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Molten-salt decomposition synthesis of SnO2 nanoparticles as anode materials for lithium ion batteries
Materials Letters 65 (2011) 3377–3379
Contents lists available at ScienceDirect
Materials Letters j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / m a t l e t
Molten-salt decomposition synthesis of SnO2 nanoparticles as anode materials for lithium ion batteries Guofeng Xia, Ning Li ⁎, Deyu Li, Ruiqing Liu, Ning Xiao, Dong Tian School of Chemical Engineering and Technology, Harbin Institute of Technology, Harbin 150001, PR China
a r t i c l e
i n f o
Article history: Received 3 May 2011 Accepted 4 July 2011 Available online 29 July 2011 Keywords: Nanoparticles Crystal growth Molten-salt Tin oxide Lithium ion battery
a b s t r a c t SnO2 nanoparticles were synthesized by a simple, easily scaled-up molten-salt decomposition method with SnSO4 as the molten salt and the reactive phase. During the synthesis process, the undecomposed molten SnSO4 makes it possible to obtain SnO2 nanoparticles by serving as the dispersion medium and keeping the particles from aggregation. The as-prepared SnO2 had a tetragonal rutile structure with an average particle size of 50 nm. When used as anode materials for lithium ion battery, SnO2 nanoparticles retained the charge capacity still as high as 402 mAh g− 1 at a current density of 156 mA g− 1 after 40 cycles. Moreover, cyclic voltammograms tests showed the formation/deformation of Li2O was partially reversible. Crown Copyright © 2011 Published by Elsevier B.V. All rights reserved.
1. Introduction As one of most promising anode materials for lithium ion batteries (LIB), tin-based materials have attracted increasing attention due to its extraordinary theoretical specific capacity (780 mAh g − 1) [1–5]. In a SnO2-based LIB electrode, Sn alloys with Li forming LixSn (0 ≤ x ≤ 4.4) during lithium insertion process, and gives rise to more than 300% of the volume expansion [6], which results in the disintegration of the electrode (so-called pulverization problem) and rapid capacity decrease over extended charge–discharge cycling. It has been demonstrated that small particles can keep the absolute volume changes of the reactive phase small and lessen the strain of lithium insertion/removal, improving cycle life [7]. From this point of view, various nanostructured SnO2 have been prepared, such as SnO2 nanorods [8,9], SnO2 nanocrystallines [10,11], SnO2 nanowires [12,13], SnO2 nanotubes [14,15] and SnO2 hollow nanospheres [16,17]. However, those nanosized SnO2 are commonly fabricated by wet-chemistry routes, such as sol–gel, hydrothermal synthesis, and homogeneous precipitation, et al. In general, these methods have disadvantages related to tedious synthetic procedures and lowyielding, which limited the large-scale synthesis of SnO 2 nanomaterials. Molten-salt synthesis is an easily scaled-up method to fabricate ultra-fine materials and has been used for the preparation of nanosized materials for LIB [18,19]. But the removal of the molten salts is just a time-consuming work. In this experiment, SnO2 nanoparticles have
⁎ Corresponding author. Tel.: + 86 451 86413721. E-mail address: [email protected] (N. Li).
been fabricated by a modified molten-salt decomposition method. By this means, the molten salt SnSO4 does not need to be removed because it also serves as the reactive phase. Moreover, the low melting point and low decomposition temperature of SnSO4 facilitate the synthesis process. The as-prepared SnO2 nanoparticles demonstrate their promising application as anode materials for LIB with their excellent electrochemical performance. 2. Experimental For SnO2 fabrication, all chemicals were of analytical grade and used without further purification. In a typical synthesis, SnSO4 with 10 ml ethanol was ball-milled for 10 h to obtain SnSO4 precursor. Before the precursor was annealed at 800 °C under Ar atmosphere for 1 h in a tube furnace, the ethanol had been removed by drying at 60 °C for 2 h in a vacuum oven. During annealing, the released gas was absorbed with NaOH solution. After cooling down to room temperature, the final product was obtained by further grounding and sieving. The total decomposition is described by the formula (Eq. (1)) as follows: SnSO4 →SnO2 + SO2 ↑
ð1Þ
The as-prepared nanoparticles were characterized with X-ray diffraction (XRD, Rigaku D/MAX-RB), scanning electron microscope (SEM, Hitachi S4800) and high resolution transmission electron microscopy (HRTEM, FEI TECNAI G2). Thermogravimetric analysis (TGA) was performed on a Netzsch STA449C. Electrochemical tests were carried out in two-electrode cells using lithium foil as counter electrode and reference electrode. The cells
0167-577X/$ – see front matter. Crown Copyright © 2011 Published by Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2011.07.008
3378
G. Xia et al. / Materials Letters 65 (2011) 3377–3379
3. Results and discussions
Fig. 1. TGA and DSC curves of the SnSO4 precursor.
