Drop That Activation Energy: Tetragonal to Cubic Transformations in Na3PS4−xSex for Solid State Sodium Ion Battery Materials

• Published in: Advanced functional materials Vol. 34; no. 13
• Main Authors: Chaudhary, Madhusudan, Pominov, Arkadii, Mumbaraddi, Dundappa, Allen, Bryce, Meyer, Jan, Kirchberger, Anna Maria, Bernard, Guy M, Nilges, Tom, Mar, Arthur, Michaelis, Vladimir K
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc 01.03.2024
• Subjects: Activation energy; Anisotropy; Atomic properties; Binomial distribution; Chemical equilibrium; Dynamic models; Electric fields; Electrolytes; High temperature; Ion currents; Ion dynamics; Molten salt electrolytes; NMR; Nuclear magnetic resonance; Sodium; Sodium-ion batteries; Solid electrolytes; Solid solutions; Substitution reactions; Tensors
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.202311829

Sodium‐containing chalcogenide materials are emerging as a class of solid electrolytes for application in inexpensive all‐solid‐state sodium‐ion batteries due to their high ionic conductivity, abundance, and degree of synthetic and structural variability. Members of the solid solution Na3PS4−xSex, which are promising solid electrolytes for sodium‐ion batteries, are prepared by reaction at high temperature. With increasing substitution of S by Se, the structure transforms from tetragonal (space group P4¯$\bar{4}$21c for x = 0, 1) to cubic (space group I4¯$\bar{4}$3m for x = 2, 3, 4). Within the solid solution, the S and Se atoms are completely disordered in the environments around the P atoms, in accordance with a binomial distribution, as inferred by the 31P nuclear magnetic resonance (NMR) spectra. In 23Na NMR experiments conducted at different magnetic fields and temperatures, quadrupolar lineshapes are observed that are influenced by sodium ion dynamics; the activation energies decrease from 0.21 to 0.15 eV on progressing from the S‐ to the Se‐rich members. A dynamic model is proposed to account for the changes in the 23Na quadrupolar lineshapes by switching the orientations of the electric field gradient and chemical shift anisotropy tensors when Na+ ions hop to the four nearest Na sites.