- Email: [email protected]
High-performance Cu-doped vanadium oxide (CuxV2O5) prepared by rapid precipitation method for rechargeable batteries
Materials Letters 61 (2007) 101 – 104 www.elsevier.com/locate/matlet
High-performance Cu-doped vanadium oxide (CuxV2O5) prepared by rapid precipitation method for rechargeable batteries Hai Xia Li, Li Fang Jiao, Hua Tang Yuan ⁎, Ming Zhao, Ming Zhang, Yong Mei Wang Institute of New Energy Material Chemistry, Nankai University, Tianjin 300071, China Received 20 January 2006; accepted 2 April 2006 Available online 11 May 2006
Abstract CuxV2O5 (x = 0, 0.15, 0.25) was prepared by acidifying aqueous NaVO3 with diluted H2SO4 followed by mixing Cu powder with V2O5 precipitate. The method is a rapid synthesis procedure, compared to the ion-exchange method. The effect of copper on the characteristics of V2O5 was also investigated. These materials maintained the layered structure typical of V2O5 xerogel. It was found that the copper-doped V2O5 material exhibits better cycle performance than the undoped V2O5. Cu0.25V2O5 showed an initial discharge capacity of 259.2 mA h/g in the potential range of 1.5–4.0 V at 96 mA/g (C/3). After the 100 consecutive cycles, the specific capacity of the Cu0.25V2O5 electrode maintained 219.5 mA h/g. The doped material prepared by the rapid method shows better a cycling performance, compared to the ion-exchange method. © 2006 Elsevier B.V. All rights reserved. Keywords: Precipitation method; Copper-doped V2O5; Layered structure; Cathode material; Lithium batteries
1. Introduction Vanadium pentoxide gel-based materials have been studied extensively for use as cathodes in high-capacity lithium batteries. Much work on xerogel and aerogel synthesis of V2O5· nH2O for battery applications has been done by Salloux et al. [1] and Smyrl et al. [2–5]. Their method is the acidification of sodium metavanadate solution using ion-exchange resin. However, the problems in the ion-exchange method are the difficulty in controlling the exchange rate in this process and the difficulty in large-scale production. Therefore, the facile acid-precipitation route has attracted more and more attention recently [6,7]. To improve the intercalation rate, the specific capacity and cycling performance of vanadium oxide bronzes such as MxV2O5 (M = Na, Ag, Cu, etc.) have been considered to be used as cathode materials because of their unique structures. Recently, Coustier et al. [5] investigated the characterization of gel-based, silver- and copper-doped V2O5 materials and demonstrated that these electrode materials had the layered structure typical of V2O5·nH2O xerogel, but with enhanced performance. ⁎ Corresponding author. Tel.: +86 22 23498089; fax: +86 22 23502604. E-mail addresses: [email protected] (H.X. Li), [email protected] (H.T. Yuan). 0167-577X/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2006.04.015
The purpose of this report is to investigate the effect of copper-doping on the characteristics of amorphous V2O5 prepared from the acid-precipitation route. In comparison to the ion-exchange method, acid precipitation is a rapid synthesis procedure. 2. Experimental Amorphous V2O5 was prepared by acidifying aqueous NaVO3 solution with diluted H2SO4. Referring to the method described by Torardi et al. [6], the NaVO3 solution was heated to the boiling point. Then, diluted H2SO4 was added into the above solution. The reddish-brown solid was formed after 20 min. The precipitate was collected on filter paper. Copper-doped V2O5 (CuxV2O5 with x = 0, 0.15, and 0.25) were prepared by mixing the selected stoichiometric amount of copper powder with V2O5 synthesized by acid precipitation. Twenty milliliters of distilled water was added and the mixtures were vigorously stirred until the red became green, which demonstrated that the copper powders were completely oxidized. Thermogravimetry (TG) was carried out using a NETZSCH TG 209 thermal analyzer at the heating rate of 10 °C min− 1. The Na+ contents were determined by induced coupled plasma atomic emission spectroscopy (ICP-9000 (N + M), USA Thermo
102
H.X. Li et al. / Materials Letters 61 (2007) 101–104 Table 1 Interlayer spacing of copper-doped V2O5 materials Material
Interlayer spacing (Å)
2θ(001) (°)
x=0 x = 0.15 x = 0.25
11.3688 10.9876 10.8795
7.770 8.040 8.120
temperature–120 °C. The weight loss (7.1%) extends to around 120 °C attributed to the loss of intermolecular water. A composition of Na0.26V2O5 (SO4)0.13·0.85H2O was derived from ICP and thermogravimetric analyses for the undoped sample. The molecular formula is written V2O5 in this paper for convenience. Fig. 1. TGA curve of the undoped sample.
