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Low temperature synthesis of a stable MoO2 as suitable anode materials for lithium batteries
Materials Science and Engineering B 121 (2005) 152–155
Low temperature synthesis of a stable MoO2 as suitable anode materials for lithium batteries Yongguang Liang, Shuijin Yang, Zonghui Yi, Xuefeng Lei, Jutang Sun ∗ , Yunhong Zhou Department of Chemistry, Wuhan University, Wuhan 430072, PR China Received 15 December 2004; received in revised form 14 March 2005; accepted 25 March 2005
Abstract Fissile molybdenum dioxide (MoO2 ) was synthesized using a rheological phase reaction as a novel method suitable for a large scale up. The oxalate precursor was initially prepared at 80 ◦ C and was treated at different temperatures. The physical characterization was carried out by thermogravimetry and differential thermal analysis (TG/DTA), X-ray diffractometer (XRD) and scanning electron microscope (SEM). The results of TG/DTA and XRD indicate that the oxalate precursor begins to yield MoO2 at 250 ◦ C and a single phase MoO2 with monocline symmetry is formed at 350 ◦ C. The electrochemical characteristics of fissile MoO2 as an anode material for lithium batteries have also been studied and the morphological properties were found to play an important role in the cycling stability. The activated MoO2 displays 484 mAh g−1 capacity in the initial charge process with a capacity retention of 83.1% after 40 cycles in the range of 0.01–2.00 V versus metallic lithium at a current density of 100 mA g−1 . The SEM results reveal that there is a correlation between the cycling performance of the MoO2 powders and their morphological properties. © 2005 Elsevier B.V. All rights reserved. Keywords: Molybdenum oxide; Chemical synthesis; Surface properties; Negative electrode; Lithium batteries
1. Introduction The fast technological progress in the area of mobile devices puts higher demands on portable power supplies. Currently, it seems that rechargeable lithium-ion batteries are the systems of choice for high-capacity cells. Since the introduction with carbon as anode material by Sony company in 1990, many studies has been undertaken to search for new anode materials to improve the energy density and cycling performance of these practical cells. Idota et al. [1] have reported that tin-based amorphous oxides as new negative electrode materials provide a high lithium storage capacity. Recently, some metal oxides and metal-based composite oxides [2,3], and intermetallics [4,5] were also found to deliver much higher specific capacity than carbonaceous materials for which the theoretical capacity is 372 mAh g−1 [6,7]. However, there are still concerns mainly associated with the improvement of the synthesis conditions and ∗
Corresponding author. Tel.: +86 27 87218494; fax: +86 27 68754067. E-mail address: [email protected] (J. Sun).
0921-5107/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.mseb.2005.03.027
cycling stability before these materials can be considered as possible anode candidates for lithium rechargeable batteries. Auborn and Barberio [8] reported the use of MoO2 powder as possible commercial anode in 1987, but their results showed a limited success because of the poor stability of their electrolyte at low potential. Furthermore, several molybdenum oxides and composite oxides, such as MoO2+δ [9], MnMoO4 [10], Moy Snx O2 [11], V9 Mo6 O40 [12], Mn1−x Mo2x V2(1−x) O6 [13] have been studied as anode materials for lithium batteries. However, these compounds obtained by different synthesis methods usually showed inconsistent lithium-intercalation properties. In this paper, we introduce a new synthesis route of fissile MoO2 by a rheological phase reaction method. The physical properties of MoO2 oxides are presented as well as the electrochemical performance of the resulting electrodes. 2. Experimental The oxalate precursor was synthesized by a rheological phase reaction route. All reagents were analytical grade and
Y. Liang et al. / Materials Science and Engineering B 121 (2005) 152–155
used without further purification. (NH4 )6 Mo7 O24 ·4H2 O and C2 H4 O2 ·2H2 O were fully mixed by grinding with a molar ratio of 1:1.05. A proper amount of absolute alcohol was added to get a rheological body. The mixture was sealed in a closed container at 80 ◦ C for 8 h. After dried under vacuum at 80 ◦ C, the white precursor was obtained. The thermal stability of the oxalate precursor was examined by means of thermogravimetry and differential thermal analysis (TG/DTA) with a Netzsch STA 449 thermal analysis system at a heating rate of 10 ◦ C min−1 from 25 to 700 ◦ C in a flow of argon. Identification of phases and structures was carried out on a Shimadzu 6000 X-ray diffractometer at a scan˚ ning rate of 2◦ min−1 , using Cu K␣ radiation (λ = 1.54056 A). The particle sizes and morphological features were observed by a scanning electron microscope (Hitachi SEM X-650). The electrochemical cell consisted of a MoO2 working electrode and a lithium foil counter electrode. Electrodes were prepared by mixing MoO2 powders with 15% acetylene black and 5% PTFE, compressing the mixture onto a nickel gauze current collector. A 1 mol L−1 solution of LiClO4 dissolved in EC/DEC (1:1) was used as the electrolyte. A Celgard 2400 microporous membrane was used as a separator. The cell was discharged and charged between 2.0 and 0.01 V versus metallic lithium at a constant current density of 100 mA g−1 . 