All-solid-state batteries and especially solid electrolytes stand in the spotlight of current energy research.^[1,2] An extremely high ion mobility, which is known for liquid electrolytes, is needed to realize batteries with ceramic electrolytes. Apart from Li-bearing materials also a range of sodium compounds exhibit extremely high ion conductivities. With regard to availability and costs Na-based energy storage systems have attracted great interest over the last years.^[3]

Here we re-investigated the most prominent representatives of this kind of functional materials viz. Na-β''-alumina^[4] and Na₃Zr₂(SiO₄)₂PO₄ (NASICON), which are known to show conductivity values in the order of mS/cm at RT.^[5,6] We used high precision impedance measurements and nuclear magnetic resonance (NMR) spectroscopy to study the diffusion mechanisms and long-range ion transport. In the case of Na-β''-alumina we focused on a commercially available sintered pellets to investigate both bulk dynamics and grain boundary effects on ionic conductivity. Impedance spectroscopy was helpful to interpret ion dynamics revealed by NMR on both short as well as long-range length scales. For well-sintered and highly dense samples ion transport across grain boundaries has only little impact on the overall fast ion transport seen.

References:

[1] J.C. Bachman, S. Muy et al., Chem. Rev. 2016, 116, 140-162.

[2] J. Janek, W. Zeier, Nature Energy 1 2016, 16141.

[3] B. L. Ellis, L. F. Nazar, Curr. Opin. Solid State Mater. Sci. 2012, 16, 168-177.

[4] M. Bettman, C. R. Peters, J. Phys. Chem. 1969, 73, 1774-1780.

[5] W. Jakubowski, D. H. Whitmore, J. Am. Chem. Soc. 1979, 62, 381-385.

[6] J. Goodenough, H.-P. Hong et al., Mat. Res. Bull. 1976, 11, 203-220.