Laurent Aldon - Academia.edu (original) (raw)
Papers by Laurent Aldon
ECS Meeting Abstracts, 2010
Journal of the American Chemical Society, 2011
The diversification of antiferromagnetic (AFM) oxides with high Néel temperature is of fundamenta... more The diversification of antiferromagnetic (AFM) oxides with high Néel temperature is of fundamental as well as technical interest if one considers the need for robust AFM in the field of spin-tronics (exchange bias, multiferroics, etc.). Within the broad series of so-called hexagonal perovskites (HP), the existence of face-sharing octahedral units drastically lowers the strength of magnetic exchanges as compared to corner-sharing octahedral edifices. Here, we show that the partial introduction of F(-) in several Fe-based HP types leads to a drastic increase of the AFM ordering close to the highest values reported in iron oxides (T(N) ≈ 700 K). Our experimental results are supported by ab initio calculations. The T(N) increase is explained by the structural effect of the aliovalent F(-) for O(2-) substitution occurring in preferred anionic positions: it leads to local changes of the Fe-O-Fe connectivity and to chemical reduction into predominant Fe(3+), both responsible for drastic magnetic changes.
Electrochemical and Solid-State Letters, 1999
ABSTRACT
Journal of Physics D: Applied Physics, 2017
The electrochemical lithiation of the mixed metal olivine LiFe0.75Mn0.25PO4 was followed by opera... more The electrochemical lithiation of the mixed metal olivine LiFe0.75Mn0.25PO4 was followed by operando x-ray absorption spectroscopy (XAS) at both Fe and Mn K edges. XAS data were interpreted using an innovating chemometric approach, allowing the detailed reconstruction of the rather complicated reaction mechanism involving two different metal centres. In this way it was possible to precisely describe the Jahn–Teller effect occurring upon oxidation of the manganese centres. The thorough comprehension of the electrochemical mechanism is of high interest for studying the effect of lithium extraction in the olivine structure in the presence of Mn, which is known to partially hamper the complete lithiation of such mixed metal systems.
Electrochimica Acta, 2017
Onepot ball-milling synthesis of a Ni-Ti-Si based composite as anode material for Li-ion batterie... more Onepot ball-milling synthesis of a Ni-Ti-Si based composite as anode material for Li-ion batteries, Electrochimica Actahttp://dx.
Physical Review B, 1998
The electric field gradients ͑EFG's͒ of 111 In(EC) 111 Cd nuclei at the different crystalline sit... more The electric field gradients ͑EFG's͒ of 111 In(EC) 111 Cd nuclei at the different crystalline sites in spinel -In 2 S 3 have been measured, using perturbed angular correlation spectroscopy. The radioactive 111 In tracers were introduced into the samples by means of ion implantation or during the chemical synthesis using natural indium doped with 111 In. The radiation damage after the implantation was annealed by heating the samples to above the transition temperature Tϭ693 K where the phase transition to cubic ␣-In 2 S 3 occurs. In contrast to previous PAC measurements, three electric field gradients were found. Their temperature dependences were measured in the temperature range between 8 and 743 K. The crystalline structure was checked by x-ray diffraction and refined by means of a Rietveld analysis. Fully consistent with the refined structure, the three observed EFG's were attributed to probes residing in the different sulphur octahedra and tetrahedra of -In 2 S 3. The EFG values are reproduced by the point charge model. A strong damping of the perturbation functions was observed in the temperature range between 150 and 370 K, which was attributed to dynamical hyperfine interactions caused by aftereffects of the electron capture decay of 111 In. ͓S0163-1829͑98͒05341-7͔
RSC Advances, 2012
Please note that technical editing may introduce minor changes to the text and/or graphics contai... more Please note that technical editing may introduce minor changes to the text and/or graphics contained in the manuscript submitted by the author(s) which may alter content, and that the standard Terms & Conditions and the ethical guidelines that apply to the journal are still applicable. In no event shall the RSC be held responsible for any errors or omissions in these Accepted Manuscript manuscripts or any consequences arising from the use of any information contained in them.
