The influence of PEO on the synthesis and electrochemical properties

The influence of PEO on the synthesis and electrochemical properties of VO2 and V3O7·nH2O nanobelts as a cathode for lithium battery V. M. Mohan, Kenji Murakami & Wen Chen

Ionics International Journal of Ionics The Science and Technology of Ionic Motion ISSN 0947-7047 Volume 18 Number 6 Ionics (2012) 18:607-614 DOI 10.1007/s11581-012-0665-4

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Author's personal copy Ionics (2012) 18:607–614 DOI 10.1007/s11581-012-0665-4

ORIGINAL PAPER

The influence of PEO on the synthesis and electrochemical properties of VO2 and V3O7·nH2O nanobelts as a cathode for lithium battery V. M. Mohan & Kenji Murakami & Wen Chen

Received: 23 March 2011 / Revised: 9 January 2012 / Accepted: 9 January 2012 / Published online: 22 January 2012 # Springer-Verlag 2012

Abstract In this paper, we report the hydrothermal synthesis of VO2, poly(ethylene oxide) (PEO)/VO2,V3O7·nH2O and PEO/V3O7·nH2O nanobelts by using 1,2-propylene carbonate (1,2-PC (C4H6O3)) and poly(ethylene glycol) (PEG) as templates, respectively. Structure and morphology of the samples were investigated by XRD, FTIR, SEM, and TEM. The vanadium oxide (VO2) nanobeltcomposite show the initial specific capacity 152 mA h g−1, whereas PEO/VO2 shows 182 mA h g−1. The pure V3O7·nH2O nanobelts shows the initial specific capacity 192 mA h g−1, while PEO/ V3O7·nH2O nanobelts show 297 mA h g−1. It was found that PEO/VO2 and PEO/V3O7·nH2O nanocomposites show better cyclic performance and high discharge stability compared to pure vanadium oxide nanomaterials. The role of the polymeric PEO component of the hybrid material seems to be the stabilization and improvement of the specific capacity due to probable homogeneous distribution between the nanobelts. The TEM images indicate that PEO works as a surfactant to decrease the dimensions of nanobelts. Keywords Hydrothermal synthesis . VO2 and V3O7 . nH2O nanobelts . Poly(ethylene oxide) . Cathode material . Electrochemical properties

V. M. Mohan (*) : K. Murakami Research Institute of Electronics, Shizuoka University, Johoku, Hamamatsu 432-8011, Japan e-mail: [email protected] V. M. Mohan : W. Chen State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, and School of Materials Science and Engineering, Wuhan University of Technology, Wuhan 430070, People’s Republic of China

Introduction The synthesis of inorganic nanoscale materials with special morphologies has been of great interest in recent years. Nanotubes, nanorods, and nanowires are accessible now in various material systems with well-developed morphology [1]. The high energy density demand from our modern society imposes a constant development and improvement in energy production and energy devices. Among the energy sources, lithium ion batteries are one of the most attractive candidates because of their long cycle life and high energy density [2]. This type of batteries has already invaded the portable market, and is expected to be a key component for the future electronic vehicles. In the present commercial technology, mostly batteries are based on the use of the layered LiMO2 (M0Co, Ni, and Mn) as cathode material while the anode is made of different kinds of carbon materials or alloys. The layered structure of LiMO2 cathode materials have serious drawbacks, namely high toxicity and limited capacity [3], many research efforts are being made to find better systems. The vanadium oxide with a wide range of oxidation states varying from +2 to +5 may accommodate multielectron transfer process in battery applications. Therefore, it has the potential to be used in rechargeable lithium batteries and to provide high specific capacities than the common oneelectron-transfer cathode materials, such as LiCoO2, LiMn2O4 and LiFePO4. In fact, several VOx compounds such as VO2 (B) multiwall carbon nanotubes [4], hollow VO2 microspheres [5], VO2 rods [6], VO2 (B) ultrathin nanowires [7], VO2 nanobelts [8], V3O7·H2O single crystal nanobelts [9] have been reported in literature on their synthesis and various potential applications. Nanostructures of VO2 and V3O7·nH2O have been prepared by various techniques. Thin films of thermochromic

