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SnS2–graphene nanocomposites as anodes of lithium-ion batteries
Solid State Sciences 31 (2014) 81e84
Contents lists available at ScienceDirect
Solid State Sciences journal homepage: www.elsevier.com/locate/ssscie
SnS2egraphene nanocomposites as anodes of lithium-ion batteries Qi Wang, Yu-Xin Nie, Bin He, Li-Li Xing, Xin-Yu Xue* College of Sciences, Northeastern University, Shenyang 110004, China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 3 February 2013 Accepted 3 March 2014 Available online 14 March 2014
SnS2egraphene nanocomposites are synthesized by a hydrothermal method, and their application as anodes of lithium-ion batteries has been investigated. SnS2 nanosheets are uniformly coating on the surface of graphene. SnS2egraphene nanocomposites exhibit high cyclability and capacity. The reversible capacity is 766 mAh/g at 0.2C rate and maintains at 570 mAh/g after 30 cycles. Such a high performance can be attributed to high electron and Li-ion conductivity, large surface area, good mechanical flexibility of graphene nanosheets and the synergetic effect between graphene and SnS2 nanostructures. The present results indicate that SnS2egraphene nanocomposites have potential applications in lithium-ion battery anodes. Ó 2014 Elsevier Masson SAS. All rights reserved.
Keywords: Graphene Nanocomposites Anode Lithium-ion battery
1. Introduction
2. Experiments
Recently, the development of self-charging power cell (SCPC) and solar-lithium integrated power pack (SLPP) has raised the requirement of the performance of the anodes in lithium-ion battery (LIB) [1,2]. Nowadays, various metal composites, metal oxides and metal sulfides, based on their transformation to lithium-metal alloys, have been studied extensively as possible alternatives to carbonaceous anode materials because of their higher capacities [3e5]. It has been reported that graphene-based nanocomposites, such as SnO2egraphene nanocomposites, can achieve nearly theoretical specific energy density without significant charge/ discharge degradation [6,7]. Scientists suggest that small quantities of high-quality graphene can dramatically improve the power and cycling stability of LIBs, while maintaining high-energy storage capacities [6,7]. Graphene exhibits a unique structure of one-atomthick and two-dimensional layers of sp2-bonded carbon, which has high surface areas (theoretical value of 2630 m2/g), mobility of charge carriers (200,000 cm2/V s) and wide electrochemical window [8e10]. These properties make graphene an ideal twodimensional supporting material for anchoring active materials, offering high performances in LIB. In this work, SnS2egraphene nanocomposites are synthesized via a hydrothermal route and exhibit high cyclability and capacity. Our results are the bases for their application in LIBs, SCPCs and SLPPs.
SnS2egraphene nanocomposites were prepared by a hydrothermal method. Typically, 449 mg SnCl4$H2O and 195 mg thiourea were ultrasound dissolved in 20 ml ethanol to form a transparent solution. 5.5 mg graphene was ultrasonically dispersed in 19 ml ethanol to form black solution. Then both the suspension was transferred into a 50 ml Teflon-lined stainless steel autoclave and maintained at 453 K for 6 h. After that, the autoclave was cooled to room temperature, the black products were washed with ethanol and distilled water for several times and dried in air at 333 K for 12 h. The characteristics of the products were measured by XRD (D/ max 2550 V, CuKa radiation, l ¼ 1.5416 A), SEM (JEOL JSM-6700F), and TEM (TECNAI F20). The fabrication process of LIBs was as follows. The samples were mixed with acetylene black and carboxymethyl cellulose (CMC) at a weight ratio of 8:1:1. The mixture was painted onto a copper foil with a diameter of 15 mm. The 2016 coin-type cells were assembled in an argon-filled glove box, and pure Li foils were used as the counter electrodes. The electrolyte was made of 1 M LiPF6 in the mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) with the volume ratio 1:1. The cells were galvanostatically charged and discharged between 1 mV and 3 V versus Liþ/Li at room temperature on a program-controlled test system. 3. Results and discussion
* Corresponding author. Tel.: þ86 24 83687658. E-mail address: [email protected] (X.-Y. Xue). http://dx.doi.org/10.1016/j.solidstatesciences.2014.03.001 1293-2558/Ó 2014 Elsevier Masson SAS. All rights reserved.
