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LixV2O5 nanobelts for high capacity lithium-ion battery cathodes
Electrochemistry Communications 12 (2010) 1154–1157
Contents lists available at ScienceDirect
Electrochemistry Communications 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 / e l e c o m
LixV2O5 nanobelts for high capacity lithium-ion battery cathodes Dmitrii A. Semenenko a, Daniil M. Itkis a, Ekaterina A. Pomerantseva a, Eugene A. Goodilin a,b,⁎, Tatiana L. Kulova c, Alexander M. Skundin c, Yurii D. Tretyakov a,b a b c
Department of Materials Science, M.V. Lomonosov Moscow State University, Moscow, Russia 119991 Department of Chemistry, M.V. Lomonosov Moscow State University, Moscow, Russia 119991 A.N.Frumkin Institute of Physical Chemistry and Electrochemistry of Russian Academy of Sciences, Moscow, Russia 119991
a r t i c l e
i n f o
Article history: Received 18 May 2010 Received in revised form 28 May 2010 Accepted 29 May 2010 Available online 4 June 2010 Keywords: Vanadium oxide Hydrothermal Nanomaterials Lithium batteries
a b s t r a c t 5–10 μm long, typically 200–300 nm wide, and several nanometers thick LixV2O5 (× ∼ 0.8) nanobelts with the δ-type crystal structure were synthesized by a hydrothermal treatment of Li+-exchanged V2O5 gel. When dried at 200 °C under vacuum prior to electrochemical testing, the as-prepared nanobelts underwent the well-known δ → ε → γ-phase transition giving a mixture of ε and γ phases as a nanocomposite electrode material. Such a simple preparation procedure guarantees a yield of material with drastically enhanced initial discharge specific capacity of 490 mAh/g and great cyclability. The enhanced electrochemical performance is attributed to the complex of experimental procedures including post-synthesis treatment of the single-crystalline LixV2O5 nanobelts. © 2010 Elsevier B.V. All rights reserved.
1. Introduction
2. Experimental
Vanadium oxides demonstrate a very rich crystal chemistry due to the diversity of vanadium oxidation states and coordination numbers. This results in the formation of a variety of unique compounds with layered and open-framework crystal structures being highly prospective in terms of reversible incorporation of lithium ions and therefore promising as new types of cathode materials for lithium-ion batteries. In detailed reviews [1,2] electrochemically active vanadium oxides were discussed and it was shown [3] that nanostructured vanadium oxides could significantly improve the performance of lithium cells. In particular, one-dimensional nanostructured vanadium oxides have been successfully used as electrode materials with greatly enhanced electrochemical properties [4–8]. The initial discharge capacities of the electrodes composed of vanadium oxide nanofibers [4], nanotubes [5], nanorods [6], and nanobelts [7,8] reached up to 300–400 mAh/g thus revealing much better functional properties than those of similar bulk materials. In this short communication, we report the synthesis of LixV2O5 nanobelts in a narrow hydrothermal condition window and their electrochemical properties. LixV2O5 nanobelts demonstrate superior performance with high capacity and excellent cyclability.
In a typical experiment, vanadium pentoxide gels were obtained as described elsewhere [9]. The Li+-exchanged gels obtained by interaction with LiCl solution (the Li:V molar ratio was kept as 1:1) were placed in Teflon-lined stainless steel 35 ml autoclaves, sealed, and heated up to 170–190 °C for 8–24 h. After such a hydrothermal treatment, the green solids were collected, thoroughly washed and dried at 70 °C for 12 h followed by drying at 200 °C under vacuum overnight. The material morphology was analyzed by scanning electron microscopy (LEO Supra 50VP). Room-temperature powder X-ray diffraction data were collected using a high intensity Rigaku D/Max2500 diffractometer with a rotating anode (Bragg–Brentano geometry) using Cu Kα radiation (step size of 0.02o in the range of 5o b 2θ b 60o). The material crystallinity and structural features were analyzed using transmission electron microscopy combined with selected area electron diffraction (LEO912 AB OMEGA). Chemical composition was controlled using inductively coupled plasma mass spectrometry (Perkin Elmer ELAN DRC II). Raman spectra were collected in a backscattering geometry at room temperature using Renishaw inVia Reflex Raman microscope. A 20× objective was used to focus laser light (He–Ne red laser operating at 633 nm) on the sample to a spot size of 25 μm2. In order to avoid distortion of the sample by the laser its power was limited to 0.1 mW. Electrochemical experiments were carried out using threeelectrode lithium cells. The working electrode consisted of 80 wt.%
