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Magnesium-ion batteries hold the potential to outperform the energy density of lithium-ion batteries, given the divalent charge carried by each Mg2+ cation, but remain in an early stage of development. Here, 25Mg solid-state nuclear magnetic resonance (ssNMR) is used to gain insight into the local structure and Mg-ion dynamics of candidate Mg-ion solid electrolytes, the antiperovskites Mg3SbN and Mg3AsN. Using the highest available magnetic field (35.2 T) for high-resolution solid-state NMR, the largest 25Mg quadrupole coupling constants (CQ) yet measured of up to 22 MHz are reported and corroborated by first-principles calculations. Predicted CQ values are shown to correlate with the antiperovskite’s tolerance factor; thus, 25Mg NMR linewidths can report on lattice distortions and phase stability of these antiperovskites. Variable-temperature 25Mg NMR spectra demonstrate changes at elevated temperatures, ascribed to Mg-ion motional effects. 25Mg T1 relaxometry measurements at ultrahigh field reveal a lower activation energy for the more distorted Mg3AsN phase, matching computational predictions of a lower energy barrier for Mg2+ ion migration and suggesting that additional scrutiny of antiperovskites as Mg-ion conductors is warranted. Given the inherent challenges of 25Mg NMR, this work demonstrates the benefits of combining ultrahigh field NMR spectroscopy, advanced pulse sequences, modern signal processing, and first-principles calculations to facilitate NMR of quadrupolar nuclei as a tool to probe the local structure and ion dynamics in beyond-Li battery materials.

Post-Doctoral Research Associate: Operando optical microscopy for battery electrodes (Fixed Term) in the Yusuf Hamied Department of Chemistry at the University of Cambridge.

Li-rich cathodes with an O2-type layer stacking offer high gravimetric capacities and fast charge-discharge rates, and are structurally more stable with respect to transition metal migration than O3-t...

Anode-free solid-state Li batteries promise significant increases in energy densities compared to current commercial batteries that rely on liquid electrolytes. Major challenges persist in controlling morphological evolution during the plating and stripping of lithium metal at the anode current collector. Elemental additives that alloy with lithium have been found to modify the plating and stripping behavior of lithium. Many alloying elements form intermetallics with lithium and the mobility of Li through these intermetallics is believed to have an important effect on morphological evolution. This study shows that Li transport coefficients through intermetallics span a wide range in values, with the B32 LiAl intermetallic predicted to have a Li tracer diffusion coefficient as high as 10–6 cm2/s at room temperature, which is 8 orders of magnitude larger than that of isostructural B32 LiZn. This work demonstrates the crucial role of vacancy concentration in controlling the mobility of Li atoms through intermetallics. While the migration barriers for Li-vacancy exchanges in both LiAl and LiZn are remarkably low, the superatomic conductivity in LiAl is shown to arise from the unique electronic structure of the B32 LiAl compound, which favors high concentrations of vacancies.

While significant magnetic interactions exist in lithium transition metal oxides, commonly used as Li-ion cathodes, the interplay between magnetic couplings, disorder, and redox processes remains poor...