The crystalline phase of SnS2egraphene nanocomposites is characterized by X-ray powder diffraction (XRD). As shown in
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Q. Wang et al. / Solid State Sciences 31 (2014) 81e84
Fig. 1a, the sharp diffraction peaks can be indexed to SnS2 crystal given by the standard data (JCPDS file No. 40-1467), suggesting the well crystalline of SnS2. The broad peak in the range of 20e30 coincides with the small crystallized portion of the graphene. EDX spectroscopy is used to examine the local elemental composition of the nanocomposites, as shown in Fig. 1b. Sn:S atomic ratio is about 1:2, which is consistent with the atomic ration of SnS2. The silicon signals are from the silicon substrate, which is used in scanning electron microscopy (SEM) observation. The morphology and structure of SnS2egraphene nanocomposites are illuminated by SEM, as shown in Fig. 2a. It can be seen that the product consists of a large amount of sheet-like nanostructures. Fig. 2b is transition electron microcopy (TEM) image of SnS2egraphene nanocomposites. The lattice fringe crystalline nature of 0.59 nm corresponds to (001) plane of SnS2 crystal. In the growth process, the formation of sheet-like SnS2 crystallites is mainly caused by the intrinsic anisotropic nature of SnS2, which has a CdI2-related crystal structure [11]. SnS2 crystallizes in the layered CdI2 type lattice with lattice constants a ¼ 53.645 A and c ¼ 55.898 A [12]. Its atomic structure consists of layers separated by a space. In the atomic structure, there are numerous vacant lattice sites. The interlayer ones are octahedrally (labeled Oh1) or tetrahedrally (labeled Td2) coordinated to sulfur atoms. The Oh1 ones are situated at the center of the interlayer space and they are relatively far from the two nearest tin atoms. The Td2 ones, symmetrically situated in the gap are also relatively far from the three
Fig. 2. (a) SEM image of SnS2egraphene nanocomposites. (b) TEM image of SnS2e graphene nanocomposites.
nearest tin atoms. It is seems likely that these vacant sites enhance the lithium intercalation [13]. Electrochemical cycling tests of the SnS2egraphene nanocomposites electrodes are performed at 0.2C rate (5 h per half cycle) between 3 V and 0 V. The voltage profiles of the sample for 30 cycles are presented in Fig. 3a. The sample exhibits plateau at about 1.2 V on the first discharge process. During the subsequent cycles, the discharge and charge plateaus are observed in the potential ranges of 0.0e0.5 V and 0.7e1.1 V. The reversible capacity of SnS2e graphene electrodes is 766.3 mAh/g. Fig. 3b shows the differential capacity curves (dC/dV vs. voltage) of SnS2egraphene nanocomposites. The broad peak at w1.2 V in the first discharge process can be ascribed to the following reaction:
SnS2 þ4Liþ þ4e /Sn þ 2Li2 S;
(1)
And the peak at w0.6 V in the first discharge process can be attributed to the redox peak couple of reaction [14e17]:
Sn þ xLiþ þ xe 4Lix Snð0 x 4:4Þ:
Fig. 1. (a) XRD pattern of SnS2egraphene nanocomposites. (b) EDX spectrum of SnS2e graphene nanocomposites.
(2)
In the first discharge process, Li-inserted SnS2 forms LixSn and amorphous Li2S [18]. During substantial charge and discharge processes, reaction between the newly formed metallic Sn and lithium leads to the formation of Li4.4Sn alloys, and the Li2S acts as an inertmatrix surrounding the active Sn grains. Usually, SnS2 shows high initial discharge capacities, but its capacity retention
Q. Wang et al. / Solid State Sciences 31 (2014) 81e84
83
Fig. 3. (a) Voltageecapacity profile of SnS2egraphene electrode at 0.2C rate. (b) Differential capacity curves of SnS2egraphene nanocomposites. Fig. 4. (a) Cycling stability of Li insertion and extraction in SnS2egraphene nanocomposites. (b) Cyclability of SnS2egraphene nanocomposites in the voltage range of 0e3 V.
