- Email: [email protected]
Synthesis and electrochemistry of a vanadium-pillared manganese oxide
www.elsevier.nl/locate/elecom Electrochemistry Communications 2 (2000) 445–447
Synthesis and electrochemistry of a vanadium-pillared manganese oxide Fan Zhang, Katana Ngala, M. Stanley Whittingham * Materials Research Center and Chemistry Department, State University of New York at Binghamton, Binghamton, NY 13902-6000, USA Received 28 February 2000; received in revised form 30 March 2000; accepted 31 March 2000
Abstract A new manganese dioxide pillared by vanadium oxide species has been synthesized hydrothermally from permanganate. It has the electrochemically active MnO2 layer structure, which has been extensively studied as a battery cathode. The vanadium oxide ions, together with the water molecules, reside in between the oxide sheets; dehydration occurs without structural change. The (VOy)0.1MnO2PnH2O has a ˚ cs22.08(2) A. ˚ It reacts readily with lithium with a capacity around rhombohedral structure, with hexagonal parameters as2.843(6) A, y1 150 mAh g ; the pillar ions do not appear to impede reaction. q2000 Elsevier Science S.A. All rights reserved. Keywords: Hydrothermal synthesis; Manganese oxide; Vanadium; Lithium cathode; Pillars
1. Introduction There is much interest in manganese and vanadium oxides for use as cathode materials for advanced lithium batteries [1–7] to replace the expensive and relatively low capacity lithium cobalt oxide system. These oxides have been synthesized using traditional high temperature methods as well as by soft chemistry techniques such as hydrothermal and solgel. Recently, layered manganates have also been prepared using hydrothermal methods, for example, by the decomposition of aqueous permanganate solutions [3]. These however tend to convert to spinel-like structures on cycling [8– 10], which is facilitated by the oxygen cubic-close-packing found in both lattices. Pillaring of the MnO2 layers by potassium appears to minimize this conversion [4,11]; however, at high rates even these compounds appear to convert to spinel-like materials [12,13]. Replacement of the potassium pillars by a redox active immobile pillar ion such as vanadium would be attractive, leading to a higher capacity. The vanadium should preferably be in square pyramidal or octahedral coordination, as VO4 tetrahedra are not readily reducible without destruction of the lattice polyhedra [14]. Attempts to form vanadium-pillared manganese dioxides frequently result in manganese ‘pillars’ in vanadium oxide lattices. Several of these have been reported by us recently including a g-MnV2O5 [15], isostructural with g-LiV2O5, a tunnel structure with a pipe-like morphology Mn7(OH)3* Corresponding author. Tel./fax: q1-607-777-4623; e-mail: stanwhit@ binghamton.edu
(VO4)4 [16], and d-MnxV2O5 [17] which belongs to the dV2O5 class of compounds which is of particular interest for potential use in batteries. V6O13, one of the most studied vanadium oxide cathodes [1], contains these sheets and cycles lithium well in secondary cells [18]. This paper discusses the synthesis and characterization of the (VOy)0.15MnO2PnH2O phase, which has vanadium-containing pillars between manganese oxide layers.
2. Experimental (VOy)0.15MnO2PnH2O was prepared by the hydrothermal treatment of vanadyl permanganate to which 1 drop of 4 M nitric acid had been added. (VO)0.5MnO4 was prepared by first passing a VOSO4 solution (4.5 g in 50 mL water) down an acid cationic ion exchange resin, and then passing a 0.3 M KMnO4 solution down the column. The reaction mixture was heated in a 125 mL Teflon-lined Parr reactor for 80 h at 165 8C. The resulting dark greenish-black powder was filtered and dried in air. The pH of the solution after reaction was weakly basic. X-ray powder diffraction was performed using Cu Ka radiation on a Scintag u–u diffractometer equipped with a Ge(Li) solid state detector. The data were collected from 2us48 to 2us908 with 0.038 steps and 15 s per step. TGA data were obtained on a Perkin-Elmer model TGA 7, and the electron microscopy on an Electroscan 2020 environmental scanning electron microscope. For electrochemical studies the manganese oxide was mixed with 10% carbon black and 10%
1388-2481/00/$ - see front matter q2000 Elsevier Science S.A. All rights reserved. PII S 1 3 8 8 - 2 4 8 1 ( 0 0 ) 0 0 0 5 8 - 8
Thursday May 04 10:26 AM
StyleTag -- Journal: ELECOM (Electrochemistry Communications)
Article: 235
446
F. Zhang et al. / Electrochemistry Communications 2 (2000) 445–447
Teflon powder, and hot-pressed for 60 min at over 100 8C to ensure removal of all absorbed water. Pure lithium metal was used as the anode and 1 M LiAsF6 in a 1:1 propylene carbonate/dimethoxyethane mixture as the electrolyte. A MacPile potentiostat was used to cycle the cells in a helium-filled glovebox.
