IVreduced to V by sulfur dioxide (SO ). After boiling2termed as the LT-M sample. The structural charac-away excess SO , the total vanadium was titrated2teristics, the morphology, and the electrochemicalwith 2.0mM KMnO solution. The lithium content of4properties of the LT-M samples have been investi-the obtained samples was determined by elementalgated and compared with the HT oxide.analysis for Li and V using atomic absorptionanalysis (Hitachi, 180-55 AAS).

The electrochemical properties were investigated2. Experimentalby galvanostatic discharge and discharge /chargecycle tests, using a galvanostat /potentiostat (TohoLi V O (LT-M) was prepared by a precipi-11x 3 8Technical Research PS-2092 and PS-08) controlledtation technique while referring to the method for theby a personal computer (NEC PC-9801FA). All theLT sample from LiOH and V O , described by2 5procedures to fabricate the electrochemical cellsPistoia et al. [17]. An equivalent amount of V O2 5were presented in detail elsewhere [25,26]. Thewas slowly added to 0.5M solution of LiOCH3

˜chemical diffusion coefficient of lithium (D ) was(Wako Pure Chemical, 12% methanol solution) / Li

obtained by the galvanostatic intermittent titrationCH OH (Junsei Chemical, .99.8% purity). This3

technique (GITT) [27]. After galvanostatic dischargeprocedure was carried out in a glove box filled withup to each x value, the rest potential was regarded asargon gas.V O used for preparation was obtained by2 5

thermal decomposition of ammonium vanadate the open circuit potential (OCP) when potential21(NH VO , Junsei Chemical, .99.0% purity) at change was within 0.01 V h . In this paper, the4 3

J. Kawakita et al. / Solid State Ionics 110 (1998) 199 –207 201

discharge capacity was denoted by the amount of sample. Absorption bands were observed which were1inserted Li ions, i.e., x in Li V O . ascribed to the stretching (n) and deformation (d)11x 3 8

The crystal structure was characterized by X-ray vibrations among oxygen, hydrogen and carbonpowder diffraction (XRD, Rigaku RINT-1300) using atoms, such as n(O–H), n(C–H) and d(C–O, C=O),Cu Ka radiation with a Ni filter, and Fourier as seen in Fig. 1(a). This observation indicatedtransform infrared (FT-IR, Bio-Rad FTS-165) existence of CH OH in the sample heated at 908C3

spectroscopic measurements using the KBr disk (LT-M90) above the boiling point of CH OH3

method. The sample for XRD measurement after (658C), and suggested that CH OH molecules were3

electrochemical test was covered with an X-Ray stabilized by binding them with the oxide lattice inMylar film (Chemplex Industry, 25 mm in thickness) the interlayer. For the LT-M sample heated at 2008Cto avoid contamination by and reaction with humid (LT-M200), the absorption bands cited above did notair. The morphology of the sample was observed by disappear as shown in Fig. 1(b), so this indicated thatthe scanning electron microscope (SEM, JEOL JSM- CH OH molecules still remained in the compound.3

T100). After heat treatment at 3508C (LT-M350), the ab-sorption bands corresponding to vibrations inCH OH molecules disappeared, and the CH OH3 3

3. Results and discussion molecule was removed from the LT-M sample, asshown in Fig. 1c.

3.1. Preparation of LT-M Li V O Fig. 2 shows TG-DTA curves of the LT-M20011x 3 8

and LT-M350 samples. The weight of the LT-M350Fig. 1 shows IR spectra of the LT-M samples sample decreased gradually on the TG curve and no

heated at various temperatures, and that of the HT obvious peak appeared on the DTA curve. Thecomposition, Li V O , was obtained by combina-1.13 3 8

tion of redox titration and elemental analysis. Proba-bly, this weight loss was due to the liberation of thetrace amount of remaining CH OH molecules in the3

Fig. 1. IR spectra (wide range) of Li V O (LT-M) heated at (a) Fig. 2. TG-DTA curves of Li V O (LT-M) heated at (a) 200 and1.2 3 8 1.2 3 8