Journal of the American Ceramic Society, 2003
This paper examines the role of iron in mullite nucleation and growth from kaolins. We chose two ... more This paper examines the role of iron in mullite nucleation and growth from kaolins. We chose two typical raw kaolins containing a reduced impurity level and characterized by very different degrees of crystallinity of the kaolinite phase. Both the structural iron in kaolinite and also some iron deposited onto phyllosilicate layers by a chemical route were considered. After firing in the 900-1100°C temperature range, the Fe environment was determined by Mössbauer spectroscopy. From X-ray spectra of samples fired at 1250°C, mullite stoichiometries were obtained by Rietveld refinements. It was shown that iron contributes to the structural reorganization stage of the material, when mullite is nucleated. Fe atoms are essentially in octahedral sites, which favors an increase of the c parameter of the orthorhombic cell. The iron quantity attains a saturation level for an Fe-to-Al ratio between 0.3 and 0.4, depending on the raw kaolinite crystallinity. Besides mullite, the excess iron associates with titanium to form a pseudobrookite phase and hematite.
Journal of Solid State Chemistry, 2012
Commercial C-LiFe 0.33 Mn 0.67 PO 4 positive electrode material has been investigated by 57 Fe Mö... more Commercial C-LiFe 0.33 Mn 0.67 PO 4 positive electrode material has been investigated by 57 Fe Mössbauer Spectroscopy (MS), X-ray Photoelectron Spectroscopy (XPS) and X-ray Absorption Spectroscopy (XAS). The combined use of these experimental techniques provides a better understanding of the electrochemical reaction involved during cycling. 57 Fe MS is very efficient to directly follow oxidation state of Fe in the electrode, and gives surprisingly indirect information on the oxidation state of Mn as observed by XAS and XPS. The electrochemical mechanism is proposed based from in situ and operando investigations using both MS and XAS, and is consistent with XPS surface studies. XPS analysis of the electrodes at the end of charge (4.4 V) reveals enhanced electrode/electrolyte interface reactivity at this high potential. Aging of C-LiFe 0.33 Mn 0.67 PO 4 /Li cells after 50 cycles at 60 1C indicates a rather good electrochemical behavior (low capacity fading) of the electrode material. Both 57 Fe MS and XPS (Mn 2p and Fe 2p) clearly show no modification on Fe and Mn oxidation state compared to fresh electrode confirming the good electrochemical performances.
Journal of Solid State Chemistry, 2010
is a powerful tool to investigate redox reactions during in electrochemical lithium insertion/ext... more is a powerful tool to investigate redox reactions during in electrochemical lithium insertion/extraction processes. Electrochemical oxidation of LiFe II PO 4 (triphylite) in Li-ion batteries results in Fe III PO 4 (heterosite). LiFePO 4 was synthesized by solid state reaction at 800 1C under Ar flow from Li 2 CO 3 , FeC 2 O 4 Á 2H 2 O and NH 4 H 2 PO 4 precursors in stoichiometric composition. FePO 4 was prepared from chemical oxidation of LiFePO 4 using bromine as oxidative agent. For both materials a complete 57 Fe Mössbauer study as a function of the temperature has been carried out. The Debye temperatures are found to be y M = 336 K for LiFePO 4 and y M =359 K for FePO 4 , leading to Lamb-Mössbauer factors f 300 K = 0.73 and 0.77, respectively. These data will be useful for a precise estimation of the relative amounts of each species in a mixture.