3. Results and discussion The crystals precipitated from the hydrothermal reaction had a greenish-black color. Energy-dispersive spectroscopy showed that they contained vanadium and manganese in an approximate 0.15:1 ratio, giving the formula (VOy)0.15MnO2. On thermal analysis, as shown in Fig. 1, this material lost 30% of its weight by 100 8C, which corresponds to nf2.2 in the formula (VOy)0.15MnO2PnH2O. This is probably surface water and very weakly bound molecules between the oxide layers. This water can therefore be readily removed for electrochemical studies by hot-pressing above 100 8C. The very small weight loss above 100 8C indicates very little strongly bound water or hydroxyl groups in this material. X-ray diffraction data of the (VOy)0.15MnO2PnH2O compound are shown in Fig. 2. The pattern shows a repeat distance ˚ X-ray diffraction of the material after comof around 7.36 A. bustion in oxygen at 400 8C showed just a slight contraction
˚ showing that the water is not in the lattice spacing to 7.2 A, necessary for stabilizing the structure. The X-ray pattern is consistent with a rhombohedral structure with hexagonal par˚ cs22.08(2) A, ˚ and is isostructural ameters as2.843(6) A, with K0.26MnO2PnH2O [3]. The structure contains MnO2 sheets between which reside the vanadium and oxygen atoms. For comparison, the lattice spacings in the hydrated potassium, sodium and lithium compounds are 7.18, 7.28 and 7.01 ˚ respectively, and in contrast to this material the lattice A, contracts when the water is removed to 6.44, 5.61 and 4.86 ˚ respectively. The repeat distances for the vanadium comA, ˚ and 7.2 A ˚ after dehydration, are consistent pound of 7.36 A, with a lattice containing three oxygen layers; two are associated with the MnO2 layers and the third with the oxygen ion pillars. As noted above, this phase is stable at 400 8C, whereas layered LixMnO2 converts to the spinel LiMn2O4 at 400 8C and the sodium and potassium compounds convert to tunnel structures on heating to elevated temperatures. Electrochemical data for the first ten cycles are shown in Fig. 3. The cathode structure had been rigorously dried by hot-pressing for 1 h and then evacuating in the glovebox antechamber overnight. The initial open-circuit emf was around 3.5 V. Between 0.5 and 0.6 lithium per formula unit could be incorporated into the structure on discharge to 2 V, comparable with the 0.6 for the potassium compound [4]. This corresponds to 150 mAh gy1. The lithium insertion
Fig. 3. Electrochemical cycling of dehydrated of (VOy)0.15MnO2. Fig. 1. TGA of (VOy)0.15MnO2 in oxygen at heating rate of 3 8C miny1.
Fig. 2. X-ray diffraction pattern of (VOy)0.15MnO2, which can be indexed ˚ and cs22.08 A. ˚ with hexagonal parameters, as2.843 A
Thursday May 04 10:26 AM
Fig. 4. Capacity as a function of cycle for (VOy)0.15MnO2.
StyleTag -- Journal: ELECOM (Electrochemistry Communications)
Article: 235
F. Zhang et al. / Electrochemistry Communications 2 (2000) 445–447
proceeded in one smooth step, suggestive of a single-phase system as in LixTiS2 [19]. After recharge to 4.0 V, the capacity was maintained at 0.5–0.6 lithium per formula unit for these ten cycles, as shown in Fig. 4. The electrochemical performance of this phase is much improved over the corresponding sodium and lithium phases [4]. 4. Conclusions A new vanadium-pillared manganese dioxide, (VOy)0.15MnO2, has been synthesized hydrothermally and its structure determined. It intercalates lithium into the structure, and in a very reversible manner. Acknowledgements The authors thank the Department of Energy, Office of Transportation Technologies, through Lawrence Berkeley Laboratory, and the National Science Foundation through Grant DMR-9810198 for partial support of this work. References [1] D.W. Murphy, P.A. Christian, F.J. Disalvo, J.N. Carides, J. Electrochem. Soc. 126 (1979) 497.
