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| 2. |
- Mahmoud, Abdelfattah, et al.
(författare)
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Electrochemical performances and mechanisms of MnSn2 as anode material for Li-ion batteries
- 2013
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Ingår i: Journal of Power Sources. - : Elsevier. - 0378-7753 .- 1873-2755. ; 244, s. 246-251
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Tidskriftsartikel (refereegranskat)abstract
- A synthesis method consisting of a mechanical ball milling activation process followed by a sinteringheating treatment is proposed to obtain MnSn2 as anode material for Li-ion batteries. This two-stepapproach strongly reduces the amount of bSn impurities and provides a better material morphology.This improves the electrochemical performances, even at high C-rate, as shown from the comparisonbetween electrode materials obtained with and without this preliminary activation process. The electrochemicalreactions have been followed at the atomic scale by in situ 119Sn Mössbauer spectroscopy.The first discharge is a restructuring step that transforms the pristine material into Mn/Li7Sn2 nanocompositewhich should be considered as the real starting material for cycling. The delithiation of thisnanocomposite is characterized by two plateaus of potential attributed to the de-alloying of Li7Sn2 followedby the back reaction of Mn with poorly lithiated LixSn alloys, respectively. The composition and thestability of the solid electrolyte interphase were characterized by X-ray photoelectron spectroscopy.
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| 3. |
- Ojwang, Dickson O., et al.
(författare)
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Structure Characterization and Properties of K-Containing Copper Hexacyanoferrate
- 2016
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 55:12, s. 5924-5934
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Tidskriftsartikel (refereegranskat)abstract
- Copper hexacyanoferrate, Cu-II[Fe-III(CN)(6)](2/3)center dot nH(2)O, was synthesized, and varied amounts of IC ions were inserted via reduction by K2S2O3 (aq). Ideally, the reaction can be written as Cu-II[Fe-III(CN)(6)](2/3)-nH(2)O + 2x/3K(+) + 2x/3e(-)K(+) <-> K-2x/3 Cu-II[Fe-x(II).Fe-1-x(II),(CN)(6)](2/3)-nH(2)O. Infrared, Raman, and Mossbauer spectroscopy studies show that Fe-II is continuously reduced to Fell with increasing x, accompanied by a decrease of the a-axis of the cubic Fn (3) over barm unit cell. Elemental analysis of K by inductively coupled plasma shows that the insertion only begins when a significant fraction similar to 10% of the Fe-III, has already been reduced. Thermogravimetric analysis shows a fast exchange of water with ambient atmosphere and a total weight loss of similar to 26 wt % upon heating to 180 degrees C, above which the structure starts to decompose. The crystal structures of Cu-III[Fe-III(CN)(6)](2/3)center dot nH(2)O and K2/3Cu[Fe(CN)(6)](2/3)center dot nH(2)O were refined using synchrotron X-ray powder diffraction data. In both, one-third of the Fe(CN)(6) groups are vacant, and the octahedron around Cull is completed by water molecules. In the two structures, difference Fourier maps reveal three additional zeolitic water sites (8c, 32f, and 48g) in the center of the cavities formed by the-Cu-N-C-Fe- framework. The K-containing compound shows an increased electron density at two of these sites (32f and 48g), indicating them to be the preferred positions for the K+ ions.
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| 4. |
- Philippe, Bertrand, et al.
(författare)
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MnSn2 electrodes for Li-ion batteries : Mechanisms at the nano scale and electrode/electrolyte interface
- 2014
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Ingår i: Electrochimica Acta. - elsevier : Elsevier BV. - 0013-4686 .- 1873-3859. ; 123, s. 72-83
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the reaction mechanisms occurring upon the first discharge/charge cycle of a MnSn2//Li electrochemical cell, by using bulk- and surface-sensitive characterization techniques (Xray Diffraction, Sn-119 Mossbauer spectroscopy, magnetic measurements, X-ray photoelectron and Auger spectroscopies). Compared to other tin-transition metal alloys, MnSn2 displays an original behaviour. Lithium insertion into MnSn2 particles results in a nanocomposite consisting of Li7Sn2 phase, and of Mn nanoparticles which are immediately oxidized at their surface. Lithium extraction from this nanocomposite leads to the formation of magnetic MnSn2 particles and to our knowledge it is the first time such a mechanism is observed in tin-based intermetallic electrode materials due to electrochemical reaction with Li. The solid electrolyte interphase (SEI) is formed at the beginning of the first discharge and its thickness slightly increases upon further lithium insertion. A partial re-dissolution process occurs upon lithium extraction from the material, while its chemical composition is very stable over the whole cycle.