needs improvement. Here, the combination of SnS2 and graphene is an effective way to overcome the huge volume expansion of the SnS2 during the chargeedischarge process [18]. As shown in Fig. 4a after the first cycle, the stability of SnS2e graphene nanocomposites is very high. And Fig. 4b illustrates the reversible capacity vs. cycle number profile of SnS2egraphene electrode. The initial reversible capacity of the SnS2egraphene electrode is over 967.6 mAh/g and the capacity drops rapidly to 766.3 mAh/g after the first cycle. It can be seen that after 30 cycles the reversible capacity maintains 570.0 mAh/g, 74.6% of the second discharge capacity. Based on the results above, SnS2egraphene nanocomposites display high reversible capacities and cyclability. Such a high performance of SnS2/graphene nanocomposites as LIB anodes can be attributed to the synergistic effect between graphene and nanostructured SnS2. Firstly, graphene nanosheets act as flexible two-dimensional supports for anchoring of SnS2 nanostructures, not only providing an elastic buffer space to accommodate the volume expansion/contraction of SnS2 nanostructures, but also efficiently preventing the aggregation of SnS2 nanostructures. Secondly, graphene nanosheets in the nanocomposites have a good electrical conductivity and serve as the conductive channels between the nanocomposites and collectors. Thirdly, graphene nanosheets can shorten the path length for Li-ion transport, increase materials/electrolyte contact area, and facilitate the Li-ion diffusing to the sites on the surface of SnS2 nanostructures. Forth, the presence of SnS2 nanostructures on graphene nanosheets effectively prevents the agglomeration of graphene nanosheets, and consequently keeps their high active surface area.
4. Conclusions SnS2egraphene nanocomposites were prepared by a hydrothermal method. And SnS2egraphene nanocomposites displayed high cyclability and capacity as anodes of LIB. The reversible capacity was 766 mAh/g, maintained 570 mAh/g after 30 cycles. Our results implied that SnS2egraphene nanocomposites had potential applications in LIBs at industrial level. Acknowledgments This work was supported by the National Natural Science Foundation of China (51102041 and 11104025), the Fundamental Research Funds for the Central Universities (N120205001 and N120405010), Program for New Century Excellent Talents in University (NCET-13-0112) and Specialized Research Fund for the Doctoral Program of Higher Education of China (No. 20110042120024). References [1] X.Y. Xue, S.H. Wang, W.X. Guo, Y. Zhang, Z.L. Wang, Nano Lett. 12 (2012) 5048e5054. [2] W.X. Guo, X.Y. Xue, S.H. Wang, C.J. Lin, Z.L. Wang, Nano Lett. 12 (2012) 2520e 2523. [3] G.Y. He, J.H. Li, H.Q. Chen, J. Shi, X.Q. Sun, S. Chen, X. Wang, Mater. Lett. 82 (2012) 61e63. [4] Y. Li, J.P. Tu, X.H. Huang, H.M. Wu, Y.F. Yuan, Electrochem. Commun. 9 (2007) 49e53.
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[5] M. Sathish, S. Mitani, T. Tomiai, A. Unemoto, I. Honma, J. Solid State Electrochem. 16 (2012) 1767e1774. [6] J.Z. Wang, L. Lu, M. Choucair, J.A. Stride, X. Xu, H.K. Liu, ACS Nano 3 (4) (2009) 907e914. [7] D. Wang, R. Kou, D. Choi, Z. Yang, Z. Nie, J. Liat, ACS Nano 4 (3) (2010) 1587e 1595. [8] S. Park, R.S. Ruoff, Nat. Nanotechnol. 4 (2009) 217e224. [9] M.J. Allen, V.C. Tung, R.B. Kaner, Chem. Rev. 110 (2010) 132e145. [10] S. Liu, X. Yin, L. Chen, Q. Li, T. Wang, Solid State Sci. 12 (2010) 712e718. [11] Q. Yang, K.B. Tang, C.R. Wang, D.Y. Zhang, Y.T. Qian, J. Solid State Chem. 164 (2002) 106e109. [12] J.T. Zai, K.X. Wang, Y.Z. Su, X.F. Qian, J.S. Chen, J. Power Sources 196 (2011) 3650e3654.
[13] I.L. Devos, J.O. Fourcade, J.C. Jumas, P. Lavela, Phys. Rev. B 61 (2000) 3110e 3116. [14] T. Brousse, S.M. Lee, L. Pasquereau, D. Defives, D.M. Schleich, Solid State Ionics 113 (1998) 51e56. [15] T. Momma, N. Shiraishi, A. Yoshizawa, T. Osaka, A. Gedanken, J. Zhu, L. Sominski, J. Power Sources 97-98 (2001) 198e200. [16] T.J. Kim, Ch Kim, D. Son, M. Choi, B. Park, J. Power Sources 167 (2007) 529e 535. [17] X.L. Gou, J. Chen, P.W. Shen, Mater. Chem. Phys. 93 (2005) 557e566. [18] H.S. Kim, Y.H. Chung, S.H. Kang, Y.E. Sung, Electrochim. Acta 54 (2009) 3606e 3610.