⁎ Corresponding author. Department of Materials Science, M.V. Lomonosov Moscow State University, Moscow, Russia 119991. Tel.: + 7 495 9394729; fax: + 7 495 9390998. E-mail address: [email protected] (E.A. Goodilin). 1388-2481/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.elecom.2010.05.045
D.A. Semenenko et al. / Electrochemistry Communications 12 (2010) 1154–1157
active material, 10 wt.% acetylene black, and 10 wt.% polyvinylidene fluoride dissolved in acetone. Pure lithium foils were used as the counter and reference electrodes and 1 M LiClO4 in a propylene carbonate (PC):dimethoxyethane (DME) mixture (7:3 by volume) as the electrolyte. The cells were assembled in an argon-filled glovebox. Cyclic volamperogramms were registered on Ecochemie Autolab 302 potentiostat with the sweep rate of 80 μV/s. Galvanostatic charge– discharge cycles were performed in most experiments with the current density of 20 mA/g related to the amount of active material using a multichannel galvanostat. The used current is equivalent to 0.2 mA/cm2 and C/25 rate for our cathode loading of about 10 mg/cm2. 3. Results and discussion The morphology of the obtained material is shown in Fig. 1. As estimated from SEM images, the LixV2O5 nanobelts are 5–10 μm long and typically 200–300 nm wide. According to the ICP-MS analysis the Li:V ratio in nanobelts has to be about 0.38:1.00 (within a 4–5% error range). TEM data (Fig. 2a) indicate that the nanobelts are characterized by the extremely small thickness of about 5–15 nm. A typical selected area electron diffraction (SAED) pattern of the LixV2O5 nanobelt is presented in Fig. 2b. Splitting of the reflections in electron diffraction patterns is induced by the tendency of thin ribbon-like particles to stick together with a slight angle mismatch. The diffraction pattern remains the same as the electron beam moves along the nanobelt thus indicating that the entire nanobelt is singlecrystalline. It is difficult to unambiguously identify a crystallographic phase of the LixV2O5 nanobelts from X-ray (Fig. 2c) and electron (Fig. 2b, inset) diffraction data because of a high extent of the material texturing. To analyze the structure, Raman spectra of the material were recorded (Fig. 2d). It is known that the Raman spectroscopy is a very sensitive
Fig. 1. (a) Low-magnification, and (b) high-magnification SEM images of the LixV2O5 nanobelts obtained after hydrothermal treatment.
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tool to detect a local structure and therefore it can be used to distinguish different LixV2O5 phases [10–12]. The Raman spectrum of the as-prepared LixV2O5 nanobelts exhibits a series of bands as indicated in Fig. 2d, which are well consistent with those of δ-V2O5. The Raman features of the γ phase, in particular, a maximum at 740 cm−1 forming a shoulder in the peak at 708 cm−1, are absent in the spectrum of the as-prepared material. This spectrum slightly differs from those typical for chemically prepared LixV2O5 powders reported in [10]. Peaks marked with the asterisks in Fig. 2d are not extensively discussed in the literature on vanadium (IV) and (V) oxides. In ref. [12] these peaks were referenced to the phases of γ-type formed from δ phases under laser light. Therefore, it was concluded that as-prepared LixV2O5 nanobelts have the δ-type crystal structure, and partial transition into γ phase occurred even when low laser power was used. XRD pattern of as-prepared LixV2O5 nanobelts (Fig. 2c, inset) is very similar to the pattern of vanadium oxide xerogels [4]. Thorough grinding of as-prepared powders with starch in order to minimize the extent of the texture made it possible to obtain the XRD pattern (Fig 2b) that can be indexed to an orthorhombic unit cell with the unit cell parameters a = 2.069 (22) Å, b = 3.649 (4) Å, c = 11.029 (18) Å within a Pmmn Space Group (no. 59) that is not typical for δ-V2O5 reported previously [10]. According to SAED, a preferential growth direction of LixV2O5 nanobelts is [010] that could evidence that