Journal of Power Sources, 2003
The irreversible mechanisms of lithium insertion in amorphous tin composite oxides SnB 0.6 P 0.4 ... more The irreversible mechanisms of lithium insertion in amorphous tin composite oxides SnB 0.6 P 0.4 O 2.9 have been studied by X-ray diffraction (XRD) and 119 Sn Mössbauer spectroscopy. The determination of the Lamb-Mössbauer factor has allowed us to evaluate the relative numbers of different tin atoms (Sn II , Sn 0). We show that insertion of lithium reduces the Sn II into Sn 0 atoms, which form nanoparticles of active species. The lithium ions act as glass modifiers, breaking the bonds within M-O-M 0 (M, M 0 ¼ B, P, Sn) bridges and forming non-bridging M-O dÀ bonds.
Journal of Power Sources, 2003
Lithium insertion mechanism in some antimony-based compounds: SnSb, CoSb 3 , CrSb 2 , TiSb 2 has ... more Lithium insertion mechanism in some antimony-based compounds: SnSb, CoSb 3 , CrSb 2 , TiSb 2 has been studied by means of 121 Sb Mössbauer spectrometry which gives valuable information about the local electronic structure of the probed element (Sb). The structural and electronic modifications induced by insertion of lithium have been characterized. For these Sb-based materials the lithium insertion mechanisms involve Li 3 Sb formation and composite multi-phase separations with one component displaced from the pristine compound.
Journal of Power Sources, 2011
In this paper we propose a new way for Mössbauer data treatment when numerous experimental spectr... more In this paper we propose a new way for Mössbauer data treatment when numerous experimental spectra are recorded in operando conditions depending on a perturbation. In our exemple, the perturbation is the Li amount extracted from a positive electrode material LiFe 0.75 Mn 0.25 PO 4. In other cases perturbation could be the recording temperature, the pressure or kinetic parameter or even time for isothermal experiments. From analysis of both synchronous and asynchronous 2D correlation spectra, we can focus our attention on the intensity variations at some specific positions deduced from crosspeaks. This analytical method is very powerful when overlap between absorption lines is observed. This is typically the case when Fe 2+ /Fe 3+ contributions are simultaneously present in a Mössbauer spectrum at lower velocities.
Journal of Power Sources, 2009
This paper deals with new tin-based composite -Sn/(CaSiO 3) 0.4 negative electrode materials for... more This paper deals with new tin-based composite -Sn/(CaSiO 3) 0.4 negative electrode materials for Li-ion batteries. The nature of the oxide matrix and of dispersed tin particles has been investigated by X-ray diffraction (XRD), scanning electron microscope (SEM) coupled with energy dispersion spectroscopy (EDS) and Mössbauer spectroscopy by both transmission (TMS) and backscattering (CEMS) mode for bulk and interface characterizations. The electrochemical behaviour of the composite has been studied during Lireaction processes. Electrochemical investigation and Mössbauer data analyses suggest the formation of Li 7 Sn 2 during Li reaction. The reversible mechanism is based on cycling between -Sn and Li 7 Sn 2. An interface composed of CaSn IV SiO 5 and a Sn II species between tin particles dispersed in the CaSiO 3 matrix is responsible of the irreversible capacity observed in this composite during the first discharge.
Journal of Power Sources, 2005
ABSTRACT The electronic changes occurring upon electrochemical delithiation of the LiCo1-yFeyO2 s... more ABSTRACT The electronic changes occurring upon electrochemical delithiation of the LiCo1-yFeyO2 solid solution were characterised by means of in situ electrochemical Fe-57 Mossbauer spectroscopy on plastic batteries for y = 0.1, 0.2 and 0.4. For the y = 0.1 and 0.2 pristine materials, two quadrupole doublets were observed in the Mossbauer spectra. The first one, with an isomer shift of 0.32-0.33 mm s(-1), is ascribable to Fe-III replacing Co-III in the octahedral sites of the CoO2 layer while the weaker second doublet, with an isomer shift of 0.24-0.19 mm s(-1), shows the presence of Fe-III in pseudotetrahedral sites of the Li2O layers. For y = 0.4, all Fe-III atoms are located on the octahedral sites of the CoO2 layer and the presence of alpha-LiFeO2 as impurity was detected (16%). During the delithiation process the Fe-III -> Fe-IV oxidation was clearly evidenced by the appearance of a new subspectrum with an isomer shift in the range -0.17 to -0.01 mm s(-1) whose intensity increases with the amount of deintercalated lithium. In all cases the amount of oxidised iron Fe-IV does not exceed 56% of the total iron content, i.e. the oxidation of the Fe-III does not continue to completeness. This means that the oxidation of Fe-III and Co-III occurs simultaneously. The presence of iron in the Li2O layer and the difficulty of complete oxidation of Fe-III can explain the poor reversibility of this process. (c) 2005 Elsevier B.V. All rights reserved.
