Sf

LYa

b

c

a

ARRAA

KLLLOE

1

rtppcrTm

ephmaTwa

0d

Journal of Alloys and Compounds 494 (2010) 415–419

Contents lists available at ScienceDirect

Journal of Alloys and Compounds

journa l homepage: www.e lsev ier .com/ locate / ja l l com

tructure and electrochemical properties of LiMnBO3 as a new cathode materialor lithium-ion batteries

ing Chena, Yanming Zhaoa,∗, Xiaoning Anb, Jianmin Liuc, Youzhong Donga,inghua Chena, Quan Kuanga

School of Physics, South China University of Technology, Guangzhou 510640, PR ChinaSchool of Chemistry, South China University of Technology, Guangzhou 510640, PR ChinaChemical Experimental Center, South China University of Technology, Guangzhou 510640, PR China

r t i c l e i n f o

rticle history:eceived 16 November 2009eceived in revised form 12 January 2010ccepted 12 January 2010vailable online 22 January 2010

a b s t r a c t

Single-phase lithium manganese borate, LiMnBO3, was obtained at the temperature higher than 850 ◦Cby one-step solid state reaction without using carbon black in the starting materials. The initial specificdischarge capacity for the cathode active material was 75.5 mAh/g at the current density of 5 mA/g and themean fade of capacity was 0.09% per cycle except for the first cycle. The LiMnBO3 compound maintained aspecific discharge capacity of 42.3 mAh/g even at the current density of 50 mA/g and the capacity fade per

3+ 2+

eywords:ithium-ion batteriesithium manganese borateiMnBO3

ne-step solid state reactionlectrochemical properties

cycle was only 0.2% during 40 cycles. The cyclic voltammograms (CV) curves show that the Mn /Mnredox couple situated at 2.23 and 4.13 V can be clearly observed during anodic and cathodic sweeps.Combined the cyclic voltammograms results with the X-ray diffraction patterns of electrodes before andafter cycling, where no significant change of the peak currents and the peak potentials during cycling, itwas anticipated that the extraction and insertion of Li-ions are totally reversible in this compounds andthe hexagonal structure for LiMnBO3 can be maintained after long cycles under high charge and dischargerate.

. Introduction

Lithium-ion batteries, due to their low price, long cycle life, envi-onmental safety and high specific energy [1–4], have triggeredhe growth of the consumer electronics market and now are theower sources of choice for many popular devices, including mobilehones, laptop computers, and Mp3 players. At present, most ofommercial cells utilize cobalt-based oxides as the cathode mate-ial, but high cost and toxicity prohibit its large-scale use [5–11].hus, many efforts have been made to find a kind of alternativeaterials to meet the enhancive require of our society [12–14].Since the demonstration of reversible lithium insertion and

xtraction for LiFePO4 in 1997 [15], lithium transition metal phos-hates with olivine-type structures, LiMPO4 (M = Co, Ni, Mn, Fe)ave received extensive attention as promising novel cathodeaterials for rechargeable lithium batteries due to electrochemical

nd thermal stability, comparable density and flat voltage profile.he excellent character is mainly afforded by such a 3D frame-ork structure. The 3D framework, made up of the PO4 tetrahedra

nd MO6 octahedra, stabilizes the structure and allows fast ion

∗ Corresponding author. Tel.: +86 20 87111963; fax: +86 20 85511266.E-mail address: zhaoym@scut.edu.cn (Y. Zhao).

925-8388/$ – see front matter © 2010 Elsevier B.V. All rights reserved.oi:10.1016/j.jallcom.2010.01.065

© 2010 Elsevier B.V. All rights reserved.

migration. In addition, it has been shown that polyanions enablelow transition metal redox energies through the inductive effec-tive effect, thereby allowing some sort tuning of such energies.Owing to the inductive effect in the Moct–O–Ptet linkage [6,15], theFermi energy of the M3+/M2+ couple is much lower than that in theoxides, with respect to the energy of lithium metal, yielding muchhigher redox potential with respect to Li1+/Li. Structures containingboron polyoxanions (borates) provide an attractive area of investi-gation, given the low atomic weight and high electronegativity ofB (only somewhat less than P and As). It is well known that boronatom can be coordinated by oxygen atoms to form a three- or four-fold co-ordination environment, affording greater variety in redoxpotential adjustment. Considering this, recent works tend to give apreliminary evaluation of the inductive effect of the much lighterBO3 group [16–18], then the borate was expect to be a promisingnew cathode material for lithium-ion batteries.