3. Results and discussion The TG and DTA curves of the precursor are shown in Fig. 1. From the TG curve, the pyrolysis of the oxalate precursor proceeds with 43% mass loss from 88.5 to 332 ◦ C. The endothermic peaks on the DTA curve at about 106 and 178 ◦ C correspond the loss of the adsorbed water and the decomposition of surplus oxalate acid. The sharp endothermic peak at about 258 ◦ C is associated with the formation of crystallized MoO2 , which is confirmed by the XRD data in Fig. 2. Fig. 2 illustrates the changes of XRD patterns when the oxalate precursor was treated at different temperatures for 4 h in argon atmosphere. A monoclinic phase of MoO2 already appeared in the sample obtained at 250 ◦ C with diffraction
153
Fig. 1. TG and DTA curves of the oxalate precursor.
Fig. 2. Changes in XRD patterns with the precursor treating at different temperatures.
lines at 26.02◦ , 37.00◦ and 53.58◦ . The XRD peaks assigned to a MoO2 phase obviously increased in intensity at ensuing higher temperature, and these patterns are mutually coincided. A single phase of MoO2 was found to be yielded after a heating treatment no less than 350 ◦ C. The XRD results of the product obtained at 400 ◦ C is well defined as a pure phase MoO2 with monocline symmetry, space group ˚ b = 4.8544(1) A, ˚ P21 /c, with cell parameters a = 5.6034(1) A, ˚ β = 120.858(3)◦ , V = 131.207(13) A ˚ 3 , which c = 5.6190(2) A, is coincided with JCPDS data, card number 73-1807. The average particle size is estimated to be about 650 nm according to the Sherrer formula, agreeing with the observation of the SEM image in Fig. 3a.
Fig. 3. SEM image of electrodes: (a) MoO2 powders and (b) MoO2 electrode after the initial discharge.
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Y. Liang et al. / Materials Science and Engineering B 121 (2005) 152–155
An example of the microstructure developed in the electrodes after the initial discharge process is shown in Fig. 3. The as-prepared MoO2 powders at 400 ◦ C (Fig. 3a) shows that the grains with average particle size about 700 nm aggregates and tightly stacks with a free porous state. It is different with coarse-grained molybdenum dioxide prepared by hightemperature reactions [14,15] or nano-sized ones obtained through solution routes [16,17]. The fully lithiated particles in Fig. 3b shows near sphere with average particle size about 300 nm. It is crucial to MoO2 powders with proper particle size as stable anode materials for lithium batteries [18]. But this change was caused by an electrochemical grinding, not a milling. In addition, an amorphous phase of particles with no clear fringe appeared after lithium fully intercalating, coinciding with the XRD diagram in Fig. 5. The discharge and charge curves of fissile MoO2 recorded with a current density of 100 mA g−1 are presented in Fig. 4. The initial discharge capacity comes to about 994 mAh g−1 and the charge capacity reaches to 484 mAh g−1 . There is no obvious potential plateau during the first discharge process. However, the charge and discharge curves in the following cycle present characteristics. There are two constant potential plateaus at 1.39 and 1.70 V on charge as well as 1.57 and 1.28 V on discharge. Based the previous research, the inflection point between these plateaus represents a transition between monoclinic phase and orthogonal phase in the partially Lix MoO2 . Activated material cycle reversibly above this inflection point, but the phase transition is electrochemically irreversible. When the cell was discharged through the phase transition, the capacity would decrease rapidly [19]. However, from the second discharge curve, the capacity between plateaus changed little. To large particles, the rate of ionic diffusion through the particle is slow relative to the effective current density (the rate of charge transfer at the surface). This would result in a radial lithium concentration gradient with the particle, with only the outer layers of the rutile-type crystals actively involved in lithium-intercalation. Therefore, its initial Coulombic efficiency is only about 48.7%. In order to evaluate any structural changes of MoO2 electrodes during Li ion extraction at different state of charge, a group of cells were stopped at 0.01, 1.39, 1.70 and 2.0 V during the initial charge process, respectively. These cells were opened in an argon-filled glove box to recover
Fig. 4. The charge and discharge curves of MoO2 /Li test cells.