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VO2 have been obtained by pulsed laser deposition onto SiO2/Si substrates [10], sol–gel deposition using vanadium alkoxides [11, 12], and atmospheric pressure chemical vapor deposition with VOCl3 [13]. VO2 nanowires and nanorods have been prepared by hydrothermal methods using glycol reduction [14] or surfactants [15, 16], structure direction reagent [3] and Liu et al. showed that VO2 nanobelts can be synthesized hydrothermally using formic acid as the reducing and acidifying agent [17]. The metastable VO2 (B) was especially interesting because of its layered structure and potential applications in lithium batteries [18]. Hydrothermal synthesis is an effective method to fabricate 1-D nanostructures because of its low temperature requirement as well as inexpensive, amenable for large scale and wide suitability for various nanomaterials. It is more effective method for the formation of nanobelts from V2O5 precursor in the presence of PEG as well as PEO polymers. Felicitous choice of a precursor is feasible to obtain desired products [19, 20]. The concept of hybridizing organic and inorganic compounds to form a unique material (with the properties not just the sum of the individual contributions) is a well-known strategy [21–23]. A synergistic effect was observed in the specific capacity if the cathodes are formed with hybrid materials with an intimate contact between the oxide and the electronic conducting polymer. The optimization was achieved based on the increase of electronic conductivity by changing the ratios of lithium salt and host polymer matrix [21, 24]. PEO have been widely used as guest materials because of its good ionic conductivity, in which most of the alkali metal salts dissolved and have promising cathode performance in lithium secondary batteries. In the present paper, PEO mixed VO2 nanobelts with length of 0.5–1.25 μm, width of 90–200 nm and thickness of 25–50 nm were synthesized by simple hydrothermal method. Similarly in the same hydrothermal technique V3O7·nH2O nanobelts with length of 1–3 μm and width of 200 nm to 250 nm were synthesized using PEG as template for V2O5 powder. The structure, complexation and morphologies were studied by X-ray diffraction (XRD), Fourier transform infrared (FTIR), SEM, and TEM studies. The electrochemical lithium insertion/extraction characteristics of the as prepared and PEO mixing nanobelts were investigated by cyclic voltametry and galvanostatic charge/discharge method.

Experimental Synthesis of vanadium oxide (VO2) and V3O7·nH2O nanobelts All the reagents used in the experiments were of analytical grade and used without any purification. In the typical procedure, 5 mmol of V2O5 powder was dispersed into

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20-ml distilled water and then 10 mmol of 1,2-propylene carbonate (1,2-PC (C4H6O3)) was added into the above solution with magnetic stirring. After 5 min, 20 ml distilled water was added to form a 40-ml homogeneous mixed solution. The mixed solution was transferred into a 50 ml stainless steel Teflon-lined autoclave. The autoclave was sealed and maintained at 180 °C for 48 h and then cooled to room temperature naturally. The products were filtered off, washed with distilled water and absolute alcohol several times to remove any possible residue, and dried in vacuum at 80 °C for 7 h. The chemical equation of this reaction can be shown as follows 8V2 O5 þ C4 H6 O3 ! 16VO2 þ 4CO2 þ 3H2 O

ð1Þ

In the preparation of V3O7·nH2O nanobelts, we used the same above process by taking 2 mmol V2O5 powder and 10 mmol PEG-400 as a starting materials. During the hydrothermal process, V2O5·nH2O is initially formed, which could be detected in a short time. Then, V2O5·nH2O was reduced to V3O7·H2O with the presence of strongly hydrophilic PEG-400. It is to say that some +5 oxidation state of vanadium was reduced to +4 oxidation state by PEG-400 under the hydrothermal condition. The general chemical equation can be written as V2 O5 þ C2n H4nþ2 Onþ1 ðPEG 400Þ ! V3 O7 þ H2 O þ CO2

ð2Þ The layered structure of V3O7·H2O was described by Oka et al. [25] which consists of VO6 octahedral and VO5 trigonal bipyramids with vanadium oxidation states of +4 and +5, respectively. One of oxygen atoms in the VO6 octahedron is replaced by the water molecule bounded to the vanadium ion, and hydrogen bonds with the octahedral in the next layer are formed. Therefore, the interlayer spaces between the VO6 octahedral and VO5 trigonal bipyramids are occupied by H2O molecules, resulting that the interactions between the layers of them are weakened, and the lamellar structures were gradually exfoliated to fabricate nanosheets. Because the nanosheet does not have reverse symmetric and the structure of the layer is often asymmetric, the surface tension made the nanoplants scroll up. In order to release the strong stress and lower the total energy, the nanosheets were split, which resulted in the formation of nanobelts. After the nanobelts were formed, they had little changes by prolonged time. Therefore, the formation process of V3O7·H2O nanobelts could be described as hydrating– reducing–exfoliating–splitting mechanism [9]. Similarly, in the preparation of PEO/VO2 and PEO/ V3O7·nH2O nanobelts composites, 0.5 mol% of the PEO was mixed to the 40 ml solution before hydrothermal treatment.

