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Real-time diffraction studies of electrode materials for Li-ion and Na-ion batteries

Mercredi 4 novembre 2015 14:30 - Duree : 1 heure
Lieu : ILL 4, Amphi Chadwick - 71 avenue des Martyrs - Grenoble

Orateur : Matteo Bianchini (Institut Laue-Langevin - Grenoble)

This presentation is a summary of my PhD work and of the relative thesis defense. Performing in situ and operando measurements on electrode materials for Li-ion and Na-ion batteries is of extreme importance for their improvement. These materials need to be studied in their environment (in situ), without exposure to reactive agents (O2, H2O, etc). They also need to be studied in real time while they function (operando), since they normally operate in non-equilibrium conditions and the reactions involved are thus extremely dynamical. Real-time experiments upon charge/discharge of the electrodes (i.e. upon lithium or sodium extraction/insertion from/into the electrodes) unveil dynamics that are not accessible by other means and allow a more complete understanding of the electrodes’ functioning. In particular our work deals with the use of operando diffraction techniques, to study the structural modifications occurring in several different electrochemical systems. The use of different probes, often combined, allows observing any atomic element in any crystalline ele ctrode. For this reason we exploited Neutron Powder Diffraction (NPD), X-Ray Powder Diffraction (XRPD) and Synchrotron radiation XRPD. However, custom setups are required to carry out operando diffraction experiments on batteries. Those for XRPD are common nowadays. The most complicated setups are those for NPD, making it a less mature technique. This is because of the many difficulties it holds when applied to a real battery. Several scattering contributions are present, coming from different components and generating unwanted Bragg reflections and a high background. I will address the development of a sample environment suitable for both electrochemistry and NPD. The task was accomplished designing an electrochemical cell featuring a (Ti,Zr) alloy and a deuterated version of the electrolyte. The resulting cell is able to function using massive electrodes (massive on the battery scale, small samples for neutrons) with good performances and able to give NPD patterns of high quality for data analysis. Our studies are conducted on the D20 high-flux diffractometer at ILL, where the feasibility of real operando experiments using commercial LiFePO4 was demonstrated. I will then discuss a few studies done with this setup, namely the observation of lithium extraction from different samples in the family of spinels Li1+xMn2-xO4 and high-voltage spinels such as LiNi0.4Mn1.6O4. Other materials were studied using neutrons combined with other probes and two main examples will be given : firstly, the lithium (de)intercalation in the oxyphosphate LiVPO4O, an interesting 2-electron positive electrode material for Li-ion batteries (working on the V4+/V5+ and V4+/V3+ couple). Secondly, a study related to the field of Na-ion batteries. We focused our efforts on Na3V2(PO4)2F3 that demonstrates extremely good capacity and rate capabilities. We observed his behavior using synchrotron X-Ray diffraction, unveiling a subtle orthorhombic distortion and thus a new crystal structure. Subsequent operando experiments also revealed the phase diagram of Na3V2(PO4)2F3 upon Na+ extraction, showing its amazing richness in terms of intermediate phases involved and ordering/disordering phenomena.

Contact : dubouloz@ill.fr

Discipline évènement : (Physique)
Entité organisatrice : (ILL)
Nature évènement : (Séminaire)
Evènement répétitif : (General ILL Seminar - College 5A)
Site de l'évènement : Polygone scientifique

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