Jarrell-Ash Corp.). X-ray powder diffraction (XRD) was carried out using XRD (D/Max-2500). The composite cathodes were prepared by pressing a mixture of the active materials, conductive material (acetylene black) and binder (PTFE) in a weight ratio of 80/10/10. These samples were dried at 120 °C for 12 h. The Li metal was used as the counter and reference electrodes. The electrolyte was 1 M LiPF6 in a 6/3/1 (volume ratio) mixture of ethylene carbonate (EC), propylene carbonate (PC) and dimethyl carbonate (DMC). The galvanostatic method was used to measure the electrochemical capacity of the samples at a current density of 96 mA/g (C/3), with cut-off voltages at 4.0 and 1.5 V for charge and discharge processes, respectively. Cyclic voltammetry experiments were also performed by using a CHI660B Electrochemical Workstation at a scan rate of 0.1 mV/s. All tests were performed at room temperature.
3.2. The XRD of the samples Fig. 2 shows the XRD patterns of CuxV2O5 (x = 0, 0.15 and 0.25). The undoped and copper-doped V2O5 materials show a set of diffraction peaks which is similar to those of a-V2O5 reported by others [6,7]. For the Cu0.25V2O5, the electrochemically inactive impurity phase develops as shown in Fig. 2. The most intense peak located at 8° is the (001) diffraction, which is related to the preservation of the layer structure typical of vanadium pentoxide (gel-based) materials. Nevertheless, the doping ion changes the interlayer spacing and the position of 001 peak of the original structure. The influence of the doping ion on the structure of samples is shown in Table 1. The doped materials exhibit a decrease of the interlayer spacing with increased doping level. The reduction of the basal distance upon doping is consistent with a shielding effect that Cu2+ ion exerts on the negative charge residing on the apical oxygens of the VO5 pyramids. Such an effect reduces the electrostatic repulsion force that acts between two adjacent V2O5 layers and allows the shrinkage of the distance between layers [5]. 3.3. FTIR of the samples
3. Results and discussion 3.1. TG result Fig. 1 shows the TG curve of the undoped material. The TG curve shows a distinct stage of weight loss in the temperature range of room
Fig. 2. XRD pattern of copper-doped V2O5 powder samples.
Fig. 3 shows the FTIR spectra of CuxV2O5 (x = 0, 0.15 and 0.25). The IR data of various samples are also listed in Table 2. A band centered at ca.1610 cm− 1 is due to bound water within these materials. The undoped sample exhibits three main vibration modes in the 380–
Fig. 3. FTIR spectra of copper-doped V2O5 powder samples.