Fig. 5. XRD patterns of the electrode at different state: (1) 0.01 V, fully lithiated MoO2 ; (2) 1.36 V, LiMoO2 (#), Li0.98 MoO2 (&); (3) 1.75 V, Li0.42 MoO2 ; (4) 2.0 V, MoO2 .
the electrodes, and the electrodes were subsequently rinsed in EC to remove the residual LiClO4 and finally dried under vacuum. The dried electrodes were subjected to XRD. Fig. 5 presents the changes of XRD patterns in the electrodes. The major diffraction peaks at different state were identified with corresponding h, k, l values. The phase of MoO2 in fully lithiated particles at 0.01 V implies that the structure of the particles limited the lithium-ion diffusion and the inner particles were not fully involved in the lithium-intercalation in the initial discharge process. The cycling behavior within forty cycles is shown in Fig. 6 and 83.1% of the initial charge capacity was maintained after 40 cycles. The charge capacity reduces slightly in the second cycle. In fact, the observed reversible capacity of MoO2 rises slowly in subsequent cycles till the 13th cycle. From the SEM image (Fig. 3b), a phenomenon of “electrochemical grinding” [20] took place in the electrode material. Smaller particles were formed after the initial lithium fully intercalating. The average particle size reduced, thereby increasing the exposed surface area. That is, lithium-ion diffusion became easier as well as better capacity utilization. Its Coulombic efficiency ascended from the first cycle to the fortieth up to 1. The capacity of the electrode after electrochemical grinding approaches calculated theoretical capacity in following cycles. Contrarily, the effective current density became lower. This would reduce the rate of electron exchange. The different effects from two facets provide the unique cycling performance. Clearly, there is a correlation between the cycling
Fig. 6. Cycling performance of the obtained MoO2 samples.
Y. Liang et al. / Materials Science and Engineering B 121 (2005) 152–155
performance of the MoO2 powders and their morphological properties.
4. Conclusions A stable MoO2 as suitable anode materials for lithium rechargeable batteries was prepared at low temperature, using a rheological phase reaction as a novel method. The activated MoO2 displays 484 mAh g−1 capacity in the initial charge process with a capacity retention of 83.1% after 40 cycles. The results above reveal a correlation between the cycling performance of the fissile MoO2 powders and their morphological properties.
Acknowledgements This work has been supported by the National Natural Science Foundation of China (20471044). The authors gratefully acknowledged the referee for helpful discussions and for carefully reviewing this paper.
References [1] Y. Idota, A. Matsufuji, Y. Miyasaki, Science 276 (1997) 1395–1397. [2] P. Poizot, S. Laruelle, S. Grugeon, L. Dupont, J.M. Tarascon, Nature 407 (2000) 496–499.
