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This is an Accepted Manuscript, which has been through the Royal Society of Chemistry peer review process and has been accepted for publication. Accepted Manuscripts are published online shortly after acceptance, before technical editing, formatting and proof reading. Using this free service, authors can make their results available to the community, in citable form, before we publish the edited article. We will replace this Accepted Manuscript with the edited and formatted Advance Article as soon as it is available. You can find more information about Accepted Manuscripts in the Information for Authors. Please note that technical editing may introduce minor changes to the text and/or graphics, which may alter content. The journal’s standard Terms & Conditions and the Ethical guidelines still apply. In no event shall the Royal Society of Chemistry be held responsible for any errors or omissions in this Accepted Manuscript or any consequences arising from the use of any information it contains.
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DOI: 10.1039/C4NR06927G
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Received 00th January 2012, Accepted 00th January 2012 DOI: 10.1039/x0xx00000x www.rsc.org/
Tingting Li,a,b Huanhuan Li,c Zhennan Wu,a Hongxia Hao,a Jiale Liu,a Tingting Huang,a Haizhu Sun,c Jingping Zhang,c Hao Zhang,*a and Zuoxing Guo*b The excellent electrochemical performance of greigite (Fe3S 4 ) coupled with their vast abundance and low toxicity exhibit the prospect as anode materials for lithium-ion batteries (LIBs). In this work, we demonstrate a facile and feasible approach for producing phase-pure, small size, shape-controllable, and stable Fe 3S 4 NPs through hot-injection of S solution into Fe(III) solution. The growth of Fe3S 4 NPs involves the primary formation of FeS 2 nucleus and subsequent Fe(III) doping. The lateral size of Fe3S 4 NPs is further controlled by tuning the experimental variabledependent reactivity of Fe sources in the nucleation and growth stage. The Fe3S 4 NPs embedded in LIBs present low electrochemical resistance and high active in lithiation/delithiation processes.
1. Introduction As a crucial part of the global biogeochemical sulfur cycle and the products of sediment magnetization, 1 iron sulfide materials that contain complex solid phase structures and various properties have attracted increasing interests in the recent investigations. 2-7 Iron sulfide nanomaterials inherently possess the advantages of high abundance, low cost, and low toxicity, which are considered as competitive candidates in approaching magnetic, electronic, and photoelectric applications. 2, 8-13 Among iron sulfide family, greigite (Fe3S4) nanocrystals (NCs) have attracted more attention because of their excellent magnetic and electronic properties. 14-18 Fe3S4 is an analogue of magnetite with ferromagnetic inverse thiospinel of iron (AB2S4), which generates the electron hopping of high-spin ferric and ferrous iron in an octahedral lattice, and the subsequent semimetallic behavior. 19 In particular, Fe3S4 NCs have attracted increasing attention as anode materials for lithium-ion batteries (LIBs). 20 The theoretical capacity of Fe3S4 is 785 mAh/g, which is two times higher than the conventional anode materials of graphite (372 mAh/g). 21 Fe3S4 NCs can be produced by magnetotactic bacteria. 22 But the yield is quite low. Despite the capability to obtain Fe3S4 NCs via artificial synthesis, 23 the products usually exhibit large size and mixed crystal phases, which can not retain the excellent properties of bulk Fe3S4. Chemical routes have been developed for large scale synthesis of Fe3S4 NCs, such as hydrothermal route, 7, 8, 24 single-source precursor approach, 25-29
This journal is © The Royal Society of Chemistry 2013