crystallization by blocks occurs during hydrothermal treatment. A vacuum annealing of the LixV2O5 nanobelts at 200 °C, consistent with the conditions for electrodes drying, results in the well-known δ → ε → γ-phase transition [10,11]. Minor impurity of the δ phase was detected in the LixV2O5 nanobelts annealed at 200 °C under vacuum by the presence of characteristic high frequency band at 1019 cm−1 in the Raman spectra (Fig. 2d). The electrochemical properties of lithium-ion intercalation/deintercalation into and out of the LixV2O5 nanobelts have been investigated. The cyclic voltammogram (CV) curve of the LixV2O5 nanobelts is shown in Fig. 3. It demonstrates two peaks at 2.5 and 2.8 V which result from the lithium-ion intercalation processes in the 1st reduction cycle and two corresponding peaks at 2.7 and 2.9 V in the 1st oxidation cycle indicating lithium-ion deintercalation. The potential difference between the anodic and cathodic peaks is ∼ 0.1– 0.2 V which is characteristic of reversible intercalation processes. Fig. 4a shows charge/discharge curves of the cell with LixV2O5 nanobelts at 1st–50th cycles. Lithium content in the active materials was estimated from the first charge cycle (Fig. 4a) to be ∼0.8 (Li0.8V2O5), which is in a good agreement with the data of ICP-MS analysis. The LixV2O5 nanobelts exhibited an initial discharge capacity of 490 mAh/g, as shown in Fig. 4a. The capacity gradually decayed in the further cycles but remained as high as 410 mAh/g (16% capacity loss) after the 50th cycle (Fig. 4). The capacity of LixV2O5 nanobelts is significantly higher than that of NH4V4O10 bronze nanobelts [7], vanadium oxide nanofibers obtained after heating of HxV4O10∙nH2O at 500 °C [4] and V3O7∙H2O nanobelts [8]. Fig. 4b shows specific capacities delivered by the Li/LixV2O5 nanobelts cell during a cycling experiment performed between 2.15 and 4.00 V under constant current densities of 50, 100 and 200 mA/g, alternating every 5 cycles. Changes in current density resulted in stepwise dependence of the specific capacity on cycle number. The capacity slowly fades at a constant rate, but drops significantly when the rate is increased. Some of the specific capacity is recovered when the rate is decreased from 200 to 100 mA/g (Fig. 4b). It is important to note, that due to their nanostructured morphology LixV2O5 nanobelts demonstrate significantly high specific capacities at high current densities. The high capacity values of LixV2O5 nanobelts can be achieved due to the large surface area and short diffusion distances typical of nanostructured materials. We believe that post-synthesis treatment conditions play a key role in electrochemical performance of the nanostructured vanadium oxides. It is important, for instance, to find
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D.A. Semenenko et al. / Electrochemistry Communications 12 (2010) 1154–1157
Fig. 2. (a) TEM image and (b) the SAED pattern taken from [001] zone axis, (c) XRD pattern registered on a sample with randomly oriented nanobelts (inset demonstrates XRD pattern of self-texturized sample), and (d) Raman spectra (before and after vacuum annealing) of the LixV2O5 nanobelts.
an optimal temperature of electrodes drying to guarantee an efficient water removal from the crystal structure of the hydrothermally synthesized material while preventing extremely thin particles from aggregation and thus preserving the high surface area. For LixV2O5 nanobelts annealing at 200 °C under vacuum resulted in a unique nanocomposite formation giving a scope to the further investigation of the lithium diffusion, boundary effects, etc. The presented results indicate that the LixV2O5 nanobelts synthesized in this work are promising cathode materials for lithium-ion batteries.
4. Conclusions In conclusion, we have synthesized LixV2O5 (× ∼0.8) nanobelts (10–15 nm × 200–300 nm × 5–10 μm) using a simple hydrothermal route. The δ-type crystal structure of the as-prepared materials transforms into the mixture of ε and γ phases with the preserved nanobelts morphology under conditions of electrodes drying (200 °C under vacuum). Electrochemical tests indicated that an electrode composed of LixV2O5 nanobelts exhibited a high initial discharge
Fig. 3. Cyclic voltammogram of the LixV2O5 nanobelts/Li cell in a voltage window of 2.1–4.2 V. The scan direction is indicated by arrows. Sweep rate 80 uV/s.