H.X. Li et al. / Materials Letters 61 (2007) 101–104
103
Table 2 The IR data of CuxV2O5 (x = 0, 0.15 and 0.25)
x=0 x = 0.15 x = 0.25
V = O (cm− 1)
V–O–V (cm− 1)
3V–O (cm− 1)
1008 1001 1000
769 770 773
554 557 560
1010 cm− 1 region. The terminal oxygen symmetric stretching mode (vs) of V = O and the bridge oxygen asymmetric and symmetric stretching modes (vas and vs) of V–O–V are at 1008, 769 and 554 cm− 1, respectively. The positions of the absorption bands in the copper-doped V2O5 samples are similar to these in the V2O5 sample, which implies that the layer structure is not significantly altered by intercalation. The V = O vibration band at around 1008 cm− 1 (x = 0) shifts down to 1000 cm− 1 (x = 0.25) with an increased doping level. The frequency shift to the lower wavenumber indicates the increase of the Cu doping for V2O5. The frequency shift of vanadyl mode is attributed to the presence of copper oxides in the vicinity of oxygen and to the distortion of the V = O bond [8]. The vs (V–O–V) and vas (V–O– V) modes shift to higher wavenumbers. These chemical shifts could be related to the reduction of oxidation state of vanadium from V5+ to V4+ and the increase of electronic conductivity [5]. The increase of electronic conductivity results in improved Li insertion capacity and cycling capacity. This result is confirmed by the electrochemical test results below.
Fig. 5. Discharge profiles of composite cathodes containing copper-doped V2O5 materials.
not be sites for Li+ ions insertion, and/or there is some variation in the conduction path of the Cu0.25V2O5 electrode as more Li+ are inserted. 3.5. Discharge capacities and cycling performance
Fig. 4 shows the cyclic voltammograms (second cycle) of CuxV2O5 (x = 0, 0.15, and 0.25). These materials show a current–voltage behavior similar to V2O5 xerogel films [9,10]: two cathodic peaks at ca.2.8 and 2.5 V vs. Li and two anodic peaks at ca.3.0 and 2.7 V vs. Li. The cathodic and anodic peaks slightly change depending upon the doped Cu content. The redox currents increase with increased doping level. The result is consistent with the FTIR result. In contrast, the CuxV2O5 (x = 0.25) material shows only one anodic peak at 2.7 V and the decrease of the cathodic peak intensity at 2.8 V. Moreover, the other cathodic peak shifts to a more negative voltage range, which leads to a decrease of the overall average cell potential compared with V2O5. This demonstrates that the intercalation process is not completely the same, as the Cu doping in the V2O5 increases. This suggests that there may
Fig. 5 illustrates the discharge curves of composite cathode materials. In agreement with the cyclic voltammetry results, the discharge curve of Cu0.25V2O5 is not the same as others. However, all materials show plateau-like curves, which are typical in the amorphous materials [10]. At the high voltage region, V N 2.7 V (vs. Li), the curves show a sharp decrease. A voltage plateau is presented between 2.7 and 2.4 V. Their redox peaks at the high potential are not well separated, so the other discharge plateau of the samples is not clear in Fig. 5. Fig. 6 illustrates the cycle performance of the doped materials. In agreement with the cyclic voltammetry and FTIR results, the discharge performance of Cu-doped V2O5 cathode is better than the undoped V2O5 cathode. The reason for the enhancement in the discharge capacity from the embedded copper oxide seems to be due to a larger electronic conductivity in the doped V2O5 cathode than in the nondoped V2O5 cathode. Cu0.25V2O5 showed an initial discharge capacity of 259.2 mA h/g in the potential range of 1.5–4.0 V. There is some capacity loss of the electrode during the consecutive cycles. About 85%
Fig. 4. Cyclic voltammetries of copper-doped V2O5 materials.
Fig. 6. Cycling performance of CuxV2O5.
3.4. CV of the samples
104
H.X. Li et al. / Materials Letters 61 (2007) 101–104
of the original electrode capacity is still available after 100 consecutive cycles in the case of the Cu0.25V2O5 electrode and at least 219.5 mA h/g is still available. However, the specific capacity of the same material (Cu0.25V2O5) prepared by ion-exchange method [5] is found to decline more rapidly from its initial value of 250 mA h/g to reach 160 mA h/g after 100 cycles at C/4 rate in the potential window of 4.0– 1.5 V. Obviously, the Cu0.25V2O5 prepared by the rapid synthesis procedure has a better cycling performance.