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Preparation of Li batteries The coin type (around 1.5 cm diameter) electrochemical cells were assembled using 5–7 mg of the active material in a dry glove box filled with an argon gas. The lithium pellets used as negative electrode. The 1 M solution of LiPF6 prepared by using ethylene carbonate/dimethyl carbonate ratios (1/1v/v) as a solvent and it is used as an electrolyte. The cathode pellets were made using active material, acetylene black and PTFE in the ratio of 6:4:1. Characterization The X-ray powder diffraction (XRD) measurement was performed on a D/MAX-III X-ray diffractrometer with CuKα (101.5418 Å) radiation and graphite monochromator. FTIR absorption spectra were recorded using the 60-SXB IR spectrometer with a resolution of 4 cm−1. The measurements were taken over a wave number range of 400– 4,000 cm−1. SEM images were obtained using JSM-5610LV scanning electron microscope at 20 kV. TEM images were taken in a JEOL JEM-2010 FEF microscope operated at 200 kV. Electrochemical studies were investigated by an Autolab Potentiostat 30 System with the scan rate of 0.5 mV s−1 at 2.0–4.0 V vs. Li/Li+ potential range and a Battery Testing System (BTS-5 V/5 mA) was operated with the constant current density of 26 mA cm−2 at 2.0–4.0 V vs. Li/Li+ potential range.

Results and discussion XRD of VO2 (B) nanobelts and PEO/VO2 (B) nanobelt composites were shown in Fig. 1. The XRD pattern of the vanadium oxide (VO2) (B) peaks can be indexed to the monoclinic system with the lattice constants a012.03 Å, b03.693 Å and c06.42 Å [JCPDS 31-1438]. The XRD peaks of the PEO/VO2 shows less intensities compared with pure VO2 nanobelts which indicate the composite material become less crystalline than pure VO2 nanobelts due to the presence of PEO. The PEO/VO2 nanobelts composite shows the (001) weakened intensity of peak probably due to less orientation or less growth of crystalline particles. From Fig. 1, it is clear that the VO2 (B) nanobelts and PEO/ VO2 (B) nanobelt composite existed similar XRD peaks which indicate that structure of the host material is preserved. Figure 2 shows the XRD patterns of V3O7·nH2O nanobelts, 0.5 mol% PEO mixed V3O7·nH2O nanobelts. All diffraction peaks of the vanadium oxide (V3O7·H2O) can be indexed to the orthorhombic system with the lattice constants a09.34 Å, b017.0 Å, and c03.626 Å (JCPDS 28-1433). Vanadium oxides with mixed valency, containingV5+ as well as V4+ cations, were usually obtained by

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hydrothermal processing of precursor and reductive organic molecules [26]. Polymers such as PVP, PEO, and PEG are multidentate ligand with poly functional groups, which can serve as bridging ligands to form multinuclear complexes [27]. The FTIR spectra of VO2 nanobelts and PEO/VO2 composites were shown in Fig. 3. The characteristic bands appeared in the both samples of VO2 nanobelts and PEO/ VO2 nanobelts at 2,919 and 2,850 cm−1 assigned to the CH3 asymmetric and symmetric stretching vibrations of the 1,2PC (C4H6O3) [28]. The broad band at 3,404 cm−1 and weak absorption band at 1,628 cm−1 were assigned to the stretching and bending vibration mode O–H and H–O–H [20]. The VO2 and PEO/VO2 nanobelts exhibit three main vibrational modes in the 500–1,040 cm−1 wavenumber region. The terminal oxygen symmetric starching mode (νs) of V═O and the bridge oxygen asymmetric and symmetric starching modes (νas and νs) of the V–O–V are at 999, 923, 534 cm−1, respectively [29]. There are other bands appeared in the composite material at 876, 1,042, 1,122, 1,155, 1,420, 1,729, 2,521 cm−1 due to the presence of PEO [30]. In the FTIR spectra (Fig. 4) of the V 3O 7·nH 2 O the band at 3,426 cm−1 and weak absorptions at 1,603 cm−1 were assigned to the stretching and bending vibration of absorbed H2O or hydroxyls [31]. The band at 1,010 cm−1 was attributed to the coupled vibration between V═O and V–O–V. The same bands appeared in PEO/V3O7·nH2O composite nanobelts also. The broad band between 480 and 715 cm−1 was assigned to the asymmetric and symmetric stretching vibration of V–O–V modes [15]. The broad band appeared 559 cm−1 in V3O7·nH2O, whereas PEO/V3O7·nH2O case it appeared at 756 cm−1. The bands at 768 cm−1 are assigned to the vibration of O–(V)3 in V3O7·nH2O where as it is appeared at 756 cm−1 in. Similar behavior was observed earlier reports [18, 20] the shifting of peaks in PEO/ V3O7·nH2O compared to the corresponding V3O7·nH2O band in further indicates may be the partially reduced valence of vanadium in the precursor. The peaks appeared (Fig. 4b) at 2,830–2,950 cm−1 due to the presence of PEO. Figure 5a and b shows the scanning electron microscopic images of VO2 nanobelts and PEO/VO2 nanobelt composite. The VO2 and V3O7·nH2O nanobelts were grown mostly individually or separately whereas the PEO/VO2 and PEO/ V3O7·nH2O nanobelts were grown together in the form of closely packed bundles. From Fig. 5a, the length and width of the nanobelts are found to be 1–3 μm and 200–250 nm, respectively. The lengths of the nanobelts were decreased with the mixing of PEO. The length and width of the nanobelts were found to be 0.5–1.25 μm and 60–200 nm, respectively (Fig. 5b). Figure 5c and d shows the scanning electron microscopic images of the V3O7·nH2O nanobelts, PEO/V3O7·nH2O nanobelts uniformly grown and clearly visible. The sample has a black color indicating some vanadium in a +4 oxidation