Fig. 2. X-ray diffraction patterns of SnO2 nanoparticles (the inset shows the EDX result, and the Au element is ascribed to gold-spray treatment).
were assembled in a glovebox filled with high purity Ar. The working electrodes consisted of 80 mass% SnO2 nanoparticle, 10 mass% acetylene black, and 10 mass% polyvinylidene fluoride (PVDF). The electrolyte was a solution of 1 M LiPF6 in a mixture of ethylene (EC) and dimethyl carbonate (DMC) (1:1, v/v). The galvanostatically charge–discharge tests were executed at the rate of 0.2 C (1 C = 780 mA g − 1) in the potential range of 0.04–2 V (vs. Li/Li +). The cyclic voltammograms (CV) tests were tested between 0.02 V and 2.7 V (vs. Li/Li +) at a scan rate of 0.5 mV s − 1. All the electrochemical tests were carried out at room temperature (20 °C).
TG-DSC measurement (Fig. 1) confirmed a rapid molten-salt synthesis reaction occurring at the temperature of 420–520 °C by calculation of the mass retention, which is around 71.6% at 520 °C (the theoretical value being 70.2%). The endothermic peak in the DSC curve is ascribed to the melting of SnSO4. The annealing temperature of 800 °C is chosen in the experiment to ensure that the reaction occurs in a liquid phase. The crystal structure of the SnO2 nanoparticles is confirmed by Xray diffraction, as shown in Fig. 2. All reflection peaks are in good agreement with a tetragonal rutile structure (JCPDS 41–1445), showing good phase purity. The Sn:O ratio was calculated to be about 2 by the EDX examination (inset of Fig. 2), confirming the presence of SnO2. A typical SEM image in Fig. 3(a) shows that the sample has a uniform particle size distribution, which indicates that SnO2 nanoparticles have been fabricated in bulk quantity with the molten-salt decomposition method. It can be seen clearly in the inset of Fig. 3(a) that SnO2 grains are consisted of nanoparticles with an average size of 50 nm. During the molten-salt synthesis process, the undecomposed molten salt SnSO4 makes it possible to obtain SnO2 nanoparticles by serving as the dispersion medium and keeping the particles from aggregation. As depicted in the HRTEM image (Fig. 3(b)), the clear lattice fringes has a interplanar spacing of about 0.334 nm, consistent with (110) atomic planes of the rutile structure, indicating the formation of a highly crystallized rutile phase. Fig. 4(a) exhibits the initial three CV curves. During the first cathodic sweep (discharge process), The large irreversible peak at 0.6 V is ascribed to the reduction of SnO2 as described in Eq. (2) and the formation of solid-electrolyte interface (SEI) [20], whereas the peak at 0.02 V is attributed to the formation of LixSn alloy as described by Eq. (3) [6]. The corresponding anodic peak at 0.7 V in the first anodic sweep (charge process) is attributed to the dealloying reaction of LixSn. It is generally accepted that the reaction of Eq. (2) is irreversible in SnO2 electrodes. But in the followed two profiles, the broad cathodic peak (0.75–1.3 V) is related to the formation of Li2O (Eq. (2)), while the broad anodic peak (0.9–1.9 V) is ascribed to the deformation of Li2O [21–23]. As presented in Fig.4 (a), the CV measurement clearly shows that the reaction process as described in Eq. (2) is partially reversible, which has been reported by other works [24–28]. Dahn and co-workers have demonstrated that the lithium removed from Li2O and the subsequently liberated oxygen backreacted with Sn atoms and form Sn–O bonding [29], which means that SnO2 is reformed. þ
−
SnO2 + 4Li + 4e →Sn + 2Li2 O þ
−
Sn + xLi + xe ↔Lix Snð0≤x≤4:4Þ
ð2Þ ð3Þ
Fig. 3. Morphology of SnO2 nanoparticles: (a) representative scanning electron micrographs (SEM) image of SnO2 (the inset shows TEM image); (b) high-resolution transmission electron microscopy (HRTEM) image of SnO2.
