A new class of solid electrolytes with an ultra-low Na-ion migration barrier

AD Dembitskiy and SN Marshenya and E Antipov and SS Fedotov and DA Aksyonov, JOURNAL OF POWER SOURCES, 642, 236979 (2025).

DOI: 10.1016/j.jpowsour.2025.236979

The development of stable solid electrolytes with fast ionic conductivity is essential for advancing all-solid-state metal-ion batteries, which provide higher energy density and improved safety compared to conventional metal-ion batteries. We present a combined theoretical and experimental study of NaGaPO4F, a new class of KTiOPO4-structured solid electrolytes. Electrochemical impedance spectroscopy measurements and large-scale machine learning-based molecular dynamics (MD) simulations reveal that the stoichiometric compound is a poor ionic conductor due to the relatively high formation energy of Na Frenkel pairs. However, quantum chemistry-based MD simulations uncover a mixed Na-ion diffusion mechanism involving single and concerted hopping, with an ultra-low activation barrier of 0.12-0.16 eV. The predicted room-temperature conductivity of similar to 0.01 S cm(-1) in the presence of extrinsic Na vacancies matches top superionic conductors. Our DFT calculations of dopant solubility indicate that aliovalent substitution of Na+ with Ba2+ and Ga3+ with Sn4+ is thermodynamically favorable, enabling the introduction of the required Na vacancy concentration and confirm the material's high oxidation potential. These results deepen the understanding of Na-ion conductivity in KTiOPO4-structured electrolytes.

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