Effect of sintering and annealing on electrochemical and mechanical characteristics of Na3Zr2Si2PO12 solid electrolyte

Abstract

AbstractNASICON (Sodium superionic conductor) type Na3Zr2Si2PO12 (NZSP) has received a lot of interest as the solid electrolyte for all‐solid‐state sodium‐ion batteries (ASSIBs). The electrolyte has superior interfacial characteristics, high thermal stability, and good ionic conductivity. Because of their higher energy density, improved mechanical stability, no liquid leakage problem, and higher operating voltages, All solid‐state batteries are expected to replace liquid electrolyte‐based batteries in many applications. The solid electrolyte also acts as a separator, and hence additional separator is not required for cell operations. Because of its 3D open architecture and continuous diffusion channels, NZSP is considered a better solid electrolyte. The NZSP solid electrolyte has been synthesized by spark plasma sintering (SPS) followed by annealing the sintered materials. The SPS method leads the material to have higher density and ionic conductivity. Conventional sintering of the materials requires a temperature as high as 1225°C; however, the temperature required for the SPS is as low as 1050°C. Moreover, conventional sintering yields samples of relative density up to 91%, while SPSed samples have achieved a maximum density of around 98%. The ionic conductivity of solid electrolyte SPSed at 1050°C for 10 min is found to be 3.5 × 10−4 S/cm with an activation energy of 0.27 eV. The annealing of the SPSed samples improves the ionic conductivity of the SPS1050‐20mins sample to roughly double the value obtained from the as‐prepared SPS sample because there are fewer secondary phases and a structural change from a rhombohedral to a monoclinic system. To ascertain the samples' crystal structure, particle shape, and ionic conductivity, materials were characterized using X‐ray diffraction, scanning electron microscopy, and electrochemical impedance spectroscopy. The samples' mechanical characteristics, for example, the hardness and fracture toughness of the samples, were also determined.