Contents lists available at ScienceDirect
Solid State Sciences journal homepage: www.elsevier.com/locate/ssscie
SnS2egraphene nanocomposites as anodes of lithium-ion batteries Qi Wang, Yu-Xin Nie, Bin He, Li-Li Xing, Xin-Yu Xue* College of Sciences, Northeastern University, Shenyang 110004, China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 3 February 2013 Accepted 3 March 2014 Available online 14 March 2014
SnS2egraphene nanocomposites are synthesized by a hydrothermal method, and their application as anodes of lithium-ion batteries has been investigated. SnS2 nanosheets are uniformly coating on the surface of graphene. SnS2egraphene nanocomposites exhibit high cyclability and capacity. The reversible capacity is 766 mAh/g at 0.2C rate and maintains at 570 mAh/g after 30 cycles. Such a high performance can be attributed to high electron and Li-ion conductivity, large surface area, good mechanical flexibility of graphene nanosheets and the synergetic effect between graphene and SnS2 nanostructures. The present results indicate that SnS2egraphene nanocomposites have potential applications in lithium-ion battery anodes. Ó 2014 Elsevier Masson SAS. All rights reserved.
Keywords: Graphene Nanocomposites Anode Lithium-ion battery
1. Introduction
2. Experiments
Recently, the development of self-charging power cell (SCPC) and solar-lithium integrated power pack (SLPP) has raised the requirement of the performance of the anodes in lithium-ion battery (LIB) [1,2]. Nowadays, various metal composites, metal oxides and metal sulfides, based on their transformation to lithium-metal alloys, have been studied extensively as possible alternatives to carbonaceous anode materials because of their higher capacities [3e5]. It has been reported that graphene-based nanocomposites, such as SnO2egraphene nanocomposites, can achieve nearly theoretical specific energy density without significant charge/ discharge degradation [6,7]. Scientists suggest that small quantities of high-quality graphene can dramatically improve the power and cycling stability of LIBs, while maintaining high-energy storage capacities [6,7]. Graphene exhibits a unique structure of one-atomthick and two-dimensional layers of sp2-bonded carbon, which has high surface areas (theoretical value of 2630 m2/g), mobility of charge carriers (200,000 cm2/V s) and wide electrochemical window [8e10]. These properties make graphene an ideal twodimensional supporting material for anchoring active materials, offering high performances in LIB. In this work, SnS2egraphene nanocomposites are synthesized via a hydrothermal route and exhibit high cyclability and capacity. Our results are the bases for their application in LIBs, SCPCs and SLPPs.
SnS2egraphene nanocomposites were prepared by a hydrothermal method. Typically, 449 mg SnCl4$H2O and 195 mg thiourea were ultrasound dissolved in 20 ml ethanol to form a transparent solution. 5.5 mg graphene was ultrasonically dispersed in 19 ml ethanol to form black solution. Then both the suspension was transferred into a 50 ml Teflon-lined stainless steel autoclave and maintained at 453 K for 6 h. After that, the autoclave was cooled to room temperature, the black products were washed with ethanol and distilled water for several times and dried in air at 333 K for 12 h. The characteristics of the products were measured by XRD (D/ max 2550 V, CuKa radiation, l ¼ 1.5416 A), SEM (JEOL JSM-6700F), and TEM (TECNAI F20). The fabrication process of LIBs was as follows. The samples were mixed with acetylene black and carboxymethyl cellulose (CMC) at a weight ratio of 8:1:1. The mixture was painted onto a copper foil with a diameter of 15 mm. The 2016 coin-type cells were assembled in an argon-filled glove box, and pure Li foils were used as the counter electrodes. The electrolyte was made of 1 M LiPF6 in the mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) with the volume ratio 1:1. The cells were galvanostatically charged and discharged between 1 mV and 3 V versus Liþ/Li at room temperature on a program-controlled test system. 3. Results and discussion
* Corresponding author. Tel.: þ86 24 83687658. E-mail address: [email protected] (X.-Y. Xue). http://dx.doi.org/10.1016/j.solidstatesciences.2014.03.001 1293-2558/Ó 2014 Elsevier Masson SAS. All rights reserved.