4. Conclusions CuxV2O5 materials were successfully prepared rapidly by acidifying aqueous NaVO3 solution with diluted H2SO4 followed by mixing with copper powder. The copper-doped V2O5 materials maintain the layered structure typical of V2O5 xerogel and show better discharge capacity. The Cu0.25V2O5 prepared by the rapid synthesis procedure shows better a cycling performance than the ion-exchange method. Acknowledgments This work was supported by National Science Fund of China (Project 50271032), the Special Fund for Major State Basic
Research of China (973 Project 2002 CB 211800), and Nankai– Tianjin University union Science Fund. References [1] K. Salloux, F. Chaput, H.P. Wong, B. Dunn, M.W. Breiter, J. Electrochem. Soc. 142 (1995) L191. [2] D.B. Le, S. Passerini, J. Guo, J. Ressler, B.B. Owens, W.H. Smyrl, J. Electrochem. Soc. 143 (1996) 2099. [3] A.L. Tipton, S. Passerini, B.B. Owens, W.H. Smyrl, J. Electrochem. Soc. 143 (1996) 3473. [4] F. Coustier, S. Passerini, W.H. Smyrl, J. Electrochem. Soc. 145 (1998) L73. [5] F. Coustier, J. Hill, B.B. Owens, S. Passerini, W.H. Smyrl, J. Electrochem. Soc. 145 (1999) 1355. [6] C.C. Torardi, C.R. Miao, M.E. Lewittes, Z. Li, J. Solid State Chem. 163 (2002) 93. [7] Tae Ahn Kim, Jong Ho Kim, Min Gyu Kim, Seung M. Oh, J. Electrochem. Soc. 150 (2003) A985. [8] H.S. Hwang, S.H. Oh, H.S. Kim, W.I. Cho, B.W. Cho, D.Y. Lee, Electrochim. Acta 50 (2004) 485. [9] S. Mege, Y. Levieux, F. Ansart, J.M. Savariault, A. Rousset, J. Appl. Electrochem. 30 (2000) 657. [10] H.-K. Park, W.H. Smyrl, M.D. Ward, J. Electrochem. Soc. 142 (1995) 1068.
High-performance Cu-doped vanadium oxide (CuxV2O5) prepared by rapid precipitation method for rechargeable batteries Hai Xia Li, Li Fang Jiao, Hua Tang Yuan ⁎, Ming Zhao, Ming Zhang, Yong Mei Wang Institute of New Energy Material Chemistry, Nankai University, Tianjin 300071, China Received 20 January 2006; accepted 2 April 2006 Available online 11 May 2006
Abstract CuxV2O5 (x = 0, 0.15, 0.25) was prepared by acidifying aqueous NaVO3 with diluted H2SO4 followed by mixing Cu powder with V2O5 precipitate. The method is a rapid synthesis procedure, compared to the ion-exchange method. The effect of copper on the characteristics of V2O5 was also investigated. These materials maintained the layered structure typical of V2O5 xerogel. It was found that the copper-doped V2O5 material exhibits better cycle performance than the undoped V2O5. Cu0.25V2O5 showed an initial discharge capacity of 259.2 mA h/g in the potential range of 1.5–4.0 V at 96 mA/g (C/3). After the 100 consecutive cycles, the specific capacity of the Cu0.25V2O5 electrode maintained 219.5 mA h/g. The doped material prepared by the rapid method shows better a cycling performance, compared to the ion-exchange method. © 2006 Elsevier B.V. All rights reserved. Keywords: Precipitation method; Copper-doped V2O5; Layered structure; Cathode material; Lithium batteries
1. Introduction Vanadium pentoxide gel-based materials have been studied extensively for use as cathodes in high-capacity lithium batteries. Much work on xerogel and aerogel synthesis of V2O5· nH2O for battery applications has been done by Salloux et al. [1] and Smyrl et al. [2–5]. Their method is the acidification of sodium metavanadate solution using ion-exchange resin. However, the problems in the ion-exchange method are the difficulty in controlling the exchange rate in this process and the difficulty in large-scale production. Therefore, the