G. Xia et al. / Materials Letters 65 (2011) 3377–3379
3379
Fig. 4(c) shows the cycling performance of the SnO2 nanoparticle electrode with high coulomb efficiencies after the 4th cycle. In detail, the first three charge capacities exceed the theoretical capacity of SnO2 (780 mAh g − 1). It indicates that the partially reversible reaction of Eq. (2) results in the additional capacity of SnO2 electrodes. The improved electrochemical performance of SnO2 nanoparticles is not only owing to the nanoparticles increasing effective interfacial reactivity and shortening the diffusion length of lithium ions and electrons, but also to the nanostructure lessening the strain of lithium insertion/removal by keeping the absolute volume changes of the reactive phase small [7]. However, the cyclability is not so satisfactory because there is a gradual capacity fading during the 40 cycles, which is induced still by the pulverization problem. Modifications are in progress to further improve the electrochemical performance.
4. Conclusions In this study, SnO2 nanoparticles of about 50 nm were prepared by a modified molten-salt decomposition method with SnSO4 as molten salt and the precursor. This nanosized SnO2 material exhibits an enhanced Li storage capacity. The SnO2 nanoparticles based electrodes showed an initial discharge/charge capacity of 1518/916 mAh g − 1. The charge capacity still remained 402 mAh g − 1 after 40 cycles. CV profiles demonstrated the formation/deformation of Li2O was partially reversible. Given the synthetic ease and excellent lithium storage properties, this method is great promising for application in large-scale fabrication of nanosized SnO2 anode materials.
References
Fig. 4. Electrochemical performance of SnO2 nanoparticles: (a) the initial three CV curves; (b) initial discharge/charge profile; and (c) the cycle performance of SnO2 nanoparticles electrode.
The initial charge/discharge voltage profiles of the SnO2 nanoparticles at a constant current density of 156 mA g − 1 (0.2 C) are presented in Fig. 4(b), with a typical plateau of 0.95 V for SnO2 electrode. The SnO2 nanoparticles exhibit a higher initial discharge capacity of 1518 mAh g − 1 and charge capacity of 916 mAh g − 1.
[1] Idota Y, Kubota T, Matsufuji A, Maekawa Y, Miyasaka T. Science 1997;276:1395–7. [2] Courtney IA, Dahn JR. J Electrochem Soc 1997;144:2943–8. [3] Mukaibo H, Osaka T, Reale P, Panero S, Scrosati B, Wachtler M. J Power Sources 2004;132:225–8. [4] Kepler KD, Vaughey JT, Thackeray MM. Electrochem Solid State 1999;2:307–9. [5] Nagayama M, Morita T, Ikuta H, Wakihara M, Takano M, Kawasaki S. Solid State Ionics 1998;106:33–8. [6] Courtney IA, Dahn JR. J Electrochem Soc 1997;144:2045–52. [7] Winter M, Besenhard JO. Electrochim Acta 1999;45:31–50. [8] Lei D, Zhang M, Hao Q, Chen L, Li Q, Zhang E, et al. Mater Lett 2011;65:1154–6. [9] Liu JP, Li YY, Huang XT, Ding RM, Hu