one - pot facile synthesis of iron oxide nanowires as high capacity anode

Accepted Manuscript Title: One-pot facile synthesis of iron oxide nanowires as high capacity anode materials for lithium ion batteries Authors: Hao Liu, David Wexler, Guoxiu Wang PII: DOI: Reference: S0925-8388(09)01602-8 doi:10.1016/j.jallcom.2009.08.043 JALCOM 20491 To appear in: Journal of Alloys and Compounds Received date: Revised date: Accepted date: 24-5-2009 10-8-2009 11-8-2009 Please cite this article as: H Liu, D Wexler, G Wang, One-pot facile synthesis of iron oxide nanowires as high capacity anode materials for lithium ion batteries, Journal of Alloys and Compounds (2008), doi:10.1016/j.jallcom.2009.08.043 This is a PDF file of an unedited manuscript that has been accepted for publication As a service to our customers we are providing this early version of the manuscript The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain One-pot facile synthesis of iron oxide nanowires as high capacity anode materials for lithium ion batteries Hao Liu*, David Wexler, Guoxiu Wang * ip t Institute for Superconducting and Electronic Materials, School of Mechanical, Materials cr and Mechatronic Engineering, University of Wollongong, NSW 2522, Australia us Abstract Alpha-Fe2O3 nanowires were synthesized by a facile hydrothermal method The crystalline an structure and morphology of the synthesized materials have been characterized by X-ray M diffraction, scanning electron microscopy and transmission electron microscopy The results revealed that the prepared alpha-Fe2O3 product was uniform nanowires with the d length/diameter ratio as high as 500 The electrochemical properties of alpha-Fe2O3 nanowires te were evaluated by cyclic voltammetry (CV) and charge/discharge measurements The initial Ac ce p charge/discharge capacities can reach 947/1303 mAh/g at the rate of 0.1C The lithium storage capacity maintained 456 mAh/g after 100 cycles This good electrochemical performance may be attributed to the large surface area and short pathways in nanowires for lithium ion migration Keywords: α-Fe2O3; Nanowires; Hydrothermal synthesis; Lithium ion batteries * Corresponding author, email: hl983@uow.edu.au, gwang@uow.edu.au, Fax: 61-2-42215731 Page of 14 Introduction Due to the low cost and abundance of the raw materials, the Fe2O3 has been widely investigated in many technological fields such as anode materials for lithium ion batteries, gas ip t sensors, catalysts and magnetic applications [1-6] In the past decade, one-dimensional (1D) cr nanomaterials have attracted great interest because of their unique morphologies and us properties in nanoscience and nanotechnology [7-9] Iron oxides also have been synthesized in a variety of 1D morphologies such as nanowires [10,11], nanoneedles [12]，nanorods an [3,4,13,14], and nanotubes [15,16] for various applications Many transition metal oxides have been investigated as anode materials for lithium ion M batteries to replace the current graphite materials [17,18] Fe2O3 has been tested as a lithium ion storage material and shows promise in the quest to achieve new anode materials with high te d capacity for lithium ion batteries [3,4,19-23] The mechanism of lithium ion intercalation/de-intercalation in Fe2O3 materials can be described by the following equation: Ac ce p Fe2O3 + 6Li ↔ 3Li2O+2Fe The Fe2O3 crystal lattice can cause six Li ions transport per formula unit during the charge/discharge process, and the theoretical capacity of Fe2O3 is as high as 1005 mAh/g, which is much higher than that of the theoretical capacity of graphite anode materials (372 mAh/g) The extraction of lithium ion from Li2O is thermodynamically impossible However, it becomes feasible for nanosize materials, as has been reported previously [17] Capacity fading is the main issue for all transition metal oxides proposed as anode materials for lithium ion batteries Using nanoscale Fe2O3 materials, especially 1D structured materials, is a feasible approach to improve its properties as an anode material, because nanostructured Page of 14 materials can provide short pathway and high kinetics for lithium ion insertion/extraction In this paper, we first report a facile method with low cost starting materials (FeCl3 and nitrilotriacetic acid) to synthesize α-Fe2O3 nanowires as anode material for lithium ion ip t batteries The electrochemical performance of the α-Fe2O3 nanowires has achieved us cr significantly higher capacity compared to the commercial graphite anode materials Experimental an The α-Fe2O3 nanowires were synthesized via a hydrothermal