facile acid-precipitation route has attracted more and more attention recently [6,7]. To improve the intercalation rate, the specific capacity and cycling performance of vanadium oxide bronzes such as MxV2O5 (M = Na, Ag, Cu, etc.) have been considered to be used as cathode materials because of their unique structures. Recently, Coustier et al. [5] investigated the characterization of gel-based, silver- and copper-doped V2O5 materials and demonstrated that these electrode materials had the layered structure typical of V2O5·nH2O xerogel, but with enhanced performance. ⁎ Corresponding author. Tel.: +86 22 23498089; fax: +86 22 23502604. E-mail addresses: [email protected] (H.X. Li), [email protected] (H.T. Yuan). 0167-577X/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2006.04.015
The purpose of this report is to investigate the effect of copper-doping on the characteristics of amorphous V2O5 prepared from the acid-precipitation route. In comparison to the ion-exchange method, acid precipitation is a rapid synthesis procedure. 2. Experimental Amorphous V2O5 was prepared by acidifying aqueous NaVO3 solution with diluted H2SO4. Referring to the method described by Torardi et al. [6], the NaVO3 solution was heated to the boiling point. Then, diluted H2SO4 was added into the above solution. The reddish-brown solid was formed after 20 min. The precipitate was collected on filter paper. Copper-doped V2O5 (CuxV2O5 with x = 0, 0.15, and 0.25) were prepared by mixing the selected stoichiometric amount of copper powder with V2O5 synthesized by acid precipitation. Twenty milliliters of distilled water was added and the mixtures were vigorously stirred until the red became green, which demonstrated that the copper powders were completely oxidized. Thermogravimetry (TG) was carried out using a NETZSCH TG 209 thermal analyzer at the heating rate of 10 °C min− 1. The Na+ contents were determined by induced coupled plasma atomic emission spectroscopy (ICP-9000 (N + M), USA Thermo
102
H.X. Li et al. / Materials Letters 61 (2007) 101–104 Table 1 Interlayer spacing of copper-doped V2O5 materials Material
Interlayer spacing (Å)
2θ(001) (°)
x=0 x = 0.15 x = 0.25
11.3688 10.9876 10.8795
7.770 8.040 8.120
temperature–120 °C. The weight loss (7.1%) extends to around 120 °C attributed to the loss of intermolecular water. A composition of Na0.26V2O5 (SO4)0.13·0.85H2O was derived from ICP and thermogravimetric analyses for the undoped sample. The molecular formula is written V2O5 in this paper for convenience. Fig. 1. TGA curve of the undoped sample.
Jarrell-Ash Corp.). X-ray powder diffraction (XRD) was carried out using XRD (D/Max-2500). The composite cathodes were prepared by pressing a mixture of the active materials, conductive material (acetylene black) and binder (PTFE) in a weight ratio of 80/10/10. These samples were dried at 120 °C for 12 h. The Li metal was used as the counter and reference electrodes. The electrolyte was 1 M LiPF6 in a 6/3/1 (volume ratio) mixture of ethylene carbonate (EC), propylene carbonate (PC) and dimethyl carbonate (DMC). The galvanostatic method was used to measure the electrochemical capacity of the samples at a current density of 96 mA/g (C/3), with cut-off voltages at 4.0 and 1.5 V for charge and discharge processes, respectively. Cyclic voltammetry experiments were also performed by using a CHI660B Electrochemical Workstation at a scan rate of 0.1 mV/s. All tests were performed at room temperature.