90, (b) 200, (c) 3508C, and of (d) Li V O (HT). (b) 3508C.1.2 3 8


compound, or the adsorbed water molecules during short-range order existed (Fig. 3(a)). Thus, the LT-the experiment. The weight of the LT-M200 sample M90 sample had an amorphous nature. Separation of

21decreased gradually up to about 2508C by 1.18 wt.%, absorption bands around 1000 cm for the LT-as seen in Fig. 2(a). A small exothermic hump was M200 sample indicated that the oxide gained shortobserved near 2908C on DTA curve and the weight range order to some extent, while long range orderincreased by 1.06 wt.%. In this region, the oxidation did not exist clearly, as shown in Fig. 3(b). Thereaction occurred accompanying uptake of oxygen wavenumbers of the vibrations, n(V=O) and n(V–O–atoms into the lattice. The composition was calcu- V), of the LT-M350 sample agreed mostly withlated to be Li V O ?0.20CH OH when these those of the HT sample, although the shoulder-like1.13 3 7.86 3

21weight losses and gains were due to the removal of absorption band appeared near 970 cm . Moreover,the CH OH molecule and the uptake of oxygen, the latter vibrational band, n(V–O–V), was shifted to3

respectively. The oxygen content agreed with the higher wavenumbers compared to that of the HTvalue calculated using the result of redox titration. sample, as shown in Fig. 3(c) and Fig. 3(d), respec-

21The absorption bands around 1000 and 750 cm tively.were attributed to the stretching vibrations of the Fig. 4 shows XRD patterns of the LT-M samplesshort range and long range order between vanadium heated at various temperatures, together with that ofand oxygen atoms, i.e. n(V=O) and n(V–O–V), the HT sample. As seen in Fig. 4(a), no diffractionrespectively [20,28]. Fig. 3 shows IR spectra in these lines were observed except two attributed to Mylarwavenumbers. An obvious absorption band was not film. Thus, the LT-M90 sample was obtained in anobserved in the LT-M90 sample and the broad band amorphous state. This sample, however, was too

21appeared around 1000 cm , showing that only hygroscopic to prepare as a pellet for the working

Fig. 3. IR spectra (narrow range) of Li V O (LT-M) heated at Fig. 4. XRD patterns of Li V O (LT-M) heated at (a) 90, (b)1.2 3 8 1.2 3 8

(a) 90, (b) 200, (c) 3508C, and of (d) in Li V O (HT). 200, (c) 3508C, and of (d) Li V O (HT).1.2 3 8 1.2 3 8


electrode in our experiment. In the pattern of the the (100) plane was stronger than that of the HTLT-M200 sample (Fig. 4(b)), many diffraction lines sample and were similar to that of JCPDS card. Thewith weak intensities indicated the existence of absolute intensity of the (100) plane of the LT-M350crystallinity to some extent but they were not sample, however, was much smaller than that of theindexed to any kind of vanadium oxides or to lithium HT sample. On the other hand, each of the grainvanadate. This phenomenon was also found in the sizes in the [100], [020] and [003] directions of thecase of the LT sample [23]. In our case, more LT-M350 sample was smaller than that of the HTreflection lines were observed because CH OH sample, as shown in Fig. 5(b). These grain sizes3

molecule existed between the layers and the oxygen were obtained using the Sherrer equation, providingdefect was contained in the crystal lattice. All the that the preferred orientation of the sample powderdiffraction lines of the LT-M350 sample were attrib- was not involved in XRD measurement. Especially,uted to Li V O (indexed in JCPDS card No. in the [100] direction the grain size of the LT-M35011x 3 7.9