LiMnBO3 exists in two polymorphs. The low-temperature formis monoclinic and has been synthesized below 400 ◦C in hydrother-mal conditions [19]. The high-temperature form, which is related

to the present work, was first reported by Legagneur et al. [20]. Inthe structure of LiMnBO3, Mn coordinates to five oxygen atoms toform MnO5 pyramids and each MnO5 pyramid shares two oppositeedges of its square base with two adjacent pyramids thus formingchains along the c-axis [20]. These MnO chains are then connected

4 and Compounds 494 (2010) 415–419

bctmicB

tttFswmsotacogdbstor

lsmwoTf

2

ia2tttt

ccsTX2u0rcs1da1[

e(rfl(a1

LiMnBO3 composites at different reaction temperature are shownin Fig. 2.

From Fig. 2, we can see that LiMnBO3 with hexagonal structureand MnO coexist although LiMnBO3 with the ordered hexagonal

16 L. Chen et al. / Journal of Alloys

y planar BO3 groups, parallel to [0 0 1] and link three chains viaorner sharing, to form a hexagonal net of MnO columns and showhe framework of LiMnBO3. The three boron atoms occupy C3 sym-

etry sites and the Mn ions connected to a specific B are alsonterrelated by the C3 rotation axis. In the case of B(2)O(2)3 theseorners are apical oxygen atoms of the MnO5 pyramid, whereas for(1)O(1)3 and B(3)O(3)3, they are oxygen atoms of the square base.

In Legagneur’s work, only a very small amount of lithium (lesshan 0.04 Li per formula unit) was deinserted reversibly from thehree compounds LiMBO3 (M = Mn, Fe, Co) [20]. However, fromhe thermodynamic study performed in the case of LiFeBO3, thee3+/Fe2+ reduction couple lies between 3.1 and 2.9 V/Li, demon-trating an important inductive effect of the BO3 group. Recently,e have synthesized LiFeBO3 successfully by solid state reactionethod [21]. The results show that at the discharge current den-

ity of 5 mA/g an initial specific capacity of 125.8 mAh/g can bebtained and even, when the discharge current density is increasedo 50 mA/g, a specific capacity of 88.6 mAh/g can still be held. Inddition, by using carbon in synthesized process a higher dischargeapacity, 158.3 mAh/g at 5 mA/g and 122.9 mAh/g at 50 mA/g, wasbtained for carbon coated LiFeBO3. This prompts us to investi-ate the structure and electrochemical properties of LiMnBO3 inetail. In our previous work [22], LiMnBO3 cathode material haseen synthesized with high specific surface carbon black as thetarting materials. Electrochemical measurement results show thathe initial discharge capacity of 82.5 mAh/g and 81.8 mAh/g can bebtained at the discharge current density of 10 mAh/g and 20 mA/gespectively.

In order to study the intrinsic electrochemical nature ofithium manganese borate, we have successfully prepared here theingle-phase LiMnBO3 without using carbon black in the startingaterials. The cyclic voltammetric (CV) measurements of LiMnBO3ere carried out for the first time, and the X-ray diffraction patterns

f electrodes before and after cycling was compared in this paper.he results demonstrate that this material is a potential candidateor the cathode material in lithium-ion batteries.

. Experimental

The LiMnBO3 powders were prepared by a one-step solid state reaction of sto-chiometric amounts of Li2CO3, MnO2, and H3BO3. The mixture was dispersed intocetone and then ball milled for 6 h in a planetary mill. The rotating speed was50 rpm and the ball-to-power weight ratio was 20:1. After evaporating the acetone,he mixture was pressed into pellets. The pellet was heated at a rate of 2 ◦C/mino 850 ◦C in a sealed laboratory tube furnace operating under a stream of a mix-ure of 70%Ar2 + 30%H2, fired at 850 ◦C for 12 h and then, left to cool down to roomemperature.