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Fig. 1 X-ray diffraction patterns of a VO2 nanobelts b PEO/VO2 nanobelt composites

state, because mixed valent V (IV, V) oxides are generally black (e.g., V6O13). From Fig. 5c, the length and width of the nanobelts are found to be around 3 to 5 μm and 100 to 200 nm, respectively. In the PEO/V3O7·nH2O nanobelts, the length was decreased. The lengths of the nanobelts are found to be from 0.5 to 2 μm (Fig. 5d). Figure 6a, b, and c show TEM images of VO2, PEO/VO2 and PEO/V3O7·nH2O nanobelts, respectively. The width and thickness of the VO2 nanobelt was found to be about 220 and 60 nm respectively, whereas in PEO mixed VO2 Fig. 2 X-ray diffraction patterns of a V3O7·nH2O b PEO V3O7·nH2O nanobelt composites

nanobelts width and thickness are about 95 and 30 nm respectively. These results indicated that the dimensions (length, width, and thickness) of the nanobelts were decreased. Hence, we can say that PEO is not only existence between nanobelts and also works as a surface reactant during hydrothermal process. We measured the cyclic voltammograms of VO2, PEO/ VO2, V3O7·nH2O and PEO/V3O7·nH2O nanobelts for the first ten cycles. The area Ai (i is the cycle time) which is surrounded by each cycle represents the amount of the Li+


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Fig. 3 FTIR spectra of a VO2 nanobelts and b PEO/VO2 nanobelt composites

ions insertion. The cycle efficiency was calculated by the following equation Qi ¼ Ai =A1 Where Qi 0cycle efficiency, A1 0the area of the first cycle, Ai 0the area of the ith cycle. The cycle efficiency of different cycle times for V3O7·nH2O and PEO/V3O7·nH2O are listed in Table 1. The third cycle efficiency of the Q3 for V3O7·nH2O and PEO/V3O7·nH2O nanobelts are 68.7% and Fig. 4 FTIR spectra of a V3O7·nH2O and b PEO V3O7·nH2O nanobelt composites

82.2%, respectively. Meantime, the tenth cycle efficiency Q10 of the PEO/V3O7·nH2O nanobelts is found to be 60.4%, which is higher than that of V3O7·nH2O (47.9%). The higher cycle efficiency of PEO/V3O7·nH2O nanobelts composite indicates that the stability of cycling property increases when compared V3O7·nH2O nanobelts. Similar type of results were observed in PEO used V2O5 nanotubes and PEG surfactant MoO3 nanobelts in our previous work [24, 32]. The different cycle efficiencies are shown in Table 1.