Journal of Power Sources, 2003
The spinel Li 4 Ti 5 O 12 , a stable phase of the Li 2 O-TiO 2 system, allows to insert three Li ... more The spinel Li 4 Ti 5 O 12 , a stable phase of the Li 2 O-TiO 2 system, allows to insert three Li atoms per formula unit at a potential of 1.5 Von the basis of a spinel $ NaCl phase transition. This mechanism leads to a reduction of three Ti(IV) atoms out of five, corresponding to a theoretical capacity of 175 mAh/g. The influence of structural defaults on the spinel ! NaCl phase transition and its reversibility during charge/discharge cycles have been studied. Solid solutions formed from chemical insertion of lithium or substitutions Ti/V, Ti/Mn, Ti/Fe modify the cation distribution on the crystallographic sites (tetrahedral 8a, octahedral 16d, space group Fd3m) and influence the electrochemical performances. A structural analysis by X-ray and neutron diffraction, X-ray absorption, 57 Fe Mössbauer spectroscopy and first principle calculations have allowed to establish a relationship between the structure and the electrochemical properties.
Journal of Non-Crystalline Solids, 2000
The local environment of the Ge and As atoms in Ge0.1AsxTe0.9−x glasses with x=0.15, 0.20, 0.46 a... more The local environment of the Ge and As atoms in Ge0.1AsxTe0.9−x glasses with x=0.15, 0.20, 0.46 and 0.54 has been investigated by X-ray absorption spectroscopy from the extended X-ray absorption fine structures (EXAFS). The analysis of the EXAFS data is carried out by considering As–Te and As–X bonds for the As K edge and Ge–Te and Ge–X bonds at the
Hyperfine Interactions, 2012
The performances of Li-ion batteries depend on many factors amongst which the important ones are ... more The performances of Li-ion batteries depend on many factors amongst which the important ones are the electrode materials and their structural and electronic evolution upon cycling. For a better understanding of lithium reactivity mechanism of many materials the combination of X-Ray Powder Diffraction (XRPD) and Transmission Mössbauer Spectroscopy (TMS) providing both structural and electronic information during the electrochemical cycling has been carried out. Thanks to the design of a specific electrochemical cell, derived from a conventional Swagelock cell, such measurements have been realised in operando mode. Two examples illustrate the greatness of combining XRPD and TMS for the study of LiFe 0.75 Mn 0.25 PO 4 as positive electrode and TiSnSb as negative electrode. Different kinds of insertion or conversion reactions have been identified leading to a better optimization and design of performing electrodes.
Hyperfine Interactions, 2004
Lithium insertion mechanisms in two antimony based compounds: CoSb 3 and CoSb have been studied b... more Lithium insertion mechanisms in two antimony based compounds: CoSb 3 and CoSb have been studied by means of 121 Sb Mössbauer spectrometry. Structural and electronic modifications induced by insertion of lithium have been characterised for different depths of discharge. In all cases the insertion mechanisms can be described from several steps. In the first step antimony is partially dispersed in the metallic matrix with amorphisation of the electrode material and in a second step we can observe the alloy forming (Li 3 Sb). However this amorphous alloy remains in interaction with the matrix allowing then a good reversibility.