Thursday May 04 10:26 AM
447
[2] F. Leroux, D. Guyomard, Y. Piffard, Solid State Ionics 80 (1995) 307. [3] R. Chen, P. Zavalij, M.S. Whittingham, Chem. Mater. 8 (1996) 1275. [4] R. Chen, M.S. Whittingham, J. Electrochem. Soc. 144 (1997) L64. [5] C. Delmas, F. Capitaine, Abstr. 8th Int. Meet. Lithium Batteries 8 (1996) 470. [6] A.R. Armstrong, P.G. Bruce, Nature 381 (1996) 499. [7] A.R. Armstrong, R. Gitzendanner, A.D. Robertson, P.G. Bruce, Chem. Commun. (1998) 1833. [8] F. Lecas, S. Rohs, M. Anne, P. Strobel, J. Power Sources 54 (1995) 319. [9] M.S. Whittingham, R. Chen, T. Chirayil, P. Zavalij, Electrochem. Soc. Proc. 96-5 (1996) 76. [10] M.S. Whittingham, in: O. Yamamoto, M. Wakihara (Eds.), Lithium Batteries, Kodansha, Tokyo, 1998. [11] S.H. Kim, S.J. Kim, S.M. Oh, Chem. Mater. 11 (1999) 557. [12] M.S. Whittingham, P. Zavalij, K. Ngala, F. Zhang, Electrochem. Soc. Proc. 99-X (2000) in press. [13] F. Zhang, M.S. Whittingham, Electrochem. Solid State Lett. 3 (2000) in press. [14] P.Y. Zavalij, M.S. Whittingham, Acta Crystallogr., Sect. B 55 (1999) 627. [15] F. Zhang, P.Y. Zavalij, M.S. Whittingham, Electrochem. Commun. 1 (1999) 564. [16] F. Zhang, P.Y. Zavalij, M.S. Whittingham, J. Mater. Chem. 9 (1999) 3137. [17] F. Zhang, M.S. Whittingham, Electrochem. Commun. 2 (2000) 69. ¨ Bergstrom, [18] O. ¨ H. Bjork, ¨ T. Gustafsson, J.O. Thomas, J. Power Sources 81–82 (1999) 685. [19] M.S. Whittingham, Science 192 (1976) 1126.
StyleTag -- Journal: ELECOM (Electrochemistry Communications)
Article: 235
Synthesis and electrochemistry of a vanadium-pillared manganese oxide Fan Zhang, Katana Ngala, M. Stanley Whittingham * Materials Research Center and Chemistry Department, State University of New York at Binghamton, Binghamton, NY 13902-6000, USA Received 28 February 2000; received in revised form 30 March 2000; accepted 31 March 2000
Abstract A new manganese dioxide pillared by vanadium oxide species has been synthesized hydrothermally from permanganate. It has the electrochemically active MnO2 layer structure, which has been extensively studied as a battery cathode. The vanadium oxide ions, together with the water molecules, reside in between the oxide sheets; dehydration occurs without structural change. The (VOy)0.1MnO2PnH2O has a ˚ cs22.08(2) A. ˚ It reacts readily with lithium with a capacity around rhombohedral structure, with hexagonal parameters as2.843(6) A, y1 150 mAh g ; the pillar ions do not appear to impede reaction. q2000 Elsevier Science S.A. All rights reserved. Keywords: Hydrothermal synthesis; Manganese oxide; Vanadium; Lithium cathode; Pillars
1. Introduction There is much interest in manganese and vanadium oxides for use as cathode materials for advanced lithium batteries [1–7] to replace the expensive and relatively low capacity lithium cobalt oxide system. These oxides have been synthesized using traditional high temperature methods as well as by soft chemistry techniques such as hydrothermal and solgel. Recently, layered manganates have also been prepared using hydrothermal methods, for example, by the decomposition of aqueous permanganate solutions [3]. These however tend to convert to spinel-like structures on cycling [8– 10], which is facilitated by the oxygen cubic-close-packing found in both lattices. Pillaring of the MnO2 layers by potassium appears to minimize this conversion [4,11]; however, at high rates even these compounds appear to convert to spinel-like materials [12,13]. Replacement of the potassium pillars by a redox active immobile pillar ion such as vanadium would be attractive, leading to a higher capacity. The vanadium should preferably be in square pyramidal or octahedral coordination, as VO4 tetrahedra are not readily reducible without destruction of the lattice polyhedra [14]. Attempts to form vanadium-pillared manganese dioxides frequently result in manganese ‘pillars’ in vanadium oxide lattices. Several of these have been reported by us recently including a g-MnV2O5 [15], isostructural with g-LiV2O5, a tunnel structure with a pipe-like morphology Mn7(OH)3* Corresponding author. Tel./fax: q1-607-777-4623; e-mail: stanwhit@ binghamton.edu
(VO4)4 [16], and d-MnxV2O5 [17] which belongs to the dV2O5 class of compounds which is of particular interest for potential use in batteries. V6O13, one of the most studied vanadium oxide cathodes [1], contains these sheets and cycles lithium well in secondary cells [18]. This paper discusses the synthesis and characterization of the (VOy)0.15MnO2PnH2O phase, which has vanadium-containing pillars between manganese oxide layers.
