Solid-State NMR of the Family of Positive Electrode Materials Li₂Ru_1–<i>y</i>Sn_<i>y</i>O₃ for Lithium-Ion Batteries

The possibilities offered by ex situ and in situ operando ⁷Li solid-state nuclear magnetic resonance (NMR) are explored for the Li₂Ru_1–<i>y</i>Sn_<i>y</i>O₃ family (0 < <i>y</i> < 1), shown previously to display cationic and anionic redox activity when used as a positive electrode for Li ion batteries. Ex situ NMR spectroscopic studies indicate a nonrandom Sn/Ru substitution in the family. In the first charge, an increased metallicity at 4 V is deduced from the NMR spectra. Surprisingly, no striking difference is observed at 4.6 V compared to the pristine electrode, although the electronic structure is expected to be very different and the local cation environment to be distorted. For in situ operando measurements, we designed a new electrochemical cell that is compatible with NMR spectroscopy and one-dimensional magnetic resonance imaging (MRI). These operando measurements validate the ex situ observations and indicate that the environment formed at 4 V is specific of the initial charge and that there is little, if no, electrolyte decomposition, even at 4.6 V. This is another attractive feature of these compounds