D.A. Semenenko et al. / Electrochemistry Communications 12 (2010) 1154–1157
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Fig. 4. (a) Charge and discharge curves of the cell with the LixV2O5 nanobelts during 1st–50th cycles in the voltage range of 2.1–4.2 V at a current density of 20 mA/g. (b) The cycling performance of the cell using the LixV2O5 nanobelts as cathode and lithium metal as anode in the voltage range of 2.15–4.00 V at a current density of 20, 50, 100 and 200 mA/g.
capacity of 490 mAh/g. The capacity was maintained above 400 mAh/ g for 50 cycles. Hopefully, LixV2O5 nanobelts can be considered as potential cathode material for lithium-ion batteries. Acknowledgements This work was supported by Russian Foundation for Basic Research and the Federal R&D Program (Project 02.513.12.3018). References [1] M.S. Whittingham, Y. Song, S. Lutta, P.Y. Zavalij, N.A. Chernova, J. Mater. Chem. 15 (2005) 3362. [2] N.A. Chernova, M. Roppolo, A.C. Dillon, M.S. Whittingham, J. Mater. Chem. 19 (2009) 2526.
[3] P.G. Bruce, B. Scrosati, J.-M. Tarascon, Angew. Chem. Int. Ed. 47 (2008) 2930. [4] C. Ban, N.A. Chernova, M.S. Whittingham, Electrochem. Commun. 11 (2009) 522. [5] V. Petkov, P.Y. Zavalij, S. Lutta, M.S. Whittingham, V. Parvanov, S. Shastri, Phys. Rev. B 69 (2004) 085410. [6] K. Takahashi, S.J. Limmer, Y. Wang, G. Cao, Jpn. J. Appl. Phys. 44 (1B) (2005) 662. [7] K.-F. Zhang, G.-Q. Zhang, X. Liu, Z.-X. Su, H.-L. Li, J. Power Sources 157 (2006) 528. [8] S. Gao, Z. Chen, M. Wei, K. Wei, H. Zhou, Electrochim. Acta 54 (2009) 1115. [9] D.V. Pyoryshkov, A.V. Grigorieva, E.A. Goodilin, D.A. Semenenko, V.V. Volkov, K.A. Dembo, Yu.D. Tretyakov, Dokl. Chem. 406 (2006) 9. [10] R. Baddour-Hadjean, E. Raekelboom, J.P. Pereira-Ramos, Chem. Mater. 18 (2006) 3548. [11] R. Baddour-Hadjean, J.P. Pereira-Ramos, Chem. Rev. 110 (2010) 1278. [12] R. Baddour-Hadjean, J.P. Pereira-Ramos, J. Power Sources 174 (2007) 1188.
Contents lists available at ScienceDirect
Electrochemistry Communications 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 / e l e c o m
LixV2O5 nanobelts for high capacity lithium-ion battery cathodes Dmitrii A. Semenenko a, Daniil M. Itkis a, Ekaterina A. Pomerantseva a, Eugene A. Goodilin a,b,⁎, Tatiana L. Kulova c, Alexander M. Skundin c, Yurii D. Tretyakov a,b a b c
Department of Materials Science, M.V. Lomonosov Moscow State University, Moscow, Russia 119991 Department of Chemistry, M.V. Lomonosov Moscow State University, Moscow, Russia 119991 A.N.Frumkin Institute of Physical Chemistry and Electrochemistry of Russian Academy of Sciences, Moscow, Russia 119991
a r t i c l e
i n f o
Article history: Received 18 May 2010 Received in revised form 28 May 2010 Accepted 29 May 2010 Available online 4 June 2010 Keywords: Vanadium oxide Hydrothermal Nanomaterials Lithium batteries
a b s t r a c t 5–10 μm long, typically 200–300 nm wide, and several nanometers thick LixV2O5 (× ∼ 0.8) nanobelts with the δ-type crystal structure were synthesized by a hydrothermal treatment of Li+-exchanged V2O5 gel. When dried at 200 °C under vacuum prior to electrochemical testing, the as-prepared nanobelts underwent the well-known δ → ε → γ-phase transition giving a mixture of ε and γ phases as a nanocomposite electrode material. Such a simple preparation procedure guarantees a yield of material with drastically enhanced initial discharge specific capacity of 490 mAh/g and great cyclability. The enhanced electrochemical performance is attributed to the complex of experimental procedures including post-synthesis treatment of the single-crystalline LixV2O5 nanobelts. © 2010 Elsevier B.V. All rights reserved.