YY, Jiang J, et al. J Mater Chem 2009;19: 1859–64. [10] Nuli YN, Zhao SL, Qin QZ. J Power Sources 2003;114:113–20. [11] Liang Y, Fan J, Xia X, Jia Z. Mater Lett 2007;61:4370–3. [12] Park MS, Wang GX, Kang YM, Wexler D, Dou SX, Liu HK. Angew Chem Int Edit 2007;46:750–3. [13] Kim H, Cho J. J Mater Chem 2008;18:771–5. [14] Wang Y, Zeng HC, Lee JY. Adv Mater 2006;18:645–9. [15] Lee WJ, Park MH, Wang Y, Lee JY, Cho J. Chem Commun 2010;46:622–4. [16] Yuan L, Guo ZP, Konstantinov K, Liu HK, Dou SX. J Power Sources 2006;159:345–8. [17] Wang Y, Su FB, Lee JY, Zhao XS. Chem Mater 2006;18:1347–53. [18] Guo ZP, Du GD, Nuli Y, Hassan MF, Liu HK. J Mater Chem 2009;19:3253–7. [19] Liang HY, Qiu XP, Chen HL, He ZQ, Zhu WT, Chen LQ. Electrochem Commun 2004;6:789–94. [20] Liu H, Long D, Liu X, Qiao W, Zhan L, Ling L. Electrochim Acta 2009;54:5782–8. [21] Brousse T, Retoux R, Herterich U, Schleich DM. J Electrochem Soc 1998;145:1–4. [22] Li NC, Martin CR. J Electrochem Soc 2001;148:A164–70. [23] Panero S, Savo G, Scrosati B. Electrochem Solid St 1999;2:365–6. [24] Xu MW, Zhao MS, Wang F, Guan W, Yang S, Song XP. Mater Lett 2010;64:921–3. [25] Demir-Cakan R, Hu Y-S, Antonietti M, Maier J, Titirici M-M. Chem Mater 2008;20: 1227–9. [26] Han SJ, Jang BC, Kim T, Oh SM, Hyeon T. Adv Funct Mater 2005;15:1845–50. [27] Deng D, Lee JY. Chem Mater 2008;20:1841–6. [28] Lou XW, Chen JS, Chen P, Archer LA. Chem Mater 2009;21:2868–74. [29] Courtney IA, Dunlap RA, Dahn JR. Electrochim Acta 1999;45:51–8.
Contents lists available at ScienceDirect
Materials Letters j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / m a t l e t
Molten-salt decomposition synthesis of SnO2 nanoparticles as anode materials for lithium ion batteries Guofeng Xia, Ning Li ⁎, Deyu Li, Ruiqing Liu, Ning Xiao, Dong Tian School of Chemical Engineering and Technology, Harbin Institute of Technology, Harbin 150001, PR China
a r t i c l e
i n f o
Article history: Received 3 May 2011 Accepted 4 July 2011 Available online 29 July 2011 Keywords: Nanoparticles Crystal growth Molten-salt Tin oxide Lithium ion battery
a b s t r a c t SnO2 nanoparticles were synthesized by a simple, easily scaled-up molten-salt decomposition method with SnSO4 as the molten salt and the reactive phase. During the synthesis process, the undecomposed molten SnSO4 makes it possible to obtain SnO2 nanoparticles by serving as the dispersion medium and keeping the particles from aggregation. The as-prepared SnO2 had a tetragonal rutile structure with an average particle size of 50 nm. When used as anode materials for lithium ion battery, SnO2 nanoparticles retained the charge capacity still as high as 402 mAh g− 1 at a current density of 156 mA g− 1 after 40 cycles. Moreover, cyclic voltammograms tests showed the formation/deformation of Li2O was partially reversible. Crown Copyright © 2011 Published by Elsevier B.V. All rights reserved.
