Thin solid-electrolytes with sodium conductive phase Na5RSi4O12 (R=Yb, Y, Gd, Sm) made via tape-casting

The sodium-ion conducting solid electrolyte is an important component in sodium-ion batteries, which are the most promising alternatives to lithium-ion batteries. The solid electrolyte not only functions as the ionic conductor, but also as the separator between the electrodes. Most established and well characterized sodium conducting ceramic solid-state electrolytes now are the Na-β-alumina and the NASICON-materials, both having their ad- and disadvantages especially regarding the manufacturability of thin and dense substrates. This work focuses on a different kind of oxide-based sodium-ion conductor, the sodium rare-earth silicates known as NaRSiO (R= Yb, Y, Gd, Sm), which contain the conductive phase Na5RSi4O12 (R=Yb, Y, Gd, Sm). These silicates can be synthesized as glasses and sintered into components as glass ceramics via the powder route at temperatures of 1050–1120 °C. In this study, four compositions based on different rare earth elements were synthesized, prepared as powders and tape-casted to produce dense substrates as thin as 300 µm. The samples showed total ionic conductivities between 0.2 and 2.1 mS cm−1 at 30 °C and activation energies between 0.29 and 0.40 eV.