18-754), as shown in Fig. 4(c). Their relative inten- sample was half of that of the HT sample. As thesities, however, seemed to be different from those of layers in the host lattice were piled up in the [100]the HT sample (Fig. 4(d)). In particular, the ratio of direction, it revealed that the LT-M350 sample had(100) /(020) on the LT-M350 sample was smaller less stacking of the layers than the HT sample. Thisthan that on the HT sample. Fig. 5(a) showed the fact might explain shifts of the absorption bands ofrelative intensities of (020) and (003) planes, nor- n(V=O) and n(V–O–V) in the IR spectra to a highmalizing (100) as 100%, in the XRD pattern of the wavenumber direction (see Fig. 3). Although theHT and LT-M350 samples, and in the JCPDS card. largest difference in the average grain sizes betweenApparently, in the case of the LT-M350 sample the both the samples, was about 50%, similar SEMrelative intensities on the (020) and (003) planes to images were obtained, in size and morphology of the

aggregated particles for both the samples, as shownin Fig. 6. Presumably, this is explained as being aresult of the same grinding and sieving conditions forthe samples. Different media of crystal nucleationand growth for the HT and LT-M samples mightbring about the anisotropic manner of crystal growthfor both cases.

3.2. Discharge behaviour of LT-M Li V O11x 3 8

Fig. 7 shows discharge curves and OCP plots forthe HT, LT-M200, and LT-M350 samples. OCPs ofthe LT-M350 sample coincided with that of the HTsample up to x53.2. For 1.5,x,3.2, the crystalstructure changed from the original to the newstructure, which was ascribed to LiV O and3 8

Li V O phases, respectively. Fig. 8(a) shows the4 3 8

XRD pattern of the latter phase at x53.2 of the HTsample. In the case of the LT-M350 sample, anotherplateau region appeared near 2.4 V (versus Li) for3.2,x,4.0. It was found that Li V O phase re-4 3 8

mained even at x54.0 because all the diffractionlines were attributed to it, as shown in Fig. 8(b).Relative intensities of most peaks of the LT-M350sample were different from those of the HT sample,Fig. 5. Relative intensity in some planes and grain size in some

directions of Li V O . presumably owing to the reason described above.1.2 3 8


Fig. 6. SEM images of Li V O , (a: LT-M350 and b: HT).1.2 3 8

22Fig. 7. Discharge curves at 20.1 mA cm and OCP plots of Fig. 8. XRD patterns of discharged sample up to (a) x53.2 on HT,Li V O , (——, d: LT-M350; ? ? ?, j: LT-M200, and - -, m: (b) x54.0 on LT-M350, and (c) x52.5 on LT-M200.1.2 3 8

HT).

M200 sample had different lithium insertion be-Thus, further lithium insertion proceeded in this haviour from either the LT-M350 sample or the HTregion as a single-phase reaction and Li V O was sample.5 3 8

finally formed, which had been expected to exist by In the case of the LT-M350 sample, the twoPicciotto et al. [29]. plateaus appeared clearly near 2.55 and 2.4 V on the

As shown in Fig. 7, OCPs of the LT-M200 sample discharge curves, corresponding to constant OCPsdropped rapidly at x52.1 and kept constant at 2.4 V observed for 2.0,x,3.2 and x.3.2, respectively.for x.2.1. XRD patterns (see Fig. 8(c)) in this range West et al. reported this phenomenon concerning theshowed much lower crystallinity than the starting LT sample prepared in an aqueous solution [23]. Thematerial at x50.1. So it was revealed that the LT- latter plateau contributed mainly to increase in


discharge capacity compared with the HT sample.This might be explained by improvement in iontransport rate. Probably, the smaller grain size re-

1sulted in a shorter diffusion path of Li ions and thelower stacking of the layers facilitated transformationof the phase. In fact, the chemical diffusion coeffi-

˜cient of lithium, D , in the LT-M350 sampleLi

became clearly larger than that of the HT sample inthe primary single phase region of x,2.0, as seen in

˜Fig. 9. Unfortunately, D for the LT-M200 sampleLi

could not be obtained because the molar volumenecessary for calculation was unclear.