ionic liquid-modulated method, 30 and thermal decomposition of iron sources. 31-34 Most of these methods are complex, and the products are inhomogeneity with the respect of lateral dimension and constituent. The synthesis of Fe3S4 NCs with pure phase, monocrystal, and small size is still challenging. Inspired by the recent success in synthesizing pure phase pyrite (FeS2) NCs via iron source thermal decomposition route, 35 the synthesis of Fe3S4 NCs are considered by selecting proper iron sources and optimizing the synthesis procedure. For thermal decomposition method, in general, the valence state and redox reaction of iron sources play a crucial role in determining the species of iron sulfide NCs. 36-39 For example, colloidal Fe3S4 NCs can be prepared using Fe(II) as the source, such as FeCl2 and Fe(acac)2. 31 The partial oxidization of Fe(II) to Fe(III) by oxidants allows to produce Fe3S4. However, if the synthesis is operated in a reducing system, FeS2 NCs are the products. In addition, the growth mechanisms of Fe3S4 and FeS2 NCs are different. The formation of FeS2 NCs has been well studied. 40-43 Ren and co-workers have proposed an oriented attachment mechanism in temperature-selective growth of FeS2 nanoplates (NPs). 5 At low growth temperature, the exposed facets of FeS2 nucleus are mainly (100) facets. The oriented attachment and crystal fusion along (100) facets generate cubic FeS2 NCs. At elevated temperature, however, the exposed facets of FeS2 nucleus are (110) facets. The oriented attachment and subsequent fusion along (110) facets produce FeS2 NPs. 44 The formation mechanism of Fe3S4 NPs is still unclear, because of the complex valence state and
Nanoscale., 2014, 00, 1-7 |
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Nanoscale Accepted Manuscript
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Colloidal Synthesis of Greigite Nanoplate Nanoplates plates with Controlled Lateral Size for Electrochemical Applications
Nanoscale
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crystalline phase of Fe3S4. In particular, the limited studies provide less evidence to give a convincing mechanism for controlled synthesis of Fe3S4 NPs. 31 In this work, we demonstrate a facile and controlled method for hot-injection synthesis of Fe3S4 NPs with the lateral dimension in 100 nm regime. The as-synthesized Fe3S4 NPs are well dispersible in non-polar solvents. This approach uses Fe(III) as the source, which is partially reduced to Fe(II) in reducing reaction mixture. Systematical studies reveal that the primarily formed crystal nucleus is FeS2. Fe3S4 NPs further form by combining the remained Fe(III) and FeS2 nucleus during the subsequent crystal growth. By comparing the crystal structure of Fe3S4 and FeS2, we propose a doping mechanism in performing the composition transformation from FeS2 to Fe3S4, which facilitates the two-dimensional orientated growth of Fe3S4 NPs. The as-synthesized Fe3S4 NPs exhibit low electrochemical resistance and high active in lithiation/delithiation cycling processes.
2. Experimental 2.1 Materials and reagents Ferric acetylacetonate (Fe(acac)3, 99.9%) were purchased from Aldrich. Octadecylamine (ODA, 90%), diphenyl ether (DE, 99%), and N-methyl-2-pyrrolidione (NMP, 99%) were obtained from Aladdin. The electrolyte, composed of 1.0 M LiPF6 in 1:1 v/v ethylene carbonate (EC)/dimethyl carbonate (DMC), was purchased from Beijing Institute of Chemical Regent. Sulfur powder (S), FeCl3· 6H2O, polyvinylidenefluoride (PVDF), acetone, chloroform, and acetylene black were all commercially available products and used as received without further purification. 2.2 Synthesis and purification 2.2.1 HOT-INJECTION SYNTHESIS OF FE3S4 NANOPLATES. 76 mg Fe(acac)3 (0.5 mmol), 2.5 mL DE, and 7.5 g ODA (0.105 mol) were mixed in a four-necked flask at 120 oC and degassed under vacuum for 1 h to produce Fe precursor solution. 96 mg S powder (3 mmol) and 5 mL DE were mixed in another threenecked flask at 70 oC and degassed for 1 h to produce the S solution. As the Fe precursor solution was heated to 220 oC under N2 atmosphere, the S solution was rapidly injected and maintained at 220 oC for 3 h. Aliquots of 1 mL reaction solution were taken at different time intervals and cooled down to room temperature for further purification and characterization. 2.2.2 EFFECT OF REACTION TEMPERATURE. In this context, the amount and molar ratio of raw materials were same as the aforementioned synthesis, whereas the temperature was varied. For studying the temperature effect on the nucleation of iron sulfides, the S solution was rapidly injected into the Fe precursor solution at 180, 190, 200, 210, and 220 oC, respectively. After injection, the solution was immediately cooled down to room temperature. To reveal the temperature effect on NC growth, the S solution was injected at 200, and