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Fig. 5 SEM images of a VO2, c V3O7·nH2O nanobelts, and b PEO/VO2, d PEO V3O7·nH2O nanobelt composites

Battery charge/discharge characteristics Figure 7 shows the curves of discharge capacity vs. the cycle number for the electrodes made from VO2 nanobelts Fig. 6 TEM images of a VO2 nanobelt and b PEO/VO2, c PEO V3O7·nH2O nanobelt composites

and PEO/VO2 nanobelt composite at 25 °C. The discharge capacity of VO2 nanobelts showed 152 mA h g−1 in the first cycle and it decreases gradually in the next cycles and still retains 115 mA h g−1 after 50 cycles, corresponding to about


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Table 1 The cyclic efficiencies of various materials at different cyclic numbers Material

Q3

Q6

Q10

VO2 nanobelts PEO/VO2 nanobelts V3O7·nH2O nanobelts PEO/V3O7·nH2O nanobelts

63.3 87.43 68.7 82.2

55.7 82.1 56.06 68.9

50.1 80.8 47.9 60.4

75.6% of its initial capacity. The PEO/VO2 nanobelt composite has an initial specific capacity of 182 mA h g−1, and its stabilized capacity still remains as high as 125 mA h g−1after 50 cycles. Figure 9 shows the curves of discharge capacity vs. the cycle number for the electrodes made from V3O7·nH2O nanobelts at a charge–discharge current density of 24.75 mA cm−2 and a temperature of 25 °C. The discharge capacity of V3O7·nH2O nanobelts is 192 mA h g−1 in the first cycle and it decreases gradually in the next cycles still retains 180 mA h g−1 after 25 cycle, corresponding to about 93.75% of its first capacity. The PEO/V3O7·nH2O nanobelts composite has an initial specific capacity of 297 mA h g−1, and its stabilized capacity still remained as high as 203 mA h g−1after 30 cycles. The discharge stability of the PEO/VO2 and PEO/ V3O7·nH2O nanobelt composites becomes higher, compared with that of pure VO2, V3O7·nH2O nanobelts, because some of the space occupied by the PEO between the nanobelts. The Li+ ions insertion/extraction is more easily through the PEO occupied space in the composite material compared to pure nanobelts. In addition, the numbers of lithium ions moving through the nanobelts were increased probably due to increasing the number spaces between the nanobelts from the formation of lower dimensions in the particular area compared to pure nanobelts. The first charge and discharge curves of VO2 and PEO/VO2 nanobelt composite were shown in Fig. 8. In

addition, the mixed PEO into VO2 nanobelt cells exhibit good capacity retention during cycling. These results obtained in organic electrolyte provide an exciting prospect for aqueous lithium batteries [33]. Comparing with the first specific discharge capacity of both materials, we note that the data showed a sharp depreciation at the second specific discharge capacities which are 143 and 159 mA h g−1, respectively. This phenomenon is likely to be due to the irreversible changes (such as crystallization) of the material’s structure after the first lithium ions insertion/extraction process and/or some of the active sites occupied by the lithium ions in the electroactive material [32]. This behavior also observed PEO/ V3O7·nH2O nanobelts in the first to fourth cycles in Fig. 9a. The cycling stability and reversibility of insertion/extraction of Li+ ions significantly enhances because PEO has relatively mixed with VO2 nanobelts by reducing the size and the complexing with Li+ ions, effectively shielding the electrostatic

Fig. 7 The discharge characteristic of a VO2 nanobelts and b PEO/ VO2 nanobelt composites

Fig. 9 The discharge characteristic of a V3O7·nH2O and b PEO V3O7·nH2O nanobelt composites

Fig. 8 The first charge, discharge cycles of VO2 nanobelts 3, 4 and PEO/VO2 1, 2 nanobelt composites


interaction between Li+ ions and VO2 nanobelts. All these results indicate that PEO/VO2 and PEO/V3O7·nH2O nanobelt composites are useful as a cathode material for the application of lithium ion batteries.

Conclusions A simple hydrothermal method was introduced for the preparation of VO2, V3O7·nH2O nanobelts and PEO/VO2 nanobelt composites. The decreased length and width of the nanobelts is due to the presence of PEO and there is no large influence on the VO2 crystal structure. The typical length and width of nanobelts are found to be around 0.5–1.25 μm and 60– 200 nm, respectively. The electrochemical results indicate that the PEO/VO2 nanobelt composite has an initial specific capacity of 182 mA h g−1, and its stabilized capacity still remains as high as 125 mA h g−1after 50 cycles. The presence of PEO in addition of PEG showed to decrease the length and width of the nanobelts, but it has some influence on the V3O7·nH2O crystal structure. The typical length and width of nanobelts are found to be around 3–5 μm, 30–40 nm, respectively. The electrochemical tests indicates that the PEO/V3O7·nH2O nanobelts composite has an initial specific capacity of 297 mA h g−1, and its stabilized capacity still remained as high as 203 mA h g−1after 30 cycles. The improved electrochemical performance is due to the reduction of dimensions of the VO2 and V3O7·nH2O nanobelts by mixing with PEO and also which shield the electrostatic interaction between Li+ ions and VO2 as well as V3O7·nH2O nanobelts. Acknowledgments One of the authors (V.M. Mohan) wishes to thank the Wuhan University of Technology, China and Shizuoka University, Japan for the financial and technical support in the form of a post-doctoral fellowship.

