Performing in situ and operando measurements on electrode materials for Li-ion and Na-ion batteries is of importance for their understanding and improvement. Electrode materials need to be studied in their environment (in situ) and in real time while they function (operando), since they normally operate in non-equilibrium conditions. 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. The use of different probes is an important requirement for the study of such reactions. The combined use of X-Ray Powder Diffraction (XRPD), Synchrotron radiation XRPD and Neutrons Powder Diffraction (NPD) allows observing any atomic element in any crystalline electrode. However, custom setups are required to carry out operandodiffraction experiments on batteries.

We will address the development of a sample environment suitable for both electrochemistry and neutron powder diffraction using an electrochemical cell featuring a (Ti,Zr) alloy and a deuterated version of the electrolyte [1]. The cell is able to function using massive electrodes (massive on the battery scale, but a small sample for neutrons) with good performances and able to give NPD patterns of high quality for data analysis. Importantly, we showed the possibility to succeed in reliable structural refinements (by the Rietveld method) and thus to observe structural modifications in details, from unit cell parameters to atomic coordinates and even site occupancy factors. We will discuss a few studies done with this setup, namely the observation of lithium extraction from different samples in the family of spinels Li_1+xMn_2-xO₄. We performed NPD in real time on three samples (LiMn₂O₄, Li_1.05Mn_1.95O₄ and Li_1.10Mn_1.90O₄) and showed how the Li/Mn ratio influences the phase diagram of the material [2]. New insights obtained from high resolution – high flux Synchrotron X-Ray diffraction data will be presented, in particular the existence of a Li⁺ and Mn³⁺/Mn⁴⁺ ordering within the spinel-delithiated composition Li_0.5Mn₂O₄[3].

Acknowledgements

This research is performed in the frame of the French network RS2E (http://www.energie-rs2e.com) and of the European network ALISTORE-ERI (http://www.alistore.eu).

References

[1] Bianchini et al., J. Electrochem. Soc., 160(11), A2176-A2183 (2013)

[2] Bianchini et al., J. Phys. Chem. C, 118(45), 25947-25955 (2014)

[3] Bianchini et al., Acta Cryst., B71, 688-701 (2015)