2. Experimental (VOy)0.15MnO2PnH2O was prepared by the hydrothermal treatment of vanadyl permanganate to which 1 drop of 4 M nitric acid had been added. (VO)0.5MnO4 was prepared by first passing a VOSO4 solution (4.5 g in 50 mL water) down an acid cationic ion exchange resin, and then passing a 0.3 M KMnO4 solution down the column. The reaction mixture was heated in a 125 mL Teflon-lined Parr reactor for 80 h at 165 8C. The resulting dark greenish-black powder was filtered and dried in air. The pH of the solution after reaction was weakly basic. X-ray powder diffraction was performed using Cu Ka radiation on a Scintag u–u diffractometer equipped with a Ge(Li) solid state detector. The data were collected from 2us48 to 2us908 with 0.038 steps and 15 s per step. TGA data were obtained on a Perkin-Elmer model TGA 7, and the electron microscopy on an Electroscan 2020 environmental scanning electron microscope. For electrochemical studies the manganese oxide was mixed with 10% carbon black and 10%
1388-2481/00/$ - see front matter q2000 Elsevier Science S.A. All rights reserved. PII S 1 3 8 8 - 2 4 8 1 ( 0 0 ) 0 0 0 5 8 - 8
Thursday May 04 10:26 AM
StyleTag -- Journal: ELECOM (Electrochemistry Communications)
Article: 235
446
F. Zhang et al. / Electrochemistry Communications 2 (2000) 445–447
Teflon powder, and hot-pressed for 60 min at over 100 8C to ensure removal of all absorbed water. Pure lithium metal was used as the anode and 1 M LiAsF6 in a 1:1 propylene carbonate/dimethoxyethane mixture as the electrolyte. A MacPile potentiostat was used to cycle the cells in a helium-filled glovebox.
3. Results and discussion The crystals precipitated from the hydrothermal reaction had a greenish-black color. Energy-dispersive spectroscopy showed that they contained vanadium and manganese in an approximate 0.15:1 ratio, giving the formula (VOy)0.15MnO2. On thermal analysis, as shown in Fig. 1, this material lost 30% of its weight by 100 8C, which corresponds to nf2.2 in the formula (VOy)0.15MnO2PnH2O. This is probably surface water and very weakly bound molecules between the oxide layers. This water can therefore be readily removed for electrochemical studies by hot-pressing above 100 8C. The very small weight loss above 100 8C indicates very little strongly bound water or hydroxyl groups in this material. X-ray diffraction data of the (VOy)0.15MnO2PnH2O compound are shown in Fig. 2. The pattern shows a repeat distance ˚ X-ray diffraction of the material after comof around 7.36 A. bustion in oxygen at 400 8C showed just a slight contraction
˚ showing that the water is not in the lattice spacing to 7.2 A, necessary for stabilizing the structure. The X-ray pattern is consistent with a rhombohedral structure with hexagonal par˚ cs22.08(2) A, ˚ and is isostructural ameters as2.843(6) A, with K0.26MnO2PnH2O [3]. The structure contains MnO2 sheets between which reside the vanadium and oxygen atoms. For comparison, the lattice spacings in the hydrated potassium, sodium and lithium compounds are 7.18, 7.28 and 7.01 ˚ respectively, and in contrast to this material the lattice A, contracts when the water is removed to 6.44, 5.61 and 4.86 ˚ respectively. The repeat distances for the vanadium comA, ˚ and 7.2 A ˚ after dehydration, are consistent pound of 7.36 A, with a lattice containing three oxygen layers; two are associated with the MnO2 layers and the third with the oxygen ion pillars. As noted above, this phase is stable at 400 8C, whereas layered LixMnO2 converts to the spinel LiMn2O4 at 400 8C and the sodium and potassium compounds convert to tunnel structures on heating to elevated temperatures. Electrochemical data for the first ten cycles are shown in Fig. 3. The cathode structure had been rigorously dried by hot-pressing for 1 h and then evacuating in the glovebox antechamber overnight. The initial open-circuit emf was around 3.5 V. Between 0.5 and 0.6 lithium per formula unit could be incorporated into the structure on discharge to 2 V, comparable with the 0.6 for the potassium compound [4]. This corresponds to 150 mAh gy1. The lithium insertion
Fig. 3. Electrochemical cycling of dehydrated of (VOy)0.15MnO2. Fig. 1. TGA of (VOy)0.15MnO2 in oxygen at heating rate of 3 8C miny1.
