Résumé
In the past decade, major efforts have been devoted to searching for materials to be used as efficient cathodes and anodes in Li-ion batteries. As a result, two approaches have emerged i) Improving the performances of known materials such as oxides and phosphates [1, 2] or ii) Exploring new chemistries like fluorosulphates family [3, 4]. Same approaches are now being applied to Na-ion batteries. A common point to these approaches is the need for a comprehensive set of analytical tools allowing the best characterization and monitoring of the chemical and physical properties of the investigated materials. To complete the information coming from commonly applied techniques, a particular effort has been made to adapt in situ spectroscopic techniques (IR, NMR, and Mössbauer [5, 6]) to the specificities of Li-ion batteries. The uses of Mössbauer spectroscopy can range from the simplest characterization of a given material (eg. accurate quantification of Fe2+/Fe3+ ratio, monitoring of the material purity etc.) to the hyperfine understanding of the physical and chemical phenomena (eg. Spin reorganization, superconductivity). Mössbauer spectroscopy has shown itself to be extremely useful for the investigation of Fe-, Sn- and Sb-based electrode materials [7]. The main strengths of this spectroscopy are i) Its selectivity, since the information extracted is solely related to the probed isotope, ii) Its sensitivity to electronic and chemical changes allowing an accurate determination of oxidation degrees and ligand coordination iii) The versatility of implementing Mössbauer spectrometry for bulk, surface and in situ analyses. In addition, chemist can appreciate the fact that Mössbauer analysis is not limited by any morphological, size or matrix aspects of the investigated materials. Recent examples for cathode (phosphates, fluorosulphates and oxides) and anode (intermetallics) materials are selected to illustrate the potentialities of this technique that can help chemists in their quest to develop new electrode materials and to understand their electrochemical mechanisms vs. Li and Na. References: [1] Padhi A. K., et al., Journal of the Electrochemical Society 1997, 144, (4), 1188-1194. [2] Andersson A. S., et al., Solid State Ionics 2000, 130, 41-52. [3] Recham N., et al., Nature Materials 2009, 9, (1), 68-74. [4] Barpanda P., et al., Nature Materials 2011, 10, (10), 772-779. [5] Johnson C. S., et al., Electrochimica Acta 2002, 47, (19), 3187-3194. [6] Burba C. M., et al., Electrochimica Acta 2006, 52, (3), 780-785. [7] Jumas J. C., et al., Mössbauer Effect Reference and Data Journal 2010, 33, (2).