1. Introduction As one of most promising anode materials for lithium ion batteries (LIB), tin-based materials have attracted increasing attention due to its extraordinary theoretical specific capacity (780 mAh g − 1) [1–5]. In a SnO2-based LIB electrode, Sn alloys with Li forming LixSn (0 ≤ x ≤ 4.4) during lithium insertion process, and gives rise to more than 300% of the volume expansion [6], which results in the disintegration of the electrode (so-called pulverization problem) and rapid capacity decrease over extended charge–discharge cycling. It has been demonstrated that small particles can keep the absolute volume changes of the reactive phase small and lessen the strain of lithium insertion/removal, improving cycle life [7]. From this point of view, various nanostructured SnO2 have been prepared, such as SnO2 nanorods [8,9], SnO2 nanocrystallines [10,11], SnO2 nanowires [12,13], SnO2 nanotubes [14,15] and SnO2 hollow nanospheres [16,17]. However, those nanosized SnO2 are commonly fabricated by wet-chemistry routes, such as sol–gel, hydrothermal synthesis, and homogeneous precipitation, et al. In general, these methods have disadvantages related to tedious synthetic procedures and lowyielding, which limited the large-scale synthesis of SnO 2 nanomaterials. Molten-salt synthesis is an easily scaled-up method to fabricate ultra-fine materials and has been used for the preparation of nanosized materials for LIB [18,19]. But the removal of the molten salts is just a time-consuming work. In this experiment, SnO2 nanoparticles have
⁎ Corresponding author. Tel.: + 86 451 86413721. E-mail address: [email protected] (N. Li).
been fabricated by a modified molten-salt decomposition method. By this means, the molten salt SnSO4 does not need to be removed because it also serves as the reactive phase. Moreover, the low melting point and low decomposition temperature of SnSO4 facilitate the synthesis process. The as-prepared SnO2 nanoparticles demonstrate their promising application as anode materials for LIB with their excellent electrochemical performance. 2. Experimental For SnO2 fabrication, all chemicals were of analytical grade and used without further purification. In a typical synthesis, SnSO4 with 10 ml ethanol was ball-milled for 10 h to obtain SnSO4 precursor. Before the precursor was annealed at 800 °C under Ar atmosphere for 1 h in a tube furnace, the ethanol had been removed by drying at 60 °C for 2 h in a vacuum oven. During annealing, the released gas was absorbed with NaOH solution. After cooling down to room temperature, the final product was obtained by further grounding and sieving. The total decomposition is described by the formula (Eq. (1)) as follows: SnSO4 →SnO2 + SO2 ↑
ð1Þ
The as-prepared nanoparticles were characterized with X-ray diffraction (XRD, Rigaku D/MAX-RB), scanning electron microscope (SEM, Hitachi S4800) and high resolution transmission electron microscopy (HRTEM, FEI TECNAI G2). Thermogravimetric analysis (TGA) was performed on a Netzsch STA449C. Electrochemical tests were carried out in two-electrode cells using lithium foil as counter electrode and reference electrode. The cells
0167-577X/$ – see front matter. Crown Copyright © 2011 Published by Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2011.07.008
3378
G. Xia et al. / Materials Letters 65 (2011) 3377–3379
3. Results and discussions
Fig. 1. TGA and DSC curves of the SnSO4 precursor.
Fig. 2. X-ray diffraction patterns of SnO2 nanoparticles (the inset shows the EDX result, and the Au element is ascribed to gold-spray treatment).
were assembled in a glovebox filled with high purity Ar. The working electrodes consisted of 80 mass% SnO2 nanoparticle, 10 mass% acetylene black, and 10 mass% polyvinylidene fluoride (PVDF). The electrolyte was a solution of 1 M LiPF6 in a mixture of ethylene (EC) and dimethyl carbonate (DMC) (1:1, v/v). The galvanostatically charge–discharge tests were executed at the rate of 0.2 C (1 C = 780 mA g − 1) in the potential range of 0.04–2 V (vs. Li/Li +). The cyclic voltammograms (CV) tests were tested between 0.02 V and 2.7 V (vs. Li/Li +) at a scan rate of 0.5 mV s − 1. All the electrochemical tests were carried out at room temperature (20 °C).
