| 1. |
- Difi, Siham, et al.
(author)
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Mechanisms and Performances of Na1.5Fe0.5Ti1.5(PO4)(3)/C Composite as Electrode Material for Na-Ion Batteries
- 2015
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In: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 119:45, s. 25220-25234
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Journal article (peer-reviewed)abstract
- The properties, insertion mechanisms, and electrochemical performances of the Na1.5Fe0.5Ti1.5(PO4)(3)/C composite as electrode material for Na-ion batteries are reported. The composite was obtained by solid-state reaction and consists of porous secondary particles of submicron-sized particles coated by carbon. Detailed characterizations were performed by combining theoretical and experimental tools. This includes the determination of the crystal structure of Na1.5Fe0.5Ti1.5(PO4)(3) from both first-principles calculations and X-ray diffraction providing Na distribution over M1 and M2 interstitial sites, which is of importance for ionic conductivity. Na1.5Fe0.5Ti1.5(PO4)(3)/C was used as an electrode material at 2.2 V versus Na+/Na-0, exhibiting good Na-storage ability with a specific capacity of 125 mAh g(-1), close to the theoretical value, for the first discharge at C/10, good capacity retention, and Coulombic efficiency of 95% and 99.5% at the 60th cycle, respectively, and high power rate with a decrease of the specific capacity of only 14% from C/10 to 2C. These good performances have been related to the morphology of the composite and substitution of Fe for Ti, leading to an insertion mechanism that differs from that of NaTi2(PO4)(3). This mechanism was quantitatively analyzed from operand Fe-57 Mossbauer spectroscopy used for the first time in both galvanostatic and GITT modes.
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| 2. |
- Difi, Siham, et al.
(author)
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Role of iron in Na1.5Fe0.5Ti1.5(PO4)(3)/C as electrode material for Na-ion batteries studied by operando Mossbauer spectroscopy
- 2016
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In: Hyperfine Interactions. - : Springer Science and Business Media LLC. - 0304-3843 .- 1572-9540.
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Conference paper (peer-reviewed)abstract
- The role of iron in Na1.5Fe0.5Ti1.5(PO4)(3)/C electrode material for Na batteries has been studied by Fe-57 Mossbauer spectroscopy in operando mode. The potential profile obtained in the galvanostatic regime shows three plateaus at different voltages due to different reaction mechanisms. Two of them, at 2.2 and 0.3 V vs Na+/Na-0, have been associated to redox processes involving iron and titanium in Na1.5Fe0.5Ti1.5(PO4)(3). The role of titanium was previously elucidated for NaTi2(PO4)(3) and the effect of the substitution of Fe for Ti was investigated with 57Fe Mossbauer spectroscopy. We show that iron is an electrochemically active center at 2.2 V with the reversible Fe3+/Fe2+ transformation and then remains at the oxidation state Fe2+ along the sodiation until the end of discharge at 0 V.
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| 3. |
- Mahmoud, Abdelfattah, et al.
(author)
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Electrochemical performances and mechanisms of MnSn2 as anode material for Li-ion batteries
- 2013
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In: Journal of Power Sources. - : Elsevier. - 0378-7753 .- 1873-2755. ; 244, s. 246-251
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Journal article (peer-reviewed)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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| 4. |
- Philippe, Bertrand, et al.
(author)
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MnSn2 electrodes for Li-ion batteries : Mechanisms at the nano scale and electrode/electrolyte interface
- 2014
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In: Electrochimica Acta. - elsevier : Elsevier BV. - 0013-4686 .- 1873-3859. ; 123, s. 72-83
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Journal article (peer-reviewed)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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