155
[3] S. Denis, E. Beudrin, M. Touboul, J.M. Tarascon, J. Electrochem. Soc. 144 (1997) 4099–4109. [4] Q.F. Dong, C.Z. Wu, M.G. Jin, Z.C. Huang, M.S. Zheng, J.K. You, Z.G. Lin, Solid State Ionics 167 (2004) 49–54. [5] N. Tamura, M. Fujimoto, M. Kamino, S. Fujitani, Electrochim. Acta 49 (2004) 1949–1956. [6] J.R. Dahn, T. Zheng, Y. Liu, J.S. Xue, Science 270 (1995) 590– 593. [7] H.Y. Wang, M. Yoshio, Mater. Chem. Phys. 79 (2003) 76–80. [8] J.J. Auborn, Y.L. Barberio, J. Electrochem. Soc. 134 (1987) 638– 641. [9] A. Manthiram, C. Tsang, J. Electrochem. Soc. 143 (1996) L143–L145. [10] S.S. Kim, S. Ogura, H. Ikuta, Y. Uchimoto, M. Wakihara, Chem. Lett. 13 (2001) 760–761. [11] M. Martos, J. Morales, L. Sanchez, Electrochim. Acta 46 (2000) 83–89. [12] Y. Takeda, R. Kanno, T. Tanaka, O. Yamamoto, J. Electrochem. Soc. 134 (1987) 641–643. [13] D. Hara, H. Ikuta, Y. Uchimoto, M. Wakihara, J. Mater. Chem. 12 (2002) 2507–2512. [14] M. Ghedira, D.C. Do, M. Marezio, J. Solid State Chem. 59 (1985) 159–164. [15] A.A. Bolzan, B.J. Kennedy, C.J. Howard, Aust. J. Chem. 48 (1995) 1473–1478. [16] A. Manthiram, A. Dananjay, Y.T. Zhu, Chem. Mater. 6 (1994) 1601–1602. [17] Y. Liu, Y. Qian, M. Zhang, Z. Chen, C. Wang, Mater. Res. Bull. 31 (1996) 1029–1033. [18] D.W. Murphy, F.J. Si Salvo, J.N. Carides, J.V. Waszczak, Mater. Res. Bull. 13 (1978) 1395–1398. [19] J.R. Dahn, W.R. Mckinnon, Solid State Ionics 23 (1997) 1–7. [20] Y. Piffard, F. Leroux, D. Guyomard, J. Power Sources 68 (1997) 698–703.
Low temperature synthesis of a stable MoO2 as suitable anode materials for lithium batteries Yongguang Liang, Shuijin Yang, Zonghui Yi, Xuefeng Lei, Jutang Sun ∗ , Yunhong Zhou Department of Chemistry, Wuhan University, Wuhan 430072, PR China Received 15 December 2004; received in revised form 14 March 2005; accepted 25 March 2005
Abstract Fissile molybdenum dioxide (MoO2 ) was synthesized using a rheological phase reaction as a novel method suitable for a large scale up. The oxalate precursor was initially prepared at 80 ◦ C and was treated at different temperatures. The physical characterization was carried out by thermogravimetry and differential thermal analysis (TG/DTA), X-ray diffractometer (XRD) and scanning electron microscope (SEM). The results of TG/DTA and XRD indicate that the oxalate precursor begins to yield MoO2 at 250 ◦ C and a single phase MoO2 with monocline symmetry is formed at 350 ◦ C. The electrochemical characteristics of fissile MoO2 as an anode material for lithium batteries have also been studied and the morphological properties were found to play an important role in the cycling stability. The activated MoO2 displays 484 mAh g−1 capacity in the initial charge process with a capacity retention of 83.1% after 40 cycles in the range of 0.01–2.00 V versus metallic lithium at a current density of 100 mA g−1 . The SEM results reveal that there is a correlation between the cycling performance of the MoO2 powders and their morphological properties. © 2005 Elsevier B.V. All rights reserved. Keywords: Molybdenum oxide; Chemical synthesis; Surface properties; Negative electrode; Lithium batteries
1. Introduction The fast technological progress in the area of mobile devices puts higher demands on portable power supplies. Currently, it seems that rechargeable lithium-ion batteries are the systems of choice for high-capacity cells. Since the introduction with carbon as anode material by Sony company in 1990, many studies has been undertaken to search for new anode materials to improve the energy density and cycling performance of these practical cells. Idota et al. [1] have reported that tin-based amorphous oxides as new negative electrode materials provide a high lithium storage capacity. Recently, some metal oxides and metal-based composite oxides [2,3], and intermetallics [4,5] were also found to deliver much higher specific capacity than carbonaceous materials for which the theoretical capacity is 372 mAh g−1 [6,7]. However, there are still concerns mainly associated with the improvement of the synthesis conditions and ∗
Corresponding author. Tel.: +86 27 87218494; fax: +86 27 68754067. E-mail address: [email protected] (J. Sun).