The discharge potential of the LT-M200 samplewas lower than that of the LT-M350 sample exceptfor the early stages of discharge though a smalldifference was observed between both samples onthe discharge capacity (see Fig. 7). As low crys-tallinity and defects in the lattice, i.e., oxygen

Fig. 10. Dependence of x in Li V O on current density, (a:11x 3 8deficiencies in this case, sometimes created a posi-LT-M350, b: LT-M200, and c: HT).

tive effect on discharge kinetics [25,30], the largegap between the discharge potential and the OCPs

22indicated that CH OH molecules in the interlayer cm , the discharge capacity of both LT-M samples31prevented Li ions from a smooth jump from a site was similar and larger than that of the HT sample

to a neighboring one. because of improvement of the discharge kinetics, asFig. 10 shows the dependence of the discharge described above. While the discharge capacity of the

capacity of the HT and LT-M samples on current HT and LT-M350 samples fell gradually with the22density. At a current density lower than 0.10 mA increase of current density over 0.1 mA cm , that

for the LT-M200 sample decreased rapidly andstayed almost constant at x52.8. Presumably, dis-charge at a larger current density brought a loweringof the crystallinity of the sample in the earlier stageof discharge. This fact might overcome the effect of

1hindrance by CH OH molecules on diffusion of Li3

ions between the layers.Fig. 11 shows the discharge /charge cycle curves

of the HT, LT-M200, and LT-M350 samples.Li V O phase formed in the last stage of discharge4 3 8

(x53.0) and returned to LiV O phase in the case of3 8

the HT sample [5,8]. The charging curve of theLT-M350 sample had two plateaus near 2.45 and 2.6V probably corresponding to each plateau on dis-charge. Moreover, only LiV O phase was observed3 8

in the XRD patterns after the discharge and chargecycle, as shown in Fig. 12(a). A slight shifting ofsome diffraction lines in the peak position was due todistortion of the structure caused by the remaining

1Li ions in it. Accordingly, it was revealed that theFig. 9. Dependence of chemical diffusion coefficient of lithium,D̃ , on x in Li V O (a: LT-M350 and b: HT). crystal structure of the LT-M350 sample was alsoLi 11x 3 8


is a common characteristic of amorphous materials.Beyond x.2.0, crystallinity of this material fellimmediately (see Fig. 8(c)). Thus, lithium vanadatewith a low crystallinity close to the amorphous state,was formed in the course of discharge (x52.0) and

1an additional two Li ions were inserted in anamorphous state. Moreover, after the discharge /charge cycle of the LT-M200 sample, the structureretained its amorphous state because no diffractionlines except Mylar film were observed in the XRDpattern, as shown in Fig. 12(c). It was considered thatlithium was extracted from amorphous lithium van-adate described above during charging. Consequent-

1ly, it was found that insertion and extraction of Liions proceeded irreversibly in the case of the LT-M200 sample.

22Fig. 11. Discharge and charge cycle curves at 60.1 mA cm of4. ConclusionLi V O , (——: LT-M350; ? ? ?: LT-M200, and - -: HT).1.2 3 8

The Li V O phase oxide bronze (LT-M sam-11x 3 8

ple) was obtained by sol-gel methods in methanol aswell as in water. The sample prepared at 3508C,resulted in attainment of both high discharge capaci-

21ty (372 mAh g : x54.0) and a reversible cyclebetween 0,x,4.0. These properties were explained

1by fast diffusion of Li ions and facilitated trans-formation from the original LiV O to the second3 8

Li V O phase during cycling owing to a smaller4 3 82grain size and less stacking of the V O layers.3 8

Heat-treated at 2008C, the LT-M sample containedCH OH molecules and oxygen defects in the lattice.3

Large polarization might be caused by hindrance of1movement of Li ions by methanol. Crystallinity

became much lower by further lithium insertion1beyond x52.0 and extraction of Li ions during the

charging process was irreversible.

Fig. 12. XRD patterns of Li V O after discharge and charge1.2 3 8

cycle, (a: HT, b: LT-M350, and c: LT-M200). References

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Lithium insertion behaviour of Li1+xV3O8 prepared by precipitation technique in CH3OH