2|
Nanoscale., 2014, 00, 1-7
Nanoscale DOI: 10.1039/C4NR06927G 220 oC, respectively, and kept for specific duration to maintain the growth of iron sulfide NCs. 2.2.3 EFFECT OF DE/ODA RATIO. By fixing other experimental variables, the effect of DE-to-ODA ratio was investigated. In studying the effect on nucleation, the DE/ODA ratio was varied from 0.7/1, 1/1, 2/1, 5/1, to 11/1. In studying the effect on the lateral size of Fe3S4 at growth stage, the DE/ODA ratio was varied from 1/1, 2/1, to 5/1. 2.2.4 EFFECT OF FE/S MOLAR RATIO. To study the effect of Fe/S ratio, the amount of Fe(acac)3 in the Fe precursor solution was varied from 132, 151, 176, 212, to 265 mg, respectively, while the amount of S powder in S solution was fixed at 96 mg. Thus, the Fe/S molar feed ratio was varied from 1/8, 1/7, 1/6, 1/5, to 1/4. 2.2.5 EFFECT OF IRON SOURCE. To further explore the effect of iron source on the formation of iron sulfides, FeCl3.6H2O rather than Fe(acac)3 is used as the iron source, while other experimental variables were fixed. 2.2.6 PURIFICATION. 1 mL as-synthesized Fe3S4 NPs in the mixture of DE and ODA was precipitated through the addition of acetone and washed with chloroform/acetone (1:2 v/v) for three times. After centrifugation, the precipitates were collected and dispersed in 2 mL chloroform. 2.3 Characterization Atomic force microscope (AFM) tapping mode measurement was performed on a Nanoscope IIIa scanning probe microscope (Digital Instruments) using a rotated tapping mode etched silicon probe tip. UV-visible absorption spectra were measured using a Shimadzu 3600 UV-VIS-NIR spectrophotometer. Transmission electron microscopy (TEM) and selected area electron diffraction (SAED) were recorded using a Hitachi H800 electron microscope at an acceleration voltage of 200 kV with a CCD camera. High-resolution TEM (HRTEM) images were implemented by a JEM-2100F electron microscope at 200 kV. An energy-dispersive X-ray spectroscopy (EDX) detector coupled with scanning electron microscope (XL 30 ESEM FEG Scanning Electron Microscope, FEI Company) was used for elemental analysis. Inductively coupled plasma (ICP) was performed with PerkinElmer OPTIMA 3300DV analyzer. Xray diffraction (XRD) was carried out on a Rigaku X-ray diffractometer using Cu K radiation (λ=1.5418 Å). Thermogravimetric analysis (TGA) was measured on an American TA Q500 analyzer under N2 atmosphere with the flow rate of 60 mL· min-1. 2.4 Electrochemical measurement The Fe3S4 powders used for electrochemical measurement were primarily treated by annealing the as-synthesized Fe3S4 NPs in a tube furnace at 400 oC for 2 h under argon atmosphere. For fabricating the anode of a coin cell battery, the Fe3S4 powder was mixed with acetylene black and PVDF with a weight ratio of 80/10/10 in NMP. The obtained slurry was coated on copper foil and dried at 120 oC for 12 h. The foil was punched into round plate with 13.0 mm in diameter to form anode electrode. In an argon-filled glove box (H2O and O2
Nanoscale Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: T. Li, H. Li, Z. Wu, H. Hao, J. Liu, T. Huang, H. sun, J. Zhang, H. Zhang and Z. Guo, Nanoscale, 2015, DOI:
This is an Accepted Manuscript, which has been through the Royal Society of Chemistry peer review process and has been accepted for publication. Accepted Manuscripts are published online shortly after acceptance, before technical editing, formatting and proof reading. Using this free service, authors can make their results available to the community, in citable form, before we publish the edited article. We will replace this Accepted Manuscript with the edited and formatted Advance Article as soon as it is available. You can find more information about Accepted Manuscripts in the Information for Authors. Please note that technical editing may introduce minor changes to the text and/or graphics, which may alter content. The journal’s standard Terms & Conditions and the Ethical guidelines still apply. In no event shall the Royal Society of Chemistry be held responsible for any errors or omissions in this Accepted Manuscript or any consequences arising from the use of any information it contains.