The crystalline phase of SnS2egraphene nanocomposites is characterized by X-ray powder diffraction (XRD). As shown in
82
Q. Wang et al. / Solid State Sciences 31 (2014) 81e84
Fig. 1a, the sharp diffraction peaks can be indexed to SnS2 crystal given by the standard data (JCPDS file No. 40-1467), suggesting the well crystalline of SnS2. The broad peak in the range of 20e30 coincides with the small crystallized portion of the graphene. EDX spectroscopy is used to examine the local elemental composition of the nanocomposites, as shown in Fig. 1b. Sn:S atomic ratio is about 1:2, which is consistent with the atomic ration of SnS2. The silicon signals are from the silicon substrate, which is used in scanning electron microscopy (SEM) observation. The morphology and structure of SnS2egraphene nanocomposites are illuminated by SEM, as shown in Fig. 2a. It can be seen that the product consists of a large amount of sheet-like nanostructures. Fig. 2b is transition electron microcopy (TEM) image of SnS2egraphene nanocomposites. The lattice fringe crystalline nature of 0.59 nm corresponds to (001) plane of SnS2 crystal. In the growth process, the formation of sheet-like SnS2 crystallites is mainly caused by the intrinsic anisotropic nature of SnS2, which has a CdI2-related crystal structure [11]. SnS2 crystallizes in the layered CdI2 type lattice with lattice constants a ¼ 53.645 A and c ¼ 55.898 A [12]. Its atomic structure consists of layers separated by a space. In the atomic structure, there are numerous vacant lattice sites. The interlayer ones are octahedrally (labeled Oh1) or tetrahedrally (labeled Td2) coordinated to sulfur atoms. The Oh1 ones are situated at the center of the interlayer space and they are relatively far from the two nearest tin atoms. The Td2 ones, symmetrically situated in the gap are also relatively far from the three
Fig. 2. (a) SEM image of SnS2egraphene nanocomposites. (b) TEM image of SnS2e graphene nanocomposites.
nearest tin atoms. It is seems likely that these vacant sites enhance the lithium intercalation [13]. Electrochemical cycling tests of the SnS2egraphene nanocomposites electrodes are performed at 0.2C rate (5 h per half cycle) between 3 V and 0 V. The voltage profiles of the sample for 30 cycles are presented in Fig. 3a. The sample exhibits plateau at about 1.2 V on the first discharge process. During the subsequent cycles, the discharge and charge plateaus are observed in the potential ranges of 0.0e0.5 V and 0.7e1.1 V. The reversible capacity of SnS2e graphene electrodes is 766.3 mAh/g. Fig. 3b shows the differential capacity curves (dC/dV vs. voltage) of SnS2egraphene nanocomposites. The broad peak at w1.2 V in the first discharge process can be ascribed to the following reaction:
SnS2 þ4Liþ þ4e /Sn þ 2Li2 S;
(1)
And the peak at w0.6 V in the first discharge process can be attributed to the redox peak couple of reaction [14e17]:
Sn þ xLiþ þ xe 4Lix Snð0 x 4:4Þ:
Fig. 1. (a) XRD pattern of SnS2egraphene nanocomposites. (b) EDX spectrum of SnS2e graphene nanocomposites.
(2)
In the first discharge process, Li-inserted SnS2 forms LixSn and amorphous Li2S [18]. During substantial charge and discharge processes, reaction between the newly formed metallic Sn and lithium leads to the formation of Li4.4Sn alloys, and the Li2S acts as an inertmatrix surrounding the active Sn grains. Usually, SnS2 shows high initial discharge capacities, but its capacity retention
Q. Wang et al. / Solid State Sciences 31 (2014) 81e84
83
Fig. 3. (a) Voltageecapacity profile of SnS2egraphene electrode at 0.2C rate. (b) Differential capacity curves of SnS2egraphene nanocomposites. Fig. 4. (a) Cycling stability of Li insertion and extraction in SnS2egraphene nanocomposites. (b) Cyclability of SnS2egraphene nanocomposites in the voltage range of 0e3 V.