3.2. The XRD of the samples Fig. 2 shows the XRD patterns of CuxV2O5 (x = 0, 0.15 and 0.25). The undoped and copper-doped V2O5 materials show a set of diffraction peaks which is similar to those of a-V2O5 reported by others [6,7]. For the Cu0.25V2O5, the electrochemically inactive impurity phase develops as shown in Fig. 2. The most intense peak located at 8° is the (001) diffraction, which is related to the preservation of the layer structure typical of vanadium pentoxide (gel-based) materials. Nevertheless, the doping ion changes the interlayer spacing and the position of 001 peak of the original structure. The influence of the doping ion on the structure of samples is shown in Table 1. The doped materials exhibit a decrease of the interlayer spacing with increased doping level. The reduction of the basal distance upon doping is consistent with a shielding effect that Cu2+ ion exerts on the negative charge residing on the apical oxygens of the VO5 pyramids. Such an effect reduces the electrostatic repulsion force that acts between two adjacent V2O5 layers and allows the shrinkage of the distance between layers [5]. 3.3. FTIR of the samples
3. Results and discussion 3.1. TG result Fig. 1 shows the TG curve of the undoped material. The TG curve shows a distinct stage of weight loss in the temperature range of room
Fig. 2. XRD pattern of copper-doped V2O5 powder samples.
Fig. 3 shows the FTIR spectra of CuxV2O5 (x = 0, 0.15 and 0.25). The IR data of various samples are also listed in Table 2. A band centered at ca.1610 cm− 1 is due to bound water within these materials. The undoped sample exhibits three main vibration modes in the 380–
Fig. 3. FTIR spectra of copper-doped V2O5 powder samples.
H.X. Li et al. / Materials Letters 61 (2007) 101–104
103
Table 2 The IR data of CuxV2O5 (x = 0, 0.15 and 0.25)
x=0 x = 0.15 x = 0.25
V = O (cm− 1)
V–O–V (cm− 1)
3V–O (cm− 1)
1008 1001 1000
769 770 773
554 557 560
1010 cm− 1 region. The terminal oxygen symmetric stretching mode (vs) of V = O and the bridge oxygen asymmetric and symmetric stretching modes (vas and vs) of V–O–V are at 1008, 769 and 554 cm− 1, respectively. The positions of the absorption bands in the copper-doped V2O5 samples are similar to these in the V2O5 sample, which implies that the layer structure is not significantly altered by intercalation. The V = O vibration band at around 1008 cm− 1 (x = 0) shifts down to 1000 cm− 1 (x = 0.25) with an increased doping level. The frequency shift to the lower wavenumber indicates the increase of the Cu doping for V2O5. The frequency shift of vanadyl mode is attributed to the presence of copper oxides in the vicinity of oxygen and to the distortion of the V = O bond [8]. The vs (V–O–V) and vas (V–O– V) modes shift to higher wavenumbers. These chemical shifts could be related to the reduction of oxidation state of vanadium from V5+ to V4+ and the increase of electronic conductivity [5]. The increase of electronic conductivity results in improved Li insertion capacity and cycling capacity. This result is confirmed by the electrochemical test results below.
Fig. 5. Discharge profiles of composite cathodes containing copper-doped V2O5 materials.
not be sites for Li+ ions insertion, and/or there is some variation in the conduction path of the Cu0.25V2O5 electrode as more Li+ are inserted. 3.5. Discharge capacities and cycling performance
Fig. 4 shows the cyclic voltammograms (second cycle) of CuxV2O5 (x = 0, 0.15, and 0.25). These materials show a current–voltage behavior similar to V2O5 xerogel films [9,10]: two cathodic peaks at ca.2.8 and 2.5 V vs. Li and two anodic peaks at ca.3.0 and 2.7 V vs. Li. The cathodic and anodic peaks slightly change depending upon the doped Cu content. The redox currents increase with increased doping level. The result is consistent with the FTIR result. In contrast, the CuxV2O5 (x = 0.25) material shows only one anodic peak at 2.7 V and the decrease of the cathodic peak intensity at 2.8 V. Moreover, the other cathodic peak shifts to a more negative voltage range, which leads to a decrease of the overall average cell potential compared with V2O5. This demonstrates that the intercalation process is not completely the same, as the Cu doping in the V2O5 increases. This suggests that there may
Fig. 5 illustrates the discharge curves of composite cathode materials. In agreement with the cyclic voltammetry results, the discharge curve of Cu0.25V2O5 is not the same as others. However, all materials show plateau-like curves, which are typical in the amorphous materials [10]. At the high voltage region, V N 2.7 V (vs. Li), the curves show a sharp decrease. A voltage plateau is presented between 2.7 and 2.4 V. Their redox peaks at the high potential are not well separated, so the other discharge plateau of the samples is not clear in Fig. 5. Fig. 6 illustrates the cycle performance of the doped materials. In agreement with the cyclic voltammetry and FTIR results, the discharge performance of Cu-doped V2O5 cathode is better than the undoped V2O5 cathode. The reason for the enhancement in the discharge capacity from the embedded copper oxide seems to be due to a larger electronic conductivity in the doped V2O5 cathode than in the nondoped V2O5 cathode. Cu0.25V2O5 showed an initial discharge capacity of 259.2 mA h/g in the potential range of 1.5–4.0 V. There is some capacity loss of the electrode during the consecutive cycles. About 85%
Fig. 4. Cyclic voltammetries of copper-doped V2O5 materials.