Thermal analysis measurement of thermogravimetry and differential scanningalorimetry (TG/DSC) was performed on the precursor mixture of the LiMnBO3

ompounds using a thermal analyzer (HCT-1, China) in the following nitrogen atmo-phere between ambient temperature and 950 ◦C with a heating rate of 10 ◦C min−1.he phase identification of LiMnBO3 compounds was carried out using powder-ray diffraction (XRD). The diffraction intensity data were collected using a D/Max-400 (Rigaku) diffractometer with Cu K� radiation. A graphite monochromator wassed for diffracted beams. A step scan mode was adopted with a scanning step of.02o and a sampling time of 2 s. Scan electron microscopy (SEM) images were car-ied out with a LEO 1530VP (LEO, Germany) electron microscopy. The electroniconductivity was measured using a RTS-8 linear four-point probe measurementystem. The LiMnBO3 powders were pressed into pellets of 10 mm in diameter andmm in thickness by the uniaxial pressing at 5 MPa in a mold. The electronic con-uctivity at different positions of the pellet is 1.44 × 10−4 S/cm, 1.60 × 10−4 S/cmnd 2.11 × 10−4 S/cm, respectively. Thus, the mean electronic conductivity is about.72 × 10−4 S/cm, which is higher than that of LiMnPO4 (∼3 × 10−9 S/cm at 572 K)23].

The electrochemical performances of the samples as cathode of the two-lectrode electrochemical cells were measured using a Land CT2001A battery tester

Land® , China). The cathode of the two-electrode electrochemical cells was fab-icated by mixing the prepared powder with acetylene black and polyvinylidineuoride (PVDF) binder in the weight ratio 75:15:10 in N-methyl-2-pyrrolidoneNMP). The obtained slurry was coated on Al foil, dried at 50 ◦C for 24 h, and pressedt the pressures of 5 MPa. The electrodes fabricated were dried again at 90 ◦C for2 h in a vacuum and cut into 1 cm × 1 cm in size. Two-electrode electrochemical

Fig. 1. TG–DTA curves of precursor mixture containing Li2CO3, MnO2, and H3BO3,measured from ambient to 950 ◦C in nitrogen with a heating rate of 10 ◦C/min.

cells were assembled in a Mikrouna glove box filled with high-purity argon wherethe lithium metal foil were used as anode, Celgard® 2320 as separator, and 1 MLiPF6 in EC:DMC (1:1 vol.%) were used as an electrolyte. The electrochemical capac-ity measurements were performed in the voltage range between 1.0 and 4.8, andthe electrochemical capacity of samples was evaluated on the active materials. Thecyclic voltammetric (CV) measurements were carried out with a Zahner IM6ex elec-trochemical workstation. The CV curves were recorded in the potential range of1.7–4.8 V at a scan rate of 0.03 mV/s at room temperature.

3. Results and discussion

The simultaneous thermogravimetric–differential thermalanalysis (TG–DTA) curves of the precursor mixture of the LiMnBO3compound are shown in Fig. 1. The TG curve presents four steps ofweight loss. Evaporation of a small amount of physically absorbedwater occurs below 100 ◦C. The endothermic DTA peak at 150 ◦Cindicates the decomposition of boric acid. A continuous weightloss between 450 and 600 ◦C should be related to thermal decom-position of the partial reactants. No more weight loss was observedin the temperature range from 800 to 950 ◦C corresponding to thephase-crystallization step. Based on the result, we choose 750, 800and 850 ◦C as heating temperatures to synthesize the LiMnBO3composite although our samples were heated under a stream of amixture of 70%Ar2 + 30%H2 gas. The XRD patterns of the prepared

Fig. 2. XRD pattern of LiMnBO3 sintered at different temperature: (a) 750 ◦C; (b)800 ◦C; (c) 850 ◦C.

and Compounds 494 (2010) 415–419 417

s(sophtctiiteaf

pttadtFsswissrotLb

crcc5apil[

trppctcOcd(mp[(ricTi

L. Chen et al. / Journal of Alloys

tructure is the dominate phase at 750 and 800 ◦C respectivelyFig. 2(a) and (b)). When the temperatures were higher than 850 ◦C,ingle-phase LiMnBO3 with the ordered hexagonal structure can bebtained (Fig. 2(c)). Our experimental results show that the tem-erature (850 ◦C) for the single-phase LiMnBO3 compound withexagonal crystal structure beginning to appear here is higher thanhat of 800 ◦C in our previous work where the high specific surfacearbon black was used as starting materials. The X-ray diffrac-ion patterns of LiMnBO3 compounds (Fig. 2(c)) were successfullyndexed with a hexagonal lattice using the program Dicvol, and thendexing result (h k l) is shown in Fig. 2. The space group was derivedo be P-6 based on the reflection conditions, and the lattice param-ters were further least-squares refined by the program PIRUM as= 8.1702 (1) Å and c = 3.1472 (1) Å, which agrees well with the data