ECS Meeting Abstracts, 2010
Journal of the American Chemical Society, 2011
The diversification of antiferromagnetic (AFM) oxides with high Néel temperature is of fundamenta... more The diversification of antiferromagnetic (AFM) oxides with high Néel temperature is of fundamental as well as technical interest if one considers the need for robust AFM in the field of spin-tronics (exchange bias, multiferroics, etc.). Within the broad series of so-called hexagonal perovskites (HP), the existence of face-sharing octahedral units drastically lowers the strength of magnetic exchanges as compared to corner-sharing octahedral edifices. Here, we show that the partial introduction of F(-) in several Fe-based HP types leads to a drastic increase of the AFM ordering close to the highest values reported in iron oxides (T(N) ≈ 700 K). Our experimental results are supported by ab initio calculations. The T(N) increase is explained by the structural effect of the aliovalent F(-) for O(2-) substitution occurring in preferred anionic positions: it leads to local changes of the Fe-O-Fe connectivity and to chemical reduction into predominant Fe(3+), both responsible for drastic magnetic changes.
Electrochemical and Solid-State Letters, 1999
ABSTRACT
Journal of Physics D: Applied Physics, 2017
The electrochemical lithiation of the mixed metal olivine LiFe0.75Mn0.25PO4 was followed by opera... more The electrochemical lithiation of the mixed metal olivine LiFe0.75Mn0.25PO4 was followed by operando x-ray absorption spectroscopy (XAS) at both Fe and Mn K edges. XAS data were interpreted using an innovating chemometric approach, allowing the detailed reconstruction of the rather complicated reaction mechanism involving two different metal centres. In this way it was possible to precisely describe the Jahn–Teller effect occurring upon oxidation of the manganese centres. The thorough comprehension of the electrochemical mechanism is of high interest for studying the effect of lithium extraction in the olivine structure in the presence of Mn, which is known to partially hamper the complete lithiation of such mixed metal systems.
Electrochimica Acta, 2017
Onepot ball-milling synthesis of a Ni-Ti-Si based composite as anode material for Li-ion batterie... more Onepot ball-milling synthesis of a Ni-Ti-Si based composite as anode material for Li-ion batteries, Electrochimica Actahttp://dx.
Physical Review B, 1998
The electric field gradients ͑EFG's͒ of 111 In(EC) 111 Cd nuclei at the different crystalline sit... more The electric field gradients ͑EFG's͒ of 111 In(EC) 111 Cd nuclei at the different crystalline sites in spinel -In 2 S 3 have been measured, using perturbed angular correlation spectroscopy. The radioactive 111 In tracers were introduced into the samples by means of ion implantation or during the chemical synthesis using natural indium doped with 111 In. The radiation damage after the implantation was annealed by heating the samples to above the transition temperature Tϭ693 K where the phase transition to cubic ␣-In 2 S 3 occurs. In contrast to previous PAC measurements, three electric field gradients were found. Their temperature dependences were measured in the temperature range between 8 and 743 K. The crystalline structure was checked by x-ray diffraction and refined by means of a Rietveld analysis. Fully consistent with the refined structure, the three observed EFG's were attributed to probes residing in the different sulphur octahedra and tetrahedra of -In 2 S 3. The EFG values are reproduced by the point charge model. A strong damping of the perturbation functions was observed in the temperature range between 150 and 370 K, which was attributed to dynamical hyperfine interactions caused by aftereffects of the electron capture decay of 111 In. ͓S0163-1829͑98͒05341-7͔
RSC Advances, 2012
Please note that technical editing may introduce minor changes to the text and/or graphics contai... more Please note that technical editing may introduce minor changes to the text and/or graphics contained in the manuscript submitted by the author(s) which may alter content, and that the standard Terms & Conditions and the ethical guidelines that apply to the journal are still applicable. In no event shall the RSC be held responsible for any errors or omissions in these Accepted Manuscript manuscripts or any consequences arising from the use of any information contained in them.