1. Introduction
2. Experimental
Vanadium oxides demonstrate a very rich crystal chemistry due to the diversity of vanadium oxidation states and coordination numbers. This results in the formation of a variety of unique compounds with layered and open-framework crystal structures being highly prospective in terms of reversible incorporation of lithium ions and therefore promising as new types of cathode materials for lithium-ion batteries. In detailed reviews [1,2] electrochemically active vanadium oxides were discussed and it was shown [3] that nanostructured vanadium oxides could significantly improve the performance of lithium cells. In particular, one-dimensional nanostructured vanadium oxides have been successfully used as electrode materials with greatly enhanced electrochemical properties [4–8]. The initial discharge capacities of the electrodes composed of vanadium oxide nanofibers [4], nanotubes [5], nanorods [6], and nanobelts [7,8] reached up to 300–400 mAh/g thus revealing much better functional properties than those of similar bulk materials. In this short communication, we report the synthesis of LixV2O5 nanobelts in a narrow hydrothermal condition window and their electrochemical properties. LixV2O5 nanobelts demonstrate superior performance with high capacity and excellent cyclability.
In a typical experiment, vanadium pentoxide gels were obtained as described elsewhere [9]. The Li+-exchanged gels obtained by interaction with LiCl solution (the Li:V molar ratio was kept as 1:1) were placed in Teflon-lined stainless steel 35 ml autoclaves, sealed, and heated up to 170–190 °C for 8–24 h. After such a hydrothermal treatment, the green solids were collected, thoroughly washed and dried at 70 °C for 12 h followed by drying at 200 °C under vacuum overnight. The material morphology was analyzed by scanning electron microscopy (LEO Supra 50VP). Room-temperature powder X-ray diffraction data were collected using a high intensity Rigaku D/Max2500 diffractometer with a rotating anode (Bragg–Brentano geometry) using Cu Kα radiation (step size of 0.02o in the range of 5o b 2θ b 60o). The material crystallinity and structural features were analyzed using transmission electron microscopy combined with selected area electron diffraction (LEO912 AB OMEGA). Chemical composition was controlled using inductively coupled plasma mass spectrometry (Perkin Elmer ELAN DRC II). Raman spectra were collected in a backscattering geometry at room temperature using Renishaw inVia Reflex Raman microscope. A 20× objective was used to focus laser light (He–Ne red laser operating at 633 nm) on the sample to a spot size of 25 μm2. In order to avoid distortion of the sample by the laser its power was limited to 0.1 mW. Electrochemical experiments were carried out using threeelectrode lithium cells. The working electrode consisted of 80 wt.%
⁎ Corresponding author. Department of Materials Science, M.V. Lomonosov Moscow State University, Moscow, Russia 119991. Tel.: + 7 495 9394729; fax: + 7 495 9390998. E-mail address: [email protected] (E.A. Goodilin). 1388-2481/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.elecom.2010.05.045
D.A. Semenenko et al. / Electrochemistry Communications 12 (2010) 1154–1157
active material, 10 wt.% acetylene black, and 10 wt.% polyvinylidene fluoride dissolved in acetone. Pure lithium foils were used as the counter and reference electrodes and 1 M LiClO4 in a propylene carbonate (PC):dimethoxyethane (DME) mixture (7:3 by volume) as the electrolyte. The cells were assembled in an argon-filled glovebox. Cyclic volamperogramms were registered on Ecochemie Autolab 302 potentiostat with the sweep rate of 80 μV/s. Galvanostatic charge– discharge cycles were performed in most experiments with the current density of 20 mA/g related to the amount of active material using a multichannel galvanostat. The used current is equivalent to 0.2 mA/cm2 and C/25 rate for our cathode loading of about 10 mg/cm2. 3. Results and discussion The morphology of the obtained material is shown in Fig. 1. As estimated from SEM images, the LixV2O5 nanobelts are 5–10 μm long and typically 200–300 nm wide. According to the ICP-MS analysis the Li:V ratio in nanobelts has to be about 0.38:1.00 (within a 4–5% error range). TEM data (Fig. 2a) indicate that the nanobelts are characterized by the extremely small thickness of about 5–15 nm. A typical selected area electron diffraction (SAED) pattern of the LixV2O5 nanobelt is presented in Fig. 2b. Splitting of the reflections in electron diffraction patterns is induced by the tendency of thin ribbon-like particles to stick together with a slight angle mismatch. The diffraction pattern remains the same as the electron beam moves along the nanobelt thus indicating that the entire nanobelt is singlecrystalline. It is difficult to unambiguously identify a crystallographic phase of the LixV2O5 nanobelts from X-ray (Fig. 2c) and electron (Fig. 2b, inset) diffraction data because of a high extent of the material texturing. To analyze the structure, Raman spectra of the material were recorded (Fig. 2d). It is known that the Raman spectroscopy is a very sensitive
Fig. 1. (a) Low-magnification, and (b) high-magnification SEM images of the LixV2O5 nanobelts obtained after hydrothermal treatment.
