Combined operando studies of new electrode materials for Li-ion batteries

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_0.75Mn_0.25PO₄ 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.     

Mössbauer Spectrometry as a Powerful Tool to Study Lithium Reactivity Mechanisms for Battery Electrode Materials

Hyperfine Interactions - The use of 57Fe as a local Mössbauer probe is of high interest for studying mechanisms induced by lithium insertion. In this way the substitutions Ti/Fe and Li/Fe have...     

How M?ssbauer spectroscopy can improve Li-ion batteries

In the domain of Li-ion batteries, M?ssbauer spectroscopy is mainly used for the characterization of electrode materials and the analysis of electrochemical reactions. Depending on the properties under investigation, different approaches are often considered, which are based on ex situ, in situ and operando measurements. The specific electrochemical cells and sample preparations used for such measurements are described in this paper. Applications to selected examples of cathode and anode materials are presented in order to show how M?ssbauer spectroscopy, when associated with other techniques, provides essential information to understand the mechanisms and improves the performances of Li-ion batteries.     

Unprecedented robust antiferromagnetism in fluorinated hexagonal perovskites

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.     

In situ 119Sn Mössbauer spectroscopy used to study lithium insertion in c-Mg2Sn

The electrochemical reactions of Li with c-Mg₂Sn have been investigated by in situ Mössbauer spectroscopy of ¹¹⁹Sn and X-ray diffraction. The lithiation transforms initially c-Mg₂Sn part into Li _x Mg₂Sn alloy (x?2MgSn ternary alloy. In situ Mössbauer spectroscopy provides valuable information on local environment of tin and swelling behavior and cracking of the particles during discharge and charge processes.     

The BM5Se9 phases: Mössbauer studies of the superconductors and the ferromagnets

Syntheses performed in the A₃B/MSe₂ (A = Sb, Ga, Sn) (B = Nb, V, Ta) (M = V, Nb, Ta) systems lead to the formation of B(M/A)₅Se₉ phases which could be ferromagnets or superconductors. It has been shown that the presence of V modifies the superconducting exchanges and allows ferromagnetic couplings. Mössbauer spectroscopy of both ¹²¹Sb and ¹¹⁹Sn gives local electronic structure of the SbNb₅Se₉ superconductor and the Sn_0.94Ga_0.06V_0.30Nb_4.70Se₉ ferromagnet. For the latter compound, a complete study as a function of temperature is carried out showing that the Sn environment is not modified when the ferromagnetic transition occurs. The Debye temperature is calculated and compared to those obtained for other selenide compounds.     

Structural transformations in lithiated Mn2Sb electrodes probed by Mössbauer spectroscopy and X-ray diffraction

The electrochemical reactions of Li with Mn₂Sb and small amounts of MnSb have been investigated by Mössbauer spectroscopy and X-ray diffraction. The lithiation transforms initially the MnSb part and later the Mn₂Sb part into amorphous LiMnSb. On further lithiation the LiMnSb phase transforms to rather well crystallized Li₃Sb. In the X-ray diffraction pattern for the fully lithiated sample extruded nanocrystalline Mn is seen for the first time in these type of electrodes. The first delithiation of Li₃Sb results in a mixture of three phases Mn₂Sb, MnSb and LiMnSb. After several cycles (charges and discharges) of the electrode the Mn₂Sb phase disappears completely.     

Handheld calculators between instrument and document

The new generations of handheld calculators can be considered either as mathematical tools with opportunities for calculation and representation or as a part of the teachers’ and students’ sets of resources. Framed by the Theory of Didactical Situations and the documentational approach, we take advantage of a particular experiment on introducing complex calculators in scientific classes to investigate the position and the role of this handheld technology both for students and teachers. The results show how different functionalities can be shared among teachers and students, but also how other functionalities remain private and may even conflict with the teacher’s intentions.     

Ionic and electronic transport in In2S3 studied via perturbed angular correlation spectroscopy

We report on Perturbed Angular Correlation measurements in polycrystalline In₂S₃ samples in the temperature range from 8 K to 1000 K where two different crystallographic phases β and α occur. As probes, implanted ¹¹¹In nuclei have been used. The three observed EFGs are attributed to probes residing substitutionally in the different sulfur-octahedra and -tetrahedra of β-In₂S₃. A strong damping between 150 K and 300 K has been attributed to EFG fluctuations following the ¹¹¹In(EC)¹¹¹Cd decay. The α-phase (above 680 K) is characterized by a different dynamical damping of the perturbation functions, caused by mobile In atoms. Therefore, the semiconductor In₂S₃ shows, in two different temperature ranges, dynamical PAC-spectra which correspond to different types of mobile charge carriers. Since ¹¹¹In is a self atom in In₂S₃, this compound is an ideal substance to study the charge transport phenomena by the PAC technique. This revised version was published online in August 2006 with corrections to the Cover Date.     

In situ 119Sn Mössbauer spectroscopy study of Sn-based electrode materials

Sn-based composite materials were synthetized by a conventional melt-quenching method, and studied by X-ray diffraction, electrochemistry and in situ ¹¹⁹Sn Mösssbauer spectroscopy. Tin was dispersed ex situ into a matrix formed from B₂O₃:P₂O₅. XRD and ¹¹⁹Sn Mössbauer spectroscopy show the formation of an interface between the active species (Sn⁰) and the matrix. This amorphous interface acts as a “buffer-zone” which compensates volume changes during the tin–lithium alloy formation and avoids aggregation of tin particles.