Journal of the American Ceramic Society, 2003
This paper examines the role of iron in mullite nucleation and growth from kaolins. We chose two ... more This paper examines the role of iron in mullite nucleation and growth from kaolins. We chose two typical raw kaolins containing a reduced impurity level and characterized by very different degrees of crystallinity of the kaolinite phase. Both the structural iron in kaolinite and also some iron deposited onto phyllosilicate layers by a chemical route were considered. After firing in the 900-1100°C temperature range, the Fe environment was determined by Mössbauer spectroscopy. From X-ray spectra of samples fired at 1250°C, mullite stoichiometries were obtained by Rietveld refinements. It was shown that iron contributes to the structural reorganization stage of the material, when mullite is nucleated. Fe atoms are essentially in octahedral sites, which favors an increase of the c parameter of the orthorhombic cell. The iron quantity attains a saturation level for an Fe-to-Al ratio between 0.3 and 0.4, depending on the raw kaolinite crystallinity. Besides mullite, the excess iron associates with titanium to form a pseudobrookite phase and hematite.
Journal of Solid State Chemistry, 2012
Commercial C-LiFe 0.33 Mn 0.67 PO 4 positive electrode material has been investigated by 57 Fe Mö... more Commercial C-LiFe 0.33 Mn 0.67 PO 4 positive electrode material has been investigated by 57 Fe Mössbauer Spectroscopy (MS), X-ray Photoelectron Spectroscopy (XPS) and X-ray Absorption Spectroscopy (XAS). The combined use of these experimental techniques provides a better understanding of the electrochemical reaction involved during cycling. 57 Fe MS is very efficient to directly follow oxidation state of Fe in the electrode, and gives surprisingly indirect information on the oxidation state of Mn as observed by XAS and XPS. The electrochemical mechanism is proposed based from in situ and operando investigations using both MS and XAS, and is consistent with XPS surface studies. XPS analysis of the electrodes at the end of charge (4.4 V) reveals enhanced electrode/electrolyte interface reactivity at this high potential. Aging of C-LiFe 0.33 Mn 0.67 PO 4 /Li cells after 50 cycles at 60 1C indicates a rather good electrochemical behavior (low capacity fading) of the electrode material. Both 57 Fe MS and XPS (Mn 2p and Fe 2p) clearly show no modification on Fe and Mn oxidation state compared to fresh electrode confirming the good electrochemical performances.
Journal of Solid State Chemistry, 2010
is a powerful tool to investigate redox reactions during in electrochemical lithium insertion/ext... more is a powerful tool to investigate redox reactions during in electrochemical lithium insertion/extraction processes. Electrochemical oxidation of LiFe II PO 4 (triphylite) in Li-ion batteries results in Fe III PO 4 (heterosite). LiFePO 4 was synthesized by solid state reaction at 800 1C under Ar flow from Li 2 CO 3 , FeC 2 O 4 Á 2H 2 O and NH 4 H 2 PO 4 precursors in stoichiometric composition. FePO 4 was prepared from chemical oxidation of LiFePO 4 using bromine as oxidative agent. For both materials a complete 57 Fe Mössbauer study as a function of the temperature has been carried out. The Debye temperatures are found to be y M = 336 K for LiFePO 4 and y M =359 K for FePO 4 , leading to Lamb-Mössbauer factors f 300 K = 0.73 and 0.77, respectively. These data will be useful for a precise estimation of the relative amounts of each species in a mixture.