1155
tool to detect a local structure and therefore it can be used to distinguish different LixV2O5 phases [10–12]. The Raman spectrum of the as-prepared LixV2O5 nanobelts exhibits a series of bands as indicated in Fig. 2d, which are well consistent with those of δ-V2O5. The Raman features of the γ phase, in particular, a maximum at 740 cm−1 forming a shoulder in the peak at 708 cm−1, are absent in the spectrum of the as-prepared material. This spectrum slightly differs from those typical for chemically prepared LixV2O5 powders reported in [10]. Peaks marked with the asterisks in Fig. 2d are not extensively discussed in the literature on vanadium (IV) and (V) oxides. In ref. [12] these peaks were referenced to the phases of γ-type formed from δ phases under laser light. Therefore, it was concluded that as-prepared LixV2O5 nanobelts have the δ-type crystal structure, and partial transition into γ phase occurred even when low laser power was used. XRD pattern of as-prepared LixV2O5 nanobelts (Fig. 2c, inset) is very similar to the pattern of vanadium oxide xerogels [4]. Thorough grinding of as-prepared powders with starch in order to minimize the extent of the texture made it possible to obtain the XRD pattern (Fig 2b) that can be indexed to an orthorhombic unit cell with the unit cell parameters a = 2.069 (22) Å, b = 3.649 (4) Å, c = 11.029 (18) Å within a Pmmn Space Group (no. 59) that is not typical for δ-V2O5 reported previously [10]. According to SAED, a preferential growth direction of LixV2O5 nanobelts is [010] that could evidence that crystallization by blocks occurs during hydrothermal treatment. A vacuum annealing of the LixV2O5 nanobelts at 200 °C, consistent with the conditions for electrodes drying, results in the well-known δ → ε → γ-phase transition [10,11]. Minor impurity of the δ phase was detected in the LixV2O5 nanobelts annealed at 200 °C under vacuum by the presence of characteristic high frequency band at 1019 cm−1 in the Raman spectra (Fig. 2d). The electrochemical properties of lithium-ion intercalation/deintercalation into and out of the LixV2O5 nanobelts have been investigated. The cyclic voltammogram (CV) curve of the LixV2O5 nanobelts is shown in Fig. 3. It demonstrates two peaks at 2.5 and 2.8 V which result from the lithium-ion intercalation processes in the 1st reduction cycle and two corresponding peaks at 2.7 and 2.9 V in the 1st oxidation cycle indicating lithium-ion deintercalation. The potential difference between the anodic and cathodic peaks is ∼ 0.1– 0.2 V which is characteristic of reversible intercalation processes. Fig. 4a shows charge/discharge curves of the cell with LixV2O5 nanobelts at 1st–50th cycles. Lithium content in the active materials was estimated from the first charge cycle (Fig. 4a) to be ∼0.8 (Li0.8V2O5), which is in a good agreement with the data of ICP-MS analysis. The LixV2O5 nanobelts exhibited an initial discharge capacity of 490 mAh/g, as shown in Fig. 4a. The capacity gradually decayed in the further cycles but remained as high as 410 mAh/g (16% capacity loss) after the 50th cycle (Fig. 4). The capacity of LixV2O5 nanobelts is significantly higher than that of NH4V4O10 bronze nanobelts [7], vanadium oxide nanofibers obtained after heating of HxV4O10∙nH2O at 500 °C [4] and V3O7∙H2O nanobelts [8]. Fig. 4b shows specific capacities delivered by the Li/LixV2O5 nanobelts cell during a cycling experiment performed between 2.15 and 4.00 V under constant current densities of 50, 100 and 200 mA/g, alternating every 5 cycles. Changes in current density resulted in stepwise dependence of the specific capacity on cycle number. The capacity slowly fades at a constant rate, but drops significantly when the rate is increased. Some of the specific capacity is recovered when the rate is decreased from 200 to 100 mA/g (Fig. 4b). It is important to note, that due to their nanostructured morphology LixV2O5 nanobelts demonstrate significantly high specific capacities at high current densities. The high capacity values of LixV2O5 nanobelts can be achieved due to the large surface area and short diffusion distances typical of nanostructured materials. We believe that post-synthesis treatment conditions play a key role in electrochemical performance of the nanostructured vanadium oxides. It is important, for instance, to find
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D.A. Semenenko et al. / Electrochemistry Communications 12 (2010) 1154–1157
Fig. 2. (a) TEM image and (b) the SAED pattern taken from [001] zone axis, (c) XRD pattern registered on a sample with randomly oriented nanobelts (inset demonstrates XRD pattern of self-texturized sample), and (d) Raman spectra (before and after vacuum annealing) of the LixV2O5 nanobelts.