method Precursors were prepared in the first step in an autoclave In a typical synthesis, 1.05 mmol FeCl3 was M dissolved in mL distilled water and mL isopropanol to form a solution mmol nitrilotriacetic acid (NTA) was then added After thorough stirring, the mixture was te d transferred into a Teflon lined autoclave and hydrothermally treated at 180℃ for 24 h The resultant white floccules were washed with deionized water and absolute ethanol, and dried at Ac ce p 60℃ in a vacuum oven Finally, the precursors were sintered at 500℃ for h to obtain α-Fe2O3 nanowires The α-Fe2O3 nanowire anode electrodes were made up by mixing the active materials with acetylene black (AB) and a binder, poly(vinylidene fluoride) (PVdF), at weight ratios of 40:40:20, in N-methyl-2-pyrrolidone (NMP) solvent The resultant slurry was uniformly pasted on Cu foil with a blade These prepared electrode sheets were dried at 120℃ in a vacuum oven for 12 hours and pressed under a pressure of approximately 200 kg/cm2 CR2032-type coin cells were assembled in a glove box for electrochemical characterization The electrolyte was 1M LiPF6 in a 1:1 mixture of ethylene carbonate (EC) and dimethyl Page of 14 carbonate (DMC) Li metal foil was used as the counter and reference electrode The microstructure and morphology of the α-Fe2O3 nanowires were characterized by X-ray diffraction (XRD, GBC MMA) in the 2theta degree range from 15 to 70°, scanning electron ip t microscopy (SEM, JEOL JEM-3000), and transmission electron microscopy (TEM, JEOL cr 2011) The specific surface area of the Fe2O3 nanowires was measured by the gas adsorption us technique using a Quanta Chrome Nova 1000 Gas Sorption Analyzer based on the Brunauer-Emmett-Teller (BET) method The cells were galvanostatically charged and an discharged at a current density of 0.1 C within the range of 0.01 V to V Cyclic voltammetry (CV) curves were measured at 0.5 mV/s within the range of 0.01 to 3.0 V, using an M electrochemistry workstation (Princeton Applied Research 2273) Results and discussion te d Fig shows the XRD pattern of the Fe2O3 nanowires, using Cu Kα radiation (λ=1.5406 Å) The diffraction pattern confirmed that the crystal structure is coincident with the standard Ac ce p hematite (α-Fe2O3) rhombohedral structure (JCPDS Card No 33-0664) No impurity was detected from the XRD pattern, indicating that the nanowires are of a single-phase rhombohedral crystal structure after the 500℃ annealing The SEM images of the nanowires and precursors are shown in Fig 2(a) It clearly demonstrated that the FeNTA precursors from the hydrothermal reaction are entirely in the form of well dispersed nanowires In the hydrothermal processing, Fe3+ ions were bonded and anchored to amino groups or carboxyl groups from the reactant of NTA, and formed 1D long-chain polymer precursors After being sintered at 500 ℃ for h, the precursors converted to alpha phase Fe2O3 nanowires Fig 2(b) shows the final product, the Fe2O3 Page of 14 nanowires, which elucidates that the one-dimensional structure was stable during the thermal treatment of the precursors The nanowires can achieve lengths as long as long 100µm However, due to the high surface energy of the nanostructured materials, the Fe2O3 nanowires ip t were partially agglomerated during the thermal treatment Adjacent nanowires running in the cr same direction combine easily with each other because there is maximum contact between the us surfaces, inducing minimum surface energy Fig 2(c) shows a TEM image of nanowires at 20k magnification The nanowires are agglomerated with other nanowires in the same an direction The inset in the upper right corner of Fig 2(c) is the selected area electron diffraction (SAED) pattern of the nanowires In the electron diffraction pattern, each ring M represents the electron diffraction from a different lattice plane, which can be fully indexed to the rhombohedral crystal structure Fig 2(d) is a TEM image of a single nanowire at 100k te d magnification It shows that the single nanowire has a polycrystalline structure with a width around 200 nm The length/diameter ratio is as high as 500 The upper right inset in Fig 2(d) Ac ce p shows a high resolution TEM (HRTEM) image of the inner part of the single nanowire The HRTEM image clearly shows the microstructure of the individual grains, which confirms the polycrystalline structure of the nanowires The spacing of the lattice planes in the image was determined to be 0.37 nm, which is consistent with the standard value for the (012) plane (0.368 nm) The polycrystal Fe2O3 nanowires exhibit a high specific surface