rom Ref. [20].In order to elucidate changes of the morphology of the LiMnBO3

owders, Fig. 3(a)–(c) exhibits the SEM images for samples heat-reated at the different temperatures. From Fig. 3(a)–(b) we can seehat there are insufficient heat-treatment for the samples preparedt lower temperature (T < 850 ◦C) under our experimental con-itions. The non-uniform particles which are agglomerated withhe particle size of about more than 10 �m can be observed inig. 3(a). As the heat-treated temperature comes to 800 ◦C, themaller particles with better crystallization and uniformity and stillome agglomerated (shown in Fig. 3(b)) appear, where LiMnBO3ith hexagonal structure and MnO coexist (Fig. 2(b)) due to the

nsufficient heat-treatment. Our experimental results suggest thatamples have the smaller uniform particle size and relative higherpecific surface area present when the heat-treated temperatureeach to 850 ◦C, where the particle size of about 2 �m can bebserved (Fig. 3(c)). The smaller uniform particle size obtained athe heat-treated temperature of 850 ◦C is due to the single-phaseiMnB3 compound appearing at this temperature and thus, withetter crystallization.

Fig. 4 shows the typical charge and discharge curves of LiMnBO3ell in the voltage range between 1 and 4.8 V at different cur-ent density. At a lower current density (5 mA/g), an initial chargeapacity of 78.4 mAh/g and discharge capacity of 75.5 mAh/gan be obtained. Even when the current density is increased to0 mA/g, the initial charge and discharge capacity of 48.6 mAh/gnd 46.8 mAh/g can still be held. Although the specific capacityresents an acute decrease with the increased current density, the

nitial charge and discharge capacity obtained here are still mucharger than that of about 4.42 mAh/g reported by Legagneur et al.20].

Fig. 5 shows the cyclic voltammograms (CVs) of LiMnBO3 inhe potential range of 1.7–4.8 V at a scan rate of 0.03 mV/s atoom temperature, starting in charge. In LiMnPO4 [24], the sam-les exhibited electrochemical activity with charge and dischargelateaus around 4.1 V vs. Li+/Li, which corresponded to the redoxouple of Mn3+/Mn2+ that accompanied with lithium-ion extrac-ion and insertion from/into LiMnPO4. In Fig. 5, one peak can belearly observed during anodic and cathodic sweep respectively.n the anodic sweep, the peak with a maximum situated at 2.23 Vorresponds to the Mn2+/Mn3+ redox couple. During the followingischarge, a large reduction peak associated to lithium reinsertionMn3+ reduced to Mn2+) is observed between 4.5 and 3.8 V, with a

aximum at 4.13 V. Such a high value of the Mn3+/Mn2+ redox cou-le is similar to that observed in the Olivine-type Li1−xMnyFe1−yPO46]. It has been reported that the use of polyanions such as (SO4)2−,PO4)3−, (AsO4)3−, (MoO4)2− or (WO4)2− can lower the Fe3+/Fe2+

edox energy [6], where the polarization of the electrons of the O2−

ons into strong covalent bonding within the polyanion reduces theovalent bonding to the iron ion, which lowers its redox energy.he stronger the covalent bonding within the polyanion, the lowers the Fe3+/Fe2+ redox energy [6]. It is believed that high value of

Fig. 3. SEM of LiMnBO3 sintered at (a) 750 ◦C, (b) 800 ◦C, (c) 850 ◦C.

the Mn3+/Mn2+ redox couple in LiMnBO3 is due to the tuning theenergy of the Mn3+/Mn2+ couple by polyanion (BO3)3−, as the resultof the strong covalent bonding within the (BO3)3− polyanion. Thepeak currents and the peak potentials did not change significantlyduring cycling, which suggest that reversible Li-ion extraction andinsertion can occur during charging and discharging process inLiMnBO .

3

It has been reported that for lithium borate the experimentalresult is very sensitive to the synthesized technique [25]. Compar-ing with LiFeBO3 synthesized by different materials or synthesisroutes which show an obvious different electrochemical properties

418 L. Chen et al. / Journal of Alloys and Compounds 494 (2010) 415–419

Fig. 4. The first charge/discharge profiles of LiMnBO3 composites with various cur-rent density. (a) 5 mA/g; (b) 10 mA/g; (c) 20 mA/g; (d) 50 mA/g.

Fs

[bosei

etca

Fv

ig. 5. Cyclic voltammograms of a LiMnBO3 taken at 0.03 mV/s. The potential wascanned between 1.70 and 4.80 V.

21], we think that the difference of the electrochemical propertiesetween Legagneur et al.’s and ours may be due to the differencef the experimental method. Furthermore, the optimization of theynthesized method and metal ion doping are expected to lead tonhance the electrochemical performance of the LiMnBO3 compos-te material in our future work.

