Colloidal route towards sodium ionic conductor (NASICON) 3D complex solid electrolyte structures fabricated by direct ink writing (DIW)

Progressing towards a sustainable energy model, safer new generation high-performance energy storage devices with large energy density and power are needed. In this sense, the improvement in terms of efficiency and sustainability has led to the interest in solid-state batteries (SSBs). Lately, sodium-ion batteries (SIBs) have become an emerging alternative due to the abundance of raw materials, low cost, and improvements in terms of fast sodium-ion conductor solid electrolytes (SCSEs). Among all the SCSEs, the sodium superionic conductor (NASICON) type electrolyte is one of the most well-known electrolytes, being widely developed in terms of synthesis and materials. However, the processing and manufacturing of these electrolytes have gone almost unnoticed, without considering that well-designed structures of electrodes/electrolytes are the bridge toward turning advanced energy materials into high-performance devices. This work presents the fabrication of 3D complex structures based on NASICON sodium solid electrolytes, obtained for the first time by direct ink writing (DIW). Through a colloidal route, fine NASICON phase powder with high pureness was prepared, enabling the manufacturing of intricate NASICON-printed electrolytes in a one-step fabrication process. By optimizing the ink, a dense electrolyte layer, acting as an ionic conductor and separator, was inserted between two complex porous pattern layers obtaining a device with a total height below 1.15 mm. Further, the densification of the 3D electrolyte was enhanced, reaching high ionic conductivities at room temperature (3.10⁻⁴ S cm⁻¹). Thus, a high-performance sodium ion conductor NASICON solid electrolyte with shorter diffusion pathways and larger interfacial surface areas between electrode/electrolyte was obtained, improving the overall electrochemical performance of the device by a 3D layer-by-layer design.