0921-5107/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.mseb.2005.03.027
cycling stability before these materials can be considered as possible anode candidates for lithium rechargeable batteries. Auborn and Barberio [8] reported the use of MoO2 powder as possible commercial anode in 1987, but their results showed a limited success because of the poor stability of their electrolyte at low potential. Furthermore, several molybdenum oxides and composite oxides, such as MoO2+δ [9], MnMoO4 [10], Moy Snx O2 [11], V9 Mo6 O40 [12], Mn1−x Mo2x V2(1−x) O6 [13] have been studied as anode materials for lithium batteries. However, these compounds obtained by different synthesis methods usually showed inconsistent lithium-intercalation properties. In this paper, we introduce a new synthesis route of fissile MoO2 by a rheological phase reaction method. The physical properties of MoO2 oxides are presented as well as the electrochemical performance of the resulting electrodes. 2. Experimental The oxalate precursor was synthesized by a rheological phase reaction route. All reagents were analytical grade and
Y. Liang et al. / Materials Science and Engineering B 121 (2005) 152–155
used without further purification. (NH4 )6 Mo7 O24 ·4H2 O and C2 H4 O2 ·2H2 O were fully mixed by grinding with a molar ratio of 1:1.05. A proper amount of absolute alcohol was added to get a rheological body. The mixture was sealed in a closed container at 80 ◦ C for 8 h. After dried under vacuum at 80 ◦ C, the white precursor was obtained. The thermal stability of the oxalate precursor was examined by means of thermogravimetry and differential thermal analysis (TG/DTA) with a Netzsch STA 449 thermal analysis system at a heating rate of 10 ◦ C min−1 from 25 to 700 ◦ C in a flow of argon. Identification of phases and structures was carried out on a Shimadzu 6000 X-ray diffractometer at a scan˚ ning rate of 2◦ min−1 , using Cu K␣ radiation (λ = 1.54056 A). The particle sizes and morphological features were observed by a scanning electron microscope (Hitachi SEM X-650). The electrochemical cell consisted of a MoO2 working electrode and a lithium foil counter electrode. Electrodes were prepared by mixing MoO2 powders with 15% acetylene black and 5% PTFE, compressing the mixture onto a nickel gauze current collector. A 1 mol L−1 solution of LiClO4 dissolved in EC/DEC (1:1) was used as the electrolyte. A Celgard 2400 microporous membrane was used as a separator. The cell was discharged and charged between 2.0 and 0.01 V versus metallic lithium at a constant current density of 100 mA g−1 . 3. Results and discussion The TG and DTA curves of the precursor are shown in Fig. 1. From the TG curve, the pyrolysis of the oxalate precursor proceeds with 43% mass loss from 88.5 to 332 ◦ C. The endothermic peaks on the DTA curve at about 106 and 178 ◦ C correspond the loss of the adsorbed water and the decomposition of surplus oxalate acid. The sharp endothermic peak at about 258 ◦ C is associated with the formation of crystallized MoO2 , which is confirmed by the XRD data in Fig. 2. Fig. 2 illustrates the changes of XRD patterns when the oxalate precursor was treated at different temperatures for 4 h in argon atmosphere. A monoclinic phase of MoO2 already appeared in the sample obtained at 250 ◦ C with diffraction
153
Fig. 1. TG and DTA curves of the oxalate precursor.