area of 152m2/g from the BET calculation The high surface area nanowires can provide more reaction sites for lithium ion transport Cyclic voltammetry (CV) is a basic instrumental method that can reveal the electrochemical mechanism of reactions Fig shows the first three cycles of CV curves of Page of 14 the nanowires in the range of 0.01-3 V It is clear that there is a substantial difference between the first and the subsequent cycles In the first cycle, with a scanning rate of 0.5 mV/s, the spiky peak at 0.62 V represents the transition from Fe3+ to Fe0 in the cathodic process, which ip t could be associated with the electrolyte decomposition and the reversible conversion reaction cr of lithium ion intercalation to form Li2O An anodic peak is present at about 1.75 V, us corresponding to the reversible oxidation of Fe0 to Fe3+ In the subsequent cycles, the cathodic/anodic peak potentials shift to 0.68 and 1.76 V, respectively During the anodic an process, both the peak current and the integrated area of the anodic peak are decreased, indicating the capacity loss during the charge/discharge process The capacity loss can be M attributed to the decomposition of electrolyte to form a SEI layer and the irreversible lithium ion loss from the formation of Li2O In the first cycle, the difference in the integrated area te d between cathodic/anodic peaks is bigger than in the subsequent cycles, which indicates that the initial capacity loss can be mostly attributed to the electrolyte decomposition For the Ac ce p one-dimensional Fe2O3 nanowires, the high surface energy causes irreversible capacity loss by decomposing the electrolyte The SEI layer could cover the reactive sites and avoid further decomposition On the other hand, the nanowires with high surface area can provide more sites for lithium ion intercalation/deintercalation The short pathways in the nanowires can also enhance lithium ion diffusion The Fe2O3 nanowires were tested as anode materials for lithium ion batteries The capacity performance and charge/discharge curves for the first cycle are shown in Fig The charge/discharge curves are shown in the inset, and they exhibit the charge/discharge plateaus at 1.76/0.78 V In CV testing, the anodic/cathodic peaks are present at 1.75/0.62 V, respectively Page of 14 The difference can be attributed to the hysteresis in CV testing, which is caused by the mismatch between the mass transfer and charge transfer processes on the electrode/electrolyte interphase The initial discharge capacity is 1303 mAh/g, which is higher than the theoretical ip t capacity of Fe2O3 (1005 mAh/g) The extra capacity beyond the theoretical value is probably cr due to the decomposition of non-aqueous electrolyte during the discharge process The initial us charge capacity is 947 mAh/g, and the initial coulombic efficiency is 72.7% In the second and third cycles, the coulombic efficiencies are increased to 91.0% and 91.3%, which indicates an that the initial irreversible capacity loss is mainly caused by the decomposition The formation of the SEI layer protects the nanowires so as to avoid further electrolyte decomposition and M enhances the coulombic efficiency in the subsequent cycles After 100 cycles, the charge/discharge capacities reach 436/456 mAh/g The charge/discharge capacity retention te d after 100 cycles is 44.8% and 35.3%, respectively Although the retention is not particularly high, the capacity is higher than that of the commercial anode materials (graphite, 372 mAh/g), Ac ce p and the performance is much better than that of the previously reported α-Fe2O3 [24] α-Fe2O3 nanowires material appears to be a promising candidate as a high capacity anode material for lithium ion batteries Conclusions α-Fe2O3 nanowires were successfully prepared by a hydrothermal method and subsequent heat treatment The nanowires are as long as 100 µm, and the diameter is less than 200 nm The Fe2O3 nanowires were tested as anode materials for lithium ion batteries The initial discharge capacity is 1303 mAh/g, which is higher than the theoretical capacity of Fe2O3 The discharge capacity retention after 100 cycles is 456 mAh/g, which represents better Page of 14 performance than the commercial graphite anode and other microsize α-Fe2O3 powders Acknowledgement We are grateful for financial support from the Australian Research Council (ARC) through ip t the ARC Discovery Project “First principles for development of novel hybrid electrochemical cr energy storage and conversion systems” (DP0772999) [1] us References M.H Cao, T.F Liu, S Gao, G.B Sun, X.L Wu, C.W Hu, Z.L