Fig. 6. Cycling performance of CuxV2O5.
3.4. CV of the samples
104
H.X. Li et al. / Materials Letters 61 (2007) 101–104
of the original electrode capacity is still available after 100 consecutive cycles in the case of the Cu0.25V2O5 electrode and at least 219.5 mA h/g is still available. However, the specific capacity of the same material (Cu0.25V2O5) prepared by ion-exchange method [5] is found to decline more rapidly from its initial value of 250 mA h/g to reach 160 mA h/g after 100 cycles at C/4 rate in the potential window of 4.0– 1.5 V. Obviously, the Cu0.25V2O5 prepared by the rapid synthesis procedure has a better cycling performance.
4. Conclusions CuxV2O5 materials were successfully prepared rapidly by acidifying aqueous NaVO3 solution with diluted H2SO4 followed by mixing with copper powder. The copper-doped V2O5 materials maintain the layered structure typical of V2O5 xerogel and show better discharge capacity. The Cu0.25V2O5 prepared by the rapid synthesis procedure shows better a cycling performance than the ion-exchange method. Acknowledgments This work was supported by National Science Fund of China (Project 50271032), the Special Fund for Major State Basic
Research of China (973 Project 2002 CB 211800), and Nankai– Tianjin University union Science Fund. References [1] K. Salloux, F. Chaput, H.P. Wong, B. Dunn, M.W. Breiter, J. Electrochem. Soc. 142 (1995) L191. [2] D.B. Le, S. Passerini, J. Guo, J. Ressler, B.B. Owens, W.H. Smyrl, J. Electrochem. Soc. 143 (1996) 2099. [3] A.L. Tipton, S. Passerini, B.B. Owens, W.H. Smyrl, J. Electrochem. Soc. 143 (1996) 3473. [4] F. Coustier, S. Passerini, W.H. Smyrl, J. Electrochem. Soc. 145 (1998) L73. [5] F. Coustier, J. Hill, B.B. Owens, S. Passerini, W.H. Smyrl, J. Electrochem. Soc. 145 (1999) 1355. [6] C.C. Torardi, C.R. Miao, M.E. Lewittes, Z. Li, J. Solid State Chem. 163 (2002) 93. [7] Tae Ahn Kim, Jong Ho Kim, Min Gyu Kim, Seung M. Oh, J. Electrochem. Soc. 150 (2003) A985. [8] H.S. Hwang, S.H. Oh, H.S. Kim, W.I. Cho, B.W. Cho, D.Y. Lee, Electrochim. Acta 50 (2004) 485. [9] S. Mege, Y. Levieux, F. Ansart, J.M. Savariault, A. Rousset, J. Appl. Electrochem. 30 (2000) 657. [10] H.-K. Park, W.H. Smyrl, M.D. Ward, J. Electrochem. Soc. 142 (1995) 1068.