TG-DSC measurement (Fig. 1) confirmed a rapid molten-salt synthesis reaction occurring at the temperature of 420–520 °C by calculation of the mass retention, which is around 71.6% at 520 °C (the theoretical value being 70.2%). The endothermic peak in the DSC curve is ascribed to the melting of SnSO4. The annealing temperature of 800 °C is chosen in the experiment to ensure that the reaction occurs in a liquid phase. The crystal structure of the SnO2 nanoparticles is confirmed by Xray diffraction, as shown in Fig. 2. All reflection peaks are in good agreement with a tetragonal rutile structure (JCPDS 41–1445), showing good phase purity. The Sn:O ratio was calculated to be about 2 by the EDX examination (inset of Fig. 2), confirming the presence of SnO2. A typical SEM image in Fig. 3(a) shows that the sample has a uniform particle size distribution, which indicates that SnO2 nanoparticles have been fabricated in bulk quantity with the molten-salt decomposition method. It can be seen clearly in the inset of Fig. 3(a) that SnO2 grains are consisted of nanoparticles with an average size of 50 nm. During the molten-salt synthesis process, the undecomposed molten salt SnSO4 makes it possible to obtain SnO2 nanoparticles by serving as the dispersion medium and keeping the particles from aggregation. As depicted in the HRTEM image (Fig. 3(b)), the clear lattice fringes has a interplanar spacing of about 0.334 nm, consistent with (110) atomic planes of the rutile structure, indicating the formation of a highly crystallized rutile phase. Fig. 4(a) exhibits the initial three CV curves. During the first cathodic sweep (discharge process), The large irreversible peak at 0.6 V is ascribed to the reduction of SnO2 as described in Eq. (2) and the formation of solid-electrolyte interface (SEI) [20], whereas the peak at 0.02 V is attributed to the formation of LixSn alloy as described by Eq. (3) [6]. The corresponding anodic peak at 0.7 V in the first anodic sweep (charge process) is attributed to the dealloying reaction of LixSn. It is generally accepted that the reaction of Eq. (2) is irreversible in SnO2 electrodes. But in the followed two profiles, the broad cathodic peak (0.75–1.3 V) is related to the formation of Li2O (Eq. (2)), while the broad anodic peak (0.9–1.9 V) is ascribed to the deformation of Li2O [21–23]. As presented in Fig.4 (a), the CV measurement clearly shows that the reaction process as described in Eq. (2) is partially reversible, which has been reported by other works [24–28]. Dahn and co-workers have demonstrated that the lithium removed from Li2O and the subsequently liberated oxygen backreacted with Sn atoms and form Sn–O bonding [29], which means that SnO2 is reformed. þ
−
SnO2 + 4Li + 4e →Sn + 2Li2 O þ
−
Sn + xLi + xe ↔Lix Snð0≤x≤4:4Þ
ð2Þ ð3Þ
Fig. 3. Morphology of SnO2 nanoparticles: (a) representative scanning electron micrographs (SEM) image of SnO2 (the inset shows TEM image); (b) high-resolution transmission electron microscopy (HRTEM) image of SnO2.
G. Xia et al. / Materials Letters 65 (2011) 3377–3379
3379
Fig. 4(c) shows the cycling performance of the SnO2 nanoparticle electrode with high coulomb efficiencies after the 4th cycle. In detail, the first three charge capacities exceed the theoretical capacity of SnO2 (780 mAh g − 1). It indicates that the partially reversible reaction of Eq. (2) results in the additional capacity of SnO2 electrodes. The improved electrochemical performance of SnO2 nanoparticles is not only owing to the nanoparticles increasing effective interfacial reactivity and shortening the diffusion length of lithium ions and electrons, but also to the nanostructure lessening the strain of lithium insertion/removal by keeping the absolute volume changes of the reactive phase small [7]. However, the cyclability is not so satisfactory because there is a gradual capacity fading during the 40 cycles, which is induced still by the pulverization problem. Modifications are in progress to further improve the electrochemical performance.
4. Conclusions In this study, SnO2 nanoparticles of about 50 nm were prepared by a modified molten-salt decomposition method with SnSO4 as molten salt and the precursor. This nanosized SnO2 material exhibits an enhanced Li storage capacity. The SnO2 nanoparticles based electrodes showed an initial discharge/charge capacity of 1518/916 mAh g − 1. The charge capacity still remained 402 mAh g − 1 after 40 cycles. CV profiles demonstrated the formation/deformation of Li2O was partially reversible. Given the synthetic ease and excellent lithium storage properties, this method is great promising for application in large-scale fabrication of nanosized SnO2 anode materials.