Wang, Angew Chem Int Ed an 44 (2005) 4197-4201 C Karunakaran, S Senthilvelan, Electrochem Commun (2006) 95-101 [3] C.Z Wu, P Yin, X Zhu, C.Z OuYang, Y Xie, J Phys Chem B 110 (2006) M [2] 17806-17812 d H Liu, G.X Wang, J.S Park, J.Z Wang, H.K Liu, C Zhang, Electrochimica Acta 54 (2009) 1733-1736 te [4] X.W Teng, X.Y Liang, S Rahman, H Yang, Adv Mater 17 (2005) 2237-2241 [6] X.L Xie, H.Q Yang, F.H Zhang, L Li, J.H Ma, H Jiao, J.Y Zhang, J Alloys Compd Ac ce p [5] 477 (2009) 90-99 [7] Y Cui, Q.Q Wei, H K Park, C.M Lieber, Science 293 (2001) 1289-1292 [8] Y Huang, X Duan, Y Cui, L.J Lauhon, K.H Kim, C.M Lieber, Science, 294 (2001) 1313-1317 [9] [10] P.G Collins, M.S Arnold, P Avouris, Science 292 (2001) 706-709 Q Han, Z.H Liu, Y.Y Xu, Z.Y Chen, T.M Wang, H Zhang, J Phys Chem C 111 (2007) 5034-5038 Page of 14 [11] Y.Y Fu, R.M Wang, J Xu, J Chen, Y Yan, A.V Narlikar, H Zhang, Chem Phy Lett 279 (2003) 373-379 X.H Sun, W.T Liu, D.X Ouyang, J Alloys Compd 478 (2009) 38-40 [13] J.J Wu, Y.L Lee, H.H Chiang, D.K.P Wong, J Phys Chem B 110 (2006) 18108-18111 [14] X.L Gou, G.X Wang, J Yang, J.S Park, D Wexler, Chem Eur J 14 (2008) 5996-6002 [15] X.P Shen, H.J Liu, L Pan, K.M Chen, J.M Hong, Z Xu, Chem.Lett 33 (2004) us cr ip t [12] 1128-1129 J Bachmann, J Jing, M Knez, S Barth, H Shen, S Mathur, U Goesele, K Nielsch, J Am Chem Soc 129 (2007) 9554-9555 an [16] P Poizot, S Laruelle, S Grugeon, L Dupont, J.M Tarascon, Nature 407 (2000) 496-499 [18] L.C Yang, Q.S.Gao, Y.H Zhang, Y Tang, Y.P Wu, Electrochem Commun 10 (2008) [19] te 118-122 d M [17] D Larcher, D Bonnin, R Cortes, I Rivals, L Personnaz, J.M Tarascon, J Electrochem [20] Ac ce p Soc 150 (2003) A1643-A1650 D Larcher, C Masquelier, D Bonnin, Y Chabre, V Masson, J.B Leriche, J.M Tarascon, J Electrochem Soc 150 (2003) A133-A139 [21] P.C Wang, H.P Ding, T Bark, C.H Chen, Electrochim Acta 52 (2007) 6650-6655 [22] M Hibino, J Terashima, T Yao, J Electrochem Soc 154 (2007) A1107-A1111 [23] W.W Zhou, K.B Tang, S.A Zeng, Y.X Qi, Nanotechnology 19 (2008) 065602 [24] H Morimoto, S.I Tobishima, Y Iizuka, J Power Sources 146 (2005) 315-318 Page of 14 Caption of figures Fig X-ray diffraction pattern of alpha phase iron oxide nanowires Fig SEM and TEM Images of Fe2O3 nanowires and precursors a) The SEM image of ip t Fe2O3 nanowires precursors b) The SEM image of Fe2O3 nanowires after sintering at 500℃ cr c) The TEM image of Fe2O3 nanowires at low magnification (the inset is SAED pattern) d) us The TEM image on single nanowire at high magnification (inset is the HRTEM image) Fig The first cycles CV curves of the Fe2O3 nanowires as anode for lithium ion cell an Fig The charge/discharge performance of Fe2O3 nanowires The top-right inset is the first Ac ce p te d M cycle charge/discharge profiles 10 Page 10 of 14 30 40 50 M 20 cr an (018) (214) (300) us (116) (024) (113) (012) (110) Intensity / a.u (104) ip t Figure(s) 60 70 te d 2 / degree Ac ce p Fig X-ray diffraction pattern of alpha phase iron oxide nanowires Page 11 of 14 ip t cr us an M d te ce p Fig SEM and TEM images of Fe2O3 nanowires and precursors: (a) SEM image of Fe2O3 Ac nanowire precursors (b) SEM image of Fe2O3 nanowires after sintering at 500℃ (c) TEM image of Fe2O3 nanowires at low magnification (with the inset showing the corresponding SAED pattern) d) TEM image of a single nanowire at high magnification (with the inset showing a corresponding HRTEM image) Page 12 of 14 2nd 0.5 1st 3rd -0.5 ip t 3rd 2nd cr -1.0 -1.5 1st -2.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 M an Potential / V us Current / mA 0.0 Ac ce p te d Fig CV curves for the first cycles of the Fe2O3 nanowires as anode in lithium ion cell Page 13 of 14 3.0 2.5 1200 1000 2.0 1.5 ip t Voltage / V 1.0 0.5 800 200 400 600 800 1000 1200 1400 Capacity / mAh/g us 600 cr 0.0 Charge capacity Discharge capacity 400 200 20 40 60 M an Capacity / mAh/g 1400 80 100 d Cycle Number te Fig The charge/discharge performance of the Fe2O3 nanowires The inset on the upper right Ac ce p shows the first cycle charge/discharge profiles Page 14 of 14 .. .One- pot facile synthesis of iron oxide nanowires as high capacity anode materials for lithium ion batteries Hao Liu*, David Wexler,... 31 5-3 18 Page of 14 Caption of figures Fig X-ray diffraction pattern of alpha phase iron oxide nanowires Fig SEM and TEM Images of Fe2O3 nanowires and precursors a) The SEM image of ip t Fe2O3 nanowires. .. the theoretical capacity of Fe2O3 is as high as 1005 mAh/g, which is much higher than that of the theoretical capacity of graphite anode materials (372 mAh/g) The extraction of lithium ion from