Fig. 2. X-ray diffraction pattern of (VOy)0.15MnO2, which can be indexed ˚ and cs22.08 A. ˚ with hexagonal parameters, as2.843 A
Thursday May 04 10:26 AM
Fig. 4. Capacity as a function of cycle for (VOy)0.15MnO2.
StyleTag -- Journal: ELECOM (Electrochemistry Communications)
Article: 235
F. Zhang et al. / Electrochemistry Communications 2 (2000) 445–447
proceeded in one smooth step, suggestive of a single-phase system as in LixTiS2 [19]. After recharge to 4.0 V, the capacity was maintained at 0.5–0.6 lithium per formula unit for these ten cycles, as shown in Fig. 4. The electrochemical performance of this phase is much improved over the corresponding sodium and lithium phases [4]. 4. Conclusions A new vanadium-pillared manganese dioxide, (VOy)0.15MnO2, has been synthesized hydrothermally and its structure determined. It intercalates lithium into the structure, and in a very reversible manner. Acknowledgements The authors thank the Department of Energy, Office of Transportation Technologies, through Lawrence Berkeley Laboratory, and the National Science Foundation through Grant DMR-9810198 for partial support of this work. References [1] D.W. Murphy, P.A. Christian, F.J. Disalvo, J.N. Carides, J. Electrochem. Soc. 126 (1979) 497.
Thursday May 04 10:26 AM
447
[2] F. Leroux, D. Guyomard, Y. Piffard, Solid State Ionics 80 (1995) 307. [3] R. Chen, P. Zavalij, M.S. Whittingham, Chem. Mater. 8 (1996) 1275. [4] R. Chen, M.S. Whittingham, J. Electrochem. Soc. 144 (1997) L64. [5] C. Delmas, F. Capitaine, Abstr. 8th Int. Meet. Lithium Batteries 8 (1996) 470. [6] A.R. Armstrong, P.G. Bruce, Nature 381 (1996) 499. [7] A.R. Armstrong, R. Gitzendanner, A.D. Robertson, P.G. Bruce, Chem. Commun. (1998) 1833. [8] F. Lecas, S. Rohs, M. Anne, P. Strobel, J. Power Sources 54 (1995) 319. [9] M.S. Whittingham, R. Chen, T. Chirayil, P. Zavalij, Electrochem. Soc. Proc. 96-5 (1996) 76. [10] M.S. Whittingham, in: O. Yamamoto, M. Wakihara (Eds.), Lithium Batteries, Kodansha, Tokyo, 1998. [11] S.H. Kim, S.J. Kim, S.M. Oh, Chem. Mater. 11 (1999) 557. [12] M.S. Whittingham, P. Zavalij, K. Ngala, F. Zhang, Electrochem. Soc. Proc. 99-X (2000) in press. [13] F. Zhang, M.S. Whittingham, Electrochem. Solid State Lett. 3 (2000) in press. [14] P.Y. Zavalij, M.S. Whittingham, Acta Crystallogr., Sect. B 55 (1999) 627. [15] F. Zhang, P.Y. Zavalij, M.S. Whittingham, Electrochem. Commun. 1 (1999) 564. [16] F. Zhang, P.Y. Zavalij, M.S. Whittingham, J. Mater. Chem. 9 (1999) 3137. [17] F. Zhang, M.S. Whittingham, Electrochem. Commun. 2 (2000) 69. ¨ Bergstrom, [18] O. ¨ H. Bjork, ¨ T. Gustafsson, J.O. Thomas, J. Power Sources 81–82 (1999) 685. [19] M.S. Whittingham, Science 192 (1976) 1126.
StyleTag -- Journal: ELECOM (Electrochemistry Communications)
Article: 235