References
Fig. 4. Electrochemical performance of SnO2 nanoparticles: (a) the initial three CV curves; (b) initial discharge/charge profile; and (c) the cycle performance of SnO2 nanoparticles electrode.
The initial charge/discharge voltage profiles of the SnO2 nanoparticles at a constant current density of 156 mA g − 1 (0.2 C) are presented in Fig. 4(b), with a typical plateau of 0.95 V for SnO2 electrode. The SnO2 nanoparticles exhibit a higher initial discharge capacity of 1518 mAh g − 1 and charge capacity of 916 mAh g − 1.
[1] Idota Y, Kubota T, Matsufuji A, Maekawa Y, Miyasaka T. Science 1997;276:1395–7. [2] Courtney IA, Dahn JR. J Electrochem Soc 1997;144:2943–8. [3] Mukaibo H, Osaka T, Reale P, Panero S, Scrosati B, Wachtler M. J Power Sources 2004;132:225–8. [4] Kepler KD, Vaughey JT, Thackeray MM. Electrochem Solid State 1999;2:307–9. [5] Nagayama M, Morita T, Ikuta H, Wakihara M, Takano M, Kawasaki S. Solid State Ionics 1998;106:33–8. [6] Courtney IA, Dahn JR. J Electrochem Soc 1997;144:2045–52. [7] Winter M, Besenhard JO. Electrochim Acta 1999;45:31–50. [8] Lei D, Zhang M, Hao Q, Chen L, Li Q, Zhang E, et al. Mater Lett 2011;65:1154–6. [9] Liu JP, Li YY, Huang XT, Ding RM, Hu YY, Jiang J, et al. J Mater Chem 2009;19: 1859–64. [10] Nuli YN, Zhao SL, Qin QZ. J Power Sources 2003;114:113–20. [11] Liang Y, Fan J, Xia X, Jia Z. Mater Lett 2007;61:4370–3. [12] Park MS, Wang GX, Kang YM, Wexler D, Dou SX, Liu HK. Angew Chem Int Edit 2007;46:750–3. [13] Kim H, Cho J. J Mater Chem 2008;18:771–5. [14] Wang Y, Zeng HC, Lee JY. Adv Mater 2006;18:645–9. [15] Lee WJ, Park MH, Wang Y, Lee JY, Cho J. Chem Commun 2010;46:622–4. [16] Yuan L, Guo ZP, Konstantinov K, Liu HK, Dou SX. J Power Sources 2006;159:345–8. [17] Wang Y, Su FB, Lee JY, Zhao XS. Chem Mater 2006;18:1347–53. [18] Guo ZP, Du GD, Nuli Y, Hassan MF, Liu HK. J Mater Chem 2009;19:3253–7. [19] Liang HY, Qiu XP, Chen HL, He ZQ, Zhu WT, Chen LQ. Electrochem Commun 2004;6:789–94. [20] Liu H, Long D, Liu X, Qiao W, Zhan L, Ling L. Electrochim Acta 2009;54:5782–8. [21] Brousse T, Retoux R, Herterich U, Schleich DM. J Electrochem Soc 1998;145:1–4. [22] Li NC, Martin CR. J Electrochem Soc 2001;148:A164–70. [23] Panero S, Savo G, Scrosati B. Electrochem Solid St 1999;2:365–6. [24] Xu MW, Zhao MS, Wang F, Guan W, Yang S, Song XP. Mater Lett 2010;64:921–3. [25] Demir-Cakan R, Hu Y-S, Antonietti M, Maier J, Titirici M-M. Chem Mater 2008;20: 1227–9. [26] Han SJ, Jang BC, Kim T, Oh SM, Hyeon T. Adv Funct Mater 2005;15:1845–50. [27] Deng D, Lee JY. Chem Mater 2008;20:1841–6. [28] Lou XW, Chen JS, Chen P, Archer LA. Chem Mater 2009;21:2868–74. [29] Courtney IA, Dunlap RA, Dahn JR. Electrochim Acta 1999;45:51–8.