The effect of polished surface microstructure of ceramic electrolyte on solid-state sodium metal batteries

Highly stable Na anode/solid-state electrolyte (SSE) interface is vital for engineering robust solid-state sodium metal battery (SSMB). To ensure the flatness and remove the surface impurities of SSE, ceramic SSE pellets commonly require to be polished. However, there are lack of standardized instructions about the polish procedure even though researchers have realized that the properties of Na/SSE interface could be influenced dramatically by the surface microstructure of SSE pellet. In this work, the Na3.3Zr1.7Pr0.3Si2PO12 SSE pellets were polished transversely and longitudinally by sandpaper with various mesh sizes on purpose for engineering Na/ SSE interfaces. It is discovered that the compatibility and wettability of Na on SSE pellets could be tuned by polish procedure due to the resultant variation of roughness, contact area and ravines. By optimizing surface microstructure of SSE pellets through polishing, the assembled symmetrical battery delivers the highest critical current density of 0.55 mA cm-2 and the lowest interface impedance (11.8 omega cm2) at room temperature, enabling the stably cycling for 5000 h at 0.1 mA cm-2. This work sheds light on the strong correlations between polishinduced surface-microstructural changes of SSE and interface stability of Na/SSE, providing a rational reference for SSE polishing when assembling SSMB.