Polarization impedance at the Na-Na5YSi4O12 interface

Na-ion solid state batteries operating at room temperature are typically supposed to have a metallic Na anode for sufficiently high energy density. The less known but due to easy processing very promising Na-conducting Na5YSi4O12 glass ceramic is investigated regarding it`s interface resistance in contact with metallic Na electrodes. Two types of this material, with and without P-addition, are investigated. The surface is treated by polishing to induce a defined roughness. Highly polished surfaces lead to incomplete covering with Na metal by application of pressure sufficiently low to avoid the breaking of ceramic. In contrast, surfaces with higher roughness could be covered more homogeneously with Na and thus exhibited significantly reduced interface resistance. These measurements reveal the intrinsically small interface resistance between Na5YSi4O12 glass ceramics and metallic Na, which makes Na5YSi4O12 to promising electrolyte for Na-ion solid state batteries. It is found that prolonged contact of the electrolyte with humid air, like several days or weeks, leads to a strongly increased interface resistance. Thus, storage conditions and surface treatment of the samples after air contact need to be considered carefully.