an optimal temperature of electrodes drying to guarantee an efficient water removal from the crystal structure of the hydrothermally synthesized material while preventing extremely thin particles from aggregation and thus preserving the high surface area. For LixV2O5 nanobelts annealing at 200 °C under vacuum resulted in a unique nanocomposite formation giving a scope to the further investigation of the lithium diffusion, boundary effects, etc. The presented results indicate that the LixV2O5 nanobelts synthesized in this work are promising cathode materials for lithium-ion batteries.
4. Conclusions In conclusion, we have synthesized LixV2O5 (× ∼0.8) nanobelts (10–15 nm × 200–300 nm × 5–10 μm) using a simple hydrothermal route. The δ-type crystal structure of the as-prepared materials transforms into the mixture of ε and γ phases with the preserved nanobelts morphology under conditions of electrodes drying (200 °C under vacuum). Electrochemical tests indicated that an electrode composed of LixV2O5 nanobelts exhibited a high initial discharge
Fig. 3. Cyclic voltammogram of the LixV2O5 nanobelts/Li cell in a voltage window of 2.1–4.2 V. The scan direction is indicated by arrows. Sweep rate 80 uV/s.
D.A. Semenenko et al. / Electrochemistry Communications 12 (2010) 1154–1157
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Fig. 4. (a) Charge and discharge curves of the cell with the LixV2O5 nanobelts during 1st–50th cycles in the voltage range of 2.1–4.2 V at a current density of 20 mA/g. (b) The cycling performance of the cell using the LixV2O5 nanobelts as cathode and lithium metal as anode in the voltage range of 2.15–4.00 V at a current density of 20, 50, 100 and 200 mA/g.
capacity of 490 mAh/g. The capacity was maintained above 400 mAh/ g for 50 cycles. Hopefully, LixV2O5 nanobelts can be considered as potential cathode material for lithium-ion batteries. Acknowledgements This work was supported by Russian Foundation for Basic Research and the Federal R&D Program (Project 02.513.12.3018). References [1] M.S. Whittingham, Y. Song, S. Lutta, P.Y. Zavalij, N.A. Chernova, J. Mater. Chem. 15 (2005) 3362. [2] N.A. Chernova, M. Roppolo, A.C. Dillon, M.S. Whittingham, J. Mater. Chem. 19 (2009) 2526.
[3] P.G. Bruce, B. Scrosati, J.-M. Tarascon, Angew. Chem. Int. Ed. 47 (2008) 2930. [4] C. Ban, N.A. Chernova, M.S. Whittingham, Electrochem. Commun. 11 (2009) 522. [5] V. Petkov, P.Y. Zavalij, S. Lutta, M.S. Whittingham, V. Parvanov, S. Shastri, Phys. Rev. B 69 (2004) 085410. [6] K. Takahashi, S.J. Limmer, Y. Wang, G. Cao, Jpn. J. Appl. Phys. 44 (1B) (2005) 662. [7] K.-F. Zhang, G.-Q. Zhang, X. Liu, Z.-X. Su, H.-L. Li, J. Power Sources 157 (2006) 528. [8] S. Gao, Z. Chen, M. Wei, K. Wei, H. Zhou, Electrochim. Acta 54 (2009) 1115. [9] D.V. Pyoryshkov, A.V. Grigorieva, E.A. Goodilin, D.A. Semenenko, V.V. Volkov, K.A. Dembo, Yu.D. Tretyakov, Dokl. Chem. 406 (2006) 9. [10] R. Baddour-Hadjean, E. Raekelboom, J.P. Pereira-Ramos, Chem. Mater. 18 (2006) 3548. [11] R. Baddour-Hadjean, J.P. Pereira-Ramos, Chem. Rev. 110 (2010) 1278. [12] R. Baddour-Hadjean, J.P. Pereira-Ramos, J. Power Sources 174 (2007) 1188.