Fig. 2. Changes in XRD patterns with the precursor treating at different temperatures.
lines at 26.02◦ , 37.00◦ and 53.58◦ . The XRD peaks assigned to a MoO2 phase obviously increased in intensity at ensuing higher temperature, and these patterns are mutually coincided. A single phase of MoO2 was found to be yielded after a heating treatment no less than 350 ◦ C. The XRD results of the product obtained at 400 ◦ C is well defined as a pure phase MoO2 with monocline symmetry, space group ˚ b = 4.8544(1) A, ˚ P21 /c, with cell parameters a = 5.6034(1) A, ˚ β = 120.858(3)◦ , V = 131.207(13) A ˚ 3 , which c = 5.6190(2) A, is coincided with JCPDS data, card number 73-1807. The average particle size is estimated to be about 650 nm according to the Sherrer formula, agreeing with the observation of the SEM image in Fig. 3a.
Fig. 3. SEM image of electrodes: (a) MoO2 powders and (b) MoO2 electrode after the initial discharge.
154
Y. Liang et al. / Materials Science and Engineering B 121 (2005) 152–155
An example of the microstructure developed in the electrodes after the initial discharge process is shown in Fig. 3. The as-prepared MoO2 powders at 400 ◦ C (Fig. 3a) shows that the grains with average particle size about 700 nm aggregates and tightly stacks with a free porous state. It is different with coarse-grained molybdenum dioxide prepared by hightemperature reactions [14,15] or nano-sized ones obtained through solution routes [16,17]. The fully lithiated particles in Fig. 3b shows near sphere with average particle size about 300 nm. It is crucial to MoO2 powders with proper particle size as stable anode materials for lithium batteries [18]. But this change was caused by an electrochemical grinding, not a milling. In addition, an amorphous phase of particles with no clear fringe appeared after lithium fully intercalating, coinciding with the XRD diagram in Fig. 5. The discharge and charge curves of fissile MoO2 recorded with a current density of 100 mA g−1 are presented in Fig. 4. The initial discharge capacity comes to about 994 mAh g−1 and the charge capacity reaches to 484 mAh g−1 . There is no obvious potential plateau during the first discharge process. However, the charge and discharge curves in the following cycle present characteristics. There are two constant potential plateaus at 1.39 and 1.70 V on charge as well as 1.57 and 1.28 V on discharge. Based the previous research, the inflection point between these plateaus represents a transition between monoclinic phase and orthogonal phase in the partially Lix MoO2 . Activated material cycle reversibly above this inflection point, but the phase transition is electrochemically irreversible. When the cell was discharged through the phase transition, the capacity would decrease rapidly [19]. However, from the second discharge curve, the capacity between plateaus changed little. To large particles, the rate of ionic diffusion through the particle is slow relative to the effective current density (the rate of charge transfer at the surface). This would result in a radial lithium concentration gradient with the particle, with only the outer layers of the rutile-type crystals actively involved in lithium-intercalation. Therefore, its initial Coulombic efficiency is only about 48.7%. In order to evaluate any structural changes of MoO2 electrodes during Li ion extraction at different state of charge, a group of cells were stopped at 0.01, 1.39, 1.70 and 2.0 V during the initial charge process, respectively. These cells were opened in an argon-filled glove box to recover
Fig. 4. The charge and discharge curves of MoO2 /Li test cells.
Fig. 5. XRD patterns of the electrode at different state: (1) 0.01 V, fully lithiated MoO2 ; (2) 1.36 V, LiMoO2 (#), Li0.98 MoO2 (&); (3) 1.75 V, Li0.42 MoO2 ; (4) 2.0 V, MoO2 .
the electrodes, and the electrodes were subsequently rinsed in EC to remove the residual LiClO4 and finally dried under vacuum. The dried electrodes were subjected to XRD. Fig. 5 presents the changes of XRD patterns in the electrodes. The major diffraction peaks at different state were identified with corresponding h, k, l values. The phase of MoO2 in fully lithiated particles at 0.01 V implies that the structure of the particles limited the lithium-ion diffusion and the inner particles were not fully involved in the lithium-intercalation in the initial discharge process. The cycling behavior within forty cycles is shown in Fig. 6 and 83.1% of the initial charge capacity was maintained after 40 cycles. The charge capacity reduces slightly in the second cycle. In fact, the observed reversible capacity of MoO2 rises slowly in subsequent cycles till the 13th cycle. From the SEM image (Fig. 3b), a phenomenon of “electrochemical grinding” [20] took place in the electrode material. Smaller particles were formed after the initial lithium fully intercalating. The average particle size reduced, thereby increasing the exposed surface area. That is, lithium-ion diffusion became easier as well as better capacity utilization. Its Coulombic efficiency ascended from the first cycle to the fortieth up to 1. The capacity of the electrode after electrochemical grinding approaches calculated theoretical capacity in following cycles. Contrarily, the effective current density became lower. This would reduce the rate of electron exchange. The different effects from two facets provide the unique cycling performance. Clearly, there is a correlation between the cycling
Fig. 6. Cycling performance of the obtained MoO2 samples.