The cyclic performance of the LiMnBO composite material was

3valuated in the voltage range 1.0–4.8 V in the Li/LiMnBO3 cell, andhe results are shown in Fig. 6. The cells were discharged at differenturrent density 5 mA/g, 10 mA/g and 20 mA/g between 1.0 and 4.8 Vnd the initial discharge capacities of 75.5 mAh/g, 60.1 mAh/g, and

ig. 6. Discharge capacities vs. cycles of LiMnBO3 at different current density in theoltage range: 1.0–4.8 V.

Fig. 7. The XRD patterns of LiMnBO3 as electrodes: (a) reference (ICSD card: no.94318), (b) before and (c) after 10 cycles.

53.4 mAh/g can be obtained, respectively. At 5 mA/g, the dischargecapacity become 72.7 mAh/g after 10 cycles and the mean fade ofcapacity is 0.09% per cycle except for the first cycle. Even whenthe current density is increased to 50 mA/g, the specific capacity of46.8 mAh/g is still remained between 1.0 and 4.8 V and the capacityfade per cycle is only 0.2% after 40 cycles except for the first cycle.Our results suggest that LiMnBO3 can be used as reversible insertionmaterials.

In order to understand the observed electrochemical behaviors(see in Fig. 6), the X-ray diffraction patterns of electrodes beforecycling and after 10 cycles were compared. As shown in Fig. 7, thevariations of peaks position, peak sharp and relative intensity ofthe X-ray diffraction patterns are not distinguishable before andafter cycling. This observation indicates that there has no structuralcollapse occurring after charge/discharge process. When combinedthe cyclic voltammograms result shown in Fig. 5, we can con-clude that the hexagonal structure with the space group of P-6 forLiMnBO3 is maintained after reversible Li-ion extraction and inser-tion process. Our X-ray diffraction patterns of electrodes beforecycling and after 10 cycles (as shown in Fig. 7) indicate that it isdifficult to relate the capacity fading with the structural collapseduring charge/discharge process. The reasons for the capacity fadeare not yet understood, and it may arise from the low ionic conduc-tivity as well as the change in cation distributions over octahedralinterstices, including Li sites. On the other hand, potential range of1.7–4.8 V was used in our experiment and potential of 4.8 V wasconsidered come to the edge of the safe limit of the electrolyte sys-tem used in this study, and detailed study requires in our futurework.

It should be noticed that even though LiMnBO3 offers someencouraging performances, its cyclic stability and discharge capac-ity is still needed to improve. Moreover, the relatively goodelectrochemical performance of LiMnBO3 compounds is achievedin a wide potential window (charge/discharge range between 1.0and 4.8 V), which is too large for application and we should madegreat efforts to get the data of the performance for more realisticvalues of potential window (between 2.5 and 4.0 V), and the data onthe performance for the more realistic values of potential window(e.g. between 2.5 and 4 V vs. lithium) is needed in the future work.

4. Conclusions

LiMnBO3 has been prepared successfully without using carbonblack in the starting materials. X-ray diffraction results indicate thatsingle-phase LiMnBO3 with hexagonal structure can be obtained atthe temperature higher than 850 ◦C. Electrochemical test shows

and Co

adetcsaccsdtttr

A

p0otf

R

[[

[[

[

[

[

[

[

[

[

[

[

L. Chen et al. / Journal of Alloys

n initial discharge capacity of LiMnBO3 is 75.5 mAh/g at currentensity of 5 mA/g and the mean fade of capacity is 0.09% per cyclexcept for the first cycle. Even when the current density is increasedo 50 mA/g, the discharge capacity still attains 42.3 mAh/g and theapacity fade per cycle is only 0.2% after 40 cycles. The CV curveshow that during anodic and cathodic sweep one peak situatedt 2.23 and 4.13 V respectively can be clearly observed, whichorresponds to the Mn3+/Mn2+ redox couple. The no significanthange of the peak currents and the peak potentials during cyclinguggest that reversible Li-ion extraction and insertion can occururing charging and discharging process in LiMnBO3. Combinedhe cyclic voltammograms result with the X-ray diffraction pat-erns of electrodes before and after cycling, it can be concludedhat the hexagonal structure for LiMnBO3 can be maintained aftereversible Li-ion extraction and insertion process.

cknowledgements

This work was funded by NSFC Grant (no. 50772039) sup-orted through NSFC Committee of China and the Foundation (no.7118058) supported through the Science and Technology Bureauf Guangdong Government, respectively. The authors are indebtedo Prof. C. Dong of Institute of Physics, Chinese Academy of Scienceor their assistance with the X-ray diffraction experiments.

eferences

[1] M. Winter, R.J. Brodd, Chem. Rev. 104 (2004) 4245–4270.[2] L.Q. Zhou, Y.G. Liang, L. Hu, X.Y. Han, Z.H. Yi, J.T. Sun, S.J. Yang, J. Alloys Compd.