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| 5. |
- Samain, Louise, et al.
(författare)
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Crystal structure and high-temperature properties of the Ruddlesden-Popper phases Sr3-xYx(Fe1.25Ni0.75)O7-delta (0 <= x <= 0.75)
- 2015
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Ingår i: Journal of Solid State Chemistry. - : Elsevier BV. - 0022-4596 .- 1095-726X. ; 227, s. 45-54
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Tidskriftsartikel (refereegranskat)abstract
- Ruddlesden-Popper n=2 member phases Sr3-xYxFe1.25Ni0.75O7-delta, 0 <= x <= 0.75, have been investigated by X-ray and neutron powder diffraction, thermogravimetry and Mossbauer spectroscopy. Both samples as-prepared at 1300 degrees C under N-2(g) flow and samples subsequently air-annealed at 900 degrees C were studied. The as-prepared x=0.75 phase is highly oxygen deficient with delta=1, the O1 atom site being vacant, and the Fe3+/Ni2+ ions having a square pyramidal coordination. For as-prepared phases with lower x values, the Mossbauer spectral data are in good agreement with the presence of both 5- and 4-coordinated Fe3+ ions, implying in addition a partial occupancy of the O3 atom sites that form the basal plane of the square pyramid. The air-annealed x=0.75 sample has a delta value of 0.61(1) and the structure has Fe/Ni ions in both square pyramids and octahedra. Mossbauer spectroscopy shows the phase to contain only Fe3+, implying that all Ni is present as Ni3+. Air-annealed phases with lower x values are found to contain both Fe3+ and Fe4+. For both the as-prepared and the air-annealed samples, the Y3+ cations are found to be mainly located in the perovskite block. The high-temperature thermal expansion of as-prepared and air-annealed x=0.75 phases were investigated by high-temperature X-ray diffraction and dilatometry and the linear thermal expansion coefficient determined to be 14.4 ppm K-1. Electrical conductivity measurements showed that the air-annealed samples have higher conductivity than the as-prepared ones.
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| 6. |
- Svensson, Gunnar, et al.
(författare)
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Crystal Structure and Coordination of B-Cations in the Ruddlesden-Popper Phases Sr3-xPrx(Fe1.25Ni0.75)O7- (0 x 0.4)
- 2018
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Ingår i: Inorganics. - : MDPI AG. - 2304-6740. ; 6:3
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Tidskriftsartikel (refereegranskat)abstract
- Compounds Sr3-xPrxFe1.25Ni0.75O7- with 0 x 0.4 and Ruddlesden-Popper n = 2 type structures were synthesized and investigated by X-ray and neutron powder diffraction, thermogravimetry, and Mossbauer spectroscopy. Both samples, prepared at 1300 degrees C under N-2(g) flow and samples subsequently air-annealed at 900 degrees C, were studied. The structures contained oxygen vacancies in the perovskite layers, and the Fe/Ni cations had an average coordination number less than six. The oxygen content was considerably higher for air-annealed samples than for samples prepared under N-2, 7 - = similar to 6.6 and similar to 5.6 per formula unit, respectively. Mossbauer data collected at 7 K, below magnetic ordering temperatures, were consistent with X-ray powder diffraction (XRD) and neutron powder diffraction (NPD) results. The electrical conductivity was considerably higher for the air-annealed samples and was for x = 0.1 similar to 30 Scm(-1) at 500 degrees C. The thermal expansion coefficients were measured in air between room temperature and 900 degrees C and was found to be 20-24 ppmK(-1) overall.
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