needs improvement. Here, the combination of SnS2 and graphene is an effective way to overcome the huge volume expansion of the SnS2 during the chargeedischarge process [18]. As shown in Fig. 4a after the first cycle, the stability of SnS2e graphene nanocomposites is very high. And Fig. 4b illustrates the reversible capacity vs. cycle number profile of SnS2egraphene electrode. The initial reversible capacity of the SnS2egraphene electrode is over 967.6 mAh/g and the capacity drops rapidly to 766.3 mAh/g after the first cycle. It can be seen that after 30 cycles the reversible capacity maintains 570.0 mAh/g, 74.6% of the second discharge capacity. Based on the results above, SnS2egraphene nanocomposites display high reversible capacities and cyclability. Such a high performance of SnS2/graphene nanocomposites as LIB anodes can be attributed to the synergistic effect between graphene and nanostructured SnS2. Firstly, graphene nanosheets act as flexible two-dimensional supports for anchoring of SnS2 nanostructures, not only providing an elastic buffer space to accommodate the volume expansion/contraction of SnS2 nanostructures, but also efficiently preventing the aggregation of SnS2 nanostructures. Secondly, graphene nanosheets in the nanocomposites have a good electrical conductivity and serve as the conductive channels between the nanocomposites and collectors. Thirdly, graphene nanosheets can shorten the path length for Li-ion transport, increase materials/electrolyte contact area, and facilitate the Li-ion diffusing to the sites on the surface of SnS2 nanostructures. Forth, the presence of SnS2 nanostructures on graphene nanosheets effectively prevents the agglomeration of graphene nanosheets, and consequently keeps their high active surface area.
4. Conclusions SnS2egraphene nanocomposites were prepared by a hydrothermal method. And SnS2egraphene nanocomposites displayed high cyclability and capacity as anodes of LIB. The reversible capacity was 766 mAh/g, maintained 570 mAh/g after 30 cycles. Our results implied that SnS2egraphene nanocomposites had potential applications in LIBs at industrial level. Acknowledgments This work was supported by the National Natural Science Foundation of China (51102041 and 11104025), the Fundamental Research Funds for the Central Universities (N120205001 and N120405010), Program for New Century Excellent Talents in University (NCET-13-0112) and Specialized Research Fund for the Doctoral Program of Higher Education of China (No. 20110042120024). References [1] X.Y. Xue, S.H. Wang, W.X. Guo, Y. Zhang, Z.L. Wang, Nano Lett. 12 (2012) 5048e5054. [2] W.X. Guo, X.Y. Xue, S.H. Wang, C.J. Lin, Z.L. Wang, Nano Lett. 12 (2012) 2520e 2523. [3] G.Y. He, J.H. Li, H.Q. Chen, J. Shi, X.Q. Sun, S. Chen, X. Wang, Mater. Lett. 82 (2012) 61e63. [4] Y. Li, J.P. Tu, X.H. Huang, H.M. Wu, Y.F. Yuan, Electrochem. Commun. 9 (2007) 49e53.
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Q. Wang et al. / Solid State Sciences 31 (2014) 81e84
[5] M. Sathish, S. Mitani, T. Tomiai, A. Unemoto, I. Honma, J. Solid State Electrochem. 16 (2012) 1767e1774. [6] J.Z. Wang, L. Lu, M. Choucair, J.A. Stride, X. Xu, H.K. Liu, ACS Nano 3 (4) (2009) 907e914. [7] D. Wang, R. Kou, D. Choi, Z. Yang, Z. Nie, J. Liat, ACS Nano 4 (3) (2010) 1587e 1595. [8] S. Park, R.S. Ruoff, Nat. Nanotechnol. 4 (2009) 217e224. [9] M.J. Allen, V.C. Tung, R.B. Kaner, Chem. Rev. 110 (2010) 132e145. [10] S. Liu, X. Yin, L. Chen, Q. Li, T. Wang, Solid State Sci. 12 (2010) 712e718. [11] Q. Yang, K.B. Tang, C.R. Wang, D.Y. Zhang, Y.T. Qian, J. Solid State Chem. 164 (2002) 106e109. [12] J.T. Zai, K.X. Wang, Y.Z. Su, X.F. Qian, J.S. Chen, J. Power Sources 196 (2011) 3650e3654.
[13] I.L. Devos, J.O. Fourcade, J.C. Jumas, P. Lavela, Phys. Rev. B 61 (2000) 3110e 3116. [14] T. Brousse, S.M. Lee, L. Pasquereau, D. Defives, D.M. Schleich, Solid State Ionics 113 (1998) 51e56. [15] T. Momma, N. Shiraishi, A. Yoshizawa, T. Osaka, A. Gedanken, J. Zhu, L. Sominski, J. Power Sources 97-98 (2001) 198e200. [16] T.J. Kim, Ch Kim, D. Son, M. Choi, B. Park, J. Power Sources 167 (2007) 529e 535. [17] X.L. Gou, J. Chen, P.W. Shen, Mater. Chem. Phys. 93 (2005) 557e566. [18] H.S. Kim, Y.H. Chung, S.H. Kang, Y.E. Sung, Electrochim. Acta 54 (2009) 3606e 3610.