References 1. Ji SD, Zhao YG, Zhanga FZ, Jin P (2010) J Crystal Growth 312:282 2. Munoz-Rojas D, Baudrin E (2007) Solid State Ionics 178:1268 3. Zhang KF, Bao SJ, Liu X, Shi J, Su ZX, Li HL (2006) Mater Res Bull 41:1985

Ionics (2012) 18:607–614 4. Rahman MM, Wang JZ, Idris NH, Chen ZX, Liu HK (2010) Electrochim Acta 56:693 5. Yan XP, Chen J, Liu JM, Zhou PP, Liu X, Su ZX (2010) Mater Lett 64:278 6. Jiang LL, Wei MD, Ye BH, Wei KM (2008) J Crystal Growth 310:4301 7. Armstrong G, Canales J, Armstrong AR, Bruce PG (2008) J Power Sources 178:723 8. Zakharova GS, Hellmann I, Volkov VL, Taschner Ch, Bachmatiuk A, Leonhardt A (2010) Mater Res Bull 45:1118 9. Zhang Y, Liu XH, Xie GY, Yu L, Yi SP, Hu MJ (2010) Mater Sci Engg B 175:164 10. Youn DH, Lee JW, Chae BG, Kim HT, Maeng SL, Kang KY (2004) J Appl Phys 95:1407 11. Guzman G, Morineau R, Livage J (1994) Mater Res Bull 29:509 12. Speck KR, Hu HSW, Sherwin ME, Potember RS (1988) Thin Solid Films 165:317 13. Qureshi U, Manning TD, Parkin IP (2004) J Mater Chem 14:1190 14. Chen XY, Wang X, Wang ZH, Wan JX, Liu JW, Qian YT (2004) Nanotechnology 15:1685 15. Pavasupree S, Suzuki Y, Kitiyanan A, Pivsa-Art S, Yoshikawa S (2005) Solid State Chem 178:2152 16. Chen W, Peng JF, Mai LQ, Yu H, Qi YY (2004) Chem Lett 33:1366 17. Liu JF, Li QH, Wang TH, Yu DP, Li YD (2004) Angew Chem Int Ed 43:5048 18. Sediri F, Gharbi N (2009) Mater Lett 63:15 19. Ferreira OP, Otubo L, Romano R, Alves OL (2006) Cryst Growth Des 6:601 20. Mao L, Liu C (2008) Mater Res Bull 43:1384 21. Hwang KS, Lee CW, Yoon TH, Son YS (1999) J Power Sources 79:225 22. Jin A, Chen W, Zhu QY, Yang Y, Volkov V, Zakharova GS (2008) Solid State Ionics 179:1256 23. Murugan AV (2005) Electrochim Acta 50:4627 24. Mohan VM, Bin H, Qiu W (2009) J Appl Electrochem 39:2001 25. Oka Y, Yao T, Yamamoto N (1990) J Solid State Chem 89:372 26. Livage J (1998) Coord Chem Rev 178:999 27. Deng Y, Wei GD, Nan CW (2003) Chem Phys Lett 368:639 28. Fei B, Chen C, Peng S, Zhao X, Wang X, Dong L (2004) Polym Int 53:2092 29. Subba Reddy ChV, Sun-il M, Kalluru RR, Williams QL (2008) J Power Sources 179:854 30. Tang Z, Wang J, Chen Q, He W, Shen C, Mao XX (2007) Electrochim Acta 52:6638 31. Nakmoto K (1991) Infrared and Raman spectra of inorganic and coordination compounds. 1st Chemical Industry Press, Beijing, p 251 (D. Huang, R.Wang, Trans.; in Chinese) 32. Mohan VM, Bin H, Chen W (2010) J Solid State Electrochem 14:1769 33. Ding N, Feng X, Liu S, Xu J, Fang X, Lieberwirth I (2009) Electrochem Commun 11:538