457 (2008) 389–393.[3] M.S. Whittingham, Chem. Rev. 104 (2004) 4271–4302.[4] P.S. Herle, B. Ellis, N. Coombs, L.F. Nazar, Nat. Mater. 3 (2004) 147–152.

[

[

[

mpounds 494 (2010) 415–419 419

[5] R. Guo, P.F. Shi, X.Q. Cheng, C.Y. Du, J. Alloys Compd. 473 (2009) 53–59.

[6] A.K. Padhi, K.S. Nanjundaswamy, J.B. Goodenough, J. Electrochem. Soc. 144(1997) 1188–1194.

[7] A.S. Andersson, J.O. Thomas, J. Power Sources 97–98 (2001) 498–502.[8] P.G. Balakrishnan, R. Ramesh, T. Prem Kumar, J. Power Sources 155 (2006)

401–404.[9] Q.S. Wang, J.H. Sun, X.L. Yao, C.H. Chen, J. Electrochem. Soc. 153 (2006)

A329–A333.10] F. Joho, P. Novak, M.E. Spahr, J. Electrochem. Soc. 149 (2002) A1020–A1024.11] J.R. Dahn, E.W. Fuller, M. Obrovac, U. von Sacken, Solid State Ionics 69 (1994)

265–270.12] C. Deng, S. Zhang, S.Y. Yang, J. Alloys Compd. 487 (2009) L18–L23.13] Y.Z. Dong, Y.M. Zhao, H. Duan, L. Chen, Z.F. He, Y.H. Chen, J. Solid State Elec-

trochem. 14 (2010) 131–137.14] L. Liu, L.F. Jiao, J.L. Sun, Y.H. Zhang, M.Z. Zhao, H.T. Yuan, Y.M. Wang, J. Alloys

Compd. 471 (2009) 352–356.15] A.K. Padhi, K.S. Nanjundaswamy, C. Masquelier, S. Okada, J.B. Goodenough, J.

Electrochem. Soc. 144 (1997) 1609–1613.16] J. Gaubicher, J. Rowsell, L. Nazar, Proceedings of the 10th International Meeting

on Lithium Batteries, Como, Italy, May 2000, 2000 (abstract 118).17] V. Legagneur, A. Le Gal La Salle, Y. Piffard, A. Verbaere, D. Guyomard, Groupe

Franc¸ais d’Etudes des Composı̌es d’Insertion, Paris, France, March 2000, 2000(abstract 105).

18] V. Legagneur, A. Le Gal La Salle, Y. Piffard, A. Verbaere, D. Guyomard, Proceed-ings of the 10th International Meeting on Lithium Batteries, Como, Italy, May2000, 2000 (abstract 202).

19] O.S. Bondareva, M.A. Simonov, Y.K. Egorov-Tismenko, N.V. Belov, Sov. Phys.Crystallogr. 23 (1978) 269–271.

20] V. Legagneur, Y. An, A. Mosbah, R. Portal, A. Le Gal La Salle, A. Verbaere, D.Guyomard, Y. Piffard, Solid State Ionics 139 (2001) 37–46.

21] Y.Z. Dong, Y.M. Zhao, Z.D. Shi, X.N. An, P. Fu, L. Chen, Electrochim. Acta 53 (2008)2339–2345.

22] X.M. Hou, Y.M. Zhao, Y.Z. Dong, Dianyuan Jishu 32 (2008) 611–613.

23] C. Delacourt, L. Laffont, R. Bouchet, C. Wurm, J.-B. Leriche, M. Morcrette, J.-M.

Tarascon, C. Masquelier, J. Electrochem. Soc. 152 (2005) A913–A921.24] H.S. Fang, Z.Y. Pan, L.P. Li, Y. Yang, G.F. Yan, G.S. Li, S.Q. Wei, Electrochem.

Commun. 10 (2008) 1071–1073.25] M. He, X.L. Chen, B.Q. Hu, T. Zhou, Y.P. Xu, J. Solid State Chem. 165 (2002)

187–192.