www.rsc.org/nanoscale
Page 1 of 8
Nanoscale View Article Online
DOI: 10.1039/C4NR06927G
Nanoscale
RSCPublishing
ARTICLE
Received 00th January 2012, Accepted 00th January 2012 DOI: 10.1039/x0xx00000x www.rsc.org/
Tingting Li,a,b Huanhuan Li,c Zhennan Wu,a Hongxia Hao,a Jiale Liu,a Tingting Huang,a Haizhu Sun,c Jingping Zhang,c Hao Zhang,*a and Zuoxing Guo*b The excellent electrochemical performance of greigite (Fe3S 4 ) coupled with their vast abundance and low toxicity exhibit the prospect as anode materials for lithium-ion batteries (LIBs). In this work, we demonstrate a facile and feasible approach for producing phase-pure, small size, shape-controllable, and stable Fe 3S 4 NPs through hot-injection of S solution into Fe(III) solution. The growth of Fe3S 4 NPs involves the primary formation of FeS 2 nucleus and subsequent Fe(III) doping. The lateral size of Fe3S 4 NPs is further controlled by tuning the experimental variabledependent reactivity of Fe sources in the nucleation and growth stage. The Fe3S 4 NPs embedded in LIBs present low electrochemical resistance and high active in lithiation/delithiation processes.
1. Introduction As a crucial part of the global biogeochemical sulfur cycle and the products of sediment magnetization, 1 iron sulfide materials that contain complex solid phase structures and various properties have attracted increasing interests in the recent investigations. 2-7 Iron sulfide nanomaterials inherently possess the advantages of high abundance, low cost, and low toxicity, which are considered as competitive candidates in approaching magnetic, electronic, and photoelectric applications. 2, 8-13 Among iron sulfide family, greigite (Fe3S4) nanocrystals (NCs) have attracted more attention because of their excellent magnetic and electronic properties. 14-18 Fe3S4 is an analogue of magnetite with ferromagnetic inverse thiospinel of iron (AB2S4), which generates the electron hopping of high-spin ferric and ferrous iron in an octahedral lattice, and the subsequent semimetallic behavior. 19 In particular, Fe3S4 NCs have attracted increasing attention as anode materials for lithium-ion batteries (LIBs). 20 The theoretical capacity of Fe3S4 is 785 mAh/g, which is two times higher than the conventional anode materials of graphite (372 mAh/g). 21 Fe3S4 NCs can be produced by magnetotactic bacteria. 22 But the yield is quite low. Despite the capability to obtain Fe3S4 NCs via artificial synthesis, 23 the products usually exhibit large size and mixed crystal phases, which can not retain the excellent properties of bulk Fe3S4. Chemical routes have been developed for large scale synthesis of Fe3S4 NCs, such as hydrothermal route, 7, 8, 24 single-source precursor approach, 25-29
This journal is © The Royal Society of Chemistry 2013
ionic liquid-modulated method, 30 and thermal decomposition of iron sources. 31-34 Most of these methods are complex, and the products are inhomogeneity with the respect of lateral dimension and constituent. The synthesis of Fe3S4 NCs with pure phase, monocrystal, and small size is still challenging. Inspired by the recent success in synthesizing pure phase pyrite (FeS2) NCs via iron source thermal decomposition route, 35 the synthesis of Fe3S4 NCs are considered by selecting proper iron sources and optimizing the synthesis procedure. For thermal decomposition method, in general, the valence state and redox reaction of iron sources play a crucial role in determining the species of iron sulfide NCs. 36-39 For example, colloidal Fe3S4 NCs can be prepared using Fe(II) as the source, such as FeCl2 and Fe(acac)2. 