Journal of Power Sources, 2003
The irreversible mechanisms of lithium insertion in amorphous tin composite oxides SnB 0.6 P 0.4 ... more The irreversible mechanisms of lithium insertion in amorphous tin composite oxides SnB 0.6 P 0.4 O 2.9 have been studied by X-ray diffraction (XRD) and 119 Sn Mössbauer spectroscopy. The determination of the Lamb-Mössbauer factor has allowed us to evaluate the relative numbers of different tin atoms (Sn II , Sn 0). We show that insertion of lithium reduces the Sn II into Sn 0 atoms, which form nanoparticles of active species. The lithium ions act as glass modifiers, breaking the bonds within M-O-M 0 (M, M 0 ¼ B, P, Sn) bridges and forming non-bridging M-O dÀ bonds.
Journal of Power Sources, 2003
Lithium insertion mechanism in some antimony-based compounds: SnSb, CoSb 3 , CrSb 2 , TiSb 2 has ... more Lithium insertion mechanism in some antimony-based compounds: SnSb, CoSb 3 , CrSb 2 , TiSb 2 has been studied by means of 121 Sb Mössbauer spectrometry which gives valuable information about the local electronic structure of the probed element (Sb). The structural and electronic modifications induced by insertion of lithium have been characterized. For these Sb-based materials the lithium insertion mechanisms involve Li 3 Sb formation and composite multi-phase separations with one component displaced from the pristine compound.
Journal of Power Sources, 2011
In this paper we propose a new way for Mössbauer data treatment when numerous experimental spectr... more In this paper we propose a new way for Mössbauer data treatment when numerous experimental spectra are recorded in operando conditions depending on a perturbation. In our exemple, the perturbation is the Li amount extracted from a positive electrode material LiFe 0.75 Mn 0.25 PO 4. In other cases perturbation could be the recording temperature, the pressure or kinetic parameter or even time for isothermal experiments. From analysis of both synchronous and asynchronous 2D correlation spectra, we can focus our attention on the intensity variations at some specific positions deduced from crosspeaks. This analytical method is very powerful when overlap between absorption lines is observed. This is typically the case when Fe 2+ /Fe 3+ contributions are simultaneously present in a Mössbauer spectrum at lower velocities.
Journal of Power Sources, 2009
This paper deals with new tin-based composite -Sn/(CaSiO 3) 0.4 negative electrode materials for... more This paper deals with new tin-based composite -Sn/(CaSiO 3) 0.4 negative electrode materials for Li-ion batteries. The nature of the oxide matrix and of dispersed tin particles has been investigated by X-ray diffraction (XRD), scanning electron microscope (SEM) coupled with energy dispersion spectroscopy (EDS) and Mössbauer spectroscopy by both transmission (TMS) and backscattering (CEMS) mode for bulk and interface characterizations. The electrochemical behaviour of the composite has been studied during Lireaction processes. Electrochemical investigation and Mössbauer data analyses suggest the formation of Li 7 Sn 2 during Li reaction. The reversible mechanism is based on cycling between -Sn and Li 7 Sn 2. An interface composed of CaSn IV SiO 5 and a Sn II species between tin particles dispersed in the CaSiO 3 matrix is responsible of the irreversible capacity observed in this composite during the first discharge.
Journal of Power Sources, 2005
ABSTRACT The electronic changes occurring upon electrochemical delithiation of the LiCo1-yFeyO2 s... more ABSTRACT The electronic changes occurring upon electrochemical delithiation of the LiCo1-yFeyO2 solid solution were characterised by means of in situ electrochemical Fe-57 Mossbauer spectroscopy on plastic batteries for y = 0.1, 0.2 and 0.4. For the y = 0.1 and 0.2 pristine materials, two quadrupole doublets were observed in the Mossbauer spectra. The first one, with an isomer shift of 0.32-0.33 mm s(-1), is ascribable to Fe-III replacing Co-III in the octahedral sites of the CoO2 layer while the weaker second doublet, with an isomer shift of 0.24-0.19 mm s(-1), shows the presence of Fe-III in pseudotetrahedral sites of the Li2O layers. For y = 0.4, all Fe-III atoms are located on the octahedral sites of the CoO2 layer and the presence of alpha-LiFeO2 as impurity was detected (16%). During the delithiation process the Fe-III -> Fe-IV oxidation was clearly evidenced by the appearance of a new subspectrum with an isomer shift in the range -0.17 to -0.01 mm s(-1) whose intensity increases with the amount of deintercalated lithium. In all cases the amount of oxidised iron Fe-IV does not exceed 56% of the total iron content, i.e. the oxidation of the Fe-III does not continue to completeness. This means that the oxidation of Fe-III and Co-III occurs simultaneously. The presence of iron in the Li2O layer and the difficulty of complete oxidation of Fe-III can explain the poor reversibility of this process. (c) 2005 Elsevier B.V. All rights reserved.