Y. Liang et al. / Materials Science and Engineering B 121 (2005) 152–155
performance of the MoO2 powders and their morphological properties.
4. Conclusions A stable MoO2 as suitable anode materials for lithium rechargeable batteries was prepared at low temperature, using a rheological phase reaction as a novel method. The activated MoO2 displays 484 mAh g−1 capacity in the initial charge process with a capacity retention of 83.1% after 40 cycles. The results above reveal a correlation between the cycling performance of the fissile MoO2 powders and their morphological properties.
Acknowledgements This work has been supported by the National Natural Science Foundation of China (20471044). The authors gratefully acknowledged the referee for helpful discussions and for carefully reviewing this paper.
References [1] Y. Idota, A. Matsufuji, Y. Miyasaki, Science 276 (1997) 1395–1397. [2] P. Poizot, S. Laruelle, S. Grugeon, L. Dupont, J.M. Tarascon, Nature 407 (2000) 496–499.
155
[3] S. Denis, E. Beudrin, M. Touboul, J.M. Tarascon, J. Electrochem. Soc. 144 (1997) 4099–4109. [4] Q.F. Dong, C.Z. Wu, M.G. Jin, Z.C. Huang, M.S. Zheng, J.K. You, Z.G. Lin, Solid State Ionics 167 (2004) 49–54. [5] N. Tamura, M. Fujimoto, M. Kamino, S. Fujitani, Electrochim. Acta 49 (2004) 1949–1956. [6] J.R. Dahn, T. Zheng, Y. Liu, J.S. Xue, Science 270 (1995) 590– 593. [7] H.Y. Wang, M. Yoshio, Mater. Chem. Phys. 79 (2003) 76–80. [8] J.J. Auborn, Y.L. Barberio, J. Electrochem. Soc. 134 (1987) 638– 641. [9] A. Manthiram, C. Tsang, J. Electrochem. Soc. 143 (1996) L143–L145. [10] S.S. Kim, S. Ogura, H. Ikuta, Y. Uchimoto, M. Wakihara, Chem. Lett. 13 (2001) 760–761. [11] M. Martos, J. Morales, L. Sanchez, Electrochim. Acta 46 (2000) 83–89. [12] Y. Takeda, R. Kanno, T. Tanaka, O. Yamamoto, J. Electrochem. Soc. 134 (1987) 641–643. [13] D. Hara, H. Ikuta, Y. Uchimoto, M. Wakihara, J. Mater. Chem. 12 (2002) 2507–2512. [14] M. Ghedira, D.C. Do, M. Marezio, J. Solid State Chem. 59 (1985) 159–164. [15] A.A. Bolzan, B.J. Kennedy, C.J. Howard, Aust. J. Chem. 48 (1995) 1473–1478. [16] A. Manthiram, A. Dananjay, Y.T. Zhu, Chem. Mater. 6 (1994) 1601–1602. [17] Y. Liu, Y. Qian, M. Zhang, Z. Chen, C. Wang, Mater. Res. Bull. 31 (1996) 1029–1033. [18] D.W. Murphy, F.J. Si Salvo, J.N. Carides, J.V. Waszczak, Mater. Res. Bull. 13 (1978) 1395–1398. [19] J.R. Dahn, W.R. Mckinnon, Solid State Ionics 23 (1997) 1–7. [20] Y. Piffard, F. Leroux, D. Guyomard, J. Power Sources 68 (1997) 698–703.