31 The partial oxidization of Fe(II) to Fe(III) by oxidants allows to produce Fe3S4. However, if the synthesis is operated in a reducing system, FeS2 NCs are the products. In addition, the growth mechanisms of Fe3S4 and FeS2 NCs are different. The formation of FeS2 NCs has been well studied. 40-43 Ren and co-workers have proposed an oriented attachment mechanism in temperature-selective growth of FeS2 nanoplates (NPs). 5 At low growth temperature, the exposed facets of FeS2 nucleus are mainly (100) facets. The oriented attachment and crystal fusion along (100) facets generate cubic FeS2 NCs. At elevated temperature, however, the exposed facets of FeS2 nucleus are (110) facets. The oriented attachment and subsequent fusion along (110) facets produce FeS2 NPs. 44 The formation mechanism of Fe3S4 NPs is still unclear, because of the complex valence state and
Nanoscale., 2014, 00, 1-7 |
1
Nanoscale Accepted Manuscript
Published on 29 January 2015. Downloaded by Selcuk University on 29/01/2015 18:12:19.
Cite this: DOI: 10.1039/x0xx00000x
Colloidal Synthesis of Greigite Nanoplate Nanoplates plates with Controlled Lateral Size for Electrochemical Applications
Nanoscale
Page 2 of 8 View Article Online
crystalline phase of Fe3S4. In particular, the limited studies provide less evidence to give a convincing mechanism for controlled synthesis of Fe3S4 NPs. 31 In this work, we demonstrate a facile and controlled method for hot-injection synthesis of Fe3S4 NPs with the lateral dimension in 100 nm regime. The as-synthesized Fe3S4 NPs are well dispersible in non-polar solvents. This approach uses Fe(III) as the source, which is partially reduced to Fe(II) in reducing reaction mixture. Systematical studies reveal that the primarily formed crystal nucleus is FeS2. Fe3S4 NPs further form by combining the remained Fe(III) and FeS2 nucleus during the subsequent crystal growth. By comparing the crystal structure of Fe3S4 and FeS2, we propose a doping mechanism in performing the composition transformation from FeS2 to Fe3S4, which facilitates the two-dimensional orientated growth of Fe3S4 NPs. The as-synthesized Fe3S4 NPs exhibit low electrochemical resistance and high active in lithiation/delithiation cycling processes.
2. Experimental 2.1 Materials and reagents Ferric acetylacetonate (Fe(acac)3, 99.9%) were purchased from Aldrich. Octadecylamine (ODA, 90%), diphenyl ether (DE, 99%), and N-methyl-2-pyrrolidione (NMP, 99%) were obtained from Aladdin. The electrolyte, composed of 1.0 M LiPF6 in 1:1 v/v ethylene carbonate (EC)/dimethyl carbonate (DMC), was purchased from Beijing Institute of Chemical Regent. Sulfur powder (S), FeCl3· 6H2O, polyvinylidenefluoride (PVDF), acetone, chloroform, and acetylene black were all commercially available products and used as received without further purification. 2.2 Synthesis and purification 2.2.1 HOT-INJECTION SYNTHESIS OF FE3S4 NANOPLATES. 76 mg Fe(acac)3 (0.5 mmol), 2.5 mL DE, and 7.5 g ODA (0.105 mol) were mixed in a four-necked flask at 120 oC and degassed under vacuum for 1 h to produce Fe precursor solution. 96 mg S powder (3 mmol) and 5 mL DE were mixed in another threenecked flask at 70 oC and degassed for 1 h to produce the S solution. As the Fe precursor solution was heated to 220 oC under N2 atmosphere, the S solution was rapidly injected and maintained at 220 oC for 3 h. Aliquots of 1 mL reaction solution were taken at different time intervals and cooled down to room temperature for further purification and characterization. 