Journal of Power Sources, 2003
The spinel Li 4 Ti 5 O 12 , a stable phase of the Li 2 O-TiO 2 system, allows to insert three Li ... more The spinel Li 4 Ti 5 O 12 , a stable phase of the Li 2 O-TiO 2 system, allows to insert three Li atoms per formula unit at a potential of 1.5 Von the basis of a spinel $ NaCl phase transition. This mechanism leads to a reduction of three Ti(IV) atoms out of five, corresponding to a theoretical capacity of 175 mAh/g. The influence of structural defaults on the spinel ! NaCl phase transition and its reversibility during charge/discharge cycles have been studied. Solid solutions formed from chemical insertion of lithium or substitutions Ti/V, Ti/Mn, Ti/Fe modify the cation distribution on the crystallographic sites (tetrahedral 8a, octahedral 16d, space group Fd3m) and influence the electrochemical performances. A structural analysis by X-ray and neutron diffraction, X-ray absorption, 57 Fe Mössbauer spectroscopy and first principle calculations have allowed to establish a relationship between the structure and the electrochemical properties.
Journal of Non-Crystalline Solids, 2000
The local environment of the Ge and As atoms in Ge0.1AsxTe0.9−x glasses with x=0.15, 0.20, 0.46 a... more The local environment of the Ge and As atoms in Ge0.1AsxTe0.9−x glasses with x=0.15, 0.20, 0.46 and 0.54 has been investigated by X-ray absorption spectroscopy from the extended X-ray absorption fine structures (EXAFS). The analysis of the EXAFS data is carried out by considering As–Te and As–X bonds for the As K edge and Ge–Te and Ge–X bonds at the
Hyperfine Interactions, 2012
The performances of Li-ion batteries depend on many factors amongst which the important ones are ... more The performances of Li-ion batteries depend on many factors amongst which the important ones are the electrode materials and their structural and electronic evolution upon cycling. For a better understanding of lithium reactivity mechanism of many materials the combination of X-Ray Powder Diffraction (XRPD) and Transmission Mössbauer Spectroscopy (TMS) providing both structural and electronic information during the electrochemical cycling has been carried out. Thanks to the design of a specific electrochemical cell, derived from a conventional Swagelock cell, such measurements have been realised in operando mode. Two examples illustrate the greatness of combining XRPD and TMS for the study of LiFe 0.75 Mn 0.25 PO 4 as positive electrode and TiSnSb as negative electrode. Different kinds of insertion or conversion reactions have been identified leading to a better optimization and design of performing electrodes.
Hyperfine Interactions, 2004
Lithium insertion mechanisms in two antimony based compounds: CoSb 3 and CoSb have been studied b... more Lithium insertion mechanisms in two antimony based compounds: CoSb 3 and CoSb have been studied by means of 121 Sb Mössbauer spectrometry. Structural and electronic modifications induced by insertion of lithium have been characterised for different depths of discharge. In all cases the insertion mechanisms can be described from several steps. In the first step antimony is partially dispersed in the metallic matrix with amorphisation of the electrode material and in a second step we can observe the alloy forming (Li 3 Sb). However this amorphous alloy remains in interaction with the matrix allowing then a good reversibility.