2.2.2 EFFECT OF REACTION TEMPERATURE. In this context, the amount and molar ratio of raw materials were same as the aforementioned synthesis, whereas the temperature was varied. For studying the temperature effect on the nucleation of iron sulfides, the S solution was rapidly injected into the Fe precursor solution at 180, 190, 200, 210, and 220 oC, respectively. After injection, the solution was immediately cooled down to room temperature. To reveal the temperature effect on NC growth, the S solution was injected at 200, and
2|
Nanoscale., 2014, 00, 1-7
Nanoscale DOI: 10.1039/C4NR06927G 220 oC, respectively, and kept for specific duration to maintain the growth of iron sulfide NCs. 2.2.3 EFFECT OF DE/ODA RATIO. By fixing other experimental variables, the effect of DE-to-ODA ratio was investigated. In studying the effect on nucleation, the DE/ODA ratio was varied from 0.7/1, 1/1, 2/1, 5/1, to 11/1. In studying the effect on the lateral size of Fe3S4 at growth stage, the DE/ODA ratio was varied from 1/1, 2/1, to 5/1. 2.2.4 EFFECT OF FE/S MOLAR RATIO. To study the effect of Fe/S ratio, the amount of Fe(acac)3 in the Fe precursor solution was varied from 132, 151, 176, 212, to 265 mg, respectively, while the amount of S powder in S solution was fixed at 96 mg. Thus, the Fe/S molar feed ratio was varied from 1/8, 1/7, 1/6, 1/5, to 1/4. 2.2.5 EFFECT OF IRON SOURCE. To further explore the effect of iron source on the formation of iron sulfides, FeCl3.6H2O rather than Fe(acac)3 is used as the iron source, while other experimental variables were fixed. 2.2.6 PURIFICATION. 1 mL as-synthesized Fe3S4 NPs in the mixture of DE and ODA was precipitated through the addition of acetone and washed with chloroform/acetone (1:2 v/v) for three times. After centrifugation, the precipitates were collected and dispersed in 2 mL chloroform. 2.3 Characterization Atomic force microscope (AFM) tapping mode measurement was performed on a Nanoscope IIIa scanning probe microscope (Digital Instruments) using a rotated tapping mode etched silicon probe tip. UV-visible absorption spectra were measured using a Shimadzu 3600 UV-VIS-NIR spectrophotometer. Transmission electron microscopy (TEM) and selected area electron diffraction (SAED) were recorded using a Hitachi H800 electron microscope at an acceleration voltage of 200 kV with a CCD camera. High-resolution TEM (HRTEM) images were implemented by a JEM-2100F electron microscope at 200 kV. An energy-dispersive X-ray spectroscopy (EDX) detector coupled with scanning electron microscope (XL 30 ESEM FEG Scanning Electron Microscope, FEI Company) was used for elemental analysis. Inductively coupled plasma (ICP) was performed with PerkinElmer OPTIMA 3300DV analyzer. Xray diffraction (XRD) was carried out on a Rigaku X-ray diffractometer using Cu K radiation (λ=1.5418 Å). Thermogravimetric analysis (TGA) was measured on an American TA Q500 analyzer under N2 atmosphere with the flow rate of 60 mL· min-1. 2.4 Electrochemical measurement The Fe3S4 powders used for electrochemical measurement were primarily treated by annealing the as-synthesized Fe3S4 NPs in a tube furnace at 400 oC for 2 h under argon atmosphere. For fabricating the anode of a coin cell battery, the Fe3S4 powder was mixed with acetylene black and PVDF with a weight ratio of 80/10/10 in NMP. The obtained slurry was coated on copper foil and dried at 120 oC for 12 h. The foil was punched into round plate with 13.0 mm in diameter to form anode electrode. In an argon-filled glove box (H2O and O2
